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Due to their optical and electro-conductive attributes, carbazole derivatives are interesting materials for a large range of biosensor applications. In this study, we present the synthesis routes and fluorescence evaluation of newly designed carbazole fluorosensors that, by modification with uracil, have a special affinity for antiretroviral drugs via either Watson-Crick or Hoogsteen base pairing. To an N-octylcarbazole-uracil compound, four different groups were attached, namely thiophene, furane, ethylenedioxythiophene, and another uracil; yielding four different derivatives. Photophysical properties of these newly obtained derivatives are described, as are their interactions with the reverse transcriptase inhibitors such as abacavir, zidovudine, lamivudine and didanosine. The influence of each analyte on biosensor fluorescence was assessed on the basis of the Stern-Volmer equation and represented by Stern-Volmer constants. Consequently we have demonstrated that these structures based on carbazole, with a uracil group, may be successfully incorporated into alternative carbazole derivatives to form biosensors for the molecular recognition of antiretroviral drugs.
2-C-branched methyl glycosides react with various alcohols under gold catalysis to transglycosylated products. The method is applicable for the convenient synthesis of disaccharides. Without nucleophile a selective anomerization occurs, giving first access to alpha-configured 2-C-nitromethyl glycosides. The results are interesting for the mechanism of gold-catalyzed glycosidations.
Biomimetic hybrid materials based on a polymeric and an inorganic component such as calcium phosphate are potentially useful for bone repair. The current study reports on a new approach toward biomimetic hybrid materials using a set of recombinamers (recombinant protein materials obtained from a synthetic gene) as crystallization additive for calcium phosphate. The recombinamers contain elements from elastin, an elastic structural protein, and statherin, a salivary protein. Via genetic engineering, the basic elastin sequence was modified with the SN(A)15 domain of statherin, whose interaction with calcium phosphate is well-established. These new materials retain the biocompatibility, "smart" nature, and desired mechanical behavior of the elastin-like recombinamer (ELR) family. Mineralization in simulated body fluid (SBF) in the presence of these recombinamers reveals surprising differences. Two of the polymers inhibit calcium phosphate deposition (although they contain the statherin segment). In contrast, the third polymer, which has a triblock structure, efficiently controls the calcium phosphate formation, yielding spherical hydroxyapatite (HAP) nanoparticles with diameters from 1 to 3 nm after 1 week in SBF at 37 degrees C. However, at lower temperatures, no precipitation is observed with any of the polymers. The data thus suggest that the molecular design of ELRs containing statherin segments and the selection of an appropriate polymer structure are key parameters to obtain functional materials for the development of intelligent systems for hard tissue engineering and subsequent in vivo applications.
Copper(I)-Catalyzed [3+2] Cycloaddition of 3-Azidoquinoline-2,4(1H,3H)-diones with terminal alkynes
(2011)
3-Azidoquinoline-2,4(1H,3H)-diones 1, which are readily available from 4-hydroxyquinolin-2(1H)-ones 4 via 3-chloroquinoline-2,4(1H, 3H)-diones 5, afford, in copper(I)-catalyzed [3 + 2] cycloaddition reaction with terminal acetylenes, 1,4-disubstituted 1,2,3-triazoles 3 in moderate to excellent yields. The structures of compounds 3 were confirmed by (1)H and (13)C-NMR spectroscopy, combustion analyses and mass spectrometry.
The interaction of Cu(II) with three beta-diketone ligands of type R(1)C(O)CH(2)C(O)R(2) (where R(1) = 2-, 3-, or 4-pyridyl and R(2) = C(6)H(5), respectively), HL(1)-HL(3), along with the X-ray structures and the pK(a) values of each ligand, are reported. HL(1) yields a dimeric complex of type [Cu(L(1))(2)](2). In this structure, two deprotonated HL(1) ligands coordinate in a trans planar fashion around each Cu(II) center, one oxygen from each CuL(2) unit bridges to an axial site of the second complex unit such that both Cu(II) centers attain equivalent five-coordinate square pyramidal geometries. The two-substituted pyridyl groups in this complex do not coordinate, perhaps reflecting steric factors associated with the closeness of the pyridyl nitrogen to the attached (conjugated) beta-diketonato backbone of each ligand. The remaining two Cu(II) species, derived from HL(2) and HL(3), are both coordination polymers of type [Cu(L)(2)](n) in which the terminal pyridine group of each ligand is intermolecularly linked to an adjacent copper center to generate the respective infinite structures. HL(2) was also demonstrated to form a fibrous metallogel when reacted with CuCl(2) in an acetonitrile/water mixture under defined conditions.
The pH-dependent influence of two different strongly alternating copolymers [poly(N,N'-diallyl-N,N'-dimethylammonium-alt-N-phenylmaleamic carboxylate) (PalPh) and poly(N,N'-diallyl-N,a-dimethylammonium-alt-3,5-bis(carboxyphenyl) maleamic carboxylate) (PalPhBisCarb)] based on N,N'-diallyl-N, -dimethylarnmonium chloride and maleamic acid derivatives on the phase behavior of a water-in-oil (w/o) microemulsion system made from toluene pentanol (1:1) and sodium dodecyl sulfate was investigated. It was shown that the optically dear phase range can be extended after incorporation of these copolymers, leading to an increased water solubilization capacity. Additionally, the required amount of surfactant to establish a clear w/o microemulsion depends on the pH value, which means the hydrophobicity of the copolymers. Conductivity measurements show that droplet droplet interactions in the w/o microemulsion are decreased at acidic but increased at alkaline pH in the presence of the copolymers. From differenctial scanning calorimetry measurements one can further conclude that these results are in agreement with a change of the position of the copolymer in the interfacial region of the surfactant film. The more hydrophobic PalPh can be directly incorporated into the surfactant film, whereas the phenyl groups of PalPhBisCarb flip into the water core by increasing the pH value.
In the present work, ideas for controlling photochemical reactions in dissipative environments using shaped laser pulses are presented. New time-local control algorithms for the stochastic Schrodinger equation are introduced and compared to their reduced density matrix analog. The numerical schemes rely on time-dependent targets for guiding the reaction along a preferred path. The methods are tested on the vibrational control of adsorbates at metallic surfaces and on the ultrafast electron dynamics in a strong dissipative medium. The selective excitation of the specific states is achieved with improved yield when using the new algorithms. Both methods exhibit similar convergence behavior and results compare well with those obtained using local optimal control for the reduced density matrix. The favorable scaling of the methods allows to tackle larger systems and to control photochemical reactions in dissipative media of molecules with many more degrees of freedom.
The title compound was prepared by the reaction of 1,4,10,13-tetraoxa-7,16-diazacyclo-octadecane with 4-chloro-2-methyl-phenoxyacetic acid in a ratio of 1:2. The structure has been proved by the data of elemental analysis, IR spectroscopy, NMR ((1)H, (13)C) technique and by X-ray diffraction analysis. Intermolecular hydrogen bonds between the azonium protons and oxygen atoms of the carboxylate groups were found. Immunoactive properties of the title compound have been screened. The compound has the ability to suppress spontaneous and Con A-stimulated cell proliferation in vitro and therefore can be considered as immunodepressant.
Through-space NMR shieldings (TSNMRSs) of a series of 2-alkylidenethiazolines subjected to push-pull activity have been calculated by the GIAO method employing the nucleus-independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSSs). The ICSSs were applied to quantify and visualize the degree of aromaticity of the studied compounds, which has been shown to be in excellent correlation with the push-pull behavior, quantified by the quotient (pi*/pi) method. Dissection of the absolute magnetic shielding values into individual contributions of bonds and lone pairs by the natural chemical shielding-natural bond orbital (NCS-NBO) analysis has revealed unexpected details.
We have performed a 15 ns molecular dynamics simulation of inverse sodium dodecyl sulfate (SDS) micelles in a mixed toluene/pentanol solvent in the absence and presence of a cationic polyelectrolyte, i.e. poly(diallyldimethylammonium chloride) (PDADMAC). The NAMD code and CHARMM force field were used. During the simulation time, the radii of SOS inverse micelles changed and the radii of the water droplets have been calculated. The behavior of SDS hydrocarbon chains has been characterized by calculating the orientation order parameter and the chain average length. The water droplet properties (water flow, water molecules displacement) have been examined. In summary the MD simulations indicate a more rigid and ordered surfactant film due to the formation of a polyelectrolyte palisade layer in full agreement with the experimental findings, e.g. the viscosity increase and shift of the percolation boundary.
The enzyme diisopropyl fluorophosphatase (DFPase) from the squid Loligo vulgaris is of great interest because of its ability to catalyze the hydrolysis of highly toxic organophosphates. In this work, the enzyme structure in solution (native state) was studied by use of different scattering methods. The results are compared with those from hydrodynamic model calculations based on the DFPase crystal structure. Bicontinuous microemulsions made of sugar surfactants are discussed as host systems for the DFPase. The microemulsion remains stable in the presence of the enzyme, which is shown by means of scattering experiments. Moreover, activity assays reveal that the DFPase still has high activity in this complex reaction medium. To complement the scattering experiments cryo-SEM was also employed to study the microemulsion structure.
The formation of secondary Ln(III) solid phases (e.g., Nd-2(CO3)(3) and Sm-2(CO3)(3)) was studied as a function of the humic acid concentration in 0.1 mol/L NaClO4 aqueous solution in the neutral pH range (5-6.5). The solid phases under investigation were prepared by alkaline precipitation under 100% CO2 atmosphere and characterized by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), time-resolved laser fluorescence spectroscopy (TRLFS), diffuse reflectance ultraviolet-visible (DR-UV-Vis), Raman spectroscopy, and solubility measurements. The spectroscopic data obtained indicated that Nd-2(CO3)(3) and Sm-2(CO3)(3) were stable and remained the solubility limiting solid phases even in the presence of increased humic acid concentration (0.5 g/L) in solution. Upon base addition in the Ln(III)-HA system, decomplexation of the previously formed Ln(III)-humate complexes and precipitation of two distinct phases occurred, the inorganic (Ln(2)(CO3)(3)) and the organic phase (HA), which was adsorbed on the particle surface of the former. Nevertheless, humic acid affected the particle size of the solid phases. Increasing humic acid concentration resulted in decreasing crystallite size of the Nd-2(CO3)(3) and increasing crystallite size of the Sm-2(CO3)(3) solid phase, and affected inversely the solubility of the solid phases. However, this impact on the solid phase properties was expected to be of minor relevance regarding the chemical behavior and migration of trivalent lanthanides and actinides in the geosphere.
Pd-Catalyzed [2+2+1] coupling of alkynes and arenes phenol diazonium salts as mechanistic trapdoors
(2011)
Alkynes and phenol diazonium salts undergo a Pd-catalyzed [2+2+1] cyclization reaction to spiro[4,5]decatetraene-7-ones. This structure was confirmed for one example by X-ray single-crystal structure analysis. The reaction is believed to proceed through oxidative addition of the phenol diazonium cation to Pd(0), subsequent insertion of two alkynes, followed by irreversible spirocyclization.
We have earlier shown that linear poly(ethylene imine) (LPEI) is an efficient growth modifier for calcium phosphate mineralization from aqueous solution (Shkilnyy et al., Langmuir, 2008, 24 (5), 2102). The current study addresses the growth process and the reason why LPEI is such an effective additive. To that end, the solution pH and the calcium and phosphate concentrations were monitored vs. reaction time using potentiometric, complexometric, and photometric methods. The phase transformations in the precipitates and particle morphogenesis were analyzed by X-ray diffraction and transmission electron microscopy, respectively. All measurements reveal steep decreases of the pH, calcium, and phosphate concentrations along with a rapid precipitation of brushite nanoparticles early on in the reaction. Brushite transforms into hydroxyapatite (HAP) within the first 2 h, which is much faster than what is reported, for example, for calcium phosphate precipitated with poly(acrylic acid). We propose that poly(ethylene imine) acts as a proton acceptor (weak buffer), which accelerates the transformation from brushite to HAP by taking up the protons that are released from the calcium phosphate precipitate during the phase transformation.
Lahn M, Dosche C, Hille C. Two-photon microscopy and fluorescence lifetime imaging reveal stimulus-induced intracellular Na+ and Cl- changes in cockroach salivary acinar cells. Am J Physiol Cell Physiol 300: C1323-C1336, 2011. First published February 23, 2011; doi: 10.1152/ajpcell.00320.2010.-The intracellular ion homeostasis in cockroach salivary acinar cells during salivation is not satisfactorily understood. This is mainly due to technical problems regarding strong tissue autofluorescence and ineffective ion concentration quantification. For minimizing these problems, we describe the successful application of two-photon (2P) microscopy partly in combination with fluorescence lifetime imaging microscopy (FLIM) to record intracellular Na+ and Cl- concentrations ([Na+](i), [Cl-](i)) in cockroach salivary acinar cells. Quantitative 2P-FLIM Cl- measurements with the dye N-(ethoxycarbonylmethyl)-6-methoxy-quinolinium bromide indicate that the resting [Cl-](i) is 1.6 times above the Cl- electrochemical equilibrium but is not influenced by pharmacological inhibition of the Na+-K+-2Cl(-) cotransporter (NKCC) and anion exchanger using bumetanide and 4,4'-diisothiocyanatodihydrostilbene-2,2'-disulfonic acid disodium salt. In contrast, rapid Cl- reuptake after extracellular Cl- removal is almost totally NKCC mediated both in the absence and presence of dopamine. However, in physiological saline [Cl-](i) does not change during dopamine stimulation although dopamine stimulates fluid secretion in these glands. On the other hand, dopamine causes a decrease in the sodium-binding benzofuran isophthalate tetra-ammonium salt (SBFI) fluorescence and an increase in the Sodium Green fluorescence after 2P excitation. This opposite behavior of both dyes suggests a dopamine-induced [Na+](i) rise in the acinar cells, which is supported by the determined 2P-action cross sections of SBFI. The [Na+](i) rise is Cl- dependent and inhibited by bumetanide. The Ca2+-ionophore ionomycin also causes a bumetanide-sensitive [Na+](i) rise. We propose that a Ca2+-mediated NKCC activity in acinar peripheral cells attributable to dopamine stimulation serves for basolateral Na+ uptake during saliva secretion and that the concomitantly transported Cl- is recycled back to the bath.
Free Radical Copolymerization Kinetics of gamma-Methyl-alpha-methylene-gamma-butyrolactone (MeMBL)
(2011)
The propagation kinetics and copolymerization behavior of the biorenewable monomer gamma-methyl-alpha-methylene-gamma-butyrolactone (MeMBL) are studied using the Pulsed laser polymerization (PLP)/size exclusion chromatography (SEC) technique. The propagation rate coefficent for MeMBL is 15% higher than that of its structural analogue, methyl methacrylate (MMA), with a similar activation energy of 21.8 kJ . mol(-1). When compared to MMA, MeMBL is preferentially incorporated into copolymers when reacted with styrene (ST), MMA, and n-butyl acrylate (BA); the monomer reactivity ratios fit from bulk MeMBL/ST, MeMBL/MMA, and MeMBL/BA copolymerizations are r(MeMBL) = 0.80 +/- 0.04 and r(ST) = 0.34 +/- 0.04, r(MeMBL), = 3.0 +/- 0.3 and r(MMA) = 0.33 +/- 0.01, and r(MeMBL) = 7.0 +/- 2.0 and r(BA) = 0.16 +/- 0.03, respectively. In all cases, no significant variation with temperature was found between 50 and 90 degrees C. The implicit penultimate unit effect (IPUE) model was found to adequately fit the composition-averaged copolymerization propagation rate coefficient, k(p,cop), for the three systems.
C-H-ax center dot center dot center dot Y-ax are a textbook prototype of steric hindrance in organic chemistry. The nature of these contacts is investigated in this work. MP2/6-31+G(d,p) calculations predicted the presence of improper hydrogen bonded C-H-ax center dot center dot center dot Y-ax of different strength in substituted cyclohexane rings. To support the theoretical predictions with experimental evidence, several synthetic 2-substituted adamantane analogues (1-24) with suitable improper H-bonded C-H-ax center dot center dot center dot Y-ax contacts of different strength were used as models of a substituted cyclohexane ring. The H-1 NMR signal separation, Delta delta(gamma-CH2), within the cyclohexane ring gamma-CH(2)s is raised when the MP2/6-31+G(d,p) calculated parameters, reflecting the strength of the H-bonded C-H-ax center dot center dot center dot Y-ax contact, are increased. In molecules with enhanced improper H-bonded contacts C-H-ax center dot center dot center dot Y-ax, like those having sterically crowded contacts (Y-ax = t-Bu) or contacts including considerable electrostatic attractions (Y-ax = O-C or O=C) the calculated DFT steric energies of the gamma-axial hydrogens are considerably reduced reflecting their electron cloud compression. The results suggest that the proton H-ax electron cloud compression, caused by the C-H-ax center dot center dot center dot Y-ax contacts, and the resulting increase in Delta delta(gamma-CH2) value can be effected not just from van der Waals spheres compression, but more generally from electrostatic attraction forces and van der Waals repulsion, both of which are improper H-bonding components.
Benzyl methacrylate (BzMA) propagation rate coefficients, k(p), were determined in ionic liquids and common organic solvents via pulsed-laser polymerizations with subsequent polymer analysis by size-exclusion chromatography (PLP-SEC). The aim of the work is to gain a deeper understanding of the solvent influence on k(p) and to develop a general correlation between solvent-induced variations in k(p) and solvent properties. Applying a linear solvation energy relationship (LSER), which correlates k(p) to solvent solvatochromic parameters, suggests that dipolarity/polarizability determines the solvent influence on k(p). To compare the solvent influence on BzMA k(p) with data for methyl methacrylate, hydroxypropyl methacrylate, and 2-ethoxyethyl methacrylate normalized k(p) data were treated by a single LSER, providing a universal treatment of the solvent influence on the propagation kinetics of the four monomers. Further, the predictive capabilities of this universal correlation were tested with additional monomers from the methacrylate family.
The stem extract of Tephrosia purpurea showed antiplasmodial activity against the D6 (chloroquine-sensitive) and W2 (chloroquine-resistant) strains of Plasmodium falciparum with IC(50) values of 10.47 +/- 2.22 mu g/ml and 12.06 +/- 2.54 mu g/ml, respectively. A new prenylated flavone, named terpurinflavone, along with the known compounds lanceolatin A, (-)-semiglabrin and lanceolatin B have been isolated from this extract. The new compound, terpurinflavone, showed the highest antiplasmodial activity with IC(50) values of 3.12 +/- 0.28 mu M (D6) and 6.26 +/- 2.66 mu M (W2). The structures were determined on the basis of spectroscopic evidence.
1-Oxo-1,3-dithiolane (4) and its cis- and trans-2-methyl (5,6), -4-methyl (7,8) and -5-methyl (9,10) derivatives were prepared by oxidizing the corresponding 1,3-dithiolanes (1-3) with NaIO(4) in water. The oxides were purified and their isomers separated using thin layer chromatography. The structural characterization was carried out with (1)H and (13)C NMR spectroscopy and molecular modelling. The sulfoxides 4-6 and 8-10 attain two S(1) type envelopes (sometimes slightly distorted) the S=O(ax) envelope greatly dominating. Cis-4-methyl-1-oxo-1,3-dithiolane is a special case exhibiting both two closely related S=O(ax) (30 and 27%) as well as S=O(eq) (21 and 22%) forms [S(1) and C(4) envelopes, respectively]. The relative energies of these conformations, the values of (1)H-(1)H coupling constants and (1)H and (13)C chemical shifts were estimated by computational methods and they support well the conclusions based on the experimental data.
Five alkynyl pyridines were prepared and cyclized to naphthylpyridines as the main products in the course of a Photo-Dehydro-Diels-Alder reaction. Four of the final products are axially chiral and the determination of the rotational barrier by DFT calculations, dynamic NMR and H PLC experiments is demonstrated. (C) 2011 Elsevier B.V. All rights reserved.
N-Substituted 4,4-dimethyl-4-silathiane 1-sulfimides Me2Si(sic)S=NSO2R [R- Ph (1), CF3 (2)] were studied experimentally by variable temperature dynamic NMR spectroscopy. Low temperature 13 C NMR spectra of the two compounds revealed the frozen ring inversion process and approximately equal content of the axial and equatorial conformers. Calculations of the 4-silathiane derivatives 1, 2 and the model compound [R Me (3)] as well as their carbon analogs, the similarly N-substituted (sic)S=NSO2R thiane 1-sulfimides [R = Ph (4), CF3 (5), Me (6)] at the DFT/B3LYP/6-311G(d, p) level in the gas phase and in chloroform solution using the PCM model at the same level of theory showed a strong dependence of the relative stability of the conformer on the solvent. The electronegative trifluoromethyl group increases the relative stability of the axial conformer.
Ab initio calculations for XPS chemical shifts of poly(vinyl-trifluoroacetate) using trimer models
(2011)
X-ray photoelectron spectra (XPS) of the polymer poly(vinyl-trifluoroacetate) show C(1s) binding energy shifts which are unusual because they are influenced by atoms which are several bonds away from the probed atom. In this work, the influence of the trifluoroacetate substituent on the 1s ionization potential of the carbon atoms of the polyethylene chain is investigated theoretically using mono-substituted, diad and triad models of trimers representing the polymer. Carbon 1s ionization energies are calculated by the Hartree-Fock theory employing Koopmans' theorem. The influence of the configuration and conformation of the functional groups as well as the degree of substitution are found to be important determinants of XPS spectra. It is further found that the 1s binding energy correlates in a linear fashion, with the total electrostatic potential at the position of the probe atom, and depends not only on nearest neighbor effects. This may have implications for the interpretation of high-resolution XP spectra.
Four copper(II) coordination compounds with the neutral ligand bis(3,5-dimethylpyrazol-1-yl)acetic acid (Hbdmpza, C(12)H(16)N(4)O(2)) and its anionic form (bdmpza(-)), namely [Cu(Hbdmpza)(2)](HSO(4))(2) (1), [Cu(Hbdmpza)(2)]Cl(2) (2), [Cu(bdmpza)(2)](CH(3)COOH)(H(2)O) (3), and [Cu(bdmpza)(2)][Cu(2)(O(2)CCH(3))(4)] (4) have been synthesized starting from different metal salts. All the compounds have been fully characterized by physical and analytical methods. In addition, a single-crystal XRD analysis revealed the 3D structure of 1, which exhibits tridentate, vicinal N,N,O-coordination of two symmetry-related Hbdmpza ligands in an elongated octahedral arrangement with four equatorial nitrogen atoms and two axial oxygen atoms. The neutral carboxylic moiety acts as a hydrogen-bond donor to a HSO(4)(-) counterion. The two hydrogensulfates form a unique hydrogen-bonded pair (HSO(4)(-))(2) with very short O center dot center dot center dot O distances (2.59 angstrom) bridged between adjacent [Cu(HL)(2)](2+) coordination units. Also a short O center dot center dot center dot O contact (2.54 angstrom) is present between the C-OH and an 0 of a hydrogensulfate. A characteristic IR C=O vibration is observed at 1700 cm(-1) for 1 and 2, whereas the v(as)(O(2)C) vibration is present at 1650 cm(-1) for 3 and 4. These IR data strongly suggest the presence of Hbdmpza ligands in 1 and 2 and the deprotonated form bdmpza- in 3 and 4. A mononuclear coordination unit [CuL(2)], as proven for 1 by X-ray diffraction, is also proposed for the other compounds 2-4. In compound 4, an additional dinuclear [Cu(2)(O(2)CCH(3))(4)] neutral coordination unit is present, as deduced from the vibration bands v(as)(O(2)C) at 1600 cm(-1) and v(s)(O(2)C) at 1420 cm(-1), which are typical of a carboxylate function, and from the two-species analysis of the chi(M)T(T) curve of the magnetic susceptibility data (2J = -322 cm(-1)). Also, the EPR spectra recorded at different temperatures agree with this structure.
Commercially available 1,2-PB was transformed into a well-defined reactive intermediate by quantitative bromination. The brominated polymer was used as a polyfunctional macroinitiator for the cationic ring-opening polymerization of 2-ethyl-2-oxazoline to yield a water-soluble brush polymer. Nucleophilic substitution of bromide by 1-methyl imidazole resulted in the formation of polyelectrolyte copolymers consisting of mixed units of imidazolium, bromo, and double bond. These copolymers, which were soluble in water without forming aggregates, were used as stabilizers in the heterophase polymerization of styrene and were also studied for their ionic conducting properties.
A new concept of a stereoselective synthesis of axially chiral biaryls, formed in the course of the dehydro-Diels-Alder (DDA) reaction, has been disclosed. It is based on asymmetric induction of the newly formed chirality axis by a chirality center, which is present in the two synthesized DDA reactants. Depending on the different length of the linkers joining the alkyne moieties the DDA reaction may be triggered photochemically or thermally, where only the thermal variant was stereoselective.
Rotation about the single bond adjoining the aryl and fluorene moieties in 9-arylfluorenes can be frozen out on the NMR timescale if methyl groups are located at either one or both of the ortho positions of the aryl substituent. In the ground-state of these rotamers, the planes of the aryl and fluorene moieties are perpendicular to each other and the methyl substituents are consequently positioned either above the fluorene moiety or in-plane with it; thus, the methyl protons are either shielded or deshielded, respectively, due to the ring current effect of the fluorene moiety. This anisotropic effect on the H-1 chemical shifts of the methyl protons has been quantified on the basis of through-space NMR shieldings (TSNMRS) and subsequently Delta delta(calcd) compared with the experimentally observed chemical shift differences, Delta delta(exp). In this context, the experimental anisotropic effects of functional groups in the H-1 NMR have proven to quantitatively be the molecular response property of theoretical spatial nucleus independent chemical shieldings (NICS). Differences between Delta delta(calcd) and Delta delta(exp) were, for the first time, also quantified as arising from steric compression.
The cis-trans isomerisation of N-benzylideneaniline (NBA) and derivatives containing a central C=N bond has been investigated experimentally and theoretically. Eight different NBA molecules in three different solvents were irradiated to enforce a photochemical trans (hv) -> cis isomerisation and the kinetics of the thermal backreaction cis (Delta)-> trans were determined by NMR spectroscopy measurements in the temperature range between 193 and 288 K. Theoretical calculations using density functional theory and Eyring transition-state theory were carried out for 12 different NBA species in the gas phase and three different solvents to compute thermal isomerisation rates of the thermal back reaction. While the computed absolute rates are too large, they reveal and explain experimental trends. Time-dependent density functional theory provides optical spectra for vertical transitions and excitation energy differences between trans and cis forms. Together with isomerisation rates, the latter can be used to identify "optimal switches" with good photochromicity and reasonable thermal stability.
A strategy to optimize the photoswitching efficiency of rigid, linear multiazobenzene constructs is presented. It consists of introducing large dihedral angles between azobenzene moieties linked via aryl-aryl connections in their para positions. Four bisazobenzenes exhibiting different dihedral angles as well as three single azobenzene reference compounds have been synthesized, and their switching behavior has been studied as well as experimentally and theoretically analyzed. As the dihedral angle between the two azobenzene units increases and consequently the electronic conjugation decreases, the photochromic characteristics improve, finally leading to individual azobenzene switches operating independently in the case of the perpendicular ortho,ortho,ortho',ortho'-tetramethyl biphenyl linker. The electronic decoupling leads to efficient separation of the absorption spectra of the involved switching states and hence by choosing the appropriate irradiation wavelength, an almost quantitative E -> Z photoisomerization up to 97% overall Z-content can be achieved. In addition, thermal Z -> E isomerization processes become independent of each other with increasing decoupling. The electronic decoupling could furthermore be proven by electrochemistry. The experimental data are supported by theory, and calculations additionally provide mechanistic insight into the preferred pathway for the thermal Z,Z -> Z,E -> E,E isomerization via inversion on the inner N-atoms. Our decoupling approach outlined herein provides the basis for constructing rigid rod architectures composed of multiple azobenzene photochromes, which display practically quantitative photoswitching properties, a necessary prerequisite to achieve highly efficient transduction of light energy directly into motion.
The analysis of the porosity of materials is an important and challenging field in analytical chemistry. The gas adsorption and mercury intrusion methods are the most established techniques for quantification of specific surface areas, but unfortunately, dry materials are mandatory for their applicability. All porous materials that contain water and other solvents in their functional state must be dried before analysis. In this process, care has to be taken since the removal of solvent bears the risk of an incalculable alteration of the pore structure, especially for soft materials. In the present paper, we report on the use of small-angle X-ray scattering (SAXS) as an alternative analysis method for the investigation of the micro and mesopores within cellulose beads in their native, i.e., water-swollen state; in this context, they represent a typical soft material. We show that even gentle removal of the bound water reduces the specific surface area dramatically from 161 to 109 m(2) g(-1) in cellulose bead sample type MT50 and from 417 to 220 m(2) g(-1) in MT100. Simulation of the SAXS curves with a bimodal pore size distribution model reveals that the smallest pores with radii up to 10 nm are greatly affected by drying, whereas pores with sizes in the range of 10 to 70 nm are barely affected. The SAXS results were compared with Brunauer-Emmett-Teller results from nitrogen sorption measurements and with mercury intrusion experiments.
A conformational study of N-acetyl glucosamine derivatives utilizing residual dipolar couplings
(2011)
The conformational analyses of six non-rigid N-acetyl glucosamine (NAG) derivatives employing residual dipolar couplings (RDCs) and NOEs together with molecular dynamics (MD) simulations are presented. Due to internal dynamics we had to consider different conformer ratios existing in solution. The good quality of the correlation between theoretically and experimentally obtained RDCs show the correctness of the calculated conformers even if the ratios derived from the MD simulations do not exactly meet the experimental data. If possible, the results were compared to former published data and commented.
We report on a new three-color FRET system which we were able to verify in peptides as well as in synthetic DNA. All three chromophores could be introduced by a building block approach avoiding postsynthetic labeling. Additional features are robustness, matching spectroscopic properties, high-energy transfer, and sensitivity. The system was investigated in detail on a set of peptides as well as an array of tailored oligonucleotides. The detailed analysis of the experimental data and comparison with theoretical considerations were in excellent agreement. It is shown that in the case of polypeptides specific interaction with the fluorescence probes has to be considered. In contrast with DNA, the fluorescence probes did not show any indications of such interactions. The novel three-color FRET toolbox revealed the potential for applications studying fundamental processes of three interacting molecules in life science applications.
Novel (co)polymers were synthesized from substances obtained from rapeseed via ADMET and thiol-ene additions. alpha,omega-Dienes derived from oleic and erucic acid were copolymerized with a ferulic acid derivative, a representative phenolic acid (p-hydroxycinnamic acid) present, for instance, in rapeseed cake. Copolymers with different ratios of these monomers were prepared via two different routes (ADMET and thiol-ene) and studied in detail. Both monomer and polymer synthesis were optimized in order to achieve high yielding synthetic procedures that meet the requirements of green chemistry. Some thermal properties of the resulting copolymer series were then studied and correlated to the co-monomer composition.
2,5-Disubstituted furans were synthesized by one-flask Heck arylation/oxidation sequences. The starting materials are 2-substituted 2,3-dihydrofurans, conveniently available by RCM/isomerization sequences, and arenediazonium salts. These react in ligand-free Heck reactions to afford 2,5-disub-stituted 2,5-dihydrofurans, which are oxidized to the corresponding furans without isolation or intermediate workup. The oxidation is conveniently achieved with chloranil or DDQ, depending on the substrate.
Reactions of trifluoromethanesulfonamide with alpha-methylstyrene, 2-methylpent-1-ene, and cycloocta-1,5-diene in the system t-BuOCl-NaI were studied. In the reaction with alpha-methylstyrene 1-iodo-2-phenylpropan-2-ol was the only isolated product. The reaction with 2-methylpent-1-ene gave a mixture of N,N'-(2-methylpentane-1,2-diyl)bis(trifluoromethanesulfonamide), trifluoro-N-(2-hydroxy-2-methylpentyl)-methanesulfonamide, and N,N'-[oxybis(2-methylpentan-2,1-diyl)]bis(trifluoromethanesulfonamide). Trifluoromethanesulfonamide reacted with cycloocta-1,5-diene to produce a mixture of 2,5-diiodo-9-(trifluoromethylsulfonyl)-9-azabicyclo[4.2.1]nonane and 2,5-diiodo-9-oxabicyclo[4.2.1]nonane; this reaction may be regarded as the first example of direct assembly of bicyclononane skeleton.
Polymer brushes on thiol-modified gold surfaces were synthesized by using terminal thiol groups for the surface initiated free radical polymerization of methacrylic acid and dimethylaminotheyl methacrylate, respectively. Atomic force microscopy shows that the resulting poly(methacrylic acid (PMAA) and poly(dimethylaminothyl methacrylate) (PDM- AEMA) brushes are homogeneous. Contact angle measurements show that the brushes are pH responsive and can reversibly be protonated and deprotonated. Mineralization of the brushes with calcium phosphate at different pH yields homogeneously mineralized surfaces, and preosteoblastic cells proliferate-on be number of living cells on the mineralized hybrid surface is ca. 3 times (P corresponding nonmineralized brushes.
In the present work, the density distribution of rhodamine 6G ions (R6G) in the gas phase and the droplets of an electrospray plume was studied by spatial and spectral imaging. The intention is to contribute to the fundamental understanding of the release mechanism of gaseous R6G in the electrospray ionization (ESI) process. Furthermore, the influence of ESI-parameters on the release efficiency of R6G, e. g. solvent flow, R6G and salt concentration were examined via direct fluorescence imaging of R6G. A solvent-shift of the fluorescence maximum,lambda(max) = 555 nm in methanolic solution and lambda(max) = 505 nm in gas phase, allows the discrimination between solvated and gaseous R6G. Two experimental setups were used for our measurements. In the first experiment, the R6G fluorescence and the light scattered from the spray plume were imaged in two spatial dimensions using a tunable wavelength filter. The second experiment was designed for obtaining 1-dimensional spatially resolved emission spectra of the spray. Here, the intensity distribution of solvated and gaseous R6G as well as scattered light (lambda = 355 nm) were measured simultaneously.
The results show the distribution of gaseous R6G in the plane, orthogonal to the ESI capillary, decreasing slightly towards the spray center and showing maxima at the cone margins. The distribution of gaseous R6G confirms the preferred release of gaseous ions from nano-droplets, indicating the ion evaporation model (IEM) to be the dominating release mechanism. Up to now, only a few fluorescence spectra of ionic compounds in the gas phase were published because the measurement of emission spectra of mass-selected ions in an ion trap is experimentally challenging. The fluorescence spectrum of gaseous lucigenin at atmospheric pressure is reported for the first time. This spectrum of lucigenin in the gas phase exhibits a blue shift of about Delta lambda = 10 nm in comparison to the corresponding spectrum in methanol.
The influence of the subphase temperature on the stripe pattern formation during Langmuir-Blodgett transfer (LB patterning) is investigated in a combined experimental and theoretical study. According to our experiments on the LB transfer of dipalmitoylphosphatidylcholine (DPPC) on planar mica substrates, even small temperature changes between 21.5 and 24.5 degrees C lead to significant changes in the monolayer patterns. For a constant surface pressure and dipper speed, the width of the stripes and the overall spatial period of the patterns increase with increasing subphase temperature. Because the stripe patterns are ascribed to alternating monolayer domains in the liquid-expanded and the liquid-condensed phases, the working regime for the formation of stripes is found to depend strongly on the respective surface pressure-area isotherm. These experimental findings are in accordance with the results of a theoretical investigation based on a model that takes hydrodynamics and the monolayer thermodynamics into account.
The occurrence of hypoxic conditions in plants not only represents a stress condition but is also associated with the normal development and growth of many organs, leading to adaptive changes in metabolism and growth to prevent internal anoxia. Internal oxygen concentrations decrease inside growing potato tubers, due to their active metabolism and increased resistance to gas diffusion as tubers grow. In the present work, we identified three hypoxia-responsive ERF (StHRE) genes whose expression is regulated by the gradual decrease in oxygen tensions that occur when potato tubers grow larger. Increasing the external oxygen concentration counteracted the modification of StHRE expression during tuber growth, supporting the idea that the actual oxygen levels inside the organs, rather than development itself, are responsible for the regulation of StHRE genes. We identified several sugar metabolism-related genes co-regulated with StHRE genes during tuber development and possibly involved in starch accumulation. All together, our data suggest a possible role for low oxygen in the regulation of sugar metabolism in the potato tuber, similar to what happens in storage tissues during seed development.
Current applications in porphyrin chemistry require the use of unsymmetrically substituted porphyrins. Many current industrial interests in optics and biomedicine require systems with either pushpull (electron-donating and -withdrawing groups) or amphiphilic systems (hydrophobic and hydrophilic groups). In this context we present the class of 5,10-A2B2-type porphyrins for which two different substituents are positioned in diagonally opposite meso positions. Thus, the intramolecular dipole moment in these tetrapyrroles is positioned along a beta-beta vector passing through two pyrrole rings. This is opposite to the situation of the frequently used 5,15-A2BC porphyrins for which the dipole moment is oriented along a mesomeso axis. We have elaborated syntheses of the 5,10-A2B2 porphyrins by using transition-metal-catalyzed transformations of 5,10-A2 porphyrins or direct substitutions reactions thereof; this gives the target molecules in 2277% overall yields. The compounds exhibit interesting structural, spectroscopic, and optical features and can serve as building blocks for new porphyrin arrays and applications.
Hole-transporting polymers based on polyethene-triphenylamine derivatives are investigated with respect to their UV/Vis spectra. Two substituents, N-phenyl-1-naphthylamine and carbazole, are examined as their respective polymer light-emitting diodes (PLEDs) show very different luminous efficiencies. In order to identify the origin of these phenomena electronic structure calculations based on TD-DFT were performed using monomer models of the hole-transporting polymers. In experiment these hole-transporting polymers show very specific differences in their absorption and emission (fluorescence and phosphorescence) spectra. The analysis of the simulated absorption and emission spectra, the MOs as well as the ground and excited state geometries give explanations for the different optical performances of the corresponding PLEDs.
Synthesis and conformational analysis of new naphth[1,2-e][1,3]oxazino[3,4-c]quinazoline derivatives
(2011)
A new highly functionalized aminonaphthol derivative, 1-(amino(2-aminophenyl)methyl)-2-naphthol (4), was synthesized by the reaction of 2-naphthol, 2-nitrobenzaldehyde and tert-butyl carbamate or benzyl carbamate, followed by reduction and/or removal of the protecting group. The aminonaphthol derivative thus obtained was converted in ring-closure reactions with formaldehyde. benzaldehyde and/or phosgene to the corresponding naphth[1,2-e][1,3]oxazino[3,4-c]quinazoline derivatives. The conformational analysis of some derivatives by NMR spectroscopy and accompanying molecular modelling are also reported.
A new class of fluorescent dyes based on 1,3-benzodioxole and [1,3]-dioxolo[4.5-f]benzodioxole
(2011)
We report on synthesis and photophysical properties of a new class of fluorescent dyes. They are characterized by large Stokes-shifts, long fluorescence lifetimes in organic solvents and a pronounced dependency of the fluorescence lifetime on the solvent polarity. Also worthy of note is the high bleaching stability. To provide access to biochemical and medical applications a series of derivatives were prepared, which exhibit specific reactivity towards different biologically relevant functional groups (carboxylic acids, amines, maleimides, N-hydroxysuccinimide esters). Furthermore, two alkynes were prepared, which could be used in 'Click' chemistry.
Molecular rods are synthetical molecules consisting of a hydrophobic backbone which are functionalized with varying terminal groups. Here, we report on the interaction of a recently described new class of molecular rods with lipid and biological membranes. In order to characterize this interaction, different fluorescently labeled rods were synthesized allowing for the application of fluorescence spectroscopy and microscopy based approaches. Our data show that the rods are incorporated into membranes with a perpendicular orientation to the membrane surface and enrich preferentially in liquid-disordered lipid domains. These characteristics underline that rods can be applied as stable membrane-associated anchors for functionalizing membrane surfaces.
Butenolides, obtained by ring-closing metathesis (RCM) of acrylates, undergo quantitative deprotonation with amide bases. Trapping of the resulting anions with electrophiles, for example, chlorophosphates, give furans. Subsequent DielsAlder reaction and acid-catalysed rearrangement of the resulting oxabicyclonorbornadienes give substituted benzenes.
Cryo-electron microscopy, atomic force microscopy, and light microscopy investigations provide experimental evidence that amphiphilic emulsion copolymerization particles change their morphology in dependence on concentration. The shape of the particles is spherical at solids content above 1%, but it changes to rod-like, ring-like, and web-like structures at lower concentrations. In addition, the shape and morphology of these particles at low concentrations are not fixed but very flexible and vary with time between spheres, flexible pearlnecklace structures, and stretched rods.
A long-standing and profound problem in astronomy is the difficulty in obtaining deep near-infrared observations due to the extreme brightness and variability of the night sky at these wavelengths. A solution to this problem is crucial if we are to obtain the deepest possible observations of the early Universe, as redshifted starlight from distant galaxies appears at these wavelengths. The atmospheric emission between 1,000 and 1,800 nm arises almost entirely from a forest of extremely bright, very narrow hydroxyl emission lines that varies on timescales of minutes. The astronomical community has long envisaged the prospect of selectively removing these lines, while retaining high throughput between them. Here we demonstrate such a filter for the first time, presenting results from the first on-sky tests. Its use on current 8 m telescopes and future 30 m telescopes will open up many new research avenues in the years to come.
Ultrasound (20 kHz, 29 W. cm(-2)) is employed to form three types of erbium oxide nanoparticles in the presence of multiwalled carbon nanotubes as a template material in water. The nanoparticles are (i) erbium carboxioxide nanoparticles deposited on the external walls of multiwalled carbon nanotubes and Er(2)O(3) in the bulk with (ii) hexagonal and (iii) spherical geometries. Each type of ultrasonically formed nanoparticle reveals Er(3+) photoluminescence from crystal lattice. The main advantage of the erbium carboxioxide nanoparticles on the carbon nanotubes is the electromagnetic emission in the visible region, which is new and not examined up to the present date. On the other hand, the photoluminescence of hexagonal erbium oxide nanoparticles is long-lived (mu s) and enables the higher energy transition ((4)S(3/2)-(4)I(15/2)), which is not observed for spherical nanoparticles. Our work is unique because it combines for the first time spectroscopy of Er(3+) electronic transitions in the host crystal lattices of nanoparticles with the geometry established by ultrasound in aqueous solution of carbon nanotubes employed as a template material. The work can be of great interest for "green" chemistry synthesis of photoluminescent nanoparticles in water.
In the present paper, the influence of the surfactant concentration and the degree of charge of a polymer on foam film properties of oppositely charged polyelectrolyte/surfactant mixtures has been investigated. To verify the assumption that the position of the isoelectric point (IEP) does not change the character of the foam film stabilities, the position of the IEP of the polyelectrolyte/surfactant mixtures has been shifted in two different ways. Within the first series of experiments, the foam. film properties were studied using a fixed surfactant concentration of 3 x 10(-5) M in the mixture. Due to the low surfactant concentration, this is a rather dilute system. In the second approach, a copolymer of nonionic and ionic monomer units was Used to lower the charge density of the polymer. This gave rise to additional interactions between the polyelectrolyte and the surfactant, which makes the description of the foam film behavior more complex. In both systems, the same characteristics of the foam film stabilities were found: The foam film stability is reduced toward the IEP of the system, followed by a destabilization around the IEP., At polyelectrolyte concentrations above the IEP, foam films are very stable. However, the concentration range where unstable films were formed was rather broad, and the mechanisms leading to the destabilization had different origins. The results were compared with former findings on PAMPS/C(14)TAB mixtures with an IEP of 10(-4)M.(1)
Strongly alternating copolymers (PalH, PalPh, PalPhBisCarb) composed of N,N'-diallyl-N,N'-dimethyl-ammonium chloride (DADMAC) and maleamic acid derivatives (MAD) are synthesized by a water-based free radical copolymerization using 4,4-azobis(4-cyanovaleric acid) (V501) as the initiator. The structure of the copolymers is verified by 1H-NMR, elemental analysis, and thermogravimetric measurements, and the physicochemical properties are investigated by viscometric and potentiometric techniques. Potentiometric titration curves show that the acidity of the carboxylic groups strongly depends on the degree of dissociation and the ionic strength. Since all copolymers behave as polycations at low degree of dissociation, a transition from an extended chain to a coil conformation can be identified by reaching the isoelectric point (IEP).
The qualitative and quantitative distinction of enantiomers is one of the key issues in chemical analysis. In the last years, circular dichroism (CD) has been combined with laser ionization mass spectrometry (LIMS), applying resonance enhanced multiphoton ionization (REMPI) with ultrashort laser pulses. We present theoretical investigations on the CD in the populations of the first electronic excited state of the REMPI process, caused by the interaction of 3-methylcyclopentanone with either left or right circular polarized fs-laser pulses. For this we performed multistate laser driven many electron dynamics based on ab initio electronic structure calculations, namely, TD-CIS(D)/6-311++(2d,2p). For a theoretical description of these experiments, a complete description of the field-dipole correlation is mandatory, including both electric field electric dipole and magnetic field magnetic dipole interactions. The effect of various pulse parameters on the CD are analyzed and compared with experimental results to gain further understanding of the key elements for an optimal distinction of enantiomers.
Molecular brush diblock copolymers were synthesized by the orthogonal overlay of the RAFT (reversible addition-fragmentation chain transfer), the ATRP (atom transfer radical polymerization), and the NMP (nitroxide-mediated polymerization) techniques. This unique combination enabled the synthesis of the complex amphiphilic polymers without the need of postpolymerization modifications, using a diblock copolymer intermediate made from two selectively addressable inimers and applying a sequence of four controlled free radical polymerization steps in total. The resulting polymers are composed of a thermosensitive poly(N-isopropylacrylamide) brush as hydrophilic block and a polystyrene brush as hydrophobic block, thus translating the structure of the established amphiphilic diblock copolymers known as macro surfactants to the higher size level of "giant surfactants". The dual molecular brushes and the aggregates formed on ultra flat solid substrates were visualized by scanning force microscopy (SFM).
Synthesis and conformational analysis of new naphth[1,2-e][1,3]oxazino[3,4-c]quinazoline derivatives
(2011)
Rotation about the single bond adjoining the aryl and fluorene moieties in 9-arylfluorenes can be frozen out on the NMR timescale if methyl groups are located at either one or both of the ortho positions of the aryl substituent. In the ground-state of these rotamers, the planes of the aryl and fluorene moieties are perpendicular to each other and the methyl protons are either shielded or deshielded, respectively, due to the ringe current effect of the fluorene moiety. This anisotropic effect on the 1H chemical shifts of the methyl protons has been quantified on the basis of through- space NMR shieldings (TSNMRS) and subsequently _______ compared with the experimentally observed chemical shift differences _____. In this context, the experimental anisotropic effects of functional groups in the !H NMR have proven to quantitatively be the molecular response property of theoretical spatial nucleus independent chemical shieldings (NICS). Differences between _______ and _____ were, for the first time, also quantified as arising from steric compression.
The conformational equilibria of 3-methyl-3-silathiane 5, 3-fluoro-3-methyl-3-silathiane 6 and 1-fluoro-1- methyl-1-silacyclohexane 7 have been studied using low temperature 13C NMR spectroscopy and theoretical calculations. The conformer ratio at 103;K was measured to be about 5ax:5eq;=;15:85, 6ax:6eq;=;50:50 and 7ax:7eq;=;25:75. The equatorial preference of the methyl group in 5 (0.35;kcal;mol;1) is much less than in 3-methylthiane 9 (1.40;kcal;mol;1) but somewhat greater than in 1-methyl-1- silacyclohexane 1 (0.23;kcal;mol;1). Compounds 5-7 have low barriers to ring inversion: 5.65 (ax;;;eq) and 6.0 (eq;;;ax) kcal mol;1 (5), 4.6 (6), 5.1 (Meax;;;Meeq) and 5.4 (Meeq;;;Meax) kcal;mol;1 (7). Steric effects cannot explain the observed conformational preferences, like equal population of the two conformers of 6, or different conformer ratio for 5 and 7. Actually, by employing the NBO analysis, in particular, considering the second order perturbation energies, vicinal stereoelectronic interactions between the Si-X and adjacent C-H, C-S, and C-C bonds proved responsible.
The syn and anti isomers of cis,cis-tricyclo[5.3.0.0(2.6)]dec-3-ene derivatives have been synthesized and their (1)H and (13)C NMR spectra unequivocally analyzed. Both their structures and their (1)H and (13)C NMR chemical shifts were calculated by DFT, the latter two calculations employing the GIAO perturbation method. Additionally, calculated NMR shielding values were partitioned into Lewis and non-Lewis contributions from the bonds and lone pairs involved in the molecules by accompanying NBO and NCS analyses. The differences between the syn and anti isomers were evaluated with respect to steric and spatial hyperconjugation interactions.
1-Oxo-1,3-dithiolane (4) and its cis- andtrans-2-methyl (5,6), -4-methyl (7,8) and -5-methyl (9,10) derivatives were prepared by oxidizing the corresponding 1,3-dithiolanes (1-3) with NaIO4 in water. The oxides were purified and their isomers separated using thin layer chromatography. The structural characterization was carried out with 1H and 13C NMR spectroscopy and molecular modelling. The sulfoxides 4-6 and 8-10 attain two S(1) type envelopes (sometimes slightly distorted) the S=Oax envelope greatly dominating. Cis-4-methyl-1-oxo-1,3-dithiolane is a special case exhibiting both two closely related S=Oax (30 and 27%) as well as S=Oeq (21 and 22%) forms [S(1) and C(4) envelopes, respectively]. The relative energies of these conformations, the values of 1H-1H coupling constants and 1H and 13C chemical shifts were estimated by computational methods and they support well the conclusions based on the experimental data.