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Mixed 1,2-Dümine-1,2-Dithiolate Ligand Complexes : Structure, Proberties and EPR Spectroscopy
(2009)
The theoretically possible stable conformers of free mn-15S2O3 maleonitrile-dithiacrown ether molecule were searched by means of a conformational study which consists of molecular dynamics and energy minimization calculations performed with MM2 force field and successive geometry optimization + frequency calculations performed first at B3LYP/3- 21G and then at B3LYP/6-31G(d) levels of theory. The obtained calculation results have clearly indicated that the free molecule in electronic ground state is very flexible and accordingly has many possible stable conformers of different conformational properties at room temperature; among them, the one having a macrocyclic ring structure in which all of the ether units oriented toward the center of the ring was determined the energetically most preferable conformer. In addition, the equilibrium geometrical parameters, vibrational normal modes and associated IR spectral data of the determined most stable three conformers of the molecule were calculated at B3LYP/6-31+G(d) and B3LYP/6-31++G(d,p) levels of theory. A successful assignment of the fundamental bands observed in the recorded experimental solid phase and solution phase IR spectra of the molecule was achieved in the light of the theoretical data obtained from these DFT calculations. To fit the calculated harmonic wavenumbers to the experimental ones, two different scaling procedures, referred to as "Scaled Quantum Mechanical Force Field (SQM FF) methodology" and "Scaling wavenumbers with empirical dual scale factors", were proceeded independently.
The influence of the reaction medium (organic solvents, water, ionic liquids, supercritical CO2) on the propagation rate in radical polymerizations has very different causes, e.g., hindered rotational modes, hydrogen bonding or electron pair donor/acceptor interactions. Depending on the origin of the solvent influence propagation rate coefficients, k(P), may be enhanced by up to an order of magnitude associated with changes in the pre-exponential or the activation energy of k(P). In contrast, non-specific interactions, size and steric effects lead to rather small changes in the vicinity of the radical chain end and are reflected by modest variations in k(P).
The influence of the reaction medium (organic solvents, water, ionic liquids, supercritical CO2) on the propagation rate in radical polymerizations has very different causes, e.g., hindered rotational modes, hydrogen bonding, or electron pair donor / acceptor interactions. Depending on the origin of the solvent influence propagation rate coefficients, kp, may be enhanced by up to an order of magnitude associated with changes in the pre-exponential or the activation energy of kp. Contrary, non-specific interactions, size and steric effects lead to rather small changes in the vicinity of the radical chain end and are reflected by modest variations in kp.
This work presents the synthesis and the self-assembly of symmetrical amphiphilic ABA and BAB triblock copolymers in dilute, semi-concentrated and highly concentrated aqueous solution. A series of new bifunctional bistrithiocarbonates as RAFT agents was used to synthesise these triblock copolymers, which are characterised by a long hydrophilic middle block and relatively small, but strongly hydrophobic end blocks. As hydrophilic A blocks, poly(N-isopropylacrylamide) (PNIPAM) and poly(methoxy diethylene glycol acrylate) (PMDEGA) were employed, while as hydrophobic B blocks, poly(4-tert-butyl styrene), polystyrene, poly(3,5-dibromo benzyl acrylate), poly(2-ethylhexyl acrylate), and poly(octadecyl acrylate) were explored as building blocks with different hydrophobicities and glass transition temperatures. The five bifunctional trithiocarbonates synthesised belong to two classes: the first are RAFT agents, which position the active group of the growing polymer chain at the outer ends of the polymer (Z-C(=S)-S-R-S-C(=S)-Z, type I). The second class places the active groups in the middle of the growing polymer chain (R-S-C(=S)-Z-C(=S)-S-R, type II). These RAFT agents enable the straightforward synthesis of amphiphilic triblock copolymers in only two steps, allowing to vary the nature of the hydrophobic blocks as well as the length of the hydrophobic and hydrophilic blocks broadly with good molar mass control and narrow polydispersities. Specific side reactions were observed among some RAFT agents including the elimination of ethylenetrithiocarbonate in the early stage of the polymerisation of styrene mediated by certain agents of the type II, while the use of the RAFT agents of type I resulted in retardation of the chain extension of PNIPAM with styrene. These results underline the need of a careful choice of RAFT agents for a given task. The various copolymers self-assemble in dilute and semi-concentrated aqueous solution into small flower-like micelles. No indication for the formation of micellar clusters was found, while only at high concentration, physical hydrogels are formed. The reversible thermoresponsive behaviour of the ABA and BAB type copolymer solutions in water with A made of PNIPAM was examined by turbidimetry and dynamic light scattering (DLS). The cloud point of the copolymers was nearly identical to the cloud point of the homopolymer and varied between 28-32 °C with concentrations from 0.01 to 50 wt%. This is attributed to the formation of micelles where the hydrophobic blocks are shielded from a direct contact with water, so that the hydrophobic interactions of the copolymers are nearly the same as for pure PNIPAM. Dynamic light scattering measurements showed the presence of small micelles at ambient temperature. The aggregate size dramatically increased above the cloud point, indicating a change of aggregate morphology into clusters due to the thermosensitivity of the PNIPAM block. The rheological behaviour of the amphiphilic BAB triblock copolymers demonstrated the formation of hydrogels at high concentrations, typically above 30-35 wt%. The minimum concentration to induce hydrogels decreased with the increasing glass transition temperatures and increasing length of the end blocks. The weak tendency to form hydrogels was attributed to a small share of bridged micelles only, due to the strong segregation regime occurring. In order to learn about the role of the nature of the thermoresponsive block for the aggregation, a new BAB triblock copolymer consisting of short polystyrene end blocks and PMDEGA as stimuli-responsive middle block was prepared and investigated. Contrary to PNIPAM, dilute aqueous solutions of PMDEGA and of its block copolymers showed reversible phase transition temperatures characterised by a strong dependence on the polymer composition. Moreover, the PMDEGA block copolymer allowed the formation of physical hydrogels at lower concentration, i.e. from 20 wt%. This result suggests that PMDEGA has a higher degree of water-swellability than PNIPAM.
Six new bifunctional bis(trithiocarbonate)s were explored as RAFT agents for synthesizing amphiphilic triblock copolymers ABA and BAB, with hydrophilic "A" blocks made from N-isopropylacrylamide and hydrophobic "B" blocks made from styrene. Whereas the extension of poly(N-isopropylacrylamide) by styrene was not effective, polystyrene macroRAFT agents provided the block copolymers efficiently. End group analysis by H-1 NMR spectroscopy supported molar mass analysis and revealed an unexpected side reaction for certain bis(trithiocarbonate)s, namely a fragmentation to simple trithiocarbonates while extruding ethylene-trithiocarbonate. The amphiphilic block copolymers with short polystyrene blocks are directly soluble in water and self-organize into thermo-responsive micellar aggregates.
A set of structures encompassing 1-(9-acridinyl)thiosemicarbazide and its 2-methyl derivative together with their various tautomeric structures; the 5-membered ring 1,3-thiazolidin-4-one products resulting from the reaction of 1- (9-acridinyl)thiosemicarbazide and its 2-methyl derivative with dimethyl acetylenedicarboxylate (DMAD) together with the alternative 6-membered ring isomeric reaction products as well as other potential isomeric structures; and the 6- membered ring 1,3-thiazin-4-one product resulting from the reaction of 2-methyl-1-(9-acridinyl)thiosemicarbazide with methyl propiolate (MP) together with the alternative 5-membered ring isomeric reaction product were all extensively studied by molecular modeling calculations using DFT at the B3LYP/6-31G(d,p) level of theory. The ring-chain tautomerism of the thiosemicarbazides, the regio- and stereoselectivity of the reactions, the adopted conformations and E/Z configurations of the products, the prototropic tautomerism of all the compounds, and the reasons for the predominance of the s-cis conformation of the Z configuration of the 1,3-thiazolidin-4-one product in particular were all extensively analyzed. Comparison of the modeled structures were also made to the 1,3-thiazolidin-4-one and 1,3-thiazin-4-one structures of the methyl derivative as well as 1-(9-acridinyl)thiosemicarbazide available from X-ray crystallographic analysis. Tactics utilizing spectroscopic methods {1R frequencies (nu) and NMR chemical shifts (delta), scalar coupling constants (J), and NOEs (eta)} in conjunction with molecular modeling calculations of the spectral parameters (frequency calculations (v) and NMR 6 using the GIAO method and J by calculation of the Fermi contact term) were evaluated in terms of proving 5- or 6-membered ring formation.
In the first section of the thesis graphitic carbon nitride was for the first time synthesised using the high-temperature condensation of dicyandiamide (DCDA) – a simple molecular precursor – in a eutectic salt melt of lithium chloride and potassium chloride. The extent of condensation, namely next to complete conversion of all reactive end groups, was verified by elemental microanalysis and vibrational spectroscopy. TEM- and SEM-measurements gave detailed insight into the well-defined morphology of these organic crystals, which are not based on 0D or 1D constituents like known molecular or short-chain polymeric crystals but on the packing motif of extended 2D frameworks. The proposed crystal structure of this g-C3N4 species was derived in analogy to graphite by means of extensive powder XRD studies, indexing and refinement. It is based on sheets of hexagonally arranged s-heptazine (C6N7) units that are held together by covalent bonds between C and N atoms. These sheets stack in a graphitic, staggered fashion adopting an AB-motif, as corroborated by powder X-ray diffractometry and high-resolution transmission electron microscopy. This study was contrasted with one of many popular – yet unsuccessful – approaches in the last 30 years of scientific literature to perform the condensation of an extended carbon nitride species through synthesis in the bulk. The second section expands the repertoire of available salt melts introducing the lithium bromide and potassium bromide eutectic as an excellent medium to obtain a new phase of graphitic carbon nitride. The combination of SEM, TEM, PXRD and electron diffraction reveals that the new graphitic carbon nitride phase stacks in an ABA’ motif forming unprecedentedly large crystals. This section seizes the notion of the preceding chapter, that condensation in a eutectic salt melt is the key to obtain a high degree of conversion mainly through a solvatory effect. At the close of this chapter ionothermal synthesis is seen established as a powerful tool to overcome the inherent kinetic problems of solid state reactions such as incomplete polymerisation and condensation in the bulk especially when the temperature requirement of the reaction in question falls into the proverbial “no man’s land” of classical solvents, i.e. above 250 to 300 °C. The following section puts the claim to the test, that the crystalline carbon nitrides obtained from a salt melt are indeed graphitic. A typical property of graphite – namely the accessibility of its interplanar space for guest molecules – is transferred to the graphitic carbon nitride system. Metallic potassium and graphitic carbon nitride are converted to give the potassium intercalation compound, K(C6N8)3 designated according to its stoichiometry and proposed crystal structure. Reaction of the intercalate with aqueous solvents triggers the exfoliation of the graphitic carbon nitride material and – for the first time – enables the access of singular (or multiple) carbon nitride sheets analogous to graphene as seen in the formation of sheets, bundles and scrolls of carbon nitride in TEM imaging. The thus exfoliated sheets form a stable, strongly fluorescent solution in aqueous media, which shows no sign in UV/Vis spectroscopy that the aromaticity of individual sheets was subject to degradation. The final section expands on the mechanism underlying the formation of graphitic carbon nitride by literally expanding the distance between the covalently linked heptazine units which constitute these materials. A close examination of all proposed reaction mechanisms to-date in the light of exhaustive DSC/MS experiments highlights the possibility that the heptazine unit can be formed from smaller molecules, even if some of the designated leaving groups (such as ammonia) are substituted by an element, R, which later on remains linked to the nascent heptazine. Furthermore, it is suggested that the key functional groups in the process are the triazine- (Tz) and the carbonitrile- (CN) group. On the basis of these assumptions, molecular precursors are tailored which encompass all necessary functional groups to form a central heptazine unit of threefold, planar symmetry and then still retain outward functionalities for self-propagated condensation in all three directions. Two model systems based on a para-aryl (ArCNTz) and para-biphenyl (BiPhCNTz) precursors are devised via a facile synthetic procedure and then condensed in an ionothermal process to yield the heptazine based frameworks, HBF-1 and HBF-2. Due to the structural motifs of their molecular precursors, individual sheets of HBF-1 and HBF-2 span cavities of 14.2 Å and 23.0 Å respectively which makes both materials attractive as potential organic zeolites. Crystallographic analysis confirms the formation of ABA’ layered, graphitic systems, and the extent of condensation is confirmed as next-to-perfect by elemental analysis and vibrational spectroscopy.
The generation of nanoscale primary poly(vinylidene fluoride) (PVDF) particles by rapid expansion of supercritical solutions (RESS) is reported. The experimental results show that RESS enables the formation of PVDF particles with median particle diameters ranging from 56 to 226 nm and that the size of PVDF particles can be influenced by polymer properties. The particle size can be decreased either by increasing molar mass, in case of identical polymer end groups, or by increasing the degree of crystallinity, in case of similar molar mass and different end groups.
In this paper, we describe our synthesis of four key building blocks for the total synthesis of psymberin (1) and its C4 epimer (2). Despite early difficulties in processing material to the advanced intermediate stage, we have been successful in developing high-yielding syntheses for the pyran core, natural side chain, 4-epi side chain, and aryl fragments of the molecule. Our findings from the optimization process are presented herein.
A set of structures encompassing 1-(9-acridinyl)thiosemicarbazide and its 2-methyl derivative together with their various tautomeric structures; the 5-membered ring 1,3-thiazolidin-4-one products resulting from the reaction of 1- (9-acridinyl)thiosemicarbazide and its 2-methyl derivative with dimethyl acetylenedicarboxylate (DMAD) together with the alternative 6-membered ring isomeric reaction products as well as other potential isomeric structures; and the 6- membered ring 1,3-thiazin-4-one product resulting from the reaction of 2-methyl-1-(9-acridinyl)thiosemicarbazide with methyl propiolate (MP) together with the alternative 5-membered ring isomeric reaction product were all extensively studied by molecular modeling calculations using DFT at the B3LYP/6-31G(d,p) level of theory. The ring-chain tautomerism of the thiosemicarbazides, the regio- and stereoselectivity of the reactions, the adopted conformations and E/Z configurations of the products, the prototropic tautomerism of all the compounds, and the reasons for the predominance of the s-cis conformation of the Z configuration of the 1,3-thiazolidin-4-one product in particular were all extensively analyzed. Comparison of the modeled structures were also made to the 1,3-thiazolidin-4-one and 1,3-thiazin-4-one structures of the methyl derivative as well as 1-(9-acridinyl)thiosemicarbazide available from X-ray crystallographic analysis. Tactics utilizing spectroscopic methods {IR frequencies (;) and NMR chemical shifts (;), scalar coupling constants (J), and NOEs (;)} in conjunction with molecular modeling calculations of the spectral parameters {frequency calculations (;) and NMR ; using the GIAO method and J by calculation of the Fermi contact term} were evaluated in terms of proving 5- or 6-membered ring formation.
Controlling interactions in synthetic polymers as precisely as in proteins would have a strong impact on polymer science. Advanced structural and functional control can lead to rational design of, integrated nano- and microstructures. To achieve this, properties of monomer sequence defined oligopeptides were exploited. Through their incorporation as monodisperse segments into synthetic polymers we learned in recent four years how to program the structure formation of polymers, to adjust and exploit interactions in such polymers, to control inorganic-organic interfaces in fiber composites and induce structure in Biomacromolecules like DNA for biomedical applications.
Di-nor-benzofuran neolignan aldehydes, Delta(7)-3,4-methylenedioxy-3'-methoxy-8',9'-dinor- 4',7-epoxy-8,3'-neolignan-7'-aldehyde (ocophyllal A) 1, Delta(7)-3,4,5,3'-tetramethoxy- 8',9'-dinor-4',7-epoxy-8,3'-neolignan-7'-aldehyde (ocophyllal B) 2, and macrophyllin-type bicyclo[3.2.1]octanoid neolignans (7R, 8R, 3'S, 4'S, 5'R)-Delta(8)'-4'-hydroxy-5'- methoxy-3,4-methylenedioxy-2',3'.4',5'-tetrahydro-2'-oxo-7.3',8.5'-neolignan (ocophyllol A) 3, (7R, 8R, 3'S, 4'S, 5'R)-Delta 8'-4'-hydroxy-3,4,5'-trimethoxy- 2',3',4',5'-tetrahydro-2'-oxo-7.3',8.5'-neolignan (ocophyllol B) 4, (7R, 8R, 3'S, 4'S, 5'R)-Delta(8)'-4'-hydroxy-3,4,5,5'-tetramethoxy- 2',3',4',5'-tetrahydro-2'-oxo-7.3',8.5'-neolignan (ocophyllol C) 5, as well as 2'-epi-guianin 6 and (+)-licarin B 7, were isolated and characterized from leaves of Ocotea macrophylla (Lauraceae). The structures and configuration of these compounds were determined by extensive spectroscopic analyses. Inhibition of platelet activating factor (PAF)-induced aggregation of rabbit platelets were tested with neolignans 1-7. Although compound 6 was the most potent PAF-antagonist, compounds 3-5 showed some activity.
The anti-inflammatory potential of 26 neolignans (14 of the bicyclooctane-type and 12 of the benzofuran-type), isolated from three Lauraceae species (Pleurothyrium cinereum, Ocotea macrophylla and Nectandra amazonum), was evaluated in vitro through inhibition of COX-1, COX-2, 5-LOX and agonist-induced aggregation of rabbit platelets. Benzofuran neolignans were found to be selective COX-2 inhibitors, whereas bicyclooctane neolignans inhibit selectively the PAF- action as well as COX-1 and 5-LOX. The neolignan 9-nor-7,8-dehydro-isolicarin B 15 and cinerin C 7 were found to be the most potent COX-2 inhibitor and PAF-antagonist, respectively. Nectamazin C 10 exhibited dual 5-LOX/COX-2 inhibition.
Macrophyllin-type bicyclo[3.2.1]octanoid neolignans from the leaves of Pleurothyrium cinereum
(2009)
Four new macrophyllin-type bicyclo[3.2.1]octanoid neolignans, (7S,8R,3'S,5'R)-Delta(8')- 5,5',3'-trimethoxy-3,4-methylenedioxy-2',3',4',5'-tetrahydro-2',4'-dioxo- 7.3',8.5'-neolignan (cinerin A), 1, (7R,8R,3'S,4'R,5'R)-Delta(8')-4'-hydroxy- 5,5'-dimethoxy-3,4-methylenedioxy-2',3',4',5'-tetrahydro-2'-oxo- 7.3',8.5'-neolignan (cinerin B), 2, (7S,8R,3'R,4'S,5'R)-Delta(8')-4'-hydroxy- 5,5',3'-trimethoxy-3,4-methylenedioxy-2',3',4',5'-tetrahydro-2'-oxo- 7.3',8.5'-neolignan (cinerin C), 3, and (7S,8R,2'RYS,5'R)-Delta(8')-2'-hydroxy- 5,5'-dimethoxy-3,4-methylenedioxy-2',3',4',5'-tetrahydro-4'-oxo- 7.3',8.5'-neolignan (cinerin D). 4, along with the known diterpene kaurenoic acid 5, were isolated from the leaves of Pleurothyrium cinercum. The structures and configuration of these compounds were determined by extensive spectroscopic analysis. Cinerins A-D (1-4) were tested for their inhibition efficacy of platelet activating factor (PAF)- induced aggregation of rabbit platelets. Compound 3 was the most potent PAF antagonist. Compounds 1-5 were tested against Mycobacterium tuberculosis (H(37)Rv strain) using the MABA method. Compound 5 induced 91.3% growth inhibition at 50 mu g mL(-1). Compounds 1-5 showed no significant inhibitory activity against some Gram-positive and Gram-negative bacteria by the agar-well diffusion method.
The self-metathesis of methyl 10-undecenoate as well as its cross-metathesis with methyl acrylate was investigated in detail by a systematic variation of the reaction conditions. Unsaturated ;,;-diesters with a chain length of 20 and 12 carbon atoms were thus obtained, respectively. Four different metathesis catalysts were investigated under solvent-free conditions at catalyst loadings ranging from 0.05 mol% to 1 mol% and at temperatures ranging from 30 °C to 90 °C. In the case of the self-metathesis reactions quantitative conversions were obtained with all catalysts, but the second generation metathesis catalysts revealed high amounts of olefin isomerization side reactions at higher temperatures. Using a small quantity of the hydrogen acceptor 1,4-benzoquinone, the isomerization process was almost completely suppressed. Thus, the second generation catalysts allowed for high conversions at very low catalyst loadings. For the cross-metathesis reaction, an interesting temperature and catalyst loading dependent selectivity was observed with the second generation catalysts. Moreover, due to these optimizations, we were able to run these cross-metathesis reactions with a 1:1 ratio of the reactants and low catalysts loadings. This is an improvement over described literature procedures. Thus, we report on the detailed investigation of the described self- and cross- metathesis reactions leading to practical and optimized reaction conditions for the synthesis of unsaturated ;,;-diesters monomers from renewable raw materials in an efficient catalytic manner.
Quantum chemical calculations of various azobenzene (AB) derivatives have been carried out with the goal to describe the energetics and kinetics of their thermal cis -> trans isomerization. The effects of substituents, in particular their type, number, and positioning, on activation energies have been systematically studied with the ultimate goal to tailor the switching process. Trends observed for mono- and disubstituted species are discussed. A polarizable continuum model is used to study, in an approximate fashion, the cis -> trans isomerization of azobenzenes in solution. The nature of the transition state(s) and its dependence on substituents and the environment is discussed. In particular for push-pull azobenzenes, the reaction mechanism is found to change from inversion in nonpolar solvents to rotation in polar solvents. Concerning kinetics, calculations based on the Eyring transition state theory give usually reliable activation energies and enthalpies when compared to experimentally determined values. Also, trends in the resulting rate constants are correct. Other computed properties such as activation entropies and thus preexponential rate factors are in only moderate agreement with experiment.
Molecular photoswitches are attracting much attention lately mostly because of their possible applications in nano technology, and their role in biology. One of the widely studied representatives of photochromic molecules is azobenzene (AB). With light, by a static electric field, or with tunneling electrons this specie can be "switched" from the flat and energetically more stable trans form, into the compact cis form. The back reaction can be induced optically or thermally. Quantum chemical calculations, mostly based on density functional theory, on the AB molecule, AB derivatives and related systems are presented. All the calculations were done for isolated species, however, with implications for latest experimental results aiming at the switching of surface mounted ABs. In some of these experiments, it is assumed that the switching process is substrate mediated, by attaching an electron or a hole to the adsorbate forming short-lived anion or cation resonances. Therefore, we calculated also cationic and anionic ABs in this work. An influence of external electric fields on the potential energy surfaces, was also studied. Further, by the type, number and positioning of various substituent groups, systematic changes on activation energies and rates for the thermal cis-to-trans isomerization can be enforced. The nature of the transition state for ground state isomerization was investigated. Applying Eyring's transition state theory, trends in activation energies and rates were predicted and are, where a comparison was possible, in good agreement with experimental data. Further, thermal isomerization was studied in solution, for which a polarizable continuum model was employed. The influence of substitution and an environment leaves its traces on structural properties of molecules and quantitative appearance of calculated UV/Vis spectra, as well. Finally, an explicit treatment of a solid substrate was demonstrated for the conformational switching, by scanning tunneling microscope, of a 1,5-cyclooctadiene (COD) molecule at a Si(001) surface, treated by a cluster model. At first, we studied energetics and potential energy surfaces along relevant switching coordinates by quantum chemical calculations, followed by the switching dynamics using wave packet methods. We show that, in spite the simplicity of the model, our calculations support the switching of adsorbed COD, by inelastic electron tunneling at low temperatures.
Phosphorus meets carbohydrates: Dimethyl phosphite reacts with ceric(IV) ammonium nitrate (CAN) to give phosphonyl radicals that add to glycals 1. The derivatives 2 were isolated in high yields and during a subsequent Horner-Emmons reaction underwent an interesting elimination to give 3,6-dihydro-2H-pyrans 3. The short sequence with simple precursors is applicable to the transformation of hexoses, pentoses, and disaccharides. Bn=benzyl.
Radical additions to glycals : synthesis and transformations of 2-functionalized carbohydrates
(2009)
Zur Charakterisierung von amphiphilen Blockcopolymeren aus N-Vinylpryrrolidon und Vinylacetat
(2009)
This paper is focused on the influence of added polyampholyte, namely poly(N,N;-diallyl-N,N;- dimethyl-alt-maleamic carboxylate) on the inverse micellar phase range of the pseudo-ternary system consisting of toluene-pentanol (1:1)/SDS/water in dependence on the pH value and the temperature. Investigations on phase behavior have revealed that a greater extension in direction to the water-rich corner can be found at pH 4 compared to pH 9. In order to understand changes in the microstructure, polymer-surfactant interactions in dependence on pH have been examined by means of diffusion-ordered spectroscopy, differential scanning calorimetry, as well as conductivity measurements. The results have proven that the present microemulsion consists of water-in-oil droplets, with the polyampholyte located more in the inner core of the water droplets at pH 9 rather than at the interphase of the surfactant film at pH 4.
The synthesis of six analogs of N,N;-diacetylchitobiose is reported, including a novel transglycosylation reaction for the preparation of S-aryl thioglycosides. The conformations of the compounds were studied by a combination of NMR spectroscopy and molecular modeling, using force field calculations. In the case of the S-aryl thioglycosides with exclusively S-glycosidic linkages, dihedral angles of the disaccharidic S-glycosidic bonds, ;; and ;; and of the S-arylglycoside bonds, ; and ;, were found to be similar, whereas they were different in mixed glycosides and in a thiazoline derivative. An adequate correlation between the calculated H,H-distances of the local minima and the measured NOE contacts was achieved by applying population-weighted averages over participating conformers based on weighted relative energies.
Films of anthracene carboxylic acids were irradiated through photomasks and oxidized at the exposed regions by singlet oxygen upon sensitization. The efficiency of a photomask to protect the material underneath was investigated by optical and infrared spectroscopy. As the thickness of the film is reduced, the efficiency of the mask drops. This is explained by the migration of singlet oxygen at the solid-air interface, which in turn reacts at the masked area. For films with a thickness of < 15 nm, the efficiency of the mask approaches zero: sufficient efficiency is achieved at thicknesses > 100 nm. From the investigations, it will become clear that the contrast between the irradiated and masked area of an image is affected by reduction of the film thickness. On the other hand, the resolution of an image, which relates to the minimum feature size of an image, is not dependent on the thickness of the film. The contributions of "inside" and "outside" reactions are examined separately, and it quantitative approximation of the spatial range of both modes of the oxygenation is given. We set tip an approximate relation between mask efficiency and experimental conditions comprising internal and external oxygen diffusion, film thickness, and mask dimensions. These results give it deeper insight into the limits of resolution and contrast in singlet oxygen lithography.
Mesoporous silica monoliths were prepared by the sol - gel technique and. lled with 1-ethyl-3-methyl imidazolium [Emim]-X (X = dicyanamide [N(CN)(2)], ethyl sulfate [EtSO4], thiocyanate [SCN], and triflate [TfO]) ionic liquids (ILs) using a methanol-IL exchange technique. The structure and behavior of the ILs inside the silica monoliths were studied using X-ray scattering, nitrogen sorption, IR spectroscopy, solid-state NMR, and thermal analysis. DSC finds shifts in both the glass transition temperature and melting points (where applicable) of the ILs. Glass transition and melting occur well below room temperature. There is thus no conflict with the NMR and IR data, which show that the ILs are as mobile at room temperature as the bulk (not confined) ILs. The very narrow line widths of the NMR spectra suggest that the ILs in our materials have the highest mobility reported for confined ILs so far. As a result, our data suggest that it is possible to generate IL/silica hybrid materials (ionogels) with bulk-like properties of the IL. This could be interesting for applications in, e.g., the solar cell or membrane fields.
Simple tripeptides are scaffolds for the synthesis and further assembly of peptide/silver nanoparticle composites. Herein, we further explore peptide-con trolled silver nanoparticle assembly processes. Silver nanoparticles with a pH-responsive peptide coating have been synthesized by using a one-step precipitation/coating route. The nature of the peptide/silver interaction and the effect of the peptide oil the formation of the silver particles have been studied via UV/Vis, X-ray photoelectron, and surface-enhanced Raman spectroscopies as well as through electron microscopy, small angle X-ray scattering and powder Xray diffraction with Rietveld refinement. The particles reversibly form aggregates of different sizes in aqueous solution. The state of aggregation call be controlled by the solution pH value. At low pH values, individual particles are present. At neutral pH values, small clusters form and at high pH values, large precipitates are observed.
Intermolecular hydrogen bonding, not hydrophobic interaction, is the driving force for the spontaneous self- assembly of glycosylated polyoxazoline chains into nanotubes in dilute aqueous solution. The structural information is encoded in the relatively simple molecular structure of chains consisting of a tertiary polyamide backbone (hydrogen- accepting) and glucose side chains (hydrogen-donating). The formation of the nanotubes should occur through bending and closing of a 2D hydrogen-bonded layer of interdigitated polymer chains.
The BLUF (blue-light sensing using flavine) domain of the AppA photoreceptor protein from Rhodobacter sphaeroides was modelled by using quantum chemical chromophore plus amino acid models at the (TD-)B3LYP/6-31G* level of theory. The models were based on NMR structures, and further refined by CHARM force field molecular dynamics simulations. The goal is to explain the total redshift by about 10 nm in the UV/Vis spectra of BLUF domains after illumination, and to relate it to structural changes. For this purpose UV/Vis spectra of the available NMR structures were calculated and related to geometrical features. In particular, the hydrogen network embedding the central chromophore is discussed. Specifically, the position of a conserved glutamine, Q63, is found to be important in agreement with findings from previous works. Additionally, however, we find a systematic dependence also on the geometry of a conserved serine, S41. Based on a series of calculations with known structures and with artificial structural models, we argue that indeed the light-induced switching of both Q63 and S41 is necessary to explain the full similar to 10 nm redshift in the light (signalling) state of serine containing BLUF domains. Following or accompanying the double switching, two structurally highly important residues W104 and M106 exchange places, but do not affect the overall UV/ Vis properties of the chromophore.
Die Kombination von Polymeren mit Peptiden vereint die Eigenschaften beider Stoffklassen miteinander. Dabei können die strukturbildenden Eigenschaften der Peptide genutzt werden, um Polymere zu organisieren. In der vorliegenden Arbeit wurde ein Polymer-Peptid-Konjugat verwendet, das sich in Wasser zu Bändern anordnet. Die treibende Kraft für diesen Prozess ist die Anordnung des Peptidteils zu β-Faltblattstrukturen. Das Polymer-Peptid-Aggregat besitzt einen Peptidkern mit funktionalen Oberflächen, der lateral von einer Polyethylenoxidschale umgeben ist. Durch Änderung der Peptidsequenz war es bisher möglich, die Eigenschaften dieser Fasern zu variieren. In der Arbeit wird ein modularer Ansatz zur vielfältigen Modifizierung einer Polymer-Peptid-Faser entwickelt. So ist es möglich, die Eigenschaften der Fasern einzustellen, ohne die strukturbildende β-Faltblattsequenz verändern zu müssen. Um weitere Funktionen an den Fasern anzubringen, wurde die 1,3-dipolaren Addition verwendet. Diese Reaktion beschreibt die konzertierte Umlagerung eines Azides mit einem Alkin. Sie ist in den meisten Lösungsmitteln unter hohen Ausbeuten durchführbar. Im Rahmen der Arbeit wird die Erzeugung von Aziden untersucht und auf die Polymer-Peptid-Fasern übertragen. Der Diazotransfer stellte dabei die Methode der Wahl dar, so können Azidgruppen aus Aminen gewonnen werden. Unter Verwendung der 1,3-dipolaren Addition konnten verschiedene alkinfunktionale Moleküle kovalent an die azidfunktionalisierten Polymer-Peptid-Fasern gebunden werden. So wurde ein Fluoreszenzfarbstoff an die Fasern gebunden, der eine Abbildung der Fasern mittels konfokaler Mikroskopie erlaubte. Weiterhin wurden die Eigenschaften der Fasern durch Addition dreier carboxylfunktionaler Moleküle modifiziert. Diese Fasern konnten weiter genutzt werden, um Kalzium zu binden. Dabei variierte die Anzahl der gebundenen Kalziumionen in Abhängigkeit der jeweiligen Fasermodifikation erheblich. Weitere Untersuchungen, die Morphologie von Kalziumcarbonatkristallen betreffend, werden aktuell durchgeführt. Die kovalente Anbringung eines reduzierenden Zuckers an die Polymer-Peptid-Fasern erlaubt die Abscheidung von Silber aus Tollens Reagenz. Durch eine Entwicklung analog zur Schwarz-Weiss-Photographie können in nachfolgenden Arbeiten so Silberdrähte in Nanogröße erzeugt werden. An die azidfunktionalen Fasern können weitere funktionale Moleküle angebracht werden, um die Eigenschaften und das Anwendungsspektrum der Polymer-Peptid-Fasern zu erweitern.
Two-photon fluorescence lifetime imaging of intracellular chloride in cockroach salivary glands
(2009)
Mass spectrometry of aminoglucan oligosaccharides using electrospray ionization MS/MS and MS/MS/MS
(2009)
The epoxy system containing diglycidyl ether of bisphenol A and 4,4'-diaminodiphenyl sulfone is modified with poly(acrylonitrile-butadiene-styrene) (ABS) to explore the effects of the ABS content on the phase morphology, mechanism of phase separation, and viscoelastic properties. The amount of ABS in the blends was 5, 10, 15, and 20 parts per hundred of epoxy resin (phr). Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) were employed to investigate the final morphology of ABS-modified epoxy blends. Scanning electron microscopic studies of 15 phr ABS-modified epoxy blends reveal a bicontinuous structure in which both epoxy and ABS are continuous, with substructures of the ABS phase dispersed in the continuous epoxy phase and substructures of the epoxy phase dispersed in the continuous ABS phase. TEM micrographs of 15 phr ABS-modified epoxy blends confirm the results observed by SEM. TEM micrographs reveal the existence of nanosubstructures of ABS in 20 phr ABS-modified epoxy blends. To the best of our knowledge, to date, nanosubstructures have never been reported in any epoxy/thermoplastic blends. The influence of the concentration of the thermoplastic on the generated morphology as analyzed by SEM and TEM was explained in detail. The evolution and mechanism of phase separation was investigated in detail by optical microscopy (OM) and small-angle laser light scattering (SALLS). At concentrations lower than 10 phr the system phase separates through nucleation and growth (NG). However, at higher concentrations, 15 and 20 phr, the blends phase separate through both NG and spinodal decomposition mechanisms. On the basis of OM and SALLS, we conclude that the phenomenon of complex substructure formation in dynamic asymmetric blends is due to the combined effect of hydrodynamics and viscoelasticity. Additionally, dynamic mechanical analysis was carried out to evaluate the viscoelastic behavior of the cross-linked epoxy/ABS blends. Finally, apparent weight fractions of epoxy and ABS components in epoxy- and ABS-rich phases were evaluated from T-g analysis.
Using a regioselective strategy for nucleophilic aromatic substitution on polyfluoropyridines, a nonacoordinating precursor was designed that is adequately suited for complexation of lanthanide cations. Further functionalizations afforded numerous applications for near-IR emission, two-photon absorption spectroscopy, or the formation of luminescent gels.
2,11-Dialkylated 1,12-diazaperylenes (alkyl = Me, Et, iPr) dmedap, detdap and dipdap have been synthesized by reductive cyclization of 3,3-dialkylated 1,1-biisoquinolines 3a-c, resulting in the first copper(I) complexes of a large- surface ligand. The new copper(I) complexes show low-energy MLCT absorptions unprecedented for bis(-diimin)copper(I) complexes. The solid structures of the complexes[Cu(dipdap)2]BF4·CH2Cl2·1.5H2O, [Cu(dipdap)2]OTf·CH2Cl2, [Cu(dipdap)2]I·C2H4Cl2·THF·2H2O, [Cu(dmedap)2]OTf and [Cu(dipdap)2]AQSO3·H2O (AQSO3 = sodium 9,10-dihydro-9,10-dioxo-2- anthracenesulfonate) are reported. In [Cu(dipdap)2]BF4·CH2Cl2·1.5H2O, each copper(I) complex cation interacts with two others by - stacking interactions forming a novel supramolecular column structural motif running along the crystallographic c axis. In the crystalline compound [Cu(dipdap)2]AQSO3·H2O, aggregation between two complex cations and two additional anions by - stacking interactions is observed, leading to a tetrameric assembly. Furthermore, the three complex compounds [Cu(L)2]BF4 (L = dmedap, detdap, dipdap) were tested for sensory applications in aqueous buffer solutions in electrochemical studies of the complex immobilized on glassy carbon electrodes.
Analytical ultracentrifugation (AUC) has made an important contribution to polymer and particle characterization since its invention by Svedberg (Svedberg and Nichols 1923; Svedberg and Pederson 1940) in 1923. In 1926, Svedberg won the Nobel price for his scientific work on disperse systems including work with AUC. The first important discovery performed with AUC was to show the existence of macromolecules. Since that time AUC has become an important tool to study polymers in biophysics and biochemistry. AUC is an absolute technique that does not need any standard. Molar masses between 200 and 1014 g/mol and particle size between 1 and 5000 nm can be detected by AUC. Sample can be fractionated into its components due to its molar mass, particle size, structure or density without any stationary phase requirement as it is the case in chromatographic techniques. This very property of AUC earns it an important status in the analysis of polymers and particles. The distribution of molar mass, particle sizes and densities can be measured with the fractionation. Different types of experiments can give complementary physicochemical parameters. For example, sedimentation equilibrium experiments can lead to the study of pure thermodynamics. For complex mixtures, AUC is the main method that can analyze the system. Interactions between molecules can be studied at different concentrations without destroying the chemical equilibrium (Kim et al. 1977). Biologically relevant weak interactions can also be monitored (K ≈ 10-100 M-1). An analytical ultracentrifuge experiment can yield the following information: • Molecular weight of the sample • Number of the components in the sample if the sample is not a single component • Homogeneity of the sample • Molecular weight distribution if the sample is not a single component • Size and shape of macromolecules & particles • Aggregation & interaction of macromolecules • Conformational changes of macromolecules • Sedimentation coefficient and density distribution Such an extremely wide application area of AUC allows the investigation of all samples consisting of a solvent and a dispersed or dissolved substance including gels, micro gels, dispersions, emulsions and solutions. Another fact is that solvent or pH limitation does not exist for this method. A lot of new application areas are still flourishing, although the technique is 80 years old. In 1970s, 1500 AUC were operational throughout the world. At those times, due to the limitation in detection technologies, experimental results were obtained with photographic records. As time passed, faster techniques such as size exclusion chromatography (SEC), light scattering (LS) or SDS-gel electrophoresis occupied the same research fields with AUC. Due to these relatively new techniques, AUC began to loose its importance. In the 1980s, only a few AUC were in use throughout the world. In the beginning of the 1990s a modern AUC -the Optima XL-A - was released by Beckman Instruments (Giebeler 1992). The Optima XL-A was equipped with a modern computerized scanning absorption detector. The addition of Rayleigh Interference Optics is introduced which is called XL-I AUC. Furthermore, major development in computers made the analysis easier with the help of new analysis software. Today, about 400 XL-I AUC exist worldwide. It is usually applied in the industry of pharmacy, biopharmacy and polymer companies as well as in academic research fields such as biochemistry, biophysics, molecular biology and material science. About 350 core scientific publications which use analytical ultracentrifugation are published every year (source: SciFinder 2008 ) with an increasing number of references (436 reference in 2008). A tremendous progress has been made in method and analysis software after digitalization of experimental data with the release of XL-I. In comparison to the previous decade, data analysis became more efficient and reliable. Today, AUC labs can routinely use sophisticated data analysis methods for determination of sedimentation coefficient distributions (Demeler and van Holde 2004; Schuck 2000; Stafford 1992), molar mass distributions (Brookes and Demeler 2008; Brookes et al. 2006; Brown and Schuck 2006), interaction constants (Cao and Demeler 2008; Schuck 1998; Stafford and Sherwood 2004), particle size distributions with Angstrom resolution (Cölfen and Pauck 1997) and the simulations determination of size and shape distributions from sedimentation velocity experiments (Brookes and Demeler 2005; Brookes et al. 2006). These methods are also available in powerful software packages that combines various methods, such as, Ultrascan (Demeler 2005), Sedift/Sedphat (Schuck 1998; Vistica et al. 2004) and Sedanal (Stafford and Sherwood 2004). All these powerful packages are free of charge. Furthermore, Ultrascans source code is licensed under the GNU Public License (http://www.gnu.org/copyleft/gpl.html). Thus, Ultrascan can be further improved by any research group. Workshops are organized to support these software packages. Despite of the tremendous developments in data analysis, hardware for the system has not developed much. Although there are various user developed detectors in research laboratories, they are not commercially available. Since 1992, only one new optical system called “the fluorescence optics” (Schmidt and Reisner, 1992, MacGregor et al. 2004, MacGregor, 2006, Laue and Kroe, in press) has been commercialized. However, except that, there has been no commercially available improvement in the optical system. The interesting fact about the current hardware of the XL-I is that it is 20 years old, although there has been an enormous development in microelectronics, software and in optical systems in the last 20 years, which could be utilized for improved detectors. As examples of user developed detector, Bhattacharyya (Bhattacharyya 2006) described a Multiwavelength-Analytical Ultracentrifuge (MWL-AUC), a Raman detector and a small angle laser light scattering detector in his PhD thesis. MWL-AUC became operational, but a very high noise level prevented to work with real samples. Tests with the Raman detector were not successful due to the low light intensity and thus high integration time is required. The small angle laser light scattering detector could only detect latex particles but failed to detect smaller particles and molecules due to low sensitivity of the detector (a photodiode was used as detector). The primary motivation of this work is to construct a detector which can measure new physico-chemical properties with AUC with a nicely fractionated sample in the cell. The final goal is to obtain a multiwavelength detector for the AUC that measures complementary quantities. Instrument development is an option for a scientist only when there is a huge potential benefit but there is no available commercial enterprise developing appropriate equipment, or if there is not enough financial support to buy it. The first case was our motivation for developing detectors for AUC. Our aim is to use today’s technological advances in microelectronics, programming, mechanics in order to develop new detectors for AUC and improve the existing MWL detector to routine operation mode. The project has multiple aspects which can be listed as mechanical, electronical, optical, software, hardware, chemical, industrial and biological. Hence, by its nature it is a multidisciplinary project. Again by its nature it contains the structural problem of its kind; the problem of determining the exact discipline to follow at each new step. It comprises the risk of becoming lost in some direction. Having that fact in mind, we have chosen the simplest possible solution to any optical, mechanical, electronic, software or hardware problem we have encountered and we have always tried to see the overall picture. In this research, we have designed CCD-C-AUC (CCD Camera UV/Vis absorption detector for AUC) and SLS-AUC (Static Light Scattering detector for AUC) and tested them. One of the SLS-AUC designs produced successful test results, but the design could not be brought to the operational stage. However, the operational state Multiwavelength Analytical Ultracentrifuge (MWL-AUC) AUC has been developed which is an important detector in the fields of chemistry, biology and industry. In this thesis, the operational state Multiwavelength Analytical Ultracentrifuge (MWL-AUC) AUC is to be introduced. Consequently, three different applications of MWL-AUC to the aforementioned disciplines shall be presented. First of all, application of MWL-AUC to a biological system which is a mixture of proteins lgG, aldolase and BSA is presented. An application of MWL-AUC to a mass-produced industrial sample (β-carotene gelatin composite particles) which is manufactured by BASF AG, is presented. Finally, it is shown how MWL-AUC will impact on nano-particle science by investigating the quantum size effect of CdTe and its growth mechanism. In this thesis, mainly the relation between new technological developments and detector development for AUC is investigated. Pioneering results are obtained that indicate the possible direction to be followed for the future of AUC. As an example, each MWL-AUC data contains thousands of wavelengths. MWL-AUC data also contains spectral information at each radial point. Data can be separated to its single wavelength files and can be analyzed classically with existing software packages. All the existing software packages including Ultrascan, Sedfit, Sedanal can analyze only single wavelength data, so new extraordinary software developments are needed. As a first attempt, Emre Brookes and Borries Demeler have developed mutliwavelength module in order to analyze the MWL-AUC data. This module analyzes each wavelength separately and independently. We appreciate Emre Brookes and Borries Demeler for their important contribution to the development of the software. Unfortunately, this module requires huge amount of computer power and does not take into account the spectral information during the analysis. New software algorithms are needed which take into account the spectral information and analyze all wavelengths accordingly. We would like also invite the programmers of Ultrascan, Sedfit, Sedanal and the other programs, to develop new algorithms in this direction.
Background & objectives: This paper reports the larvicidal activity of seventeen Tanzanian plant species against the malaria vector, Anopheles gambiae s.s. Giles larvae. Some of the plants are used traditionally as sources of insecticidal materials. Methods: The crude extracts from the leaves, stem and root barks of the investigated plants were obtained by solvent extraction and then bio-assayed following WHO protocols showed LC50 values 10 to 400 ppm after 24 h exposure. The structures were determined on interpretation of spectroscopic data. Results: The most active extracts were those from the stem and root barks of Annona squamosa, Uvaria faulknerae, U. kirkii and Uvariodendron pycnophyllum, all of which had LC50 values between 10 and 100 ppm. Long-term exposure beyond 24 h also showed more susceptibility of the larvae to the extracts. Larvae deformities by forming tail-like structures were observed for the methanol extracts of Tessmannia martiniana var pauloi. Interpretation & conclusion: The results suggest that the investigated plant extracts are promising as larvicides against An. gambiae s.s. Giles mosquitoes and could be useful leads in the search for new and biodegradable plant derived larvicide products.