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Driven mostly by the search for chemical syntheses under biocompatible conditions, so called "click" chemistry rapidly became a growing field of research. The resulting simple one-pot reactions are so far only scarcely accompanied by an adequate optimization via comparably straightforward and robust analysis techniques possessing short set-up times. Here, we report on a fast and reliable calibration-free online NMR monitoring approach for technical mixtures. It combines a versatile fluidic system, continuous-flow measurement of H-1 spectra with a time interval of 20 s per spectrum, and a robust, fully automated algorithm to interpret the obtained data. As a proof-of-concept, the thiol-ene coupling between N-boc cysteine methyl ester and ally] alcohol was conducted in a variety of non-deuterated solvents while its time-resolved behaviour was characterized with step tracer experiments. Overlapping signals in online spectra during thiol-ene coupling could be deconvoluted with a spectral model using indirect hard modeling and were subsequently converted to either molar ratios (using a calibration free approach) or absolute concentrations (using 1-point calibration). For various solvents the kinetic constant k for pseudo-first order reaction was estimated to be 3.9 h(-1) at 25 degrees C. The obtained results were compared with direct integration of non-overlapping signals and showed good agreement with the implemented mass balance. (C) 2017 Elsevier Inc. All rights reserved.
Ionic liquids are well known for their high gas absorption capacity. It is shown that this is not a solvent constant, but can be enhanced by another factor of 10 by pore confinement, here of the ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate (EmimOAc) in the pores of carbon materials. A matrix of four different carbon compounds with micro- and mesopores as well as with and without nitrogen doping is utilized to investigate the influence of the carbons structure on the nitrogen uptake in the pore-confined EmimOAc. In general, the absorption is most improved for IL in micropores and in nitrogen-doped carbon. This effect is so large that it is already seen in TGA and DSC experiments. Due to the low vapor pressure of the IL, standard volumetric sorption experiments can be used to quantify details of this effect. It is reasoned that it is the change of the molecular arrangement of the ions in the restricted space of the pores that creates additional free volume to host molecular nitrogen.
The aim of this study was to develop a one-step synthesis of gold nanotriangles (NTs) in the presence of mixed phospholipid vesicles followed by a separation process to isolate purified NTs. Negatively charged vesicles containing AOT and phospholipids, in the absence and presence of additional reducing agents (polyampholytes, polyanions or low molecular weight compounds), were used as a template phase to form anisotropic gold nanoparticles. Upon addition of the gold chloride solution, the nucleation process is initiated and both types of particles, i.e., isotropic spherical and anisotropic gold nanotriangles, are formed simultaneously. As it was not possible to produce monodisperse nanotriangles with such a one-step procedure, the anisotropic nanoparticles needed to be separated from the spherical ones. Therefore, a new type of separation procedure using combined polyelectrolyte/micelle depletion flocculation was successfully applied. As a result of the different purification steps, a green colored aqueous dispersion was obtained containing highly purified, well-defined negatively charged flat nanocrystals with a platelet thickness of 10 nm and an edge length of about 175 nm. The NTs produce promising results in surface-enhanced Raman scattering.
Somewhat surprisingly, inverted ("O-down") CO adsorbates on NaCl(100) were recently observed experimentally after infrared vibrational excitation (Lau et al., Science, 2020, 367, 175-178). Here we characterize these species using periodic density functional theory and a quantum mechanical description of vibrations. We determine stationary points and minimum energy paths for CO inversion, for low (1/8 and 1/4 monolayers (ML)) and high (1 ML) coverages. Transition state theory is applied to estimate thermal rates for "C-down" to "O-down" isomerization and the reverse process. For the 1/4 ML p(1 x 1) structure, two-dimensional and three-dimensional potential energy surfaces and corresponding anharmonic vibrational eigenstates obtained from the time-independent nuclear Schrodinger equation are presented. We find (i) rather coverage-independent CO inversion energies (of about 0.08 eV or 8 kJ mol(-1) per CO) and corresponding classical activation energies for "C-down" to "O-down" isomerization (of about 0.15 eV or 14 kJ mol(-1) per CO); (ii) thermal isomerization rates at 22 K which are vanishingly small for the "C-down" to "O-down" isomerization but non-negligible for the back reaction; (iii) several "accidentally degenerate" pairs of eigenstates well below the barrier, each pair describing "C-down" to "O-down" localized states.
This paper focuses on two different strategies to incorporate gold nanoparticles (AuNPs) into the matrix of polyacrylamide (PAAm) hydrogels. Poly(ethyleneimine) (PEI) is used as both reducing and stabilizing agent for the formation of AuNPs. In addition, the influence of an ionic liquid (IL) (i.e., 1-ethyl-3-methylimidazolium ethylsulfate) on the stability of the nanoparticles and their immobilization in the hydrogel is investigated The results show that AuNPs surrounded by a shell containing PEI and IL, synthesized according to the one-pot approach, are much better immobilized within the PAAm hydrogel. Hereby, the IL is responsible for structural changes in the hydrogel as well as the improved stabilization and embedding of the AuNPs into the polymer gel matrix.
Nanostructured inorganic materials are routinely synthesized by the use of templates. Depending on the synthesis conditions of the product material, either “soft” or “hard” templates can be applied. For sol-gel processes, usually “soft” templating techniques are employed, while “hard” templates are used for high temperature synthesis pathways. In classical templating approaches, the template has the unique role of structure directing agent, in the sense that it is not participating to the chemical formation of the resulting material. This work investigates a new templating pathway to nanostructured materials, where the template is also a reagent in the formation of the final material. This concept is described as “reactive templating” and opens a synthetic path toward materials which cannot be synthesised on a nanometre scale by classical templating approaches. Metal nitrides are such kind of materials. They are usually produced by the conversion of metals or metal oxides in ammonia flow at high temperature (T > 1000°C), which make the application of classical templating techniques difficult. Graphitic carbon nitride, g-C3N4, despite its fundamental and theoretical importance, is probably one of the most promising materials to complement carbon in material science and many efforts are put in the synthesis of this material. A simple polyaddition/elimination reaction path at high temperature (T = 550°C) allows the polymerisation of cyanamide toward graphitic carbon nitride solids. By hard templating, using nanostructured silica or aluminium oxide as nanotemplates, a variety of nanostructured graphitic carbon nitrides such as nanorods, nanotubes, meso- and macroporous powders could be obtained by nanocasting or nanocoating. Due to the special semi-conducting properties of the graphitic carbon nitride matrix, the nanostructured graphitic carbon nitrides show unexpected catalytic activity for the activation of benzene in Friedel-Crafts type reactions, making this material an interesting metal free catalyst. Furthermore, due to the chemical composition of g-C3N4 and the fact that it is totally decomposed at temperatures between 600°C and 800°C even under inert atmosphere, g-C3N4 was shown to be a good nitrogen donor for the synthesis of early transition metal nitrides at high temperatures. Thus using the nanostructured carbon nitrides as “reactive templates” or “nanoreactors”, various metal nitride nanostructures, such as nanoparticles and porous frameworks could be obtained at high temperature. In this approach the carbon nitride nanostructure played both the role of the nitrogen source and of the exotemplate, imprinting its size and shape to the resulting metal nitride nanostructure.
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.
The fruit of Aristotelia chilensis is considered a "super fruit" due to its high concentration of polyphenols displaying exceptional antioxidant capacities ORAC. From maqui berries have been reported several anthocyanins and glycosylated flavonoids, those benefits increase the attention to restudy the plant. From the leaves of A. chilensis several indole alkaloids have been reported, we in addition to aristoteline, aristone, aristoquinoline and 3-fromylindole report the spectroscopic elucidation of 8-oxo-9-dehydromakomakine (1), hobartine (2) and a new alkaloid named 8-oxohobartine (3). Compound 1 to 3 did not show bactericidal activity against E. coli and S. aureus till 200 mu g.
Lobelia tupa, also called devil's tobacco, is a native plant from the center-south of Chile which has been used by the native people of Chile as a hallucinogenic and anesthetic plant. A new piperidine alkaloid, called pentylsedinine, which comprises five carbons in the side chain, was isolated from the aerial part of L. tupa, along with lobeline and lobelanidine. The structure was established on the basis of 1D and 2D NMR spectroscopy. While lobeline is a neutral antagonist at alpha 3 beta 2/alpha 3 beta 4 nAChR and alpha 7 nAChR, both lobelanidine and pentylsedinine act as partial agonists at nAChR
The spatial magnetic properties (Through-Space NMR Shieldings-TSNMRS) of already synthesized dehydro[n]annulenes of various ring size (from C-12 to C-20) have been computed, visualized as Isochemical Shielding Surfaces (ICSS) of various size and direction, and were examined subject to present (anti)aromaticity. For this purpose the thus quantified ring current effect of the macro cycles on proximate protons in proton NMR spectra was employed.
Molecular excitons play a central role in processes of solar energy conversion, both natural and artificial. It is therefore no wonder that numerous experimental and theoretical investigations in the last decade, employing state-of-the-art spectroscopic techniques and computational methods, have been driven by the common aim to unravel exciton dynamics in multichromophoric systems. Theoretically, exciton (de)localization and transfer dynamics are most often modelled using either mixed quantum-classical approaches (e.g., trajectory surface hopping) or fully quantum mechanical treatments (either using model diabatic Hamiltonians or direct dynamics). Yet, the terms such as "exciton localization" or "exciton transfer" may bear different meanings in different works depending on the method in use (quantum-classical vs. fully quantum). Here, we relate different views on exciton (de)localization. For this purpose, we perform molecular surface hopping simulations on several tetracene dimers differing by a magnitude of exciton coupling and carry out quantum dynamical as well as surface hopping calculations on a relevant model system. The molecular surface hopping simulations are done using efficient long-range corrected time-dependent density functional tight binding electronic structure method, allowing us to gain insight into different regimes of exciton dynamics in the studied systems.
We dissect the sources of error leading to inaccuracies in the description of the geometry and optical excitation energies of pi-conjugated polymers. While the ground-state bond length alternation is shown to be badly reproduced by standard functionals, the recently adapted functionals PBEh* and omega PBE* as well as the double hybrid functional XYGJ-OS manage to replicate results obtained at the CCSD(T) level. By analysis of the bond length alternation in the excited state, a sensitive dependence of the exciton localization on the long-range behavior of the functional and the amount of Hartree-Fock exchange present is shown. Introducing thermal disorder through molecular dynamics simulations allows the consideration of a range of thermally accessible configurations of each oligomer, including trans to cis rotations, which break the conjugation of the backbone. Thermal disorder has a considerable effect when combined with functionals that overestimate the delocalization of the excitation, such as B3LYP. For functionals with a larger amount of exact exchange such as our PBEh* and omega PBE*, however, the effect is small, as excitations are often localized enough to fit between twists in the chain.
A series of new N2S2 mixed ligand transition metal complexes, where N-2 is phenanthroline and S-2 is 1,2- dithiooxalate (dto) or 1,2-dithiosquarate (dtsq), has been synthesized and characterized. IR spectra reveal that the 1,2- dithiolate ligands are coordinated via the sulfur atoms forming a N2S2 coordination sphere. The copper(II) complex [Cu(phen)(dto)] was studied by EPR spectroscopy as a diamagnetically diluted powder. The diamagnetic dilution resulted from doping of the copper complex into the isostructural host lattice of the nickel complex [Ni(phen)(dto)]. The electronic situation in the frontier orbitals of the copper complex calculated from the experimental data is compared to the results of EHT and DFT calculations. Furthermore, one side product, chlorobis(1,10-phenanthroline)copper(I) ethanol solvate hydrate [(phen)(2)CuCl]center dot C2H5OH center dot H2O, was formed by a reduction process and characterized by X-ray diffraction. In the crystal packing one-dimensional columns of dimers are formed, stabilized by significant pi-pi interactions.
A series of new monocationic iridium(III) complexes [Ir((CN)-N-boolean AND)(2)((NN)-N-boolean AND)]PF6 with "large-surface" alpha,alpha'-diimin ligands (NN)-N-boolean AND (dap = 1,12-diazaperylene, dmedap = 2,11-dimethyl-1,12-diazaperylene, dipdap = 2,11-diisopropyl-1,12-diazaperylene) and different cyclometalating ligands (CN)-N-boolean AND (piq = 1-phenylisoquinoline, bzq = benzo[h]quinoline, ppz = 1-phenylpyrazole, thpy = 2-(2-thienyl)pyridine, ppy = 2-phenylpyridine, meppy = 2-(4-methylphenyl)pyridine, dfppy = 2-(2,4-difluorophenyl)pyridine) were synthesized. The solid structures of the complexes [Ir(piq)(2)(dap)]PF6, [Ir(bzq)(2)(dap)]PF6, [Ir(ppy)(2)(dipdap)]PF6, [Ir(piq)(2)(dmedap)]PF6, [Ir(ppy)(2)(dap)]PF6 and [Ir(ppz)(2)(dap)]PF6 are reported. In [Ir(piq)(2)(dap)]PF6, the dap ligand and one of the piq ligands of each cationic complex are involved in pi-pi stacking interactions forming supramolecular channels running along the crystallographic c axis. In the crystalline [Ir(bzq)(2)(dap)]PF6 pi-pi stacking interactions between the metal complexes lead to the formation of a 2D layer structure. In addition, CH-pi interactions were found in all compounds, which are what stabilizes the solid structure. In particular, a significant number of them were found in [Ir(piq)(2)(dap)]PF6 and [Ir(bzq)(2)(dap)]PF6. The crystal structures of [Ir(ppy)(2)(dipdap)]PF6 and [Ir(ppy)(2)(dmedap)]PF6 are also presented, being the first examples of bis-cyclometalated iridium(III) complexes with phenanthroline-type alpha,alpha'-diimin ligands bearing bulky alkyl groups in the neighbourhood of the N-donor atoms. These ligands implicate a distorted octahedral coordination geometry that in turn destabilized the Ir-N-N boolean AND N bonds. The new iridium (III) complexes are not luminescent. All compounds show an electrochemically irreversible anodic peak between 1.15 and 1.58 V, which is influenced by the different cyclometalated ligands. All of the new complexes show two reversible successive one-electron "large-surface" ligand-centred reductions around -0.70 V and -1.30 V. Electrospray ionisation mass spectrometry (ESI-MS) and collision induced decomposition (CID) measurements were used to investigate the stability of the new complexes. Thereby, the stability agreed well with the order of the Ir-N-N boolean AND N bond lengths.
Herein, we represent cation-responsive fluorescent probes for the divalent cations Zn2+, Mg2+ and Ca2+, which show cation-induced fluorescence enhancements (FE) in water. The Zn2+-responsive probes Zn1, Zn2, Zn3 and Zn4 are based on o-aminoanisole-N,N-diacetic acid (AADA) derivatives and show in the presence of Zn2+ FE factors of 11.4, 13.9, 6.1 and 8.2, respectively. Most of all, Zn1 and Zn2 show higher Zn2+ induced FE than the regioisomeric triazole linked fluorescent probes Zn3 and Zn4, respectively. In this set, ZN2 is the most suitable probe to detect extracellular Zn2+ levels. For the Mg2+-responsive fluorescent probes Mg1, Mg2 and Mg3 based on o-aminophenol-N,N,O-triacetic acid (APTRA) derivatives, we also found that the regioisomeric linkage influences the fluorescence responds towards Mg2+ (Mg1+100 mM Mg2+ (FEF=13.2) and Mg3+100 mM Mg2+ (FEF=2.1)). Mg2 shows the highest Mg2+-induced FE by a factor of 25.7 and an appropriate K-d value of 3 mM to measure intracellular Mg2+ levels. Further, the Ca2+-responsive fluorescent probes Ca1 and Ca2 equipped with a 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) derivative show high Ca2+-induced FEs (Ca1 (FEF=22.1) and Ca2 (FEF=23.0)). Herein, only Ca1 (K-d=313 nM) is a suitable Ca2+ fluorescent indicator to determine intracellular Ca2+ levels.
The first Si-H-containing azasilaheterocycle, 1,3-dimethyl-3-silapiperidine 1, was synthesized, and its molecular structure and conformational properties were studied by gas-phase electron diffraction (GED), low temperature NMR, IR and Raman spectroscopy and quantum chemical calculations. The compound exists as a mixture of two conformers possessing the chair conformation with the equatorial NMe group and differing by axial or equatorial position of the SiMe group. In the gas phase, the SiMeax conformer predominates (GED: ax/eq = 65(7):35(7)%,Delta G = 0.36(18) kcal/mol; IR: ax/eq = 62(5):38(5)%,Delta G = 0.16(7) kcal/mol). In solution, at 143 k the SiMeeq conformer predominates' in the frozen equilibrium (NMR: ax/eq = 31.5(1.5):68.5(1.5)%, Delta G = -0.22(2) kcal/mol). Thermodynamic parameters of the ring inversion are determined (Delta G(double dagger) = 8.9-9.0 kcal/mol, Delta H-double dagger = 9.6 kcal/mol, Delta S-double dagger = 2.1 eu). High-level quantum chemical calculations :(MP2, G2, CCSD(T)) nicely reproduce the experimental geometry and the predominance of the axial conformer in the gas phase.
1-Methylthio-1-phenyl-1-silacyclohexane 1, the first silacyclohexane with the sulfur atom at silicon, was synthesized and its molecular structure and conformational preferences studied by gas-phase electron diffraction (GED) and low temperature C-13 and Si-29 NMR spectroscopy (LT NMR). Quantum-chemical calculations were carried out both for the isolated species and solvate complexes in gas and in polar medium. The predominance of the 1-MeSaxPheq conformer in gas phase (1-Ph-eq :1-Ph-ax = 55:45, Delta G degrees = 0.13 kcal/mol) determined from GED is consistent with that measured in the freon solution by LT NMR (1-Ph-eq:1-Ph-ax = 65:35, Delta G degrees = 0.12 kcal/mol), the experimentally measured ratios being close to that estimated by quantum chemical calculations at both the DFT and MP2 levels of theory. (C) 2019 Elsevier Ltd. All rights reserved.
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.
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.
13 C NMR Chemical shift calculations for some substituted pyridines - a comparative consideration
(1997)
13C NMR chemical shifts of unbranched 2-Alkyn-1-ols, w-Alkyn-1-ols and "internal" Alkyn-1-ols
(1995)
Selenides of the type R1Se-EMe3 (E = Si, Ge, Sn, Pb) react with xenon difluoride by cleavage of the Se-E bond to yield the R1Se-F intermediate and the fluorides Me3E-F, whereas the Se-C bond in PhSe-tBu (E = C) is stable against XeF2. The presence of R1Se-F intermediates is confirmed by addition to acetylenes (4-octyne, 3-hexyne). Thus, the fluoroselenenylation of acetylenes gives fluoro(organylseleno)olefins in preparative yields. In the cases of E = Si, Ge, Sn, and Pb, aryl and n-alkyl groups are suitable as the substituent R1. The X-ray crystal structural analysis of (E)-3- (p-carboxyphenylseleno)-4-fluorohex-3-ene - the first example of an uncharged fluoroselenoolefin synthesized from p- EtO2C-C6H4-Se-SnMe3, XeF2, and 3-hexyne followed by an ester hydrolysis - shows that the addition of the selenenylfluoride intermediate to the acetylene proceeds via a trans-addition, as is known for the R2Se2-XeF2 reagents.
1H NMR Lanthanideinduced Shift (LIS) investigations of highly flexible molecules : a new approach
(1993)
1H, 13C, and 15N NMR study of the solution structure of metabridged bis(benzo-15-crown-5-ether)s
(1995)
Block copolymers of 1H,1H,2H,2H-perfluorodecyl acrylate (AC8) were obtained from ARGET ATRP. To obtain block copolymers of low dispersity the PAC8 block was synthesized in anisole with a CuBr(2)/PMDETA catalyst in the presence of tin(II) 2-ethylhexanoate as a reducing agent. The PAC8 block was subsequently used as macroinitiator for copolymerization with butyl and tert-butyl acrylate carried out in scCO(2). To achieve catalyst solubility in CO(2) two fluorinated ligands were employed. The formation of block copolymers was confirmed by size exclusion chromatography and DSC.
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.
User-friendly protocols for the protecting group-free synthesis of 2,2'-biphenols via Suzuki-Miyaura coupling of o-halophenols and o-boronophenol are presented. The reactions proceed in water in the presence of simple additives such as K2CO3, KOH, KF, or TBAF and with commercially available Pd/C as precatalyst. Expensive or laboriously synthesized ligands or other additives are not required. In the case of bromophenols, efficient rate acceleration and short reaction times were accomplished by microwave irradiation.
New spin probes bearing the 2,2,6,6-tetramethylpiperidine-1-yloxyl covalently bound to the imidazolium ion via a methylene spacer and an amide group are synthesized. If the anion is bis(trifluoromethylsulfonylimide) instead of iodide, the new spin probe has a similar structure as that of an ionic liquid. Nevertheless, the new spin probes are useful tools to investigate ionic liquids.
A series of 5-unsubstituted and 5-substituted 2-alkylidene-4-oxothiazolidine-S-oxides were synthesized by the sulfur-oxidation with m-CPBA. The stereochemistry of 5-substituted sulfoxides was determined by means of NMR spectroscopy and DFT theoretical calculations. It was found that the thermodynamically less stable anti-isomer was initially formed in the course of the oxidation, but it underwent epimerization to the mixture enriched in the more stable syn-isomer, during the work-up process. The higher stability of syn-isomers is ascribed to the stronger hyperconjugative sigma(C-H)->sigma*(S-O) interaction versus the weaker sigma(C-C)->sigma*(S-O) delocalization in their anti-counterparts and to the existence of intramolecular 1,5-CH center dot center dot center dot C hydrogen bonds.
The complete H-1 and C-13 NMR chemical shifts assignment for various 2-substituted and 2,2-disubstituted adamantane derivatives 1-38 in CDCl3 solution was realized on the basis of NMR experiments combined with chemical structure information and DFT-GIAO (B3LYP/6-31+G(d,p)-GIAO) calculations of chemical shifts in solution. Substituent-induced C-13 NMR chemical shifts (SCS) are discussed. C-H-ax center dot center dot center dot Y-ax contacts are a textbook prototype of steric hindrance in organic chemistry. The nature of these contacts will be further investigated in this work on basis of new adamantane derivatives, which are substituted at C-2 to provide models for 1,4-C-H-ax center dot center dot center dot Y-ax and 1,5-C-H-ax center dot center dot center dot Y-ax contacts. The B3LYP/6-31+G(d,p) calculations predicted the presence of NBO hyperconjugative attractive interactions between C-H-ax and Y-ax groups along C-H-ax center dot center dot center dot Y-ax contacts. The H-1 NMR signal separation, Delta delta(gamma-CH2), reflects the strength of the H-bonded C-H-ax center dot center dot center dot Y-ax contact. (C) 2015 Elsevier Ltd. All rights reserved.
Two new 3-hydroxyisoflavanones, (S)-3,4',5-trihydroxy-2',7-dimethoxy-3'-prenylisoflavanone (trivial name kenusanone F 7-methyl ether) and (S)-3,5-dihydroxy-2',7-dimethoxy-2 '',2 ''-dimethylpyrano[5 '',6 '':3',4']isoflavanone (trivial name sophoronol-7-methyl ether) along with two known compounds (dalbergin and formononetin) were isolated from the stem bark of Dalbergia melanoxylon. The structures were elucidated using spectroscopic techniques. Kenusanone F 7-methyl ether showed activity against Mycobacterium tuberculosis, whereas both of the new compounds were inactive against the malaria parasite Plasmodium falciparum at 10 mu g/ml. Docking studies showed that the new compounds kenusanone F 7-methyl ether and sophoronol-7-methyl ether have high affinity for the M. tuberculosis drug target INHA.
The stem bark extract of Schizozygia coffaeoides (Apocynaceae) showed moderate antiplasmodial activity (IC50 = 8-12 mu g/mL) against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum. Chromatographic separation of the extract led to the isolation of a new schizozygane indoline alkaloid, named 3-oxo-14 alpha, 15 alpha-epoxyschizozygine. In addition, two dimeric anthraquinones, cassiamin A and cassiamin B, were identified for the first time in the family Apocynaceae. The structures of the isolated compounds were deduced on the basis of spectroscopic evidence. The schizozygane indole alkaloids showed good to moderate antiplasmodial activities (IC50 = 13-52 mu m). (C) 2014 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.
Hepcidin-25 (Hep-25) plays a crucial role in the control of iron homeostasis. Since the dysfunction of the hepcidin pathway leads to multiple diseases as a result of iron imbalance, hepcidin represents a potential target for the diagnosis and treatment of disorders of iron metabolism. Despite intense research in the last decade targeted at developing a selective immunoassay for iron disorder diagnosis and treatment and better understanding the ferroportin-hepcidin interaction, questions remain. The key to resolving these underlying questions is acquiring exact knowledge of the 3D structure of native Hep-25. Since it was determined that the N-terminus, which is responsible for the bioactivity of Hep-25, contains a small Cu(II)-binding site known as the ATCUN motif, it was assumed that the Hep-25-Cu(II) complex is the native, bioactive form of the hepcidin. This structure has thus far not been elucidated in detail. Owing to the lack of structural information on metal-bound Hep-25, little is known about its possible biological role in iron metabolism. Therefore, this work is focused on structurally characterizing the metal-bound Hep-25 by NMR spectroscopy and molecular dynamics simulations. For the present work, a protocol was developed to prepare and purify properly folded Hep-25 in high quantities. In order to overcome the low solubility of Hep-25 at neutral pH, we introduced the C-terminal DEDEDE solubility tag. The metal binding was investigated through a series of NMR spectroscopic experiments to identify the most affected amino acids that mediate metal coordination. Based on the obtained NMR data, a structural calculation was performed in order to generate a model structure of the Hep-25-Ni(II) complex. The DEDEDE tag was excluded from the structural calculation due to a lack of NMR restraints. The dynamic nature and fast exchange of some of the amide protons with solvent reduced the overall number of NMR restraints needed for a high-quality structure. The NMR data revealed that the 20 Cterminal Hep-25 amino acids experienced no significant conformational changes, compared to published results, as a result of a pH change from pH 3 to pH 7 and metal binding. A 3D model of the Hep-25-Ni(II) complex was constructed from NMR data recorded for the hexapeptideNi(II) complex and Hep-25-DEDEDE-Ni(II) complex in combination with the fixed conformation of 19 C-terminal amino acids. The NMR data of the Hep-25-DEDEDE-Ni(II) complex indicates that the ATCUN motif moves independently from the rest of the structure. The 3D model structure of the metal-bound Hep-25 allows for future works to elucidate hepcidin’s interaction with its receptor ferroportin and should serve as a starting point for the development of antibodies with improved selectivity.
We report on the fabrication of a complex electrode architecture for efficient direct bioelectrocatalysis. In the developed procedure, the redox enzyme pyrroloquinoline quinone-dependent glucose dehydrogenase entrapped in a sulfonated polyaniline [poly(2-methoxyaniline-5-sulfonic acid)-co-aniline] was immobilized on macroporous indium tin oxide (macroITO) electrodes. The use of the 3D-conducting scaffold with a large surface area in combination with the conductive polymer enables immobilization of large amounts of enzyme and its efficient communication with the electrode, leading to enhanced direct bioelectrocatalysis. In the presence of glucose, the fabricated bioelectrodes show an exceptionally high direct bioelectrocatalytical response without any additional mediator. The catalytic current is increased more than 200-fold compared to planar ITO electrodes. Together with a high long-term stability (the current response is maintained for >90% of the initial value even after 2 weeks of storage), the transparent 3D macroITO structure with a conductive polymer represents a valuable basis for the construction of highly efficient bioelectronic units, which are useful as indicators for processes liberating glucose and allowing optical and electrochemical transduction.
The CH2Cl2/MeOH (1: 1) extract of the stem bark of Millettia oblata ssp. teitensis showed antiplasmodial activity (IC50 = 10-12 mu g/mL) against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum. Chromatographic separation of the extract led to the isolation of a new isoflavone, 4'-prenyloxyderrone (1), together with known isoflavones (8-O-methylretusin, durmillone, maximaisoflavone B, maximaisoflavone H and maximaisoflavone J), a rotenoid (tephrosin) and a triterpene (lupeol). Similar investigation of Millettia leucantha resulted in the identification of the isoflavones afrormosin and wistin, and the flavone chrysin. The identification of these compounds was based on their spectroscopic data. Five of the isoflavones isolated from these plants as well as 11 previously reported compounds from Millettia dura were tested and showed good to moderate antiplasmodial activities (IC50 = 13-53 mu M), with the new compound, 4'-prenyloxyderrone, being the most active (IC50 = 13-15 mu M).
4,4 '-Bis(tert-butyl)-2,2 '-bipyridinedichlorometal(II) - Synthesis, structure and EPR spectroscopy
(2011)
Due to the better solubility of the 4,4'-substituted bipyridine ligand a series of 4,4'0-bis(tert-butyl)-2,2'-bipyridinedichlorometal(II) complexes, [M(tbbpy)Cl(2)], with M = Cu, Ni, Zn, Pd, Pt was synthesised and characterised. The blue copper complex 4,4'-bis(tert-butyl)-2,2'-bipyridinedichlorocopper(II) was isolated in two different polymorphic forms, as prisms 1 with a solvent inclusion and solvent-free as needles 2. Both structures were determined by X-ray structure analysis. They crystallise in the monoclinic space group P2(1)/c with four molecules in the unit cell, but with different unit cells and packing motifs. Whereas in the prisms 1, with the unit cell parameters a = 12.1613(12), b = 10.6363(7), c = 16.3074(15) angstrom, eta = 94.446(8)degrees, the packing is dominated by intra-and intermolecular hydrogen bonds, in the needles 2, with a = 7.738(1), b = 18. 333(2), c = 13.291(3) angstrom, beta = 97.512(15)degrees, only intramolecular hydrogen bonds appear and the complex molecules are arranged in columns which are stabilised by p-p-stacking interactions. In both complexes the copper has a tetrahedrally distorted coordination sphere. These copper complexes were also studied by EPR spectroscopy in solution, as frozen glass and diamagnetically diluted powder with the analogue [Pd(tbbpy)Cl(2)] as host lattice.
4-Alkyl-2,2,6,6-tetramethyl-1,4,2,6-oxaazadisilinanes RN[CH2Si(Me)2]2O [R = Me (1), i-Pr (2)] were synthesized by two methods which provided good yields up to 84%. Low temperature NMR study of compounds (1) and (2) revealed a frozen ring inversion with the energy barriers of 8.5 and 7.7 kcal/mol at 163 and 143 K, respectively, which is substantially lower than that for their carbon analog, N-methylmorpholine. DFT calculations performed on the example of molecule (1) showed that N-Meax conformer to exist in the sofa conformation with the coplanar fragment C-Si-O-Si-C, and its N-Meeq conformer in a flattened chair conformation.
The shape and the actuation capability of state of the art robotic devices typically relies on multimaterial systems from a combination of geometry determining materials and actuation components. Here, we present multifunctional 4D-actuators processable by 3D-printing, in which the actuator functionality is integrated into the shaped body. The materials are based on crosslinked poly(carbonate-urea-urethane) networks (PCUU), synthesized in an integrated process, applying reactive extrusion and subsequent water-based curing. Actuation capability could be added to the PCUU, prepared from aliphatic oligocarbonate diol, isophorone diisocyanate (IPDI) and water, in a thermomechanical programming process. When programmed with a strain of epsilon(prog) = 1400% the PCUU networks exhibited actuation apparent by reversible elongation epsilon'(rev) of up to 22%. In a gripper a reversible bending epsilon'(rev)((be)(nd)()) in the range of 37-60% was achieved when the actuation temperature (T-high) was varied between 45 degrees C and 49 degrees C. The integration of actuation and shape formation could be impressively demonstrated in two PCUU-based reversible fastening systems, which were able to hold weights of up to 1.1 kg. In this way, the multifunctional materials are interesting candidate materials for robotic applications where a freedom in shape design and actuation is required as well as for sustainable fastening systems.
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.
The CH2Cl2/MeOH (1: 1) extract of the roots of Tephrosia villosa showed good antiplasmodial activity against the chloroquine-sensitive (D6) and chloroquine-resistant (W2) strains of Plasmodium falciparum with IC50 values of 3.1 +/- 0.4 and 1.3 +/- 0.3 mu g/mL, respectively. Chromatographic separation of the extract yielded a new rotenoid, 6 alpha-hydroxy-alpha-toxicarol, along with five known rotenoids, (rotenone, deguelin, sumatrol, 12 alpha-hydroxy-alpha-toxicarol and villosinol). Similar treatment of the extract of the stem of Tephrosia purpurea (IC50 = 4.1 +/- 0.4 and 1.9 +/- 0.2 mu g/mL against D6 and W2 strains of P. falciparum, respectively) yielded a new flavone having a unique substituent at C-7/C-8 [trivial name (+)-tephrodin], along with the known flavonoids tachrosin, obovatin methyl ether and derrone. The relative configuration and the most stable conformation in (+)-tephrodin was determined by NMR and theoretical energy calculations. The rotenoids and flavones tested showed good to moderate antiplasmodial activities (IC50 = 9 +/- 23 mu M). Whereas the cytotoxicity of rotenoids is known, the flavones (+)-tephrodin and tachrosin did not show significant cytotoxicity (IC50 > 100 mu M;) against mammalian African monkey kidney (vero) and human larynx carcinoma (HEp2) cell lines. (C) 2014 Phytochemical Society of Europe. Published by Elsevier B.V. All rights reserved.
7a-O-methyldeguelol, a modified rotenoid with an open ring-C, from the roots of Derris trifoloata
(2005)
From the acetone extract of the roots of Derris trifoliata an isollavonoid derivative, named 7a-O- methyldeguelol, a modified rotenoid with an open ring-C, representing a new sub-class of isollavonoids (the sub-class is here named as rotenoloid), was isolated and characterised. In addition, the known rotenoids, rotenone, deguelin and alpha-toxicarol, were identified. The structures were determined on the basis of spectroscopic evidence. Rotenone and deguelin were identified as the larvicidal principles of the acetone extract of the roots of Derris trifoliata. (c) 2005 Elsevier Ltd. All rights reserved