Search results for " method"

Synthesis of peptides with α,β‐dehydroamino acids, V. coupling experiments with C‐terminal dehydrophenylalanine and dehydroalanine residues

1986

N-Protected model dipeptides of C-terminal (Z)-ΔPhe and ΔAla couple with glycine esters after activation with either diphenyl phosphorazidate (DPPA), N-cyclohexyl-N′-[2-(N-methylmorpholinio)ethyl]carbodiimide p-toluenesulfonate (WSC), N,N′-dicyclohexylcarbodiimide + 1-hydroxybenzotriazole (DCC + HOBt), or the mixed anhydride (MA) with isobutyl chlorocarbonate to give in good or mostly moderate yields the (Z)-ΔPhe-containing tripeptides 1 – 9 and ΔAla-containing tripeptides 11 – 19, respectively. In the MA and DPPA methods, further acylation products 20a – d are formed to a great extent, expecially during the ΔAla peptide syntheses. (E)-TFA-Gly-ΔPhe and Gly-OtBu, irrespective of the activati…

Die bestimmung der molekulargewichtsverteilung von nichtkristallisierenden polymeren mit dem elektronenmikroskop, 7. Präparation durch verdampfung de…

1977

A preparation method is described by means of which it is possible to transfer individual molecules of a high molecular weight polymer on a support, in order to determine their mass and therefrom their molecular weight distribution, using our previously published electron microscopic method. The advantages of the new procedure as compared to the previously described freeze-drying are 1 that the range of solvents, which can be used is much larger, and 2 that the preparation is performed by evaporation from a dilute solution, which means that the molecules are distributed statistically on the support. The risk of formation of associates is avoided by keeping the polymer concentration correspo…

DLPNO-CCSD(T) scaled methods for the accurate treatment of large supramolecular complexes

2017

In this work, we present scaled variants of the DLPNO-CCSD(T) method, dubbed as (LS)DLPNO-CCSD(T) and (NS)DLPNO-CCSD(T), to obtain accurate interaction energies in supramolecular complexes governed by noncovalent interactions. The novel scaled schemes are based on the linear combination of the DLPNO-CCSD(T) correlation energies calculated with the standard (LoosePNO and NormalPNO) and modified (Loose2PNO and Normal2PNO) DLPNO-CCSD(T) accuracy levels. The scaled DLPNO-CCSD(T) variants provide nearly TightPNO accuracy, which is essential for the quantification of weak noncovalent interactions, with a noticeable saving in computational cost. Importantly, the accuracy of the proposed schemes is…

EXTRACTION OF BIOLOGICALLY ACTIVE COMPONENTS FROM FRESHWATER SAPROPEL

2019

Sapropel has been used for different purposes - in agriculture as fertilizer, in construction as building material, in cosmetic products, in balneology also in medicine and pharmaceuticals as bioactive component. Previously sapropel has been commonly used in raw form and there is no general accepted method or standard method for obtaining sapropel extract. However, most extraction methods follow the same path. Currently, there are few extraction methods using several extractants for obtaining bioactive components from raw sapropel. The most commonly used extractant is alkaline solution. When sapropel is subjected to alkaline environment, the humic and fulvic acids, together with some lipids…

1988

Monte Carlo simulations are presented for binary (AB) symmetric polymer mixtures (chain lengths NANBN) for the case that an attractive interaction ϵ exists between monomers of the same kind, and the limiting case that one species (B) is very diluted. It is shown that with increasing interaction strength ϵ/(kB · T), T being the absolute temperature, the minority chains collapse to a very dense configuration, while the majority chains stay nearly Gaussian. Both chain radii, structure factors and numbers of nearest neighbour contacts are discussed.

Pentadecamer 2,5-Dipropoxy-1,4-phenylenevinylene

2002

The conjugated, all-(E)-configured pentadecamer 2,5-dipropoxy-1,4-phenylenevinylene 1j was prepared by a multistep synthesis on the basis of hydroquinone. The procedure consists of a general method for the repetitive extension of oligo(phenylenvinylene) chains by two styryl units (7a ⇄ 10 ⇄ 12 ⇄ 14). The relatively rigid oligomer 1j represents a molecular wire of about 100 A. The absorption of 1j provides a proof for the convergence theory for electronic properties of conjugated oligomers with increasing number of repeat units. The corresponding conjugated polymer 1p with the same substitution matches the values which were extrapolated from the oligomer series 1a−1j. (© Wiley-VCH Verlag Gmb…

High Yield Syntheses of Stable, Singly Bonded Pd26+ Compounds

2006

A general method for the syntheses of dipalladium compounds having a singly bonded Pd26+ core and the formula R,S-cis-Pd2(C6H4PPh2)2(O2CR)2Cl2 is described. When the alkyl group in the carboxylate ligands is an electron donating group, the compounds are stable and the yields high. The Pd-Pd distances for the diamagnetic compounds with R = CF3 and CMe3 are 2.5434(4) and 2.5241(9) A, respectively. Calculations at the DFT level suggest that the electronic configuration is sigma2pi4delta2delta*2pi*4. These represent rare examples of palladium(III) compounds.

Determination of Plasma Lipid Hydroperoxides by an NADPH/NADP + Coupled Enzyme Reaction System. Evaluation of a Method

1998

Summary: Several techniques based on different principles have been proposed to measure lipid hydroperoxides. Enzymatic methods are sensitive and can be quite specific but they are subject to interference by inhibitors and not all are stoichiometric. The present work proposes some modifications of the Heath & Tappel (Anal Biochem 1976; 7:184—91) enzymatic method of determination of lipid hydroperoxides in order to standardize and automate it and to meet the analytical criteria required for a biological assay. The proposed new protocol and the automated assay give acceptable within-run and between-run precisions, with coefficients of variation of 3.34% and 5.80%, respectively, at the usual p…

Isoniazid cocrystallisation with dicarboxylic acids: vapochemical, mechanochemical and thermal methods

2016

Cocrystallisation with a series of related compounds allows for the exploration of trends and limitations set by structural differences between these compounds. In this work, we investigate how the length of a dicarboxylic acid influences the outcome of cocrystallisation with isoniazid. We have performed a systematic study on the mechanochemical, thermal and solvent vapour-assisted cocrystallisation of aliphatic dicarboxylic acids (C3–C10) with isoniazid. Our results demonstrate that the rate of mechanochemical and vapour-assisted cocrystallisation depends on the acid chain length and shows alternation between odd- and even-chain acids. The results of thermal cocrystallisation showed that t…

Are Heme-Dependent Enzymes Always Using a Redox Mechanism? A Theoretical Study of the Kemp Elimination Catalyzed by a Promiscuous Aldoxime Dehydratase

2020

The design of biocatalysts is a goal to improve the rate, selectivity and environmental friendship of chemical processes in biotechnology. In this regard, the use of computational techniques has provided valuable assistance in the design of enzymes with remarkable catalytic activity. In this paper, hybrid QM/MM simulations have allowed getting an insight into the mechanism of a promiscuous aldoxime dehydratase (OxdA) for the Kemp elimination. We first demonstrate that, based on the use of linear response approximation (LRA) methods, the lowest energy electronic state of the benzisoxazole placed in the active sit of OxdA corresponds to a singlet state, being the triplet and the quintet state…