Search results for "Methods"
showing 10 items of 4526 documents
Fractionated precipitation of acid macropolyanions by dialysis, a simple method for the estimation of DNA in complex biological samples.
1976
Abstract After efficient extraction by para-aminosalicylate, (hopping, grinding and eventual sonication, the macropolyanions are transformed into their cetyltrimethylammonium salts. These have differing solubilities, strongly depending on ionic strength. The cationic detergent-macropolyanionic salts are solubilized by high salt concentration. Salt is then dialysed out, rendering the polyanions highly insoluble in a sequential fashion. The insolubilized components are determined quantitatively by monitoring turbidity, which in case of DNA is strictly proportionate to its concentration. This relation is not affected by other components. This makes DNA determination possible even in crude aque…
Biophysical approaches for the study of metal-protein interactions
2019
Protein-protein interactions play important roles for a variety of cell functions, often involving metal ions; in fact, metal-ion binding mediates and regulates the activity of a wide range of biomolecules. Enlightening all of the specific features of metal-protein and metal-mediated protein-protein interactions can be a very challenging task; a detailed knowledge of the thermodynamic and spectroscopic parameters and the structural changes of the protein is normally required. For this purpose, many experimental techniques are employed, embracing all fields of Analytical and Bioinorganic Chemistry. In addition, the use of peptide models, reproducing the primary sequence of the metal-binding …
Predominance of 2-arylhydrazones of 1,3-diphenylpropane-1,2,3-trione over its proton-transfer products
2001
2-Phenylhydrazones of 1,3-diphenyl-1,2,3-trione are the dominant tautomeric form detected in chloroform solution by 15N NMR chemical shifts. The substituent in the phenylhydrazone moiety does not affect this tautomeric preference. The substituent effect is transmitted effectively only to the hydrazone nitrogen and hydrogen atoms. Ab initio calculations show that the ketohydrazone tautomer is really very much favoured over its proton-transfer products in chloroform solution. The same tautomer was also detected in the crystal state by X-ray crystallography. Copyright © 2001 John Wiley & Sons, Ltd.
Regio- and stereoselective synthesis of constrained enantiomeric β-amino acid derivatives
2008
Abstract Chlorosulfonyl isocyanate addition to (−)- and (+)-apopinene furnished monoterpene-fused β-lactams in highly regio- and stereospecific reactions. β-Lactams 5 and 13 exhibited reactivities similar to those of the cycloalkane-fused analogs and were easily converted to the β-amino acid and its protected derivatives. The base-catalyzed isomerization of the cis -amino ester afforded the corresponding trans -amino acid enantiomers in excellent yields. The complete isomerization is explained by the stability difference, which was estimated by ab initio calculations between the cis- and trans -diastereomers.
Comparison of extraction methods for polycyclic aromatic hydrocarbon determination in sediments
1990
Different sample preparation methods for the determination of polycyclic aromatic hydrocarbons (PAHs) in lake and river sediments were compared and evaluated. Freeze‐dried sediment materials were e...
Theoretical study of the OH addition to the β-pinene
2004
The initial step of the mechanism of the OH + β-pinene gas-phase reaction was investigated by means of ab initio calculations. Four different possibilities for the OH addition to the double bond are discussed, corresponding to the addition on each C atom of the double bond, and for each one, either the syn or anti OH attack to the two methyl groups on the (bi)cyclic molecule. Energy barriers calculated at the QCISD(T)/6-31G(d) level of theory on UMP2/6-31G(d) optimised structures, show that there are preferred orientations for the OH addition under atmospheric conditions of temperature and pressure.
Bonding in the heavy analogue of hydrogen cyanide: the curious case of bridged HPSi.
2010
The bonding of firstand second-row elements differ dramatically. The simplest unsaturated silicon hydrides Si2H2 and Si2H4 exhibit quite unusual geometries [1] compared to the analogous hydrocarbon molecules. For example, the most stable form of Si2H2 is nonplanar with C2v symmetry and two bridging H atoms, in sharp contrast to linear acetylene, HC! CH. Phosphorus and nitrogen share many of the same bonding characteristics, but P prefers single over multiple bonds. For these reasons, it may be difficult to predict the most stable isomeric arrangement, even for a small molecule with a single Por Si atom and especially when it contains both. Silicon–phosphorus bonds are important in materials…
1,2-Dipolar addition model for the cytoprotective activity of selected α,β-unsaturated compounds with CO functionality: an ab initio study
2001
Abstract The mechanism of the addition of a nucleophile (an alkylthiol group) to a double bond of α,β-unsaturated systems in the gas phase was explored. In this study, intermediates of the reaction were also investigated using ab initio calculations (RHF/6-31G ∗ and MP2/6-31+G ∗ ). Our results indicate that direct dipolar attack of the S–H group of an alkylthiol on the CC double bond is a reasonable reaction path. The present results represent, therefore, additional support for our hypothesis. This suggests that the mechanism of cytoprotection might be mediated, at least in part, by a reaction between the olefinic acceptor and the sulfhydryl-containing groups of the mucosa.
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…