Search results for "COMPUTATION"
showing 10 items of 7362 documents
Determination of the lowest-energy oxidation site in nucleotides: 2'-deoxythymidine 5'-monophosphate anion.
2006
High level ab initio computations anticipate nucleobases as the most favorable sites for oxidation in nucleotides. At the CASPT2 level, the lowest ionization channel for the 2'-deoxythymidine 5'-monophosphate anion is related to a pi-orbital of the thymine base. The present findings lead to revision of the recent assignments of the photodetachment photoelectron spectra of mononucleotide anions in the gas phase and support the classical view of the nucleobase being the main actor in the oxidation process of both nucleosides and nucleotides.
Function of biomolecules as a probe for studying the effects of organic co-solvents on their conformations
1980
Abstract Conformation changes associated with the function of biomolecules can bring out variations of the extent and specific structure of their hydrophobic areas exposed to solvent, with consequent local rearrangements of the solvent. This is one of the channels through which the solvent exerts its role in the functional equilibria of biomolecules. The function of biological macromolecules in perturbed aqueous solvent can therefore be a suitable probe for studying the response of macromolecule-solvent systems to perturbations caused by organic co-solvents. We shall discussed the effects that the presence of some monohydric alcohols and some amides in the aqueous medium have on some thermo…
Coordination chemistry of N,N′-bis(coordinating group substituted)oxamides: a rational design of nuclearity tailored polynuclear complexes
1999
Abstract The coordinating properties of N , N ′-bis(coordinating group substituted)oxamides have been thoroughly investigated both in aqueous solution and in the solid state. The easy cis – trans isomerization equilibria that they exhibit together with the great variety of N , N ′-substituents which can be used to play on the overall charge, complexing ability and polarity, make them very suitable ligands in designing homo- and heterometallic species. The knowledge of their complex formation in aqueous solution by potentiometry and using the hydrogen ion concentration as a probe, allowed us to settle the basis of a rational design of oxamidate-containing polynuclear species whose nuclearity…
On the tautomerization process of glycine in aqueous solution
2000
The experimental activation energy for the tautomerization of glycine zwitterion neutral form has been reported to be 14.6 kcalrmol. It has been generally assumed that this energy barrier is needed for proton transfer to occur. However, previous theoretical results do not support this interpretation. In the present work, we examine this question using density functional calculations, extended basis sets and a polarizable continuum solvent model. Our results suggest that the limiting step for the tautomerization process corresponds basically to H-atom reorientation in the -COOH group. This could be a general feature in the tautomerization of amino acids. q 2000 Elsevier Science B.V. All righ…
Interaction of Alkyltin(IV) Compounds with Ligands of Interest in the Speciation of Natural fluids: Complexes of (CH3)2Sn2+ with Carboxylates
1997
Complex formation by (CH3)2Sn 2+ with acetate (ac), malonate (mal), 1,2,3-propanetricarboxylate (tricarballylate, tca) and 1,2,3,4-butanetetracarboxylate (btc) ligands in aqueous solution is reported. The study has been performed by potentiometry ([H + ]‐glass electrode) at T = 25 °C, and in the 0 < I < 1 mol dm 2 3 ionic strength range. In order to evaluate the salt effects on the formation constants of the complex species, and to contribute to the definition of the chemical speciation of diorganotin(IV) compounds in natural waters where carboxylic ligands are naturally present, interactions of NaCl (which is the major component of all natural fluids), with the components of the systems un…
A detailed MSn study for the molecular identification of a dimer formed from oxidation of pinene
2016
Abstract Dimeric products formed in the oxidation of α- and β-pinene have been frequently observed in laboratory and field studies of biogenic SOA formation. While their existence is undoubted, their exact chemical structures remain unclear. This study uses a combined two step approach aiming on the molecular identification of the most important of the various dimers that have been observed in biogenic secondary organic aerosol formation, a dimer with the molecular weight 358 g mol−1. The first step is the application of a functional group derivatization technique (esterification) to quantify the number of carboxylic acid groups in the target molecule. Based on the detailed interpretation o…
Structure and fluxional behaviour of heptaleneirontricarbonyl and heptalenebis (Irontricarbonyl)
1987
Abstract The synthesis of heptaleneirontricarbonyl ( 4 ) is described. The structures of 4 and of the closely related heptalenebis(irontricarbonyl) ( 3 ) are elucidated by NMR spectroscopy ( 1H and 13C) and by X-ray crystallography. Compounds 3 and 4 are shown by dynamic NMR to undergo an isodynamic 1 ,2-migration of the Fe(CO3)-groups as well as a carbonyl scrambling. The relevant kinetic data allow for a mechanistic discussion of the dynamics and a comparison with other irontricarbonyl complexes.
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 …
Geometric and electronic structure of dithiapyranylidine: evolution upon oxidation
1993
Abstract We present a theoretical investigation of the modifications that successive oxidation induces on the geometric and electronic structures of the π-electron donor dithiapyranylidene. The lengthening of the double bonds and the shortening of the single bonds calculated as the molecular charge increases indicate a gain of aromaticity with oxidation. Both the geometricand the electronic structure of dithiapyranylidene show a clear evolution towards those of biphenyl as oxidation takes place.
A molecular electron density theory study of the mechanism, chemo- and stereoselectivity of the epoxidation reaction of R -carvone with peracetic acid
2019
The epoxidation reaction of R-carvone 8 with peracetic acid 9 has been studied within the molecular electron density theory at the B3LYP/6-311(d,p) computational level. The chemo- and stereoisomeric reaction paths involving the two C–C double bonds of R-carvone 8 have been studied. DFT calculations account for the high chemoselectivity involving the C–C double bond of the isopropenyl group and the low diastereoselectivity, in complete agreement with the experimental outcomes. The Baeyer–Villiger reaction involving the carbonyl group of R-carvone 8 has also been analysed. A bonding evolution theory analysis of the epoxidation reaction shows the complexity of the bonding cha…