The Synthesis and X-Ray Structural Studies of Bis(1,3,2-Dithiaphospholane)

Abstract

The title compound 1 [³¹P NMR (CD₃CN): σ=36.7ppm] has been identified among the products of controlled hydrolysis of 2-dimethoxyphosphory1-1,3,2-dithiaphospholane (2) [1].     

Photochemical Synthesis of N4-Substituted Cytosines

The convenient method for the preparation of N⁴-substituted cytosines is described. The irradiation with UV light of N-(1H-2-oxo-4-pyrimidinyl) amino acids provides the proper N⁴-substituted cytosines in a good yield.     

Surmounting the Multiple-Minima Problem in Protein Folding

Protein folding is a very difficult global optimization problem. Furthermore it is coupled with the difficult task of designing a reliable force field with which one has to search for the global minimum. A summary of a series of optimization methods developed and applied to various problems involving polypeptide chains is described in this paper. With recent developments, a computational treatment of the folding of globular proteins of up to 140 residues is shown to be tractable.     

Scattering from interface islands: enhanced lifetimes through non-linear effect of cation defects

We present quantitative calculations of scattering lifetimes associated with isovalent anion and cation defects in GaSb/InAs detector heterostructures, and identify the dependence upon the proximity of the defects to the heterointerfaces. The carrier lifetimes arising through scattering from interface islands of anion defects are shown to depend non-linearly upon the presence of additional cation defects. These weakly scattering cation defects are shown to control the larger scattering from the anion islands, enabling lifetimes to be enhanced by more than an order of magnitude through the inclusion of additional lattice imperfections.     

Fixed points of asymptotically regular semigroups in Banach spaces

In this paper we study in Banach spaces the existence of fixed points of (nonlinear) asymptotically regular semigroups. We establish for these semigroups some fixed point theorems in spaces with weak uniform normal structure, in a Hilbert space, inL ^p spaces, in Hardy spacesH ^p and in Sobolev spacesW ^r.p for 1<p<∞ andr≥0, in spaces with Lifshitz’s constant greater than one. These results are the generalizations of [8, 10, 16].     

On a universal best choice algorithm for partially ordered sets

For the only known universal best choice algorithm for partially ordered sets with known cardinality and unknown order (proposed by J. Preater) we improve the estimation of the lower bound of its chance of success from the hitherto known constant 1/8 to 1/4. We also show that this result is the best possible for this algorithm, i.e., the 1/4 bound cannot be further improved. © 2007 Wiley Periodicals, Inc. Random Struct. Alg., 2008     

Synthesis of α-arylnaphthalenes from diphenylacetaldehydes and 1,1-diphenylacetones

Condensation of diphenylacetaldehydes and 1,1-diphenylacetones with malonodinitrile and cyclization of obtained aryl-ylidenemalonodinitriles in concentrated sulfuric acid leads to 1-amino-4-arylnaphthalene-2-carbonitriles. The benzannulation reaction is accompanied by a quasi-aromatic rearrangement. Preliminary tests of some synthesized aminonitriles have revealed their considerable biological activity against phytopathogenic fungi.     

Impact of Mercury(II) on proteinase K catalytic center: investigations via classical and Born-Oppenheimer molecular dynamics

Mercury(II) has a strong affinity for the thiol groups in proteins often resulting in the disruption of their biological functions. In this study we present classical and first-principles, DFT-based molecular dynamics (MD) simulations of a complex of Hg(II) and proteinase K, a well-known serine protease with a very broad and diverse enzymatic activity. It contains a catalytic triad formed by Asp39, His69, and Ser224, which is responsible for its biological activity. It was found previously by X-ray diffraction experiments that the presence of Hg(II) inhibits the enzymatic action of proteinase K by affecting the stereochemistry of the triad. Our simulations predict that (i) the overall structure as well as the protein backbone dynamics are only slightly affected by the mercury cation, (ii) depending on the occupied mercury site, the hydrogen bonds of the catalytic triad are either severely disrupted (both bonds for mercury at site 1, and the His69–Ser224 contact for mercury at site 2) or slightly strengthened (the Asp39–His69 bond when mercury is at site 2), (iii) the network of hydrogen bonds of the catalytic triad is not static but undergoes constant fluctuations, which are significantly modified by the presence of the Hg(II) cation, influencing in turn the triad’s ability to carry out the enzymatic function—these facts explain the experimental findings on the inhibition of proteinase K by Hg(II).     

Adducts of nitrogenous ligands with rhodium(II) tetracarboxylates and tetraformamidinate: NMR spectroscopy and density functional theory calculations

Complexation of tetrakis(μ₂‐N,N'‐diphenylformamidinato‐N,N')‐di‐rhodium(II) with ligands containing nitrile, isonitrile, amine, hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups has been studied in liquid and solid phases using ¹H, ¹³C and ¹⁵N NMR, ¹³C and ¹⁵N cross polarisation–magic angle spinning NMR, and absorption spectroscopy in the visible range. The complexation was monitored using various NMR physicochemical parameters, such as chemical shifts, longitudinal relaxation times T₁, and NOE enhancements. Rhodium(II) tetraformamidinate selectively bonded only unbranched amine (propan‐1‐amine), pentanenitrile, and (1‐isocyanoethyl)benzene. No complexation occurred in the case of ligands having hydroxyl, sulfhydryl, isocyanate, and isothiocyanate functional groups, and more expanded amine molecules such as butan‐2‐amine and 1‐azabicyclo[2.2.2]octane. Such features were opposite to those observed in rhodium(II) tetracarboxylates, forming adducts with all kind of ligands. Special attention was focused on the analysis of Δδ parameters, defined as a chemical shift difference between signal in adduct and corresponding signal in free ligand. In the case of ¹H NMR, Δδ values were either negative in adducts of rhodium(II) tetraformamidinate or positive in adducts of rhodium(II) tetracarboxylates. Experimental findings were supported by density functional theory molecular modelling and gauge independent atomic orbitals chemical shift calculations. The calculation of chemical shifts combined with scaling procedure allowed to reproduce qualitatively Δδ parameters. Copyright © 2013 John Wiley & Sons, Ltd.