Unraveling the concerted catalytic mechanism of the human immunodeficiency virus type 1 (HIV-1) protease: a hybrid QM/MM study

Structural Chemistry - We give an account of a one-step concerted catalytic mechanism of HIV-1 protease (PR) hydrolysis of its natural substrate using a hybrid QM/MM method. The mechanism is a...     

A general class of Euclidean stars

In this paper we revisit the problem of modeling radiating stars in which the areal radius is equal to the proper radius throughout the stellar evolution. We provide a new family of solutions that completely describes the dynamical behaviour of these so-called Euclidean stars. The solution satisfies all the energy conditions, and importantly, admits a barotropic equation of state.     

Radiating stars with generalised Vaidya atmospheres

We model the gravitational behaviour of a radiating star when the exterior geometry is the generalised Vaidya spacetime. The interior matter distribution is shear-free and undergoing radial heat flow. The exterior energy momentum tensor is a superposition of a null fluid and a string fluid. An analysis of the junction conditions at the stellar surface shows that the pressure at the boundary depends on the interior heat flux and the exterior string density. The results for a relativistic radiating star undergoing nonadiabatic collapse are obtained as a special case. For a particular model we demonstrate that the radiating fluid sphere collapses without the appearance of the horizon at the boundary.     

Catalytic asymmetric carbon–carbon bond forming reactions catalyzed by tetrahydroisoquinoline (TIQ) N,N′-dioxide ligands

The use of TIQ-N,N′-dioxide ligands in asymmetric C–C bond forming reactions is described. In the Michael addition of cyclohexane-1,3-dione and malonates to β,γ-unsaturated α-ketoesters, excellent yields (up to 93%) and moderate to good enantioselectivities (70–89% ee) were obtained. The catalytic hetero-ene reaction of 2-methoxypropene with phenylglyoxal gave the ene product in excellent yield (95%) with moderate enantioselectivity (77% ee). The catalyst system performed well at temperatures ranging from 0 to 30 °C and relatively low catalyst loading (0.2–5 mol %) with dichloromethane being the preferred solvent for all reactions.     

The effect of mechanical and thermal anisotropy on the stability of gravity driven convection in rotating porous media in the presence of thermal non-equilibrium

We investigate Rayleigh–Benard convection in a porous layer subjected to gravitational and Coriolis body forces, when the fluid and solid phases are not in local thermodynamic equilibrium. The Darcy model (extended to include Coriolis effects and anisotropic permeability) is used to describe the flow, whilst the two-equation model is used for the energy equation (for the solid and fluid phases separately). The linear stability theory is used to evaluate the critical Rayleigh number for the onset of convection and the effect of both thermal and mechanical anisotropy on the critical Rayleigh number is discussed.     

On the Effect of Anisotropy on the Stability of Convection in Rotating Porous Media

We investigate natural convection in an anisotropic porous layer subjected to centrifugal body forces. The Darcy model (including centrifugal and permeability anisotropy effects) is used to describe the flow and a modified energy equation (including the effects of thermal anisotropy) is used in the current analysis. The linear stability theory is used to evaluate the critical Rayleigh number for the onset of convection in the presence of thermal and mechanical anisotropy. It is found that the convection is stabilized when the thermal anisotropy ratio (which is a function of the thermal and mechanical anisotropy parameters) is increased in magnitude.     

Hydrogen bonds, improper hydrogen bonds and dihydrogen bonds

The structures, interaction energies and vibrational spectra of a large number of molecular complexes, formed by binary combination of the covalent hydrides of some of the elements of the first two rows of the periodic table, have been determined by means of ab initio molecular orbital theory at the MP2 level, using the 6-311++G(d,p) basis set. The results are discussed in terms of a variety of different types of interaction experienced by the monomer species as they undergo association, namely conventional hydrogen bonding, improper hydrogen bonding, dihydrogen bonding and electron donor–acceptor interaction.     

NMR elucidation of some ligands derived from the pentacycloundecane skeleton

The complete NMR elucidation of three novel pentacycloundecane (PCU)-derived ligands is reported. 2D NMR techniques are used to overcome the problem of major overlapping of methine signals on the cage skeleton. The compounds were synthesized as potential ligands to be used in asymmetric catalysis. They represent the first instance where aromatic moieties have been attached directly to the cage skeleton using lithiation techniques. The X-ray crystal structure of one of the ligands was obtained. The X-ray structure was helpful in determining the potential NOESY interactions within the set of molecules. For the other ligands a high level Density Functional Theory (DFT) optimization was performed [B3LYP/6-31+g(d)] to visualize possible NOE interactions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A new polymorph of a cobalt(III) Schiff base complex exhibits a one‐dimensional C—H⋯O hydrogen‐bonded extended structure with helical 21 symmetry

In a new polymorph of acetato(2,2′‐{imino­bis[(E)‐propane‐3,1‐diylnitrilo­methyl­idyne]}diphenol­ato)­cobalt(III), [Co(C₂₀H₂₃N₃O₂)(C₂H₃O₂)], in the space group P2₁/c, the Co^III ion is six‐coordinate, with unequal Co—O_phenolate distances that average 1.908 (12) Å and more similar Co—N_imine distances averaging 1.937 (4) Å. The acetate ion occupies the sixth coordination site and forms an intra­molecular hydrogen bond (H⋯O = 1.95 Å) with the Co‐bound NH group of the penta­dentate chelate. The extended structure is a one‐dimensional (aryl)C—H⋯O(carbonyl) hydrogen‐bonded polymer with 2₁ (helical) symmetry and is thus distinct from the simple hydrogen‐bonded stack of the P2₁/n polymorph [Matsumoto, Imaizumi & Ohyoshi (1983). Polyhedron, 2 , 137–139].