The dynamics of gallamine: A potent neuromuscular blocker. A determination by quantum mechanics and molecular dynamics (i) in vacuo studies

The potent neuromuscular blocker, gallamine, possesses three chemically equivalent, flexible side chains, the motion of which has been proposed as important in its mode of action on the acetylcholine receptor in vivo. The flexibility of the side chains has been investigated in the present initial study by a combination of quantum mechanics and molecular dynamics on the isolated, unsolvated molecule. Net atomic charges for the gallamine molecule have been calculated using the semiempirical program MOPAC for use in the molecular dynamics simulation. The flexibility of the side chains has been shown to correlate with the range of fluctuations in torsion angles observed in the crystal structure of gallamine.     

Evolution of Packets of Surface Gravity Waves over Strong Smooth Topography

Wave packets in a smoothly inhomogeneous medium are governed by a nonlinear Schrödinger (NLS) equation with variable coefficients. There are two spatial scales in the problem: the spatial scale of the inhomogeneities and the distance over which nonlinearity and dispersion affect the packet. Accordingly, there are two limits where the problem can be approached asymptotically: when the former scale is much larger than the latter, and vice versa. In this paper, we examine the limit where the spatial scale of (periodic or random) inhomogeneities is much smaller than that of nonlinearity/dispersion (i.e., the latter effects are much weaker than the former). In this case, the packet undergoes rapid oscillations of the geometric-optical type, and also evolves slowly due to nonlinearity and dispersion. We demonstrate that the latter evolution is governed by an NLS equation with constant (averaged) coefficients. The general theory is illustrated by the example of surface gravity waves in a channel of variable depth. In particular, it is shown that topography increases the critical frequency, for which the nonlinearity coefficient of the NLS equation changes sign (in such cases, no steady solutions exist, i.e., waves with frequencies lower than the critical one disperse and cannot form packets).     

Nuclear shielding calculations on the primary structure of the gellan polysaccharide

Ab initio, GIAO and IGLO, nuclear shielding calculations are performed on each of the four pyranose ring residues of the tetrasaccharide repeating unit in a single chain of the gellan polysaccharide, [→ 3)- -Glcp-(1 → 4)-β- -GlcpA-(1 → 4)-β- -Glcp-(1 → 4)-- -Rhap(1 _n. The results provide an insight into the effects of the changing primary molecular electronic structure on the calculated ¹³C, ¹⁷O and ¹H shieldings. In particular, the observed trends in the calculated isotropic (σⁱ) shielding values are rationalised withi the framework of the localised molecular orbital shielding contributions and Mulliken population analyses (MPA).     

The crystal structures of 2-(2′-pyridyl)phenyltellurium(II) bromide and of the inclusion compound bis[2-(2′-pyridyl)phenyltellurium(II) chloride]·p-ethoxyphenyl-mercury(II) chloride

In 2-(2′-pyridyl)phenyltellurium(II) bromide (1) the coordination about tellurium may be described as pseudo-trigonal bipyramidal wth bromine (Te---Br = 2.707(11) Å) and nitrogen (Te---N) = 2.236(11) Å) atoms occupying axial positions. The equatorial plane comprises a carbon atome (Te---C = 2.111(6) Å) and two lone pairs of electrons. There are no significant intermolecular interactions between the six independent molecules in the unit cell. Bis[2-2′-pyridyl)phenyltellurium(II) chloride]·p-ethoxy-phenylmercury(II) chloride (2) may be regarded as an “inclusion compound” obtained by replacement of two RTeX (X = Cl or Br) molecules by two p-ethoxyphenylmercury(II) chloride entities. There is approximately linear coordination about mercury (C---Hg---Cl = 179.2°(4), Hg-C = 2.044(14) and Hg---Cl = 2.328(4) Å) and 2-(2′-pyridyl)phenyltellurium(II) chloride, with a structure similar to that of (1) above (Te---N = 2.2366(6), Te---Cl = 2.558(1), Te---C = 2.080(25) Å). There are no significant intermolecular contacts.     

Molecular simulation of the comparative flexibility of bridging linkages in poly(aryl ether sulfone)s and poly(aryl ether ketone)s from a study of isolated oligomers

Atomistic molecular modelling of the bridging linkages in poly(aryl ether sulfone)s and poly(aryl ether ketone)s have been studied in vacuo. The results of these simulations indicate that models that have bond lengths and angles that agree with X-ray data are produced from the energy minimised structures and additionally that conformational analysis of these linkages produces low energy conformers that are also accessible in the X-ray data. The results of these simulations provide confidence in the modelling techniques used and indicate the potential for these models in further simulation of the bulk amorphous state.     

Examining the kinetics of the thermal polymerization of commercial aromatic bis‐benzoxazines

Three commercial bis‐benzoxazine monomers based on the aniline derivatives of bisphenol A (BA‐a), bisphenol F (BF‐a), and 3,3′‐thiodiphenol (BT‐a) are examined using a variety of spectroscopic, chromatographic, and thermomechanical techniques. The kinetics of the polymerization of BA‐a were found to be well described using an autocatalytic model for which values of n = 1.39 and m = 2.49 were obtained for the early and later stages of reaction respectively (activation energy = 81–88 kJ/mol.). Following recrystallization the same monomer yielded values of n = 1.80, m = 0.92, and E_a = 94–97 kJ/mol. BF‐a and BT‐a were also found to be well described using an autocatalytic model for which values of n = m = 2.11 (BF‐a) and n = 2.10, m = 1.47 (BT‐a) were obtained for the early and later stages of reaction (activation energy = 80–84 kJ/mol. for BF‐a and 88–95 kJ/mol. for BT‐a). The kinetic data are compared with parallel studies involving chemically initiated benzoxazine monomers. Molecular simulation is used to examine the rotational freedom of the central bridging units and this is related to the degree of conversion achieved. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2068–2081