Neutron reflectivity measurements of the translational motion of tris(naphthylbenzene) at the glass transition temperature

The translational dynamics of the low molecular weight glass-former tris(naphthylbenzene) have been studied on the length scale of a few nanometers at the glass transition temperature Tg. Neutron reflectivity was used to measure isotopic interdiffusion of multilayer samples created by physical vapor deposition. Deposition with the substrate held at Tg-6 K allows observation of dynamics characterizing the equilibrium supercooled liquid. The diffusion coefficient measured at q = 0.03 A(-1) was determined to be 1x10(-17) cm2/s at 342 K (Tg). The self-part of the intermediate scattering function I(s)(q,t) decays exponentially. Samples deposited well below Tg show a substantial thermal history effect during subsequent translational motion at Tg.     

Initiating a crystallographic study of UDP-galactopyranose mutase from escherichia coli. erratum

In the paper by McMahon, Leonard, Buchanan, Giraud & Naismith [Acta Cryst. (1999). D55, 399-402] an author's error has resulted in the fifth sentence of the Abstract being incorrect. The sentence should read 'They are monoclinic, space group P21, with unit-cell dimensions a = 71.12, b = 58.42, c = 96.38 A, beta = 96.38 degrees. 92% (native) and 94% (selenomethionine) complete data sets have been recorded to 2.9 A (Rmerge = 5.0%) and 3.0 A (Rmerge = 6.9%), respectively.'     

An experimental and Ab initio study of the nature of the binding in gas-phase complexes of sodium ions

Fourier transform ion cyclotron resonance (FT-ICR) ligand exchange equilibrium experiments have been used to establish a relative scale of sodium binding free energies of about fifty organic molecules. Ab initio calculations yield accurate enthalpies and entropies of complexation for a new set of 30 molecules. These calculations establish an absolute basis for the relative experimental free energy scale. In addition, they provide structural information for the complexes which permits considerable insight into the nature of sodium ion binding. We found that when the binding site is a first row atom, the sodium ion aligns with the molecular dipole axis in order to maximize charge-dipole electrostatic interactions. Strong deviations from this behavior occur when the ion is attached to a heavier atom such as sulfur, chlorine or bromine. For flexible molecules such as the isomers of butyl chloride, there are several isomers of low energy, and differences exist between the enthalpy and free energy orders of stability. Finally, sodium ion affinities have been obtained for several aromatic molecules which lend support to the importance of charge-quadrupole interactions in such cation-pi complexes.     

Singlet-triplet energy separation of cyclobutylidene

Ab initio (MP2, CCSD(T)) and density functional theory (BLYP, B3LYP) calculations provide insight concerning novel aspects of structure and bonding in cyclobutylidene (1). Singlet cyclobutylidene ((1)1) adopts a bicyclobutane-like structure (C(s) symmetry) that includes a weak, transannular bonding interaction between the carbene carbon and the opposing CH(2) group. Conformational ring inversion in (1)1 occurs through a transition state of C(2)(v)() symmetry (TS(1)1) with an enthalpy barrier of approximately 3 kcal/mol. Stabilization afforded the singlet state by the transannular interaction appears to be largely offset by a loss of hyperconjugative stabilization from the adjacent C-H bonds. Triplet cyclobutylidene ((3)1) exhibits a C(2)(v)() structure and conventional bonding. The triplet state lies 5.9 kcal/mol above the singlet ground state at the CCSD(T)/TZP//CCSD(T)/DZP level of theory. The singlet-triplet energy gap of cyclobutylidene (-5.9 kcal/mol) lies between that of an acyclic analogue, dimethylcarbene (-1.6 kcal/mol), and a highly strained analogue, cyclopropylidene (-13.8 kcal/mol). The magnitude of the energy gap suggests that triplet cyclobutylidene ((3)1) will be thermally accessible under a variety of experimental conditions.     

Molecular structure of (tBu)3AlP(nPr)3

The crystal and molecular structure of (^tBu)₃AlP(ⁿPr)₃ has been determined. The Al(1)?P(1) bond distance [2.594(3) Å] is slightly longer than other aluminum-phosphine complexes; however, the geometry about aluminum is similar to that of the [AlCl(^tBu)₃]^? anion, suggesting that the geometry about the aluminum in tri-tert-butylaluminum complexes is defined by the size of thetert-butyl ligands and not as a consequence of the steric bulk of the Lewis base. Crystal data: Monoclinic,P2_t,a=8.932(2),b=16.832(3),c=9.328(2), Å, β=114.36(3)°,V=1277.6(6) ų,Z=4,R.=0.055,R _w =0.053.     

Preparation and Fungitoxicity of Some Dibromo-8-quinolinols

Summary.  2,5-, 3,5-, 3,6-, 3,7-, 4,5-, 5,6-, 5,7-, and 6,7-dibromo-8-quinolinols were prepared and tested against six fungi (Aspergillus niger, Aspergillus oryzae, Myrothecium verrucaria, Trichoderma viride, Mucor cirinelloides, and Trichophyton mentagrophytes) in Sabouraud dextrose broth. Most of the compounds were strongly antifungal, inhibiting five of the fungi below 1μg/cm³, but were somewhat less fungitoxic than the corresponding chloro analogues. M. cirinelloides was not inhibited by any of the compounds except 4,5-dibromo-8-quinolinol. This high level of fungitoxicity is attributed to intramolecular synergism. Received December 28, 2000. Accepted (revised) February 3, 2001     

Solitary waves in plasmonic Bragg gratings

Light propagation in a Bragg periodic structure containing thin films with metallic nanoparticles is studied. The plasmonic resonance frequency, Bragg frequency, and the light carrier frequency are assumed to be close. Exact solutions describing solitary gap-waves are found, and a light arrest phenomenon due to the nonlinearity of plasmonic oscillations is studied. PACS 42.55.Tv; 42.65.-k; 42.70.Qs; 81.07.Bc     

Freeze-drying of protein pharmaceuticals--the application of thermal analysis

This review describes the range of thermal analysis techniques that may be used to investigate the key thermal properties of formulations to be freeze-dried and the resultant products. The use of these allows development of cost-effective processing while maintaining optimum product quality.     

A partial-wave analysis of the neutral 3π system produced in the reaction π−p → (π+π−π0) n at 12 and 15 GeV/c

Data on the charge-exchange reaction π^?p → (π⁺π^?π⁰)n have been taken at beam momenta of 12 and 15 GeV/c, using the CERN Omega Multiparticle Spectrometer. A partial-wave analysis has been made of the (3π)⁰ system. We observe both natural and unnatural spin-parity production. The natural parity states can be identified with established resonances. In addition a natural spin-parity enhancement is observed at a mass of about 2 GeV/c² with J^P = 4⁺ preferred. We have called this effect the A₂¹ (2030). The unnatural spin-parity production found is consistent with reggeized Deck model predictions. No unambiguous A₁ or A₃ production is observed.