Photoelectron spectroscopy of some biological molecules

The ultraviolet photoelectron spectra (UPS) of the following biologically-active compounds are reported and/or assigned: 2,4-dinitrophenol, nicotinic acid, nicotinamide, barbituric acid, xanthine, hypoxanthine, uric acid, uracil, thymine, cytosine, adenine, guanine, β-carotene, menadione, purine and pyrimidine. The importance of UPS data is exemplified in two ways: First, by investigating the validity of the Pullman k-index approach ¹⁴ to ionization energies; and, second, by generating an experimental scale of electron-donating ability.     

Functional equations for local normal zeta functions of nilpotent groups

We give explicit formulae for the local normal zeta functions of torsion-free, class-2-nilpotent groups, subject to conditions on the associated Pfaffian hypersurface which are generically satisfied by groups with small centre and sufficiently large abelianization. We show how the functional equations of two types of zeta functions – the Weil zeta function associated to an algebraic variety and zeta functions of algebraic groups introduced by Igusa – match up to give a functional equation for local normal zeta functions of groups. We also give explicit formulae and derive functional equations for an infinite family of class-2-nilpotent groups known as Grenham groups, confirming conjectures of du Sautoy.Received: September 2003 Revision: February 2004with Appendix by A. Beauville     

Correlation of volumes and entropies of activation for oxidation of coordinated sulfur in bis-ethylenediaminecobalt(III) complexes by peroxodisulphate,hydrogen peroxide and periodate and for peroxodisulphate oxidation of diimine-cyanide–iron(II) complexes

Activation parameters H , S and V and correlations between S and V are reported for peroxodisulphate oxidation of [Fe(CN)₆]^4–, [Fe(bipy)₃]²⁺ (bipy = (2, 2-bipyridyl), [Fe(phen)₃]²⁺ (phen = 1,10-phenanthroline), cis-[Fe(bipy)₂(CN)₂], [Fe(bipy)(CN)₄]^2–, [Fe(phen)(CN)₄]^2–, [Co(en)₂(glyS)]⁺ (glyS = mercaptoacetate, SCH₂COO^2–), [Co(en)₂(cyS)]⁺ (cyS = cysteinate, SOCH₂CH(COO)NH₂ ^2–) and [Co(en)₂(amS)]²⁺ (amS = ethanesulphenaminate, SCH₂CH₂NH₂ ^–) and for periodate and hydrogen peroxide oxidation of the three last-named complexes. Activation parameters are discussed in terms of electrostriction, solvation and ligand size contributions. Opposite trends for S /V correlations were found for oxidations of Fe^II complexes in comparison with oxidations of coordinated sulphur in the Co^III complexes.     

Constant-rate titrations in studies of chemical kinetics: Part 5. Thermometric Titrations of Ethyl Glycolate with Sodium Hydroxide,and Simultaneous Determination of Glycolic Acid and Evaluation of the Rate Constant for Alkaline Hydrolysis

The data obtained in a constant-rate thermometric titration of an aqueous solution of ethyl glycolate with standard sodium hydroxide can be used to evaluate the rate constant and change of enthalpy for the reaction and also to determine the percentage of glycolic acid present as an impurity in the ester.     

Solvent Effect on the Kinetics of Oxidation of [Co(en)2SCH2CH2 NH2]2+ by S2O8 2−

The effect of the solvent on rate of the oxidation of [Co(en)₂SCH₂CH₂NH₂]²⁺ by S₂O₈ ²⁻ in aqueous mixtures of methanol (MeOH), tert-butyl alcohol (Bu ^t OH), acetonitrile (AN), ethylene glycol (EG) and ethylene carbonate (EC) has been analysed as regards initial and transition state contributions. From kinetic measurements and solubilities of the reactants, the Gibbs transfer functions, ΔG _t°, corresponding to transfer of reactants and activated complex from water to water-organic mixtures were evaluated. The trends of the transfer functions are discussed in terms of ion-solvent interactions and the structural effects in the solvent mixtures. This revised version was published online in June 2006 with corrections to the Cover Date.     

Smectic A mesophases from luminescent sandic platinum(II) mesogens

Square planar platinum(II) thienyl pyridyl complexes with board-shaped structures assemble into lamellar (SmA) liquid crystal phases at elevated temperatures. Liquid crystals of this type are expected to have stronger biaxial correlations than typical calamitic mesogens. The mesophase stability improves with decreasing alkyl chain lengths with C₈H₁₇ having the widest range of stability. All complexes are luminescent in solution.     

Etheric bimesogens and the twist-bend nematic phase

Despite the relationship between molecular structure and the occurrence of the twist-bend nematic phase being partially understood, very little is known about how these relationships are manifested for ether-linked bimesogens. In this article, we report several novel ether-linked bimesogens that exhibit the N_TB phase and explore how the thermal properties of these materials are largely governed by the angle between the two aromatic, carbocyclic or rigid cyclic units.     

Surface plasmon dynamics in silver nanoparticles studied by femtosecond time-resolved photoemission

Multiphoton photoelectron spectroscopy reveals the multiple excitation of the surface plasmon in silver nanoparticles on graphite. Resonant excitation of the surface plasmon with 400 nm femtosecond radiation allows one to distinguish between photoemission from the nanoparticles and the substrate. Two different previously unobserved decay channels of the collective excitation have been identified, namely, decay into one or several single-particle excitations.     

Design,synthesis, and NMR structure of linear and cyclic oligomers containing novel furanoid sugar amino acids

Sugar Amino Acids (SAAs) are sugar moieties containing at least one amino and one carboxyl group. The straightforward synthesis of two furanoid SAAs, 3-amino-3-deoxy-1,2-isopropylidene-alpha-D-ribofuranoic acid (f-SAA1) and 3-amino-3-deoxy-1,2-isopropylidene-alpha-D-allofuranoic acid (f-SAA2) starting from diacetone glucose, is described. These SAAs were used as structural templates aiming at new structures for peptidomimetic drug design. f-SAA1 resembles a beta-amino acid, whereas f-SAA2 is a gamma-amino acid mimetic. Thus, for the synthesis of the mixed, linear and cyclic oligomers of f-SAA1, beta-homo-glycine (beta-hGly, also called beta-alanine) was chosen as an amino acid counterpart, while for the oligomer of f-SAA2 gamma-amino butyric acid (GABA) was chosen. Fmoc-[f-SAA1-beta-hGly](3)-OH (3) and cyclo[f-SAA1-beta-hGly](3) (5) resemble linear and cyclic beta-peptides with a very different substitution pattern, compared with the beta-peptides known so far in the literature, whereas Fmoc-[f-SAA2-GABA](3)-OH (4) resembles a gamma-peptide. The linear f-SAA oligomers 3 and 4 were synthesized on the solid-phase using Fmoc strategy. 23 unambiguous interresidue NOE contacts (from a total of 76 NOE values), obtained from extensive NMR studies in C(3)CN, were used in subsequent simulated annealing and MD calculations, to elucidate the 12/10/12-helical structure of oligomer 3 in CH(3)CN. The results indicate that f-SAA1 strongly induces a secondary structure. A characteristic CD curve for the linear oligomer 3 is observed up to 75 degrees C in both CH(3)CN and CH(3)CN/H(2)O, even though 3 contains beta-hGly, which is known to destabilize helices. By contrast, 4 does not seem to form a stable conformation in solution. The cyclic SAA containing oligomer cyclo [f-SAA1-beta-hGly](3) (5) exhibits a C(3) symmetric conformation on the NMR chemical shift time scale.