Electronic coupling through intramolecular π-π interactions in biscobaltocenes: a structural, spectroscopic, and magnetic study

The paramagnetic dinuclear complexes 1,8-bis(cobaltocenyl)naphthalene (2) and 1,8-bis[(pentamethyl-η(5)-cyclopentadienyl)(η(5)-cyclopentadiendiyl)cobalt(II)]naphthalene (4) were synthesized. The molecular structures were characterized by X-ray structure analysis and consisted of two cobaltocenes linked through a distorted naphthalene clamp. Electronic interactions between the two cobalt atoms were observed by cyclic voltammetric studies. Superconducting quantum interference device (SQUID) measurements of the pure compounds and diluted in their diamagnetic iron derivatives, as well as variable-temperature NMR spectroscopy experiments in solution are presented. Magnetic measurements revealed an antiferromagnetic coupling of the electrons in complexes 2 and 4. From NMR spectroscopy experiments, Curie behavior in the temperature range from -60 to +60 °C can be deduced. The electronic structure and magnetic behavior is supported by results of broken-symmetry DFT and multireference calculations along with UV/Vis spectroscopic data, which revealed an intramolecular through space π-π interaction between the cobaltocene units.     

Probing the acceptor substrate binding site of Trypanosoma cruzi trans-sialidase with systematically modified substrates and glycoside libraries

Systematically modified octyl galactosides and octyl N-acetyllactosamines were assessed as inhibitors of, and substrates for, T. cruzi trans-sialidase (TcTS) in the context of exploring its acceptor substrate binding site. These studies show that TcTS, which catalyses the α-(2→3)-sialylation of non-reducing terminal β-galactose residues, is largely intolerant of substitution of the galactose 2 and 4 positions whereas substitution of the galactose 6 position is well tolerated. Further studies show that even the addition of a bulky sugar residue (glucose, galactose) does not impact negatively on TcTS binding and turnover, which highlights the potential of 'internal' 6-substituted galactose residues to serve as TcTS acceptor substrates. Results from screening a 93-membered thiogalactoside library highlight a number of structural features (notably imidazoles and indoles) that are worthy of further investigation in the context of TcTS inhibitor development.     

Distribution of N-glycosylation sequons in proteins: how apart are they?

N-glycosylation is a common protein modification process, which affects a number of properties of proteins. Little is known about the distribution of N-glycosylation sequons, for example, the distance between glycosylated sites and their position in the protein primary sequence. Using a large set of experimentally confirmed eukaryotic N-glycoproteins we analyzed the relative position and distribution of sequons. N-Glycosylation probability was found to be lower in the termini of protein sequences compared to the mid region. N-glycosylated sequons were found much farther from C terminus compared to the N-terminus of the protein sequence and this effect was more pronounced for NXS sequons. The distribution of sequons, modeled based on balls-in-boxes classical occupancy, showed a near-maximum probability. Considerable proportion of sequons was found within a distance of ten amino acids, indicating that the steric hindrance was not a key factor in protein N-glycosylation. Interestingly, the distribution of all sequons present in N-glycoproteins showed a pattern very similar to that of glycosylated sequons. The results indicate that protein N-glycosylation chiefly follows a random design.     

Photocatalytic methane decomposition over vertically aligned transparent TiO2 nanotube arrays

We report here on a study of vertically aligned TiO(2) nanotube arrays grown by the one-step anodic oxidation technique and their photocatalytic performance for methane decomposition. Quantitative activity data as a function of film thickness is obtained.     

Limit theorems for multipower variation in the presence of jumps

In this paper we provide a systematic study of how the probability limit and central limit theorem for realised multipower variation changes when we add finite activity and infinite activity jump processes to an underlying Brownian semimartingale.     

An absolute and relative rate study of the reaction of oh radicals with dimethyl sulfide

The gas phase reaction of OH radicals with dimethyl sulfide (CH₃SCH₃, DMS) has been studied using both an absolute and a relative technique at 295 ± 2 K and a total pressure of 1 atm. The absolute rate technique of pulse radiolysis combined with kinetic spectroscopy was applied. Using this technique a rate constant of (3.5 ± 0.2) × 10^?12 cm³ molecule^?1 s^?1 was obtained. For the relative rate method, rate constants for the reaction of OH with DMS were found to increase with increasing concentrations of added NO. These results are compared with the large body of kinetic and mechanistic data previously reported in the literature.     

High energy electronic neutrino (ve) and antineutrino (ve) interactions

The total cross-sections for $\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{(}\text{v}{}_{\mathrm{<mtext>e</mtext>}}\text{)}$-nucleon scattering have been measured. A test has been made of the muon number conservation law. A limit of 2.4 GeV is found the mass of the “Georgi-Glashow type” heavy lepton     

Numerical solution of the Gel'fand-Levitan equation

The inverse Sturm-Liouville problem is solved by using the Gel'fand-Levitan equation. The equation is discretized by the trapezoidal rule and the problem reduced to solving a sequence of systems of linear equations. The convergence of the method is established. It is shown that the problem can be arbitrarily ill conditioned. Finally, the accuracy of the method is illustrated by two numerical examples.