Synthesis and circular dichroism studies of steroidal schiff bases of biogenic amines

A number of imines (Schiff bases) have been prepared from ketosteroids (estrone, estrone-3-methyl ether, androsterone, epiandrosterone, 5α-cholestan-3-one, 6-ketocholestanol and testosterone) and primary amines (phenethylamine, tyramine and hexanamine). The CD spectra of these compounds have been measured in methanol. Except for the testosterone imines, the azomethine n-π^* band (~ 235 nm) exhibited the same sign (but not as high an ellipticity) as the parent ketone's n - π^* band (~295 nm). The imines of the estrogens (estrone and estrone 3-methyl ether) gave CD spectra characterized by a negative ¹L_b Cotton effect ([θ] ? -1000) near 280 nm and a band near 230 nm ([θ] ? +19,000) which is considered the sum of a positive azomethine n - π^* Cotton effect and positive aromatic ¹L_a Cotton effect(s). The ¹L_a band originating in the amine moiety was prominent in the CD of 5α-cholestan-3-one and 6-ketocholestanol phenethylamine imines. When aromatic Cotton effects originating in the amine moiety were detected, they were of the same sign as the n - π^* Cotton effect.     

Quantum theory of the structure and bonding in proteins : Part 14. The serine dipeptide

The energies of the conformations of the serine dipeptide are computed by ab initio molecular orbital theory in order to demonstrate the existence of the hydrogen bonds, torsion barriers and non-bonded repulsions which govern the relative energies of these conformations. The Ramachandran map of the dipeptide is computed and found to resemble closely those of alanine and ethyl glycine. The side-chain maps are them computed and analysed to show the above physical effects in terms of the torsion barrier-free maps.

There is generally good agreement between the experimental and theoretical results in the sense that all three side-chain conformations which are staggered about CC^β (₁ = + 60, 180 and −60°) are computed to be close in energy and all three values of ₁ occur with similar frequencies in the proteins examined. The fact that serine, unlike all other comparable residues except threonine, tends to favour a ₁ value of + 60° in the bridge region is reproduced clearly by the computations and analysis of the physical factors involved shows that this conformation is stabilised by side chain to backbone hydrogen bonding.     

Heuristic charge assignment for deconvolution of electrospray ionization mass spectra

We propose a new algorithm for deconvolution of electrospray ionization mass spectra based on direct assignment of charge to the measured signal at each mass-to-charge ratio (m/z). We investigate two heuristics for charge assignment: the entropy-based heuristic is adapted from a deconvolution algorithm by Reinhold and Reinhold;10 the multiplicative-correlation heuristic is adapted from the multiplicative-correlation deconvolution algorithm of Hagen and Monnig.6 The entropy-based heuristic is insensitive to overestimates of z(max), the maximum ion charge. We test the deconvolution algorithm on two single-component samples: the measured spectrum of human beta-endorphin has two prominent and one very weak line whereas myoglobin has a well-developed quasi-gaussian envelope of 17 peaks. In both cases, the deconvolution algorithm gives a clean deconvoluted spectrum with one dominant peak and very few artefacts. The relative heights of the peaks due to the parent molecules in the deconvoluted spectrum of a mixture of two peptides, which are expected to ionize with equal efficiency, give an accurate measure of their relative concentration in the sample.     

Annual Meeting of the Division of Biochemistry,Biophysics, and Chemistry of Physiologically Active Compounds of the Russian Academy of Sciences

Information

Annual Meeting of the Division of Biochemistry, Biophysics, and Chemistry of Physiologically Active Compounds of the Russian Academy of Sciences     

Beiträge zur Chemie der Silicium-Schwefel-Verbindungen. XXXIX. Blei(II)-bis-tri-tert-butoxysilanthiolat

Contributions to the Chemistry of Silicon Sulfur Compounds. XXXIX. Lead(II)-bis-tritertbutoxysilanethiolate The title compound 1 is formed from (t-C₄H₉O)₃SiSH and PbO by an exothermic reaction. In benzene solution 1 is monomeric, whereas a solvated dimer the structure of which was determined crystallizes from glyme solutions. The F.I. mass spectrum only shows the mass of the monomeric unit. The ²⁹Si n.m.r. spectrum shows only one sharp signal at δ = ?68.33 ppm. The central four-membered (Pb₂S₂) ring of the dimer is puckered (butterfly; 51.2°). The folding takes place at the Pb atoms. The Pb atoms are threefold coordinated by S atoms (d_endo = 278.9 pm; d_exo = 258.6 pm) whereas the S atoms are bonded to two Pb atoms and one Si atom (208.8–214.3 pm).     

Ir6In32S21, a polar,metal-rich semiconducting subchalcogenide

Subchalcogenides are uncommon, and their chemical bonding results from an interplay between metal–metal and metal–chalcogenide interactions. Herein, we present Ir₆In₃₂S₂₁, a novel semiconducting subchalcogenide compound that crystallizes in a new structure type in the polar P31m space group, with unit cell parameters a = 13.9378(12) Å, c = 8.2316(8) Å, α = β = 90°, γ = 120°. The compound has a large band gap of 1.48(2) eV, and photoemission and Kelvin probe measurements corroborate this semiconducting behavior with a valence band maximum (VBM) of −4.95(5) eV, conduction band minimum of −3.47(5) eV, and a photoresponse shift of the Fermi level by ∼0.2 eV in the presence of white light. X-ray absorption spectroscopy shows absorption edges for In and Ir do not indicate clear oxidation states, suggesting that the numerous coordination environments of Ir₆In₃₂S₂₁ make such assignments ambiguous. Electronic structure calculations confirm the semiconducting character with a nearly direct band gap, and electron localization function (ELF) analysis suggests that the origin of the gap is the result of electron transfer from the In atoms to the S 3p and Ir 5d orbitals. DFT calculations indicate that the average hole effective masses near the VBM (1.19m_e) are substantially smaller than the average electron masses near the CBM (2.51m_e), an unusual feature for most semiconductors. The crystal and electronic structure of Ir₆In₃₂S₂₁, along with spectroscopic data, suggest that it is neither a true intermetallic nor a classical semiconductor, but somewhere in between those two extremes.

Subchalcogenides are uncommon, and their chemical bonding results from an interplay between metal–metal and metal–chalcogenide interactions.     

Bidentate ligands capable of variable bond angles in the self-assembly of discrete supramolecules

Flexible donor ligands like 1,2-bis(3-pyridyl)ethyne or 1,4-bis(3-pyridyl)-1,3-butadiyne self-assemble into discrete supramolecules instead of infinite networks upon combination with organoplatinum 90, 120, and 180 degree acceptor units. These systems are unique examples of versatile pyridine donors adjusting their bonding directionality to accommodate rigid platinum acceptors in the formation of closed macrocycles.     

The evaluation of a tenax GR diffusive sampler for the determination of benzene and other volatile aromatics in outdoor air

The applicability of a tube-type diffusive sampler as an environmental monitor for benzene, toluene, ethylbenzene and xylene (BTEX) is reported. Uptake rates have been experimentally determined for a novel type adsorbent, Tenax GR, and compared to theoretical values. It is shown, that the uptake rates are virtually independent of environmental parameters within the experimental conditions studied. The response of the sampler to transient changes in concentrations has been determined in the laboratory. It is found that the sampler is capable of following an extreme concentration profile. Field comparisons with pumped samplers have been performed and good agreement is observed between the results of the two independent methods. The samplers have also been applied as environmental monitors at different locations.     

Fast and slow deposition of silver nanorods on planar surfaces: application to metal-enhanced fluorescence

Two methods have been considered for the deposition of silver nanorods onto conventional glass substrates. In the first method, silver nanorods were deposited onto 3-(aminopropyl)triethoxysilane-coated glass substrates simply by immersing the substrates into the silver nanorod solution. In the second method, spherical silver seeds that were chemically attached to the surface were subsequently converted and grown into silver nanorods in the presence of a cationic surfactant and silver ions. The size of the silver nanorods was controlled by sequential immersion of silver seed-coated glass substrates into a growth solution and by the duration of immersion, ranging from tens of nanometers to a few micrometers. Atomic force microscopy and optical density measurements were used to characterize the silver nanorods deposited onto the surface of the glass substrates. The application of these new surfaces is for metal-enhanced fluorescence (MEF), whereby the close proximity of silver nanostructures can alter the radiative decay rate of fluorophores, producing enhanced signal intensities and an increased fluorophore photostability. In this paper, it is indeed shown that irregularly shaped silver nanorod-coated surfaces are much better MEF surfaces as compared to traditional silver island or colloid films. Subsequently, these new silver nanorod preparation procedures are likely to find a common place in MEF, as they are a quicker and much cheaper alternative as compared to surfaces fabricated by traditional nanolithographic techniques.     

Übergangsmetallkomplexe [Et2P(S)NR]M/n,Vierringchelate mit Thiophosphinsäure-Organylamidato-Liganden [1]

Transition Metal Complexes [Et₂P(S)NR]M/n, Chelates containing 4-membered Rings and Phosphinothioic-organylamidato Ligands Phosphinothioic-organylamidato complexes [Et₂P(S)NR]M/n (R = Me, Et, tBu, cHex, Ph; M = Ti^III, V^III, Cr^III, Co^II, Zn^II) are obtained by reaction of metal halides with [Et₂P(S)NR]Li or from ZnEt₂ and Et₂P(S)NHR. In contrast to the analogous phosphinothioic complexes [R′₂P(S)X]M/n (X = O, S, Se) they are extremely hydrolyzable. The ligand field parameters Δ and β of Et₂P(S)NR^? are found to be similar to those of R′₂P(S)S^? indicating a low ligand field strength and a strong nephelauxetic effect. In contrast to [R′₂P(S)O]₂M (M = Co, Zn), which are highly polymerised, there is only a weak tendency of the corresponding tetrahedral phosphinothioicorganylamidato complexes to form ligand bridges.