Stereochemistry of cis- and trans-1-hydroxy-1-phenylquinolizidines

cis and trans-1-Hydroxy-1-phenylquinolizidines were prepared from 1-ketoquinolizidine and isolated by column chromatography. Infrared and nuclear magnetic spectral data were utilized for the elucidation of the structures.     

The effect of arsenic exposure on the biochemical and mineral contents of Labeo rohita bones: An FT-IR study

Arsenic compounds are ubiquitous and widespread in the environment as a result of natural or anthropogenic occurrence. Fish are the major source of protein for human consumption. They are also a source of contamination, because of the amounts of heavy elements they can contain, some of which are highly toxic. Fish bones are high in calcium, which is an essential mineral for normal body function. It consists of water, organic material, and mineral matter. Chelating agents have been used clinically as antidotes for acute and chronic metal intoxications. In the present study, an attempt is made to investigate the bio-accumulation of arsenic and its effect on the biochemical and mineral contents of Labeo rohita bones using, Fourier transform infrared (FT-IR) spectroscopy. The results of the present study indicate that arsenic exposure induces significant reduction on the biochemical and mineral contents of the L. rohita bones. Further, the DMSA treatment significantly improves these levels. This shows that DMSA is an effective chelator for arsenic toxicity. Quantitative curve-fitting analyses of amide I band have proved useful in studying the nature and the extent of protein conformational changes. A decrease in α-helical and random coil structures and an increase in β-sheet structures have been observed due to arsenic exposure. In conclusion, the present study shows that the FT-IR spectroscopy coupled with second derivative and curve-fitting analysis gives useful information about the biochemical and mineral contents of the L. rohita bones.     

FTIR study of zinc-induced biochemical changes in the liver of Indian carp <Emphasis Type="Italic">Labeo rohita</Emphasis>

Zinc is an essential metal for different physiological functions and becomes toxic when elevated concentrations are introduced into the environment. In the present study, an attempt is made to analyze zinc-induced biochemical changes in the liver tissues of freshwater fingerlings of Labeo rohita using Fourier Transformation Infrared Spectroscopy. Several important features have been observed in the FTIR spectra of zinc-intoxicated liver tissues, namely, altered membrane lipid, altered protein profile, and increased glycogen content, indicating an alteration in the lipid and protein profiles leading to modification in membrane composition. Further, it is observed that acute exposure to zinc causes some alteration in protein profile with a decrease in α-helix and an increase in random coil structure. Treatment with the chelating agent D-penicillamine reduces the biochemical contents in the liver tissues. This shows that D-penicillamine is a good antidote for zinc toxicity. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 746–752, September–October, 2008.     

Structural determinant of protein designability

Here we present an approximate analytical theory for the relationship between a protein structure's contact matrix and the shape of its energy spectrum in amino acid sequence space. We demonstrate a dependence of the number of sequences of low energy in a structure on the eigenvalues of the structure's contact matrix, and then use a Monte Carlo simulation to test the applicability of this analytical result to cubic lattice proteins. We find that the lattice structures with the most low-energy sequences are the same as those predicted by the theory. We argue that, given sufficiently strict requirements for foldability, these structures are the most designable, and we propose a simple means to test whether the results in this paper hold true for real proteins.     

NMR study of proton transport in the inorganic ion-exchange compounds SnO2·nH2O and TiO2·nH2O

Proton NMR relaxation times (T₂, T₁, T_1? and T₁D) are reported for hydrous tin oxide (SnO₂·nH₂O) and hydrous titania (TiO₂·nH₂O) in the temperature range 135 K<T<336 K at 60 and 20 MHz. The data show proton transport including exchange between three environments: (1) surface hydroxyl groups, (2) “acid solution” in micropores (diameter <100 Å) and (3) “acid solution” in macropores (diameter>1000 Å). The NMR behaviour has many features in common with that of adsorbed water systems. A consistent interpretation of both NMR and conductivity data is presented.     

Structural studies of highly non-stoichiometric polycrystalline sodium and silver beta-aluminas

Highly non-stoichiometric (x ≈ 0.45) sodium and silver beta-aluminas have been studied by power neutron diffraction. Results on the sodium material confirm the defect mechanism previously observed in materials with a lower degree of non-stoichiometry but accurate sodium occupations in the mirror plane could not be obtained. In contrast, for the silver beta-alumina prepared by ion exchange, the silver ion distribution could be satisfactorily refined. The stable site in stoichiometric silver beta-alumina is no longer occupied.     

Ligand topology variations and the importance of ligand field strength in non-heme iron catalyzed oxidations of alkanes

A series of iron(II)-bis(triflate) complexes [Fe(L)(OTf)2] containing linear tetradentate bis(quinolyl)-diamine and bis(quinolylmethyl)-diamine ligands with a range of ligand backbones has been prepared. The coordination geometries of these complexes have been investigated in the solid state by X-ray crystallography and in solution by 1H and 19F NMR spectroscopy. Because of the labile nature of high-spin iron(II) complexes in solution, dynamic equilibria of complexes with different coordination geometries (cis-alpha, cis-beta, and trans) are observed with certain ligand systems. In these cases, the geometry observed in the solid-state does not necessarily represent the only or even the major geometry present in solution. The ligand field strength in the various complexes has been investigated by variable-temperature (VT) magnetic moment measurements and by UV-vis spectroscopy. The strongest ligand field is observed with the most rigid ligand that generates [Fe(L)(OTf)2] complexes with a cis-alpha coordination geometry, and the corresponding [Fe(L)(CH3CN)2]2+ complex displays spin crossover behavior. The catalytic properties of the complexes for the oxidation of cyclohexane have been investigated using hydrogen peroxide as the oxidant. An increased flexibility in the ligand results in a weaker ligand field, which increases the lability of the complexes. The activity and selectivity of the catalysts appear to be related to the strength of the ligand field and the stability of the catalyst.