The selective enhancement of band intensities in resonance Raman spectra of cobalt corrinoids

The role of point group symmetry in relation to localized-site cluster expansions is elucidated. Simple ways in which to accomplish symmetry adaptation are described, and new supersymmetries are found to arise for certain types of wave function ansätze. These new supersymmetries are shown to provide additional quantum numbers, which although often approximate are found in some model cases to be exact.     

Far infrared spectra,vibrational assignment and normal coordinate analysis of the tricyanomethanideion

Far infrared spectra of the tricyanomethanide ion C(CN)₃^? in solution and in the solid state have been investigated. The results allow a complete vibrational assignment to be made. A normal coordinate analysis has been carried out, the results of which are compatible with the existence of some double bond character in the C-C bonds of C(CN)₃^?.     

Agostic deformations based on electron delocalization in the alkyllithium-complex [(2-(Me3Si)2CLiC5H4N)2

Topological analysis of experimental and theoretical charge densities in the title complex [(2-(Me3Si)2CLiC5H4N)2] 1 reveals the nature of the agostic deformation postulated for this complex: delocalization of the Li-C bonding electrons over the entire agostic alkyl group controls the formation of an acute Li-C-Si angle and thus a sufficient electronic saturation of the electron deficient lithium atom via secondary interactions.     

Synthesis and solid state conformation of phenylalanine mimetics constrained in a proline-like conformation

We present the synthesis of five- and six-membered cyclic phenylalanine mimics (1, 9, 16 and 17) that are constrained in a proline-like conformation. The five-membered mimetic 16 was prepared by Ring Closing Metathesis (RCM) of diene 15, itself prepared by alpha-benzylation of the L-methionine derived oxazolidinone 10, followed by oxidative elimination, ring hydrolysis and N-allylation. The six-membered mimetic 1 was prepared by allylating the L-phenylalanine-derived oxazolidinone 5, followed by hydrolysis, N-allylation and RCM. Olefins 1 and 16 were catalytically hydrogenated to give 9 and 17, respectively. The solid state structures of 9 and 16 were determined by X-ray crystallography and their conformations compared with that of 1.     

Cellulose synthesis in the Arabidopsis secondary cell wall

The identification of genes responsible for cellulose synthesis has led to a significant advance in our understanding of the synthesis of this important polymer. The identification of these genes has arisen from the identification of cellulose deficient mutants. The irregular xylem (irx) mutants of Arabidopsis are caused by a severe reduction in cellulose synthesis in the secondary cell wall. Three irx mutants deficient in secondary cell wall cellulose are the result of mutations in three different members of the cellulose synthase catalytic subunit (CesA) gene family. The three proteins encoded by these genes all associate within the same membrane bound complex, and the presence of all three, but not their activity, is required for correct assembly and targeting of this complex. The knowledge that these three proteins associate provides a good opportunity to purify the cellulose synthase complex, and recent results working towards this goal are discussed.     

Electrolyte—formamide interactions studied by raman spectroscopy

The effects of dissolved electrolytes on the structure of liquid formamide have been investigated by Raman spectroscopy. The spectral features are dependent on the concentration and nature of the dissolved electrolyte and are discussed in terms of direct electrolyte formamide interactions. Two vN—H bands, arising from ion—formamide species, have been observed superimposed on the spectrum of residual liquid formamide. The results lend further support to the interaction model for electrolytes in liquid formamide previously proposed by us on the basis of nuclear magnetic resonance and infrared spectral data.     

Combination of neutron activation analysis and argon plasma emission spectrocopy in the elemental analysis of biological materials

Trace elements and major constituents are analyzed in solid biological material and body fluids in order to compare the range of application of instrumental neutron activation analysis and plasma emission spectroscopic techniques. It is demonstrated that both methods should be regarded as complementary analytical techniques. In separate or sequential combination of both techniques the elemental coverage in the analysis of biological material is extended.     

Fourier transform infrared spectroscopic characterisation of heavy metal-induced metabolic changes in the plant-associated soil bacterium Azospirillum brasilense Sp7

Structural and compositional features of whole cells of the plant-growth-promoting rhizobacterium Azospirillum brasilense Sp7 under standard and heavy metal-stressed conditions are analysed using Fourier transform infrared (FTIR) spectroscopy and compared with the FT-Raman spectroscopic data obtained previously [J. Mol. Struct. 563–564 (2001) 199]. The structural spectroscopic information is considered together with inductively coupled plasma-mass spectrometric (ICP-MS) analytical data on the content of the heavy metal cations (Co²⁺, Cu²⁺ and Zn²⁺) in the bacterial cells. As a bacterial response to heavy metal stress, all the three metals, being taken up by bacterial cells from the culture medium (0.2 mM) in significant amounts (ca. 0.12, 0.48 and 4.2 mg per gram of dry biomass for Co, Cu and Zn, respectively), are shown to induce essential metabolic changes in the bacterium revealed in the spectra, including the accumulation of polyester compounds in bacterial cells and their enhanced hydration affecting certain IR vibrational modes of functional groups involved.