Molecular properties and odour. Effects of substituents on pyridine and pyridine odour

It is investigated how the odour of pyridine changes when substituents of different kinds are inserted on the pyridine ring. The relation between the space filling and electronic properties of molecules and odour is studied. Far infrared spectra have been recorded for pyridines in order to test a hypothetical correlation between odour and vibrational energies.     

Microbial metabolism of the pyridine ring. Metabolic pathways of pyridine biodegradation by soil bacteria.

1. Two bacteria, a Bacillus sp. and a Nocardia sp. (strain Z1) were isolated from soil by enrichment with 0.1 percent (v/v) pyridine and grew rapidly on this compound as sole C, N and energy source. The monohydroxypyridines, tetrahydropyridine, piperidine and some other analogues were not utilized for growth or oxidized by washed suspensions of either bacterium. 2. Cell-free extracts were unable to metabolize pyridine even after supplementation with a variety of cofactors or protecting agents. Treatment of cells with toluene led to rapid loss of the ability to oxidize pyridine. 3. In the presence of 10mM-semicarbazide at pH 6.0, Nocardia Z1 accumulated a semialdehyde idenditied as its 2,4-dinitrophenylhydrazone by chromatography, mixed melting point, mass spectrometry and isotope trapping from [2,6(-14)C]pyridine as glutarate semialdehyde. 4. Extracts of this bacterium prepared from cells grown with pyridine or exposed to the gratuitous inducer 2-picoline, contained high activities of a specific glutarate semialdehyde dehydrogenase. 5. Cells grown with pyridine or glutarate also contained a glutaric dialdehyde dehydrogenase, an acyl-CoA synthetase and elevated amounts of isocitrate lyase but no glutaryl-CoA dehydrogenase. 6. Bacillus 4 accumulated in the presence of 10mM-semicarbazide several acidic carbonyl compounds from pyridine among which was succinate semialdehyde. Extracts of this bacillus after growth of the cells with pyridine contained an inducible succinate semialdehyde dehydrogenase in amounts at least 50-fold over those found in succinate-grown cells. 7. Two mutants of this bacillus, selected for their inability to grow on pyridine were deficient in succinate semialdehyde dehydrogenase. 8. In the presence of 0.2mM-KCN, washed suspensions of Bacillus 4 accumulated formate and possibly formamide from pyridine. The use of [14C]pyridine showed that formate was derived from C-2 of the pyridine ring. 9. The organism had a specific formamide amidohydrolase cleaving formamide quantitatively to formate and NH3. 10. Formate was further oxidized by the particle fraction. There was no soluble formate dehydrogenase in extracts.     

Sesquiterpene pyridine alkaloids from Hippocratea excelsa

Nineteen sesquiterpene pyridine alkaloids including 17 new compounds have been isolated from the 70% aq. EtOH extract of stem barks of Hippocratea excelsa. The structures of these compounds were elucidated by various spectroscopic means.     

A complex of pyridine and phosphatidylcholine

The effect of pyridine on the electronic structure and conformational state of cell phosphatidylcholine was studied by the methods of quantum chemistry and 13C NMR spectroscopy. It was shown that the interaction of the pi-system of pyridine electrons with the choline group of phosphatidylcholine leads to the formation of a complex. Changes in the conformational states due to the formation of this complex were revealed.     

A microsomal ATP-activated pyridine nucleotide transhydrogenase

An ATP-activated transhydrogenase which catalyzes the reduction of TPN⁺ by DPNH has been demonstrated in the microsomal fraction from the endosperm of immature Echinocystis macrocarpa seeds. The activity is specifically dependent on the presence of ATP (K_m of approximately 0.1 mm) of several nucleotides tested. The reaction is stimulated by MgCl₂ addition up to concentrations of 6 mm. When 10^?2m EDTA is added to the assay mixture in the absence of added MgCl₂, a transhydrogenation reaction is observed which no longer shows any dependence on added ATP. A TPN⁺-dependent ATPase activity can be demonstrated in these preparations, but no fixed stoichiometry between ATP cleavage and TPNH formation could be established. A lag in attaining the maximal rate of transhydrogenation is seen unless the enzyme is preincubated for 10 min with ATP before initiating the reaction. It can further be shown that preincubation of the enzyme with ATP followed by removal of the ATP on a Dowex 1 column produces an enzyme capable of catalyzing the transhydrogenation without the further addition of ATP. 2,4-Dinitrophenol and thyroxin are effective inhibitors of the transhydrogenase and 2,4-dinitrophenol was shown to inhibit the activating effect of ATP during the preincubation period. It is concluded that the role of ATP is in the modification of the enzyme rather than direct participation in the transhydrogenation. The transhydrogenase is inhibited by ADP and AMP. This results in a response of the enzyme to adenylate energy charge in a manner characteristic for regulatory enzymes which participate in ATP-utilizing metabolic sequences.     

The formation of pyridine haemochromogen.

1. Titration of haem with pyridine in alkaline media of low ionic strength yields a true pyridine haemochromogen, compound III, at very low concentrations of pyridine. 2. Graphical analysis of this titration gives the first spectrophotometric evidence for a dimeric haem. 3. Compound III is unstable and tends to aggregate to a second compound, compound II, whose formation is enhanced under those conditions favourable to hydrophobic bonding. 4. At higher concentrations of pyridine, compound II is dispersed to yield the classical pyridine haemochromogen, compound I, whose spectral properties are essentially those of pyridine haemochromogen in a non-aqueous medium.     

Recent developments in pyridine nucleotide regeneration

NAD(P)-dependent oxidoreductases are valuable tools for the synthesis of chiral compounds. Due to the high cost of the pyridine cofactors, in situ cofactor regeneration is required for preparative applications. In recent years, existing regeneration methodologies have been improved and new approaches have been devised. These include the use of newly discovered dehydrogenases that are stable in high contents of organic solvent and novel enzymes that can regenerate either the reduced or oxidized forms of the cofactor. The use of electrochemical methods has allowed cofactor regeneration for monooxygenases and natural or engineered whole-cell systems provide alternatives to approaches relying on purified enzymes.