Enzyme catalysed non-oxidative decarboxylation of aromatic acids II. Identification of active site residues of 2,3-dihydroxybenzoic acid decarboxylase from Aspergillus niger

In order to understand the mechanism of decarboxylation by 2,3-dihydroxybenzoic acid decarboxylase, chemical modification studies were carried out. Specific modification of the amino acid residues with diethylpyrocarbonate, N-bromosuccinimide and N-ethylmaleiimide revealed that at least one residue each of histidine, tryptophan and cysteine were essential for the activity. Various substrate analogs which were potential inhibitors significantly protected the enzyme against inactivation. The modification of residues at low concentration of the reagents and the protection experiments suggested that these amino acid residues might be present at the active site. Studies also suggested that the carboxyl and ortho-hydroxyl groups of the substrate are essential for interaction with the enzyme.

Dust aerosols over India and adjacent continents retrieved using METEOSAT infrared radiance Part II: quantification of wind dependence and estimation of radiative forcing

Long-range transport of continental dust makes these particles a significant constituent even at locations far from their sources. It is important to study the temporal variations in dust loading over desert regions and the role of meteorology, in order to assess its radiative impact. In this paper, infrared radiance (10.5-12.5 mu m), acquired by the METEOSAT-5 satellite (similar to 5-km resolution) during 1999 and 2003 was used to quantify wind dependence of dust aerosols and to estimate the radiative forcing. Our analysis shows that the frequency of occurrence of dust events was higher during 2003 compared to 1999. Since the dust production function depends mainly on the surface wind speed over regions which are dry and without vegetation, the role of surface wind on IDDI was examined in detail. It was found that an increase of IDDI with wind speed was nearly linear and the rate of increase in IDDI with surface wind was higher during 2003 compared to 1999. It was also observed that over the Indian desert, when wind speed was the highest during monsoon months (June to August), the dust production rate was lower because of higher soil moisture (due to monsoon rainfall). Over the Arabian deserts, when the wind speed is the highest during June to August, the dust production rate is also highest, as soil moisture is lowest during this season. Even though nothing can be said precisely on the reason why 2003 had a greater number of dust events, examination of monthly mean soil moisture at source regions indicates that the occurrence of high winds simultaneous with high soil moisture could be the reason for the decreased dust production efficiency in 1999. It appears that the deserts of Northwest India are more efficient dust sources compared to the deserts of Saudi Arabia and Northeast Africa (excluding Sahara). The radiative impact of dust over various source regions is estimated, and the regionally and annually averaged top of the atmosphere dust radiative forcing (short wave, clear-sky and over land) over the entire study region (0-35 degrees N; 30 degrees-100 degrees E) was in the range of -0.9 to +4.5 W m(-2). The corresponding values at the surface were in the range of -10 to -25 W m(-2). Our studies demonstrate that neglecting the diurnal variation of dust can cause errors in the estimation of long wave dust forcing by as much as 50 to 100%, and nighttime retrieval of dust can significantly reduce the uncertainties. A method to retrieve dust aerosols during nighttime is proposed. The regionally and annually averaged long wave dust radiative forcing was +3.4 +/- 1.6 W m(-2).

Cobalt(II), nickel(II) and copper(II) complexes of bidentate bibenzimidazoles

Complexes of cobalt(II), nickel(II) and copper(II) with novel bidentate bibenzimidazoles, [M(L-L)Cl2], where L-L are methylenebis(1, 1prime-benzimidazole), methylenebis(2, 2prime-benzimidazole) and dimethylenebis(2, 2prime-benzimidazole) are described and characterized by different physical measurements. The four coordinate complexes have distorted tetrahedral or square coplanar structures. The bridging entity between the two donor groups apparently influences the ligand field strength and the ligands occupy a higher position than that of benzimidazole in the spectrochemical series.

Intermolecular Chelate Linkage Isomerism of the Hydroxyimino Group in the Nickel(II), Copper(II), and Palladium(II) Complexes of Quadridentate Schiff-base Ligands

The C-nitrosation of bivalent quadridentate β-imino ketone complexes of nickel(II), copper(II), and palladium(II), with nitrosating reagents has been investigated. The chemical analysis and spectroscopic results reveal that one of the α-CH groups of the coordinated lignad undergoes selective nitrosation forming mono(hydroxyimino) derivative. The hydroxyimino group introduced coordinates through either N- or O- atom to metal(II) by dislodging the carbonyl group already coordinated. This gives rise to two linkage isomers, one with N-bonded and the other with O-bonded hydroxyimino group in the case of nickel(II) (except for 1d) and palladium(II), and a single isomer with O-bonded hydroxyimino group in copper(II) complexes. The isomers obtained from 1b and 1i have been separated by column chromatography. In chloroform each of the isomers of nickel(II) isomerizes to give an equilibrium mixture of two isomers, but not those of copper(II) and palladium(II).

Theoretical gain‐optimization studies in CO2–N2 gasdynamic lasers. II. Results of parametric study

Based on a method presented in detail in a previous work by the authors, similar solutions have been obtained for the steady inviscid quasi‐one‐dimensional nonreacting flow in the supersonic nozzle of a CO2–N2 gasdynamic laser system, with either H2O or He as the catalyst. It has been demonstrated how these solutions could be used to optimize the small‐signal gain coefficient on a specified vibrational‐rotational transition. Results presented for a wide range of mixture compositions include optimum values for the small‐signal gain, area ratio, reservoir temperature, and a binary scaling parameter, which is the product of reservoir pressure and nozzle shape factor.

Studies in biogas technology. Part II. Optimisation of plant dimensions

In this paper, the design basis of the conventional Khadi and Village Industries Commission biogas plants has been elucidated. It has been shown that minimisation of the cost of the gas holder alone leads to the narrow and deep digesters of conventional plants. If instead, the total capital cost of the gas holder plus digester is minimised, the optimisation leads to wide and shallow digesters, which are less expensive. To test this alternative, two prototype plants have been designed, constructed and operated. These plants are not only 25–40% cheaper, but their performance is actually slightly better than the conventional plants.

Reactions of Mixed-Valent Palladium (IV,II) Complexes of Tetradentate Schiff-Bases Involving Bond Isomerization

Reactions of [PdIVB-(AI)2]++ [PdIICl4]-- (i) B-(AI)2 = dianion of N,N'-ethylene-/i-propylene-/n-propylene-bis(acetyl-acetoneimine) with some π-acceptor ligands, aliphatic primary amines and nitrosating reagents have been investigated. In all these reactions except nitrosation, 1:1 adducts having the formula, [PdIVB-(AI)2.X] [PdIICl4] [X = triphenylphosphine (TPP), triphenylarsine (TPA), pyridine (Py), methylamine (CH3NH2) or ethylamine (C2H5NH2)] are obtained. The formation of these complexes is associated with a bond isomerization - from Pd-Cxo-π -allylic bond prevailing in [PdIVB-(AI)2]2+ to PdIV-O bonding.Reaction of (i) with nitrosating reagents reduces PdIV to PdII and subsequently transform the γ-CH group, into an ambidentate isonitroso group (°C = NOH). The latter enters into coordination with PdII by dislodging the already coordinated carbonyl group. Further, selective nitrosation (mono- and dinitrosation) has been carried out by controlling the amount of the nitrosating reagent and the reaction time. The complexes have been characterized by elemental analyses, electrical conductivity, magnetic susceptibility and ir spectral data.

Syntheses, X-ray structure and properties of (5-cyclopentadienyl)ruthenium(II) complexes of pyridyl-2-hydrazone ligands

Complexes of the formulae [(-Cp)Ru(PPh3)(2-PPH)]Cl and [(Cp)Ru(PPh3) (py)(1-PPH)]Cl were prepared by reacting pyridyl-2-phenylhydrazone [PPH, C5H4N-2-CH=NNHPh] with (-Cp)Ru(PPh3)2Cl and (-Cp)Ru(PPh3)(py)Cl, respectively. In these complexes the PPH ligand displays bidentate chelating and unidentate modes of bonding. The molecular structure of [(-Cp)Ru(PPh3)(2-PPH)](ClO4)·CH2Cl2 was determined by X-ray crystallography. In this complex the metal is bonded to the N-pyridyl and N-imine atoms of the chelating ligand. 1H NMR spectral data suggests that PPH is bonded to ruthenium through the pyridine moiety of the PPH ligand in [(η-Cp)Ru(PPh3)(py)(η1-PPH)]Cl.

Preparation and characterization of hydrazine derivatives. Part-II: Reaction of transition metal ammonium double sulphates with hydrazine hydrate

Transition metal ammonium double sulphates (NH4)2M(SO4)2· 6H2O, where M = Fe, Co and Ni react with hydrazine hydrate in air giving crystalline compounds of the general formula (N2H5) [M(N2H3COO)3] H2O. The reaction proceeds through (N2H5)2 M(SO4)2, · 3N2H4, (N2H5)2 [M(OH)4 · (N2H4)2], M(N2H3COO)2 · (N2H4)2 and N2H5 [M(N2 H3 COO)3] intermediates. The reaction sequence is followed by chemical analysis and infrared spectra. A possible reaction mechanism has been suggested.

Studies on ß-arylhydrazone-imine nickel(II) complexes—Examples of metal template syntheses

ß-arylhydrazone-imine ligand complexes of nickel(II), namely, 4,10-dimethyl-5,9-diazatrideca-4,9-diene-2,12-dione-3,11-diphenylhydrazonato nickel(II), Ni(acacpn)(N2Ph-R)2 and 1,11-diphenyl-3,9-dimethyl-4,8-diazaun-deca-3,8-diene,1,11-dione-2,10-diphenyl hydrazonato nickel(II), Ni (beacpn) (N2Ph-R)2, [R = H, o-CH3p-CH3] have been prepared by metal template reactions and characterized. Both the azomethine nitrogens and α-nitrogens of bis-hydrazone form the coordination sites of the square-planar geometry around the nickel(II) ion. Loss of CO from the molecule and subsequently an interesting methyl group migration to the nucleus of the chelate ring have been observed in the mass spectrum. Structures are proposed based on the spectral and magnetic properties.

Three different co-ordination geometries in the pentacopper(II) unit of [Cu5(OH)2(H2O)(O2CMe)6(Him)4][ClO4]2(Him = imidazole)

The reaction of imidazole (Him) with [Cu2(µ-O2CMe)4(H2O)2] in water–NaClO4 led to the formation of a polynuclear copper(II) complex, [Cu5(OH)2(H2O)(O2CMe)6(Him)4][ClO4]21, in which the pentanuclear units, showing four, five and six co-ordination geometries for the copper(II) centres and Cu Cu distances of 3.043(1), 3.178(1) and 3.578(1)Å, were linked by aqua bridges to give an intra-chain inter-unit Cu Cu separation of 4.507(1)Å.