A Convenient Route for the Synthesis of Complex Metal Oxides Employing Solid-Solution Precursors

Synthesis of complex metal oxides by the thermal decomposition of solid-solution precursors (formed by isomorphous compounds of component metals) has been investigated since the method enables mixing of cations on an atomic scale and drastically reduces diffusion distances to a few angstroms. Several interesting oxides such as Ca2Fe03,5C, aCoz04,C a2C0205a, nd Ca,FeCo05 have been prepared by this technique starting from carbonate solid solutions of the type Ca,-,Fe,C03, Cal-,Co,C03, and Ca,-,,M,M'yC03 (M, M' = Mn, Fe, Co). The method has been extended to oxalate solid-solution precursors, and the possibility of making use of other kinds of precursor solid solutions is indicated.

On the Specificity of Carbohydrate-Lectin Recognition The Interaction of a Lectin from Ricinus communis Beans with Simple Saccharides and Concanavalin A

A galactose-specific protein (RC1) isolated from Ricinus communis beans was found to give a precipitin reaction with concanavalin A. Its carbohydrate content amounted to 8–9% of the total protein and was found to be rich in mannose. The interaction of RC1 with galactose and lactose was measured in 0.05 M phosphate buffer containing 0.2 M NaCl (pH 6.8) by the method of conventional equilibrium dialysis. From the analysis of the binding data according to Scatchard method the association constant (Ka) at 5°C was calculated as 3.8 mM−1 and 1.2 mM−1 for lactose and galactose, respectively. In both cases the number of binding sites per molecule of RC1 with molecular weight of 120000 was found to be 2. From the temperature-dependent Ka values for the binding of lactose, the values of –5.7 kcal/mol and –4.3 cal × mol−1× K−1 were calculated for ΔH and ΔS, respectively. The addition of concanavalin A to RC1 or vice versa led to the formation of the insoluble complex RC1· ConA4 containing one molecule of RC1 and one molecule of tetrameric concanavalin A (ConA4) which could be dissociated upon addition of concanavalin A-specific sugars. The complex formation results in a time-dependent appearance of turbidity in the time range from 10s to 10 min. From the measurement of the time-dependent appearance and disappearance of the turbidity the formation (kf) and dissociation (kd) rate constants were calculated as 3 mM−1× s−1 and 0.07 ks−1 respectively. The ratio kf/kd (43μM −1), that corresponds to the association constant of complex RC1· ConA4, is higher than that of mannoside · ConA4 and thereby suggests that protein-protein interaction contributes significantly in stabilising glycoprotein · lectin complexes. The relevance of this finding to the understanding of the chemical specificities that are involved in a model cell-lectin interaction is discussed.

Thermodynamic characterization of the reversible, two-state unfolding of maltose binding protein, a large two-domain protein

The folding and stability of maltose binding protein (MBP) have been investigated as a function of pH and temperature by intrinsic tryptophan fluorescence, far- and near-UV circular dichroism, and high-sensitivity differential scanning calorimetric measurements. MBP is a monomeric, two-domain protein containing 370 amino acids. The protein is stable in the pH range of 4-10.5 at 25 degrees C. The protein exhibits reversible, two-state, thermal and guanidine hydrochloride-mediated denaturation at neutral pH. The thermostability of MBP is maximal at pH 6, with a Tm of 64.9 degrees C and a deltaHm of 259.7 kcal mol(-1). The linear dependence of deltaHm on Tm was used to estimate a value of deltaCp of 7.9 kcal mol(-1) K(-1) or 21.3 cal (mol of residue)(-1) K(-1). These values are higher than the corresponding deltaCp's for most globular proteins studied to date. However, the extrapolated values of deltaH and deltaS (per mole of residue) at 110 degrees C are similar to those of other globular proteins. These data have been used to show that the temperature at which a protein undergoes cold denaturation depends primarily on the deltaCp (per mol of residue) and that this temperature increases with an increase in deltaCp. The predicted decrease in stability of MBP at low temperatures was experimentally confirmed by carrying out denaturant-mediated unfolding studies at neutral pH at 2 and 28 degrees C.

Indoleacetaldoxime hydro-lyase : II. Purification and properties

The purification and some properties of the enzyme indoleacetaldoxime hydrolyase (EC 4.2.1.29) from the fungus Gibberella fujikuroi, which dehydrates indoleacetaldoxime (IAOX) to indoleacetonitrile (IAN), are described. The enzyme activity in the fungus is present only under certain culture conditions. It is a soluble enzyme, has an optimum pH at 7, shows an energy of activation of —15,670 cal/mole, and has a Michaelis constant of 1.7 × 10−4 Image at 30 °. It appears to be specific for IAOX, and 1 mole of IAN is produced per mole of IAOX utilized. The enzyme is inhibited by a number of aldoximes of which phenylacetaldoxime (PAOX) is the most potent inhibitor. Inhibition by PAOX is competitive (Ki = 2.2 × 10−8 Image ). The enzyme is inhibited by SH reagents such as p-hydroxymercuribenzoate and N-ethylmaleimide, and by a number of SH compounds such as cysteine, β-mercaptoethanol, and 2,3-dimercaptopropanol (BAL). However, glutathione activates the enzyme. Metal chelating agents such as 8-OH-quinoline and diethyl dithiocarbamate inhibit the enzyme; the inhibition is partly reversed by ferric citrate. Ascorbic acid, and particularly dehydroascorbic acid (DHA), are good activators of the enzyme. Several other biological oxidants had either no action or had a slight effect. Potassium cyanide activates the enzyme at low concentration but inhibits at higher concentrations. Reduction of the enzyme with NaBH4 reduces activity, and the effect is partly reversed by pyridoxal phosphate and also by DHA. The above properties indicate that both an SH function and an oxidized function are required for activity.

Biosynthesis of valine and isoleucine in plants II. Dihydroxyacid dehydratase from Phaseolus radiatus

1. 1. An enzyme catalysing the conversion of α,β-dihydroxyisovalerate and α,β-dihydroxy-β-methylvalerate to α-ketoisovalerate and α-keto-β-methylvalerate has been partially purified from green gram (Phaseolus radiatus), and its characteristics studied. 2. 2. A natural inhibitor, heat stable and inorganic in nature, was observed in the crude extracts. 3. 3. The observed Km values for α-β-dihydroxyisovalerate and α,β-dihydroxy-β-methylvalerate were 2.4 · 10-3 M and 9 · 10-4 M, respectively. 4. 4. The enzyme required the presence of a divalent metal ion (Mg2+, Mn2+ or Fe2+) for maximal activity. Heavy metals like Ag+ and Hg2+ were inhibitory. 5. 5. The optimal activity was around pH 8.0 and the optimum temperature at 52°. The activation energy is found to be 12 600 cal/mole. 6. 6. The enzyme was inhibited by p-hydroxymercuribenzoate, N-ethylmaleimide and sulphydryl compounds like cysteine, glutathione, 2-mercaptoethanol and 2,3-dimercaptopropanol. The inhibition by p-hydroxymercuribenzoate could not be reversed by any of the sulfhydryl compounds tested.

Biosynthesis of valine and isoleucine in plants I. Formation of α-acetolactate in Phaseolus radiatus

1. 1. The presence of an enzyme system in plants catalyzing the formation of α-acetolactate from pyruvate has been demonstrated; the system in green gram (Phaseolus radiatus) has been partially purified and its characteristics have been studied.2. Free acetaldehyde is formed as a product of the reaction and so the reaction is mainly diverted towards the formation of acetoin. 3. The system requires thiamine pyrophosphate and a divalent metal ion (Mn2+ or Mg2+) for maximum activity. The optimum pH is around 6.0 and the optimum temperature is 60°. 4. The system is very labile in absence of pyruvate, Mn2+ and DPT. 5. The Km values for pyruvate, Mn2+, Mg2+ and DPT are 3·10−2 M. 5·10−5 M, 2·10−5 M, and e·10−6 M respectively. The activation energy is 3540 cal/mole. 6. The enzyme is strongly inhibited by p-chloromercuribenzoate and the inhibition can be reversed partially by 2-mercaptoethanol, BAL or cysteine. Heavy metals, such as Hg2+ and Ag+, are inhibitory but l-valine does not inhibit the reaction.

Studies on the brookite-rutile transformation

Brookite, the orthorhombic modification of titanium dioxide, transforms to the tetragonal modification, rutile, on heating. The kinetics and energetics of the transformation have been studied. Below 715±10°C, the rate of transformation is extremely slow. There appears to be little or no induction time. The kinetic data can be fitted reasonably well by the first-order equation. The energy of activation is about 60 kcal/mole and the frequency factor is of the order of 1013 h-1. The entropy of activation from Eyring's theory is about -18 cal/mole deg. at 800°C. The heat of this transformation is -100±75 cal/mole. The kinetic results may be explained qualitatively in terms of various analogies but more clearly by the application of the order-disorder theory to diffusionless transformation in solids. It has been shown that the ratio of propagation rate constant to the nucleation rate constant is small and that there is little or negligible phase aggregation.

Aspects of tautomerism. Part IV. A kinetic study of the dimerization reaction of pseudo-acid chlorides

The kinetics of dimerization of 4-substituted- and unsubstituted o-benzoylbenzoyl chlorides, with iodide ion can be described by the expression, rate =k2[acid chloride][iodide]. The value for the reaction in dimethylformamide solution is –0·38. The entropy of activation for the reaction is –34·2 cal mol–1 K–1 and the activation energy is 10·7 kcal mol–1. These results have been interpreted as evidence for the formation of pseudo-iodide in the rate-determining step and its fast decomposition to radicals which combine to give a mixture of stereoisomeric dilactones.

Calculation of Coulomb interaction strengths for 3d transition metals and actinides

Coulomb interaction strengths (Udd and Uff) have been calculated from Hartree-Fock-Slater atomic calculations for 3d transition and 5f actinide elements, respectively. By decomposing the different contributions to the response (screening) to the 3d charge fluctuation, we show that a substantial reduction in Udd arises due to the relaxation of the 3d charge distribution itself. This, combined with the screening due to the response of the 4s charge density, is shown to provide a very compact screening charge comparable to the metallic case, explaining the success of the atomic calculations for estimating U even in the metals. A pronounced dependence of Udd (or Uff) on the number of electrons nd (nf) or the electronic configuration is also shown here.

A spectroscopic study of the interaction of isoflavones with human serum albumin

Genistein and daidzein, the major isoflavones present in soybeans, possess a wide spectrum of physiological and pharmacological functions. The binding of genistein to human serum albumin (HSA) has been investigated by equilibrium dialysis, fluorescence measurements, CD and molecular visualization. One mole of genistein is bound per mole of HSA with a binding constant of 1.5 +/- 0.2 X 10(5) m(-1). Binding of genistein to HSA precludes the attachment of daidzein. The ability of HSA to bind genistein is found to be lost when the tryptophan residue of albumin is modified with N-bromosuccinimide. At 27 degrees C (pH 7.4), van't Hoff's enthalpy, entropy and free energy changes that accompany the binding are found to be -13.16 kcal.mol(-1), -21 cal.mol(-1)K(-1) and -6.86 kcal.mol(-1), respectively. Temperature and ionic strength dependence and competitive binding measurements of genistein with HSA in the presence of fatty acids and 8-anilino-1-naphthalene sulfonic acid have suggested the involvement of both hydrophobic and ionic interactions in the genistein-HSA binding. Binding measurements of genistein with BSA and HSA, and those in the presence of warfarin and 2,3,5-tri-iodobenzoic acid and Forster energy transfer measurements have been used for deducing the binding pocket on HSA. Fluorescence anisotropy measurements of daidzein bound and then displaced with warfarin, 2,3,5-tri-iodobenzoic acid or diazepam confirm the binding of daidzein and genistein to subdomain IIA of HSA. The ability of HSA to form ternery complexes with other neutral molecules such as warfarin, which also binds within the subdomain IIA pocket, increases our understanding of the binding dynamics of exogenous drugs to HSA.

Crystal structure and conformation study of N-methyl-t-3-methyl-r-2, c-6-diphenylpiperidin-4-one thiosemicarbazone

Thiosemicarbazones are having the ability to bind with metal and inhibit the enzyme ribonucleoside diphosphate reductase(RDR),an enzyme which is involved in the synthesis of DNA precursors in the mammalian cells.The title compound N-methyl-t-3-methyl-r-2, c-6-diphenylpiperidin-4-one thiosemicarbazone (NMMDPT), CCDC 218052, was prepared using Mannich reaction and characterized by X-ray diffraction methods.The crystal data are:C20H24N4S; M.W= 352.49, triclinic,space group P (1) over bar, a = 8.467(2)angstrom, b = 10.228(2)angstrom, c = 12.249(2)angstrom; lpha=92.595(3)degrees, beta=104.173(3)degrees, gamma=13.628(3)degrees; V=930.0(3)angstrom(3), Z=2, D-cal=1.259Mgm(-3),mu=0.184mm(-1),lambda (MoKalpha)=0.71073 angstrom, final R1 and wR2 are 0.0470 and 0.1052, respectively. The piperidine rings adopt chair conformation. The planar phenyl rings are oriented equatorially at 2,6-positions of the piperidine ring. The molecular packing can be viewed as dimers held together by two N-H...S types of intermolecular hydrogen bonds. Weak C-H...pi interactions also support the stability of the molecules in the crystal in addition to van der Waals forces. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Chemical approaches to penicillin allergy—IV. Binding of carrier receptor protein with penicillin and its analogues

The availability of electrophoretically homogeneous rabbit penicillin carrier receptor protein (CRP) by affinity chromatography afforded an idealin vitro system to calculate the thermodynamic parameters of binding of penicillin and analogues with CRP as well as competitive binding of such analogues with CRP in presence of14C-penicillin G. The kinetics of association of CRP with 7-deoxy penicillin which does not bind covalently with CRP have been studied through equilibrium dialysis with14C-7-deoxybenzyl penicillin and found to be K=2·79×106M−1.−ΔG=8·106 k cal/mole as well as fluorescence quenching studies with exciter λ 280 K=3·573×106M−1,−ΔG=8·239 k cal/mole. The fluorescence quenching studies have been extended to CRP-benzyl penicillin and CRP-6-aminopenicillanic acid (6APA) systems also. The fluorescence data with benzyl penicillin indicate two conformational changes in CRP—a fast change corresponding to the non-covalent binding to CRP with 7-deoxy penicillin and a slower change due to covalent bond formation. With 6-APA the first change is not observed but the conformational change corresponding to covalent binding is only seen. Competitive binding studies indicate that the order of binding of CRP with the analogues of penicillin is as follows: methicillin > 6APA > carbenicillin >o-nitrobenzyl penicillin > cloxacillin ≈ benzyl penicillin ≈ 6-phenyl acetamido penicillanyl alcohol ≈ 7 phenyl acetamido desacetoxy cephalosporanic acid ≈p-amino benzyl penicillin ≈p-nitro benzyl penicillin > ticarcillin >o-amino benzyl penicillin > amoxycillin > 7-deoxy benzyl penicillin > ampicillin.From these data it has been possible to delineate partially the topology of the penicillin binding cleft of the CRP as well as some of the functional groups in the cleft responsible for the binding process.

Phase relationships in the system Ni-W-O and thermodynamic properties of NiWO,

The phase diagram of the Ni-W-O system at 1200 K was established by metallographic and X-ray identification of the phases present after equilibration at controlled oxygen potentials. The oxygen partial pressures over the samples were fixed by metered streams of CO+CO2 gas mixtures. There was only one ternary oxide, nickel tungstate (NiWO4), in the Ni-W-O system at a total pressure of 1 atm, and this compound decomposed to a mixture of Ni+WO2.72 on lowering the oxygen potential. The Gibbs' free energy of formation of NiWO4 was determined from the measurement of the e.m.f. of the solid oxide galvanic cell, Pt, Ni+NiWO4+WO2.72/CaO-ZrO2/Ni+NiO, Pt and thermodynamic properties of tungsten and nickel oxides available in the literature. For the reaction, NiO(s)+WO3(s)rarrNiWO4(s) DeltaG°=–10500–0.708 T (±250) cal mol–1.

Ab initio studies of the structure and vibrational spectra of methyl isocyanide-borane and acetonitrile-borane

The SCF/DZP and MP2/DZP methods of ab initio quantum chemistry have been utilized to study the structure, vibrational spectra, binding energy, and barrier to internal rotation of methyl isocyanide-borane and acetonitrile-borane adducts. The eclipsed conformation of the complexes was predicted to be a minimum, and the staggered form is a transition state with a barrier height of about 10 cal/mol. The vibrational analyses of CH3NC-BH3 and CH3CN-BH3 and several of their isotopomers have been carried out by the GF matrix method. Computations have also been carried out for free CH3NC and CH3CN in order to investigate the changes in CH3NC and CH3CN as a result of their complex formation with BH3. To obtain an acceptable set of force constants, a recently proposed procedure ''RECOVES'' has been utilized. The increase in the N=C/C=N stretching force constant of CH3NC/CH3CN on adduct formation is interpreted with the help of Parr and Borkman's model. The binding energies for the two adducts have been determined taking basis set superposition error (BSSE) into consideration. The effect of the BSSE on structure, dipole moment, and vibrational frequencies of CH3CN and CH3NC is also evaluated. The predicted infrared band intensities for the two complexes are in good agreement with the experimentally observed features, and they have been utilized in the assignment of vibrational frequencies.

Crystal and molecular structure of synthetic cholesterol compounds vitamin D3-analogues (I) 24(S)-hydroxy coprastan-3-one & (II) 24(R)-hydroxy coprastan-3-one

The title compound I (24-(S)-Hydroxy Coprastan-3-one) crystallises in orthorhombic space group P2(1)2(1)2(1) with Z = 4. The unit cell dimensions are a = 6.701(2)Angstrom, b = 11.506(8)Angstrom, c = 32.183(4)Angstrom, V = 2481(2)Angstrom (3), D-cal = 1.077 Mg/m(3). The tide compound II (24-(R)-Hydroxy Coprastan-3-one) crystallises in orthorhombic space group P212121 with two molecules per assymetric unit and with Z = 8. The Unit cell dimensions are a = 10.954(2)Angstrom, b = 21.757(6)Angstrom, c = 21.130(7)Angstrom, V = 5035.0(2)Angstrom (3), D-cal = 1.062 Mg/m(3). In compound I and in both the molecules of compound II, the rings A, B & C are in chair conformation and the five membered ring D is in envelope conformation. The priority sequence attached to the chiral carbon C24 has "S" designation in compound I and "R" designation in compound II. The structures are stabilized by C-H . . .O and O-H---O hydrogen bonds.