NMR (1H, 13C) and MO (ab initio, CNDO/2, EHT) studies on basic and N-protonated hydrazinecarbothioamide

The conformational preferences of hydrazinecarbothioamide (HCTA, H2NNHCSNH2) in its basic and N-protonated (PHCTA, H3NNNHCSNH2) forms have been studied by 1H and 13C NMR spectroscopy and by theoretical LCAO-MO methods (ab initio, CNDO/2 and EHT). The hindered rotation around the C---N bond has been investigated by a total line shape analysis for the thioamide protons and by the three MO methods. Changes in the molecular conformation and electronic structure on protonation are briefly discussed.

Basic Needs and Much More With One Kilowatt Per Capita

Conventional thinkin g holds that increased energy consumption is a prerequisite for economic and social development. This belief, together With the prospect of dwindling global petroleum supplies and the high costs of expanding energy supply generally, lead many to believe that it is not feasible to improve living standards substantially in the developing countries. But by shifting to high-quality energy carriers and by exploiting cost-effective opportunities for more efficient energy use, it would be possible to satisfy basic human needs and to provide considerable further improvements in living standards without significantly increasing per-capita energy use above the present level.

A comparison of the molecular orbital (ab initio, CNDO and EHT) methods applied to the conformational study of thiocarbonohydrazide in its basic and diprotonated forms

Conformational preferences of thiocarbonohydrazide (H2NNHCSNHNH2) in its basic and N,N′-diprotonated forms are examined by calculating the barrier to internal rotation around the C---N bonds, using the theoretical LCAO—MO (ab initio and semiempirical CNDO and EHT) methods. The calculated and experimental results are compared with each other and also with values for N,N′-dimethylthiourea which is isoelectronic with thiocarbonohydrazide. The suitability of these methods for studying rotational isomerism seems suspect when lone pair interactions are present.

Distribution of phosphorus and oxygen between liquid steel and basic oxygen steelmaking slag

The efficiency of dephosphorisation is governed by the thermodynamic behaviour of phosphorus and oxygen in molten metal, and P2O5 and FeO in slag. The equilibrium distribution of phosphorus and oxygen, for a wide range of chemical compositions simulating the evolution of slag composition during a typical BOF blow, has been experimentally determined. A mathematical model for estimation of the activity coefficients, as a function of the chemical composition, was also attempted.

Effect of deprivation of vitamin A on the basic proteins of the nuclei of rat testes

The relative concentrations of the major histones, namely, H1, TH1, H2A, H2B, H3 and H4 are not significantly changed in the testes of the vitamin A-deficient rats, as compared to those in the normal controls. But the testis-specific protein, TP, which is synthesized at the mid-spermatid stage, is markedly reduced in the testes of the deficient rats. On supplementation of the deficient rats with retinyl acetate for 28 days, there was a 50% recovery in the relative concentration of the TP with respect to the total amounts of H1 and TH1.

Thermodynamic and kinetic analysis of carbohydrate binding to the basic lectin from winged bean (Psophocarpus tetragonolobus)

A basic lectin (pI approximately 10.0) was purified to homogeneity from the seeds of winged bean (Psophocarpus tetragonolobus) by affinity chromatography on Sepharose 6-aminocaproyl-D-galactosamine. The lectin agglutinated trypsinized rabbit erythrocytes and had a relative molecular mass of 58,000 consisting of two subunits of Mr 29,000. The lectin binds to N-dansylgalactosamine, leading to a 15-fold increase in dansyl fluorescence with a concomitant 25-nm blue shift in the emission maximum. The lectin has two binding sites/dimer for this sugar and an association constant of 4.17 X 10(5) M-1 at 25 degrees C. The strong binding to N-dansylgalactosamine is due to a relatively positive entropic contribution as revealed by the thermodynamic parameters: delta H = -33.62 kJ mol-1 and delta S0 = -5.24 J mol-1 K-1. Binding of this sugar to the lectin shows that it can accommodate a large hydrophobic substituent on the C-2 carbon of D-galactose. Studies with other sugars indicate that a hydrophobic substituent in alpha- conformation at the anomeric position increases the affinity of binding. The C-4 and C-6 hydroxyl groups are critical for sugar binding to this lectin. Lectin difference absorption spectra in the presence of N-acetylgalactosamine indicate perturbation of tryptophan residues on sugar binding. The results of stopped flow kinetics with N- dansylgalactosamine and the lectin are consistent with a simple one- step mechanism for which k+1 = 1.33 X 10(4) M-1 s-1 and k-1 = 3.2 X 10(- 2) s-1 at 25 degrees C. This k-1 is slower than any reported for a lectin-monosaccharide complex so far. The activation parameters indicate an enthalpically controlled association process.

Cloning and sequencing of winged bean (Psophocarpus tetragonolobus) basic agglutinin (WBA I): presence of second glycosylation site and its implications in quaternary structure

We report cloning of the DNA encoding winged bean basic agglutinin (WBA I). Using oligonucleotide primers corresponding to N- and C-termini of the mature lectin, the complete coding sequence for WBA I could be amplified from genomic DNA. DNA sequence determination by the chain termination method revealed the absence of any intervening sequences in the gene. The DNA deduced amino acid sequence of WBA I displayed some differences with its primary structure established previously by chemical means. Comparison of the sequence of WBA I with that of other legume lectins highlighted several interesting features, including the existence of the largest specificity determining loop which might account for its oligosaccharide-binding specificity and the presence of an additional N-glycosylation site. These data also throw some light on the relationship between the primary structure of the protein and its probable mode of dimerization.

Nonquantum Entanglement Resolves a Basic Issue in Polarization Optics

The issue raised in this Letter is classical, not only in the sense of being nonquantum, but also in the sense of being quite ancient: which subset of 4 X 4 real matrices should be accepted as physical Mueller matrices in polarization optics? Nonquantum entanglement or inseparability between the polarization and spatial degrees of freedom of an electromagnetic beam whose polarization is not homogeneous is shown to provide the physical basis to resolve this issue in a definitive manner.

Amino acid sequence of the winged bean (Psophocarpus tetragonolobus) basic lectin. Adenine binding and identification of the active-site tryptophan residue

The complete amino acid sequence of winged bean basic agglutinin (WBA I) was obtained by a combination of manual and gas-phase sequencing methods. Peptide fragments for sequence analyses were obtained by enzymatic cleavages using trypsin and Staphylococcus aureus V8 endoproteinase and by chemical cleavages using iodosobenzoic acid, hydroxylamine, and formic acid. COOH-terminal sequence analysis of WBA I and other peptides was performed using carboxypeptidase Y. The primary structure of WBA I was homologous to those of other legume lectins and more so to Erythrina corallodendron. Interestingly, the sequence shows remarkable identities in the regions involved in the association of the two monomers of E. corallodendron lectin. Other conserved regions are the double metal-binding site and residues contributing to the formation of the hydrophobic cavity and the carbohydrate-binding site. Chemical modification studies both in the presence and absence of N-acetylgalactosamine together with sequence analyses of tryptophan-containing tryptic peptides demonstrate that tryptophan 133 is involved in the binding of carbohydrate ligands by the lectin. The location of tryptophan 133 at the active center of WBA I for the first time subserves to explain a role for one of the most conserved residues in legume lectins.

Thermodynamic and kinetic studies on the mechanism of binding of methylumbelliferyl galactosides to the basic agglutinin from winged bean (Psophocarpus tetragonolobus)

The binding of winged bean basic agglutinin (WBA I) to 4-methylumbelliferyl (MeUmb) galactosides was examined by extrinsic fluorescence titration and stopped-flow spectrofluorimetry. Upon binding to WBA I, MeUmb alpha-galactosides show quenching in fluorescence intensity, decrease in UV absorbance with a concomitant blue shift, and decrease in fluorescence excited-state lifetimes. However, their beta-analogues show enhancement in fluorescence intensity, increase in UV absorbance with a red shift, and an increase in fluorescence excited-state lifetimes. This implies that the umbelliferyl groups of alpha- and beta-galactosides experience non-polar and polar microenvironments, respectively, upon binding to WBA I. Replacement of the anomeric hydroxyl group of galactose by 4-methylumbelliferyl moiety increases the affinity of resulting saccharides. Substitution of C-2 hydroxyl of galactose by an acetamido group leads to increased affinity due to a favorable entropy change. This suggests that acetamido group of MeUmb-alpha/beta-GalNAc binds to a relatively non-polar subsite of WBA I. Most interestingly, this substitution also reduces the association rate constants dramatically. Inspection of the activation parameters reveals that the enthalpy of activation is the limiting factor for the differences in the forward rate constants for these saccharides and the entropic contribution to the activation energy is small

Crystallization and Preliminary X-ray Studies of the Basic Lectin from Winged Bean (Psophocarpus tetragonolobus)

The basic lectin from winged bean (Psophocarpus tetragonolobus) could be crystallized using polyethyleneglycol (PEG) 4000 (I), PEG 8000 (II) and 2-methylpentane-2,4-diol (MPD) (III) as precipitants. Crystal forms I and II grew in the presence of methyl-α-Image -galactopyranoside or N -acetylgalactosamine while III grew in the absence of sugar. The three forms have the same space group (P21212) and similar unit cell dimensions with two dimeric molecules in the asymmetric unit. The unit cell dimensions are a = 156·8 Å, b = 89·0 Å, c = 73·3 Å for I, a = 155·5 Å, b = 92·3 Å, c = 72·5 Å for II and a = 148·3 Å, b = 90·7 Å, c = 73·8 Å for III. The crystals, particularly those grown using PEG 8000, are suitable for high resolution X-ray analysis, which is in progress.

Thermodynamics of the binding of galactopyranoside derivatives to the basic lectin from winged bean (Psophocarpus tetrogonolobus)

The thermodynamics of the binding of D-galactopyranoside (Gal), 2-acetamido-2-deoxygalactopyranoside (GalNAc), methyl-alpha-D-galactopyranoside, and methyl-beta-D-galactopyranoside to the basic agglutinin from winged bean (WBAI) in 0.02 M sodium phosphate and 0.15 M sodium chloride buffer have been investigated from 298.15 to 333.15 K by titration calorimetry and at the denaturation temperature by differential scanning calorimetry (DSC). WBAI is a dimer with two binding sites. The titration calorimetry yielded single-site binding constants ranging from 0.56 +/- 0.14 x 10(3) M-1 for Gal at 323.15 K to 7.2 +/- 0.5 x 10(3) M-1 for GalNAc at 298.15 K and binding enthalpies ranging from -28.0 +/- 2.0 kJ mol-1 for GalNAc at 298.15 K to -14.3 +/- 0.1 kJ mol-1 for methyl-beta-D-galactopyranoside at 322.65 K. The denaturation transition consisted of two overlapping peaks over the pH range 5.6-7.4. Fits of the differential scanning calorimetry data to a two-state transition model showed that the low temperature transition (341.6 +/- 0.4 K at pH 7.4) consisted of two domains unfolding as a single entity while the higher temperature transition (347.8 +/- 0.6 K at pH 7.4) is of the remaining WBAI dimer unfolding into two monomers. Both transitions shift to higher temperatures and higher calorimetric enthalpies with increase in added ligand concentration at pH 7.4. Analysis of the temperature increase as a function of added ligand concentration suggests that one ligand binds to the two domains unfolding at 341.6 +/- 0.6 K and one ligand binds to the domain unfolding at 347.8 +/- 0.6 K.

Carbohydrate binding specificity of the basic lectin from winged bean (Psophocarpus tetragonolobus)

The carbohydrate binding specificity of the basic lectin from winged bean (Psophocarpus tetragonolobus) was investigated by quantitative precipitin analysis using blood group A, B, H, Le and I substances and by precipitation inhibition with various mono- and oligosaccharides. The lectin precipitated best with A1 substances and moderately with B and A2 substances, but not with H or Le substances. Inhibition assays of lectin-blood group A1 precipitation demonstration that A substance-derived oligosaccharides having the common structure: d-Ga1NAcα(1 → 3)d-Gal-(β1 → Image ) to a d-Glc, were the best inhibitors and about 8 and 4 times more active than d-Ga1NAc and d-Ga1NAcα(1 → 3)d-Ga1, respectively. A difucosyl A-specific oligosaccharide (A-penta), a monofucosyl (A-tetra) and a non-fucosyl containing (A5 II) oligosaccharide, d-Ga1NAcα(1 → 3)d-Ga1β(1 → 3)d-G1cNAc, had almost the same reactivity, suggesting that the fucose linked to the sub-terminal d-Ga1 or to the third sugar, d-GlcNAc, from the non-reducing end made no contribution to the carbohydrate binding. Although a terminal non-reducing d-Ga1NAc or d-Ga1 residue was indispensible for binding, the lectin bound not only to these terminal non-reducing galactopyranosyl residues, but also showed increased binding to oligosaccharides in which it was bonded to a sub-terminal d-Ga1 joined to a d-GlcNAc residue, as in blood group A or B substances. This defines the site, thus far, as complementary to a disaccharide plus the β linkage to the third sugar (d-Glc or d-GlcNAc) from the non-reducing end. The role of the β(1 → 3) or β(1 → 4) linkage of the sub-terminal non-reducing d-Gal to the d-GlcNAc requires further study.

Free energy of mixing of divalent basic oxides with silica

An expression derived for the free energy of mixing of a divalent basic oxide (MO) with SiO2 based on a model of silicate structure, takes into account the distribution of O2- (from MO) into the silica network, the mixing of silicate ions with O2- and the enthalpy of mixing. The resulting expression is ΔGmix=RT{N11n (2N1-N)2/4N1(1-N)+N21n N 2-N/1-N}, where N={(β+N1)-√(β+N 1)2-8βN1N2}/2β β=characteristic constant for the system N1=mol fraction of silica N2=mol fraction of MO. For the proper choice of β, calculated values of the activity of MO for the system PbO-SiO2, MnO-SiO2, FeO-SiO2 and CaO-SiO2 are in good agreement with experiment. The model predicts that the activity of the basic oxide decreases with increase in temperature.