Showing papers by "University of Madras published in 1971"
TL;DR: Calculation of σ‐ and π‐charges were made on nucleotides and nucleic acids, making use of suitable parameters which gave a good qualitative correlation of calculated bond orders with experimentally determined bond lengths.
Abstract: Calculation of σ- and π-charges were made on nucleotides and nucleic acids. The σ-charges were calculated using LCAO MO method suggested by Del Re, making use of Berthod and Pullman parameters. The π-charges were calculated by Huckel's method, making use of suitable parameters which gave a good qualitative correlation of calculated bond orders with experimentally determined bond lengths. General features of the charge distribution are discussed.
101 citations
TL;DR: Steric and energy contour diagrams have been plotted for disaccharide‐like and for helical structures of linear β‐D‐glucans having (1 → 2), ( 1 → 3) and (1→ 4) linkages, indicating that the freedom of rotation of glucose residues is highly restricted in all the three polysaccharides.
Abstract: Steric and energy contour diagrams have been plotted for disaccharide-like and for helical structures of linear β-D-glucans having (1 → 2), (1 → 3) and (1 → 4) linkages. The allowed conformations constitute only about. 4% of the total conformations, indicating that the freedom of rotation of glucose residues is highly restricted in all the three polysaccharides. The additional restrictions of the monomer unit, as one passes from disaccharide to polysaccaride structures, are severe in the case of (1 → 2) and (1 → 3) linked polysaccharides but not in (1 → 4) linked polysaccharide. The difference in the nature of linkages also has shown to affect the energetically preferred conformations: (1 → 2) linkages lead only to left handed helical conformations; (1 → 3) linkages lead to both right and left handed wide and extended helical conformations, (1 → 4) linkages lead to both right and left handed extended helical conformations. The possible hydrogen bonds between adjacent residues are also dependent on the nature of linkage.
65 citations
TL;DR: The results bring out the important fact that even in large molecules, the conformation of local segments are predominantly governed by the short‐range intramolecular interactions.
Abstract: Potential energies of conformation of a dipeptide unit with butyl, seryl, threonyl, eysteinyl, and valyl side groups have been computed by using classical energy expressions. The presence of a γ-atom introduces characteristic restrictions on the backbone rotational angles φ and ψ the γ-atom itself is restricted to three staggered positions about the C α -C β bond. The important results are that a γ-carbon in position I (χ 1 ⋍ 60°) cannot be accommodated in the standard right-and left-handed α-helices, whereas a γ-oxygen or sulfur could easily be accommodated in the right-handed α-helix. Further, a γ-carbon or a heteroatom in position II (χ 1 ⋍ 180 ° ) does not favor a conformation ψ ⋍ 180 ° , compared to two other positions. The valyl side group significantly reduces the allowed φ and ψ values and energetically prefers a α-conformation compared to right-or left-handed α-helical conformations. The less favorable α-helical conformation is possible only for γ (III, II) combination of the valyl residue. The observed φ, ψ, and χ 1 values of all the amino acid residues in the three protein molecules, lysozyme, myoglobin, and chymotrypsin are compared with the theoretical predictions and the agreement is excellent. The results bring out the important fact that even in large molecules, the conformation of local segments are predominantly governed by the short-range intramolecular interactions.
47 citations
TL;DR: The calculated energy-values not only explain the favored conformations assigned from n.m.r. studies but are also found to be in fairly good agreement with the energy values assigned by Angyal.
42 citations
TL;DR: The observed ϕ, ψ, χ1, and χ2 values of amino acids, simple peptides, and of the three protein molecules lysozyme, myoglobin, and chymotrypsin have been compared with the theoretical predictions, and the agreement is found to be excellent.
Abstract: Backbone-side group conformations of amino acid residues including one or two δ-carbons in the side group have been investigated. Conformational energies of norvalyl, leucyl, phenylalanyl, tyrosyl, tryptophenyl, and histidinyl side groups in a dipeptide unit have been calculated by using classical energy expressions. The side group conformations about the C α -C ⓼ and C β -C γ bonds are restricted to specific values of the respective rotational angles. Thus, most favourable positions of γ- and δ-atoms of a linear side-chain (norvalyl) are restricted to (γ I , δ II ) (γ II , δ I ), (γ II , δ II ), (γ III , δ II ), and (γ III , δ III ), whereas those of the side-chain branching at a sp 3 γ-atom (leueyl) are further restricted. It is also shown that there is a definite correlation between the orientations of the two peptide planes and that of the planar group of the aromatic side chain of phenylalanyl type residues. The studies bring out an important fact that while the γ-atoms have definite and characteristic effects on the backbone rotational angles φ and ψ, the δ atoms and beyond have no effects on the preferred φ and ψ values. Thus, the preferred backbone conformations are independent of the preferred side group conformations beyond the γ-atom and vice versa. The observed φ, ψ, χ 1 , and χ 2 values of amino acids, simple peptides, and of the three protein molecules lysozyme, myoglobin, and chymotrypsin have been compared with the theoretical predictions, and the agreement is found to be excellent.
39 citations
TL;DR: A lumped, deterministic, nonlinear mathematical model is developed and proposed for the simulation of hydrologic systems in this paper, which is based on expansion of a general storage function.
Abstract: A lumped, deterministic, nonlinear mathematical model is developed and proposed for the simulation of hydrologic systems. The model is developed from expansion of a general storage function of inpu...
29 citations
TL;DR: The suggestion that enzymes such as phosphorylase, alkaline phosphatase and carbonic anhydrase are involved in the process of calcification is supported by experimental evidence of inhibition of the action of enzymes by enzyme inhibitors.
Abstract: In the anomuran Clibanarius olivaceousHenderson, the cuticle of the cephalic and thoracic regions is calcified, while that of the abdominal region is uncalcified. Histochemical observations have been made on the possible enzymes involved in the process of calcification of cuticle. The calcified regions show the presence of enzymes such as phosphorylase, alkaline phosphatase and carbonic anhydrase. The possible role of phosphorylase in calcification may be production of phosphoric esters, which form the required substrate for alkaline phosphatase. The latter appear to be associated with the production of phosphate ions from phosphoric esters. The carbonic anhydrase may be associated with the production of carbonate ions. The suggestion that these enzymes are involved in the process of calcification is further supported by experimental evidence of inhibition of the action of enzymes by enzyme inhibitors. The inhibition of enzymes leads to reduction in the amount of calcium added to the cuticle.
22 citations
TL;DR: Extracts of queen heads of A. florea, A. cerana and A. dorsata are found to contain queen substance, 9-oxodec- trans -2-enoic acid, identical with that produced by queens of a. mellifera as mentioned in this paper.
21 citations
01 Apr 1971
TL;DR: In this paper, the 1-aminocyclooctanecarboxylic acid hydrobromide was solved in projections by direct methods and later refined with three-dimensional data using a full-matrix least-squares treatment.
Abstract: Crystals of 1-aminocyclooctanecarboxylic acid hydrobromide are orthorhombic, witha= 26·026,b=7·087,c= 6·149,Z= 4 and space groupP212121.The structure was solved in projections by direct methods and later refined with three-dimensional data using a full-matrix least-squares treatment. All hydrogen atoms were located from a difference Fourier and the finalRfactor for the 1128 observed reflections was 8·62 %. The molecules are held together by a series of hydrogen bonds in a three-dimensional network. A detailed discussion of the intramolecular and the intermolecular features of the structure is presented. The cyclooctane ring is found to exist in theboat-chair conformation.
16 citations
TL;DR: In this paper, a kinetic study of the thermal polymerization of acrylonitrile initiated by chromic acid-reducing agent (n-butanol, ethylene glycol, cyclohexanone, and acetaldehyde) systems was made.
Abstract: A kinetic study of the thermal polymerization of acrylonitrile initiated by chromic acid–reducing agent (n-butanol, ethylene glycol, cyclohexanone, and acetaldehyde) systems was made. Chromic acid alone did not initiate polymerization under deaerated or undeaerated conditions. On the basis of the experimental determination of the dependencies of various variables on the rate of polymerization Rp, the rate of chromium (VI) disappearance −RM, the degree of polymerization DP, etc., a reasonable kinetic scheme was arrived at. The mechanism with the reducing agents, n-butanol, cyclohexanone, and ethylene glycol, was found to be similar but different from that with acetaldehyde. Evidence has been presented to prove the formation of radical intermediates formed by the oxidation of the reducing agent by Cr(IV). Rate parameters for oxidation of the reducing agent and polymerization of the monomer were evaluated.
14 citations
TL;DR: The substrate-specificity of the phenolase of P. multae strongly recalls thephenolase found in the unhardened cuticle of the insect Periplaneta americana and the larval cuticles of Calliphora vomitoria.
TL;DR: The green colour obtained in metachromatic regions is established as not due to any green impurity of the dye by chromatographic analysis but due to the fluid dehydrants combining with the dye as dye-organic solvent mixture showed green.
Abstract: Ethanol abolishes the metachromatic reaction of toluidine blue O with un-combined chromotropes but not when they are in association with protein. The green colour obtained in metachromatic regions is established as not due to any green impurity of the dye by chromatographic analysis but due to the fluid dehydrants combining with the dye as dye-organic solvent mixture showed green. The loss of metachromasia is not due to a dehydration effect of ethanol alone for the following reasons: (i) Stained samples of chromotropes dried in vacuuo continued to retain the metachromatic colour, (ii) Although other dehydrating agents likewise abolished the metachromasia, alcohols which have very slight affinity to water also abolished it, (iii) Ethanol does not abolish metachromasia produced in an acid mucopolysaccharide-protein complex. This has been suggested as due to the inability of ethanol to separate the dye from such compounds and to bring about a shift to green.
TL;DR: In Emerita asiatica and Ligia exotica, starvation for 1 week steadily depleted the free sugar values, indicating their involvement in nutritive physiology; it is suggested that they may be involved in the moulting physiology related to the synthesis of structural components such as chitin.
Abstract: In Emerita asiatica and Ligia exotica, starvation for 1 week steadily depleted the free sugar values, indicating their involvement in nutritive physiology. Protein-bound blood sugars showed no change during starvation, indicating their non-involvement in general carbohydrate metabolism; it is suggested that they may be involved in the moulting physiology related to the synthesis of structural components such as chitin. The extent of glycogen storage is found to be greater in the anomuran E. asiatica than in the isopod L. exotica. In the latter, the fall in free sugar values during starvation is greater, due to meagre storage of glycogen in the hepatopancreas. these features are related to habitat and availability of food in the environment.
TL;DR: In this article, the kinetics of polymerization of acrylamide and acrylic acid in aqueous solution photoinitiated by the complex, diazidotetramminecobalt(III) was systematically studied at 35°C and pH = 3.
Abstract: The kinetics of polymerization of acrylamide and acrylic acid in aqueous solution photoinitiated by the complex, diazidotetramminecobalt(III) was systematically studied at 35°C and pH = 3. Monochromatic radiation at γ = 365, 405, and 435 mμ was employed. The kinetics of polymerization were followed by measurements of the rates of monomer disappearance (bromometrically) and complex disappearance (spectrophotometrically) and the chainlengths of the polymers formed (viscometrically). The dependences of the rate of polymerization on variables like light intensity, light absorption by the complex, wavelength, monomer concentration, and hydrogen ion concentration were studied. The rates of polymerization of acrylamide and acrylic acid were found to be propertional to the square of the monomer concentration and to the first power of light absorption fraction ke and light intensity I. A kinetic scheme is proposed in the light of experimental results involving (1) a primary photochemical act of excitation of the complex, followed by the dark reaction of electron transfer within the complex producing the azide radical; (2) initiation of polymerization by the azide radical; (3) termination of the chain process by the complex molecule.
TL;DR: In this paper, X-ray data of crystal structures have been analyzed to reveal the conformation of the cyclooctane ring system and it is found to prefer predominantly a boat chair conformation, but there is a tendency to adopt the crown form when there is either extensive replacement of ring C atoms or extensive substitution of the ring hydrogens.
TL;DR: In this paper, the characteristic ratio of the β -D(1 → 4')-linked polysaccharides xylan and mannan has been computed as a function of the angle τ at the bridge oxygen atom and the degree of polymerization.
Abstract: The characteristic ratio CN = 〈r2〉0/Nlv2 of the β -D(1 → 4')-linked polysaccharides xylan and mannan has been computed as a function of the angle τ at the bridge oxygen atom and the degree of polymerization N The calculated values of the characteristic ratio CN are very high relative to their free rotational dimensions The characteristic ratio of these polysaecharides converges to the asymptotic value at low degree of polymerization at higher τ values The low values of the calculated characteristic ratio of xylan compared to cellulose and mannan for the same τ value indicate that the former is more flexible and assumes a compact configuration A pronounced difference in the values of the characteristic ratio CN of cellulose and mannan has also been observed lower τ angles (<120°) On the other hand, nearly the same values of CN have been obtained at higher Τ angles (120°-125°), which suggests that, cellulose and mannan may have similar configuralons in certain solvents
TL;DR: In this article, the shape of 90Y was studied as an overall check of the spectrometer response and the measured form factor was found to be free from any distorting effect to within 0.3% perm 0c2.
Abstract: The shape of90Y is studied as an overall check of the spectrometer response. The measured form factor of90Y,viz. (q2 + 9L1/L0)· ·{1 − (0.001 ± 0.003)W} indicates that the spectrometer is free from any distorting effect to within 0.3% perm0c2. This agrees very well with the conclusion arrived at by a direct study of the instrumental effects. The large hyperbolic terms reported for90Y and a few other allowed and 1st unique spectra are characteristic of only 180° spectrometers whose line-shapes are highly asymmetrical. The shape deviation of32P for optimal base position is found to be small (a = −0.006 ± 0.005) in spite of its large logft value. Wrong positioning of the entrance base resulted in large hyperbolic deviation and shape with double slopes. These anomalies resembled some of the results reported in the literature. The two prevailing approaches,viz. l-forbiddenness and cancellation effect in allowed matrix elements to explain the large logft value, small linear-shape deviation and longitudinal polarization of (−p/W) are only qualitatively successful.
TL;DR: The theoretically predicted conformations for the arginine side chain are found to be in excellent agreement with observations and to predict the barrier to rotation about the C-N bond of the guanidyl group.
01 Jun 1971
TL;DR: In this article, 1-aminocyclohexane carboxylic acid hydrochloride was solved by beta synthesis and refined threedimensionally to an R factor of 10·9% with 817 observed re-flexions.
Abstract: 1-aminocyclohexane carboxylic acid hydrochloride crystallizes in the monoclinic space group P2 1 with unit cell dimensions a=9·36, b=6·40, c=7·40A and β=96·0°. The structure has been solved by beta synthesis and refined three-dimensionally to an R factor of 10·9% with 817 observed re-flexions. The conformation of the cyclohexane ring is a slightly distorted chair.
TL;DR: In this article, the shape factor of the O−→O+ transition of144Pr was analyzed with the present spectrometer, which is ideally suited for such high-energy transitions as144Pr, for which scattering is a serious problem in other spectrometers.
Abstract: The shape factor result of Daniel on the O−→O+ transition of144Pr is at variance with all earlier reports, requiring terms up toW2. For166Ho O−→O+ decay, Danielet al. require terms up toW3, whereas Beekhuiset al. who treatWo as a free parameter fit the experimental shape with a fewer number of terms. In view of these disagreements, it is considered worth-while to perform an accurate analysis of the144Pr spectral shape with the present spectrometer, which is ideally suited for such high-energy transitions as144Pr, for which scattering is a serious problem in other spectrometers. The measured shape of144Pr isC(W)=k{1-(0.0975±0.013)/W}. An analysis, employing the exact formulation of Bhalla and Rose yieldsCp/Ca≈10 and a ratio of axial vector matrix elements λ=−11. These results exclude the predictions of partially conserved axial vector current theory in the form proposed by Tadic. The nonzero limit ofP-contribution may arise due to the inadequacy of the treatment ofP-coupling by Rose and Osborne or the neglect of higher-order matrix elements in the present analysis. The parameter obtained in the present work agrees with the theoretical, predictions of Ahrens and Feenberg, and Pursey and excludes those of Rose and Osborn, and Pearson.
TL;DR: The haemocytes of a centipede Scolopendra morsitans was studied by means of phase contrast and ordinary microcopy and the significance of the occurrence of oenocytoids is discussed with reference to the phylogeny of the group.
Abstract: 1. The haemocytes of a centipede Scolopendra morsitans was studied by means of phase contrast and ordinary microcopy.2. Six distinct types of haemocytes comparable to the prohaemocytes, plasmatocytes, granular haemocytes, spherule cells, adipohaemocytes and oenocytoids of insects are observed.3. The possible interrelations between the different types of haemocytes are discussed.4. The significance of the occurrence of oenocytoids is discussed with reference to the phylogeny of the group.
TL;DR: In this article, the Fox-Flory constant was determined for polymers by viscometry in several good and bad solvents, and application of some empirical methods for evaluation of K are also briefly discussed in relation to their results.
Abstract: Poly(ethyl methacrylate) and poly(methyl methacrylate) prepared by benzoyl peroxide-catalyzed polymerization were fractionated. The Fox-Flory constant K was determined for these polymers by viscometry in several good and bad solvents. Application of some empirical methods for evaluation of K are also briefly discussed in relation to our results.
TL;DR: Even though Beekhuis carried out a careful measurement of the shape of 803 keV beta transition, his result is at variance with the recent works reported concurrently with the present measurement as mentioned in this paper.
Abstract: Even though Beekhuis carried out a careful measurement of the shape of 803 keV beta transition, his result is at variance with the recent works reported concurrently with the present measurement The source material used by Beekhuis was obtained as a fission product which contained numerous interfering activities The angular-correlation results indicate the validity of the ζ-approximation for this transition The present measurement (a=−017±001) indicates a breakdown of the ζ-approximation and an admixture ofg7/2 andd
5/2 proton orbitals to the 91 keV level of147Pm is found necessary to explain the present measurement A strong attenuation of angular correlation by internal fields due to the finite lifetime of the 91 keV level has been reported by Bodenstedt in liquid sources A correction due to this effect and a measurement of energy and angle dependence of circular polarization will be helpful in eliciting further information about this transition
01 Apr 1971
TL;DR: In this article, Aminocycloheptanecarboxylic acid hydrobromide monohydrate was solved in the hkO and hOl projections, and refined with the three-dimensional data to an R factor of 9'86%.
Abstract: l-Aminocycloheptanecarboxylic acid hydrobromide monohydrate crystallizes in space group P212121 with cell dimensions a = 25.69, b = 6-85 and c = 6.6t . The structure was solved in the hkO and hOl projections, and refined with the three-dimensional data to an R factor of 9'86%. The cycloheptane ring is disordered, which leads to 'predominant' and 'alternative' conformations. Both of these conformations correspond to a skew-chair form. The structure is stabilized by a threedimensional network of hydrogen bonds.
TL;DR: In this paper, the inertia defects of some vinylidene halides and their deuterates were calculated on the basis of the general formulation developed by Oka and Morino, and the initial sets of force constants, based on published data, were adjusted by a least squares procedure until they reproduced the fundamental vibrational frequencies to within 1 %.
TL;DR: In this article, the distortion constants of halogenated ethylene-like molecules (C 2 X 4 and H 2 CCX 2 ) are calculated by evaluating all the seven independent τ αβδ's for these planar asymmetric top molecules.
TL;DR: In this paper, the kinetics of polymerization of methacrylamide in aqueous solution photoinitiated by trans-diazidotetramminecobalt(III)azide was systematically studied at 35°C and pH ≥ 3.
Abstract: The kinetics of polymerization of methacrylamide in aqueous solution photoinitiated by trans-diazidotetramminecobalt(III)azide was systematically studied at 35°C and pH≈3. Monochromatic radiations of λ=365, 405, and 435 mμ were employed. The rate of monomer disappearance was followed bromometrically and the rate of complex disappearance spectrophotometrically. The effect of variables such as monomer concentration, light-absorption fraction by the complex, light intensity, and wave length on the kinetics was studied. The rate of polymerization was found to be proportional to the monomer concentration and independent of the light-absorption fraction (ke) and light intensity (I). A kinetic scheme consisting of (1) a primary photochemical act of excitation of the complex followed by electron transfer producing the azide radical, (2) initiation of polymerization by the azide radical, and (3) termination of the chain process by the excited complex molecules is proposed and discussed in the light of experimental results.