Showing papers by "University of Madras published in 1968"

Conformation of Polypeptides and Proteins

Abstract: Publisher Summary This chapter deals with the recent developments regarding the description and nature of the conformation of proteins and polypeptides with special reference to the stereochemical aspects of the problem. This chapter considers the parameters that are required for an adequate description of a polypeptide chain. This chapter focuses the attention on what may be called “internal parameters”—that is, those which can be defined in terms of the relationships among atoms or units that form the building blocks of the polypeptide chains. This chapter also provides an account of the mathematical method of utilizing these parameters for calculating the coordinates of all the atoms in a suitable frame of reference, so that all the interatomic distances, and bond angles, can be calculated and their consequences worked out. This chapter observes conformations in amino acids, peptides, polypeptides, and proteins.

Interchain hydrogen bonds via bound water molecules in the collagen triple helix

Abstract: If the collagen triple helix is so built as to have one set of NH O hydrogen bonds of the type N3H3(A) O2(B), then it is possible to have a linkage between N1H1(B) and O1(A) through the intermediary of a water molecule with an oxygen O leading to the formation of the hydrogen bonds N1(B) O and O (A). In the same configuration, another water molecule with an oxygen O can link two earbonyl oxygens of chains A and B forming the hydrogen bonds O O1(A) and O O0 (B). The two water oxygens also become receptors at the same time for CH O hydrogen bonds. Thus, the neighboring chains in the triple helix are held together by secondary valence bond linkages occurring regularly sit intervals of about 3 A along the length of the protofibril. The additional water molecules occur on the periphery of the proto-fibril and will contribute their full share towards stabilizing the structure in the solid state. In solution, they will be disturbed by the medium unless they are protected by long side groups. It appears that this type of two-bonded structure, in which one NH O bond is to a water molecule, can explain several observations on the stability and hydrogen exchange properties of collagen itself and related synthetic polypeptides. The nature of the water bonds and their strength are found to be better in the one-bonded structure proposed from Madras than in the one having the coordinates of Rich and Crick.

Stereochemical criteria for polypeptides and proteins. IV. Standard dimensions for the cis‐peptide unit and conformation of cis‐polypeptides

Abstract: Using potential energy formulas for variation of bond angles and for ω-distortion, the conformation of minimum energy for the cis form of the peptide unit has been worked out. This agrees very well with the corresponding set of atoms in the crystal structure of Leu-Pro-Gly and the dimensions of a standard cis peptide unit are given based on these. The conformational (ϕ,Ψ) map for a cis peptide unit has been worked out from contact criteria, both for a pair of linked units as well as for-helices having constant (ϕ,Ψ). The small allowed region of the helical map contains the conformation experimentally observed for poly-L-proline I.

Vinyl polymerization initiated by ceric ion reducing agent systems in sulfuric acid medium

Abstract: Polymerization of the monomers, methyl acrylate (MA) and methyl methacrylate (MMA) was carried out in sulfuric acid medium at 15°C. With the redox initiator system, ceric ammonium sulfate-malonic acid. There was no induction period, and a steady state was attained in a short time. There was found to be no polymerization even after 1 hr. in the absence of the reducing agent R. The initiation was by the radical produced from the Ce 4+ -malonic acid reaction. The rate of monomer disappearance was proportional to [M] 1.5 , [R] 0.5 , and [Ce 4+ ] 0.3-0.5 , and the rate of ceric disappearance was directly proportional to [R] and [Ce 4+ ]. Chain lengths of the polymers were directly proportional to [M] and inversely to [R] ½ and [Ce 4+ ] ½ . The experimental results were explained by a kinetic scheme involving the following steps: (a) oxidation of the substrate to give the primary radical which reacts with Ce 4+ to give the products, (b) initiation by the primary radical, (c) propagation, and (d) termination of the growing polymer radicals by the mutual type. For the polymerization of acrylonitrile (AN) by the redox system, ceric ammonium sulfate-cyclohexanone (CH), in sulfuric acid at 15°C., the scheme was modified to include linear type of termination by Ce 4+ , along with the mutual termination to explain the results especially under conditions with [Ce 4+ ] ≥ [CH].

Kinetics and mechanism of the alkali‐catalysed addition of formaldehyde to phenol and substituted phenols

Abstract: In view of the differences in the positional reactivities, reported by different authors, in phenol and methylol phenols, an exhaustive kinetic study using quantitative paper chromatography has been carried out not only on phenol and methylol phenols but also on phenols with methyl group and chlorine atom substituents. The o-position is less reactive than the p-position in phenol and substituted phenols for the addition of formaldehyde in the presence of alkali catalyst, with a correspondingly higher activation energy. The effect of the methylol group appears to be intermediate between the activating effect of the electron repelling methyl group and the deactivating effect of the electron attracting chlorine atom. But the marked activating effect of the methyl and methylol group in the o-position is tried to be accounted for by intra-molecular hydrogen bonding. The activating effect of chlorine atom in the o-position is explained in terms of the electron repulsion between chlorine atom and the phenoxide anion. The few characteristic differences in the positional reactivities observed in the results of earlier workers are not found in the results obtained in the present investigation.

Ceric ion-reducing agent redox initiated vinyl polymerisation

Abstract: Ceric perchlorate/formaldehyde (F)redox couple initiated polymerisation of the monomer methyl acrylate (MA), acrylonitrile (AN), and methyl methacrylate (MMA) in perchloric acid (25°C) was carried out The rate of polymerisation was directly proportional to [M]2 and [F] for all the systems The rate was independent of [Ce4+] for the systems with MA or AN, but inversely proportional to [Ce4+] with MMA as the monomer The rate of ceric disappearance was directly proportional to [Ce4+], [F], and [M] The results were explained by a kinetic scheme involving the oxidation of the substrate by Ce4+ to give the primary radical and further reaction of the latter with Ce4+ to give the final product, and initiation of polymerisation both by Ce4+ and the primary radical, propagation followed by termination by the metal ion Only with MMA as the monomer, the initiation by Ce4+ was found to be negligible compared to that by primary radicals In the system with the reducing agents t-butanol and n-butanol, there was found to be 1:1 complex formation between the substrate and Ce4+ Otherwise the scheme is similar to that proposed for the Ce4+/HCHO/HClO4/AN (MA) systems Die vom Ceriperchlorat/Formaldehyd-Redoxpaar gestartete Polymerisation von Methylacrylat, Methylmethacrylat und Acrylnitril wurde in wasriger Perchlorsaure bei 25°C ausgefuhrt Die Polymerisationsgeschwindigkeit in allen Systemen war direkt proportional zu [F] und [M]2 Bei Methylacrylat und Acrylnitril war die Geschwindigkeit von der Cerionenkonzentration unabhangig; beim Methylmethacrylatsystem war sie dagegen umgekehrt proportional der Ce4+-Konzentration Die Geschwindigkeit des Umsatzes der Ce4+-Ionen war direkt proportional zu [Ce4+], [F] und [M] Die Ergebnisse werden folgendermasen erklart: Oxydation des Substrats durch Ce4+-Ionen zu Primarradikalen, die teilweise mit weiteren Ce4+-Ionen abbrechen Start der Polymerisation sowohl durch Ce4+-Ionen als auch durch Primarradikale Der Abbruch erfolgt durch Metallionen Nur im Fall des Methylmethacrylats wurde gefunden, das der Start durch Ce4+-Ionen im Vergleich zum Start durch Primarradikale vernachlassigbar war In Systemen mit t-Butanol und n-Butanol als Reduktionsmitteln erfolgt eine Komplexbildung (1:1) zwischen Alkohol und Ce4+-Ionen; sonst gilt dasselbe Reaktionsschema wie fur die Systeme mit Formaldehyd

Some New Species and New Records of Marine Isopods From San Juan Archipelago, Washington, U.S.a

Abstract: Isopodes marins nouveaux obtenus au cours de chalutages, de dragages et de recoltes intertidales dans les parages des laboratoires de Friday Harbor, Washington, U.S.A. Ils comprennent un genre nouveau, Munnogonium, et quatre especes nouvelles: Munnogonium waldronense, Munna (Munna) fernaldi, Jaeropsis setosa et Exosphaeroma media. Douze especes precedemment inconnues de cette region sont signalees et deux especes sont redecrites.

Graft polymers from poly(vinyl chloride) and chlorinated rubber

Abstract: Graft polymers from poly(vinyl chloride) (PVC) and chlorinated rubber (CIR) with side chains of poly(methyl methacrylate) (PMMA), poly(methyl acrylate) (PMA), or poly(ethyl methacrylate) (PEMA) were synthesized. For this purpose, a vinyl monomer was polymerized in the presence of small quantities of PVC or CIR with benzoyl peroxide as catalyst. The graft polymers were separated from both homopolymers by precipitation with methanol from methyl ethyl ketone solutions of the reaction products and the grafting efficiency was calculated. The graft polymers were characterized by infrared spectra, elemental analysis, NMR, and osmometric or light-scattering determinations. From the results it is concluded that the PVC or CIR molecules contain side chains of PMMA, PMA, or PEMA. The graft polymers showed higher molecular weights, and the values of second virial coefficient for these polymers were much different from those of the starting polymers.

Polymerisation of acrylonitrile by V5+/cyclohexanol‐redox system

Abstract: The effects of the concentrations of monomer, cyclohexanol, V 5+ , H 2 SO 4 , HSO 4 - , SO 4 2- , Cl − and ionic strength at 40 to 60°C on the rate of V 5+ disappearance and the rate of polymerisation of acrylonitrile were studied. From the experimental results, it was concluded that the organic free radicals formed during the decomposition of the V 5+ -cyclohexanol complex, initiated polymerisation and that the polymer radicals were terminated by V 5+ ion. An appropriate kinetic scheme was proposed and the various rate and energy parameters were evaluated.

Stereochemical studies on cyclic peptides

Abstract: The study deals with the molecular structure of the cyclic disulphide which can be obtained by the oxidation of twol-cysteine residues. It is not possible to have atrans peptide unit in this structure. Calculations made on an electronic computer with the hard-sphere model showed that the structure could not also be built with a planarcis peptide unit. A satisfactory structure could, however, be constructed with a non-planarcis peptide unit. The possible conformations have been analysed on the basis of stereochemical criteria based on non-bonded contacts, and it was found that structures are possible for a deviation Δω=−10° and ±20° from the planar conformation. The former is expected to be more stable. Energy calculations are in progress.

Possible formation of the left-handed α-helix of poly-L-serine.

Abstract: A conformational study of poly-L-serine has shown that it can exist in the left-handed α-helical form. A study of a pair of peptide units with the serine sidegroup attached to the α carbon atom linking the two units showed that OH O hydrogen bonds between the OH group of the side chain and a carbonyl oxygen of the first peptide group in the backbone can occur in two regions of ϕ, namely, ϕ = 15°-30° for χ1 = 300° and for ϕ = 225°-230° for ϕ = 60°. The latter is close to a possible left-handed helix of poly-L-serine, stabilized by NH O hydrogen bonds. From a study of contact criteria, the best conformation for this helix is found to be ϕ = 227°, Ψ = 238°, χ1 = 65° which has n = 3.65, h = 1.51 A. The NH O hydrogen bond has a length of 2.90 A. (6°) and the OH O hydrogen bond is of length 2.60 A. (0°). There are no other bad short contacts in the structure. The cylindrical coordinates of the atoms, as well as a perspective view of the structure arc given in this paper.

Polymerization of acrylamide and methacrylamide photoinitiated by azidopentamminecobalt(III) chloride

Abstract: The kinetics of polymerization of acrylamide and methacrylamide, photoinitiated by azidopentamminecobalt(III) chloride in homogeneous aqueous acid medium was studied systematically. Monochromatic wavelengths 365, 405, and 435 mμ were employed for irradiation. Polymerization proceeded without any induction period, and the reaction was followed by measurements of rate of monomer disappearance (bromometrically), rate of complex disappearance (spectrophotometrically), and the chain lengths of the polymer formed (viscometrically). The dependences of the rate of polymerization on variables like light intensity, light absorption fraction by the complex, wavelength, monomer concentration, hydrogen ion concentration, nature of the acid used (HClO4, HNO3, and H2SO4), etc., were studied. The rate of polymerization of acrylamide depended on the unit power of monomer concentration and on the square root of light absorption fraction ke and light intensity I. The rate of methacrylamide polymerization was proportional to the unit power of monomer concentration and fractional powers of 0.25 and 0.30 of ke and I, respectively. A kinetic reaction scheme is proposed and discussed in the light of the experimental results, and it has been concluded that (1) the primary photochemical act is an electron transfer reaction from the azide ion to Co(III) in the complex, (2) initiation of polymerization is by azide radical, (3) termination is by mutual destruction of polymer radicals.

Solution properties of poly(methyl acrylate) and (1:1) poly(styrene‐co‐methyl acrylate)

Abstract: Poly(methyl acrylate) (PMA) and 1:1 poly(styrene-co-methyl acrylate) (PSMA) were prepared by solution and bulk polymerization, respectively. The copolymer was analyzed with NMR to ascertain its composition and microstructure. The solution properties of unfractionated PMA and fractionated PSMA in ethyl acetate were investigated by light-scattering and viscosity techniques at 35°C. Narrow composition heterogeneity as revealed from the light-scattering measurements in different solvents justified the use of a single solvent for the copolymer characterization. The equations relating the limiting viscosity number to molecular weight, the molecular dimension to molecular weight, etc., were found for homopolymer and copolymers in ethyl acetate at 35°C. In the evaluation of the Flory constant K for the unperturbed state by methods based on Flory-Fox-Schaefgen, Kurata-Stockmayer, and Stockmayer-Fixman expressions, only the first method gave a value for PMA in ethyl acetate, consistent with that obtained in other solvents, whereas similar values of K were obtained by the three methods for PSMA in ethyl acetate. The studies indicate reduced thermodynamic interaction for PSMA-ethyl acetate compared to PMA-ethyl acetate, but increased steric effect in the copolymer compared with the homopolymer.

Studies on the bottom fauna in a tropical freshwater fish pond

Abstract: Quantitative samples of the bottom fauna obtained from a tropical freshwater fish pond during a period of two years were studied with regard to species composition, zonal variation and seasonal fluctuation. Two different zones with differences in faunal composition could be distinguished. The littoral zone was dominated by Mollusca, whereas Oligochaetes were predominant in the profundal zone. Most of the organisms showed their peaks in the months January to April. Breeding activities of Vivipara bengalensis, Digoniostoma cerameopoma, Melanoides granifera and Pisidium clarkeanum as evidenced by presence of younger length groups in the populations were also observed during the same period (January to April). The influence of environmental factors as temperature, alkalinity and food were discussed as probable causes for the peaks in abundance. The average number of total organisms per square metre was found to be comparatively high indicating a high standing crop. Differences observed in the total number of organisms present have been attributed to inflow of water resulting in sudden alteration of the nutrient condition of the bottom mud. The seasonal variations of the standing crop of bottom fauna during both the years have been found to be influenced by fluctuations of the bivalve mollusc, Lamellidens corrianus. The availability of sufficient amount of benthic fauna for consumption by bottom feeding fishes has been indicated.

Role of symbiotes in tanning of termite cuticle

Abstract: Chez la termiteReticulitermes assamensis Gardner la cuticule des ouvriers aposymbiotics est de couleur plus claire que celle des individus normaux. Ceci est du a l'approvisionnement inadequat des precurseurs de tannage, en l'absence de la formation de l'exocuticule. La reinfection des formes aposymbiotiques par des symbiotes cause l'acquisition de la couleur ambree semblable a celle des individus normaux. Il est probable que les composes aromatiques du regime alimentaire des termites sont dus aux symbiotes.

The Description of Particles of Arbitrary Spin

Abstract: The search for relativistically invariant wave equations, which could (hopefully) serve as a basis for the description of elementary particles, was carried on most intensively during the ‘thirties and ‘forties, and resulted in the discovery of a variety of equations with some claim to be considered as suitable for describing particles of any given spin. Since then, this field has appeared to be essentially a closed one, and it might seem inappropriate to bring it up at a symposium devoted primarily to certain aspects of elementary particle physics which are in almost explosive growth. However, part of this “explosion” has been the discovery of large numbers of new particles among which are some higher-spin particles (with spin>l). This fact makes it essential to give fresh consideration to higher-spin wave equations, which had earlier suffered from neglect as much due to fact that no higher-spin particles were then known, as due to the not-so-satisfactory nature of the theories themselves.