13C and 1H n.m.r. dynamic study of poly(γ-benzyl-l-glutamate) poly(β-benzyl-l-aspartate) and poly(l-alanine) in solution

¹H T₁ relaxation times were measured in solutions of poly (γ-benzyl-l-glutamate), PBLG, and poly(β-benzyl-^l-aspartate), PBLA, and ¹³C T₁ relaxation times, NOE factors and line widths in solutions of the two polypeptides and of poly(l-alanine), PLA, over a broad range of solvent composition (CDCI₃—trifluoroacetic acid) including the helix—coil transition. PBLG was also studied through temperature-induced inverted helix—coil transition. Most relaxation parameters change smoothly over the studied range, and the observed changes correspond to increase of mobility with increasing content of trifluoroacetic acid and with increasing temperature except for PBLG which undergoes an inverted helix—coil transition with temperature. Analysis of experimental data by means of the isotropic model yielded, for the backbone carbons of all three polypeptides, τ_eff ～ 2 × 10^?8 sec in the helix and τ_eff ～ 1 × 10^?9 sec in the coil form. For the side-chain carbons, τ_eff decreases in the range 10^?9 ? 10^?10 sec with increasing distance from the backbone, with τ_eff values consistently lower in the coil form. Results of analysis by means of a model with two correlation times are discussed.     

Application of 13C nmr spectroscopy to the elucidation of the electrochemical oxidation mechanism of the l-ascorbic and d-araboascorbic acids

The previously proposed electrochemical oxidation mechanism of the l-ascorbic and d-araboascorbic acids in basic medium must be rejected because of the variation in the carbon chemical shifts and coupling constants with the pH, which shows that the supposed rupture of the furanose rings at pH ～ 9 does not occur. Electrolysis in basic medium yields the same products as those obtained when the pH of the products of the electrolysis in acid medium are raised to pH ～ 11. This suggests that the oxidation mechanisms in acid and basic media are similar. The assigned carbon chemical shifts of the oxidation products in acid medium $\text{3}$ (or $\text{4}$) and in basic medium $\text{5}$ (or $\text{6}$) and $\text{7}$ (or $\text{8}$) are reported.     

Sequence peptide polymers: 3. Synthesis and conformational study in solution of poly (l-leucyl-l-leucyl-ε-N-carbo-benzyloxy-l-lysine

The synthesis and characterization of poly[Leu-Leu-(ε-Z)-Lys] and its conformational study in organic solvents are reported. The sequential polypeptide has been obtained with a satisfactory optical purity by the self-condensation method of the p-nitrophenyl ester of the corresponding tripeptide derivative according to the general procedure of De Tar et al. Poly[Leu-Leu-(ε-Z)-Lys] showed a right-handed α-helical conformation in solution of helicogenic solvents, as displayed by circular dichroism measurements and ultra-violet absorption spectra. The presence of the α-helix has been also detected in the solid state by infra-red spectroscopy. The helix stability of the polypeptide in chloroform—dichloroacetic acid solution is considerably high. This property may be related to the ordered sequence of the bulky leucyl residues which give rise to a screening effect, protecting the chain backbone from the acid solvent molecules.     

In situ laser raman spectroscopy of the sulfiding of Moγ-Al2O3 catalysts

Raman spectra of sulfided $\text{Mo}\text{γ-}\text{Al}{}_2\text{O}{}_3$ catalysts were obtained using in situ techniques for two sulfiding methods. For samples sulfided by 10% $\text{H}{}_2\text{S}\text{H}{}_2$ at 400 °C, MoS₂ structures were observed. A stepwise sulfiding using 10% $\text{H}{}_2\text{S}\text{H}{}_2$, with spectra recorded at 150, 250, and 350 °C, resulted in observation of molybdenum oxysulfide, reduced molybdate, and surface “MoS₂” phases. Reexposure of these samples to air led to radical modification of the oxysulfide structures as well as transformation of some sulfide phases. A model incorporating terminal and bridging MoS bonding and anion vacancies is proposed. This model is based on the conversion of isolated and aggregated molybdate and MoO₃ species to oxysulfide and reduced molybdenum phases. Conversion of reduced molybdenum phases to sulfides is observed to be slow.     

Heat transfer in an indirect-heat agitated dryerWärmeübertragung in indirekt beheizten Trommeltrocknern

The heat transfer coefficients between the heating plane and the granular material under agitation in a small indirect-heat agitated dryer with both moving and stationary heating planes were measured in order to obtain data for its design and to analyse the heat transfer mechanism. Based on the ‘particle heat transfer model’ suggested by Schlünder and partly revised by Mollekopf and Martin, heat transfer models for both types of heating planes were proposed to correlate the observed heat transfer coefficients. Comparison between the experimental and calculated heat transfer coefficients showed no serious deviation in either case. Using these models, it is possible to estimate the heat transfer coefficient between the heating plane and the granular material in this type of dryer.     

Syntheses and conformational studies of poly(S-menthyloxycarbonylmethyl l- and d-cysteines)

S-menthyloxycarbonylmethyl l- and d-cysteines were prepared by the reaction of l- or d-cysteine and (?)-menthyl chloroacetate in liquid ammonia and were then polymerized to poly(S-menthyloxycarbonylmethyll- and d-cysteines) by the N-carboxyanhydride (NCA) method. From the results obtained by means of infra-red spectra, X-ray diffractions, optical rotatory dispersions (o.r.d.), and circular dichroisms (c.d.), $\text{poly}\text{(S-}\text{menthyloxycarbonylmethyl-}\text{l}\text{-cysteine}\text{)}$ was found to be a right-handed α-helix in the solid state and in ethyl ether/chloroform and chloroform solutions. Similarly, $\text{poly}\text{(S-}\text{menthyloxycarbonylmethyl-}\text{d}\text{-cysteine}\text{)}$ was a left-handed α-helix. The helix-coil transition of these polymers was observed in the vicinity of 3–4% trifluoroacetic acid (TFA) in chloroform/TFA mixtures.     

The combustion of methane on platinum—alumina fibre catalysts—I: Kinetics and mechanism

As a part of a study of a convective—diffusive type catalytic combustor, the oxidation of methane has been studied over platinum supported on porous and non-porous alumina fibre. New and used catalysts have been carefully characterised, and the kinetics of the reaction have been measured at temperatures above and below 815 K, where a change in the apparent activation energy was found to occur. Comparison with Langmuir—Hinshelwood models suggests that the mechanism involves the reaction between adsorbed methane and oxygen adsorbed or in the gas phase. This mechanism is supported by the characterisation studies, which also suggest that the formation of carbonaceous intermediates may affect the reaction selectivity. Permanent catalyst deactivation occurs as a result of the sintering of platinum or of alumina; the latter effect is accelerated in the presence of steam.     

Synthesis and homopolymerization studies of vinylimidazolium salts

The preparations and characterizations of several monomeric vinylimidazolium salts are presented from the quaternizations of 1-vinylimidazole and 2-methyl-1-vinylimidazole with n-alkyl iodides and with dimethyl sulphate. Although vinylimidazolium salts have been reported in the patent literature, many of these salts were not isolated and characterized prior to their polymerization. From the reactions of 1-vinylimidazole with n-alkyl iodides, a homologous series of 3-n-alkyl-1-vinylimidazolium iodides were prepared in which the longer chain derivatives appeared to form micelles in aqueous solution. Dicationic crosslinking agents were also prepared through similar quaternization reactions. All the cationic vinyl monomers were homopolymerized in aqueous solution by free radical initiation. The solution behaviour of the resulting polyions indicated that the longer side-chain polyions had polysoap properties.     

Cation exchange kinetics on carboxylic acid resins in a multicomponent system H-Me+Me2+

The exchange kinetics in systems where a carboxylic cation exchange resin in the free acid form comes into contact with solutions, containing Na⁺, Mg²⁺, Ca²⁺, HCO^?₃ and SO^2?₄ have been followed by a shallow bed technique.The relations between the sorption rates of univalent and bivalent cations as well as kinetics of competitive exchange in a ternary system $\text{H}\text{-}$Na⁺Mg²⁺ were studied at low solution concentrations. The effect of polymer matrix crosslinking is studied. The behavior of sulfonic acid resin under the same conditions is given for comparison. The results are discussed in terms of different degrees of selectivities and degrees of dissociation of the carboxylic and sulfonic functional groups.     

Small-angle neutron scattering from polymer solutions: 2. The semi-concentrated region near the upper critical solution temperature

Small-angle neutron scattering experiments have been made on solutions of polystyrene in cyclohexane. From these experiments the radius of gyration has been determined as a function of polymer concentration at a fixed temperature (60°C). Additionally, the screening length has been determined as a function of temperature for a fixed polymer concentration of 36% (w/v). The results support the notion of an additional region of solution behaviour, the semi-concentrated region, predicted by mean field-type theory.     

Circular dichroism study of poly(l-tyrosine), poly(l-glutamic acid) and of random and sequential copolymers of l-glutamic acid and l-tyrosine in trimethylphosphate

Random and sequential copolypeptides containing l-glutamic acid and l-tyrosine, as well as poly(l-tyrosine) and poly(l-glutamic acid) were investigated by means of c.d. spectroscopy in trimethylphosphate as solvent. In random copolymers, variation of ellipticities at 202.5 and 230 nm versus tyrosyl content follows a smooth curve, without any sharp change. This led to the conclusion that poly(l-tyrosine) α-helix is right-handed. From c.d. studies on sequential copolymers we were able to recognize that the 230 nm contribution of tyrosyl side chains is closely related to the array in which tyrosyl residues are arranged in the chain. For instance, it was found that (n, n + 2) and (n, n + 3) pairings of tyrosyl side-chains in (Tyr-Glu)_n and (Glu-Tyr-Glu)_n respectively, were poorly effective, while the (n, n + 4) pairing in (Glu-Glu-Tyr-Glu)_n is more. However, the strongest contribution at 230 nm was observed on the alternating-páirs copolymer (Glu-Tyr-Tyr-Glu)_n. This result suggests a new conformational arrangement of tyrosyl side chains in sequential copolymers, as well as in poly(l-tyrosine) and other aromatic polypeptides, based on a regular pairing of the aromatic groups, arranged in two contiguous superhelices.     

Macromolecular properties of heparin in dilute solution: 1. Application of various hydrodynamic models in 0·5 M NaCl,pH 2·5

Bovine heparin was fractionated according to molecular weight by fractional precipitation utilizing a method described previously. The solution data from sedimentation analysis, intrinsic viscosities and partial specific volumes at pH 2·5 and in 0·5 M NaCl were treated according to the Mandelkern and Flory theory for random coil in calculating the constant β. It was found that the calculated β values for all the fractions were in close agreement with the theoretical value. Based on this observation, the solution data were then treated in light of various hydrodynamic theories for linear polymers to calculate various dimensional and other physical parameters, e.g., $\text{(}\text{r}\text{?}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, α (expansion factor), A₂. In comparing $\text{(}\text{r}\text{?}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ of a fraction to that calculated from the experimental value of $\text{(}\text{s}\text{?}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ obtained from low angle X-ray scattering for a comparable molecular weight sample, it was found that heparin in solution with suppressed charges may best be described as approximating the closely related models of Debye and Bueche, Flory and Fox, or Kuhn and Kuhn.     

Adsorption of phloroglucinol at the mercury/aqueous solution interface

The adsorption of phloroglucinol on mercury electrodes has been studied from 0.5 M NaClO₄ aqueous solution by means of capacitance and electrocapillary methods. Capacitance curves show a condensation type behaviour. Congruence Tests indicate simultaneous congruence at negative surface charges. Frumkin isotherm is obeyed both at constant charge and contant potential. The interaction parameter obtained through Frumkin fit corresponds to a repulsive interaction. A new isotherm based on Free Volume Theory was tried. A model for the structure of the double layer in presence of phloroglucinol has been advanced, based on these results and the available crystallographic data of phloroglucinol and its dihydrate.     

Macromolecular properties of heparin in dilute solution: 2. Dimensional parameters as a function of pH,ionic strength and desulphation

A bovine heparin fraction was examined by sedimentation analysis and intrinsic viscosity measurements as a function of ionic strength in the range of 0·1 to 1·0 M, and at pH 2·5 and 6·0. The following experimental parameters were obtained: M, S⁰_20,W, D⁰_20,W, $\text{V}\text{?}$, and [η]. Other physical parameters were calculated based on a random coil model (supported by the theory of Mandelkern and Flory) e.g., $\text{(}\text{r}\text{?}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, $\text{(}\text{s}\text{?}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. Similar studies were made on a heparin sample as a function of desulphation as resulting from graded mild hydrolysis. Since desulphation is accompanied by decreasing anticoagulant activity of heparin, the latter was correlated with various calculated and measured physical parameters. Significantly $\text{(}\text{r}\text{?}{}^2\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ decreases with decreased desulphation and therefore decreased biological activity.     

The electrochemical oxidation of lead in various H2OH2SO4 mixtures—II. Ring-disc electrode study

The rotating ring-disc electrode technique was used to study the generation of soluble Pb(II) species during the anodic oxidation of the lead electrode in various H₂OSO₄ media. The concentration range extended from 0.06 to 10.3 M H₂SO₄. For every concentration it was possible to detect a small cathodic ring current variation which was attributable to the reduction of Pb(II) to Pb. Quantitative measurements of the collection efficiency showed that the small cycle life of the lead-acid battery in 5.6 M H₂SO₄ cannot be ascribed to the dissolution step.     

The electrochemical oxidation of lead in various H2OH2SO4 mixtures—I. Linear sweep voltammetry

The linear sweep voltammetry technique was used in order to detect a change in the lead oxidation mechanism around 5 M H₂SO₄. This change could explain the strong decrease in cycle life of the lead-acid battery when increasing H₂SO₄ concentration from 4.7 to 5.6 M. In the concentration range studied (3.6–10 M) no change was detected. The same behaviour was observed when cycling the electrode, when increasing sweep rate and when rotating the electrode.     

Studies on viscosity behaviour of alkali halides in aqueous N,N′ dimethyl urea solution

The viscosity behaviour of ternary systems comprising alkali halides (concentration range 0.125–3 M) in aqueous N,N′ dimethyl urea (0.6 M) solution, over the temperature range 25–40°C has been investigated. It has been found that Moulik's equation (ν/ν_$\text{0}$)² = M + KC² holds good for these systems for the concentrated region. From the relative viscosity data, the “effective” rigid molar volume, V_e and apparent B coefficient have been computed employing the Breslau-Miller procedure at temperatures 25, 30, 35 and 40°C. These data have been used to explain the structuring effect in N,N′ dimethyl urea solution.     

Redox reaction of tri(2-deoxy-2-L-ascorbyl)amine. Formation of a persisting free radical species in water

Electrochemical studies showed that tri(2-deoxy-2-L-ascorbyl)amine ($\text{1}$), a new compound isolated as one of the products of reaction of dehydro-L-ascorbic acid with phenylalanine (with added L-ascorbic acid) in ethanol, is oxidized in aqueous solution in two reversible one-electron transfer steps, on mercury or platinum electrode. The first step occurs through the dianion, and its product is an unusually stable blue anion radical giving a characteristic ESR signal. The product of the second step of oxidation is labile and is slowly converted into the oxidized form of di(2-deoxy-2-L-ascorbyl)amine, presumably by hydrolysis with splitting of L-ascorbic acid.