Circular dichroism of poly(β-benzyl-l-aspartate) films in the α, β and ω conformations

The conformations of poly(β-benzyl l-aspartate) (PBLA) in film were studied by means of circular dichroism (c.d.). Films of PBLA show c.d. which is related to the benzyl chromophores of this polypeptide. The magnitude and sign of the c.d. of the benzyl chromophores depend on the conformation i.e. α-helix, ω-helix or β-form. The aromatic c.d. of the left-handed α-helix or the left-handed ω-helix is negative in sign, and that of the β-form is positive in sign. The absolute magnitude of the c.d. of PBLA is much larger in the ω-helical conformation than in the α-helical or the β-conformations. In the left-handed α-helical PBLA (α-PBLA), the positive dichroism band of the $\text{n?π1}$ peptide electronic transition is observed at about 226 nm. When the α-PBLA is converted to the left-handed ω-helical PBLA (ω-PBLA), the band at 226 nm shifts to 224 nm, and its magnitude becomes much smaller. In the β-form PBLA (β-PBLA), this band is negative in sign and observed at 223 nm. The absolute magnitude of the c.d. relative to this electronic transition follows the order: β-form < ω-helix < α-helix.     

Conversion of bituminous coal in COH2O systems: 2. pH Dependence

Under $\text{CO}\text{H}{}_2\text{O}$ systems at initial pH values s> 12.6, an Illinois No. 6 coal, PSOC-26, was converted to a fully pyridine-soluble product, with benzene and hexane solubilities of 50% and 18%, respectively. The product gases were H₂ and CO₂. However, the expected $\text{H}{}_2\text{CO}{}_2$ ratio of 1.0 based on the water gas shift reaction was not observed, but the deficit in hydrogen was found in the increased hydrogen content of the coal product. 95% coal carbon recovery and good hydrogen balances were obtained, and the coal products were found to be very similar to those from conventional tetralin systems. The results suggest an efficient base-catalysed process, and that $\text{CO}\text{H}{}_2\text{O}$ systems are useful for coal studies.     

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.     

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.     

Improved synthetic method and conformation studies of polymers and copolymers of l-β-3,4-dihydroxyphenyl-α-alanine with l-glutamic acid

Eight different copolymers of l-β-3,4-dihydroxyphenyl-α-alanine (l-Dopa) and l-glutamic acid with high degrees of polymerization have been synthesized by the treatment of a series of $\text{copoly}\text{(O,O′-}\text{dimethyl-}\text{l}\text{-Dopa}$, γ-benzyl-l-glutamate) with boron tribromide in chloroform. The conformation of poly(l-Dopa) has been established to be a right-handed helix in trimethyl phosphate on the basis of the following observations. The [θ]₂₂₂ and b₀ values of the copolymers were almost linear with composition in trimethyl phosphate. The linear relationship between the rotation properties and composition indicates that poly(l-Dopa) has the same helical sense as that of poly(l-glutamic acid) which is a right-handed α-helix.     

Reinvestigation of the system C4A.nH2O  C4A.Co2.nH2O

The system C₄A.nH₂O  C₄A.CO₂.nH₂O has been reinvestigated at 22°, 100 % and 65 % relative humidity. Formation conditions, composition and crystallographic properties of the phases C₄A.nH₂O, C₄A.1/2CO₂.nH₂O, C₄A.CO₂nH₂O and their dehydration products have been studied by X-ray and elektron diffraction, infrared and Raman spectroscopy, dynamic weight-loss curves and differential thermal analysis. Only very limited solid solution occurs in the system. X-ray single crystal studies showed the quaternary compound C₄A.1/2CO₂.12H₂O to be trigonal with space group R3c or R$\text{3}$c, lattice parameters $\text{a}{}_{\mathrm{o}}\text{=5.77}\text{a}\text{?}\text{,}\text{C}{}_{\mathrm{<mtext>o</mtext>}}\text{=49.16}\text{a}\text{?}$. C₄A.CO₂11H₂O is triclinic with $\text{a}{}_{\mathrm{o}}\text{=5,}{}_{\mathrm{o}}\text{=5.74}\text{A}\text{?}\text{,}\text{C}{}_{\mathrm{o}}\text{=7.86}\text{A}\text{?}\text{α=92.61°, β=101.96°, δ=120.09°}$. Indexed powder diffraction data of both compounds are given.     

Effects of metal-support interactions on the hydrogenation of CO over PdSiO2 and PdLa2O3

A study of CO hydrogenation over $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$ has been carried out for the purpose of identifying the effects of Pd dispersion, Pd morphology, and support composition on the catalytic activity of supported Pd. The specific activity of each catalyst for methanol and methane synthesis was determined from microreactor studies carried out at a fixed set of reaction conditions. Palladium dispersion was measured by H₂O₂ titration, and the morphology of the Pd crystallites, as expressed by the distribution of Pd(100) and Pd(111) planes, was determined from in situ infrared spectra of adsorbed CO. The crystallite morphology of the $\text{Pd}\text{SiO}{}_2$ catalysts is the same, independent of Pd weight loading: 90% of the surface is comprised of Pd(100) planes and 10% of the surface is comprised of Pd(111) planes. By contrast, the crystallite morphology of the $\text{Pd}\text{La}{}_2\text{O}{}_3$ catalysts changes with Pd loading. Primarily Pd(100) planes are exposed at low-weight loadings while Pd(111) planes are exposed at high-weight loadings. The Pd dispersion has little effect on the methanol turnover frequency over both $\text{Pd}\text{SiO}{}_2$ and $\text{Pd}\text{La}{}_2\text{O}{}_3$, for dispersions between 10 and 20%. On the other hand, the methane turnover frequency is independent of Pd dispersion over $\text{Pd}\text{SiO}{}_2$, but increases with decreasing dispersion over $\text{Pd}\text{La}{}_2\text{O}{}_3$. It is further observed that the Pd morphology influences the specific activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ for methanol synthesis: Pd(100) is nearly threefold more active than Pd(111). For a fixed morphology, the specific methanol synthesis activity of $\text{Pd}\text{La}{}_2\text{O}{}_3$ is a factor of 7.5 greater than that of $\text{Pd}\text{SiO}{}_2$.     

Selective steam reforming of aromatic hydrocarbons: IV. Steam conversion and hydroconversion of selected monoalkyl- and dialkyl-benzenes on Rh catalysts

Steam conversion and hydroconversion of a series of monoalkylbenzenes (C₆H₅R, R = C₂H₅, n-C₃H₇, i-C₃H₇, tert-C₄H₉) and of dialkylbenzenes (o- and p-xylenes) are studied at 713 K and atmospheric pressure on supported rhodium catalysts ($\text{Rh}\text{Al}{}_2\text{O}{}_3$, $\text{Rh}\text{SiO}{}_2$ and $\text{Rh}\text{TiO}{}_2$), and compared to the toluene steam dealkylation previously studied on the same catalysts. Three types of reaction, namely dealkylation (CC rupture on the side chain), dehydrogenation (on the side chain), and degradation (i.e., ring opening) account for virtually the whole product spectrum. Isomerization, transalkylation, and dehydrocyclization reactions may, in general, be discounted. In the presence of steam, the main initial product of monoalkylbenzene dealkylation is invariably benzene, but the splitting of the CC bonds in the middle or end of the side chain always increases with conversion. As a rule, the specific activities (per metal site) in dealkylation decrease with the degree of substitution in the alkyl group (primary > secondary > tertiary > quaternary carbon). On the other hand, the specific activities in ring opening remain constant for all the hydrocarbons and even for the benzene. In the presence of hydrogen, multiple CC bond splittings are invariably observed and benzene is no longer, in general, the principal initial product. The activities in ring opening are equally constant, but at a lower level than in steam conversion. These results are in overall agreement with the model of the dual active sites: sites I appear operative for dealkylation and dehydrogenation, whereas ring opening takes place at sites II with a high probability, independent of the alkyl group size. Possible adsorbed species on each type of site are described. An attempt is made to rationalize the effects of assorted selectivity-determining factors (metal particle size, support effects, selective poisons such as S and CO) in terms of electronic or geometric effects.     

The kinetics of the catalytic hydrogenolysis of ethane over Ni/SiO2

The rate of hydrogenolysis of ethane over a Ni/SiO₂ catalyst, studied over a large range of pressure and of temperature, is shown to be related to the degree of hydrogen coverage θ_H, by the equation: with K₀ nearly equal to the number of ethane molecules colliding with the Ni surface, E₀ = 14 ? 1 kcal/mole, Y = ?1 ? 2 and X = 15 ? 2. The rate-limiting step is believed to be the irreversible, dissociative adsorption of ethane on an ensemble of at least 12 adjacent Ni atoms, free from adsorbed hydrogen, resulting in the complete cracking of C₂H₆: C₂H₆ + 12Ni → 2

Irreversible adsorption of ethane is assumed to compete with the reversible adsorption of hydrogen. This mechanism, which is compared with those proposed earlier, is in good agreement with data on ethane adsorption studied by magnetic methods, and with a study of ethane hydrogenolysis over NiCu/SiO₂ catalysts.     

Synthesis and conformation studies of copolypeptides composed of γ-methyl-l-glutamate and ε-N-carbobenzyloxy-l-lysine

Copolypeptides (PMGCL) composed of γ-methyl-l-glutamate(MLG) and $\text{?-N-}\text{carbobenzyloxy-}\text{l}\text{-lysine(CBL)}$ covering the whole range of copolymer composition were synthesized by the N-carboxyanhydride (NCA) method. The experimentally obtained monomer reactivity ratios were r₁(MLG)=2·0±0·4 and r₂(CBL)=0·5±0·1, from which the fractions of monomer dyads and triads in copolymer were plotted against the initial comonomer composition. From experimental results on thermally induced coil-to-helix transition of the copolypeptides in dichloroacetic acid/1,2-dichloroethane (DCA-DCE) systems, it has been found that these copolypeptides can exist in the α-helix conformation in the same manner as homopolypeptides PMLG and PCBL. The van't Hoff heat of transition ΔH showed a minimum against the initial monomer composition. The enthalpy ΔH_res of formation of intramolecular hydrogen bonds per peptide bond also showed a minimum against copolymer composition. Such behaviour on ΔH and ΔH_res was also found for copolypeptide (PBGCL) composed of γ-benzyl-l-glutamate(BLG) and $\text{?-N-}\text{carbobenzyloxy-}\text{l}\text{-lysine(CBL)}$ in DCA-DCE systems reported in a previous paper. The presence of a minimum in these relationships may be attributed to specific interactions between the side chain of one comonomer and that of the other comonomer in a two component copolymer. It is also pointed out that these copolymer molecules can exist in the α-helix conformation in the solid state.     

Measurements of anisotropic light scattering: application to the determination of the difference Hh−Hv for θ=π2

By improving the performance of a photogoniodiffusometer, a technique for the accurate determination of various light scattering components has been developed. An original adaptation of the method is the measurement of $\text{(H}{}_{\mathrm{h}}\text{?H}{}_{\mathrm{v}}\text{)}{}_{\mathrm{90°}}\text{(H}{}_{\mathrm{v}}\text{)}{}_{\mathrm{90°}}$, the value of which is dependent only on the scattering particles shape. A few examples are presented.     

The θ-behaviour of heterogeneous macromolecules

A polymer chain consisting of N_r segments with a repulsive interaction (binary cluster integral β_r) and N_a ? N_r segments with a stronger, attractive and pairwise saturable interaction (β_a), which is at the averaged θ-point N²_rβ_r + N²_aβ_a = 0 deviations from the predictions of the two parameter theory: $\text{α}{}^2{}_{\mathrm{<mtext>R</mtext>}}\text{? 1 ～ δz}{}_{\mathrm{<mtext>r</mtext>}}\text{< 0}$ and A₂ ～ δz_r > 0 with $\text{δz}{}_{\mathrm{<mtext>r</mtext>}}\text{～ β}{}_{\mathrm{<mtext>r</mtext>}}\text{(}\text{N}{}_{\mathrm{<mtext>a</mtext>}}\text{N}{}_{\mathrm{<mtext>r</mtext>}}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. It is shown that the deviations from the universal behaviour are due to the existence of an intermediate length scale $\text{～}\text{N}{}_{\mathrm{<mtext>a</mtext>}}\text{N}{}_{\mathrm{<mtext>r</mtext>}}$.     

Stabilization effect of Co for Mo phase in CoMoAl2O3 hydrodesulfurization catalysts studied with X-Ray photoelectron spectroscopy

The promotional effects of Co in $\text{CoMo}\text{Al}{}_2\text{O}{}_3$ hydrodesulfurization (HDS) catalysts were studied by means of X-ray photoelectron spectroscopy. The higher MoO₃-content $\text{Mo}\text{Al}{}_2\text{O}{}_3$ catalysts (10 and 20 wt% MoO₃) contain mobile Mo, which migrates from the pores to the outermost surface layers of the catalysts and segregates to form less active crystalline MoS₂ during the HDS reaction, while in the case of $\text{Mo}\text{Al}{}_2\text{O}{}_3$ (5 wt% MoO₃) catalyst: no migration of Mo was observed. It is revealed that the Co in $\text{CoMo}\text{Al}{}_2\text{O}{}_3$ catalyst inhibits the migration and segregation of Mo and that it keeps Mo effective for the HDS reaction, since no surface enrichment of Mo was observed. It is concluded that stabilization of the Mo monomolecular layer is the main role of Co. The active species of Mo is suggested to have the composition of S/Mo(IV) = 1 on the basis of the sulfur contents of the catalysts under the mild HDS reaction conditions.     

Conversion of bituminous coal in COH2O systems: 3. Soluble metal catalysis

The oxyanions of the highest oxidation states of several transition metals, including W, Mo, Cr and Mn, were found to catalyse the liquefaction of Illinois No. 6 coal in $\text{CO}\text{H}{}_2\text{O}$ systems at 400°C. Unlike the high pH (s> 12) required in the base-catalysed system, the effective range for these metal-mediated conversions extend down to pH < 5.0. The benzene-soluble product was found to have a higher $\text{H}\text{C}$ ratio than the starting coal, and the metals were reduced to water-insoluble, lower oxidation states during conversion. A chain scheme is suggested as an explanation for the data.     

Determination of C4A3S in type K cement and clinker using maleic acid-methanol and ammonium chloride-water as extracting agents

This paper describes a simple chemical method for determining $\text{C}{}_4\text{A}{}_3\text{S}$ in Type K cement and clinker. The method combines two separation procedures, a maleic acid-methanol leach and an ammonium chloride-water leach. All silicates and sulfates, except $\text{C}{}_4\text{A}{}_3\text{S}$, are extracted. The remaining SO₃ in the residue which can be quantitatively determined exists only as $\text{C}{}_4\text{A}{}_3\text{S}$.     

Expansive properties of the mixture C4ASH12 − 2CS III. Effects of temperature and restraint

The effects of temperature and restraint upon the hydration and the expansion of $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}\text{? 2}\text{C}\text{S}$ mixture compacts in different contact solutions have been investigated. Temperatures above 20°C do apparently hinder the formation of an impervious felt-like layer of ettringite around the $\text{C}{}_4\text{A}\text{S}\text{H}{}_{12}$ particles, thus greatly reducing the retarding effect of the lime. An uniaxial restraint of 1 Kg/cm² is enough to reduce sensibly the expansions which remain however high (about 100%). The results can be satisfactorily interpreted by the reaction and expansion mechanism hypothesized in our previous papers.     

Nucleophilic substitution onto poly(methylmethacrylate): 4. Dilute solution properties of substituted polymethacrylates

The morphological and hydrodynamic properties of a series of homogeneous fractions of substituted poly(methylmethacrylate) (A units) bearing keto-β-functional groups (B units) of the general structureCOCH₂R, with R = SO_xCH₃ (x = 1,2) or SO₂N(CH₃)₂, were investigated by intrinsic viscosity, light scattering and partial specific volume measurements in dimethylformamide (DMF) solution at 25°C. For molar substitution degrees $\text{DS}{}_{\mathrm{m}}\text{< 0.5}$, the copolymers behave as flexible random coils. The Stockmayer-Fixman-Yamakawa analysis of the $\text{[η]-}\text{M}\text{?}{}_{\mathrm{w}}$ data leads to slightly higher unperturbed dimensions K_o and steric factor σ than those for PMMA, and to stronger chain expansion as a result of the weak hydrogen bonding between DMF and COCH₂R units and a positive X_AB interaction parameter. For $\text{DS}{}_{\mathrm{m}}\text{> 0.5}$ however, copolymers bearing COCH₂SO₂N(CH₃)₂ groups behave as worm-like chains, as derived from the Fujii-Yamakawa analysis of the $\text{[η]-}\text{M}\text{?}{}_{\mathrm{w}}\text{-}\text{v}\text{?}$ data: the persistence length increases from 380 to 570 Å within the $\text{DS}$_m range 0.57–0.75. This transition from a random coil to a worm-like chain for $\text{DS}{}_{\mathrm{m}}\text{> 0.5}$ was tentatively correlated with the accumulation of B units in sterically hindered and self-associated short blocks of average length l_B ? 1.6 which provide drastically increased rigidity to the copolymer chain.     

Generalization of correlation between polymer glass transition Tg and an e.s.r. parameter T50G

The tumbling of five nitroxide spin probes (molecular weights between 172–486 g/mol) in a standard unfractionated polyisobutylene [$\text{M}\text{?}{}_{\mathrm{v}}\text{= (1.26 ± 0.18) × 10}{}^6\text{g/mol}$] has been studied by means of the electron spin resonance (e.s.r.) technique. The temperature at which the separation of the outermost peaks of the e.s.r. spectrum is 50 G (T_50G) attained a limiting value T′_50G = 330K at probe M_W = 332 g/mol. This temperature coincided with the temperature of the loss maximum of the merged glass transition (T_g) and segmental relaxations at the corresponding frequency (3 × 10⁷ Hz). A literature survey indicated that an analogous situation exists in the case of poly(vinylidene fluoride) and polyamide-6,10 while T′_50G values of poly(2,6-dimethyl phenylene oxide) and polycarbonate are correlated only to segmental relaxations of polymer chains. It is concluded that the equation:

$\text{T}{}_{\mathrm{<mtext>50</mtext><mtext>G</mtext>}}\text{= T}{}_{\mathrm{g}}\text{[1 + (}\text{exp}\text{T}{}_{\mathrm{g}}\text{/T}{}_{\mathrm{c}}\text{)}{}^{\mathrm{?1}}\text{]}$

describes generally the temperature shift between glass transitions at low and high frequencies and can be applied to determine experimentally low frequency T_g values from T′_50G values if T_g and T < T_g relaxations (if any are present) are already merged at this temperature.     

Mechanisms and kinetics of C4AF hydration with gypsum

The mechanisms and kinetics of early stage C₄AF hydration with gypsum was studied by measuring the heat of hydration with a conduction calorimeter. The heat of the reaction was 173 cal/ g-C₄AF. The reaction equation was estimated to be

$\text{C}{}_4\text{AF}\text{+ 4}\text{CaSO}{}_4\text{·2}\text{H}{}_2\text{O}\text{+ 35}\text{1}\text{3}\text{H}{}_2\text{O}\text{→}\text{4}\text{3}\text{C}{}_3\text{(}\text{A}{}_{0.75}\text{,}\text{F}{}_{0.25}\text{)·3}\text{C}\text{S}\text{H}{}_{31}\text{+}\text{2}\text{3}\text{FH}{}_3$

The equation for rate of hydration was ζ = 0.25t as the thickness (ζ) or hydrated C₄AF increased from 0 to 0.6 μm.     

Effects of metal-support interactions on the synthesis of methanol over palladium

The synthesis of methanol and other products from CO and H₂ was studied over Pd catalysts prepared by adsorption of Pd(π-C₃H₃)₂ on MgO, ZnO, La₂O₃, γ-Al₂O₃, SiO₂, TiO₂, and ZrO₂ as well as over a SiO₂-supported Pd catalyst prepared from PdCl₂ and Pd black. Both the activity and selectivity of Pd were affected strongly by the nature of the support and the composition of the Pd precursor. The specific activity for methanol synthesis decreased in the order $\text{Pd}\text{La}{}_2\text{O}{}_3$ ? $\text{Pd}\text{SiO}{}_2$ [derived from PdCl₂] > $\text{Pd}\text{ZrO}{}_2$ > $\text{Pd}\text{ZnO}\text{≈}\text{Pd}\text{MgO}$ > PdTiO₂ > $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{≈}\text{Pd}\text{SiO}{}_2$ [derived from Pd(π-C₃H₅)₂] ? Pd black, while the specific activity for hydrocarbon synthesis decreased in the order $\text{Pd}\text{TiO}{}_2\text{?}\text{Pd}\text{ZrO}{}_2$ > $\text{Pd}\text{La}{}_2\text{O}{}_3$ > $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{≈}\text{Pd}\text{SiO}{}_2$ [derived from PdCl₂] ? $\text{Pd}\text{SiO}{}_2$ [derived from Pd(π-C₃3H₅)₂] ≈ Pd black ? $\text{Pd}\text{MgO}\text{?}\text{Pd}\text{ZnO}$. Dimethyl ether production was observed over four of the catalysts and the activity for formation of this product decreased in the order $\text{Pd}\text{Al}{}_2\text{O}{}_3\text{?}\text{Pd}\text{TiO}{}_2\text{?}\text{Pd}\text{MgO}\text{≈}\text{Pd}\text{ZrO}{}_2$. The effects of support composition on the catalytic properties of Pd are discussed in the light of current ideas concerning metal-support interactions and the acid-base properties of the support.