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.     

Studies of polymers and copolymers of O,O′-dicarbobenzoxy-l-β-3,4-dihydroxyphenyl-l-alanine with γ-benzyl-l- and d-glutamates

The synthesis of ten different copolymers of $\text{O,O′-}\text{dicarbobenzoxy-}\text{l}\text{-β-3,4,-}\text{dihydroxyphenyl}\text{-α-}\text{alanine}$ ($\text{O,O′-}\text{dicarbobenzoxy-}\text{l}\text{-Dopa}$) and γ-benzyl-l- and d-glutamates with degree of polymerization of 40–270 is described. It has been concluded that $\text{poly}\text{(O,O′-}\text{dicarbobenzoxy-}\text{l}\text{-Dopa}\text{)}$ and poly(γ-benzyl-l-glutamate) exist as helices with the opposite sense of twist in dioxane on the basis of the following observations. The copolymers of $\text{O,O′-}\text{dicarbobenzoxy-}\text{l}\text{-Dopa}$ with γ-benzyl-l-glutamate show a linear variation of circular dichroism properties with composition in methylene dichloride, whereas the copolymers do not in dioxane. The results for the copolymers with γ-benzyl-d-glutamate are the reverse in dioxane and methylene dichloride.     

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.     

Synthesis and conformational study of poly(l-β-3,4-dihydroxyphenyl-α-alanine)

High molecular weight poly(l-β-3,4-dihydroxyphenyl-α-alanine) has been synthesized. Both optical rotatory dispersion and circular dichroism spectra of the polypeptide are anomalous and give little information about its conformation. From the total results obtained by a study of the optical rotation, nuclear magnetic resonance and infra-red absorption, poly(l-β-3,4-dihydroxyphenyl-α-alanine) is most probably right-handed helical in trimethyl phosphate, methanol or water/trimethyl phosphate ($\text{1:1}\text{v}\text{v}$) mixed solvents below pH 10.4. It is in the random coil structure in dimethyl sulphoxide or water/trimethyl phosphate mixed solvents above pH 11. The transition midpoint is pH 10.6 in water/trimethyl phosphate mixed solvents. The results were compared with those of poly(l-tyrosine).     

Synthesis and conformational studies of polymers and copolymers of O,O′-dimethyl-l-β-3,4-dihydroxyphenyl-α-alanine with γ-benzyl-l-glutamate

Eight different copolymers of $\text{O,O′-}\text{dimethyl-}\text{l}\text{-β-3,4-}\text{dihydroxyphenyl}\text{-α-}\text{alanine}$ ($\text{O,O′-}\text{dimethyl-}\text{l}\text{-}\text{Dopa}$) and γ-benzyl-l-glutamate with degrees of polymerization of 320-80 have been synthesized by the N-carboxyanhydride method. From the results obtained by a study of the optical rotatory dispersion and circular dichroism for the copolymer series, the conformation of $\text{poly}\text{(O,O′-}\text{dimethyl-}\text{l}\text{-Dopa}\text{)}$ is a right-handed helix in helicogenic solvents such as chloroform, dioxane or 2-chloroethanol. Copolymers containing less than 50 mol % glutamate show a circular dichroism peak at 285 nm suggesting stacking of aromatic groups in the side chain. $\text{Poly}\text{(O,O′-}\text{dimethyl-}\text{l}\text{-Dopa}\text{)}$ is in the random coil structure in trifluoroacetic acid or hexafluoroacetone. The results were compared with those of $\text{poly}\text{(O,O′-}\text{dicarbobenzoxy-}\text{l}\text{-Dopa}\text{)}$ and poly(l-Dopa).     

Monitoring oil shale retorts by off-gas alkenealkane ratios

Data from 125 kg and 6000 kg oil shale pilot retorts indicate that off-gas ethene/ethane and $\text{propene}\text{propane}$ ratios are useful for monitoring retort performance. Information supplied by these ratios may be particularly valuable for in situ retorts. Since response time is short, the ratios may be useful for control as well as diagnosis of retort operation. The pilot retort data show that, for a smoothly operating combustion retort, the ratios provide an estimate of the effective shale heating rate. Rough operation, indicated by wide fluctuations in peak temperature, is reflected by fluctuations in the ratios. Particularly high ratios indicate exposure of oil to excessive temperature and/or oxygen with resultant loss of oil yield. A relation between elevated ratios and oil loss via conversion to gaseous hydrocarbons is demonstrated for retorting of shale blocks immersed in a bed of smaller shale particles. Chemical interpretation of the data is made by comparison with the thermal cracking of straight-chain hexadecane and pyrolysis of polyethylene. A free radical, chain reaction scheme is proposed. The dependence of $\text{alkene}\text{alkane}$ values on heating rate is attributed to competition between carboncarbon bond cleavage versus hydrogen atom-transfer processes. The contribution of oxidation reactions to elevated $\text{alkene}\text{alkane}$ values is also discussed.     

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.     

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.     

Syntheses and conformational studies of poly(γ-N-alkyl-l-α,γ-diaminobutyric acids) and their carbobenzoxy derivatives

Three types of high molecular weight $\text{poly}\text{(γ-N-}\text{methyl}\text{, γ-N-}\text{carbobenzoxy-}\text{l}\text{-α, γ-}\text{diaminobutyric acid}\text{)}$, $\text{poly}\text{(γ-N-}\text{ethyl}\text{, γ-N-}\text{carbobenzoxy-}\text{l}\text{-α, γ-}\text{diaminobutyric acid}\text{)}$, and $\text{poly}\text{(γ-N-}\text{benzyl}\text{, γ-N-}\text{carbobenzoxy-}\text{l}\text{-α, γ-}\text{diaminobutyric acid}\text{)}$ were synthesized by the N-carboxyanhydride method. The helix-coil transition of these $\text{poly}\text{(γ-N-}\text{alkyl}\text{, γ-N-}\text{carbobenzoxy-}\text{l}\text{-α, γ-}\text{diaminobutyric acids}\text{)}$ in chloroform-dichloroacetic acid was followed by optical rotation measurements. The introduction of a methyl, an ethyl, or a benzyl group to the side chain of the carbobenzoxylated derivative of poly(l-α, γ-diaminobutyric acid) appeared to weaken the helical conformation at 25°C and altered the direction of the temperature induced helix-coil transition from a ‘normal’ to an ‘inverse’. For water-soluble $\text{poly}\text{(γ-N-}\text{alkyl-}\text{l}\text{-α, γ-}\text{diaminobutyric acids}\text{)}$, the coil-to-helix transition was little observed even when the polypeptides were uncharged at pH 12. At sufficiently high methanol concentration, however, the polypeptides underwent a complete transition from the random coil to the α-helical conformation even at pH 3.     

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.     

Reactivity ratios for the copolymerization systems styrenep-ethoxystyrene and methyl methacrylatep-ethoxystyrene

Reactivity ratios for the systems $\text{styrene}\text{p-}\text{ethoxystyrene}$ and methyl $\text{methacrylate}\text{p-}\text{ethoxystyrene}$ have been determined at 50°C. The values found by the computational method of Tidwell and Mortimer were 1.08 and 0.74 for the first system, and 0.37 and 0.24 for the second; the 90% joint confidence limit envelopes were also calculated.     

Preparation and properties of poly(Nε,Nε-dicarboxymethyl-l-lysine)

A new ampholytic homopolypeptide, $\text{poly}\text{(N}{}^{\mathrm{\epsilon }}\text{,N}{}^{\mathrm{\epsilon }}\text{-}\text{dicarboxy-methyl-}\text{l}\text{-lysine}\text{)}$, which has one tertiary amino and two carboxyl groups in the side chain has been derived from a hydrochloride salt of poly(L-lysine). The polymer in aqueous solution seems to be in the coil form with locally extended structure (LES) at neutral pH. In both the acidic and alkaline regions, the molar ellipticity of the polymer changes as a result of change in net charge on the side chain. The conformational changes may be from the coil with LES to other coiled forms. 5–7 M NaClO₄ and 80% aqueous methanol induce the α-helix in the polymer at neutral pH. Divalent cations, Cu²⁺ and Ca²⁺, do not induce any remarkably ordered structures such as α-helix or β-structure in the polymer in aqueous solution at any pH. Ultraviolet absorption studies show an absorption peak of the polymer-Cu²⁺ complex near 240 nm. Dependence of the peak intensity on pH at various q values ($\text{q =}\text{[}\text{Cu}{}^{\mathrm{2+}}\text{]}\text{[}\text{residue}\text{]}$) indicates the two steps of the complex formation. At q less than 0.64, the formation is described only with the first step. An average coordination number for Cu²⁺ at the first step was calculated to be about 2 by the method of Mandel and Leyte. The association constant of Cu²⁺ with the residue at the step was determined from the absorption data to be far smaller than that for the Cu²⁺-EDTA complex. The second step of the formation occurs in the case of large q but the absorption data for the second step cannot be obtained exactly due to precipitation.     

Atomic HC ratios and the generation of oil from coals and kerogens

The amount of oil that can be generated from a kerogen under natural conditions is an important parameter in source rock assessment. Similarly, the quantity of oil able to be formed from a coal or kerogen during much more rapid pyrolysis is a crucial factor in oil shale and coal conversion studies. An approximate relation based on atomic ratios is derived for slow geological heating but is also valuable for comparing samples under other conditions. The percentage of oil, on a weight basis, that can be generated is given by: $\text{Oil}\text{= 66.7}\text{H}\text{C}\text{? 57.0}\text{O}\text{C}\text{?33.3}$. Typical results for twelve Australian coals and twelve world oil shales are given as examples.     

N.m.r. of random copolymers of benzyl-l-aspartate with o- and p-nitrobenzyl-l-aspartate

The p- and o-substitution of the benzene ring of poly(β-benzyl-l-aspartate) (PBLA) with a nitro group induces a reversal of the helix sense in the PBLA. Therefore, two series of random copolymers of benzyl-l-aspartate with o- and p-nitrobenzyl-^l-aspartate were prepared in order to study the left-handed→right-handed α-helix transition. The conformational behaviour has been studied by nuclear magnetic resonance spectroscopy and the left-handed→right-handed α-helix transition has been observed from the α-CH shift, from CDCl₃ solutions. Moreover, for each copolymer, the α-helix→coil transition was also studied in $\text{CDCl}{}_3\text{trifluoroacetic acid}$ mixtures. In this case, the transition can be observed from the α-CH shift and from the splitting of the β-CH₂ resonance in the α-helical form also.     

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 $\text{Pd}\text{SiO}{}_2$.     

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.     

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.     

Synthesis,characterization, and conformational studies of N-t-butyloxycarbonyl-oligo-l-leucine methyl esters

The conformational properties of $\text{N-}\text{t-butyloxycarbonyl-oligo-}\text{l}\text{-leucine}$ methyl esters were examined in anhydrous and aqueous organic solvents. This study demonstrates that these oligomers may exist in predominantly β-associated or unordered conformations depending upon the solvent. The β-structure, which appears at the pentamer in ethylene glycol (EG) and trifluoroethanol (TFE)-water (20:80 v/v), could be disrupted by dilution or by increasing the temperature. The stability of the β-structures was found to be lower than those formed by oligopeptides derived from l-isoleucine and l-valine and comparable to those formed by oligo-l-methionines.     

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.     

Linear oligopeptides: 53. Conformations of poly(ethylene glycol)-bound alanine and valine homo-l-oligopeptides in alcoholic solution

The conformational properties of poly(ethylene glycol)-bound $\text{N-}\text{t-butyloxycarbonyl-homo-oligo}\text{-}\text{l}\text{-}\text{alanines}$ and l-valines to Ala₈ and Val₈ have been examined in alcoholic solution using circular dichroism. This study demonstrates that the l-alanine peptides may exist in right-handed α helical, β and statistical coil conformations depending upon chain length, solvent polarity, temperature and presence of the N-blocking group. In addition, the β structures formed by the oligo-l-valines are more stable than those formed by the corresponding l-alanine oligopeptides. The effect of mono- and bifunctional poly(ethylene glycol) upon oligopeptide conformation is also discussed. It was concluded that poly(ethylene glycol)-bound peptides represent a valuable tool for delineating the intrinsic conformational preferences of oligopeptides in alcoholic solution.