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.     

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.     

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).     

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.     

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.     

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.     

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.     

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.     

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.     

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).     

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.     

Poly(N-acryloyl-l-prolyl morpholine): a g.p.c. packing exhibiting novel temperature dependence in solute distribution coefficients

The synthesis of $\text{poly}\text{(N-}\text{acryloyl-}\text{l}\text{-prolyl morpholine}\text{)}$, a new bead packing for the g.p.c. of small molecules, is described. Characteristic g.p.c. behaviour and high column efficiencies were observed in water and benzyl alcohol. Novel, reversible temperature variations in solute Wheaton and Bauman distribution coefficients were observed. This effect, which is most marked in water, is caused by thermo-reversible changes in network pore size distribution in the bead packing.     

Critical chain length for the formation of the α-helix in the solid state: synthesis and conformation of sequential oligopeptides and polypeptide having l-leucyl-l-leucylglycine sequence

Synthesis and conformation in the solid state of a novel series of sequential oligopeptides and polypeptides having the sequence of l-leucyl-l-leucylglycine have been studied to demonstrate critical chain length for the formation of the α-helix of the peptide. The far infra-red spectra and X-ray powder diffraction patterns suggest that the dodeca and lower peptides take the β-structure and the pentadeca and higher peptides form the α-helix in the solid state. This result leads to the conclusion that the formation of the α-helix of this peptide system begins at the pentadecapeptide. This is consistent with the result of our earlier study on the sequential oligopeptide Nps-(l-Ala-l-Leu-Gly)_n-OEt.     

Thermal motion of α-helical molecules in highly crystalline poly(γ-methyl l-glutamate) films

Solid films of poly (γ-methyl l-glutamate) were prepared by casting solutions in chloroform, dichloromethane, and m-cresol. The mode and amplitude of thermal molecular fluctuations in the crystalline phase were studied by X-ray diffraction. All the films contain α-helical molecules and have hexagonal crystal structures, but differ from each other in their crystallinity and crystallite size. The calculated molecular fluctuation amplitudes also differ considerably. Below a threshold temperature in the range 140°–190°C (different for each sample), the segmental molecular motion is composed of translation along the chain axes coupled with rotation about the axes. At higher temperatures, the structure changes thermoreversibly into a modification, in which a screw-type motion along the α-helix axis is predominant.     

Conformations of macromolecular sequential polypeptides in solution: 2. Sequential polypeptides containing both d- and l-residues

The conformations adopted in solution by two series of macromolecular sequential polypeptides containing up to four γ-benzyl-d-glutamyl and one γ-benzyl-l-glutamyl or l-leucyl residue in the repeating unit have been studied by spectroscopic methods (i.r., o.r.d., n.m.r.). The nature of the ordered conformations encountered is discussed; it is suggested that they are a distorted form of the α-helix and special types of cross β-structure.     

Conformational studies of poly(N-methyl-l-alanine) by n.m.r. spectroscopy

Nuclear magnetic resonance (n.m.r.) and circular dichroism of $\text{poly}\text{(N-}\text{methyl-}\text{l}\text{-alanine}\text{)}$ in methylene $\text{chloride}\text{-d}{}_2\text{dichloroacetic acid}$ were investigated. In methylene chloride-d₂$\text{poly}\text{(N-}\text{methyl-}\text{l}\text{-alanine}\text{)}$ was found to consist of nearly all-trans amide bonds and assume a stable secondary structure. Trace amounts of cis amide bonds were also present. The addition of dichloroacetic acid destroyed the secondary structure and induced a drastic change of the n.m.r. spectrum, which was similar to that observed with the monomeric amide, $\text{N-}\text{acetyl}\text{-N-}\text{methyl-}\text{l}\text{-alanine}$ dimethylamide. In comparison of the polymer with the monomeric amide, it was concluded that the transition of $\text{poly}\text{(N-}\text{methyl-}\text{l}\text{-alanine}\text{)}$ was caused by the isomerization of amide bonds. The complex n.m.r. spectrum was interpreted in terms of the distribution along the polymer chain of various non-planar amide links as well as planar cis and trans amide links. The difference of the mechanism of conformational transition between poly(amino acid) and poly(imino acid) is also discussed.     

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.     

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.     

Electrochemical reduction of polymeric carbon

It was found that the electrochemical reduction of poly (tetrafluoroethylene) with lithium amalgam leading to the mixture of polymeric carbon and lithium fluoride as solid product is followed by a consecutive electrochemical reaction via a polymeric anion radical, [$\text{(}\text{?}$C_n$\text{)}\text{?}$^?]_m. The value of n was determined as 4.75 and was found to be independent of the reaction conditions. The charge of this radical is during the reaction neutralised with Li⁺ ions diffusing through the solid phase to form a chemical compound $\text{(}\text{?}$C_nLi$\text{)}\text{?}$_m whose CLi bonds have a localized character. Therefore, this compound does not evolve hydrogen in contact with water as the intercalation compounds C_nLi, but hydrolyses to a solid hydrocarbon $\text{(}\text{?}$C_nH$\text{)}\text{?}$_m.     

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 $\text{C}{}_4\text{A}{}_3\text{S}$.