Optical Rotatory Dispersion Measurements Research Articles

Birefringence of a polymeric cholesteric liquid crystal measured by refractometry

AbstractThe Abbé refractometer provides a convenient way to measure the refractive indices and birefringence of polymeric liquid crystalline solutions. The cholesteric mesophase formed by (acetoxypropyl) cellulose and its solutions in dibutyl phthalate were examined at 26°C and 50°C. The measured refractive indices were dependent on the direction of shear when the polymer was applied to the refractometer plates. The initial shear‐induced nematic‐like order relaxed slowly to the equilibrium planar cholesteric structure. The refractive index for the isotropic solutions and the two refractive indices for the anisotropic solutions all varied linearly with polymer concentration, and the width of the intermediate two‐phase region was readily determined. The changes in refractive index with polymer concentration and with orientation on the refractometer plate were rationalized with a simple model of the cellulosic mesophase, and an order parameter of 0.7 was estimated. The layer birefringence calculated from optical rotatory dispersion measurements of the cholesteric reflection band intensity was in good agreement with the birefringence measurements.

New polarization-modulation spectrometer for simultaneous circular dichroism and optical rotary dispersion measurements (I): Instrument design, analysis, and evaluation

The Mueller matrix approach is used for designing, analyzing, and evaluating a new polarization-modulation spectrometer for simultaneous measurements of circular dichroism (CD) and optical rotatory dispersion (ORD). The same approach is applied to commercial CD spectropolarimeters for the evaluation of their performance in order to clarify our new spectrometer. On the basis of the results obtained, our JASCO J-500 CD spectropolarimeter was converted into the new spectrometer. Preliminary experiments indicate that CD and ORD can be measured simultaneously above 400 nm. It is also shown that this new spectrometer can be used for measuring linear dichroism and linear birefringence simultaneously.

Inhibition of β-lactamase-I by 6-β-sulfonamidopenicillanic acid sulfones: Evidence for conformational change accompanying the inhibition process

A number of 6-β-sulfonamidopenicillanic acid sulfones were examined for their ability to inhibit Bacillus cereus 569 H β-lactamase I. Among these, 6-β-trifluoromethane sulfonamidopenicillanic acid sulfone was found to be the most potent inhibitor, effecting rapid and irreversible inactivation of the enzyme. Optical rotatory dispersion and differential scanning calorimetry were employed to probe the possible conformational changes accompanying the inactivation of B. cereus 569 H β-lactamase 1 by 6-β-trifluoromethane sulfonamidopenicillanic acid sulfone. Optical rotatory dispersion measurements indicated the presence of approximately 29 and 17% helical structure in the native and inactivated enzyme, respectively. Differential scanning calorimetry determinations revealed that the inactivated enzyme was less thermostable than the native β-lactamase. The temperatures of maximum heat absorption were 48.4(±0.5) and 57.4(±0.1)°C for the inactivated and the native enzyme, respectively. Extensive conformational changes accompanying the interaction of the enzyme with the inhibitor may be responsible for the irreversible loss in the catalytic activity.

Effect of temperature on the conformation of soybean glycinin in 8 M urea or 6 M guanidine hydrochloride solution

The effect of temp. on soybean glycinin in 8M urea or 6M guanidine hydrochloride solution was studied by circular dichroism and optical rotatory dispersion measurements. At room temp. the protein assumes an unordered conformation in the presence of the denaturant. With increase in temp., mean residue ellipticity in the range 250-210 nm assumes more negative values, suggesting formation of ordered conformations at higher temperatures.

Optical rotatory dispersion measurements in the third cholesteric blue phase

The results of optical rotatory dispersion (ORD) measurements in the third cholesteric blue phase (BP III) are reported for both pure compounds and mixtures. The spectra possess weak, broad, anomalous regions at short wavelength, the sign and wavelength dependence of which follows the sense and pitch of the cholesteric helix. A temperature-pitch phase diagram for the alkyl esters of cholesterol is presented which, together with the calorimetric measurements of others, indicates that the BP III---isotropic transition is in fact the liquid crystal to isotropic liquid transition. In addition, the ORD measurements reported here provide evidence for a BP III structure which lacks longrange periodic order.

Induced distant cotton effects in complexes of Cr(III) with l-malic acid and heterocyclic ligands

Complexes of Cr(III) with l-malic acid and aromatic bases [2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen)] and different counter ions were synthesized. Analyses and experiments carried out indicate that no more than one l-malate ligand enters the coordination sphere and that it behaves as a bidentate ligand. Optical rotatory dispersion and circular dichroism measurements always show a vicinal effect in the d-d transitions, and it is proposed that chromium adopts the lowest possible microsymmetry in all the complexes: induction of optical activity in the π-π* transitions in the UV region is not always present.

Macrozin, a Novel Storage Globulin From Seeds of Macrozamia communis L. Johnson

The isolation, characterization and amino acid composition are reported for macrozin, the major storage globulin found in seeds of Macrozamia communis. Electrophoresis of macrozin on cellulose acetate membranes at neutral pH resulted in a single broad band indicating limited charge heterogeneity. Isoelectric focusing under dissociating and reducing conditions showed this globulin to be composed of a family of polypeptide chains with apparent isoelectric points in the range pH 6.0-7.5. Sedimentation equilibrium studies showed that the main component purified by gel filtration in aqueous buffers at neutral pH has a molecular weight of 260 000 and a sedimentation coefficient S020.w = 10.9 S. This component dissociates in 8 M urea to yield subunits of molecular weight 126 000. Each subunit is composed of disulfide-bonded polypeptide chains of approximate molecular weight 44 000. The apparent molecular weights for the macrozin subunit and its constituent polypeptides were 130 000 and 46 000 from dodecyl sulfate-polyacrylamide gradient gel electrophoresis. The dimeric nature of the main oligomer in aqueous solution was confirmed by crosslinking the subunits with dithiobis(succinimidylpropionate); the presence of three polypeptide chains per subunit is inferred from the molecular weights. Optical rotatory dispersion and circular dichroism measurements suggest that macrozin is devoid of α-helix in its native conformation, but contains some 25% α-helix after incubation with sodium dodecyl sulfate.

Physicochemical and structural studies of phaseolin from French bean seed

Phaseolin, the main reserve globulin in seeds of the French bean (Phaseolus vulgaris L.), has been purified for sedimentation equilibrium analysis. The major protomer at neutral pH has a molecular weight of 150 000±5 000 which associates to a tetrameric form of molecular weight 596 000±20 000 at pH 4.5. The trimeric nature of the protomer is apparent from protein crosslinking experiments. Initial structural studies were made using optical rotatory dispersion and circular dichroism measurements. Two different crystal forms of the protein have been grown and characterised by X-ray diffraction; one of these forms appears suitable for high resolution X-ray analysis.

Isolation and characterization of the 7S protein from glanded cottonseed (Gossypium herbacium)

The major protein from glanded cottonseed has been isolated in a homogeneous form. Its S20 w value at 1 protein concentration is 6S in 1 M NaCl solution. It contains 1 carbohydrate and is free from phosphorus, gossypol (bound or free) and nucleic acid impurities. It consists of atleast seven non-identical subunits. The protein has an ultraviolet absorption maximum at 278 nm and fluorescence excitation and emission maxima at 280 nm and 325 nm respectively. Optical rotatory dispersion and circular dichroism measurements indicate that the protein consists predominantly of Β-structure and random coil. The observed near-ultraviolet circular dichroic bands can be attributed to tyrosine, phenylalanine and tryptophan residues of the protein.

Pretransitional effects in the isotropic phase of a lyotropic polymer liquid crystal

AbstractConsolidation of chiral orientational ordering in concentrated solutions of poly(benzylglutamates) has been investigated by polarization microscopy, measurements of birefringence and optical rotatory dispersion. A pretransitional region was examined where the temperature and concentration of polymer are held just below critical conditions for phase separation of anisotropic, liquid crystal spherulites. Optical rotations observed in this visually isotropic region are considerably in excess of those found in dilute solution of the polymer and exhibit a strong temperature dependence. This critical enhancement of optical activity is attributable to short‐range chiral ordering of the long axes of macromolecules in the isotropic phase.

Subunit structure and dissociation of Callinectes sapidus hemocyanin

The hemocyanin of the blue crab, Callinectes sapidus has two major components sedimenting with approximate sedimentation coefficients of 17 S and 25 S. Molecular weight data based on light scattering and sedimentation equilibrium measurements at pH 7.8 suggest that the two components have molecular weights of approximately 450 000 and 900 000 in the presence of stabilizing Ca 2+. In the absence of Ca 2+, the molecular weights are found to be about 5% lower, suggesting some dissociation of the hemocyanin components. Circular dichroism and optical rotatory dispersion measurements in the far-ultraviolet region gave nearly identical spectra for the two components. Based on the reference parameters of Chen et al. (Chen, Y.H., Yang, J.T. and Martinez, H.M. (1972) Biochemistry 11, 4120—4131 and Chen, Y.H., Yang, J.T. and Chan, K.H. (1974) Biochemistry 13, 3350–3359), estimates of 16–20% α-helix, 40–60% β-structure, and 30–40% random organization were obtained for the two hemocyanin components. Exposure to 6 M Gdn HCl gave light scattering molecular weights of approx. 68 000 and 77 000, which is close to one-sixth of the molecular weight of the 17 S component. These results support the view that the two components of C. sapidus hemocyanin share the hexameric and dodecameric organization common to arthropod hemocyanins. The salts of the Hofmeister series and the ureas are found to dissociate the dodecameric component with the former exhibiting the usual order of effectiveness of NaCl, NaBr, NaI, and NaClO 4 dissociation, while the ureas show an inverse order of decreasing effectiveness in going from urea to methyl-, ethyl- and propylurea. This suggests that polar and ionic interactions are relatively more important than hydrophobic interactions for the stabilization of the dodecameric form of C. sapidus hemocyanin. The dissociation behavior of the 17 S hexameric species by GdnHCl in the 0–1.5 M concentration region (where essentially no denaturation occurs), based on light scattering molecular-weight measurements, is satisfactorily accounted for by equations describing the dissociation of hexamers to monomers.

Physicochemical and Ultrastructural Studies on Glycogenosomes in Newborn Rat Hepatocytes

In the newborn rat liver, glycogenosomes appeared at about 6 hours after birth and gradually increased in number, despite high activity of lysosomal acid alpha-glucosidase. The glycogenosomes then disappeared completely with 2 days after birth. Glycogen extracted from fetal rat liver differed in molecular structure from that of adult rat liver. In measurements of optical rotatory dispersion (ORD) and circular dichroism (CD) absorption spectra, fetal-type glycogen showed the Cotton effect whereas the adult rat liver glycogen did not. The degree of branching and S-values of the two glycogens were also different. With the disappearance of glycogenosomes, fetal-type glycogen disappeared completely, and adult-type glycogen then appeared strongly. This was demonstrated in the intracytoplasmic matrix by electron microscopy. The present experiments indicate that glycogenosomes may be formed even under conditions of high acid alpha-glucosidase, and that autophagy of glycogen macromolecules in the lysosomal system is closely related to different structural features of fetal-type glycogen in the neonatal period.

Solution Properties of Synthetic Polypeptides. XXII. Helix–Coil Transition of Poly(Nγ-carbobenzoxy-L-α,γ-diaminobutyric acid)

The helix–coil transition of poly(Nγ-carbobenzoxy-L-α,γ-diaminobutyric acid) (PCLB) in mixtures of dichloroacetic acid (DCA) and 1,2-dichloroethane (EDC) was studied by optical rotatory dispersion (ORD) measurement. At DCA contents between 55 and 58 vol%, the Moffitt parameter b0 increased with increasing temperature, passed through a maximum, and gradually decreased above 40°C. This result indicates that in mixtures of DCA and EDC of appropriate compositions, PCLB undergoes a dual transition: one which is normal (helix to coil) at lower temperatures and one which is inverse (coil to helix) at higher temperatures. The ORD data were analyzed theoretically to evaluate the equilibrium constant s for the helix formation as a function of temperature T and solvent composition. A plot of In s at a fixed solvent composition against 1/T followed a curve convex downward, corresponding to the dual transition. The conformation of PCLB in a helicogenic solvent, dimethyl sulfoxide, was investigated by light scattering and viscometry, and it was found from the observed relation between the mean-square radius of gyration ‹S2› and molecular weight that PCLB takes on the form of an interrupted helix in this solvent. The molecular weight dependence of ‹S2› and intrinsic viscosity indicates that the helix of PCLB is as stable as those of poly(Nε-carbobenzoxy-L-lysine) and poly(Nδ-carbobenzoxy-L-ornithine), but less stable than that of poly(γ-benzyl L-glutamate).

Physicochemical Studies of Conglutin γ, a Storage Globulin From Seeds of Lupinus angustifolius

Physicochemical studies are reported for conglutin �, the minor globulin isolated from seeds of L. angustifolius cv. Uniwhite. Isoelectric focusing of the native protein in polyacrylamide gel slabs resolved major and minor broad bands near pH 8.0 and 7.8 respectively. Following reduction of disulfide bonds with β-mercaptoethanol in 8 M urea, the smaller polypeptide chain of known sequence focused near pH 6.9 while the larger chain focused near pH 8.0. Sedimentation equilibrium studies showed that the major component in aqueous buffers at neutral pH is a hexamer of molecular weight 280 000 which dissociates to the monomer of molecular weight 47 000 at pH 4.8. The sequence molecular weight of the small subunit polypeptide is 16 517 [Elleman, T.C. (1977). Aust. J. Biol. Sci. 30, 33-45]. The molecular weights determined for the larger chain by sedimentation equilibrium or column chromatography in 6 M guanidine hydrochloride, and by dodecyl sulfate-polyacrylamide gel electrophoresis, were in the range 28 000-30 000. Optical rotatory dispersion and circular dichroism measurements have been used to establish the approximate proportions of α-helix (15%), β-structure (35%), β-turns (18%) and unordered regions (32%) in the native protein. The denaturation curve for guanidine hydrochloride and the proportions of α-helix (50%), β-turns (18%) and unordered regions (32%) in 80 % trifluoroethanol have been determined.

Conformational Studies of Poly(β-phenethyl L-aspartate)

Poly(β-phenethyl L-aspartate) was synthesized and its conformational transitions in chloroform–dichloroacetic acid and chloroform–trifluoroacetic acid mixed solvents were examined by optical rotatory dispersion, circular dichroism and viscosity measurements. Poly(β-phenethyl L-aspartate), having a right-handed α-helical form in chloroform, undergoes a transition to a left-handed α-helical form by the addition of 2.0% dichloroacetic acid at 21°C. In the range of dichloroacetic acid content between 1.2% and 2.0%, the polymer exhibits a thermally-induced inversion of the helix sense from the right-handed to the left-handed. The transition temperature is dependent on the solvent composition. Furthermore, in the chloroform–trifluoroacetic acid system, the polymer exhibits both the helix-sense inversion and the helix–coil transition when the composition of the mixed solvent is varied. The thermally- and acid-induced inversions of the helix sense are discussed in terms of the change in the side chain conformation.

Chemische synthese verzweigter Polysaccharide, 8. Vergleichende struckturuntersuchungen an amylose‐ und Cellulosederivaten mit verschiedenen Substituenten an C‐6 durch optische Rotationsdispersion und circular‐dichroismus

AbstractCarbanilated and tritylated derivatives of amylose and cellulose previously studied by light scattering were further characterized by measurement of optical rotatory dispersion (ORD) and circular dichroism (CD). No anomalous ORD and only a weak CD was found for 6‐tritylamylose in 1,4‐dioxane, indicating a widely unordered structure which is in accordance with the low viscosity of the compound. In comparison with the other carbanilated derivatives having substituents in C‐6 position, i.e. trityl‐, carbanilyl‐ or glucosyl groups, 2,3‐dicarbanilylamylose is distinguished by an especially high Cotton effect. This result suggests a helical chain,— clearly visible by excition splitting—, that may adopt a more regular orientation in case of free C‐6 hydroxyl groups, whereas trityl‐, carbanilyl‐, and glucosyl groups almost equally will contribute to a lower state of orientation. Conversely in the cellulose derivatives a clear steric dependence on the size of the C‐6 substituent was found. The increase of the Cotton effect observed for the bulky trityl group may arise from the β(1 → 4) linkage that causes an alternating or syndiotactic like structure in cellulose, which is more sensitive to restrictions of the free rotation due to steric effect. In addition, viscosity and optical rotation in NMP and 1,4‐dioxane were measured in the range of 20 to 70°C. An unusual behaviour is observed for 6‐trityl‐2,3‐dicarbanilylamylose in NMP indicating a conformation transition near 45°C, and is discussed in connection with the findings from light scattering measurements.

Radical copolymerization of optically active l‐menthyl vinyl ether with maleic anhydride, dimethyl maleate, and dimethyl fumarate

AbstractThe copolymerizations of l‐menthyl vinyl ether (l‐MVE) with the monomers, that is, maleic anhydride (MAn), dimethyl maleate (DMM), and dimethyl fumarate (DMFu), were undertaken to obtain optically active copolymers. The optically active l‐menthyl group in the side chain of copolymers was removed by the ether cleavage reaction with dry‐hydrogen bromide gas. The ethercloven copolymers were still optically active. Hence it was concluded that asymmetric carbon atoms were introduced into the copolymer main chain, the reason given being that l‐MVE and comonomers (MAn, DMM, and DMFu) made the stereoselective charge‐transfer complex one another and copolymerized stereospecifically. From the results of the measurements of optical rotatory dispersion (ORD) and circular dichroism (CD) for copolymers before and after the ether cleavage reaction, the mode of bond opening for α,β‐substituted monomers (MAn, DMM, and DMFu) was discussed and the microstructures of copolymers were prepared.

Evidence for Polymorphism within the So-called “Blue Phase” of Cholesteric Esters. II. Selective Reflection and Optical Rotatory Dispersion

Abstract In cholesteryl nonanoate the existence of two polymorphic forms of the so-called “blue phase” has been evidenced by selective reflection and optical rotatory dispersion measurements. The spectroscopic results indicate a discontinuous transition between the two phases

Poly (γ-benzyl-L-glutamate) Liquid Crystals in Benzene

Abstract Contrary to reports that the synthetic polypeptide, pol(γ-benzyl-L-glutamate), adopts a smectic molecular organization in benzene solution we find this lyotropic system to be a cholesteric liquid crystal. Direct optical and optical rotatory dispersion measurements are reported that support this conclusion. The influence of a magnetic field and small amounts of halogenated organic acids on the cholesteric structure was also examined.

Conformational Induction in Block Copolypeptide of γ-Benzyl L-Glutamate and ε-Carbobenzoxy L-Lysine

Conformations of triblock copolypeptide [Glu(OBzl)]m—[Lys(Cbz)]n—[Glu(OBzl)]m in m-cresol and in mixtures of dichloroacetic acid (DCA) and 1, 2-dichloroethane (EDC) were studied by optical rotatory dispersion measurements. It was found that the polypeptide was essentially helical in m-cresol, while it underwent a conformational transition from random coil to helix with raising temperature in mixtures of DCA and EDC of appropriate compositions. In order to elucidate the correlation between these transition behaviors of the copolypeptide and those of the constituent homopolypeptides, the Zimm–Bragg–Nagai formalism of helix-coil transition in homopolypeptide has been extended to triblock copolypeptides. The helical fraction is expressed as a function of the transition parameters s and σ of the two residues and the degree of polymerization of each block. The helix formation in m-cresol can be reasonably interpreted by this theory if s and σ are given experimental values of the corresponding homopolypeptides. In mixtures of DCA and EDC, however, the observed helical fraction was always larger than the theoretical value computed by using the homopolypeptide parameters. The copolymer data and the homopolymer data can be explained consistently by this theory if the helical conformation is assumed to be stabilized at each of the block boundaries.