Circular dichroism of some steroid alkaloids

Summary 1. The trans-linkage of rings A/B in compounds (I-III) and of rings B/C and E/F in veralodine and the equatorial orientation of the OH group at C₃ in isogermine has been confirmed by CD spectroscopy.2. A relationship has been established between the nature of the substituents and the configurations at C₂₀ and the sign of the CE in the 200 nm region for compounds (I-III).3. The 22R configuration has been established for veralomidine.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 630–633, September–October, 1976.     

Small-angle-scattering study of 12-hydroxystearic physical organogels and lubricating greases

We study the structure of the aggregates formed with two 12-hydroxystearic derivatives (acid HSA and Li salt HSLi), respectively, in xylene or hexadecane and decalin. SAXS and preliminary SANS experiments are used. The scattering curves are analyzed by comparison with simple geometrical models. Aggregates are described by infinitely long fibers of squared cross-section. For HSA fibers, the mean radius of gyration of the cross-section is 85 Å, corresponding to a square with 240 Å sides. A solvent and concentration dependence of the fibrillar structure is noticed. Diffraction peaks reveal the short-range order of the internal structure of the fibers or aggregates of fibers in the junction zones of the solid-like gel network. A 47 Å periodicity, approximately twice the hydroxystearic molecular length, supports a bilayered aggregation mechanism. The influence of a non-gelling stearic homologue, as found in industrial lubricating greases, is discussed.     

Optical anisotropy of absorbing particles: Light scattering depolarization,electric- and flow birefringence and dichroism of suspensions of carbon blacks

Summary The use of a rather: elongated spheroid, the compacity of which decreases with its weight, equivalent to the aggregates allows to explain the effects of depolarized light scattering and of birefringence. In particular, a very unusual negative macroform birefringence has been found. Moreover the theoretical expressions concerning the absorbing particles which simultaneously exhibit an electric dichroism and birefringence have been written. They were tested by means of suspensions of carbon blacks.

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Zusammenfassung Die Effekte der Depolarisation von Streulicht und der Str?mungsdoppelbrechung k?nnen mit Hilfe des Modells von relativ gestreckten Rotationsellipsoiden erkl?rt werden. Insbesondere wurde die Existenz eines ganz ungew?hnlichen Ph?nomens wahrscheinlich gemacht, n?mlich eine negative Formdoppelbrechung. Weiter wurden theoretische Beziehungen entwickelt, die Suspensionen von absorbierenden Teilchen betreffen, die zugleich Doppelbrechung und Dichroismus zeigen. Diese Gleichungen werden anhand von Ru?-Suspensionen verifiziert.

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Résumé Les effets de dépolarisation de la lumiére diffusée et de la biréfringence d'écoulement peuvent être expliqués á l'aide de modéles d'ellipsoídes de révolution équivalents relativement allongés. En particulier, on a mis en évidence l'existence d'un phénoméne tout-á-fait inhabituel: celui d'une biréfringence de macroforme négative. De plus, on a développé des relations théoriques concernant des suspensions de particules absorbantes, présentant à la fois de la biréfringence et du dichroisme. Ces expressions ont été vérifiées á l'aide de suspensions de noirs de carbone.

     

Foldamer organogels: a circular dichroism study of glucose-mediated dynamic helicity induction and amplification

This paper reports a systematic study of the dynamic process for the self-assembly of chiral organogels from achiral hydrogen bonded hydrazide foldamers by induction of chiral glucose. Six foldamers incorporated with six decyl chains and two benzene, naphthalene, anthracene, or pyrene units at the ends are revealed to strongly gelate apolar and polar solvents, including alkanes, arenes, esters, alcohols, and 1,4-dioxane. The gels are characterized by UV-vis, fluorescent, XRD, SEM, and AFM methods, based on which a dislocated "tail-to-tail" stacking pattern is proposed. Addition of octylated glucose considerably enhances the capacity of the foldamers to gelate apolar solvents due to strong complexation. The complexation also causes unique dynamic helicity induction in the gels, which is studied systematically by circular dichroism. The results are treated with the Avrami theory according to a reported method (J. Am. Chem. Soc. 2005, 127, 4336), which suggests that the gelation involves a nucleation-elongation mechanism. In addition, the "Sergeants and Soldiers" effect in the gel phase is also revealed.     

Light transmission, linear dichroism and birefringence of nematic/polymer dispersions

A theoretical study of light transmission, linear dichroism and birefringence of partially ordered dispersions of bipolar nematic droplets in a polymer matrix is presented. The treatment rests on the single scattering approach to an ensemble of uncorrelated and noninteracting anisotropic particles. Theoretical evaluations of the extinction cross sections and phase functions are performed in the anomalous diffraction approximation. Four basic model systems are analysed: PDLC and NCAP films in an external electric field, and PDLC and NCAP films under uniaxial mechanical deformation. The calculated dependences of the generalized parameters characterizing the light transmission, dichroism and birefringence on the angle of incidence of the probing light, droplet size and shape, refractive indices of the LC and polymer, and parameters of the external field are presented graphically and discussed in detail.     

Optical anisotropy of polyisobutylene: Strain birefringence

Strain birefringence measurements on crosslinked polyisobutylene (butyl rubber) confirm earlier work of Stein and Tobolsky on the linear polymer indicating the optical anisotropy to be much greater than should have been expected from the structural symmetry of the polyisobutylene (PIB) chain. The configuration–optical anisotropy parameter Δa for PIB at 25°C is 4.1(±0.1) × 10^?24 cm³, or about half the value for crosslinked polymethylene, both polymers being undiluted and amorphous. Swelling with cyclohexane, CCl₄, and CBrCl₃ lowers Δa to values of 3.8, 3.4, and 2.8 × 10^?24 cm³, respectively. Contributions from intermolecular correlations in the bulk polymer and from form anisotropy in the diluted systems are small, if not negligible. Temperature coefficients measured isometrically yield d In Δa/dT ≈ 0.2 × 10^?3 deg^?1. Both Δa and its temperature coefficient are much greater than calculated from rotational isomeric state theory assuming additivity of bond polarizabilities. The disparity (more than tenfold for Δa) cannot be relieved by any rational adjustment of the structural parameters. It is suggested that the severe crowding of groups in the PIB chain may affect the anisotropies of group polarizabilities.     

Optical analysis of dichroism measurements in polymer science

The polarization properties of an optical system, source–interferometer–polarizer–polymer film–detector, have been calculated. Using Mueller matrices, the intensity has been obtained as a function of polarizer angle. It is shown in some detail how polarization of the beam in both interferometer and detector optics distort the spectra. The contributions from the finite extinction ratio of the polarizer are also calculated and intensity variations caused by beam-wandering are discussed. It is shown that the commonly used procedure for correcting the spectra is wrong. Better methods for correcting the spectra are proposed. The influence of a uniaxial refractive index on the data is discussed, and experimental methods that can deal with refraction effects are presented. © 1993 John Wiley & Sons, Inc.     

Optical rotatory dispersion and circular dichroism. LXXV. Circular dichroism of some aryl-amino acids

CD. curves have been recorded for α-aryl-α-amino acids, esters and amides related to α-phenylglycine, α-phenyl-alanine and their N-dimethyl derivatives, and for the corresponding α-cyclohexyl-α-amino acids and esters. Compounds with the (S)-configuration at the single asymmetric carbon atom give strong positive Cotton effects near 220 nm. The conformations of the acids are discussed and compared with those of other α-amino acids.     

Reduction of linear birefringence in vibrational circular dichroism measurement: use of a rotating half-wave plate

A new method has been developed to suppress the effects of linear birefringence (LB) associated with sample cells in the measurement of vibrational circular dichroism (VCD) spectra by adding a rotating half-wave plate (RHWP) to the optical train. The method functions in combination with the previously developed dual polarization modulation (DPM) technique and involves placing the RHWP after the second photo-elastic modulator (PEM) of the DPM setup. In the DPM setup without the RHWP, all sources of LB terms are first reduced and then further cancelled by real time electronic subtraction, except for one remaining LB term associated with sample cell. Not infrequently, however, this remaining source of LB between the two PEMs with axes at 45° relative to the stress axes of the PEMs leads to noticeable deviations of the VCD baseline that cannot be eliminated. The new method described here depends on the use of an achromatic half-wave plate which is currently available in the near-infrared region with a low-frequency cut off near 2,000 cm⁻¹. It is demonstrated theoretically, and experimentally in the CH stretching region, that the addition of a RHWP eliminates this last remaining source of LB from the VCD measurement. Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users.     

Optical birefringence and molecular orientation of electrospun polycaprolactone fibers by polarizing-interference microscopy

The potential of polarizing-interference Pluta microscope for determination of optical birefringence of individual nanofibers formed by electrospinning was shown. This technique can be applied for measurements of fiber birefringence, practically at diameter above 300 nm. The molecular orientation of individual polycaprolactone (PCL) nanofibers was determined from birefringence assuming the same orientation of both phases, crystal and amorphous. The molecular orientation was determined using DSC crystallinity, crystal intrinsic birefringence calculated for the first time for PCL from bond polarizabilities as well as estimated value of amorphous intrinsic birefringence. Our results indicate that the birefringence and thus molecular orientation are strongly inhomogeneous along the nanofibers, reflecting a complex nature of forces acting during electrospinning process. The average molecular orientation is weak if any, being dependent together with fiber thickness and crystallinity on electrospinning parameters, like applied voltage, concentration and type of solvent. The obtained results indicate that the average molecular orientation displays similar dependence on applied voltage as fiber diameter. Relatively low melting temperature of electrospun nanofibers suggests low crystal size and/or high concentration of defects in crystals. This observation corresponds with low crystallinity and molecular orientation, indicating together relatively low degree of crystal ordering due to high rate of cooling and solvent evaporation during electrospinning, limiting thus crystallization process.     

Optical circular dichroism of the fullerene amino acid derivatives

The dependence of the circular dichroism spectra of the amino acid derivatives of fullerene C₆₀ on the structure of the initial α-amino acid was studied.     

Optical properties of certain steroid hormones and related compounds

Summary Optical properties of one adrenal cortex, one corpus luteum, two testes, six gluco corticoid, and three unclassified steroids were determined. These data afford a positive identification of these compounds with only minute amounts of material.

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Zusammenfassung Die optischen Eigenschaften von 13 Steroiden (ein Nebennierenrindensteroid, ein Gelhkörpersteroid, zwei Keimdrüsensteroide, sechs Glucocortieosteroide, drei nicht näher klassifizierte Steroide) wurden bestimmt. Die gefundenen Daten ermöglichen die einwandfreie Identifizierung dieser Verbindungen mit sehr geringem Materialaufwand.

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Résumé On a déterminé les propriétés optiques de 13 stéroïdes (un stéroïde cortico-surrénal, un stéroïde du corps jaune, deux stéroïdes des glandes génitales, six glueocorticostéroïdes, trois stéroïdes n'appartenant pas aux classifications précédentes). Les données trouvées permettent l'identification rigoureuse de ces composés sur très peu de substance.

     

Tailoring the physical properties of some high birefringence isothiocyanato-based liquid crystals

This paper describes the synthesis and characterization of several liquid crystal compounds having a tolane or terphenyl core structure and a high polarizability, isothiocyanato (NCS), terminal group. The synthesized compounds have high optical birefringerce (0.35 and 0.52), the highest being exhibited by the olefin-tolanes. Several eutectic mixtures are formulated and show improved properties over the single compounds, such as a broad nematic range, low melting temperature and relatively high clearing point. The birefringence of these mixtures is in the range 0.35-0.37. UV, viscosity and electro-optical measurements of the synthesized compounds are also reported. Dipole moment and polarizability calculations were made using CS-MOPAC and Hyperchem software computational programmes.     

Optical birefringence in a fluid near its critical point with stratification under gravity

Electromagnetic wave propagation in an inhomogeneous medium is discussed in the context of light propagation in a fluid near its critical point, stratified under gravity. The system exhibits birefringence, where the transverse electric (te) and the transverse magnetic (tm) waves travel with different phase-velocities, depending upon the density-gradients with height set up in the system. The possibility of experimentally detecting the predicted phenomenon is also discussed.