Dichroic Behavior Research Articles

Changes in CD of hyaluronates and chondroitins upon periodate oxidation.

AbstractChanges in conformation of hyaluronate and chondroitin sulfates following periodate oxidation were studied by CD. We monitored the progressive oxidation of these polymers by periodic acid at 4°C in pH 5.6 buffer. The negative CD band of hyaluronate at 208 nm decreased in intensity upon oxidation and changed its sign after 16 h of oxidation. In contrast, the 208‐nm CD band of chondroitin sulfates decreased, but showed no change in sign even after 48 h of oxidation. A specific difference in solution conformation between hyaluronate and chondroitins may be responsible for the difference in oxidation‐induced dichroic behavior. The results are discussed in terms of available x‐ray diffraction analyses of these polymers.

Structural properties of Langmuir–Blodgett films of charge transfer salts: Pristine and iodine doped conducting films of (N-docosyl-pyridinium)TCNQ

We have investigated the molecular constitution and ordering of Langmuir–Blodgett films prepared by deposition of N-docosylpyridinium–TCNQ charge transfer salt onto CaF2 substrates and by their subsequent doping with iodine vapor to yield reasonably good (∼10−1 Ω−1 cm−1) conducting films. Optical and electron scanning microscopy of the precursor film show that it is made up of a mosaic of highly crystalline platelets lying flat on the substrate though with random orientation. Structural information at the molecular level is gained by measuring and analyzing the ESR spectra and their angular and temperature dependence as well as the UV-visible and infrared spectra and their linear dichroism. A triplet fine structure is observed in the ESR spectra of the precursor films with zero field splitting parameters ‖D‖=7.48×10−3 cm−1 and ‖E‖=1.2×10−3 cm−1 and singlet–triplet activation energy J=0.20 eV, markedly different from those of the N-docosylpyridinium–TCNQ powder salt. The UV-visible and infrared spectra show features typical of a system containing weakly interacting (TCNQ−)2 dimers similar to those found in a water solution. The dichroic behavior of the observed infrared active modes of the TCNQ− anion and of N-docosylpyridinium as well as of the vibronically induced absorptions of the interacting TCNQ system are analyzed both for the precursor and for the iodine doped film. According to such an analysis and to that of the angular dependence of the ESR line shapes, the polar sheets in the precursor film consist of slipped (ring-bond overlap) (TCNQ−)2 dimers with their molecular planes almost parallel to the plane of the supporting slide. The spectroscopic and linear dichroism data allow us to monitor the changes induced by the iodination process and to show that, besides the partial oxidation of TCNQ− anions to TCNQ0, there is a complete change in the orientation of the TCNQ units. In many respects, the UV-visible and infrared spectra of the conducting film resemble those of mixed valence, intermediate conductivity salts like, e.g., (TEA) (TCNQ)2. The TCNQ molecules stand edge on with their molecular planes roughly perpendicular to the plane of the slide and with their long axes close to being normal to it.

Polarized infrared absorption spectra of Na 2 [Fe (CN) 5NO] · 2H 2O with part of the anions in the electronically excited metastable state

IR spectra of the nitroprusside ion in Na 2[Fe (CN) 5NO]. 2H 2O in the metastable electronic state produced by irradiation at boiling air temperature with the 514.5 nm line of an Ar + LASER were obtained for thin (100) single crystal plates in the ranges 4000-430 cm -1 and 4000-550 cm -1 for polarizations along the 1b and c -axes, respectively. The spectra showed that the suggested bending of the FeNO group upon excitation occurs in the (a,b) mirror plane of the ground state crystal. In addition to bands corresponding to Raman lines reported as due to excited nitroprusside, new bands appeared in the infrared spectra. Some of them showed a strong dichroic behavior. On heating the samples some of the new bands disappeared earlier than the bands correspon d ing to the Raman lines. No explanation is still available for those bands.

Contribution of Infrared Spectroscopy to the Study of Corrensite

AbstractA corrensite from Taro Valley, Italy, was studied by infrared analysis at different temperatures in the natural state and after exchange with seven different cations. The vibrational bands in the OH-stretching region can be divided into three main absorption regions: 3690-3640, 3580-3560, and 3500-3000 cm−1. The influence of the cation hydration water was observed in the third region only, whereas the intensity, frequency, and shape of the residual bands were not related to the nature of the exchangeable cations. The bands of region I were unaffected by heating the sample to 500°C; however, those in regions II and III were destroyed. Deuteration was not observed for any of the three OH-stretching regions. The dichroic behavior of the OH-stretching bands in the three regions were relatively affected by the exchangeable cations. Generally, the bands in region I exhibited a more dichroic behavior than those in regions II and III.From the IR data corrensite appears to consist of: (1) a trioctahedral silicate layer with an OH-stretching band at about 3685 cm−1, (2) a hydroxide layer with OH-stretching bands at about 3570 and 3420 cm−1, and (3) a distinct interlayer space that is not interstratified with the hydroxide layers.

Optical Anisotropy and Dichroism of A‐Centres in NaCl and KCl Single Crystals Irradiated with X‐Rays under DC Fields

AbstractThe optical absorption characteristics of the Petroff A‐band reported in our earlier work on NaCl and KCl single crystals X‐ray irradiated under dc fields, are studied in greater detail using polarized light. The results seem to indicate that the A‐centres exhibit anisotropic and dichroic behaviour. A possible explanation of the results is attempted.

Segmental orientation studies of polyether polyurethane block copolymers with different hard segment lengths and distributions

The orientation behavior of two series of segmented polyether polyurethanes containing different hard segment length distributions has been studied as a function of the average hard segment length which was varied from one to five methylene bis (p-phenyl isocyanate) (MDI) units. The orientation behavior of the soft segments, isolated hard segments, and of hard segments aggregated in hard domains was determined from the dichroic behavior of representative infrared bands. As the hard segment length increases, a transition in orientation behavior is observed which corresponds to a change in sample morphology.

Dichroic behavior of the absorbance signals from dyes NK2367 and WW375 in skeletal muscle fibers.

Absorbance signals were recorded from voltage-clamped single muscle fibers stained with the nonpenetrating potentiometric dyes NK2367 and WW375 and illuminated with quasimonochromatic light from 560 to 800 nm, linearly polarized either parallel (0 degree) or perpendicular (90 degrees) to the fiber long axis. The signals from both dyes depend strongly on the incident polarization. At any wavelength and/or polarization condition, the total absorbance signal is a superposition of the same two signal components previously identified with unpolarized light (Heiny, J. A., and J. Vergara, 1982, J. Gen. Physiol., 80:203)--namely, a fast step signal from the voltage-clamped surface membrane and a signal reflecting the slower T-system potential changes. The 0 degree and 90 degrees spectra of both membranes have similar positive and negative absorbance peaks (720 and 670 nm, respectively, for dye NK2367; 740 and 700 nm for dye WW375); in addition, they have the same dichroic maxima (670 for NK2367; 700 for WW375). However, for the surface membrane, the 0 degrees spectra are everywhere more positive than the 90 degrees spectra, whereas the reverse is true for the T-system, which results in a dichroism of opposite sign for the two membranes. These spectral characteristics were analyzed using a general model for the potential-dependent response of an absorbing dye (Tasaki, I., and A. Warashina, 1976, Photochem. Photobiol., 24:191), which takes into account both the dye response and the membrane geometries. They are consistent with the proposal that the dye responds via a common mechanism in both membranes that consists of a dye reorientation and a change in the absorption maxima.

Vacuum‐ultraviolet circular dichroism of chondroitins and their complexes with poly(L‐arginine)

AbstractThe vacuum‐ultraviolet circular dichroism (VUCD) of chondroitin and chontroitin‐6‐sulfate has been measured to 160 nm for films and to 170 nm for D2O solutions. The pD‐dependent dichroic behavior of these glycosaminoglycans in D2O is similar above 200 nm and is in agreement with previous studies. Near 190 nm, the CD band sign is also dependent on pD. VUCD spectra were recorded for films and solutions of poly(L‐arginine). In trifluoroethanol the polypeptide is α‐helical, while in D2O it exists as a random coil. The well‐characterized coil–helix transition of poly(L‐arginine) during complexation with chondroitin‐6‐sulfate was observed by VUCD, including the previously inaccessible entire π → π* band. By construction of difference spectra it was also possible to monitor the VUCD of the polysaccharide component during complexation.

Vtbrational spectra of the triclinic K 3[ReO 2(CN) 4] single crystal

Infrared spectra of K 3[ReO 2(CN) 4] have been recorded using polarized radiation and oriented single crystals. The dichroic behaviour of the bands is analyzed and discussed on the basis of molecular geometry and the oriented molecular model. Experimentally determined dichroic ratios are used to obtain a full set of vibrational frequencies. By combining these data with those obtained from Raman spectra, the fundamental internal and lattice vibrations are assigned.

ChemInform Abstract: BOND FIXATION IN ANNULENES. 8. ASSESSMENT OF THE RING INVERSION AND BOND SHIFTING BARRIERS IN 1,2,3‐TRIMETHYLCYCLOOCTATETRAENE. RESOLUTION, ABSOLUTE CONFIGURATION, AND CIRCULAR DICHROIC BEHAVIOR OF AN (8)ANNULENE HYDROCARBON

Chemischer InformationsdienstVolume 11, Issue 43 Isocyclic Compounds ChemInform Abstract: BOND FIXATION IN ANNULENES. 8. ASSESSMENT OF THE RING INVERSION AND BOND SHIFTING BARRIERS IN 1,2,3-TRIMETHYLCYCLOOCTATETRAENE. RESOLUTION, ABSOLUTE CONFIGURATION, AND CIRCULAR DICHROIC BEHAVIOR OF AN (8)ANNULENE HYDROCARBON L. A. PAQUETTE, L. A. PAQUETTESearch for more papers by this authorJ. M. GARDLIK, J. M. GARDLIKSearch for more papers by this author L. A. PAQUETTE, L. A. PAQUETTESearch for more papers by this authorJ. M. GARDLIK, J. M. GARDLIKSearch for more papers by this author First published: October 28, 1980 https://doi.org/10.1002/chin.198043143AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume11, Issue43October 28, 1980 RelatedInformation

ChemInform Abstract: OPTICAL ABSORPTION OF SILVER IN PHOTOCHROMIC GLASSES: OPTICALLY INDUCED DICHROISM

AbstractDas Absorptionsspektrum von UV‐geschwärzten photochromen Gläsern auf Aghalogenid‐Basis ändert sich mit der Glaszusammensetzung und der photochromen Wärmebehandlung.

Bond fixation in annulenes. 8. Assessment of the ring inversion and bond shifting barriers in 1,2,3-trimethylcyclooctatetraene. Resolution, absolute configuration, and circular dichroic behavior of an [8]annulene hydrocarbon

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTBond fixation in annulenes. 8. Assessment of the ring inversion and bond shifting barriers in 1,2,3-trimethylcyclooctatetraene. Resolution, absolute configuration, and circular dichroic behavior of an [8]annulene hydrocarbonLeo A. Paquette and John M. GardlikCite this: J. Am. Chem. Soc. 1980, 102, 15, 5016–5025Publication Date (Print):July 1, 1980Publication History Published online1 May 2002Published inissue 1 July 1980https://doi.org/10.1021/ja00535a032RIGHTS & PERMISSIONSArticle Views127Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Optical Absorption of Silver in Photochromic Glasses: Optically Induced Dichroism

The absorption spectrum of silver halide‐based photochromic glasses darkened by uv light is shown to vary with glass composition and photochromic heat treatment. The nature of the absorption is explained in terms of the anisotropic geometry of the photolytically produced silver specks. A correlation is established between the uv‐induced spectrum and the dichroic behavior that can be induced by bleaching with polarized light. A specific model is proposed for the silver‐speck geometry and calculations show goad agreement with experimental data.

ChemInform Abstract: SUBMILLIMETER WAVE ABSORPTION IN A HOMOLOGOUS SERIES OF LIQUID CRYSTALS

The far‐infrared absorption spectra of the first seven homologs (C1–C7) of the p,p ′‐di‐n‐alkoxyazoxy‐benzene series of liquid crystals have been studied in the range 30–200 cm−1. Comparison of the different spectra in the isotropic phase shows that the intensity of absorption is maximum in C1. In C2 and C3, the intensity as also the peak position of the central band decrease as compared to C1. A broad and shallow absorption profile without any central band is observed in C4–C7. The various factors that can possibly contribute to the far‐infrared absorption in the fluid phases of these mesogens are considered. It is found that the Poley absorption may be the dominant factor in C4–C7, but it can not account for the distinct changes associated with the central band in C1–C3. The observed decrease in the intensity and the shift in the peak position of this band on going from C1 to C2 strongly suggest that this band originates from the torsion of the end alkoxy groups around the phenyl‐oxygen bonds. This assignment is also consistent with (i) the virtual disappearance of the central band in C4–C7 (ii) the dichroic behavior of the band in C1 in the homogeneously aligned nematic phase and (iii) the considerably reduced intensity of absorption in the liquid phase of the related, but nonmesomorphic compound p,p ′‐azoxytoluene. We conclude that in the composite absorption profiles due to a superposition of the Poley and torsional bands, the latter contribution becomes increasingly important for the lower homologs of this series.

Submillimeter wave absorption in a homologous series of liquid crystals

The far-infrared absorption spectra of the first seven homologs (C1–C7) of the p,p′-di-n-alkoxyazoxy-benzene series of liquid crystals have been studied in the range 30–200 cm−1. Comparison of the different spectra in the isotropic phase shows that the intensity of absorption is maximum in C1. In C2 and C3, the intensity as also the peak position of the central band decrease as compared to C1. A broad and shallow absorption profile without any central band is observed in C4–C7. The various factors that can possibly contribute to the far-infrared absorption in the fluid phases of these mesogens are considered. It is found that the Poley absorption may be the dominant factor in C4–C7, but it can not account for the distinct changes associated with the central band in C1–C3. The observed decrease in the intensity and the shift in the peak position of this band on going from C1 to C2 strongly suggest that this band originates from the torsion of the end alkoxy groups around the phenyl-oxygen bonds. This assignment is also consistent with (i) the virtual disappearance of the central band in C4–C7 (ii) the dichroic behavior of the band in C1 in the homogeneously aligned nematic phase and (iii) the considerably reduced intensity of absorption in the liquid phase of the related, but nonmesomorphic compound p,p′-azoxytoluene. We conclude that in the composite absorption profiles due to a superposition of the Poley and torsional bands, the latter contribution becomes increasingly important for the lower homologs of this series.

Circular dichroism study of the solution conformation of luteinizing hormone releasing hormone

A systematic investigation has been made into the circular dichroic behavior of luteinizing hormone releasing hormone and its peptide fragments and deletion analogues. The results are interpreted to mean that the hormone exists in solution as an ensemble of conformers with different sensitivities to temperature and solvent composition. The far-ultraviolet circular dichroic spectra exhibited by the hormone under different experimental conditions can be simulated satisfactorily by the weighted addition of the spectra of its aliphatic- and aromatic-containing halves. However, the structure of the hormone is not simply the sum of its halves, since some conformational feature of the intact molecule perturbs the near-ultraviolet circular dichroism of its aromatic residues.

Circular dichroism studies on lysozymes from different sources

1. 1. A comparative study on the secondary structure of hen egg-white, turtle egg-white ( Testudo graeca) and fruit fly ( Ceratitis capitata) egg lysozymes has been carried out by circular dichroism. 2. 2. Differences in the near-u.v. spectra of these enzymes agree with the different content in tryptophan residues. 3. 3. The far-u.v. circular dichroism spectra show the existence of a high content of unordered structure in the insect lysozyme in comparison with the high participation of α-helical conformation in the hen egg-white enzyme. 4. 4. Differences in the dichroic behaviour between both enzymes are also remarkable under denaturating conditions.

Optical characteristics of carboxyl group in relation to the circular dichroic properties and dissociation constants of glycosaminoglycans

Circular dichroism studies of glycosaminoglycan including chemically transformed heparins at various pH values reveal that carboxyl chromophore plays an important role in the dichroic behavior of the polymers. With decreasing pH, iduronic acid-containing glycosaminoglycans show increased negative ellipticity near 220 nm whereas the polymers containing glucuronic acid display enhanced negative dichroism near 230 nm and decreased negative dichroism around 210 nm. The pH-dependent optical properties have been utilized to determine the p K a values of uronic acid moieties. The acid strengths of the iduronic acid-containing glycosaminoglycans are inherently smaller than those of corresponding glucuronic acid-containing polymers. Glycosaminoglycans in which the amino sugars are linked with iduronic acid display a very weak n → π ∗ amide transition, or none. The rotational strength at 210 nm of these polymers is largely due to iduronic acid moieties. The CD variations above 200 nm with change in pH do not indicate any major conformational transition of the molecules but the difference between dermatan sulfate and heparin can be attributed to difference either in iduronic acid conformation or in intersaccharide linkages.

A new type of F3‐centre in additively coloured CaF2

AbstractTwo new absorption bands at 450 and 320 nm appear in additively coloured CaF2 crystals by bleaching in the α‐band (375 nm) at temperatures ≈ 160 K. These two bands have dichroic behaviour, from which is found, that they are due to two different optical transitions in the same centre, which have their electric dipoles perpendicular, and parallel to the 〈110〉 directions, for the 450 nm band; and along the 〈100〉 directions, for the 320 nm band. Thermal reorientation measurements show that the dichroism induced by light with E ∥ [110], disappears at 210 K, while the dichroism induced by light with E ∥ [100] does not disappear until 270 K. This 270 K disorientation is accompanied by a transformation to the linear F3‐centre, which appears with some dichroism. A model for the centre responsible for these two bands, consisting of three F‐centres forming a right‐angled triangle in a (100) plane, gives good agreement with the experimental results. This is a new type of F3‐centre in the fluorite structure, in contrast with the linear F3‐centre found by bleaching in the α‐band at RT.

Vibrational spectra and assignments for tetrahydrothiophene, tetrahydroselenophene and tetrahydrotellurophene

The i.r. spectra of tetrahydrothiophene, -selenophene and -tellurophene as liquids and solids at 100K have been studied from 4000- to 250 cm −1. The Raman spectra of liquids have also been recorded and depolarization values have been measured. An assignment of the 33 fundamental vibrations for the 3 molecules is proposed based on depolarization values, dichroic behaviour and group-frequency correlations.