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Optical Activity (optical + activity)
Kinds of Optical Activity Selected AbstractsComputational Interpretation of Vibrational Optical Activity: The ROA Spectra of (4S)-4-Methylisochromane and the (4S)-Isomers of Galaxolide®HELVETICA CHIMICA ACTA, Issue 9 2004Gérard Zuber The reliable computation of Raman- optical-activity (ROA) spectra of molecules of the size of the title compounds has, until now, not been possible. We show that our rarefied basis sets yield results in good agreement with the experimental data for (4S)-4-methylisochromane (=(4S)-3,4-dihydro-4-methyl-1H -2-benzopyran; 1), provided the equilibrium between the pseudo -equatorial and the pseudo -axial conformers is taken into account. Comparison between the measured and the computed ROA back-scattering spectra allows the unequivocal assignment of the absolute configuration of the molecule. Comparison with more-approximate calculations for the larger (4S)-isomers of Galaxolide® (2), which contain the (4S)-4-methylisochromane moiety, shows large-scale group frequencies on the same chiral fragments of the two molecules. The data confirm that ROA can be generated by interactions extending over several bonds, i.e., over larger distances than can be probed by NMR spectroscopy. Thus, the absolute configuration at C(7) of Galaxolide® is assignable independently of that at C(4). The computation of ROA for forward-scattering, which will soon be measurable for Galaxolide®, suggests that this scattering geometry provides additional stereochemical information that will be valuable in situations where absolute configurations at several stereogenic centers have to be assigned. [source] Supramolecular Chirogenesis with Bis-Chlorin versus Bis-Porphyrin Hosts: Peculiarities of Chirality Induction and Modulation of Optical Activity.CHEMINFORM, Issue 3 2006Victor V. Borovkov No abstract is available for this article. [source] Reversible Mechanical Induction of Optical Activity in Solutions of Soft-Matter NanophasesCHEMISTRY - AN ASIAN JOURNAL, Issue 11 2009Oriol Arteaga Abstract Nanophases of J-aggregates of several achiral amphiphilic porphyrins, which have thin long acicular shapes (nanoribbons), show the immediate and reversible formation of a stationary mechano-chiral state in the solution by vortex stirring, as detected by their circular dichroic signals measured by 2-modulator generallized ellipsometry. The results suggest that when a macroscopic chiral force creates supramolecular chirality, it also creates an enantiomeric excess of screw distortions, which may be detected by their excitonic absorption. An explanation on the effect of the shear flow gradients is proposed on the basis of the orientation of the rotating particles in the vortex and the size, shape, and mechanical properties of the nanoparticles. [source] Growth and optical characterization of cerium and lead-doped Bi12TiO20 sillenite single crystalsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2005J. F. Carvalho Abstract Bi12TiO20 (BTO) single crystals doped with PbO and CeO2 were grown by the Top Seeded Solution Growth (TSSG) technique from the liquid phase with nominal compositions of 10Bi2O3 : (1,x)TiO2 : x PbO and 10Bi2O3 : (1,x)TiO2 : xCeO2 with x = 0.25 and 0.10. No growth-related difficulties were encountered other than those typical of sillenite crystals. Samples with good optical quality were obtained and were characterized by optical absorption, dark current, spectral photocurrent dependence, optical activity and electro-optic coefficient measurements. A comparison is made of the results of the optical measurements of doped and undoped BTO crystals. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Large Second-Order NLO Activity in Poly(4-vinylpyridine) Grafted with PdII and CuII Chromophoric Complexes with Tridentate Bent Ligands Containing HeterocyclesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2008Fabio Borbone Abstract Two N -salicylidene- N,-acylhydrazines tridentate ligands containing heterocycles were prepared and utilized for the synthesis of mononuclear acentric complexes of CuII and PdII and pyridine serves as an additional ligand (MLxPy, M = metal, Lx = ligand). Characterization also includes single-crystal X-ray diffraction analysis. These complexesshow high second-order nonlinear optical activity (,, = 620,×,10,48esu for both CuLIIPy and PdLIIPy and ,, = 1600,×,10,48 and 1400,×,10,48 esu for CuLIPy and PdLIPy, respectively, at incident wavelength of 1907 nm). The properties of polymers (PMLx) obtained by grafting poly(4-vinylpyridine) with fragments of the complexes are also reported. The polymers exhibit good thermal stability, high glass-transition temperatures and the absence of crystallinity. The second-order nonlinear optical (NLO) properties of thin, transparent poled films, prepared by spin coating and thermal corona poling, were investigated for some of the polymers. The value of the d33 parameter was measured at 1064 and 1500 nm (i.e., with and without resonance contribute). In the latter case, the d33 values are 21 and 12 pm/V for PCuLII and PPdLII, respectively. A high time stability of the NLO properties of these materials was found. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] How Do the Different Defect Structures and Element Substitutions Affect the Nonlinear Optical Properties of Lacunary Keggin Polyoxometalates?EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2006A DFT Study Abstract Systematic DFT calculations have been carried out on the lacunary ,-Keggin polyoxometalate derivatives [PW11O39]7,, [XW9O34]n, (X = AlIII, SiIV, GeIV, PV, AsV, and SbV), [XW9M2O39]n,, and [XW9M3O40]n, (X = PV and SiIV, M = MoVI, VV, NbV, and TaV) to investigate the geometric structure and element substitution effects on the molecular nonlinear optical response. Analysis of the computed static second-order polarizability (,0) predicts that the molecular nonlinear optical activity of lacunary Keggin polyoxometalate derivatives can be modified by replacing the central heteroatom and the addenda metal atom. Substitution of the central Al atom or the addenda V atom causes significant enhancement in the molecular nonlinearity. Moreover, the ,0 values are substantially dependent on the defect structures. This class of inorganic complexes possesses remarkably large molecular optical nonlinearity, especially for the partial substitution complex [SiW9Nb2O39]10, (IIIc), which has a computed ,0 value of 2071.0 a.u. Thus, lacunary Keggin polyoxometalates could become excellent candidates in the field of second-order NLO. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Czochralski-grown Single Crystals with Acentric Symmetry Group 32,ADVANCED ENGINEERING MATERIALS, Issue 7 2004R.B. Heimann Single crystals with calcium gallium germanate (Ca3Ga2Ge4O14, CGG) structure such as langasite La3Ga5SiO14 (LGS), its niobium (,langanite', La3Ga5.5Nb0.5O14, LGN) and tantalum (,langataite', La3Ga5.5Ta0.5O14, LGT) analogs as well as strontium niobium gallium silicate (Sr3NbGa3Si2O14, SNGS) and strontium tantalum gallium silicate (Sr3TaGa3Si2O14, STGS) were grown with high perfection by the Czochralski pulling technique. Specific electric conductivity, optical activity, and dielectric, piezoelectric, bulk and surface acoustic, elastic, and electro-optic properties were measured. [source] Defect-Related Optical Behavior in Surface Modified TiO2 NanostructuresADVANCED FUNCTIONAL MATERIALS, Issue 1 2005M. Prokes Abstract The surface modification of TiO2 nanostructures to incorporate nitrogen and form visible light absorbing titanium oxynitride centers is studied. Anatase TiO2 structures in the 5,20,nm range, formed by a wet chemical technique, were surface modified and the nitridation of the highly reactive TiO2 nanocolloid surface, as determined by X-ray photoelectron spectroscopy (XPS) studies, is achieved by a quick and simple treatment in alkyl ammonium compounds. The nitriding process was also simultaneously accompanied by metal seeding resulting in a metal coating layer on the TiO2 structures. The structure of the resultant titanium oxynitride nanostructures remains anatase. These freshly prepared samples exhibited a strong emission near 560,nm (2.21,eV), which red-shifted to 660,nm (1.88,eV) and dropped in intensity with aging in the atmosphere. This behavior was also evident in some of the combined nitrogen doped and metal seeded TiO2 nanocolloids. Electron spin resonance (ESR) performed on these samples identified a resonance at g,=,2.0035, which increased significantly with nitridation. The resonance is attributed to an oxygen hole center created near the surface of the nanocolloid, which correlates well with the observed optical activity. [source] Absolute Conformations of the (,)-[9](2,5)Pyridinophane MoleculeHELVETICA CHIMICA ACTA, Issue 8 2009Maxim Fedorovsky Abstract [9](2,5)Pyridinophane was first synthesized, and its enantiomers were separated, more than 40 years ago, but the molecule's absolute conformations could not be determined up to now. We show here, by the comparison of measured and computed vibrational optical activity (VOA), that the CIP descriptor (P) applies to the (,)-enantiomer. This assignment is based on the VOA of bands from vibrations localized on the pyridine ring bent by the tense (CH2)9 chain extending from position 2 to 5. The VOA of vibrations localized on the chain is in agreement with this assignment. Its behavior differs from the VOA of the bent pyridine ring, and conclusions drawn from the chain's VOA alone would not be sufficient, because the close-to-enantiomorphic geometries of the chain present in some of the 14 conformers of (,)-[9](2,5)pyridinophane lead to VOA with an opposite sign. Understanding of how VOA is generated is crucial for the unambiguous assignment of the molecule's absolute conformations. [source] Chiral and Achiral Crystal StructuresHELVETICA CHIMICA ACTA, Issue 4 2003Howard An extensive study and analysis of the concepts, classification, presentation, and nomenclature of chirality and lack of chirality in crystal structures and their constituents is presented. Oriented crystal structures are classified. The chirality rules for existence of molecular crystal structures are examined and the relation to segmentation and latent symmetry highlighted. The nomenclature of chirality and related terms, and the relationship of chirality to optical activity is covered. The uses and limitations of the Euclidean normalizer are treated. An improved glossary of terms is included. [source] Use of vibrational spectroscopy to study protein and DNA structure, hydration, and binding of biomolecules: A combined theoretical and experimental approachINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2006K. J. Jalkanen Abstract We report on our work with vibrational absorption, vibrational circular dichroism, Raman scattering, Raman optical activity, and surface-enhanced Raman spectroscopy to study protein and DNA structure, hydration, and the binding of ligands, drugs, pesticides, or herbicides via a combined theoretical and experimental approach. The systems we have studied systematically are the amino acids (L -alanine, L -tryptophan, and L -histidine), peptides (N -4271 acetyl L -alanine N,-methyl amide, N -acetyl L -tryptophan N,-methyl amide, N -acetyl L -histidine N,-methyl amide, L -alanyl L -alanine, tri- L -serine, N -acetyl L -alanine L -proline L -tyrosine N,-methyl amide, Leu-enkephalin, cyclo-(gly- L -pro)3, N -acetyl (L -alanine)nN,-methyl amide), 3-methyl indole, and a variety of small molecules (dichlobenil and 2,6-dochlorobenzamide) of relevance to the protein systems under study. We have used molecular mechanics, the SCC-DFTB, SCC-DFTB+disp, RHF, MP2, and DFT methodologies for the modeling studies with the goal of interpreting the experimentally measured vibrational spectra for these molecules to the greatest extent possible and to use this combined approach to understand the structure, function, and electronic properties of these molecules in their various environments. The application of these spectroscopies to biophysical and environmental assays is expanding, and therefore a thorough understanding of the phenomenon from a rigorous theoretical basis is required. In addition, we give some exciting and new preliminary results which allow us to extend our methods to even larger and more complex systems. The work presented here is the current state of the art to this ever and fast changing field of theoretical spectroscopic interpretation and use of VA, VCD, Raman, ROA, EA, and ECD spectroscopies. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006 [source] Identification of a human estrogen receptor ,-derived antiestrogenic peptide that adopts a polyproline II conformationJOURNAL OF PEPTIDE SCIENCE, Issue 7 2009Josef Kapitán Abstract Polyproline II (PPII) helix is an extended secondary structure present in a number of proteins. PPII-containing sequences mediate specific protein,protein interactions with partners containing appropriate cognate domains called PPII-recognizing domains (PRDs) and are involved in the activation of intracellular signaling pathways. Thus, the identification of PPII structures in proteins is of great interest, not only to explore molecular and physiological mechanisms, but also to elaborate new potential drugs. By revisiting X-ray crystal structures of liganded ,-type human estrogen receptor (ER,), we have identified an 11-residue PPII-helical sequence (D321AEPPILYSEY331) in the ligand-binding domain of the receptor. The data recorded by far-ultraviolet circular dichroism (far-UV CD), vibrational Raman optical activity (ROA) and differential scanning calorimetry (DSC) show that the corresponding peptide (Ac-DAEPPILYSEY-NH2) is particularly well structured in PPII, with the same proportion of PPII as observed from X-ray structures (,85%). In addition, studies carried out on ER,-negative Evsa-T breast cancer cells transiently co-transfected with a pcDNA3-ER, plasmid and a Vit-tk-Luc reporter gene revealed that the peptide antagonizes the estradiol-induced transcription providing perspectives for researching new molecules with antagonistic properties. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd. [source] Counterintuitive influence of microscopic chirality on helical order in polymersJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 9 2004Kap Soo Cheon Abstract Studies of copolymers of chiral and achiral units forming a helical array correlate to statistical physical predictions of the influence of the chiral units on the helical sense taken by the array. In the absence of conflict among the chiral units for helical sense control, the sergeants and soldiers experiment, a larger chiral bias leads to increased control. However, when conflict exists among the chiral units for helical sense control, the majority rule experiment, a larger chiral bias leads to decreased control of the helical sense and therefore a smaller optical activity. Changing the achiral units in the majority rule experiment can change the nature of the statistical physics between statistical and thermal randomness. In general, the experiments quantitatively demonstrate that the effect of chirality is not an intrinsic property of the chiral moiety but rather depends on the molecular environment. Copyright © 2004 John Wiley & Sons, Ltd. [source] Side-chain supramolecular polymers with induced supramolecular chirality through H-bonding interactionsJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2008Francisco Vera Abstract Side-chain supramolecular polymers that show columnar mesomorphism have been prepared through H-bonding interactions between a polyvinylpyridine polymer as H-acceptor and different H-donors derived from benzoic acid. These compounds have been designed according to a promesogenic structure, that is, either disk-like or banana-like, to promote stacking and therefore the formation of columnar arrangements. IR studies confirmed the formation of H-bonds and demonstrated that the H-bond intensity decreases upon increasing temperature. The mesophase organizations were studied by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction. Associations containing poly-3-methyl-4-vinylpyridine showed supramolecular optical activity, as evidenced by circular dichroism studies on thin films. It is proposed that these supramolecular polymers adopt a helical structure that can be biased toward a given handedness by virtue of the configuration of the stereogenic centers in the peripheral tails of the acids. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5528,5541, 2008 [source] Stability control of the electrooptic effect with new maleimide copolymers containing photoreactive tricyanopyrrolidene-based chromophoresJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 3 2007Sang Kyu Lee Abstract New photocrosslinkable maleimide copolymers have been synthesized by the attachment of a tricyanopyrrolidene-based chromophore. The 2-(3-cyano-4-(2-{4-[hexyl-(6-hydroxy-hexyl)-amino]-phenyl}-vinyl)-5-oxo-1-{4-[4-(3-oxo-3-phenyl-propenyl)- phenoxy]-butyl}-1,5-dihydro-pyrrol-2-ylidene)-malononitrile chromophore exhibits nonlinear optical activity and contains a chalcone moiety that is sensitive to UV light (, = 330,360 nm) for crosslink formation. The maleimide monomers have also been functionalized with chalcone moieties. The resultant copolymers exhibit great processability, and one of them shows a maximum electrooptic coefficient of 90 pm/V at 1300 nm. We could control the thermal stability of the electrooptic coefficient with the newly synthesized photoreactive copolymers successfully. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 531,542, 2007 [source] Raman optical activity of an achiral element in a chiral environmentJOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2009Andrew M. Smith Abstract Raman optical activity (ROA) is a relatively new technique used to determine the structure of chiral molecules and is proving useful in the study of biological molecules such as proteins and DNA/RNA. Here, for the first time, we demonstrate the applicability of ROA as a technique to study achiral groups in chiral environments, detecting the induced chirality of N -(fluorenyl-9-methoxycarbonyl) (Fmoc) in a chiral self-assembled structure of Fmoc-dipeptides. This technique is therefore of interest to those studying self-assembled systems that adopt a chiral structure. Copyright © 2009 John Wiley & Sons, Ltd. [source] Observation of SERS effect in Raman optical activity, a new tool for chiral vibrational spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2006Salim Abdali Abstract A new tool for chiral vibrational spectroscopy is reported here. A surface enhanced effect was observed using Raman optical activity (ROA). This observation opens new possibilities for ROA as a tool for vibrational spectroscopy. The combination of surface enhanced effect (SE) and ROA into surface enhanced Raman optical activity (SEROA) takes this tool to another level, where a single molecule may be studied with respect to chirality, secondary structure and fold determination. ROA has been able to provide information about important dynamics in molecular understanding. Until recently, however, ROA measurements required a longer exposure and higher concentration of the sample. With SEROA these obstacles can be overcome because both studies on single molecule, i.e. very low concentration, and faster acquisition of the signal can be carried out. In the present, work silver colloids were mixed with solution, in which a pentapeptide, Met-Enkephalin, was dissolved. SEROA signals were recorded and the results are reported here. Copyright © 2006 John Wiley & Sons, Ltd. [source] Optically Active Methacrylic Copolymers Bearing Side-Chain Bisazoaromatic and Bulky Achiral MoietiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2007Luigi Angiolini Abstract The synthesis of two novel series of optically active methacrylic copolymers that contain a side-chain chiral moiety linked to a photochromic bisazoaromatic chromophore has been carried out by radical copolymerization of the monomer (S)-3-methacryloyloxy-1-[4,-phenylazo-(4-azobenzene)]pyrrolidine with highly sterically hindered monomers such as tert- butyl methacrylate or triphenylmethyl methacrylate with the aim to investigate the effect on the optical activity of the resulting derivatives. The copolymeric products have been fully characterized and their spectroscopic and thermal properties compared to those of the related optically active homopolymer and the copolymers with methyl methacrylate, previously reported. The optical activity displayed by the polymers is discussed in terms of extent of chiral conformations assumed by the macromolecules as a consequence of the insertion of co-monomers capable of affecting the dipole-dipole interactions that occur in these derivatives between the side-chain bisazoaromatic chromophores disposed according to a mutual chiral arrangement. [source] Chiroptical Properties of Terthiophene Chromophores Dispersed in Oriented and Unoriented Polyethylene FilmsMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 6 2004Andrea Pucci Abstract Summary: Two new chiral terthiophene chromophores II and III were prepared with 99% enantiomeric excess. Chiroptical properties of these dyes dispersed in ultra high molecular weight polyethylene (UHMWPE) films were determined and compared with the same properties in solution. In the solid state, the optical activity strongly depends on the interaction mechanisms within small crystalline aggregates of chromophores. The film morphology and chromophore dispersion were also investigated by scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The good correlation between chromophore aggregation and chiroptical activity of the binary films promotes circular dichroism (CD) as an effective technique for monitoring the phase dispersion behaviour of dichroic dyes into polymer matrices. By mechanical stretching of the film a linearly dichroic orientation of the chromophores is obtained which results in a high degree of linear dichroism. The influence of the uniaxial orientation of terthiophene molecules along the drawing direction of UHMWPE on the chiroptical properties of the films, and the possible application of the oriented devices as linear polarizers are discussed. Absorption and CD spectra of unoriented UHMWPEII film at different rotation angles ,. [source] Study on optical properties of La3Ga5SiO14 crystals by interferometry of polarized lightPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2006Haifeng Qi Abstract The birefringence and optical activity of La3Ga5SiO14 crystal were studied by interferometry of polarized light. The corresponding characteristic parameters were calculated from the transmittance spectra with different orientational configuration between parallel polarisers. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Role of extended defects in brown colouration of diamondPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2007L. S. Hounsome Abstract The absorption spectrum of brown diamond is broad and featureless, in both natural type IIa and CVD-grown material. It is argued that such an absorption is due to an extended, rather than a point, defect. Ab-initio modelling studies have been conducted on dislocations and extended vacancy-related defects. While certain dislocations could potentially explain the origin of colour, their density is too low to account for experimentally observed absorption magnitudes. It is demonstrated that a vacancy disk lying in the {111} plane has an absorption spectrum similar to that seen in natural and CVD brown diamond. Such disks are unstable above about 200 vacancies and should relax to dislocation loops in natural diamond. Hydrogen is shown to passivate the optical activity of the disks. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Thermal activation of beryllium-related photoluminescence by annealing of GaN grown by molecular beam epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2005Kyoungnae Lee Abstract Surface polarity related differences in the optical activity of Be in GaN epilayers grown by rf-plasma molecular beam epitaxy are investigated. N-polar GaN doped with Be exhibits a significantly higher intensity of donor-acceptor pair (DAP) photoluminescence (PL) than similarly doped Ga-polar GaN, indicating the Be is incorporating at microscopically different sites, or possibly is forming different compensating complexes. Highly Be-doped Ga-polar GaN forms isolated polarity-inverted regions which then incorporate Be via the N-polar mechanism resulting in the DAP PL. High temperature annealing of the Ga-polar layers both under nitrogen/hydrogen mixtures and under pure nitrogen atmospheres activates the DAP PL. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Lower critical solution temperatures of thermo-responsive poly(N -isopropylacrylamide) copolymers with racemate or single enantiomer groupsPOLYMER INTERNATIONAL, Issue 2 2009Peng-Fei Li Abstract BACKGROUND: Thermo-responsive copolymers with racemate or single enantiomer groups are attracting increasing attention due to their fascinating functional properties and potential applications. However, there is a lack of systematic information about the lower critical solution temperature (LCST) of poly(N -isopropylacrylamide)-based thermo-responsive chiral recognition systems. In this study, a series of thermo-responsive chiral recognition copolymers, poly[(N -isopropylacrylamide)- co -(N -(S)- sec -butylacrylamide)] (PN- S -B) and poly[(N -isopropylacrylamide)- co -(N -(R,S)- sec -butylacrylamide)] (PN- R,S -B), with different molar compositions, were prepared. The effects of heating and cooling processes, optical activity and amount of chiral recognition groups in the copolymers on the LCSTs of the prepared copolymers were systematically studied. RESULTS: LCST hysteresis phenomena are found in the phase transition processes of PN- S -B and PN- R,S -B copolymers in a heating and cooling cycle. The LCSTs of PN- S -B and PN- R,S -B during the heating process are higher than those during the cooling process. With similar molar ratios of N -isopropylacrylamide groups in the copolymers, the LCST of the copolymer containing a single enantiomer (PN- S -B) is lower than that of the copolymer containing racemate (PN- R,S -B) due to the steric structural difference. The LCSTs of PN- R,S -B copolymers are in inverse proportion to the molar contents of the hydrophobic R,S -B moieties in these copolymers. CONCLUSION: The results provide valuable guidance for designing and fabricating thermo-responsive chiral recognition systems with desired LCSTs. Copyright © 2008 Society of Chemical Industry [source] Louis Pasteur's discovery of molecular chirality and spontaneous resolution in 1848, together with a complete review of his crystallographic and chemical workACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2009H. D. Flack Pasteur's chemical and crystallographic work is described. The article commences with a brief overview of related science (chemical structure, crystallography, optical activity) before and after 1848, the year of the discovery of molecular chirality and spontaneous resolution. Concerning this discovery, three separate and varying reports are described. These are: (i) the publications in the scientific literature, (ii) the early (auto)biographies and (iii) Pasteur's handwritten laboratory notebooks. The three versions give differing views on the topic. Subsequently all of Pasteur's crystallographic and chemical work is passed in review, a topic very rarely broached. Pasteur's view in later life on this part of his work is examined. The article concludes with a discussion of the term dissymmetry used by Pasteur. [source] Renaissance in chiroptical spectroscopic methods for molecular structure determinationTHE CHEMICAL RECORD, Issue 2 2007Prasad L. Polavarapu Abstract Two of the chiroptical spectroscopic methods, namely optical rotatory dispersion (ORD) and electronic circular dichroism (ECD), have been around for several decades. But their use in determining the absolute configuration and predominant conformation is gaining renewed interest with the availability of quantum mechanical methods for predicting ORD and ECD. Two other methods, namely vibrational circular dichroism (VCD) and vibrational Raman optical activity (VROA), are relatively new and offer convenient approaches for deducing the structural information in chiral molecules. With the availability of quantum mechanical programs for predicting VCD and VROA, these methods have attracted numerous new researchers to this area. This review summarizes the latest developments in these four areas and provides examples where more than one method has been used to confirm the information obtained from individual methods. © 2007 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 7: 125,136; 2007: Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/tcr.20117 [source] 2,4-Dinitrophenylhydrazones of 2,4-dihydroxybenzaldehyde, 2,4-dihydroxyacetophenone and 2,4-dihydroxybenzophenoneACTA CRYSTALLOGRAPHICA SECTION C, Issue 2 2004Russell G. Baughman In 2,4-dihydroxybenzaldehyde 2,4-dinitrophenylhydrazone N,N -dimethylformamide solvate {or 4-[(2,4-dinitrophenyl)hydrazonomethyl]benzene-1,3-diol N,N -dimethylformamide solvate}, C13H10N4O6·C3H7NO, (X), 2,4-dihydroxyacetophenone 2,4-dinitrophenylhydrazone N,N -dimethylformamide solvate (or 4-{1-[(2,4-dinitrophenyl)hydrazono]ethyl}benzene-1,3-diol N,N -dimethylformamide solvate), C14H12N4O6·C3H7NO, (XI), and 2,4-dihydroxybenzophenone 2,4-dinitrophenylhydrazone N,N -dimethylacetamide solvate (or 4-{[(2,4-dinitrophenyl)hydrazono]phenylmethyl}benzene-1,3-diol N,N -dimethylacetamide solvate), C19H14N4O6·C4H9NO, (XII), the molecules all lack a center of symmetry, crystallize in centrosymmetric space groups and have been observed to exhibit non-linear optical activity. In each case, the hydrazone skeleton is fairly planar, facilitated by the presence of two intramolecular hydrogen bonds and some partial N,N double-bond character. Each molecule is hydrogen bonded to one solvent molecule. [source] Optical, Redox, and NLO Properties of Tricyanovinyl Oligothiophenes: Comparisons between Symmetric and Asymmetric Substitution PatternsCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2006Juan Casado Dr. Abstract A series of tricyanovinyl (TCV)-substituted oligothiophenes was synthesized and investigated with a number of physical methods including UV/Vis, IR, and Raman spectroscopy, nonlinear optical (NLO) measurements, X-ray diffraction, and cyclic voltammetry. Mono- or disubstituted oligomers were prepared by the reaction of tetracyanoethylene with mono- or dilithiated oligomers. The comparative effects of the symmetric and asymmetric substitutions in the electronic and molecular properties have been addressed. These oligomers display dramatic reductions in both their optical and electrochemical band gaps in comparison with unsubstituted molecules. The analysis of the electronic properties of the molecules was assisted by density functional theory calculations, which are in excellent agreement with the experimental data. TCV substitution influences the energies of the frontier orbitals, especially with respect to the stabilization of LUMO orbitals. X-ray structural characterization of a monosubstituted oligomer exhibits ,-stacking with favorable intermolecular interactions. NLO results agree with the role of the intramolecular charge-transfer feature in the asymmetric samples. These results furthermore exalt the role of conformational flexibility in the disubstituted compounds and reveal an unexpected nonlinear optical activity for symmetric molecules. Regarding the electronic structure, the interpretation of the vibrational data reflects the balanced interplay between aromatic and quinoid forms, finely tuned by the chain length and substitution pattern. The electronic and structural properties are consistent with the semiconducting properties exhibited by these materials in thin film transistors (TFTs). [source] Enantiomerically Pure Titanium Complexes Containing an [OSSO]-Type Bis(phenolate) Ligand: Synthesis, Structure, and Formation of Optically Active OligostyrenesCHEMISTRY - AN ASIAN JOURNAL, Issue 8-9 2008Geert-Jan M. Meppelder Abstract Chiral 1,2- trans -dithiocyclohexanediyl-bridged bis(phenols) of the type [2,2,-{HOC6H2 -6-R1 -4-R2}2S2C6H10] ([OSSO]H2, R1=tBu, iPr, H; R2=tBu, iPr, Me) could be conveniently and selectively synthesized in three steps, starting from cyclohexene oxide and arene thiolate. The racemic bis(phenols) could be resolved using an enantiopure (S)-camphorsulfonic ester auxiliary or by (chiral) HPLC. Complexation of the racemic bis(phenols) to TiX4 (X=Cl, OiPr) proceeds in a diastereoselective fashion to give only the ,,R,R and ,,S,S enantiomers. Racemic [Ti{(OC6H2 -6- tBu-4-Me)2S2C6H10}Cl2] reacts with benzyl magnesium bromide to afford the crystallographically characterized dibenzyl complex. The benzyl cation formed using B(C6F5)3 in C6D5Br slowly decomposes at temperatures above +10,°C. When treated with methylaluminoxane, the dichloro complexes [Ti{OSSO}Cl2] polymerize styrene with activities up to 146,kg,(mol,catalyst),1,[styrene,(mol,L,1)],1,h,1; diisopropoxy complexes [Ti{OSSO}(OiPr)2] show mere trace activity. With 1-hexene as a chain-transfer agent, activated enantiopure titanium complexes give low-molecular-weight homochiral isotactic oligostyrenes, terminated by one to five 1-hexene units with Mn values as low as 750,g,mol,1 for R=tBu and 1290,g,mol,1 for R=Me. Below Mn,5000 these oligostyrenes show optical activity. [source] Calculated Raman Optical Activity Signatures of Tryptophan Side ChainsCHEMPHYSCHEM, Issue 15 2008Christoph R. Jacob Dr. Raman optical activity: The different local chirality of an adjacent group can cause a different sign of the ROA intensity of an amino-acid side chain (here tryptophan, see picture centre), even though the normal mode is unchanged. Calculated spectra clearly confirm that ROA spectroscopy can be utilized to determine the absolute conformation of tryptophan side chains in proteins (see figure, left and right). [source] Theoretical Determination of the Vibrational Raman Optical Activity Signatures of Helical Polypropylene ChainsCHEMPHYSCHEM, Issue 11 2006Ewa Lamparska Abstract Raman and vibrational Raman optical activity (VROA) spectra of helical conformers of polypropylene chains are simulated using ab initio methods to unravel the relationships between the vibrational signatures and the primary and secondary structures of the chains. For a polypropylene chain containing three units, conformational effects are shown to lead to more acute signatures for VROA than for Raman spectra. In addition to regular polypropylene chains, which can display right and left helicities with the same probability, chirality and therefore helicity are enforced by substituting one chain end with a phenyl group. The simulations predict that the threefold helical structures, which correspond to (TG)N conformations of the backbone, have a specific VROA backward signature in the form of an intense couplet around 1100 cm,1. This couplet is associated with collective wagging and twisting motions, while most of its intensity comes from the anisotropic invariants combining normal coordinate derivatives of the electric dipole,electric dipole polarizability and of the electric dipole,magnetic dipole polarizability. A similar signature has already been found in model helical polyethylene chains, whereas it is very weak in forward VROA. 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