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Circular Dichroism Spectra (circular + dichroism_spectrum)
Selected AbstractsTrityl Ethers: Molecular Bevel Gears Reporting Chirality through Circular Dichroism Spectra,ANGEWANDTE CHEMIE, Issue 38 2009Jacek, ciebura Mehr als nur eine Schutzgruppe: Die Tritylgruppe wird in Tritylethern von der Chiralität eines Alkylsubstituenten beeinflusst, wie aus den CD-Spektren solcher tritylgeschützten chiralen Alkohole hervorgeht. Das Trityl-CD-Verfahren gibt Einblicke in die Struktur und Funktion chiraler molekularer Getriebe und belegt den Zusammenhang zwischen der Absolutkonfiguration von Molekülen und dem Muster ihres Cotton-Effekts. [source] Study of Structural Stability of Cyclophilin A by NMR and Circular Dichroism SpectraCHINESE JOURNAL OF CHEMISTRY, Issue 7 2006Yan-Hong Shi Abstract The structural stability of cyclophilin A (CypA) was investigated using H/D exchange and temperature coefficients of chemical shifts of amide protons, monitored by 2D heteronuclear NMR spectroscopy. Amide proton exchange rates were measured by H/D exchange experiments for slow-exchange protons and measured by SEA (Solvent Exposed Amides)-HSQC experiments for fast-exchange protons. Temperature coefficients of chemical shifts and hydrogen exchange rates of amide protons show reasonably good correlation with the protein structure. Totally, 44 out of 153 non-proline assigned residues still exist in 86 d of hydrogen-deuterium exchange at 4 °C, suggesting that CypA structure should be highly stable. Residues in secondary structures of ,2, ,1, ,2, ,5, ,6 and ,7 might constitute the hydrophobic core of the protein. The change in free energy of unfolding (,Gu) of CypA was estimated to be (21.99±1.53) kJ·mol,1 by circular dichroism (CD). The large free energy change is also an indicator of the high structural stability. [source] WHEN POSITIVELY CHARGED MILK PROTEINS CAN BIND TO DNAJOURNAL OF FOOD BIOCHEMISTRY, Issue 6 2002MAHMOUD SITOHY ABSTRACT The binding of three esterified milk proteins (,-lactoglobutin, ,-lactalbumin and ,-casein) to plasmid DNAs at pH 7.1 was followed by agarose-gel electrophoresis. Highly esterified ,-lactoglobulin and ,-lactalbumin samples showed DNA-binding capacities comparable to those exhibited by native basic proteins such as lysozymes and histones. All the studied esterified ,-casein samples failed to bind to DNA at the applied pH. Complete retardation of DNA migration on agarose gel was observed at a 1:1 ratio of protein basic groups (Lys + Arg) to DNA phosphate add groups in the case of highly esterified ,-lactoglobulin, esterified ,-lactalbumin and native basic proteins (lysozyme and histone). Binding capacity was dependent on the degree of esterification of the milk proteins. Hydrolysis of esterified milk proteins either suppressed or reduced their DNA-binding capacities according to the degree of hydrolysis and consequently to the average size of the resulting peptides. A prolonged peptic hydrolysis (25% degree of hydrolysis) completely suppressed DNA-binding capacity probably because of the small sizes of the resulting peptic peptides (< 1 kDa). Treatment with trypsin, which hydrolyzed the esterified proteins into relatively large peptide fragments, reduced the DNA-binding capacity to levels inversely proportional to the degree of hydrolysis. In the range of 2.7,12.3 kb, there was no influence of the DNA size on the binding of esterified milk proteins. The interactions DNA-esterified milk proteins did not depend on the DNA shape (circular or linear). Circular dichroism spectra of DNA in complex with methylated ,-lactoglobulin were markedly altered as compared to those obtained when DNA was in complex with native ,-lactoghbutin. [source] Solution conformation of a tetradecapeptide stabilized by two di- n -propyl glycine residuesJOURNAL OF PEPTIDE SCIENCE, Issue 8 2010Vijayalekshmi Sarojini Abstract The solution conformation of a designed tetradecapeptide Boc-Val-Ala-Leu-Dpg-Val-Ala-Leu-Val-Ala-Leu-Dpg-Val-Ala-Leu-OMe (Dpg-14) containing two di- n -propyl glycine (Dpg) residues has been investigated by 1H NMR and circular dichroism in organic solvents. The peptide aggregates formed at a concentration of 3 mM in the apolar solvent CDCl3 were broken by the addition of 12% v/v of the more polar solvent DMSO-d6. Successive NiH Ni+1H NOEs observed over the entire length of the sequence in this solvent mixture together with the observation of several characteristic medium-range NOEs support a major population of continuous helical conformations for Dpg-14. Majority of the observed coupling constants () also support , values in the helical conformation. Circular dichroism spectra recorded in methanol and propan-2-ol give further support in favor of helical conformation for Dpg-14 and the stability of the helix at higher temperature. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd. [source] Phage display selection of efficient glutamine-donor substrate peptides for transglutaminase 2PROTEIN SCIENCE, Issue 11 2006Zsolt Keresztessy Abstract Understanding substrate specificity and identification of natural targets of transglutaminase 2 (TG2), the ubiquitous multifunctional cross-linking enzyme, which forms isopeptide bonds between protein-linked glutamine and lysine residues, is crucial in the elucidation of its physiological role. As a novel means of specificity analysis, we adapted the phage display technique to select glutamine-donor substrates from a random heptapeptide library via binding to recombinant TG2 and elution with a synthetic amine-donor substrate. Twenty-six Gln-containing sequences from the second and third biopanning rounds were susceptible for TG2-mediated incorporation of 5-(biotinamido)penthylamine, and the peptides GQQQTPY, GLQQASV, and WQTPMNS were modified most efficiently. A consensus around glutamines was established as pQX(P,T,S)l, which is consistent with identified substrates listed in the TRANSDAB database. Database searches showed that several proteins contain peptides similar to the phage-selected sequences, and the N-terminal glutamine-rich domain of SWI1/SNF1-related chromatin remodeling proteins was chosen for detailed analysis. MALDI/TOF and tandem mass spectrometry-based studies of a representative part of the domain, SGYGQQGQTPYYNQQSPHPQQQQPPYS (SnQ1), revealed that Q6, Q8, and Q22 are modified by TG2. Kinetic parameters of SnQ1 transamidation (KMapp = 250 ,M, kcat = 18.3 sec,1, and kcat/KMapp = 73,200) classify it as an efficient TG2 substrate. Circular dichroism spectra indicated that SnQ1 has a random coil conformation, supporting its accessibility in the full-length parental protein. Added together, here we report a novel use of the phage display technology with great potential in transglutaminase research. [source] Structural composition of ,I - and ,II -proteinsPROTEIN SCIENCE, Issue 2 2003Narasimha Sreerama Abstract Circular dichroism spectra of proteins are sensitive to protein secondary structure. The CD spectra of ,-rich proteins are similar to those of model ,-helices, but ,-rich proteins exhibit CD spectra that are reminiscent of CD spectra of either model ,-sheets or unordered polypeptides. The existence of these two types of CD spectra for ,-rich proteins form the basis for their classification as ,I - and ,II -proteins. Although the conformation of ,-sheets is largely responsible for the CD spectra of ,I -proteins, the source of ,II -protein CD, which resembles that of unordered polypeptides, is not completely understood. The CD spectra of unordered polypeptides are similar to that of the poly(Pro)II helix, and the poly(Pro)II-type (P2) structure forms a significant fraction of the unordered conformation in globular proteins. We have compared the ,-sheet and P2 structure contents in ,-rich proteins to understand the origin of ,II -protein CD. We find that ,II -proteins have a ratio of P2 to ,-sheet content greater than 0.4, whereas for ,I -proteins this ratio is less than 0.4. The ,-sheet content in ,I -proteins is generally higher than that in ,II -proteins. The origin of two classes of CD spectra for ,-rich proteins appears to lie in their relative ,-sheet and P2 structure contents. [source] Effect of intramolecular interactions on circular dichroism of ortho-substituted 1-phenethylamines,CHIRALITY, Issue 8 2004V.M. Demyanovich Abstract The synthesis of ortho-substituted (S)-1-phenethylamines via ortho-lithiation of its N,N-dimethyl derivative followed by reactions with different reagents is described. Circular dichroism spectra of synthesized compounds were measured. It is shown that the observed short-wave Cotton effects greatly depend on the existence of cyclic structure due to possible interactions such as hydrogen bond or electrostatic interaction. Chirality 16:486,492, 2004. © 2004 Wiley-Liss, Inc. [source] Role of the N-terminal Region in the Function of the Photosynthetic Bacterium Transcription Regulator PpsR,PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2008Yoichi Yamazaki PpsR is a transcription repressor for the gene cluster encoding photosystem genes in Rhodobacter sphaeroides. Repression activity is accomplished by DNA binding on the promoter regions of the photosystem gene clusters, and depends on both the redox potential and the presence of antirepressor protein AppA. To understand DNA repression regulation by PpsR, we investigated the function of PpsR domains in self-association for DNA binding. We constructed domain-deletion mutants and verified DNA-binding activity and dimer formation. Gel shift assay for measuring the DNA-binding activity of three sequential N-terminal deletion mutants revealed that N-terminal deletions (of minimum 121 residues) caused loss of binding activity. Size-exclusion gel chromatography revealed that deletion mutant which lacks the N-terminal 121-amino acid deletion mutant to exist as a dimer, although it was less stable than the intact PpsR. The mutants lacking the adjacent regions, Q-linker region and the first Per-Ant-Sim domain, did not form dimers, suggesting the involvement of the N-terminal region in dimer formation. This region is thus considered to be a functional domain in self-association, although not yet identified as a structural domain. Circular dichroism spectrum of the N-terminal region fragment exhibited a ,/, structure. We conclude that this region is a structural and functional domain, contributing to PpsR repression through dimer stabilization. [source] The optimization of protein secondary structure determination with infrared and circular dichroism spectraFEBS JOURNAL, Issue 14 2004Keith A. Oberg We have used the circular dichroism and infrared spectra of a specially designed 50 protein database [Oberg, K.A., Ruysschaert, J.M. & Goormaghtigh, E. (2003) Protein Sci. 12, 2015,2031] in order to optimize the accuracy of spectroscopic protein secondary structure determination using multivariate statistical analysis methods. The results demonstrate that when the proteins are carefully selected for the diversity in their structure, no smaller subset of the database contains the necessary information to describe the entire set. One conclusion of the paper is therefore that large protein databases, observing stringent selection criteria, are necessary for the prediction of unknown proteins. A second important conclusion is that only the comparison of analyses run on circular dichroism and infrared spectra independently is able to identify failed solutions in the absence of known structure. Interestingly, it was also found in the course of this study that the amide II band has high information content and could be used alone for secondary structure prediction in place of amide I. [source] Pyridoxal 5,-phoshate Schiff base in Citrobacter freundii tyrosinephenol-lyaseFEBS JOURNAL, Issue 6 2000Ionic, tautomeric equilibria Spectral properties of the internal Schiff base in tyrosine phenol-lyase have been investigated in the presence of an activating cation K+ and a cation-inhibitor Na+. The holoenzyme absorption spectra in the pH range 6.5,8.7 were recorded in the presence of K+. No apparent pKa value of the coenzyme chromophore was found in this pH range, indicating that the internal Schiff base does not change its ionic form on going from pH 6.5 to 8.7. To determine the ionic state and tautomeric composition of the Schiff base in tyrosine phenol-lyase, the absorption and circular dichroism spectra were analyzed using lognormal distribution curves. The predominant form of the internal Schiff base is that with protonated pyridinium and aldimine nitrogen atoms and deprotonated 3,-hydroxy group, i.e. the ketoenamine. This form is in prototropic equilibrium with its enolimine tautomer. The internal aldimine ionic form is changed upon replacement of K+ with Na+. This replacement leads to a significant decrease in the pKa value of pyridinium nitrogen of the pyridoxal- P. [source] Complexation of 4-dimethylaminoazobenzene with various kinds of cyclodextrins: Effects of cyclodextrins on the thermal cis-to-trans isomerizationINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2002Yoshimi Sueishi On the basis of the change in electronic and induced circular dichroism spectra for complex formation, the complexation of 4-dimethylaminoazobenzene (DAAB) with four kinds of cyclodextrins (,- and ,-cyclodextrin (CD), heptakis(2,6-di- O -methyl)-,-cyclodextrin, and heptakis(2,3,6-tri- O -methyl)-,-cyclodextrin) was studied in methanol,water and dimethyl sulfoxide,water mixtures. It was found that the trans and cis isomers of DAAB form two different types of complex (inclusion and lid type) with CDs, depending on the kinds of CDs and solvents. Further, we have examined the effect of CDs on the thermal cis-to-trans isomerization of DAAB. The accelerated or decelerated effect on the thermal isomerization was observed upon adding CDs. The effects of CDs on the thermal isomerization are discussed in connection with the complexation of the cis-isomer of DAAB with CDs. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 481,487, 2002 [source] Extraction of native collagen from limed bovine split wastes through improved pretreatment methodsJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 7 2008Dong Li Abstract BACKGROUND: The large amount of limed bovine split wastes discharged by the leather industry has raised concerns regarding their environmental effect. The objective of this work was to perform pilot plant trials to extract high-value native collagen from these wastes through improved pretreatment methods. RESULTS: EDTA- and HCl-pretreatment gave similar removal percentages of inorganic substances. Owing to the open structure of fibers, the collagen yield of HCl-pretreated splits (HPS) (41.31%) was higher than that of EDTA-pretreated splits (EPS) (10.42%). Furthermore, HCl-pretreated split collagen (HPC) had a more acidic isoelectric point, lower content of primary amino groups, larger Z-average particle size and higher relative viscosity than EDTA-pretreated split collagen (EPC). Electrophoretic analysis and circular dichroism spectra revealed the maintenance of polypeptide and triple helix conformation, respectively. In addition, the transition temperatures of EPC (34.7 °C) and HPC (34.6 °C) detected by differential scanning calorimetry (DSC) were close to that of commercial collagen from calfskin (CCC) (35.7 °C). CONCLUSION: A process of native collagen extraction from limed bovine split wastes was proposed. While both EPC and HPC represented similar physicochemical properties to those of CCC, the collagen yield of HPS was much higher than that of EPS. Copyright © 2008 Society of Chemical Industry [source] First observation of natural circular dichroism spectra in the extreme ultraviolet region using a polarizing undulator-based optical system and its polarization characteristicsJOURNAL OF SYNCHROTRON RADIATION, Issue 4 2009Masahito Tanaka Natural circular dichroism (CD) spectra in the extreme ultraviolet (EUV) region down to a wavelength of 80,nm have been observed for the first time, using an alanine thin film deposited on sodium salicylate coated glass as a sample. Calibrated EUV-CD spectra of l -alanine exhibited a large negative peak at around 120,nm and a positive CD signal below 90,nm, which were roughly predicted by theoretical calculations. A CD measurement system with an Onuki-type polarizing undulator was used to obtain the EUV-CD spectra. This CD system, the development of which took five years, can be used to observe even weak natural CD spectra. The polarization characteristics of this system were also evaluated in order to calibrate the recorded CD spectra. [source] Selective recognition of thymidine homopolymer (poly T) oligonucleotide with cobalt(II),4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene complexLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 3 2009Feng Ling Guo Abstract The interactions of cobalt(II),4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene (5-Cl-PADAB) complex with different kinds of homopolymer oligonucleotides in basic medium were investigated based on the measurements of resonance light scattering, UV,vis, circular dichroism spectra and dark field light-scattering imaging. Experiments showed that only thymidine homopolymer (poly T) oligonucleotides with the length in the range of poly T6 to poly T18 could interact with the Co(II),5-Cl-PADAB complex in alkaline conditions and cause evident color and spectral change. Thus, the binary complex of Co(II),5-Cl-PADAB could be employed as a visual probe for selectively recognizing the poly T oligonucleotides. Copyright © 2009 John Wiley & Sons, Ltd. [source] The acid-induced folded state of Sac7d is the native statePROTEIN SCIENCE, Issue 10 2000Jennifer L. Bedell Abstract Sac7d unfolds at low pH in the absence of salt, with the greatest extent of unfolding obtained at pH 2. We have previously shown that the acid unfolded protein is induced to refold by decreasing the pH to 0 or by addition of salt (McCrary BS, Bedell J, Edmondson SP, Shriver JW, 1998, J Mol Biol 276:203,224). Both near-ultraviolet circular dichroism spectra and ANS fluorescence enhancements indicate that the acid- and salt-induced folded states have a native fold and are not molten globular. 1H, 15N heteronuclear single quantum coherence NMR spectra confirm that the native, acid-, and salt-induced folded states are essentially identical. The most significant differences in amide 1H and 15N chemical shifts are attributed to hydrogen bonding to titrating carboxyl side chains and through-bond inductive effects. The 1H NMR chemical shifts of protons affected by ring currents in the hydrophobic core of the acid- and salt-induced folded states are identical to those observed in the native. The radius of gyration of the acid-induced folded state at pH 0 is shown to be identical to that of the native state at pH 7 by small angle X-ray scattering. We conclude that acid-induced collapse of Sac7d does not lead to a molten globule but proceeds directly to the native state. The folding of Sac7d as a function of pH and anion concentration is summarized with a phase diagram that is similar to those observed for other proteins that undergo acid-induced folding except that the A-state is encompassed by the native state. These results demonstrate that formation of a molten globule is not a general property of proteins that are refolded by acid. [source] Study of nobiletin binding to bovine serum albumin by capillary electrophoresis,frontal analysis and circular dichroismBIOMEDICAL CHROMATOGRAPHY, Issue 9 2010Lian Yi Abstract A very recent epidemiological study provided strong support for nobiletin (NOB) as a potential candidate chemopreventive agent against cancer. From the pharmacology point of view, drug,protein interactions are determining factors in therapeutic, pharmacodynamic and toxicological drug properties. In this work, for the first time, detection of NOB at near-physiological conditions was accomplished by means of capillary electrophoresis,frontal analysis (CE-FA), and then the binding constants of NOB with bovine serum albumin (BSA) at the same conditions were determined. Complexation of NOB,BSA led to a decrease of the height for free NOB with increasing concentration of BSA. These results revealed the presence of a single class of binding site on BSA, and provided the binding constant of 103/m, showing the strong affinity of NOB for BSA. Furthermore, circular dichroism spectra showed that, when the molar ratio of NOB to BSA was up to 2:1, NOB did not affect the overall protein conformation significantly and the protein thus retained a native-like structure. These results may provide important information for preclinical studies of nobiletin in pharmaceutical research. Copyright © 2010 John Wiley & Sons, Ltd. [source] Effects of hydrophobicity and anions on self-assembly of the peptide EMK16-IIBIOPOLYMERS, Issue 4 2010Dawei Zou Abstract Effects of hydrophobic and electrostatic interactions on the self-assembling process of the ionic-complementary peptide EMK16-II are investigated by atomic force microscopy imaging, circular dichroism spectra, light scattering, and chromatography. It is found that the hydrophobicity of the peptide promotes the aggregation in pure water even at a very low concentration, resulting in a much lower critical aggregation concentration than that of another peptide, EAK16-II. The effect of anions in solution with different valences on electrostatic interactions is also important. Monovalent anions (Cl, and Ac,) with a proper concentration can facilitate the formation of peptide fibrils, with Cl, of smaller size being more effective than Ac, of larger size. However, only small amounts of fibrils, but plenty of large amorphous aggregates, are found when the peptide solution is incubated with multivalent anions, such as SO, C6H5O, and HPO. More importantly, by gel filtration chromatography, the citrate anion, which induces a similar effect on the self-assembling process of EMK16-II as that of SO and HPO, can interact with two or more positively charged residues of the peptide and reside in the amorphous aggregates. This implies a "salt bridge" effect of multivalent anions on the peptide self-assembling process, which can interpret a previous puzzle why divalent cations inhibit the formation of ordered nanofibrils of the ionic-complementary peptides. Thus, our results clarify the important effects of hydrophobic and electrostatic interactions on the self-assembling process of the ionic-complementary peptides. These are greatly helpful for us to understand the mechanism of peptides' self-assembling process and protein folding and aggregation. © 2009 Wiley Periodicals, Inc. Biopolymers 93: 318,329, 2010. This article was originally published online as an acceptedpreprint. The "Published Online" date corresponds to the preprintversion. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] Aspergillus niger lipase: Heterologous expression in Pichia pastoris, molecular modeling prediction and the importance of the hinge domains at both sides of the lid domain to interfacial activationBIOTECHNOLOGY PROGRESS, Issue 2 2009Zhengyu Shu Abstract Aspergillus niger lipase (ANL) is an important biocatalyst in the food processing industry. However, there is no report of its detailed three-dimensional structure because of difficulties in crystallization. In this article, based on experimental data and bioinformational analysis results, the structural features of ANL were simulated. Firstly, two recombinant ANLs expressed in Pichia pastoris were purified to homogeneity and their corresponding secondary structure compositions were determined by circular dichroism spectra. Secondly, the primary structure, the secondary structure and the three-dimensional structure of ANL were modeled by comparison with homologous lipases with known three-dimensional structures using the BioEdit software, lipase engineering database (http://www.led.uni-stuttgart.de/), PSIPRED server and SwissModel server. The predicted molecular structure of ANL presented typical features of the ,/, hydrolase fold including positioning of the putative catalytic triad residues and the GXSXG signature motif. Comparison of the predicted three-dimensional structure of ANL with the X-ray three-dimensional structure of A. niger feruloyl esterase showed that the functional difference of interfacial activation between lipase and esterase was concerned with the difference in position of the lid. Our three-dimensional model of ANL helps to modify lipase structure by protein engineering, which will further expand the scope of application of ANL. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] Trianglamines,Readily Prepared, Conformationally Flexible Inclusion-Forming Chiral HexaminesCHEMISTRY - A EUROPEAN JOURNAL, Issue 6 2006Jacek Gawronski Prof. Dr. Abstract Trianglamines, macrocyclic heteraphanes, were readily synthesised through a [3+3] cyclocondensation of (R,R)-1,2-diaminocyclohexane with terephthalaldehyde, followed by NaBH4 reduction and N-alkylation. The macrocyclic ring shows a remarkable ability to change its conformation, as a consequence of rotation about the CN bonds or nitrogen inversion due to protonation or N-alkylation, as revealed by circular dichroism spectra, computational modelling and X-ray diffraction analysis. The flexible natures of the trianglamine macrocycles allow ready accommodation of a variety of guest molecules to form crystalline inclusion complexes of highly diversified interpenetrating structures. [source] Electronic Structure, Spectra, and Magnetic Circular Dichroism of Cyclohexa-, Cyclohepta-, and CyclooctapyrroleCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2005Alexander Gorski Abstract Three recently obtained expanded porphyrins represent nice examples of compounds for which the electronic and spectral properties can be predicted from symmetry considerations alone. Perimeter-model-based theoretical analysis of the electronic structure of doubly protonated cyclo[6], cyclo[7], and cyclo[8]pyrrole leads to the anticipation of qualitatively the same electronic absorption and magnetic circular dichroism patterns for all three compounds. These predictions are fully confirmed by experiments, as well as DFT and INDO/S calculations. Due to a characteristic pattern of frontier molecular orbitals, a degenerate HOMO and a strongly split LUMO pair, the three cyclopyrroles show comparable absorption intensity in the Q and Soret regions. Magnetic circular dichroism spectra reveal both A and B Faraday terms, of which the signs and magnitudes are in remarkably good agreement with theoretical expectations. The values of the magnetic moments of the two lowest degenerate excited states have also been obtained. [source] Calculation of the Vibrationally Resolved, Circularly Polarized Luminescence of d -Camphorquinone and (S,S)- trans -,-HydrindanoneCHEMPHYSCHEM, Issue 11 2010Benjamin Pritchard Abstract Circularly polarized luminescence (CPL), the differential emission of left- and right-handed circularly polarized light from a molecule, is modeled by using time-dependent density functional theory. Calculations of the CPL spectra for the first electronic excited states of d -camphorquinone and (S,S)- trans -,-hydrindanone under the Franck,Condon approximation and using various functionals are presented, as well as calculations of absorption, emission, and circular dichroism spectra. The functionals B3LYP, BHLYP, and CAM-B3LYP are employed, along with the TZVP and aug-cc-pVDZ Gaussian-type basis sets. For the lowest-energy transitions, all functionals and basis sets perform comparably, with the long-range-corrected CAM-B3LYP better reproducing the excitation energy of camphorquinone but leading to a blue shift with respect to experiment for hydrindanone. The vibrationally resolved spectra of camphorquinone are very well reproduced in terms of peak location, widths, shapes, and intensities. The spectra of hydrindanone are well reproduced in terms of overall envelope shape and width, as well as the lack of prominent vibrational structure in the emission and CPL spectra. Overall the simulated spectra compare well with experiment, and reproduce the band shapes, emission red shifts, and presence or absence of visible vibrational fine structure. [source] Absolute configuration of eremophilane sesquiterpenes from Petasites hybridus: Comparison of experimental and calculated circular dichroism spectraCHIRALITY, Issue 3 2010Antje Bodensieck Abstract In-depth conformational analyses of 10 known eremophilane (= (1S,4aR,7R,8aR)-decahydro-1,8a-dimethyl-7-(1-methylethyl)napththalene) sesquiterpenes, 1,10, from Petasites hybridus were performed with molecular mechanics as well as density functional theory methods. Electronic transition energies and rotational strengths of these eight eremophilane lactones and two petasins were calculated by time-dependent density functional theory (B3PW91/TZVP). The absolute configurations of the constituents could be assigned by comparison of their simulated and experimental circular dichroism (CD) spectra in methanol as (4S,5R,8S,10R) (1, 2), (2R,4S,5R,8S,10R) (3, 4, 5), (2R,4S,5R,8R,9R,10R) (6), (2R,4S,5R,8R,10R) (7, 8), and (3R,4R,5R) (9, 10). Single-crystal X-ray diffraction data of 8,-hydroxyeremophilanolide ((8S)-8-hydroxyeremophil-7(11)-en-12,8-olide) (1) served as starting point for the theoretical conformational calculations of the 8,-epimers of the eremophilane lactones. Experimental CD spectra as well as 1H NMR spectra of compound 1 in methanol were considerably dependent on sample concentration. Chirality, 2010. © 2009 Wiley-Liss, Inc. [source] Synthesis and characterization of novel chiral ionic liquids and investigation of their enantiomeric recognition propertiesCHIRALITY, Issue 2 2008David K. Bwambok Abstract We report the synthesis and characterization of amino acid ester based chiral ionic liquids, derived from L - and D -alanine tert butyl ester chloride. The synthesis was accomplished via an anion metathesis reaction between commercially available L - and D -alanine tert butyl ester chloride using a variety of counterions such as lithium bis (trifluoromethane) sulfonimide, silver nitrate, silver lactate, and silver tetrafluoroborate. Both enantiomeric forms were obtained as confirmed by bands of opposite sign in the circular dichroism spectra. The L - and D -alanine tert butyl ester bis (trifluoromethane) sulfonimide were obtained as liquids at room temperature and intriguingly exhibited the highest thermal stability (up to 263°C). In addition, the ionic liquids demonstrated enantiomeric recognition ability as evidenced by splitting of racemic Mosher's sodium salt signal using a liquid state 19F nuclear magnetic resonance (NMR) and fluorescence spectroscopy. The L - and D -alanine tert butyl ester chloride resulted in solid salts with nitrate, lactate, and tetrafluoroborate anions. This illustrates the previously observed tunability of ionic liquid synthesis, resulting in ionic liquids of varying properties as a function of varying the anion. Chirality, 2008. © 2007 Wiley-Liss, Inc. [source] Resolution, configurational assignment, and enantiopharmacology at glutamate receptors of 2-amino-3-(3-carboxy-5-methyl-4-isoxazolyl)propionic acid (ACPA) and demethyl-ACPA,CHIRALITY, Issue 9 2001Tommy N. Johansen Abstract We have previously described (RS)-2-amino-3-(3-carboxy-5-methyl-4-isoxazolyl)propionic acid (ACPA) as a potent agonist at the (RS)-2-amino-3-(3-hydroxy-5-methyl-4-isoxazolyl)propionic acid (AMPA) receptor subtype of (S)-glutamic acid (Glu) receptors. We now report the chromatographic resolution of ACPA and (RS)-2-amino-3-(3-carboxy-4-isoxazolyl)propionic acid (demethyl-ACPA) using a Sumichiral OA-5000 column. The configuration of the enantiomers of both compounds have been assigned based on X-ray crystallographic analyses, supported by circular dichroism spectra and elution orders on chiral HPLC columns. Furthermore, the enantiopharmacology of ACPA and demethyl-ACPA was investigated using radioligand binding and cortical wedge electrophysiological assay systems and cloned metabotropic Glu receptors. (S)-ACPA showed high affinity in AMPA binding (IC50 = 0.025 ,M), low affinity in kainic acid binding (IC50 = 3.6 ,M), and potent AMPA receptor agonist activity on cortical neurons (EC50 = 0.25 ,M), whereas (R)-ACPA was essentially inactive. Like (S)-ACPA, (S)-demethyl-ACPA displayed high AMPA receptor affinity (IC50 = 0.039 ,M), but was found to be a relatively weak AMPA receptor agonist (EC50 = 12 ,M). The stereoselectivity observed for demethyl-ACPA was high when based on AMPA receptor affinity (eudismic ratio = 250), but low when based on electrophysiological activity (eudismic ratio = 10). (R)-Demethyl-ACPA also possessed a weak NMDA receptor antagonist activity (IC50 = 220 ,M). Among the enantiomers tested, only (S)-demethyl-ACPA showed activity at metabotropic receptors, being a weak antagonist at the mGlu2 receptor subtype (KB = 148 ,M). Chirality 13:523,532, 2001. © 2001 Wiley-Liss, Inc. [source] Characterization of site I of human serum albumin using spectroscopic analyses: Locational relations between regions Ib and Ic of site IJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 12 2004Keishi Yamasaki Abstract Site I of human serum albumin is an important and complex region for high-affinity binding of drugs. Equilibrium dialysis showed independent binding of dansyl- L -asparagine (DNSA) and n -alkyl p -aminobenzoates (p -ABEs) to regions Ib and Ic, respectively, in the pH range 6.0,9.0. However, individual binding of DNSA increased with pH in the same range. Binding of the four n -alkyl p -ABEs strongly perturbed the circular dichroism spectrum of bound DNSA, and the effect increased with concentration and the number of carbon atoms in the alkyl moiety. A similar effect was observed by increasing pH from 6.0 to 9.0, a pH range in which human serum albumin is known to undergo the neutral-to-base transition. The spectral changes propose spatial orientation changes of DNSA at region Ib. This proposal was supported by increased fluorescence anisotropy values: n -alkyl p -ABEs binding and the pH-dependent conformational change each restricted the mobility of the naphthalene ring of bound DNSA. Despite the similar effects on the spatial orientation of DNSA, clear differences were observed between the effects of n -alkyl p -ABEs and neutral-to-base transition. The former hardly changed the affinity and maximum fluorescence emission wavelength of bound DNSA; in contrast, the latter significantly affected them. The results give new information about site I and, according to our knowledge, represent a new type of ligand interaction, because the binding site of DNSA could be changed by simultaneous binding of the n -alkyl p -ABEs without affecting the binding constant. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 93:3004,3012, 2004 [source] Exclusive Observation of the (132R)-Enantiomer of Chlorophyll- c from a Diatom Chaetoseros calcitransPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 2 2010Tadashi Mizoguchi Chiral high-performance liquid-chromatography (HPLC) for quantitative analysis of optically active chlorophyll(Chl)- c molecules, which are seen in many marine photosynthetic organisms, was developed. Chls- c have a single asymmetric carbon at the 132 -position, so their stereoisomers are (132R)- and (132S)-enantiomers. After the separation of each enantiomer, the stereochemistry was unambiguously characterized using its circular dichroism spectrum in comparison with that of the structure-related compound, protochlorophyllide- a. Moreover, Chls- c were carefully extracted from the cells of a diatom Chaetoseros calcitrans without racemization and were subjected to the chiral HPLC. The results clearly demonstrated that naturally occurring Chl- c molecules are enantiomerically pure (132R)-forms, which are generally found in photosynthetically active chlorophyllous pigments. [source] | |||||||||||||||||||||||||