Optical Rotatory Dispersion Studies Research Articles

A combined experimental and theoretical study of optical rotatory dispersion for (R)-glycidyl methyl ether in aqueous solution.

The dispersive optical activity for aqueous solutions of non-rigid (R)-glycidyl methyl ether (R-GME) has been explored synergistically from experimental and theoretical perspectives. Density functional theory analyses performed with the polarizable continuum model for implicit solvation identified nine low-lying stable conformers that are interconverted by rotation about two large-amplitude torsional coordinates. The antagonistic chiroptical signatures predicted for these structural isomers were averaged under a Boltzmann-weighting ansatz to estimate the behavior expected for a thermally equilibrated ensemble. This led to optical rotatory dispersion profiles that reproduced the overall shape of observations but failed to achieve uniform agreement with measured specific-rotation values even when anharmonic vibrational corrections were applied. A mixed QM/FQ paradigm, whereby quantum-mechanical (QM) calculations of optical activity were combined with classical molecular dynamics simulations of explicit solvation that included mutual-polarization effects by means of fluctuating charges (FQ), was enlisted to elucidate the microsolvation environment and gauge its impact upon conformer distributions and response properties. Although quantitative accord with experiments remained elusive, this approach revealed strong variations in the magnitude and sign of rotatory powers for R-GME as the configuration of surrounding water molecules evolved, thereby highlighting the inherently dynamical nature of the solvated chiroptical response, calling into question the validity of "static" descriptions based on the presumption of distinct energy minima, and giving insight into the inherent complexity posed by the modeling of such properties for solvated systems.

Effect of Ascorbic Acid Isomeric Forms on Antibacterial Activity of Its Chitosan Salts

Optical rotatory dispersion studies revealed water solutions of chitosan in L- and D-ascorbic acid to exhibit right rotation with anomalous dispersion and left rotation with normal dispersion, respectively. Microbiological investigation and transmission electron microscopy revealed the chitosan salt with D-ascorbic acid to cause deeper destructive changes than pure chitosan, which resulted in higher antibacterial activity against Staphylococcus aureus 209P and Escherichia coli 113-13.

Absolute Configurations of Fungal and Plant Metabolites by Chiroptical Methods. ORD, ECD, and VCD Studies on Phyllostin, Scytolide, and Oxysporone

The absolute configuration (AC) of the bioactive metabolites phyllostin (1) and scytolide (2), two hexahydro-1,4-benzodioxines produced by Phyllosticta cirsii, and oxysporone (3), a dihydrofuropyranone recently isolated from a strain of Diplodia africana, has been assigned by computational analysis of their optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) spectra. Computational prediction of ORD, ECD, and VCD allowed us to assign (3S,4aR,8S,8aR) AC to naturally occurring (-)-1, while (4aR,8S,8aR) AC was assigned to (-)-2 employing only ECD and VCD, because in this case ORD analysis turned out to be unsuitable for AC assignment. Theoretical prediction of both ORD and ECD spectra of 3 led to assignment of (4S,5R,6R) AC to (+)-3. In this case a satisfactory agreement between experimental and calculated VCD spectra was obtained only after taking into account solvent effects. This study shows that in the case of flexible and complex natural products only a concerted application of more than a single chiroptical technique permits unambiguous assignment of absolute configuration.

Non-Native Heme−Histidine Ligation Promotes Microsecond Time Scale Secondary Structure Formation in Reduced Horse Heart Cytochromec

Previous far-UV time-resolved optical rotatory dispersion (TRORD) studies of the sub-millisecond (burst) phase of secondary structure formation in horse and tuna cytochromes c after photoreduction in denaturant suggested that the non-native His18-Fe-His33 heme ligation dominant in the unfolded horse protein facilitated this fast folding better than did the His18-Fe-His26 coordination dominant in tuna [Chen, E., Goldbeck, R.A., and Kliger, D.S. (2003) J. Phys. Chem. A 107, 8149-8155; Chen, E., Goldbeck, R.A., and Kliger, D.S. (2004) J. Am. Chem. Soc. 126, 11175-11181]. Whether His18-Fe-His33 coordination actually facilitates fast secondary structure formation or just slows folding less than His18-Fe-His26 coordination is probed by examining the double histidine mutant H26QH33N of horse heart cytochrome c. The fast folding phase is absent in H26QH33N, indicating that His18-Fe-His33 misligation does promote fast secondary structure formation, as does His18-Fe-His26 to a lesser extent. His33 may be better able to facilitate folding because it is not as constrained by hydrogen bonding interactions in the denatured state as is His26. A greater flexibility, not only because of weakened or disrupted Van der Waals interactions in the presence of guanidine hydrochloride (GuHCl) but also because of its position relative to His18, may allow His33 to ligate to the heme group more easily than His26. These results are discussed along with the results of far-UV CD and Soret and visible region MCD measurements, which were performed to probe heme ligation in H26QH33N and to understand how GuHCl affects its folding stability and cooperativity.

Liquid crystal polymorphism in F-actin: Optical microscopic and rotatory dispersion studies

Filamentous actin (F-actin), which occurs abundantly and ubiquitously in living mechanisms such as muscle, nonmuscle cells, and cytoskeleton, exhibits a liquid crystal polymorphism as its concentration is increased. The double-stranded, helical F-actin filaments are 1–70 μm long in our samples. The chirality of the filaments is consistent with the experimental observation of the characteristic cholesteric fingerprint and uniform textures. In addition to the chiral nematic phase, our optical microscopic studies show the occurrence of tilted chiral smectic phases, e.g., smectic C*, I*, or F*, and a smectic B phase. Measurement of optical rotatory dispersion in the cholesteric phase confirms the prediction of the de Vries equation describing the optical rotatory dispersion behavior for cholesterics. The observed lyotropic polymorphism is consistent with the Flory lattice model and a semiflexible polymer mesogen model of F-actin.

Unconventional, Amphiphilic Polymers Based on Chiral Poly(ethylene oxide) Derivatives. 2. Ordering and Assembly

The poly(ethylene oxide) derivatives 1−3 (Figure 1) arein designsynthetic analogues of coiled-coil-forming peptides. A comparative optical rotatory dispersion (ORD) study and TEM measurements have been used to investigate the ordering and assembly processes that are involved in the aggregation of these amphiphilic polymers 1−3 in H2O. ORD measurements have shown that various ethylene oxide derivatives display an inversion of optical rotation upon complexation with KSCN, i.e. upon adoption of a helical conformation. This observation has led to the proposal that polymers 1−3 are helically ordered in H2O, since the methyl-substituted polymer 3 exhibits an inversion of optical rotation on going from apolar (THF) to polar (H2O) solvents; phase separation prohibits the detection of such an inversion for the isobutyl-substituted polymers 1 and 2. TEM studies on surfaces onto which polymers 1−3 were deposited from aqueous solutions revealed granular and threadlike aggregates. The formation of the threadlike highe...

Raman and optical rotatory dispersion study of amylose in water–ethanol mixtures

AbstractRaman spectroscopy and optical rotatory dispersion techniques were used to investigate the transitions of the coil–helix and helix–helix forms and the conformation of functional groups in amylose in water–ethanol mixtures. The conditions of the transitions of a random coil form to the left‐ and right‐handed helix of V‐amylose under the influence of ethanol were determined. The Raman measurements also provided information on different trans and gauche conformations of CH2OH groups. The correlation between the process of adopting the right‐handed helix of V‐amylose and the (g, g) conformation of CH2OH groups is discussed.

FTIR measurements of optical rotatory dispersion and circular dichroism

FTIR methods for measuring optical rotatory dispersion (ORD) and circular dichroism (CD) were developed. The measurements of both phenomena are accomplished by means of various techniques. The study of ORD makes use of linearly polarized IR radiation while that of CD requires a circular polarizer (retarder) able to convert linearly polarized IR radiation into circularly polarized one. Examples of induced cholesteric solutions are shown.

Optical rotatory dispersion and circular dichroism studies of copolyaspartates with long alkyl side chain

Copoly(hexyl- l-aspartate-benzyl- l-aspartate), copoly(nonyl- l-aspartate-benzyl- l-aspartate) and copoly(dodecyl- l-aspartate-benzyl- l-aspartate) with various compositions were prepared by ester exchange reaction of poly(β-benzyl- l-aspartate). Copolyaspartates of low degree of alkylation were found to take a left handed α helix, similar to poly(β-benzyl- l-aspartate), and those of high degree of alkylation changed to a right handed α helix. Copoly(hexyl- l-aspartate-benzyl- l-aspartate) and copoly(dodecyl- l-aspartate-benzyl- l-aspartate) changed helix sense from left to right at 50% hexylation and 10% dodecylation, respectively. A small induced circular dichroism trough appeared around 230nm for these two copolyaspartates above 75% alkylation, indicative of a certain ordering of the carbonyl group due to the formation of an ordered structure of a long alkyl side chain. However, copoly(nonyl- l-aspartate-benzyl- l-aspartate) of 13% nonylation exhibited the induced circular dichroism spectrum and took a left handed α helix. Copoly(nonyl- l-aspartate-benzyl- l-aspartate) caused the reversal in helix sense above 70% nonylation according to a stabilizing effect of the ordered structure of the side chain.

Phase diagrams of the blue phases

Polarizing microscopy, selection reflection measurements, and optical rotatory dispersion studies are used to investigate the stability of all three blue phases as a function of temperature and cholesteric pitch. The results demonstrate that as the cholesteric pitch is increased, BP III first becomes unstable, then BP II, and finally BP I.

Conformation and stability of the chymotrypsin inhibitor from winged bean seed (Psophocarpus tetragonolobus (L.) DC).

Spectrophotometric measurement was found to be a sensitive method for evaluating the stability of the chymotrypsin inhibitor from the winged bean. The thermal stability of this protein in aqueous solution was much greater at pH 3 than at pH 8 or pH 11. Evidence from u.v. absorption and from circular dichroism indicated that irreversible conformation changes occurred at higher temperature (greater than 70 degrees). Circular dichroism and optical rotatory dispersion studies at pH 8 show that the inhibitor is rich in beta-structure and virtually devoid of alpha-helix in aqueous solution. We conclude from experiments with denaturing solvents that the inhibitor is very stable and that high concentrations of denaturant are required before unfolding occurs. Chemical modification experiments with tetranitromethane were consistent with a tight stable structure; even in 6M guanidine hydrochloride only three of the five tyrosine residues in the inhibitor molecule were nitrated. However, tyrosine does not seem to be implicated at the reactive site of the inhibitor. Interaction of the inhibitor with alpha-chymotrypsin and chymotrypsin B was also followed by difference spectroscopy in the ultraviolet region. Difference spectra were detected that were characteristic of changes in the environment of both tyrosine and tryptophan chromophores. Comparison of the spectral data obtained for the interaction of the inhibitor with bovine alpha-chymotrypsin and with chymotrypsin B indicated that a tryptophan residue may be involved at the reactive site of the inhibitor. Spectral changes were also detected for the interaction between the chymotrypsin inhibitor and trypsin, although it is well established that the specificity of this inhibitor is restricted to the chymotrypsins.(ABSTRACT TRUNCATED AT 250 WORDS)

Suppression of the statistical coil state during the α ↔ β transition in homopolypeptides

A matrix formulation of the conformational partition function has been used to examine helix sheet transitions in homopolyamino acids. α-Helices are weighted by Zimm-Bragg parameters σ and s. Antiparallel β-sheets with tight bends are weighted by the parameters t, δ, and τ, where t is the propagation parameter. In addition, each bend contributes a factor δ, and each residue in the sheet that does not have a partner in the preceding strand contributes a factor τ. The helix can be the dominant conformation in a long chain only if two conditions are satisfied simultaneously: (i) s > 1, and (ii) either s > t, or σ, δ, and τ are assigned values that inflict a greater penalty on antiparallel sheets than on helices. The maximum amount of coil developed during the helix sheet transition is strongly influenced by the size of τ, but it is only weakly dependent on the size of δ. Previously reported optical rotatory dispersion, CD, laser Raman, and nmr studies of thermally induced α β transitions in homopolyamino acids, notably poly(L-lysine), demonstrate that little random coil is present. If the random coil content is to remain small during the helix sheet transition, τ must be significantly less than unity. A small value for τ means that there is a significant penalty assessed to lysyl residues in an antiparallel sheet that do not have a partner in a preceding strand.

Stability and physicochemical properties of a trypsin inhibitor from winged bean seed ( psophocarpus tetragonolobus (L)DC)

The stability and physicochemical properties of the major trypsin inhibitor from the winged bean seed (designated trypsin inhibitor 2) have been studied in solution. The purified inhibitor, which stoichiometrically inhibits bovine trypsin in the molar ratio 1:1, is stable over the pH range 3–11 at ambient temperatures. Only a slight decrease in inhibitory activity occurs down to pH 2, but a sharper decrease occurs at pH values above 11. The inhibitor is stable to heat up to 60°C, but at higher temperatures (60–90°C) it is more stable at pH 3 than at pH 5.5 or pH 8.0. Trypsin inhibitor 2 retains its inhibitory activity in 8 M urea at pH 8.0, but is more susceptible to 8 M urea at pH 4.0. The stronger denaturant 6 M guanidine hydrochloride, however, abolishes the inhibitory activity at both pH 4.0 and pH 8.0. The inhibitor was not inactivated in 0.14 M β-mercaptoethanol at either pH; however, reduction in the presence of 8 M urea or 6 M guanidine hydrochloride results in a loss of inhibitory activity. Circular dichroism and optical rotatory dispersion studies indicate that the inhibitor structure is characterized by β-sheet and unordered forms and the absence of α-helix. The positive CD band centered at 227 nm has been used to follow conformation change as a function of temperature. In line with the stability studies, the inhibitor conformation was thermally most stable at pH 3.0 and changed increasingly as the pH was raised. This band showed little change at neutral pH up to 8 M guanidine hydrochloride. Tyrosine titration in aqueous solution indicates that 1 or 2 of the 11 tyrosines are difficult to titrate even at pH 13. A more normal titration curve is obtained in 6 M guanidine hydrochloride, although at least one tyrosine side-chain appears to be buried in the protein interior and resists complete titration at pH values in excess of 12. These data show that this inhibitor has a high degree of stability, typical of other known protein proteinase inhibitors.

Suppression of the statistical coil state during the alpha in equilibrium beta transition in homopolypeptides.

AbstractA matrix formulation of the conformational partition function has been used to examine helix ↔ sheet transitions in homopolyamino acids. α‐Helices are weighted by Zimm‐Bragg parameters σ and s. Antiparallel β‐sheets with tight bends are weighted by the parameters t, δ, and τ, where t is the propagation parameter. In addition, each bend contributes a factor δ, and each residue in the sheet that does not have a partner in the preceding strand contributes a factor τ. The helix can be the dominant conformation in a long chain only if two conditions are satisfied simultaneously: (i) s > 1, and (ii) either s > t, or σ, δ, and τ are assigned values that inflict a greater penalty on antiparallel sheets than on helices. The maximum amount of coil developed during the helix ↔ sheet transition is strongly influenced by the size of τ, but it is only weakly dependent on the size of δ. Previously reported optical rotatory dispersion, CD, laser Raman, and nmr studies of thermally induced α ↔ β transitions in homopolyamino acids, notably poly(L‐lysine), demonstrate that little random coil is present. If the random coil content is to remain small during the helix ↔ sheet transition, τ must be significantly less than unity. A small value for τ means that there is a significant penalty assessed to lysyl residues in an antiparallel sheet that do not have a partner in a preceding strand.

Optical rotatory dispersion studies. 136. Enzymic reduction of 2-methyl-2-(trideuteriomethyl)cyclohexane-1,3-dione. Unusual conformation of 2,2-dimethyl-3-hydroxycyclohexanone

Optical rotatory dispersion studies. 136. Enzymic reduction of 2-methyl-2-(trideuteriomethyl)cyclohexane-1,3-dione. Unusual conformation of 2,2-dimethyl-3-hydroxycyclohexanone

Optical rotatory dispersion studies. 135. Synthesis and chiroptical properties of (S)- and (R)-(3-2H1)-2,2-dimethylcyclobutanone. Evidence for conformational effects in substituted cyclobutanones

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOptical rotatory dispersion studies. 135. Synthesis and chiroptical properties of (S)- and (R)-(3-2H1)-2,2-dimethylcyclobutanone. Evidence for conformational effects in substituted cyclobutanonesR. N. Harris III, P. Sundararaman, and C. DjerassiCite this: J. Am. Chem. Soc. 1983, 105, 8, 2408–2413Publication Date (Print):April 1, 1983Publication History Published online1 May 2002Published inissue 1 April 1983https://doi.org/10.1021/ja00346a050RIGHTS & PERMISSIONSArticle Views240Altmetric-Citations19LEARN 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 (730 KB) Get e-Alerts Get e-Alerts

Chirality changes in reactions of asymmetric molybdenum complexes

Optical rotatory dispersion and circular dichroism studies have allowed the determination of the changes in configuration at the molybdenum center upon displacement of carbonyl and iodide in neomenthylcyclopentadienyl—Mo(allyl)(NO)X systems. Displacement of carbonyl by iodide occurs with retention of configuration. Replacement of iodide with benzenesulfonate followed by replacement of the sulfonate with iodide occurs stereospecifically with net retention of configuration. In the case of cyclopentadienylMo(cyclooctenyl)(NO)I, the enantiomers were separated via a spontaneous resolution through crystallization of the complex in the space group P2 12 12 1. These studies have allowed the correlation not only of the absolute configuration at the metal center with CD studies, but also have established that a long wavelength optically active transition at approximately 400 nm can be correlated with endo-exo isomerism. Comparison of the rates of interconversion suggest that endo to exo isomerization occurs via a clockwise rotation of the allyl in the ( R)-isomer. Crystallographic details: (—)-( S)-(NMCp)Mo(allyl)(NO)I crystallizes in the space group P2 12 12 1 with a 7.221(1), b 12.686(7), c 21.603(7) Å, Z = 4, V = 1979(2) Å 3; R 1 = 0.039, R 2 = 0.046; (—)-( S)-(Cp)Mo(cyclooctenyl)(NO)I crystallizes in the space group P2 12 12 1 with a 8.466(1), b 10.449(2), c 16.372(2) Å, Z = 4, V = 1448.3(6), R 1 = 0.038, and R 2 = 0.046.

Additions and Corrections - Optical Rotatory Dispersion Studies. 127. Chirality Due to 13C Substitution. Synthesis and Chiroptical Properties of (1S)-2-Adamantanone-413C and (1S)-2-4-Adamamantanedione-413C

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAdditions and Corrections - Optical Rotatory Dispersion Studies. 127. Chirality Due to 13C Substitution. Synthesis and Chiroptical Properties of (1S)-2-Adamantanone-413C and (1S)-2-4-Adamamantanedione-413CY. Lawrence Sing, N. Numan, Hans Wynberg, and Carl DjerassiCite this: J. Am. Chem. Soc. 1979, 101, 24, 7439Publication Date (Print):November 1, 1979Publication History Published online19 February 2004Published inissue 1 November 1979https://doi.org/10.1021/ja00518a613RIGHTS & PERMISSIONSArticle Views14Altmetric-Citations1LEARN 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 (120 KB) Get e-Alerts Get e-Alerts

Optical rotatory dispersion studies. 125. Independent evidence for preference of axial deuterium vs. axial hydrogen through variable-temperature circular dichroism spectra of (4S)-2,2-dimethyl-4-deuteriocyclohexanone and (3S)-3-deuterio-4,4-dimethylcyclohexanone

The temperature-dependent circular dichroism (CD) spectra of (4S)-2,2-dimethyl-4-deuteriocyclohexanone(III) and (3S)-3-deuterio-4,4-dimethylcyclohexanone(IV) now present independent and additional evidence supporting earlier conclusions that the observed intensity changes of (3R)-2,2-dimethyl-3-deuteriocyclohexanone(I) and (5S)-2,2-dimethyl-5-deuteriocyclohexanone(II) reflect a shift of the equilibrium toward that conformer in which the deuterium is in the axial orientation. A significant increase in the rotational strength (R)/sub obsd/ is observed for III by lowering the temperature from 293 to 77/sup 0/K. The (R)/sub obsd/ for IV remains virtually unchanged over the same temperature range. The two chair conformations involved in the equilibrium and their octant diagrams together with the estimated rotational strengths in their axial (R)/sub ax/ and equatorial (R)/sub eq/ positions are illustrated. The decrease of the (R)/sub obsd/ with lowering the temperature leads to the unambiguous conclusion that the conformer with the deuterium in the axial position is energetically preferred. In contrast to III, the (R)/sub ax/ and (R)/sub eq/ values for IV are very small numbers since the methyl groups lie in a symmetry plane in both conformations and do not contribute to the rotational strength. The independent CD of IV has particular relevance since it excludes the alternative possibility that the observed changes of the rotational strength in I, more » II, and III are associated with the presence of twist conformations. 2 figures. « less

ChemInform Abstract: OPTICAL ROTATORY DISPERSION STUDIES. 123. EXPERIMENTAL EVIDENCE FOR PREFERENCE OF AXIAL DEUTERIUM OVER AXIAL HYDROGEN

Chemischer InformationsdienstVolume 9, Issue 37 Physical Organic Chemistry ChemInform Abstract: OPTICAL ROTATORY DISPERSION STUDIES. 123. EXPERIMENTAL EVIDENCE FOR PREFERENCE OF AXIAL DEUTERIUM OVER AXIAL HYDROGEN S.-F. LEE, S.-F. LEESearch for more papers by this authorG. BARTH, G. BARTHSearch for more papers by this authorK. KIESLICH, K. KIESLICHSearch for more papers by this authorC. DJERASSI, C. DJERASSISearch for more papers by this author S.-F. LEE, S.-F. LEESearch for more papers by this authorG. BARTH, G. BARTHSearch for more papers by this authorK. KIESLICH, K. KIESLICHSearch for more papers by this authorC. DJERASSI, C. DJERASSISearch for more papers by this author First published: September 12, 1978 https://doi.org/10.1002/chin.197837075AboutPDF 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 onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume9, Issue37September 12, 1978 RelatedInformation