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Results for “Optical Rotation”

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PubMed2000

Nonlinear magneto-optical rotation via alignment-to-orientation conversion

Nonlinear magneto-optical rotation is investigated at high light powers where the rotation is significantly modified by ac Stark shifts. These shifts are shown to change the overall sign of rotation for closed F-->F+1 transitions compared to the low light power limit. The effect is demonstrated by measurements in rubidium and density matrix calculations. The results are important for applications of nonlinear optical rotation such as sensitive magnetometry.

Journal Article↗
PubMed1996

On the structure of aggregated kappa-carrageenan helices. A study by cryo-TEM, optical rotation and viscometry.

Cryo-transmission electron microscopy (cryo-TEM), viscometry and optical rotation have been used to study the microstructure of dilute solutions of helical kappa-carrageenan under varied electrolyte composition (0.1 M of NaI, CsI and mixtures of the two salts). Microfibers (300-400 nm in length) were observed above a critical cesium content, while below that no microstructure was seen in the micrographs. A drastic increase in the specific viscosity and an onset of thermal hysteresis in the optical rotation above the same critical cesium content provide clear evidence of aggregate formation. This leads to the conclusion that the observed microfibers are aggregates consisting of several helices. At high proportions of cesium, further aggregation of the microfibers was observed by cryo-TEM.

Biopolymers↗
PubMed1993

Polarity reversal of the optical rotation signals with change in direction of impulse conduction along the lobster nerve.

1. The optical rotation signal of nerve associated with excitation was recorded from peripheral nerve taken from a walking leg of a spiny lobster and its properties were analysed. 2. The polarity of the optical rotation signal was reversed when the site of stimulation was changed with reference to the site of optical recording, so that the direction of impulse conduction was reversed, in most of the preparations. 3. Apart from the main response, which is associated with the conducted impulse, a pre-response was found to exist, which manifested itself on anodic stimulation, in a tetrodotoxin-treated nerve, or during the refractory period of the nerve, when the site of stimulation was close to the site of optical recording. The polarity of the pre-response was also reversed when the site of stimulation was changed with reference to the site of optical recording. 4. When the nerve was inclined from the horizontal level, so that the angle of incidence of light to the nerve was changed, the main response changed its amplitude and sometimes its polarity, whereas the pre-response remained practically unchanged. Thus the dependence on the angle of incidence was different between the pre-response and the main response. 5. It is suggested that the dependence of amplitude and polarity of the main response on the angle of incidence of light cannot be explained by the change in molecular axes of the membrane macromolecules, but can only be explained by their conformational change; and therefore the main response can be used as a monitor for the molecular conformation.

Animals↗
PubMed2002

Optical rotation: recent advances in determining the absolute configuration.

The field of optical rotations is currently undergoing a renaissance, which is a direct result of the advances in quantum mechanics and the availability of faster desktop computers. In the last few years, the field of optical rotations has taken an important role for determining the three-dimensional molecular structure (absolute configuration and conformations) with confidence. The purpose of this review is to present the latest advances in this area so that practicing chemists can utilize them in their respective areas of research and development.

Journal Article↗
PubMed1993

The existence of conformationally labile (preformed) drug binding sites in human serum albumin as evidenced by optical rotation measurements.

The ability of certain drugs to induce conformational changes in human serum albumin has been examined by differential optical rotation measurements at 233 nm. At drug:protein molar ratios ([D]/[P]) of unity, the optical rotation increased, decreased or remained the same depending on the drug used. The change in the optical rotatory dispersion (ORD) signal was investigated as a function of the drug concentration. Drug-protein interactions were relatively specific. There exists at least one, and possibly more, stable preformed high affinity sites for the binding of drugs to albumin. At low [D]/[P] ratios, the ORD titration curves suggest that the high affinity sites are conformationally labile and that the albumin molecule is flexible.

Binding Sites↗
PubMed2003

Optical tweezers and fluid characteristics of an optical rotator with slopes on the surface upon which light is incident and a cylindrical body.

The characteristics of the optical trapping force, optical torque, and viscous drag force for a newly proposed cylindrical optical rotator are analyzed. The optical trapping force and torque are evaluated by use of a ray optics model for both parallel and focused laser beam illumination. The drag force is calculated from computational fluid dynamics to be the sum of the components of both the pressure and the shearing stress on all the surfaces of the rotator. We analyze the rotation rate by balancing the optical torque with the drag force. A cylindrical optical rotator is expected to rotate at a high speed because of its highly efficient generation of optical torque and its small viscous drag force.

Journal Article↗
PubMed2005

Ammodendrine and N-methylammodendrine enantiomers: isolation, optical rotation, and toxicity.

Ammodendrine (1) was found to occur as a mixture of enantiomers in two different collections of plants identified as Lupinus formosus. The ammodendrine fraction was reacted in a peptide coupling reaction with 9-fluorenylmethoxycarbonyl-L-alanine (Fmoc-L-Ala-OH) to give diastereomers, which were separated by preparative HPLC. The pure D- and L-ammodendrine enantiomers were then obtained by Edman degradation. Optical rotation measurements revealed that the D- and L-enantiomers had optical rotations of [alpha]24D +5.4 and -5.7, respectively. D- and L-N-methylammodendrine enantiomers were synthesized from the corresponding ammodendrine enantiomers, and their optical rotations established as [alpha]23D +62.4 and -59.0, respectively. A mouse bioassay was used to determine the difference in toxicity between these two pairs of naturally occurring enantiomers. The LD50 of (+)-D-ammodendrine in mice was determined to be 94.1 +/- 7 mg/kg and that of (-)-L-ammodendrine as 115.0 +/- 7 mg/kg. The LD50 of (+)-D-N-methylammodendrine in mice was estimated to be 56.3 mg/kg, while that of (-)-L-N-methylammodendrine was determined to be 63.4 +/- 5 mg/kg. These results establish the rotation values for pure ammodendrine and N-methylammodendrine and indicate that there is little difference in acute murine toxicity between the respective enantiomers.

Animals↗
PubMed1997

Conformational analysis and molecular dynamics simulation of alpha-(1-->2) and alpha-(1-->3) linked rhamnose oligosaccharides: reconciliation with optical rotation and NMR experiments.

Molecular mechanics and dynamics calculations were carried out on the disaccharides alpha-L-Rhap-(1-->2)-alpha-L-Rhap-(1-->OMe) (1) and alpha-L-Rhap-(1-->3)-alpha-L-Rhap-(1-->OMe) (2), and the trisaccharide alpha-L-Rhap-(1-->2)-alpha-L-Rhap-(1--> 3)-alpha-L-Rhap-(1-->OMe) (3). The semiflexible conformational behavior of these molecules was characterized by the occupation of a combination of different glycosidic linkage and side-chain conformational positions whose relative occupations were sensitive to dielectric screening. Molecular dynamics simulations of the trisaccharide 3 showed little difference between the linkage conformations in the trisaccharide and the component disaccharides 1 and 2 Experimental optical rotation data of 1 and 2 were obtained as a function of temperature in varying solvents. The molecular models were combined with the semiempirical theory of Stevens and Sathyanarayana to yield calculated optical rotations. Interpretation of the data of both 1 and 2 implied that a combination of conformations, both in glycosidic and side-chain positions, could explain the experimental data. Solvents effects were important in influencing the conformational mix and averaged optical rotation. Three-bond heteronuclear coupling constants 3JC H were obtained for the glycosidic linkages of 1 and 2 in D2O and DMSO. Analysis of the coupling constants with a Karplus curve showed that small reductions in the glycosidic torsion angles of the conformations of the models used here of ca. 10 degrees-15 degrees in phi and 5 degrees-10 degrees in psi were required to give better agreement with experiment; a combination of conformations for both 1 and 2 was consistent with the data. There was a negligible influence on the coupling constants of 1 on changing the solvent from D2O to DMSO.

Carbohydrate Conformation↗
PubMed2000

An improved model for calculating the optical rotation of simple saccharides.

A calculational model for the optical rotation (OR) at the sodium D-line of simple saccharides has been developed that eliminates deficiencies of a previous model. Conformational conclusions based on the earlier model are not affected, as established by a recalculation of the OR phi,psi-map of methyl 3-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside. The model relocates the strong long-wavelength sigma-sigma* circular dichroism (CD) component, which is mainly responsible for the NaD OR from 160 to below 130 nm, where it is now known to occur. That correction allows future modeling of CD bands of different origins that appear in the 150-190 nm region. In order to demonstrate the utility of the revised model, it was applied to calculating the OR of methyl 3-O-(alpha-L-rhamnopyranosyl)-alpha-L-rhamnopyranoside. The results provide experimental support for conformational conclusions derived from a molecular mechanics study of that molecule.

Carbohydrates↗
PubMed2002

Optical rotation and linear and circular depolarization rates in diffusively scattered light from chiral, racemic, and achiral turbid media.

The polarization properties of light scattered in a lateral direction from turbid media were studied. Polarization modulation and synchronous detection were used to measure, and Mueller calculus to model and derive, the degrees of surviving linear and circular polarization and the optical rotation induced by turbid samples. Polystyrene microspheres were used as scatterers in water solutions containing dissolved chiral, racemic, and achiral molecules. The preservation of circular polarization was found to exceed the linear polarization preservation for all samples examined. The optical rotation induced increased with the chiral molecule concentration only, whereas both linear and circular polarizations increased with an increase in the concentrations of chiral, racemic, and achiral molecules. This latter effect was shown to stem solely from the refractive index matching mechanism induced by the solute molecules, independent of their chiral nature.

Biophysical Phenomena↗
PubMed2006

Temperature dependence of the optical rotation of fenchone calculated by vibrational averaging.

On the basis of vibrational averaging, the temperature dependence of the optical rotation for fenchone has been calculated using TDDFT with the B3LYP hybrid functional at three wavelengths. The results show that very good agreement is obtained between theory and experiment. It is concluded that temperature-dependent vibrational effects are likely to account for much of the observed temperature dependence in optical rotation exhibited by rigid organic molecules in case there is only a weak temperature-dependent interaction with the solvent.

Journal Article↗
PubMed2007

Density functional theory calculations of optical rotation: employment of ADZP and its comparison with other basis sets.

Density function theory calculations of frequency dependent optical rotations ([alpha]omega) for 30 rigid chiral molecules are reported. Calculations have been carried out at the sodium D line frequency, using the augmented double zeta valence quality plus polarization functions (ADZP) basis set and the BP86 nonhybrid and B3LYP hybrid functionals. Gauge-invariant atomic orbitals were used to guarantee origin-independent values of [alpha]D. Comparison between corresponding results obtained with nonhybrid and hybrid functionals as well as with theoretical optical rotations reported in the literature is done. Excited electronic states of three molecules are also discussed in light of circular dichroism spectra and B3LYP and BP86 calculated excitation energies and rotatory strengths. One verifies that the B3LYP/ADZP results are in better agreement with experiment.

Journal Article↗
PubMed2004

Determination of absolute configuration using concerted ab Initio DFT calculations of electronic circular dichroism and optical rotation: bicyclo[3.3.1]nonane diones.

The concerted use of ab initio time-dependent density functional theory (TDDFT) calculations of transparent spectral region optical rotation and of circular dichroism has recently become practicable, permitting the concerted use of transparent spectral region optical rotation and circular dichroism in determining the absolute configurations of chiral molecules. Here, we report concerted TDDFT calculations of the transparent spectral region specific rotations and of the circular dichroism spectra originating in n --> pi C=O group excitations of four bicyclo[3.3.1]nonane diones, 1-4. Comparison to experiment yields absolute configurations for 1-4. For each dione, specific rotations and circular dichroism spectra give identical absolute configurations. Our results are consistent with previous work, with the exception of the Octant Rule-derived absolute configuration of the 2,9-dione.

Journal Article↗
PubMed2006

Calculation of origin-independent optical rotation tensor components in approximate time-dependent density functional theory.

We outline an implementation of the origin-independent optical rotation tensor, which includes electric dipole-magnetic dipole and electric dipole-electric quadrupole polarizability. The method is based on approximate time-dependent density functional theory. We utilize time-periodic magnetic-field-dependent basis functions as well as a modified velocity-gauge formulation of dynamic polarizability tensors in order to obtain a gauge-origin independence. To ensure gauge-origin independence of the results within a given numerical accuracy, density fit coefficient derivatives are employed. A damping constant has been introduced into the linear response equations to treat both resonance and nonresonance regions of optical activity. We present calculations for trans-2,3-dimethyloxirane and derivatives thereof as well as calculations for androst-4,17-dien-3-one. In the Appendix, we derive the equivalence between the common-gauge origin and gauge-including atomic orbitals formulations for the optical rotation tensor in time-dependent DFT.

Journal Article↗
PubMed2001

Responses of neurons in the medial column of the inferior olive in pigeons to translational and rotational optic flowfields.

The responses of neurons in the medial column of the inferior olive to translational and rotational optic flow were recorded from anaesthetized pigeons. Panoramic translational or rotational flowfields were produced by mechanical devices that projected optic flow patterns onto the walls, ceiling and floor of the room. The axis of rotation/translation could be positioned to any orientation in three-dimensional space such that axis tuning could be determined. Each neuron was assigned a vector representing the axis about/along which the animal would rotate/translate to produce the flowfield that elicited maximal modulation. Both translation-sensitive and rotation-sensitive neurons were found. For neurons responsive to translational optic flow, the preferred axis is described with reference to a standard right-handed coordinate system, where +x, +y and +z represent rightward, upward and forward translation of the animal, respectively (assuming that all recordings were from the right side of the brain). t(+y) neurons were maximally excited in response to a translational optic flowfield that results from self-translation upward along the vertical (y) axis. t(-y) neurons also responded best to translational optic flow along the vertical axis but showed the opposite direction preference. The two remaining groups, t(-x+z) and t(-x-z) neurons, responded best to translational optic flow along horizontal axes that were oriented 45 degrees to the midline. There were two types of neurons responsive to rotational optic flow: rVA neurons preferred rotation about the vertical axis, and rH135c neurons preferred rotation about a horizontal axis at 135 degrees contralateral azimuth. The locations of marking lesions indicated a clear topographical organization of the six response types. In summary, our results reinforce that the olivo-cerebellar system dedicated to the analysis of optic flow is organized according to a reference frame consisting of three approximately orthogonal axes: the vertical axis, and two horizontal axes oriented 45 degrees to either side the midline. Previous research has shown that the eye muscles, vestibular semicircular canals and postural control system all share a similar spatial frame of reference.

Animals↗
PubMed2000

A PET study of visuomotor learning under optical rotation.

We measured the regional cerebral blood flow (rCBF) in six healthy volunteers with PET (positron emission tomography) and H(15)(2)O to identify the areas of the human brain involved in sensorimotor learning. The learning task was visually guided reaching with sensorimotor discrepancy caused by optical rotation. PET measurements were performed in the early and late stages of the adaptation to the sensorimotor perturbation. Control measurements were obtained during an eye movement task and a reaching task without optical rotation. The rCBF data of each learning stage were compared to those of both control conditions. During the early stage, rCBF increases were detected in the rostral premotor cortex bilaterally, the posterior part of the left superior parietal lobule (SPL), and the right SPL including the intraparietal sulcus (IPS). During the late stage, rCBF increases were detected in the left caudal premotor area, the left supplementary motor area proper, the left SPL, the right SPL including the IPS, and the right postcentral sulcus extending to the inferior parietal lobule. These results reveal that sensorimotor learning accompanies changes in the recruited cortical areas during different stages of the adaptation, reflecting the different functional roles of each area for different components of adaptation, from learning of new sensorimotor coordination to retention or retrieval of acquired coordination.

Adult↗
PubMed1993

Optical rotation signal of nerve and the Faraday effect.

The polarity of the optical rotation signal, recorded from the lobster nerve, was reversed when the direction of incident light was changed by 180 degrees. This is a property of the Faraday rotation, but the magnetic field by the action current was too small to explain the size of the observed signal.

Action Potentials↗