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Results for “Optical Rotation”

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PubMed1993

Solvent dependence of optical rotation of (S)-N-[1-(2-fluorophenyl)- 3,4,6,7-tetrahydro-4-oxo-pyrrolo[3,2,1-jk][1,4]benzodiazepine-3-yl]- 1H-indole-2-carboxamide.

A new cholecystokinin-A antagonist, (S)-N-[1-(2-fluorophenyl)- 3,4,6,7-tetrahydro-4-oxo-pyrrolo[3,2,1-jk][1,4]benzodiazepine-3-yl]- 1H-indole-2-carboxamide (FR120480; 1), is a chiral compound that shows considerable solvent dependence of its optical rotation. Not only the absolute values, but also the signs (+ or -) for this compound change in various solvents. The optical rotation of 1 inherently correlated to the electron donating property characterized by donor number of the solvent. The 1H NMR study implied that hydrogen bonds were formed between electron donor groups of the solvents and the NH groups of indole and amide of 1. In accordance with the NMR results, X-ray crystallography of the tetrahydrofuran solvate of 1 showed that hydrogen bond formation occurred between the oxygen atom of tetrahydrofuran and the amide group of 1.

Benzodiazepinones↗
PubMedDate not supplied

TORNADO: omnistereo video imaging with rotating optics.

One of the key techniques for vision-based communication is omnidirectional stereo (omnistereo) imaging, in which stereoscopic images for an arbitrary horizontal direction are captured and presented according to the viewing direction of the observer. Although omnistereo models have been surveyed in several studies, few omnistereo sensors have actually been implemented. In this paper, a practical method for capturing omnistereo video sequences using rotating optics is proposed and evaluated. The rotating optics system consists of prism sheets, circular or linear polarizing films, and a hyperboloidal mirror. This system has two different modes of operation with regard to the separation of images for the left and right eyes. In the high-speed shutter mode, images are separated using postimage processing, while, in the low-speed shutter mode, the image separation is completed by optics. By capturing actual images, we confirmed the effectiveness of the methods.

Computer Simulation↗
PubMed1975

[Studies on the magneto-optical rotation of porphyrins, hemins and methemoglobin compounds].

Using the method of magneto-optical rotation (MOR) various porphyrin derivatives, hemin and heme compounds, and a number of methemoglobin complexes were investigated. The spectra were recorded from 450-600 nm; with methemoglobin also in the Soret region. 1. The metalfree porphyrin derivatives (deutero-, meso-, hemato- and protoporphyrins) were measured in strongly acidic aqueous solution. The derivatives thus present as di-cations yield highly resolved MORspectra, where the Q-bands (Oo leads to; Oo leads to 1) originated from the pi-pi transitions of the porphyrin display the curve shape characteristic of an A-term, this proving the presence of the D4h symmetry. An exception is the protoporphyrin, in which the pi-electron system of the porphyrin is perturbed by the influence of pi-electrons of the vinyl group, causing poor resolution, line broadening, and shift of the Q-bands into the lower-energy spectral region. 2. With iron porphyrins (hemin, heme and their complexes) the charge of the iron and the nature of axial ligands determine the position and intensity of the O-bands in the MOR spectrum. Low-spin complexes have a higher symmetry than the high-spin complexes. Whereas with hemin (S = 5/2), the iron located outside the heme plane strongly disturbs the porphyrin pi-system, the high symmetry of porphyrin is greatly retained in the case of heme. This can be explained by the enhanced binding distance between the bivalent iron and the porphyrin to great for a strong coupling between the microsymmetry of the iron and the macrosymmetry of the porphyrin pi-system.

Heme↗
PubMed2005

Calculation of optical rotation with time-periodic magnetic-field-dependent basis functions in approximate time-dependent density-functional theory.

We report the implementation of a method for the calculation of optical rotation. This method is based on the time-dependent density-functional theory and utilizes time-periodic magnetic-field-dependent basis functions. The calculations are based on a density fit. It is demonstrated that additional terms in the analytical expression appearing from derivatives of the approximated Coulomb potential are necessary to provide the gauge-origin independence of the results within a given numerical accuracy. Contributions from these terms also restore the symmetry between the electric and magnetic perturbations in the optical rotation tensor.

Algorithms↗
PubMed2006

Is the optical rotation sign/absolute configuration relationship still a problem? Examples taken from unnatural quaternary aminoacids.

The optical rotation sign/absolute configuration relationships of several alpha-methyl-alpha-arylglycines have been reinvestigated by crystallographic methods, as they have been found to be inconsistent in recent literature. Assignments previously made by enzymatic resolution, by analogy with natural tertiary aminoacids were found to be erroneous in the case of these quaternary aminoacids.

Amino Acids↗
PubMed2002

Ab initio calculations for the optical rotations of conformationally flexible molecules: a case study on six-, seven-, and eight-membered fluorinated cycloalkanol esters.

Based on the time-dependent density functional response theory, an approach for the prediction of optical rotations of enantiomers of conformationally flexible molecules was developed. The method was applied successfully for the determination of the absolute configuration of trans-2-fluorocycloalkanol acetates with different ring sizes. The largest deviations between experimental and theoretical [alpha](D) values are 10 deg x [dm x (g/cc)](-1) (about 20% error). These theoretical results suggest that the optical rotation in these molecules is dominated by the local (1R;2R) configuration of the two substituents and that different ring and even axial/equatorial orientations play a less important role.

Journal Article↗
PubMed2000

Optical rotation per refractive index unit, or enantiomeric (e) factor, for screening enantioselective catalysts through asymmetric activation or carbohydrates.

A super high-throughput screening (SHTS) system can be constructed by combining high-performance liquid chromatography (HPLC), optical rotation (OR), and refractive index unit (RIU) to determine not only the enantioselectivity of the addition of diethylzinc to an aliphatic aldehyde catalyzed by a binaphthol-zinc complex through asymmetric activation with chiral Schiff bases, but also the enantiopurity of a carbohydrate. The enantiomeric (e) factor, which we define here as optical rotation per refractive index unit, is linearly related to the percent enantiomeric excess (%ee) and is independent of concentration.

Acetonitriles↗
PubMedDate not supplied

Noninvasive glucose monitoring of the aqueous humor of the eye: Part I. Measurement of very small optical rotations.

We have described the concept of using the aqueous humor glucose as a measure of the blood glucose concentration, with a view to developing a noninvasive glucose monitor for diabetic individuals. We have conceived of a scleral lens that houses a light source, polarizers, other electro-optic units, and a light detector, and which measures the optical rotation of the aqueous humor continuously. We have built an optical bench mock-up of the glucose sensor and assessed the limits of its capabilities. We have described a physical method, employing the Faraday effect, that modulates the incident light and uses a compensator to introduce a feedback mechanism giving a null-point technique capable of measuring extremely small rotations with an accuracy of 0.4 s of arc. We have used this and have measured the optical rotations of glucose solutions from 0.02 to 0.1%, and have demonstrated linearity in both cases. Miniaturization of the technique is discussed.

Animals↗
PubMed2004

Polarizability and optical rotation calculated from the approximate coupled cluster singles and doubles CC2 linear response theory using Cholesky decompositions.

A new implementation of the approximate coupled cluster singles and doubles CC2 linear response model using Cholesky decomposition of the two-electron integrals is presented. Significantly reducing storage demands and computational effort without sacrificing accuracy compared to the conventional model, the algorithm is well suited for large-scale applications. Extensive basis set convergence studies are presented for the static and frequency-dependent electric dipole polarizability of benzene and C60, and for the optical rotation of CNOFH2 and (-)-trans-cyclooctene (TCO). The origin-dependence of the optical rotation is calculated and shown to persist for CC2 even at basis set convergence.

Journal Article↗
PubMed2002

Ab initio prediction of optical rotation: comparison of density functional theory and Hartree-Fock methods for three 2,7,8-trioxabicyclo[3.2.1]octanes.

We report ab initio calculations of the frequency-dependent electric dipole-magnetic dipole polarizabilities, beta(nu), at the sodium D line frequency and, thence, of the specific rotations, [alpha](D), of 2,7,8-trioxabicyclo[3.2.1]octane, 1, and its 1-methyl derivative, 2, using the Density Functional Theory (DFT) and Hartree-Fock/Self-Consistent Field (HF/SCF) methodologies. Gauge-invariant (including) atomic orbitals (GIAOs) are used to ensure origin-independent [alpha](D) values. Using large basis sets which include diffuse functions DFT [alpha](D) values are in good agreement with experimental values (175.8 degrees and 139.2 degrees for (1S,5R)-1 and -2, respectively); errors are in the range 25-35 degrees. HF/SCF [alpha](D) values, in contrast, are much less accurate; errors are in the range 75-95 degrees. The use of small basis sets which do not include diffuse functions substantially lowers the accuracy of predicted [alpha](D) values, as does the use of the static limit approximation: beta(nu) approximately beta(o). The use of magnetic-field-independent atomic orbitals, FIAOs, instead of GIAOs, leads to origin-dependent, and therefore nonphysical, [alpha](D) values. We also report DFT calculations of [alpha](D) for the 1-phenyl derivative of 1, 3. DFT calculations find two stable conformations, differing in the orientation of the phenyl group, of very similar energy, and separated by low barriers. Values of [alpha](D) predicted using two different algorithms for averaging over phenyl group orientations are in good agreement with experiment. In principle, the absolute configuration (AC) of a chiral molecule can be assigned by comparison of the optical rotation predicted ab initio to the experimental value. Our results demonstrate the critical importance of the choice of ab initio methodology in obtaining reliable optical rotations and, hence, ACs, and show that, at the present time, DFT constitutes the method of choice.

Journal Article↗
PubMed2006

Time dependent density functional theory calculations for electronic circular dichroism spectra and optical rotations of conformationally flexible chiral donor-acceptor dyad.

Twelve conformations of a chiral donor-acceptor (charge-transfer) dyad and six conformations of its dimer complex were structurally optimized by using the Kohn-Sham density functional theory (BLYP/TZV2P) incorporating a recently developed empirical correction scheme that uses C6/R6 potentials for van der Waals interactions (DFT-D). Subsequent time-dependent DFT calculations with BH-LYP and B3-LYP functionals (with triple-zeta basis set) were performed to obtain theoretical circular dichroism (CD) spectra. The experimental CD spectra obtained independently were properly reproduced by averaging the calculated spectra of individual conformers according to a Boltzmann population derived from single-point SCS-MP2 energies. The optical rotations of the monomer were also calculated by using the same functionals with an aug-cc-pVDZ basis set. Dielectric continuum solvation models (COSMO) applied to correct the relative energies from the isolated molecule calculations resulted in conformer distributions that piled the same or even poorer level of agreement with the experimental CD spectrum. Our results clearly show the advantage of the DFT-D method for the geometry optimization of large systems with donor-acceptor interactions and the TD-DFT/BH-LYP calculations for reproducing the experimental CD spectra. As compared with the calculated optical rotations, the wealthy information embedded in the experimental/calculated CD spectra is requisite for the configurational and/or conformational analyses of relatively large and flexible chiral organic molecules in solution.

Journal Article↗
PubMed2002

Effective index of refraction, optical rotation, and circular dichroism in isotropic chiral liquid crystals.

This paper concerns optical properties of the isotropic phase above the isotropic-cholesteric transition and of the blue phase BP III. We introduce an effective index, which describes spatial dispersion effects such as optical rotation, circular dichroism, and the modification of the average index due to the fluctuations. We derive the wavelength dependence of these spatial dispersion effects quite generally without relying on an expansion in powers of the chirality and without assuming that the pitch of the cholesteric P is much shorter than the wavelength of the light lambda, an approximation that has been made in previous studies of this problem. The theoretical predictions are supported by comparing them with experimental spectra of the optical activity in the BP III phase.

Journal Article↗
PubMed2001

The Laser-assisted Optical Rotational Cell Analyzer (LORCA) as red blood cell aggregometer.

The Laser-assisted Optical Rotational Cell Analyzer (LORCA) is unique in its capacity to measure at least two important hemorheological parameters, i.e., deformability of red blood cells (RBC) as well as their aggregation behaviour. In this communication the main principles and characteristics of the aggregometer mode of this instrument are described. Via syllectometry (i.e., laser backscatter versus time), the method allows the measure of both static and kinetic parameters of the aggregation process, e.g., total extent of aggregation, aggregation half time and a combination of these, defined as aggregation index. When the syllectogram deviates from that representing normal rouleaux formation, e.g., in the case of RBC clump formation, this is signalled by a fit error. Maximal flexibility is obtained by various options like an automated re-iteration procedure (which enables to measure the aggregation tendency and/or the aggregate stability) and aggregation at low shear rate. Experiments dealing with reproducibility, stability and sensitivity of the instrument are described. The latter include a few "classic" methods for inducing subtle changes in RBC aggregation behaviour both regarding cellular factors (heat treatment) and changes in medium constituents (fibrinogen, dextrans).It can be concluded that the aggregometer mode of the LORCA considerably increases the feasibility of this instrument for hemorheological investigations.

Cryoglobulinemia↗
PubMed2006

Determination of the absolute configurations of natural products via density functional theory calculations of optical rotation, electronic circular dichroism, and vibrational circular dichroism: the cytotoxic sesquiterpene natural products quadrone, suberosenone, suberosanone, and suberosenol A acetate.

The determination of the absolute configurations (ACs) of chiral molecules using the chiroptical techniques of optical rotation (OR), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) has been revolutionized by the development of density functional theory (DFT) methods for the prediction of these properties. Here, we demonstrate the significance of these advances for the stereochemical characterization of natural products. Time-dependent DFT (TDDFT) calculations of the specific rotations, [alpha](D), of four cytotoxic natural products, quadrone (1), suberosenone (2), suberosanone (3), and suberosenol A acetate (4), are used to assign their ACs. TDDFT calculations of the ECD of 1 are used to assign its AC. The VCD spectrum of 1 is reported and also used, together with DFT calculations, to assign its AC. The ACs of 1 derived from its [alpha](D), ECD, and VCD are identical and in agreement with the AC previously determined via total synthesis. The previously undetermined ACs of 2-4, derived from their [alpha](D) values, have absolute configurations of their tricyclic cores identical to that of 1. Further studies of the ACs of these molecules using ECD and, especially, VCD are recommended to establish more definitively this finding. Our studies of the OR, ECD, and VCD of quadrone are the first to utilize DFT calculations of all three properties for the determination of the AC of a chiral natural product molecule.

Animals↗
PubMed2002

Ordering in aqueous polysaccharide solutions. II. Optical rotation and heat capacity of aqueous solutions of a triple-helical polysaccharide schizophyllan.

Deuterium oxide solutions of schizophyllan, a triple-helical polysaccharide, undergoing an order-disorder transition centered at 17 degrees C, were studied by optical rotation (OR) and heat capacity (C(p)) to elucidate the molecular mechanism of the transition and water structure in the solution and frozen states. The ordered structure at low temperature consisted of the side chains and water in the vicinity forming an ordered hydrogen-bonded network surrounding the helix core and was disordered at higher temperature. In the solution state appeared clearly defined transition curves in both the OR and C(p) data. The results for three samples of different molecular weights were analyzed theoretically, treating this transition as a typical linear cooperative transition from the ordered to disordered states and explained quantitatively if the molecular weight polydispersity of the sample was considered. The excess heat capacity C(EX)(p) defined as the C(p) minus the contributions from schizophyllan and D(2)O was estimated. In the frozen state it increased with raising temperature above 150 K until the mixture melted. This was compared with the dielectric increment observed in this temperature range and ascribed to unfreezable water. From the heat capacity and dielectric data, unfreezable water is mobile but more ordered than free water. In the solution state, the excess heat capacity originates from the interactions of D(2)O molecules as bound water and structured water, and so forth. Thus the schizophyllan triple helix molds water into various structures of differing orders in solution and in the solid state.

Adjuvants, Immunologic↗
PubMed2006

Square-wave self-modulation in diode lasers with polarization-rotated optical feedback.

The square-wave response of edge-emitting diode lasers subject to a delayed polarization-rotated optical feedback is studied in detail. Specifically, the polarization state of the feedback is rotated such that the natural laser mode is coupled into the orthogonal, unsupported mode. Square-wave self-modulated polarization intensities oscillating in antiphase are observed experimentally. We find numerically that these oscillations naturally appear for a broad range of values of parameters, provided that the feedback is sufficiently strong and the differential losses in the normally unsupported polarization mode are small. We then investigate the laser equations analytically and find that the square-wave oscillations are the result of a bifurcation phenomenon.

Journal Article↗
PubMed2003

Assignment of the molecular absolute configuration through the ab initio Hartree-Fock calculation of the optical rotation: can the circular dichroism data help in reducing basis set requirements?

In this paper the calculation of the optical rotation (OR) of some rigid organic molecules, using the Hartree-Fock method with small (6-31G, DZP) basis sets, has been studied thoroughly to carefully evaluate the scope and limitations of this method, previously introduced by other authors. Calculations on test molecules (compounds 1-13) together with a careful analysis of their CD spectra allow a simple criterion for the reliability of this approach to be formulated: for unsaturated and/or aromatic (i.e., absorbing in the near-UV region) molecules, if the [alpha](D) is quantitatively determined by the lowest energy Cotton effect (at wavelengths >220 nm), then the HF/6-31G result is reliable. The usefulness of this method for the experimental organic chemist has been further demonstrated because the OR (sign and order of magnitude) of compounds 14-19 (i.e., large molecules having considerable interest in organic chemistry), which fulfill the above criterion and for which an extended basis set treatment is not feasible owing to their size, is correctly predicted.

Journal Article↗
PubMedDate not supplied

Assessment of erythrocyte deformability with the laser-assisted optical rotational cell analyzer (LORCA).

The erythrocyte deformability of 28 patients with anemia was evaluated with the laser-assisted optical rotational cell analyzer (LORCA), an image analyzer that converts into numerical form the degree of refraction of a laser beam induced by red cells subjected to a range of torsional stresses. The patients were 10 thalassemics, including three with intermediate forms (1 HbC/beta degree, 1 homozygote beta for Orkin's haplotype VI, 1 beta degree/beta delta Sicilian type) and seven heteroygotes for beta Th; six with hereditary spherocytosis (including 2 with structural alteration of the spectrin beta chain); three with type II congenital dyserythropoietic anemia (HEMPAS), two hemizygotes and one heterozygote for G-6PD deficiency, and six with severe hypochromic hyposideremic anemia. Red cell deformability was reduced in intermediate thalassemia, hereditary spherocytosis and HEMPAS, normal in heterozygous beta thalassemia and G-6PD deficiency, and increased in hypochromic hyposideremic anemia. These results show that erythrocyte deformability can be impaired by an Hb chain imbalance, membrane and cyto skeleton structure anomalies and changes in the red cell area/volume ratio.

Adolescent↗