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PubMed2006

Observation of discrete solitons and soliton rotation in optically induced periodic ring lattices.

We report the first experimental demonstration of ring-shaped photonic lattices by optical induction and the formation of discrete solitons in such radially symmetric lattices. The transition from discrete diffraction to single-channel guidance or nonlinear self-trapping of a probe beam is achieved by fine-tuning the lattice potential or the focusing nonlinearity. In addition to solitons trapped in the lattice center and in different lattice rings, we demonstrate controlled soliton rotation in the Bessel-like ring lattices.

Journal Article↗
PubMed2005

Nonlinear optical spectroscopy of chiral molecules.

We review nonlinear optical processes that are specific to chiral molecules in solution and on surfaces. In contrast to conventional natural optical activity phenomena, which depend linearly on the electric field strength of the optical field, we discuss how optical processes that are nonlinear (quadratic, cubic, and quartic) functions of the electromagnetic field strength may probe optically active centers and chiral vibrations. We show that nonlinear techniques open entirely new ways of exploring chirality in chemical and biological systems: The cubic processes give rise to nonlinear circular dichroism and nonlinear optical rotation and make it possible to observe dynamic chiral processes at ultrafast time scales. The quadratic second-harmonic and sum-frequency-generation phenomena and the quartic processes may arise entirely in the electric-dipole approximation and do not require the use of circularly polarized light to detect chirality. They provide surface selectivity and their observables can be relatively much larger than in linear optical activity. These processes also give rise to the generation of light at a new color, and in liquids this frequency conversion only occurs if the solution is optically active. We survey recent chiral nonlinear optical experiments and give examples of their application to problems of biophysical interest.

Circular Dichroism↗
PubMed1970

Double-helical character of ribonucleic acid from virus-like particles found in Penicillium chrysogenum.

1. RNA was isolated from virus-like particles found in Penicillium chrysogenum and resolved into two fractions by gel filtration through agarose columns. 2. Fraction 1 was excluded and had the following properties: 50.9% G+C [AMP 0.246, UMP 0.246, CMP 0.252, GMP 0.255 (mole fraction)]; mol.wt. about 1.2x10(6) daltons; s(20,w) 12.3S and ;melting' temperature about 100 degrees C (solvent 0.15m-sodium chloride-0.015m-sodium citrate pH7.2); optical rotation [alpha](max.) 6000 degrees at 278nm; circular dichroism (epsilon(L)-epsilon(R))(max.)=8.181mol(-1) cm(-1) at 260nm. 3. Properties of fraction 2 include 37.8% G+C [AMP 0.313, UMP 0.312, CMP 0.186, GMP 0.189 (mole fraction)]; mol.wt. about 140000 daltons; s(20,w) 7.3S, T(m) about 85 degrees C (solvent 0.15m-sodium chloride-0.015m-sodium citrate, pH7.2); optical rotation [alpha](max.) 6000 degrees at 278nm; circular dichroism (epsilon(L)-epsilon(R))(max.)=8.241mol(-1) cm(-1) at 260nm. 4. The properties of both fractions were consistent with a double-helical conformation.

Buffers↗
PubMed1966

The properties of bovine serum albumin and chymotrypsinogen A in solvent mixtures containing phenol.

1. The optical rotation and reduced viscosity of bovine serum albumin and chymotrypsinogen A in solvents containing phenol, acetic acid and water were studied. 2. The changes brought about in the properties of the proteins by varying the composition of the solvent or by heat treatment in these solvents were established to be reversible. 3. A method for returning the proteins to aqueous media, based on these observations, was worked out. 4. The recovered proteins were shown to be very similar to, if not identical with, the native proteins on the basis of measurements of optical rotation, viscosity, sedimentation, ultraviolet spectroscopy, immunochemical behaviour (serum albumin) and proteolytic activity (chymotrypsinogen A, after activation with trypsin). 5. The importance of the findings for partitioning of polyelectrolytes in the phenol-aqueous buffer systems is discussed.

Acetates↗
PubMed1976

The mechanism of folding of globular proteins. Equilibria and kinetics of conformational transitions of penicillinase from Staphylococcus aureus involving a state of intermediate conformation.

1. The thermodynamically reversible unfolding and refolding of penicillinase between the native and fully unfolded states were followed by using guanidinium chloride as denaturant. 2. The equilibria, studied by optical rotation, u.v. absorption, viscosity and enzyme activity, show the presence of a state of intermediate conformation, termed state H, which is stable at 20 degrees C in 0.8 M-guanidinium chloride. 3. The physical properties of this state show that it is slightly expanded with an intrinsic viscosity of 8 ml-g-1, that the 13 tyrosine residues, which are distributed through the primary sequence, are maximally exposed to the solvent and that the helix content is the same as that of the native state. 4. The kinetics of the transition between the native state, state H and the fully unfolded state were followed by u.v. absorption and by optical rotation. They are interpreted as showing that state H lies on the folding pathway between the native and fully unfolded states. 5. The transition between the native state and state H exhibits monophasic unfolding kinetics and biphasic refolding kinetics. This indicates that there must be at least two intermediate states in this process, at least one of which lies on the folding pathway which may also involve cul-de-sac paths. 6. The results are discussed in terms of a mechanism involving rapid stabilization of nucleation regions in a moderately compact but internally solvated structure, with 'native format' [Anfinsen (1973) Science 181, 233-230] secondary structure stabilized by tertiary interaction. The final and rate-limiting step in refolding involves shuffling of these structural elements into the native state. 7. This model is discussed in relation to folding in vivo.

Guanidines↗
PubMed1986

Energetics of proline racemase: transition-state fractionation factors for the two protons involved in the catalytic steps.

The isotope effects for the interconversion of L-proline and D-proline, catalyzed by proline racemase, have been determined in the saturated region with both [2-2H]proline and [2-3H]proline. The deuterium fractionation factors for each of the protons in flight have been obtained from two kinds of experiment: by measuring the rate of racemization of one [2-2H]proline enantiomer as it racemizes into an equilibrated pool of unlabeled proline and by measuring the deuterium content of a proline sample at the optical rotation maximum that occurs when an equimolar mixture of one deuterium-labeled enantiomer and the other unlabeled enantiomer runs to equilibrium. The tritium fractionation factors for each of the protons in flight have been determined from measurements of the rate of loss of tritium to the solvent as one [2-3H]proline enantiomer runs to equilibrium. Good agreement is found among the fractionation factors determined by each method. The deuterium fractionation factors for the two protons are not identical: that for the proton derived from L-proline is 0.375 and that for the proton derived from D-proline is 0.44. This difference has been confirmed by a double-competition experiment in which the optical rotation of a mixture of DL-[2-2H]proline and unlabeled DL-proline is followed with time. The rotation (initially zero) passes through a maximum, from which the ratio of the two fractionation factors (0.86) is obtained. These data, coupled with the equilibrium fractionation factor for the 2-position of proline (which has been determined to be 1.17), provide the transition-state factors for each of the in-flight protons, and delineate the nature of the transition state(s) for the enzyme-catalyzed racemization.

Amino Acid Isomerases↗
PubMed1976

Effects of the aliphatic carboxylate series of salts on the conformation of proteins.

The effects of the aliphatic acid series of salts, formate, acetate, propionate, butyrate, valarate, and caproate, on the conformation of sperm whale myoglobin, human hemoglobin A, and horse heart cytochrome c were investigated by spectral measurements in the Soret region, optical rotation, and intrinsic viscosity measurements. The effectiveness of the aliphatic acid salts as unfolding reagents for proteins is found to increase with increasing hydrocarbon content of the alkyl chains of the salts, which is analogous in behavior to effects of the urea, amide, and alcohol series of protein denaturants. The denaturation midpoints, Sm, as a function of the unfolding reagent were analyzed using the equations of Peller (Peller, L. (1959), J. Phys, Chem- 63, 1199) and Flory (Flory, P.J. (1957), J. Cell. Comp. Physiol. 49, 175) with binding constants based in part on the Scherage-Nemethy theory of hydrophobic bonding or evaluated from free-energy transfer data of nonpolar amino acid side chains from aqueous to nonaqueous solvents. The summation of the polar KP and hydrophobic KHphi contributions of solvent to protein amino acid side chain interactions were found to give best account of the protein denaturation data. Intrinsic viscosity and optical rotation data obtained on hemoglobin and myoglobin at high salt concentrations, above the unfolding transition regions, indicate that the product of denaturation by the aliphatic acid salts is less unfolded than in 6 M guanidine hydrochloride solutions. Residual elements of the helical regions of the proteins seem to either escape unfolding or are reformed at high concentrations of the denaturing salts.

Binding Sites↗
PubMed2004

Coupled cluster calculations of optical rotatory dispersion of (S)-methyloxirane.

Coupled cluster (CC) and density-functional theory (DFT) calculations of optical rotation, [alpha](lambda), have been carried out for the difficult case of (S)-methyloxirane for comparison to recently published gas-phase cavity ringdown polarimetry data. Both theoretical methods are exquisitely sensitive to the choice of one-electron basis set, and diffuse functions have a particularly large impact on the computed values of [alpha](lambda). Furthermore, both methods show a surprising sensitivity to the choice of optimized geometry, with [alpha](355) values varying by as much as 15 deg dm(-1) (g/mL)(-1) among molecular structures that differ only negligibly. Although at first glance the DFT/B3LYP values of [alpha](355) appear to be superior to those from CC theory, the success of DFT in this case appears to stem from a significant underestimation of the lowest (Rydberg) excitation energy in methyloxirane, resulting in a shift of the first-order pole in [alpha](lambda) (the Cotton effect) towards the experimentally chosen incident radiation lines. This leads to a fortuitous positive shift in the value of [alpha](355) towards the experimental result. The coupled cluster singles and doubles model, on the other hand, correctly predicts the position of the absorption pole (to within 0.05 eV of the experimental result), but fails to describe correctly the shape/curvature of the ORD region lambda=355, resulting in an incorrect prediction of both the magnitude and the sign of the optical rotation.

Journal Article↗
PubMed2003

Nonlinear magneto-optical kerr rotation of an oxide superlattice with artificially broken symmetry.

Simultaneously broken time-reversal and spatial-inversion symmetries can be realized in the epitaxially grown oxide "tricolor" superlattices composed of three sequential kinds of perovskite layers including a ferromagnetic one (manganese oxide). As a generic feature of such a system, the magnetic-field-induced second-harmonic generation and the resultant Kerr rotation of second-harmonic light were demonstrated. The signal intensity probes the interface magnetization of the superlattice, where temperature variation is shown to be distinct from the bulk feature.

Journal Article↗
PubMed1996

Imaging brain injury using time-resolved near infrared light scanning.

Conventional brain imaging modalities are limited in that they image only secondary physical manifestations of brain injury, which may occur well after the actual insult to the brain and represent irreversible structural changes. A real-time continuous bedside monitor that images functional changes in cerebral blood flow or oxygenation might allow for recognition of brain tissue ischemia or hypoxia before the development of irreversible injury. Visible and near infrared light pass through human bone and tissue in small amounts, and the emerging light can be used to form images of the interior structure of the tissue and measure tissue blood flow and oxygen utilization based on light absorbance and scattering. We developed a portable time-of-flight and absorbance system which emits pulses of near infrared light into tissue and measures the transit time of photons through the tissue. Images can then be reconstructed mathematically using either absorbance or scattering information. Pathologic brain specimens from adult sheep and human newborns were studied with this device using rotational optical tomography. Images generated from these optical scans show that neonatal brain injuries such as subependymal and intraventricular hemorrhages can be successfully identified and localized. Resolution of this system appears to be better than 1 cm at a tissue depth of 5 cm, which should be sufficient for imaging some brain lesions as well as for detection of regional changes in cerebral blood flow and oxygenation. We conclude that light-based imaging of cerebral structure and function is feasible and may permit identification of patients with impending brain injury as well as monitoring of the efficacy of intervention. Construction of real-time images of brain structure and function is now underway using a fiber optic headband and nonmechanical rotational scanner allowing comfortable, unintrusive monitoring over extended periods of time.

Animals↗
PubMed2004

Nonlinear Faraday rotation for optical limitation.

The possible use of the nonlinear Faraday effect for optical limitation of the laser power is investigated in a resonant Faraday medium placed between two crossed polarizers. The results are comparable with those obtained at strong magnetic fields as a result of the linear Faraday effect. Advantages of the method are the narrow bandwidth and the wide field of view. The investigations are interesting from the viewpoint of applications for optical sensor protection and automation of the experiment. All measurements are performed at the F(g) = 2 --> F(e) = 1 hyperfine structure transition of the 87Rb D1 line.

Journal Article↗
PubMed1973

O-methyl sugars in lipopolysaccharides of Rhodospirillaceae. Identification of 3-O-methyl-D-mannose in Rhodopseudomonas viridis and of 4-O-methyl-D-xylose and 3-O-methyl-6-deoxy-D-talose in Rhodopseudomonas palustris respectively.

1. This paper deals with the identification of three O-methyl sugars in lipopolysaccharides isolated from strains of the Gram-negative photosynthetic family Rhodospirillaceae. In addition to the previously described 3-O-methyl-l-xylose, a second O-methyl sugar was encountered in the lipopolysaccharide of Rhodopseudomonas viridis F, namely 3-O-methyl-d-mannose. The lipopolysaccharides of two strains of Rhodopseudomonas palustris (strain 1e5 and 8/1) contain two O-methylsugars, 4-O-methyl-d-xylose and 3-O-methyl-6-deoxy-d-talose (d-acovenose). 4-O-Methyl-d-xylose, but not 3-O-methyl-6-deoxy-d-talose, could be identified in the lipopolysaccharides of the strains K/1 and 2/2 of the same species. 2. The O-methyl sugars described in this communication were isolated by paper chromatography and identified by g.l.c., paper chromatography, high-voltage electrophoresis and mass spectrometry. Besides the genuine sugars, their alditol acetates and their demethylated (parental) forms were investigated. Optical rotation measurements and, in one case, enzymic reactions were used to establish the optical configuration of the sugars under investigation.

Chromatography, Paper↗
PubMed1999

Wigner rotations and Iwasawa decompositions in polarization optics.

Wigner rotations and Iwasawa decompositions are manifestations of the internal space-time symmetries of massive and massless particles, respectively. It is shown to be possible to produce combinations of optical filters which exhibit transformations corresponding to Wigner rotations and Iwasawa decompositions. This is possible because the combined effects of rotation, phase-shift, and attenuation filters lead to transformation matrices of the six-parameter Lorentz group applicable to Jones vectors and Stokes parameters for polarized light waves. The symmetry transformations in special relativity lead to a set of experiments which can be performed in optics laboratories.

Journal Article↗
PubMed2000

First total synthesis of aspinolide B, a new pentaketide produced by Aspergillus ochraceus.

The first asymmetric total synthesis of Aspinolide B (1), a new 10-membered lactone discovered by chemical screening methods in the cultures of Aspergillus ochraceus, has been accomplished. The key steps included a selective Felkin-type addition of TMS-acetylene to aldehyde 3a and a Nozaki-Hiyama-Kishi coupling reaction to build the required 10-membered ring. This synthesis confirmed the absolute stereochemistry of aspinolide B, established through Helmchen's method and corrected its previously reported specific optical rotation.

Aspergillus ochraceus↗