Generation of circular dichroism from superposed porphyrin films.

Circular dichroism (CD) was observed from the superposed porphyrin deposited glass plates, which were prepared by the vapor deposition of achiral porphyrin molecules and oriented to one direction by rubbing parallel to the surface of plate. The CD spectra depended on the twisted angle between the plates and the number of plates superposed. The observed CD spectra agreed with the simulated ones by the Mueller matrices superposition calculation using the observed linear dichroism spectra and linear birefringence spectra of each plate.

Critical Detection of Agglomeration of Magnetic Nanoparticles by Magnetic Orientational Linear Dichroism.

Magnetic orientational linear dichroism (MOLD) spectroscopy was found to be useful for detecting the initiation of the agglomeration process of COOH-modified iron-oxide magnetic nanoparticles (MNPs) in water, which was produced by the addition of a small amount of a cationic surfactant or a metal ion. The critical association of MNPs leading to agglomeration was detected from the increase of the maximum MOLD value as well as from the shift of the maximum wavelength of the MOLD spectrum. The magnetic field dependence of MOLD was analyzed by the Langevin equation, and the apparent association numbers of MNPs in the agglomerates were obtained.

Magnetophoretic Mole-Ratio Method.

The principle of the mole-ratio method utilizing magnetophoretic velocimetry was demonstrated for the first time. The feasibility of the magnetophoretic mole-ratio method was studied for the determination of the stoichiometry of the complexes formed between a hydrophobic phosphate ligand adsorbed in mesoporous hydrophobic silica particles and paramagnetic metal ions of Co(II), Tb(III), and Dy(III) in aqueous solutions. The present method is a nonspectroscopic method and carried out by a simple magnetic device.

Chiral Recognition of 2-Alkylalcohols with Magnetic Circular Dichroism Measurement of Porphyrin J-Aggregate on Silica Gel Plate.

Simple chiral recognition method of 2-alkylalcohols on a silica gel plate was proposed by using the induced circular dichroism (ICD) of J-aggregates of diprotonated tetraphenylporphyrin and magnetic circular dichroism (MCD) spectrometry. To the silica gel on a glass slide including a chiral 2-alkylalcohol and 4 M sulfuric acid, the porphyrin in toluene was added and mixed. Then, the glass slide was used for in situ MCD measurement. The observed ICD spectra could recognize well the chirality of the alcohols and the ICD intensity normalized by the MCD intensity of the J-aggregate correlated linearly to the amount of the chiral alcohols in the silica gel.

Faraday rotation dispersion microscopy imaging of diamagnetic and chiral liquids with pulsed magnetic field.

We have constructed an experimental setup for Faraday rotation dispersion imaging and demonstrated the performance of a novel imaging principle. By using a pulsed magnetic field and a polarized light synchronized to the magnetic field, quantitative Faraday rotation images of diamagnetic organic liquids in glass capillaries were observed. Nonaromatic hydrocarbons, benzene derivatives, and naphthalene derivatives were clearly distinguished by the Faraday rotation images due to the difference in Verdet constants. From the wavelength dispersion of the Faraday rotation images in the visible region, it was found that the resonance wavelength in the UV region, which was estimated based on the Faraday B-term, could be used as characteristic parameters for the imaging of the liquids. Furthermore, simultaneous acquisition of Faraday rotation image and natural optical rotation image was demonstrated for chiral organic liquids.

Alignment and chirality of porphyrin J aggregates formed at the liquid-liquid interface of a centrifugal liquid membrane cell.

Previous direct observations of the J aggregates of diprotonated 5,10,15,20-tetraphenyl-21H,23H-porphine (H4TPP(2+)) formed at the dodecane-water interface in a centrifugal liquid membrane (CLM) cell using conventional CD spectroscopy have shown the existence of circular dichroic signals with a bisignated shape whose sign depends on the rotation direction of the cell. Herein we demonstrate that the determination of the optical Mueller matrix with a two-photoelastic modulator generalized ellipsometer (2-MGE), working in transmission mode, along with the assumption of a two superimposed twin Mueller matrices model (two opposite interfaces in the cylindrical rotation cell) allows us to infer the CD spectra due to overlapping linear polarizations from J aggregates at the front and back liquid-liquid interfaces in the rotating cell. The rotation direction dependence of the CD spectra was thoroughly interpreted by the present model considering the sign and the magnitude of the orientation angle between the front and back J aggregates. The present analysis should help us to understand the optical chirality due to the structural changes in supramolecular and macromolecular systems under flow shear forces as well as changes in birefringence.

New rotenoids and coumaronochromonoids from the aerial part of Boerhaavia erecta.

From the aerial part of Boerhaavia erecta L., three new rotenoids (3, 8, 10) and two new coumaronochromonoids (6, 11) were isolated, together with ten known compounds. The structure of the new compounds was established by one dimensional (1D)- and 2D-NMR spectroscopy, as well as high resolution-electrospray ionization (HR-ESI)-MS analysis. The absolute configuration of compound 11 was determined by UV circular dichroism spectroscopy. Compounds were evaluated for their cytotoxic activity against HeLa (human epithelial carcinoma), NCI-H460 (human lung cancer) and MCF-7 (human breast cancer) cell lines at the concentration of 100 µg/mL. Rotenoids 3, 4 and 5 showed a strong cytotoxic activity against HeLa cell line and rotenoids 5 and 8 showed good activity against MCF-7 cell line.

Single-molecule lactonization of octadecylrhodamine B at a liquid-liquid interface.

The total internal reflection laser fluorescence microscope method was used to observe the lateral diffusion of a single octadecylrhodamine B (C(18)RB) molecule at the toluene-water interface. The interfacial diffusion constant of single fluorescent cation C(18)RB(+) was obtained from the maximum residence time in a small observation area with pH <2. For pH >3, the maximum residence time was remarkably shortened, indicating that single fluorescent zwitterion C(18)RB(±) rapidly converted to the nonfluorescent lactone at the interface. The lactonization rate was completed within 0.13 ms at the toluene-water interface but slowed to 67 ms at an interface saturated with dimyristoylphosphatidylcholine.

Brownian motion-magnetophoresis of nano/micro-particles.

A new magnetophoresis method to determine the magnetic susceptibility of single nano/microparticles was developed by applying Brownian motion analysis to determine the size of the particle. This method could measure simultaneously both the magnetophoretic velocity and the radius of the identical single nano/microparticles, which are necessary for the determination of the magnetic susceptibility of the particle. The advantage of this method was demonstrated by the measurement of the diamagnetic susceptibilities of polystyrene particles 500 nm-3 µm in diameter in a paramagnetic 0.5 M manganese(II) chloride solution under a high magnetic field gradient of 5180 T(2) m(-1) generated by a small magnetic circuit.

Chiral recognition of 2-alkyl alcohols with porphyrin J-nanoaggregates at the liquid-liquid interface.

The J-aggregate of diprotonated tetraphenylporphyrin (H(4)TPP(2+)) formed at the dodecane-water interface showed circular dichroism spectra corresponding to the chirality of 2-alkyl alcohols, longer than 2-butanol, added to the dodecane phase. The phenomenon suggested the preferential interaction between the nano-sized J-aggregates and the chiral alcohols at the interface, and provided a potential use of the J-nanoaggregate as a chiral recognition probe.

Two-dimensional flow magnetophoresis of microparticles.

A new two-dimensional micro-flow magnetophoresis device was constructed in a superconducting magnet (10 T) using triangular shaped pole pieces, which could apply a magnetic strength, B(dB/dx), in the range of ca. 0-14,000 T(2) m(-1) across a capillary cell. Polystyrene particles with diameters of 1, 3, and 6 µm were used as test samples in a paramagnetic medium of 1 M MnCl(2) to evaluate the performance of this method. Microparticles migrated across the capillary along the edge of the pole pieces, and then flowed through the gap in the pole piece at a position defined as the migration distance, depending on the magnetic susceptibility and the size of particles as well as the flow rate. The most effective flow rate to exhibit the largest resolution among the particles was theoretically predicted and experimentally confirmed. By this method, the magnetic susceptibilities of individual deoxygenated and non-deoxygenated red blood cells were measured from the relative migration distance.

Raman optical activity study on insulin amyloid- and prefibril intermediate.

The amyloid fibril of bovine insulin and its renaturing intermediates were studied by using Raman optical activity (ROA). In the spectrum of the amyloid, the sharp +/- ROA couplet of amide I band characteristic of the ß-sheet-rich proteins was observed, together with a sharp peak at 1271 cm(-1) characteristic of a turn structure. The shoulder ROA peak of the native insulin at ~ 1340 cm(-1), which was assigned to the hydrated α-helix, was not observed in the amyloid, suggesting that the hydrated α-helix was converted to the parallel ß-sheet structure in the amyloid. Recovery of the amyloid to the native state was also monitored by ROA. The intermediate states showed distinct features from the amyloid or native ones. The intermediates did not show a characteristic ROA peak of the poly(L-proline) II helix at ~ 1318 cm(-1). The hydrated α-helix ROA peak was not recovered in the intermediate states. In a process of the amyloid formation, at first the hydrated α-helix of the native insulin is converted to a specific partially unfolded structure, and then, it was converted to the parallel ß-sheet structure with many turns.

Monitoring the backbone conformation of valinomycin by Raman optical activity.

Raman optical activity (ROA) spectroscopy is used to investigate the backbone conformation of valinomycin in methanol and dioxane solution. Experimental Raman and ROA spectral differences are interpreted by using density functional calculations, molecular dynamics, and Cartesian tensor transfer. Of the several conformers with different numbers of intramolecular hydrogen bonds which were preselected by calculations of relative energies, the dominant ones are identified on the basis of ROA. To separate the backbone signal from that of the side chains, conformational search for the isopropyl residues is performed for each backbone conformer. In dioxane, the most populated conformer does not exhibit C(3) symmetry, but adopts a distorted "bracelet" structure, similar to a crystal structure. This complements previous NMR spectroscopic results that could not distinguish the nonsymmetric structures. In methanol, a different, "propeller" conformer is indicated by ROA, which has three loops resembling a standard ß-turn peptide motif. Molecular dynamics simulations suggest that the propeller structure is very flexible in methanol. Spectra simulated for geometries not having the ß-turn do not agree with experiment. On the basis of these results, a distinct +/- ROA couplet at ∼1335/1317 cm(-1) observed in the extended amide III region is assigned to a turn in the valinomycin backbone.

SERS study of rotational isomerization of cysteamine induced by magnetic pulling force.

The effects of unidirectional pulling forces on covalently bridged cysteamine between superparamagnetic particles and Ag nanoparticles (NPs) were studied with SERS spectroscopy. With an increase in the pulling force from 0 to 100 pN per magnetic particle, the nu(C-S)(Trans)/nu(C-S)(Gauche) intensity ratio was increased from 0.6 to 1.08, the Raman frequency of nu(C-S)(Trans) was shifted from 716 to 719 cm(-1), and the Raman bands associated with the amide groups were diminished. From these observations, it was concluded that the magnetic forces induced the extension of distance between the magnetic particle surface and the Ag NP surface and the rotational isomerization equilibrium of SC-CN was shifted from the gauche to the trans conformation with the longer molecular length.

Controllable adsorption and ideal H-aggregation behaviors of phenothiazine dyes on the tungsten oxide nanocolloid surface.

The monomer-aggregate equilibrium of four phenothiazine (PN) dyes, containing thionine (TH), methylene blue (MB), new methylene blue (NMB), and 1,9-dimethylmethylene blue (DMB), in the tungsten(VI) oxide (WO(3)) nanocolloid solution has been investigated by means of UV-vis spectroscopy. Addition of PN dye into the WO(3) nanocolloid solution brought about significant changes in the absorption spectrum, suggesting the formation of H-type (face-to-face fashion) trimer on the WO(3) nanocolloid surface. The adsorptivity of PN dyes onto the WO(3) nanocolloid surface was diminished by the raising the ionic strength, indicating the evidence of the electrostatic interaction between cationic PN dye and negatively charged WO(3) nanocolloids. The detail analysis of each spectral data provided insight into the effect of molecular structure of PN dyes on the adsorption and aggregation behaviors on the WO(3) nanocolloid surface. Moreover, in situ measurement of PN dye aggregation using the centrifugal liquid membrane (CLM) technique revealed that the aggregation of PN dyes on the WO(3) nanocolloid surface proceeded in a two-step three-stage (monomer --> dimer --> trimer) formation. The aggregation mechanism of PN dyes on the WO(3) nanocolloid surface was discussed on the basis of Kasha's exciton theory.

Dynamic electromagnetophoretic force analysis of a single binding interaction between lectin and mannan polysaccharide on yeast cell surface.

Using the electromagnetophoretic buoyancy for a microparticle in a silica capillary containing an electrolyte solution, the dynamic force dissociation kinetics of the interaction between the mannan polysaccharide on a yeast cell surface and lectins bound to the silica capillary wall have been studied by using the two different modes of the increasing force mode and the constant force mode. Lectins used in the study were concanavalin A (Con A), Hippeastrum hybrid lectin (HHL), Galanthus nivalis lectin (GNL) and Narcissus pseudonarcissus lectin (NPL). The dynamic force measurement by the two different modes gave the spontaneous dissociation rate constant, k(off), of the polysaccharide-lectin binding and the critical increment of bond length at the transition state, Deltax. It was found that the value of k(off) for Con A was the smallest among the lectins studied, due to the strongest binding interaction. It was also confirmed that the magnetophoretic pulling force decreased the transition free energy just like an enzyme.

Formation and structure of the potassium complex of valinomycin in solution studied by Raman optical activity spectroscopy.

The formation and structure of the potassium complex with valinomycin in solution were studied by means of Raman and Raman optical activity (ROA) spectroscopy. The complexation caused significant spectral changes, particularly in the region 1200-1400 cm(-1). The experimental spectra were interpreted using first principles computations. A complete computational conformational search combined with the spectral analysis revealed the arrangement of the isopropyl side chains in the complex. From a total of 6579 unique conformers two predominant ones were confirmed in the solution by ROA. A third one was predicted theoretically, but its population in the experiment could be estimated only roughly. The most populated conformer does not exhibit C(3) symmetry, and is different from that present in the crystal and the NMR-derived structure. Molecular dynamics techniques were used to estimate the molecular flexibility and its effect on the spectra. Density functional computations and Cartesian coordinate transfer (CCT) techniques provided the ROA and Raman spectral shapes and intensities well comparable with the experiment. The polar solvent (methanol) environment modeled with a polarizable continuum model (PCM) leads to rather minor changes in the conformer populations and vibrational properties as compared to vacuum computations, due to the hydrophobic character of the complex. Additional computational experiments suggest that the vibrational interactions determining the ROA spectra are quite local, which contributes to the good spatial resolution of the method. A reduction of the noise in the experimental spectra as well as increased precision of the simulations is desirable for the further exploration of the potential of the ROA spectroscopy for biomolecular studies in the future.

Effect of static magnetic fields on the budding of yeast cells.

The effect of static magnetic fields on the budding of single yeast cells was investigated using a magnetic circuit that was capable of generating a strong magnetic field (2.93 T) and gradient (6100 T² m⁻¹). Saccharomyces cerevisiae yeast cells were grown in an aqueous YPD agar in a silica capillary under either a homogeneous or inhomogeneous static magnetic field. Although the size of budding yeast cells was only slightly affected by the magnetic fields after 4 h, the budding angle was clearly affected by the direction of the homogeneous and inhomogeneous magnetic fields. In the homogeneous magnetic field, the budding direction of daughter yeast cells was mainly oriented in the direction of magnetic field B. However, when subjected to the inhomogeneous magnetic field, the daughter yeast cells tended to bud along the axis of capillary flow in regions where the magnetic gradient, estimated by B(dB/dx), were high. Based on the present experimental results, the possible mechanism for the magnetic effect on the budding direction of daughter yeast cells is theoretically discussed.

Magnetophoretic mole-ratio method in solvent extraction systems.

The magnetophoretic mole-ratio method was applied to the solvent extraction systems of paramagnetic metal ions with bis(2-ethylhexyl)hydrogen phosphate in 2-fluorotoluene. In the extraction of Mn(II), Co(II), Ni(II), Tb(III) and Dy(III), the compositions of the extracted metal complexes were determined from the measurements of the magnetophoretic velocity of a single droplet as a function of the mole ratio of the metal ion and the ligand.

Effective transition probability for the Faraday effect of lanthanide(III) ion solutions.

The Faraday effects of 14 lanthanide(III) ion solutions were systematically analyzed on the basis of the Faraday C term. The effective transition probability, K, which measures the magneto-optical contribution of the 4f(n) --> 4f(n-1)5d transition to the molar Verdet constant, was determined. Linear correlations between K and the square root of the molar magnetic susceptibility of the lanthanide(III) ions, chi(m)(1/2), were obtained. From the observed new regularity, K for promethium(III) was estimated.