The efficient direct synthesis of N,O-acetal compounds as key intermediates of discorhabdin A: oxidative fragmentation reaction of alpha-amino acids or beta-amino alcohols by using hypervalent iodine(III) reagents

Hypervalent iodine(III) reagents are readily available, easy to handle, and have a low toxicity and similar reactivities to those of heavy metal reagents, and hence they are used for various oxidative reactions. The oxidative cleavage of alkynes or carbonyl compounds by using bis(trifluoroacetoxy)iodo(III) pentafluorobenzene (C(6)F(5)I(OCOCF(3))(2)) has been reported. Herein, the efficient direct synthesis of N,O-acetal compounds as key intermediates of discorhabdin A, by the oxidative fragmentation reaction of alpha-amino acids or beta-amino alcohols by using C(6)F(5)I(OCOCF(3))(2), is described.     

Conformational changes during apoplastocyanin folding observed by photocleavable modification and transient grating

A new method to investigate the initial protein folding dynamics is developed based on a pulsed laser light triggering method and a unique transient grating method. The side chain of the cysteine residue of apoplastocyanin (apoPC) was site-specifically modified with a 4,5-dimethoxy-2-nitrobenzyl derivative, where the CD and 2D NMR spectra showed that the modified apoPC was unfolded. The substituent was cleaved with a rate of about 400 ns by photoirradiation, which was monitored by the disappearance of the absorption band at 355 nm and the increase in the transient grating signal. After a sufficient time from the photocleavage reaction, the CD and NMR spectra showed that the native beta-sheet structure was recovered. Protein folding dynamics was monitored in the time domain with the transient grating method from a viewpoint of the molecular volume change and the diffusion coefficient, both of which reflect the global structural change, including the protein-water interaction. The observed volume decrease of apoPC with a time scale of 270 micros is ascribed to the initial hydrophobic collapse. The increase in the diffusion coefficient (23 ms) is considered to indicate a change from an intermolecular to an intramolecular hydrogen bonding network. The initial folding process of apoPC is discussed based on these observations.     

Systematic structural control of multichromic platinum(II)-diimine complexes ranging from ionic solid to coordination polymer

Reactions of a Pt(II)-diimine-based metalloligand Na(2)[Pt(CN)(2)(4,4'-dcbpy)] (4,4'-H(2)dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) with alkaline-earth metal salts Mg(NO(3))(2)·6H(2)O, CaCl(2), SrCl(2)·6H(2)O, and BaBr(2)·2H(2)O in aqueous solution gave luminescent complexes formulated as [Mg(H(2)O)(5)][Pt(CN)(2)(4,4'-dcbpy)]·4H(2)O (MgPt-4·9H(2)O), {[Ca(H(2)O)(3)][Pt(CN)(2)(4,4'-dcbpy)]·3H(2)O}(∞) (CaPt-4·6H(2)O), {[Sr(H(2)O)(2)][Pt(CN)(2)(4,4'-dcbpy)]·H(2)O}(∞) (SrPt-4·3H(2)O), and {[Ba(H(2)O)(2)][Pt(CN)(2)(4,4'-dcbpy)]·3H(2)O}(∞) (BaPt-4·5H(2)O), respectively. The crystal structures of all MPt-4 complexes were determined by X-ray crystallography. In these structures, the alkaline-earth metal ions are commonly coordinated to the carboxyl groups of the [Pt(CN)(2)(4,4'-dcbpy)](2-) metalloligand. In the case of MgPt-4·9H(2)O, the Mg(II) ion is bound by five water molecules and one oxygen atom of a carboxyl group to form a neutral complex molecule [Mg(H(2)O)(5)][Pt(CN)(2)(4,4'-dcbpy)]. In contrast, the alkaline-earth metal ion and metalloligand form two-dimensional (CaPt-4·6H(2)O) and three-dimensional (SrPt-4·3H(2)O and BaPt-4·5H(2)O) coordination networks, respectively. All fully hydrated complexes exhibited a strong phosphorescence from the triplet π-π* transition state. Luminescence spectroscopy revealed that MgPt-4·9H(2)O exhibited interesting multichromic (i.e., thermo-, mechano-, and vapochromic) luminescence, whereas CaPt-4·6H(2)O showed only thermochromic luminescence. The other two complexes did not exhibit any chromic behaviour. Combination analysis of powder X-ray diffraction, thermogravimetry, and IR spectroscopy suggests that the dimensionality of the coordination network contributes considerably to both the structural flexibility and luminescence properties; that is, the low-dimensional flexible coordination network formed in MPt-4 complexes with smaller alkaline-earth metal ions enables a structural rearrangement induced by thermal and mechanical stimuli and vapour adsorption, resulting in the observed multichromic behaviour.     

Gravitational compression dynamics of charged colloidal crystals

We examine the compression of charged colloidal crystals under the influence of gravitational force by monitoring the spatiotemporal variations of Bragg diffraction from the crystal lattice. We use the dilute aqueous dispersions of colloidal silica particles (diameter=216 nm, charge number=733, a particle volume fraction φ=0.06) in the presence of 5-15 μM sodium chloride. The sedimentation profiles of the colloidal crystals along the crystal height are determined by in situ fiber optics reflection spectroscopy. The time evolutions of the sedimentation profiles are calculated by numerical simulations based on a phenomenological continuum model that explicitly incorporates the electrostatic interparticle interactions. The simulation results correctly describe the experiments at sufficiently high ionic strength.     

Combinatorial and approximative analyses in a spatially random division process

For a spatial characteristic, there exist commonly fat-tail frequency distributions of fragment-size and -mass of glass, areas enclosed by city roads, and pore size/volume in random packings. In order to give a new analytical approach for the distributions, we consider a simple model which constructs a fractal-like hierarchical network based on random divisions of rectangles. The stochastic process makes a Markov chain and corresponds to directional random walks with splitting into four particles. We derive a combinatorial analytical form and its continuous approximation for the distribution of rectangle areas, and numerically show a good fitting with the actual distribution in the averaging behavior of the divisions.     

Benzoin reaction in water as an aqueous medium catalyzed by benzimidazolium salt

Benzoin reactions are catalyzed by N,N-dialkylbenzimidazole to yield α-hydroxy ketones; the reaction proceeds in water as an aqueous medium under mild conditions. The utility of these salts as pre-catalysts in these reactions has been demonstrated.     

Elution of residual ions with etching of heavy ion-injected polyimide

The experiment was carried out to estimate the amount of residual ions after the etching of polyimide irradiated by heavy ions, where etching resulted in a channel of measurable depth in the polyimide. None of the analytical techniques presents each ion separately in etched polyimide containing heavy ions. Activation analysis was used for the irradiated polyimide to see how the injected ions were eluted into the solution by etching. When the irradiated polyimide was etched for only a little longer than the time needed to dissolve a selected range of incident ions, the bulk began subsequently to dissolve. The residual radioactivity in polyimide was found to fall below the limit of detection when the depth of the etched channel appeared 10% deeper than the expected value.