Ab initio calculations of isomerization reaction of diphosphene 1-sulfide to thiadiphosphirane

Ab initio Calculations of the isomerization reaction of diphosphene 1-sulfide (2′) to thiadiphosphirane (3′) suggest that the energy barrier of the reaction in the ground state is 25 kcal/mol and that 2′ lies 21 kcal/mol above 3′, while the calculations show that there exists one local minimum on the lowest triplet energy surface.     

Synthesis and characterization of poly(ethylene oxide) star polymers possessing a tertiary amino group at each arm end by organized polymerization using macromonomers

Functional poly(ethylene oxide) star polymers possessing a tertiary amino group at each arm end were prepared by free-radical copolymerization of poly(ethylene oxide) macromonomers with divinylbenzene (DVB) in water or ethanol. The poly(ethylene oxide) arm was prepared by anionic polymerization using 2-[2-(N,N-dimethylamino)ethoxy]ethanol potassium alkoxide as the initiator. The star polymers had narrow molecular weight distribution. The arm number was controlled by varying the feed ratio [DVB]/[M], the initial concentration of macromonomer [M], and solvent media. The branching factor g' in methanol ([eta]S/[eta]L are the intrinsic viscosities of the star and linear molecules, respectively) exhibited a power-law dependence on the arm number, f, with a negative exponent. This means that the dimensions of a star were in agreement with the Daoud-Cotton scaling model.     

Evaluation of thyroid scintigraphy in small animals

Thyroid scintigraphy in rats and mice with 99mTc and 123I was attempted to examine whether this modality might be used in small animals and to describe the possibilities of its application in examining experimentally produced thyroid diseases. A human gamma camera with a pinhole collimator improved for small animals was used for imaging. Thyroid images with 99mTc were obtained 20 minutes after injection and those with 123I were 24 hours after administration. All the scintigrams, although those obtained from mice with 99mTc displayed overlapped salivary gland images, demonstrated sufficiently clear images in size and shape, which showed that thyroid scintigraphy in small animals should be applicable in examining experimentally produced thyroid diseases.     

Silver nanoparticles dispersed within amphiphilic star-block copolymers as templates for plasmon band materials

Formation of silver nanoparticles has been developed based on a template technique. Amphiphilic star-block copolymers employed as single molecule template, utilizing the coordination of Ag⁺ ions with carboxyl groups in the core of the star-block copolymer. Silver nanoparticles have been prepared by the addition of chemical reductant, e.g., NaBH₄. The solution of the resultant nanosphere composites showed yellow due to the surface plasmon resonance. These composites were soluble in organic solvents, because hydrophobic corona of the star-block copolymer protected the fabricated silver nanoparticles from aggregation.     

NMR study on the photoresponsive DNA tethering an azobenzene. Assignment of the absolute configuration of two diastereomers and structure determination of their duplexes in the trans-form

Two diastereomers of a photoresponsive oligodeoxyribonucleotide tethering a trans-azobenzene, based on the chirality of the central carbon of a diol linker, were separated by reversed-phase HPLC. On the basis of 2D NMR analysis, absolute configurations of the diastereomers alpha and beta (tentatively designated from differences in their retention time) were determined as R- and S-forms, respectively. For both diastereomers, their NMR-determined duplex structure showed that trans-azobenzene intercalates between base pairs, because distinct NOEs were observed between the protons of azobenzene and those of the adjacent base pairs, such as with the imino protons and methyl protons of thymine. The melting temperatures of both duplexes were higher than that of the corresponding native duplex, which contained no azobenzene residue, due to the intercalated trans-azobenzene stabilizing the duplex by a stacking interaction. Between these two diastereomers, differences in T(m) were also found: the melting temperature of the R-form duplex (alpha-isomer) was higher than that of the S-form (beta-isomer). On the basis of the NMR-determined structure, this difference was attributed to the fact that the S-form (beta isomer) causes more stress forming the duplex than does the R-form (alpha isomer) due to disturbances of the right-hand helix.     

SPECTRAL ANALYSIS OF CHLOROPHYLL a AGGREGATES IN THE PRESENCE OF WATER-SOLUBLE MACROMOLECULES

Abstract— The absorption and fluorescence spectra of chlorophyll a (Chi a) aggregates formed in aqueous solutions of polyvinyl alcohol) (PVA), polyvinyl pyrrolidone) (PVP), and bovine serum albumin (BSA) were analyzed by curve-fitting methods in the wavelength region from 650 to 800 nm. The results indicated that the aggregation of Chi a to polymeric forms such as (Chia–2H₂0), was suppressed in the presence of the macromolecules. The suppression was due to a coordination of macromolecule bound ligands to Chi a and was strongest in BSA and weaker in PVA. There were differences in the spectra even though the same types of polymeric Chi a forms were observed due to characteristically different composition of these forms. Fluorescence patterns indicated that energy was transferred from the shorter to the longer wavelength forms.     

Construction of an asymmetric quaternary carbon via an asymmetric aza-Claisen rearrangement and its application in the total synthesis of (+)-α-cuparenone

Excess lithium hexamethyldisilazide (LHMDS) with LiCl prompted the asymmetric aza-Claisen rearrangement of carboxamide and retarded the decomposition of its amide enolate. The addition of these two reagents was a key step that led to the total synthesis of (+)-α-cuparenone with a stereogenic quaternary center.