Reaction kinetics of multiphoton excited BCI3 with H2S

In order to investigate unique behaviors in kinetics of the reaction of multiphoton excited BCl₃ with H₂S, two kinds of experiments were performed. The first, parallel beam experiment, gives the activation energy of the primary reaction pathway considerably smaller than the bond strength. The second, focussed beam experiment, shows that the isotope selectivity increase with incident pulse energy. Both results were found different from typical multiphoton dissociation experiments, showing its own characteristics.     

Effects of localized triplet exciton on reactivity of photoinduced omega-bond dissociation in naphthyl phenyl ketones having pi,pi* lowest triplet (T1) states studied by laser flash photolysis

Photochemical properties of photoinduced omega-bond dissociation in naphthyl phenyl ketones having a phenylthiyl moiety as a leaving group, p-(alpha-naphthoyl)benzyl phenyl sulfide (NBPS) and 4-benzoyl-1-naphthylmethyl phenyl sulfide (BNMPS), in solution were investigated by laser flash photolysis techniques. Both ketones were shown to undergo photoinduced omega-bond cleavage of the C-S bond to release the phenyl thiyl radical (PTR) at room temperature. Irrespective of excitation wavelengths of NBPS, a quantum yield (Phi(rad)) of the PTR formation was obtained to be 0.1, whereas that for BNMPS was found to depend on the excitation wavelength, i.e., absorption bands from the ground state (S0) to the excited singlet states, S3, S2, and S1 of BNMPS; Phi(rad)(S3) = 0.77 and Phi(rad)(S2) = Phi(rad)(S1) = 1.0. By using triplet sensitization of p-phenylbenzophenone (PBP), efficiencies (alpha(rad)) of the radical formation in the lowest triplet state (T1(pi,pi*)) of NBPS and BNMPS were determined to be 0 and 1.0, respectively. The agreement between Phi(rad)(S1) and alpha(rad) values for BNMPS indicates that the C-S bond dissociation occurs in the T1 state via the S1 state via a fast intersystem crossing from the S1 to the T1 state. The wavelength dependence of the radical yields upon direct excitation of BNMPS was interpreted in terms of the C-S bond cleavage in the S3 state competing with internal conversion from the S3 to the S2 state. The smaller value of Phi(rad)(S3) than those of Phi(rad)(S1) and Phi(rad)(S2) was proposed to originate from the geminate recombination of singlet radical pairs produced by the bond dissociation via the S3 state. Photoinduced omega-cleavage of NBPS was concluded to take place only in the S1(n,pi*) state. Difference in reactivity of omega-cleavage between the triplet states of NBPS and BNMPS was interpreted in terms of localized triplet exciton in the naphthoyl moieties.     

High concentration trans form unsaturated lipids detected in a HeLa cell by Raman microspectroscopy

High concentration trans form unsaturated lipids have been found in a HeLa cell by Raman microspectroscopy. Two CC stretch bands are observed simultaneously at 1669 cm⁻¹ (trans form) and at 1656 cm⁻¹ (cis form) in a Raman spectrum obtained from a small area (1 µm in diameter) in a HeLa cell. The intensity ratio 1669/1656 indicates that the concentration of the trans form is as high as that of the cis. It is demonstrated that Raman microspectroscopy provides a powerful and unique means for in situ and noninvasive structural characterization of unsaturated lipids in a living cell. Copyright © 2008 John Wiley & Sons, Ltd.     

Formation of an exciplex with mixed ligands in the mercury-photosensitized luminescence of alcohol-amine mixtures in the liquid phase

The liquid-phase mercury-photosensitized luminescence of tert-butyl alcohol (TL)-tert-butylamine (TM) mixtures has been investigated by a steady-state illumination method over a wide range of substrate concentrations. The emission bands from exciplexes (HgTL* and HgTM*) between an excited mercury atom and an alcohol or an amine molecule were observed at about 330 nm and 370 nm, respectively, in TL and TM solutions in cyclohexane. Two other bands appeared at 405 nm and 455 nm for TM at high concentrations. These bands were previously assigned to two types of 1:2 exciplexes (HgTM(2)* and HgTM(2)**). In TL-TM mixed solutions, a new band appeared at about 400 nm. The intensity of this band increased with increasing concentrations of TL and TM. This band was attributed to an exciplex with mixed ligands (HgTLTM*). This band was observed for the first time in this study. The energized intermediate, (HgTLTM*)(not equal), formed between HgAL* and AM can be effectively stabilized by collisions with solvent molecules in solution, while it decomposes to HgAM* and AL in the gas phase. The results for TL-TM mixtures can be explained by the proposed reaction mechanism.     

Photoinduced omega-bond dissociation of m-halomethylbenzophenones studied by laser photolysis techniques and DFT calculations. Substituted position effects

Photochemical profiles of omega-cleavage of carbon-X (X = Br and Cl) bonds in m-bromo- and m-chloromethylbenzophenones (m-BMBP and m-CMBP) were investigated by laser photolysis techniques and DFT calculations. m-BMBP and m-CMBP were found to undergo omega-bond cleavage to yield the m-benzoylbenzyl radical (m-BBR) at 295 K, and the quantum yields were determined. No CIDEP signal was detected upon 308 nm laser photolysis of both the compounds. From these observations, it was inferred that the omega-bond of these m-halomethylbenzophenones (m-HMBP) cleaves in the lowest excited singlet state (S(1)(n,pi(*))) upon direct excitation. Upon triplet sensitization of acetone (Ac), the m-BBR formation was observed in transient absorption for an Ac-m-BMBP system, and an efficiency of the C-Br bond cleavage in the lowest triplet state (T(1)(n,pi(*))) of m-BMBP was determined. In contrast, formation of triplet m-CMBP was seen for an Ac-m-CMBP system. Absence of C-Cl bond cleavage in the triplet state of m-CMBP indicated the reactive state of m-CMBP for omega-cleavage is only the S(1)(n,pi(*)) state. Based on the efficiencies and DFT calculations for excited state energies, photoinduced omega-bond dissociation of m- and p-HMBPs was characterized.     

Synthesis of the Carbohydrate Moiety of Glycoproteins from the Parasite Echinococcus granulosus and Their Antigenicity against Human Sera

Stereocontrolled syntheses of biotin-labeled oligosaccharide portions containing the carbohydrate moiety of glycoprotein from Echinococcus granulosus have been accomplished. Trisaccharide Galβ1-3Galβ1-3GalNAcα1-R (A), tetrasaccharide Galα1-4Galβ1-3Galβ1-3GalNAcα1-R (B), and pentasaccharide Galα1-4Galβ1-3Galβ1-3Galβ1-3GalNAcα1-R (C), (R = biotinylated probe) were synthesized by stepwise condensation and/or block synthesis by the use of 5-(methoxycarbonyl)pentyl 2-azido-4,6-O-benzylidene-2-deoxy-α-d-galactopyranoside as a common glycosyl acceptor. The synthesis of the tetrasaccharide and the pentasaccharide was improved from the viewpoint of reducing the number of synthetic steps and increasing the total yield by changing from stepwise condensation to block synthesis. Moreover, hexasaccharide E, which contains the oligosaccharide sequence which occurs in E. granulosus, was synthesized from trisaccharide D. We examined the antigenicity of these five oligosaccharides by an enzyme-linked immunosorbent assay (ELISA). Although compounds of C–E did not exhibit antigenicity against cystic echinococcosis (CE) patient sera, compounds B, D, and E showed good serodiagnostic potential for alveolar echinococcosis (AE).     

Structure of monardaein,a bis-malonylated anthocyanin isolated from golden balm, monarda didyma

Structure of monardaein was determined to be 3-0-(6-0-$\text{trans}$-p-coumaryl-β-D-glucopyranosyl)-5-O- (4,6-di-O-malonyl-β-D-glucopyranosyl) pelargonidin (1).