Time-resolved cavity ringdown spectroscopy on nanoparticle generation in a SiH4–H2 VHF plasma

Time-resolved cavity ringdown (τ-CRD) spectroscopy has been applied to monitor the silyl (SiH₃) radicals and nanoparticles in a pulsed very high frequency (VHF) silane-hydrogen plasma under microcrystalline silicon (μc-Si:H) deposition conditions. The measured cavity loss reveals four time intervals (I up to VI) in the first 4 s of the plasma pulse. By variation of the laser wavelength, it is demonstrated that the small cavity loss at 220 nm reflects the SiH₃ absorption in interval I. In intervals II and III, an additional cavity loss appears. This additional cavity loss corresponds to Rayleigh and Mie scattering by growing nanoparticles. Interval IV reflects the loss of nanoparticles between the electrodes during the afterglow of the plasma pulse. The evolution of the nanoparticle generation determined from the τ-CRD measurements are further confirmed by additional scanning electron microscopy analyses on the nanoparticles created in the plasma pulse.     

Self-aggregation of synthetic zinc oxo-bacteriochlorins bearing substituents characteristic of chlorosomal chlorophylls

We prepared novel zinc 8-ethyl-8-methyl-7-oxo- and 7-ethyl-7-methyl-8-oxo-bacteriochlorins 1 and 2 possessing substituents characteristic of chlorosomal chlorophylls, exclusively observed in extramembraneous light-harvesting antennas of photosynthetic green bacteria. The electronic absorption spectra of monomeric 1 and 2 in THF were obviously different: the Q(y) maximum of the former was 724 and that of the latter was 683 nm. This observed spectral difference was clearly explained by theoretical ZINDO/S calculation of their energetically minimized molecules. The optical properties of monomeric 1/2 were controlled by the electronic effect of the 7/8-oxo groups. Specific spectral changes in the electronic, CD, and FT-IR absorption spectra by dilution of the monomeric THF solutions of 1/2 with a 100/200-fold volume of cyclohexane showed the formation of chlorosomal self-aggregation species constructed by 13-C=O...H-O(3(1))...Zn and pi-pi stacking. Especially, the red-shift values in the Q(y) band of 1/2 by self-aggregation were 2450/1970 cm(-1), indicating that exciton interaction among the composite molecules in the self-aggregation of 1 was stronger than in those of 2. Molecular model calculations for dodecamers of 1/2 based on a parallel chain arrangement gave partially different supramolecular structures; the specific hydrogen-bonding distances in 2-dodecamer were larger than those of 1-dodecamer, while both coordinations gave the same Zn-O distance. These modeling results showed that 1 was more tightly packed in the self-aggregates to give a larger red-shift value in the Q(y) band by self-aggregation than 2. The difference in the supramolecular structures is mainly ascribable to the steric effect of 8/7-dialkyl groups in self-aggregates of 1/2.     

A study of embolizing materials for chemo-embolization therapy of hepatocellular carcinoma: embolic effect of cisplatin albumin microspheres using chitin and chitosan in dogs, and changes of cisplatin content in blood and tissue.

Hepatic artery of dogs was embolized with cisplatin (CDDP) albumin microspheres containing chitin and chitosan to investigate the in vivo CDDP release kinetics from CDDP albumin microspheres, the CDDP cumulative characteristics in the liver, and the influence of microsphere administration on hepatic tissue. Results showed that changes in blood CDDP content were dependent on CDDP albumin microsphere type and that release kinetics were better sustained when chitin was added to the microspheres or when the microspheres were treated with chitosan. In particular, the administration of CDDP in the chitin-containing CDDP chitosan albumin microspheres showed a blood CDDP content of approximately 0.26 micrograms Pt/ml 14 d after administration. The administration of chitin-containing or chitosan treated CDDP microspheres showed a CDDP content in the hepatic tissue of 0.14 to 0.23 micrograms Pt/g 28 d after administration. They also showed better control of CDDP release than those without chitin or chitosan treatment. No CDDP influence on hepatic tissue was observed. We conclude that, even in vivo, chitin and chitosan are effective embolic materials.     

Optical studies of pulsed-laser fragmentation of biliary calculi

The fragmentation of gallstones and kidney stones using pulsed visible laser radiation has recently been demonstrated; however, the fragmentation mechanism is not well understood. The temporal and spectral characteristics of the bright flash of light accompanying fragmentation of gallstones were studied using 0.8 and 360-s-long, 690-nm-wavelength, dye-laser pulses. Time-resolved visible emission spectra show a broad continuum upon which line spectra are superimposed. The continuum emission is due to free-free and free-bound electron transitions indicative of a plasma and the line spectra are due to neutral and ionized calcium. Initiation of this plasma is fluence rather than intensity dependent. A model is proposed in which laser energy is coupled to the plasma, which then impulsively expands, generating intense acoustic transients which fracture the stone.     

14C-labeling of bromobutide, 2-bromo-3,3-dimethyl-N-(alpha, alpha-dimethylbenzyl)butyramide

Bromobutide, a novel herbicide, was labeled with carbon-14 independently at the carbonyl group and the phenyl ring for use in metabolic studies. 14C-Carbonation of neopentylmagnesium chloride (3) gave 3,3-dimethyl[1-14C]butyric acid (4a) quantitatively. Chlorination of 4a with thionyl chloride followed by alpha-bromination with bromine yielded 2-bromo-3,3-dimethyl[1-14C]-butyryl halide (5a), which was subsequently condensed with alpha, alpha-dimethylbenzylamine (6a) to afford [carbonyl-14C]bromobutide (1a). The overall yield of 1a was 76% from barium [14C]-carbonate (2). Similarly, condensation of alpha, alpha-dimethyl[phenyl-14C]benzylamine (6b), which was prepared from alpha-methyl[phenyl-U-14C]styrene (7) in three steps, with 2-bromo-3,3-dimethylbutyryl halide (5b) gave [phenyl-14C]bromobutide (1b) in 67% yield after purification. The specific activities of 1a and 1b were 1.38 and 0.781 GBq/mmol (37.2 and 21.1 mCi/mmol), respectively.     

Amphotericin B covalent dimers forming sterol-dependent ion-permeable membrane channels

Polyenemacrolides such as amphotericin B (AmB) were thought to assemble together and form an ion channel across plasma membranes. Their antimicrobial activity has been accounted for by this assemblage, whose stability and activity are dependent on sterol constituents of lipid bilayer membranes. The structure of this channel-like assemblage formed in biomembranes has been a target of extensive investigations for a long time. For the first step to this goal, we prepared several AmB dimers with various linkers and tested for their channel-forming activity. Among these, AmB dimers that bore an aminoalkyl-dicarboxylate tether covalently linked between amino groups of AmB showed potent hemolytic activity. Furthermore, K+ influx actions monitored by measuring the pH of the liposome lumen by 31P NMR revealed that the dimers formed the molecular assemblage similar to that of AmB in phospholipid membrane. Judging from changes in 31P NMR spectra, the dimers appeared to induce "all-or-none"-type ion flux across the liposome membrane in the presence of ergosterol, which suggested that the ion channel formed by ergosterol/dimer is similar to that of AmB. With these data in hand, we are now trying to elucidate the structure of the ion-channel complex by making the labeled conjugates of AmB for NMR measurements.