The Effects of pH and Ionic Strength on the Aggregation of Bacteriochlorophyll c in Aqueous Organic Media: The Possibility of Two Kinds of Aggregates

The aggregation behavior of two homologs of bacteriochlorophyll c (BChl c) in various media was investigated for the effects of pH and salt, and the corresponding structures were analyzed by Fourier transform (FT)-IR spectroscopy. R-[P, E] BChl c_F (3¹-R-form of BChl c with a propyl group at the C-8 position and an ethyl group at the C-12 position) and R-[E, E] BChl c_F (3¹-R-form of BChl c with two ethyl groups at positions C-8 and C-12) were isolated from the green sulfur bacterium Chloro-bium limicola. Aggregates of each homolog showed a pH-dependent shift of the absorption maximum; at low pH, the peak moved to the red. This tendency was also revealed by circular dichroic spectra. A similar red shift of the peak was also induced by a high concentration of salt (NaCl) or buffer for both homologs. The FT-IR spectrum indicates that at low pH, both homologs formed a rather amorphous aggregate. On the other hand, a regular structure of R-[P, E] BChl c_F was indicated in an acetone-water mixture. This structure was stabilized by a triangular interaction among three pigment molecules through the Mg-OH (3>) O = C (13¹) linkage. This structure was not found for R-[E, E] BChl c_F. These results indicate that the replacement of the side chain at the C-8 position on the macrocycle induces a change in aggregation behavior. A possible heterogeneity of the in vivo rod structure of chlorosomes in green sulfur bacteria is discussed based on the above results.     

A convenient synthesis of diacyl sulfides using a novel sulfur transfer reagent

Various diacyl sulfides were synthesized by reaction of acyl chlorides with LiAlHSH. Reaction of glutaryl chloride with LiAlHSH afforded glutaric thioanhydride. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:633–635, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10217     

An experimental study on the kinetics and mechanisms of styrene polymerization in oil‐in‐water microemulsion initiated by oil‐soluble initiators

In order to clarify the kinetic role of oil‐soluble initiators in microemulsion polymerization, the oil‐in‐water (O/W) microemulsion polymerizations of styrene are carried out using four kinds of azo‐type oil‐soluble initiators with widely different water‐solubility. The results are compared with those observed when a water‐soluble initiator, potassium persulfate (KPS) is used. For all the oil‐soluble initiators used, the molecular weight of polymers and the average size of polymer particles do not change with the monomer conversion and the initial initiator concentration. The monomer conversion is expressed as a function of r_i^0.5t, where r_i is the rate of radical generation in the whole reaction system and t is the reaction time. These characteristics are quite the same as those observed when KPS is used as an initiator. When the polymerizations are carried out with the rate of radical generation in the whole reaction system fixed at the same value, the rates of polymerization are almost the same for all the oil‐soluble initiators employed, irrespective of their water‐solubility, but are significantly lower (ca. 1/3) than that with KPS. Then, the following conclusions are given: (1) The radicals generated not only in the aqueous phase, but also in the micelle and polymer particle phase are almost equally effective for the polymerization. However, (2) only a small portion (ca. 1/9) of the radicals generated in both phases participate in the polymerization. (3) Bimolecular termination of a growing radical in the polymer particle with an entering radical and with a pair of radicals generated in the polymer particles is negligible, and hence, the molecular weight of polymers is determined only by chain transfer to monomer.     

Syntheses of cyanoselenoamides and diselenoamides: Conversion into selenazoles and selenazines

Reactions of dicyano compounds with a potassium selenocarboxylate afforded the corresponding cyanoselenoamides and diselenoamides in good yields of experimentally determined ratios. The obtained cyanoselenoamides were allowed to react with potassium selenocarboxylate, again to afford the corresponding diselenoamides in higher yields. The cyanoselenoamides and diselenoamides were investigated as substrates for preparations of selenazoles and selenazines. © 2003 Wiley Periodicals, Inc. Heteroatom Chem 14:106–110, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10111     

Syntheses of 2‐alkylthio‐1,3‐thiazine derivatives from S‐alkyldithiocarbamates and α,β‐unsaturated ketones

Various 2‐alkylthio‐1,3‐thiazine derivatives were synthesized by the reactions of S‐alkylthiocarbamates with α,β‐unsaturated ketones in the presence of BF₃ · Et₂O. The thiazine was converted into two isomeric dehydrated products in the presence of a Lewis acid. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:377–379, 2002; Published online in Wiley Interscience (www.interscience.wiley.com). DOI 10.1002/hc.10055