Study of plant coumarins: X. Peurutenicin triflate in cross-coupling reactions

By Suzuki cross-coupling reaction of peurutenicin triflate with arylboric, furanylboric, pyridinylboric, and indolylboric acids the corresponding 7-aryl(hetaryl)coumarins were synthesized. The high activity of hetaryl-substituted boric acids in the Suzuki reaction was observed. Heck reaction of 7-O-trifluoromethylsulfonylpeur utenicin with terminal olefins (styrene, vinylpyridines, vinylpyrazine, vinyltriazole) was used to prepare (E)-7-[aryl(hetaryl)vinyl]coumarins. The dependence of reaction products yield on the nature of the catalytic system was found.     

Study of plant coumarins: XIV. Catalytic amination of 7-hydroxycoumarin derivatives

Catalytic amination of 7-hydroxy-6-cyanocoumarin or 7-hydroxy-6-methoxycarbonylcoumarin triflates with substituted anilines, isoquinolin-5-amine, 1H-pyrazol-3-amine, or amino acids of penicillin series affords the corresponding 7-(N-substituted) aminocoumarins. In the amination of the mentioned triflates and also of peuruthenicine tosilate with 2-(piperidin-1-yl)aniline the catalytic system Pd(OAc)₂-BINAP has been efficient.     

Synthesis of polycyclic tetramethyl-tetraphenylcyclooctasilsesquioxane

Conclusions A new polycyclic compound, namely tetramethyltetraphenylcyclooctasilsesquioxane, was obtained by the reaction of cis-1,3,5,7-tetrahydroxy-1,3,5,7-tetraphenylcyclotetrasiloxane with tetramethylcyclotetrasiloxane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 956–957, April, 1973.     

Maleic anhydride and acetylene plasma copolymer surfaces for SPR immunosensing

We report on the successful application of carboxyl-rich plasma polymerized (PP) films as a matrix layer for bioreceptor immobilization in surface plasmon resonance (SPR) immunosensing. Composition and chemical properties of the carboxyl-rich PP films deposited from a mixture of maleic anhydride and acetylene were investigated. Changes in the films stored in air, water, and buffer were studied and the involved chemical changes were described. Performance in SPR immunosensing was evaluated on interactions of human serum albumin (HSA) with a specific monoclonal antibody. The comparison with the mixed self-assembled monolayer of mercaptoundecanoic acid and mercaptohexanol (MUA/MCH) and one of the most widely used surfaces for SPR, the 2D and 3D carboxymethylated dextran (CMD), was presented to show the efficacy of plasma polymerized matrix layers for biosensing. The PP film-based SPR immunosensor provided a similar detection limit of HSA (100 ng/mL) as MUA/MCH- (100 ng/mL) and 3D CMD (50 ng/mL)-based sensors. However, the response levels were about twice higher in case of the PP film-based immunosensor than in case of MUA/MCH-based alternative. The PP film surfaces had similar binding capacity towards antibody as the 3D CMD layers. The response of PP film-based sensor towards HSA was comparable to 3D CMD-based sensor up to 2.5 μg/mL. For the higher concentrations (> 10 μg/mL), the response of PP film-based immunosensor was lower due to inaccessibility of active sites of the immobilized antibody inside the flat PP film surface. We have demonstrated that due to its high stability and cost-effective straightforward preparation, the carboxyl-rich PP films represent an efficient alternative to self-assembled monolayers (SAM) and dextran-based layers in label-free immunosensing.

Graphical abstract

     

Carotenoids Do Not Protect Bacteriochlorophylls in Isolated Light-Harvesting LH2 Complexes of Photosynthetic Bacteria from Destructive Interactions with Singlet Oxygen

The effect of singlet oxygen on light-harvesting (LH) complexes has been studied for a number of sulfur (S⁺) and nonsulfur (S⁻) photosynthetic bacteria. The visible/near-IR absorption spectra of the standard LH2 complexes (B800-850) of Allochromatium (Alc.) vinosum (S⁺), Rhodobacter (Rba.) sphaeroides (S⁻), Rhodoblastus (Rbl.) acidophilus (S⁻), and Rhodopseudomonas (Rps.) palustris (S⁻), two types LH2/LH3 (B800-850 and B800-830) of Thiorhodospira (T.) sibirica (S⁺), and an unusual LH2 complex (B800-827) of Marichromatium (Mch.) purpuratum (S⁺) or the LH1 complex from Rhodospirillum (Rsp.) rubrum (S⁻) were measured in aqueous buffer suspensions in the presence of singlet oxygen generated by the illumination of the dye Rose Bengal (RB). The content of carotenoids in the samples was determined using HPLC analysis. The LH2 complex of Alc. vinosum and T. sibirica with a reduced content of carotenoids was obtained from cells grown in the presence of diphenylamine (DPA), and LH complexes were obtained from the carotenoidless mutant of Rba. sphaeroides R26.1 and Rps. rubrum G9. We found that LH2 complexes containing a complete set of carotenoids were quite resistant to the destructive action of singlet oxygen in the case of Rba. sphaeroides and Mch. purpuratum. Complexes of other bacteria were much less stable, which can be judged by a strong irreversible decrease in the bacteriochlorophyll (BChl) absorption bands (at 850 or 830 nm, respectively) for sulfur bacteria and absorption bands (at 850 and 800 nm) for nonsulfur bacteria. Simultaneously, we observe the appearance of the oxidized product 3-acetyl-chlorophyll (AcChl) absorbing near 700 nm. Moreover, a decrease in the amount of carotenoids enhanced the spectral stability to the action of singlet oxygen of the LH2 and LH3 complexes from sulfur bacteria and kept it at the same level as in the control samples for carotenoidless mutants of nonsulfur bacteria. These results are discussed in terms of the current hypothesis on the protective functions of carotenoids in bacterial photosynthesis. We suggest that the ability of carotenoids to quench singlet oxygen (well-established in vitro) is not well realized in photosynthetic bacteria. We compared the oxidation of BChl850 in LH2 complexes of sulfur bacteria under the action of singlet oxygen (in the presence of 50 μM RB) or blue light absorbed by carotenoids. These processes are very similar: {[BChl + (RB or carotenoid) + light] + O₂} → AcChl. We speculate that carotenoids are capable of generating singlet oxygen when illuminated. The mechanism of this process is not yet clear.