Photoinduced electron and hole transfer involving eosin conjugates of tryptophan derivatives

The preparation of several covalent conjugates of the dye, eosin Y (EY^2-) with the amino acid, L-tryptophan (Trp), the dipeptide, Trp-Trp, and with poly(L)-tryptophan is described. Intramolecular photochemical electron transfer is responsible for the quenching of dye excited singlet states (flourescence) in these systems. The sacrificial acceptor, tetranitromethane (TNM), was used to irreversibly oxidize pendant dye groups; the transfer of charge (“holes”) from the oxidized eosin moiety located at the N-terminus of the peptides was monitored by laser flash photolysis. Both modes of electron transfer involve charge transfer from indole side chains associated with Trp groups for the various peptide links. Study of the kinetics of hole transfer provided rate constants in the range of 103–104 s^-1 for several solvent media including aqueous poly(vinylpyrrolidinone) (PVP), a polymer that provides a protein-like microdomain. The observed temperature dependence of the hole transfer rate is consistent with non-adiabatic electron transfer over distances determined by molecular modeling to be about 1.0 nm (through-space) and involving through-bond interactions via a network of σ-π overlaps. Findings are discussed in terms of demonstration of the entrainment of charge along peptide chains and the efficient separation of charge in (bio)polymer structures of some size that display vectorial properties.     

Synthesis of some substituted benzimidazoles with potential antimicrobial activity

Summary The synthesis andin vitro antimicrobial evaluation of several benzimidazole derivatives with different heterocyclic nuclei at position-2 are described.

---

Synthese einiger substituierter Benzimidazole mit potentieller antimikrobieller Aktivität

Zusammenfassung Die Synthese und antimikrobielle Prüfung einiger Benzimidazole mit verschiedenen heterozyklischen Substituenten in 2-Stellung wird beschrieben.

     

Synthetic Routes to Pyrazole‐3(5)‐carboxylates

The data on the synthetic methods of the pyrazole‐3(5)‐carboxylates published over the last years are reviewed here for the first time.     

The Thiophene “Sigma‐Hole” as a Concept for Preorganized,Specific Recognition of G⋅C Base Pairs in the DNA Minor Groove

In spite of its importance in cell function, targeting DNA is under‐represented in the design of small molecules. A barrier to progress in this area is the lack of a variety of modules that recognize G ? C base pairs (bp) in DNA sequences. To overcome this barrier, an entirely new design concept for modules that can bind to mixed G ? C and A ? T sequences of DNA is reported herein. Because of their successes in biological applications, minor‐groove‐binding heterocyclic cations were selected as the platform for design. Binding to A ? T sequences requires hydrogen‐bond donors whereas recognition of the G‐NH₂ requires an acceptor. The concept that we report herein uses pre‐organized N‐methylbenzimidazole (N‐MeBI) thiophene modules for selective binding with mixed bp DNA sequences. The interaction between the thiophene sigma hole (positive electrostatic potential) and the electron‐donor nitrogen of N‐MeBI preorganizes the conformation for accepting an hydrogen bond from G‐NH₂. The compound–DNA interactions were evaluated with a powerful array of biophysical methods and the results show that N‐MeBI‐thiophene monomer compounds can strongly and selectively recognize single G ? C bp sequences. Replacing the thiophene with other moieties significantly reduces binding affinity and specificity, as predicted by the design concept. These results show that the use of molecular features, such as sigma‐holes, can lead to new approaches for small molecules in biomolecular interactions.     

Adhesion of Escherichia coli onto quartz, hematite and corundum: Extended DLVO theory and flotation behavior

The adhesion of Escherichia coli onto quartz, hematite and corundum was experimentally investigated. A strain of E. coli was used that had the genes for expressing protein for silica precipitation. The maximum cell adhesion was observed at pH <4.3 for quartz and at pH 4.5–8.5 for corundum. For hematite, cell adhesion remained low at all pH values. The microbe–mineral adhesion was assessed by the extended DLVO theory approach. The essential parameters for calculation of microbe–mineral interaction energy (Hamaker constants and acid–base components) were experimentally determined. The extended DLVO approach could be used to explain the results of the adhesion experiments. The effect of E. coli on the floatability of three oxide minerals was determined and the results showed that E. coli can act as a selective collector for quartz at acidic pH values, with 90% of the quartz floated at 1.5 × 10⁹ cells/ml. However, only 9% hematite and 30% corundum could be floated under similar conditions. By using E. coli and no reagents, it was possible to separate quartz from a hematite–quartz mixture with Newton's efficiency of 0.70. Removal of quartz from the corundum mixture was achieved by E. coli with Newton's efficiency of 0.62.     

Facile synthesis of benzobisimidazole and bibenzimidazole-based bisnitriles as potential precursors for DNA minor groove binders

The synthesis of bisnitrile derivatives of benzobisimidazole and bibenzimidazole in a good yield is described in detail for the first time. Nucleophilic substitution of 1,5-difluoro-2,4-dinitrobenzene using different amines produced the intermediate diamines that were reduced using sodium borohydride/Pd(C) to produce the tetramines. These tetramines were allowed to couple with different aldehydes to produce the final benzimidazoles. In a different investigation, these bisnitrile derivatives will be used to make benzimidazole diamidines that could be used as potential mixed sequence minor groove binders.     

Synthesis and anticonvulsant properties of a novel series of 2-substituted amino-5-aryl-1,3,4-oxadiazole derivatives

A novel series of 2-substituted amino-5-aryl-1,3,4-oxadiazole derivatives were synthesized for their potential anticonvulsant activity. The synthesis involved the cyclodesulfurization of variously substituted salicylthiosemicarbazides with DCCD and mercuric oxide. Representative examples of the title compounds were also prepared by a one-pot cyclodesulfurization of mixtures of salicylhydrazides and phenylisothiocyanate with DCCD.     

Pellet freezing of in vitro produced bovine embryos using dry ice

In vitro produced bovine embryos were frozen by pellet freezing or vitrification method. In the pellet freezing method, the embryos were cooled on the dry ice and then frozen as pellets. At warming, the pellets were immersed directly into 0.5 M sucrose. The survival rates of blastocysts frozen by the pellet freezing method were higher (P<0.01) in 40% ethylene glycol (EG) than those in the lower concentrations (20 and 30% EG). Higher survival rates of blastocysts frozen by the pellet freezing method were obtained but the development rates did not differ, as compared with those by the vitrification method. There were no significant differences between the pellet freezing and vitrification method in the frequencies of post-thaw survival of hatched blastocysts. These results demonstrate that the pellet freezing method using dry ice can be used successfully for the cryopreservation of blastocysts.