A hydrazine- and phosgene-free synthesis of tetrazinanones, precursors to 1,5-dialkyl-6-oxoverdazyl radicals.

A complementary approach to published synthetic methods for tetrazinanones, precursors to verdazyl radicals, is described herein. This approach uses carbohydrazide, a commercially available reagent, as a common starting material. Unlike previous methods described in the literature, this synthetic scheme does not rely on phosgene, phosgene substitutes, or the limited pool of commercially available monosubstituted hydrazines for its execution. A large variety of alkyl substitution patterns at the N-1 and N-5 positions of verdazyl radicals are possible, including both symmetrically and unsymmetrically substituted products. An initial condensation reaction of carbohydrazide with a specific aldehyde introduces the desired C-3 substituent in the final verdazyl radical product and protects the NH(2) groups during the subsequent N-1 and N-5 alkylation reactions. A succeeding methanolysis and concomitant ring-closing reaction gives the tetrazinanone. A number of known oxidation methods can then be employed to form the final verdazyl radical product.

Verdazyl radicals as substrates for organic synthesis: a synthesis of 3-methyl-5-aryl-1,3,4-oxadiazolones.

The synthesis of oxadiazolones under hydrolytic conditions is described for a series of 3-methyl-5-aryl-1,3,4-oxadiazolone compounds. The unique starting materials for the hydrolysis reaction are obtained from efficient 1,3-dipolar cycloaddition reactions of styrene and azomethine imine dipoles derived from verdazyl radicals via a disproportionation reaction. A proposed mechanism for the formation of these biologically relevant oxadiazolones includes an opening of the tetrazinone ring followed by a 5-exo-trig ring closure. In support of the mechanism, in one case the ring-opened intermediate was isolated and subsequently treated with acid to give the relevant oxadiazolone.

Inhibition of microbial growth by silver-starch nanocomposite thin films.

A sago starch biopolymer with embedded silver nanoparticles has been studied as a material for the prevention of microbial growth. Approximately 8 nm in size, silver nanoparticles have been synthesized by reduction of the silver salt in aqueous solution in the presence of sago starch using sodium borohydride as a reducing agent. The obtained solutions were cast on glass plates to obtain thin supported silver-starch nanocomposite films. The morphology of the nanocomposites was investigated by scanning and transmission electron microscopy. UV-Vis absorption spectroscopy showed that during the film formation a part of the silver nanoparticles has been trapped in the water present in the sample, which enabled their partial oxidation into active Ag(+) species. The oxidation of the silver nanoparticles was confirmed by X-ray photoelectron spectroscopy. The antimicrobial activity tests have shown that the nanocomposite material can be successfully employed to prevent the viability and growth of the common pathogens Staphylococcus aureus, Escherichia coli and Candida albicans.

Adsorption of sulfur onto a surface of silver nanoparticles stabilized with sago starch biopolymer.

Adsorption of sulfide ions onto a surface of starch capped silver nanoparticles upon addition of thioacetamide was investigated. UV-vis absorption spectroscopy revealed that the adsorption of the sulfide ion on the surface of the silver nanoparticles induced damping as well as blue shift of the silver surface plasmon resonance band. Further increase in thioacetamide concentration led to shift of the resonance band toward higher wavelengths indicating the formation of the continuous Ag2S layer on the silver surface. Thus fabricated nanoparticles were investigated using electron microscopy techniques (TEM, HRTEM, and HAADF-STEM) and X-ray photoelectron spectroscopy (XPS), which confirmed their core-shell structure.