Fmoc-chemistry of a stable phosphohistidine analogue

We report the synthesis of the phosphohistidine analogue, Fmoc-4-diethylphosphonotriazolylalanine 5 and its incorporation into peptides. Our synthesis of 5 has enabled us to demonstrate that the analogue is compatible with Fmoc-solid phase peptide synthesis (SPPS) conditions. Standard cleavage conditions yield the diethyl phosphonate-protected peptide, however this can be subsequently deprotected using trimethylsilyl bromide to yield the free phosphonic acid-containing peptides.     

Molecular recognition in a uradinyl-functionalized stable radical

Stable radical 2-(6-uradinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl (1) binds to hydrogen-bonding complement 2,6-di(propylamido)pyridine (DAP) in chloroform with Ka=220 M(-1) at 33 degrees C; ESI-MS shows not only 1:DAP complementary dyad formation, but also 1:(DAP)2 formation at higher concentrations of DAP.     

Nem method of obtaining a stable diphosphirane

The stable monomer diphosphirane 2 is produced by the reaction of the diazomethane on the diphosphène 1.     

Reaction of a stable silylene with tetrahydrofuran

Reduction of 1,3-di-tert-butyl-2,2-dichloro-2,3-dihydro-1H-1,3,2-diazasilole with metallic potassium gave, instead of a stable silylene, 1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2λ²-diazasilylolene, a product of insertion of the latter into the carbon-oxygen bond of tetrahydrofuran, 1,4-di-tert-butyl-6-oxa-1,4-diaza-5-silaspiro[4,5]dec-2-ene.     

Reactions of a stable silylene with halocarbons

An unusual product formation is observed for the insertion reaction of the thermally stable silylene Si[(NCH(2)Bu(t))(2)C(6)H(4)-1,2][abbrev. as Si(NN)] into the carbon-halogen bond of alkyl or aryl halides RHal (Hal=Cl, Br). In general, depending on the halogen, the reaction either results in a disilane of type (NN)Si(Hal)-(R)Si(NN) for Hal=Cl or a mixture of disilane and the monosilane (NN)Si(R)(Hal) for Hal=Br. The results are put into context to previously suggested mechanisms. The disilane (NN)Si(Hal)-(R)Si(NN)(Hal=Cl or Br) is thermally labile and mild thermolysis yields the corresponding monosilane (NN)Si(R)(Hal) and silylene 1. Additionally, strong evidence is presented for a radical pathway for the reaction of 1 and RHal.     

Synthesis of a double spiro-polyindenofluorene with a stable blue emission

[reaction: see text] A novel polyindenofluorene containing a double spiro-anthracene structure with solublizing alkyl groups was synthesized. Enhanced spectral stability of the polymer was investigated by heat treatment and photoirradiation in air. The EL spectrum of the polymer showed an enhanced sensitivity to the human eye and good color purity as a blue-emitting material.     

Insights into the making of a stable silylene

Reduction of Cl2Si[(NR)2C6H4-1,2] (R = CH2Bu(t)) with potassium is known to lead to the stable silylene Si[(NR)2C6H4-1,2] (1). However, silylene is now shown to react further with an alkali metal (Na or K) to yield the (1)(2)2-, c-(1)(3)-*, c-(1)(3)2- or c-(1)(4)2- derivatives. Reduction of Cl2Si[(NR)2C6H4-1,2] (R = CH2CH3 or CH2CHMe2) with potassium does not lead to an isolable silylene, but such a silylene is proposed to be an intermediate and, as for 1, reacts further to afford the potassium salts of c-[Si{(NR)2C6H4-1,2}]4-* and c-[Si{(NR)2C6H4-1,2}](4)2-. The pathways leading to the anionic cyclotri- and cyclotetrasilanes are discussed and supported experimentally; including by X-ray structures of relevant intermediates.     

Synthesis of stable ketenimines via a four-component reaction

Abstract  

An efficient one-pot synthesis of ketenimine derivatives is described. It involves a four-component reaction between benzylamines, 2,2-dichloroethanoyl chloride, alkyl isocyanide, and dialkyl acetylenedicarboxylates under mild conditions at ambient temperature.     

Emission topography of a stable spark discharge train

Time and space resolved spectroscopy are used to photograph the emission from a stable spark discharge train attacking a rotating copper beveled disk in flowing argon. The spark is generated at 60 Hz with a Bardocz type adjustable waveform source. Photographic density over background of sets of lines in the Cu I and Cu II term system is plotted as a function of lateral displacement from the vertical interelectrode axis and time at discrete horizontal distances away from the copper cathode surface to form spatially connected sets of lateral emission profiles. Data from secondary cathodes of silver and gold are presented, along with spectral evidence for radial compression of the cathode jets accompanying their charge transfer ionization and excitation. Spectrochemical applications utilizing time-space structural details are discussed.     

The formation of a stable o-semidine rearrangement intermediate

Treatment of 5,6,11,12-tetrahydrodibenzo-[b, f][1,2] diazocine with dilute acids affords a spiro-1,2,3,4-tetrahydroquinoline derivative which represents the first isolated stable o-semidine rearrangement intermediate.     

Antimicrobial polyethyleneimine-silver nanoparticles in a stable colloidal dispersion

Excellent colloidal stability and antimicrobial activity are important parameters for silver nanoparticles (AgNPs) in a range of biomedical applications. In this study, polyethyleneimine (PEI)-capped silver nanoparticles (PEI-AgNPs) were synthesized in the presence of sodium borohydride (NaBH(4)) and PEI at room temperature. The PEI-AgNPs had a positive zeta potential of approximately +49 mV, and formed a stable nanocolloid against agglomeration due to electrostatic repulsion. The particle size and hydrodynamic cluster size showed significant correlations with the amount of PEI and NaBH(4). PEI-AgNPs and even PEI showed excellent antimicrobial activity against Staphylococus aureus and Klebsiella pneumoniae. The cytotoxic effects of PEI and PEI-AgNPs were confirmed by an evaluation of the cell viability. The results suggest that the amount of PEI should be minimized to the level that maintains the stability of PEI-AgNPs in a colloidal dispersion.     

Studies on stable free radicals. XVI. Copolymerizationo of a stable N-oxyl biradical with p-xylylene

Six copolymers were obtained by the reaction of a sterically hindered N-oxyl biradical with pseudodiradical p-xylylene using the reactivity of an N-oxyl toward the carbon radical. The feed ratio of the N-oxyl biradical to α-chloro-p-xylene, which was used as the precursor of the pseudodiradical p-xylylene, governed the properties of the copolymers produced. The copolymers with a terminalN-oxyl group, were obtained when a 0.4-1.2 molar ratio of the N-oxyl biradical to α-chloro-p-xylene. The polymerization process was also discussed.     

New thermally stable polymer with a graphite-type structure

A new thermally stable polymer with a structure resembling that of graphite has been synthesized by the condensation of 1,4,5,8-tetraaminoanthraquinone and 1,3,6,8-tetraketo-1,2,3,6,7,8-hexahydropyrene (naphthalene-1,8,4,5-diindandione). Prepolymers, with an open structure, were soluble to some extent in concentrated sulfuric acid but were more completely solubilized by methanesulfonic acid. The final polymer with a closed-ring structure, which was obtained by heating the prepolymer having an inherent viscosity of 0.4, was completely insoluble in these acids. Elemental analysis indicated that a high degree of cyclization was achieved, and the final polymer showed good thermal stability. Prepolymers with inherent viscosities in the range 0.11–1.58 have been obtained but, usually, a high viscosity was accompanied by a low acid solubility. Prepolymers with an inherent viscosity of 0.4, which were very soluble (>90%) in strong acids, were solubilized to a high degree by reduction with sodium dithionite in alkaline, aqueous dimethylacetamide. The highest molecular weight prepolymer (inherent viscosity of 1.30–1.58) was solubilized to a greater extent in this base mixture than in methanesulfonic acid. However, it was not completely soluble, under the conditions employed. The propolymers of higher molecular weight showed some fiber- and film-forming properties.     

Insertion of a stable dialkylsilylene into silicon-chlorine bonds

The reactions of a stable dialkylsilylene with chlorosilanes such as tetrachlorosilane, dimethyldichlorosilane, and dichlorosilane occurred smoothly at room temperature in hydrocarbon solvents to give the corresponding Si-Cl bond insertion products. In the reaction of the silylene with dichlorosilane, only the Si-Cl bond insertion product was obtained, while a similar reaction with dimethylchlorosilane gave only the Si-H insertion product, emphasizing the remarkable difference in the steric requirements between these two insertion reactions. No reaction took place during the treatment of the silylene with trimethylchlorosilane. The Si-Cl insertion reactions are expected to be applied in the synthesis of new organosilicon frameworks that cannot be obtained by conventional methods.