Diazomethane umpolung atop anthracene: an electrophilic methylene transfer reagent

Formal addition of diazomethane's terminal nitrogen atom to the 9,10-positions of anthracene yields H2CN2A (1, A = C14H10 or anthracene).

Theoretical Studies on the Mechanism of the Azido-Tetrazole of Azido-s-triazine

The B3LYP/aug-cc-pvDZ level of theory has been applied to the study of the molecular structures, electronic structures and the azido-tetrazole isomerization of 1-azido-s-triazine, 1,3-diazido-s-triazine and 1,3,5-triazido-s-triazine. NBO analysis was applied to investigate the atomic natural charge and stabilization interaction energies among molecules. The results showed that the reaction initially proceeds through the loss of the linearity of the azido group and the approaching of the terminal nitrogen atom of the azide group to the nitrogen atom of the ring. This is followed by an attack of the lone pairs on N atoms in the ring to the azido group, leading to the formation of the N-N bonds. Many factors, including bending of the bond angle, electrostatic attraction, orbital delocalization and the stabilization interaction give rise to a large free energy barrier for the cyclization process. The results also show that the second and third cyclization is relatively easier than the first one.

Calmodulin antagonists: Structure of N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7) and comparison with trifluoperazine (TFP) — Calmodulin binding

The crystal structure of the title compound contains one N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride molecule in the asymmetric unit. The molecule adopts an extended conformation with a linear hexyl group. Protonation occurs at the side chain terminal nitrogen atom. Hydrophobic packing and a three-dimensional hydrogen-bond network, involving all the hydrogen atoms capable of making hydrogen-bond contacts, stabilizes the crystal structure. Due to head-to-head and tail-to-tail arrangement of these hydrophobic molecules, an unusually long cell constant (b = 61.27 Å) characterizes the crystal structure. A stereochemical comparison with trifluoperazine suggests similar calmodulin binding mechanisms.Key words: crystal structure, stereochemistry, W-7, calmodulin binding, TFP.

Transition metal complexes with thiosemicarbazide-based ligands, part 46: Synthesis and physico-chemical characterization of mixed ligand cobalt(III)-complexes with salicylaldehyde semi-, thiosemi- an

Mixed ligand octahedral cobalt(III) complexes with the tridentate salicylaldehyde semi-, thiosemi- and isothiosemicarbazone and pyridine of general formula [CoIII(L1-3)(py)3]X(H2L1=salicylaldehyde semicarbazone X=[CIICl3(py)]-, ClO4-.H2O, I-. 0.5 I2; H2L2=salicylaldehyde thiosemicarbazone, X=[CoIICl3(py)]-, CoIIBr3(py)]-, ClO4-. H2O, I3-; H2L3 = salicylaldehyde S-methylisothiosemicarbazone, X=[CoIIBr3(py)]-, ClO4-. H2O, BF4-) were synthesized. The tridentate coordination of all the three dianionic forms of the ligands involves the phenol oxygen, hydrazine nitrogen and the chalcogen (O or S) in case of salicylaldehyde semi thiosemicarbazone and the terminal nitrogen atom in the case of isothiosemicarbazone. For all the complexes, a meridial octahedral arrangement is proposed, which is a consequence of the planarity of the chelate ligand. The compounds were characterized by elemental analysis molar conductivity, magnetic susceptibility, IR and electronic absorption spectra. The thermal decomposition of the complexes was investigated by thermogravimetry, coupled TG-MS measurements and DSC.

NMR Investigation of the Copper(II)-Ciprofloxacin System

A proton NMR study was performed on the copper(ll)-ciprofloxacin system. The proton relaxation times (T1) were determined from the titration data in acidic and basic media. In acidic medium the H5 signal is dramatically affected and it is assumed that copper is bonded to the quinolone through carbonyl and one of the carboxyl oxygens. Such bonding is in agreement with the X-ray literature data for the complex [Cu(cf)2]Cl2.6H2O isolated from the slightly acidic solution. There are additional significant changes in T1 of H3′ and H5′ atoms which suggest that the terminal nitrogen atom of the piperazine ring system-N4′ also interacts with copper in the basic conditions. Thus it is plausible that more than one species are present in the solution at high pH values.

Na+-Ca2+ exchange in human neutrophils

The pathway for inward Ca2+ movements in isolated human neutrophils was investigated. One-way 45Ca2+ influx into resting, steady-state cells amounted to approximately 6 mumol.l cell water-1.min-1. This uptake can be entirely accounted for on the basis of a carrier-mediated exchange of external Ca2+ for internal Na+. The counter transport exhibited trans stimulation of 45Ca2+ influx by internal Na+ (Km approximately equal to 26 mM) with a Hill coefficient of approximately equal to 2.6. There was substrate saturation by external Ca2+ (Km approximately equal to 0.15 mM) and by external Na+ (Km approximately equal to 30 mM); the two ions competed for the same binding sites. The exchange was noncompetitively inhibited by benzamil (Ki approximately 75 microM) and by some other amiloride analogues bearing a substituent on the terminal nitrogen atom of the guanidino group. Membrane depolarization enhanced the rate of 45Ca2+ entry, suggesting an electrogenic process; this voltage dependence was consistent with a coupling ratio of approximately 3 Na+:1 Ca2+. Hence, the Na+-Ca2+ exchange mechanism of neutrophils displays many features in common with those of other cell types. Studies in cells exposed to the tripeptide N-formylmethionyl-leucyl-phenylalanine (FMLP) indicate activation of the counter-transport system by the chemotactic factor. Thus, Na+-Ca2+ exchange may be at least partly responsible for the increase in 45Ca2+ influx and transient rise in intracellular free Ca2+ that are seen following stimulation.

Reactions of aryl diazonium salts and alkyl arylazo ethers. XI. Further evidence for the mechanism of dediazoniation in basic alcoholic solution

A comparison of the relative amounts of dediazoniation, SNAr and aryne reactions of 4-chloro-3- nitrobenzenediazonium ion with methoxide ion in CH3OH and in CD3OH confirms that the dediazoniation reaction involves hydride abstraction from the alkoxide ion by the electrophilic terminal nitrogen atom of the diazonium ion. Furthermore, the relative amounts of anionic and free-radical dediazoniation are the same in CH3OH and in CD3OH. This confirms that the partitioning between the free-radical and anionic pathways for dediazoniation is on the aryl diimide and not on the free diazonium ion. Some previously reported results on the solvent effect (methanol against ethanol) for the reaction have been reinterpreted in the light of the above conclusions.

Metal–Amino Polycarboxylic Acid Complexes. IV. A Polarographic Study of Lead (II) Complexes with Diethylenetriaminepentaacetic Acid in Aqueous Solution

The polarographic behavior of the lead ion in the presence of excess DTPA was studied over the pH range 2–10. Three different polarographic waves can be distinguished. The wave occurring at the most negative potentials and highest pH values is assigned to an irreversible reduction of PbHA2−. The kinetic current treatment gives the results[Formula: see text]The wave occurring at intermediate potentials and pH values is also assigned to an irreversible reduction of PbHA2−. The kinetic current treatment gives the results[Formula: see text]Protonation is assumed to occur at different coordination sites. In the former case it occurs at the center carboxyl group; in the latter case it occurs at a terminal nitrogen atom. The reversible wave occurring at the most positive potentials and lowest pH values can be interpreted in either of two ways[Formula: see text]For the stability constant we obtained log KpbA = 19.1. All values above were obtained at 25° and an ionic strength of 0.2.

Metal – Aminopolycarboxylic Acid Complexes. I. Studies of Lead(II) and Cadmium(II) Complexes with Diethylenetriaminepentaacetic Acid in Aqueous Solution by Proton Magnetic Resonance Spectroscopy

Lead(II) and cadmium(II) each form a 1:1 complex with DTPA. Nuclear magnetic resonance (n.m.r.) spectroscopy was used to show that each complex has three metal–nitrogen bonds and labile metal–oxygen bonds to terminal acetate groups. The latter lead to proton equivalence for the methylene protons of the terminal acetate groups of the lead complex, and near equivalence for those of the cadmium complex. The central carboxylate group is coordinated to the lead but not to the cadmium. Protonation occurs below pH 5.5 for the lead complex and occurs predominantly at a terminal nitrogen atom with consequent breaking of the metal–nitrogen bond. In the cadmium complex protonation occurs below pH 5 at the terminal nitrogen, breaking the metal–nitrogen bond, and also to almost the same extent at the central, uncoordinated carboxylate group. These differences in behavior of the lead and cadmium complexes are attributed to differences in ionic size. Possible structures are proposed and allowances are made for the possibility of coordination number greater than six. In the protonated complexes, structures and interconversion of protonated forms are discussed in the light of the observed simplification of the n.m.r. spectra.