Oxidative decarboxylation of cyclic amino acids and dehydrogenation of cyclic secondary amines with iodosobenzene

Cyclic amino acids L-proline, pipecolinic acid and L-2-pyrrolidinone-5-carboxylic acid undergo oxidative decarboxylation with iodosobenzene in various solvents (including water) to yield the lactam and imide in the latter case. The reaction proceeds via initial imine formation.     

Dielectric relaxation in vanadium phosphate glasses

An asymmetric distribution of relaxation times has been inferred from an increase in the Cole-Cole distribution parameter α with increasing values of ωτ in 62% v₂O₅–38% P₂O₂ glass. The conventional Debye type relaxation loss peaks in the frequency range 10²–10⁵ Hz are observed in this sample above 85°K. The extrapolated values of dielectric constant and relaxation time below 100°K seem unexpectedly large while the high temperature extrapolated values of ?' are close to ?_∞ as expected. Probably the conventional dielectric loss peaks are observed only above a critical temperature at which the carriers gain sufficient energy to be excited to the conduction band edge. Below this temperature hopping of carriers within kT of the Fermi level may dominate and conventional Debye type dielectric loss peaks may lose their significance as envisaged in the models of frequency dependent ac conductivity.     

A porphyrin with a C═C unit at its center

The molecule (C═C)TTP (TTP = tetra-p-tolylporphyrin) and the triflate salt of its dication, [(C═C)TTP][OTf](2), have been synthesized and characterized. NMR spectroscopy, nucleus-independent chemical shift calculations, and the crystal structure of (C═C)TTP indicate that (C═C)TTP is antiaromatic and (C═C)TTP(2+) is aromatic.     

Synthesis, characterization, and calculated electronic structure of the crystalline metal-organic polymers [Hg(SC6H4S)(en)]n and [Pb(SC6H4S)(dien)]n

The reaction of Hg(OAc)(2) with 1,4-benzenedithiol in ethylenediamine at 80 °C yields [Hg(SC(6)H(4)S)(en)](n), while the reaction of Pb(OAc)(2) with 1,4-benzenedithiol in diethylenetriamine at 130 °C yields [Pb(SC(6)H(4)S)(dien)](n). Both products are crystalline materials, and structure determination by synchrotron X-ray powder diffraction revealed that both are essentially one-dimensional metal-organic polymers with -M-SC(6)H(4)S- repeat units. Diffuse reflectance UV-visible spectroscopy indicates band gaps of 2.89 eV for [Hg(SC(6)H(4)S)(en)](n) and 2.54 eV for [Pb(SC(6)H(4)S)(dien)](n), while density functional theory (DFT) band structure calculations yielded band gaps of 2.24 and 2.10 eV, respectively. The two compounds are both infinite polymers of metal atoms linked by 1,4-benzenedithiolate, the prototypical molecule for single-molecule conductivity studies, yet neither compound has significant electrical conductivity as a pressed pellet. In the case of [Pb(SC(6)H(4)S)(dien)](n) calculations indicate fairly flat bands and therefore low carrier mobilities, while the conduction band of [Hg(SC(6)H(4)S)(en)](n) does have moderate dispersion and a calculated electron effective mass of 0.29·m(e). Hybridization of the empty Hg 6s orbital with SC(6)H(4)S orbitals in the conduction band leads to the band dispersion, and suggests that similar hybrid materials with smaller band gaps will be good semiconductors.     

Aluminum and lithium octa(pentoxy)phthalocyanine radicals

A lithium phthalocyanine radical and the analogous aluminum phthalocyanine radical were synthesized as part of an investigation of isostructural dopants. An improved synthesis of the free base of octa(pentoxy)phthalocyanine (H₂Pc*) involves the reduction of 1,2-dicyano-4,5-dipentoxybenzene with hydroquinone. Deprotonation with lithium bis(trimethylsilyl)amide leads to the dilithium derivative Li₂Pc* and subsequent oxidation with ferrocenium yields the radical LiPc*. Treatment of H₂Pc* with Et₂AlCl gives ClAlPc* and reduction with sodium amalgam yields AlPc*, the first reported aluminum phthalocyanine radical. In the solid state LiPc* and AlPc* are electrical conductors with pressed-pellet conductivities of 8 × 10⁻¹¹ Ω⁻¹ cm⁻¹ and 5 × 10⁻⁷ Ω⁻¹ cm⁻¹, respectively.     

An efficient synthesis of LY544344·HCl: a prodrug of mGluR2 agonist LY354740

LY544344·HCl was efficiently prepared in two steps from LY354740. The key step highlighted the in situ masking of the carboxylic acid groups as trimethylsilyl esters to facilitate an effective acylation reaction.     

Effect of borate buffer on the photolysis of riboflavin in aqueous solution

The photolysis of riboflavin (RF) in the presence of borate buffer (0.1-0.5M) at pH 8.0-10.5 has been studied using a specific multicomponent spectrophotometric method for the determination of RF and photoproducts, formylmethylflavin (FMF), lumichrome (LC) and lumiflavin (LF). The overall first-order rate constants for the photolysis of RF (1.55-4.36 x 10(-2)min(-1)) and the rate constants for the formation of FMF (1.16-3.52 x 10(-2)min(-1)) and LC (0.24-0.84 x 10(-2)min(-1)) have been determined. The values of all these rate constants decrease with an increase in buffer concentration suggesting the inhibition of photolysis reaction by borate species. The kinetic data support the formation of a RF-borate complex involving the ribityl side chain to cause the inhibition of photolysis. The second-order rate constants for the borate inhibited reaction range from 1.17-3.94 x 10(-2)M(-1)min(-1). The log k-pH profiles for the reaction at various buffer concentrations indicate a gradual increase in rate, with pH, up to 10 followed by a decrease in rate at pH 10.5 probably due to ionization of RF and quenching of fluorescence by borate species. A graph of second-order rate constants against pH is a sigmoid curve showing that the rate of photolysis increases with an increase in pH. The results suggest the involvement of excited singlet state, in addition to excited triplet state, in the formation of LC.     

The doubly oxidized, antiaromatic tetraphenylporphyrin complex [Li(TPP)][BF4

[reaction: see text] Oxidation of dilithium tetraphenylporphyrin, Li(2)(TPP), yields the doubly oxidized porphyrin complex [Li(TPP)][BF(4)]. Free TPP appears to be unstable. The crystal structure of [Li(TPP)][BF(4)] reveals that the 16-atom C-N inner ring of the porphyrin consists of alternating single and double bonds. NMR spectroscopy and nucleus-independent chemical shift (NICS) calculations, in addition to the distortion from planarity observed in the crystal structure, indicate that the 16 pi-electron inner C-N ring of the porphyrin is antiaromatic.