EPR study of the Ag6S3O4 compound prepared by two methods

The temperature dependence of the EPR spectra of the recently discovered Ag₆S₃O₄ phase in the Ag-O-S system prepared by two methods, the known method of co-precipitation from aqueous solution and a new method depending on the interaction of Ag₂S and Ag₂SO₄ solid reagents, has been investigated. No EPR spectra were observed at room temperature, while at liquid helium temperature a number of EPR spectra have been recorded, which disappeared upon increasing temperature up to liquid nitrogen temperature. The sample obtained by the co-precipitation method revealed an intense, rich EPR spectrum that has been tentatively interpreted assuming the presence of at least two different Ag²⁺ ion complexes, one monomer resulting in an intense anisotropic, rhombic EPR powder pattern with g₁ = 1.93(1), g₂ = 2.025(3), g₃ = 2.094(5), hyperfine constants A₁ = = A₂ = 60(5) · 10^?4 cm^?1,A ₃ = 90(5) · 10^?4 cm^?1 and one dimer EPR pattern presumably involving a pair of Ag²⁺ ions with internuclear separation of 4.3 Å. However, the presence of larger clusters could not be excluded. On the other hand, the sample obtained by a solid state reaction method has given rise to two rather weak EPR lines centered at g_eff = 2.105(3) and g_eff = 4.213(3), respectively.     

Synthesis and electrochemical study of nitrophenyl derivatives of β‐cyclodextrin

A series of nitrophenyl β‐cyclodextrin derivatives: mono[6‐deoxy‐6‐(4‐nitrobenzamido)]‐per‐ O‐methyl‐β‐cyclodextrin (R₁? Ph? NO₂), mono[6‐deoxy‐6‐(3‐nitrobenzamido)]‐per‐O‐methyl‐β‐cyclodextrin (R₂? Ph? NO₂) and heptakis[6‐deoxy‐6‐(4‐nitrobenzamido)‐2,3‐di‐O‐methyl]‐β‐cyclodextrin [R₃? (Ph? NO₂)₇] were synthesized. Purity and composition of the obtained substances were checked. Electroreduction of nitro groups of the new synthesized compounds was investigated on mercury electrode using cyclic voltammetry and chronocoulometry. The parameters of the reduction processes of ? NO₂ groups of the investigated compounds were found not to be comparable to the reduction of nitrobenzene under the same experimental conditions. Moreover, the electroreduction of nitro groups in these nitrophenyl derivatives was dependent on pH, the type of the studied compound, and slightly on the solvent composition. All the reactants were strongly adsorbed on mercury electrode. In the case of R₃? (Ph? NO₂)₇, its seven nitro groups were reduced practically at the same potential, and no radical anion formation was observed. Copyright © 2007 John Wiley & Sons, Ltd.     

Adaptive edge detection method for images

The novel two-dimensional (2D) wavelet with anisotropic property and application of it has been presented. Wavelet is constructed in the polar coordinate system to obtain anisotropic properties. A novel edge detection method has been developed with the aid of this wavelet. This method detects gradient jump and than follows along this jump. In this way the number of calculation for edge localization is reduced. Moreover, the presented method is able to detect all edges in an image in multi-scale together with its spatial orientation. Proposed wavelet as well as edge extraction method seems to be new way to edge detection for an image.     

Gonadal steroids differentially modulate neurotoxicity of HIV and cocaine: testosterone and ICI 182,780 sensitive mechanism

Background  

HIV Associated Dementia (HAD) is a common complication of human immunodeficiency virus (HIV) infection that erodes the quality of life for patients and burdens health care providers. Intravenous drug use is a major route of HIV transmission, and drug use is associated with increased HAD. Specific proteins released as a consequence of HIV infection (e.g., gp120, the HIV envelope protein and Tat, the nuclear transactivating protein) have been implicated in the pathogenesis of HAD. In primary cultures of human fetal brain tissue, subtoxic doses of gp120 and Tat are capable of interacting with a physiologically relevant dose of cocaine, to produce a significant synergistic neurotoxicity. Using this model system, the neuroprotective potential of gonadal steroids was investigated.     

An improved external loop resonator for in vivo L-band EPR spectroscopy

An improved external loop resonator (ELR) used for L-band electron paramagnetic resonance (EPR) spectroscopy is reported. This improvement is achieved by shortening the parallel coaxial line. The resonant structure is formed by two single turn coils (10mm in diameter) that are connected to a parallel coaxial line. A resonance frequency of 1197 MHz and a quality factor of 466 were obtained in the absence of biological tissue and were approximately 1130 MHz and approximately 50 with a living animal, respectively. The sensitivity of the new ELR was compared to the previously developed ELR using three types of EPR samples: (1) paramagnetic material with no biological tissue, (2) paramagnetic material in a leg and in the peritoneal cavity of a dead rat, and (3) paramagnetic material in the back of an anesthetized rat. The sensitivity was 1.2-1.6 times greater in the rat and 4.2 times without tissue.     

New mesogenic compounds having fork-like or cyclic amide terminal groups

Two homologous series of mesogenic materials with molecules containing an amide moiety, cyclic or symmetrically branched, as the terminal group have been synthesized. Materials of both series form lamellar liquid crystal phases. It was observed that elongation of the amide chains in 'fork-like' compounds destabilizes the mesophases, while 'cyclic' materials, even with quite large terminal amide rings, exhibit enantiotropic liquid crystalline phases.     

N-methylation of etioporphyrin I and octaalkyl-5-azaporphyrins : X-ray structure of trans-Na,Nb-dimethyletioporphyrin I triiodide

Improved procedures are reported for the preparation of mono-, di- and tri-N-methyl-etioporphyrin I. Demethylation of N_a, N_b, N_c-trimethyletioporphyrin I under acidic, basic or thermal conditions gives N_a, N_b-dimethyl etioporphyrin I. N-Methylation of octaalkyl-5-azaporphyrins leads, in general, to mixtures of the isomeric mono-, di- and tri-N-alkylated 5-azaporphyrins. An X-ray crystal structure of N_a,N_b-dimethyl etioporphyrin I triiodide confirms the trans arrangement of the N-Me groups. The two N-methylated pyrrole rings are twisted 27° to each other.     

Anomalous (S2 → S0) luminescence of some derivatives of triphenylmethane dyes and their complexes with rare earth metals

Anomalous S₂ → S₀ fluorescence and T₂ → S₀ phosphorescence have been found in several triphenylmethane derivatives. This phenomenon can be explained by a large energy gap between the S₂ and S₁ levels, approximately 14000 cm^?1. Some of the investigated compounds exhibit also a normal long-wave fluorescence in spite of the fact, that the S₂ ? S₁ energy gap does not change significantly. However, in these cases absorption spectra reveal a high oscillator strength of the S₁ → S₀ transition. The coordination of a lanthanide ion quenches in several cases the normal S₁ → S₀ fluorescence whereas the S₂ → S₀ one is not affected significantly.