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.     

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.     

Atom interferometry with Bose-Einstein condensates in a double-well potential

A trapped-atom interferometer was demonstrated using gaseous Bose-Einstein condensates coherently split by deforming an optical single-well potential into a double-well potential. The relative phase between the two condensates was determined from the spatial phase of the matter wave interference pattern formed upon releasing the condensates from the separated potential wells. Coherent phase evolution was observed for condensates held separated by 13 microm for up to 5 ms and was controlled by applying ac Stark shift potentials to either of the two separated condensates.     

Coherent control of polariton parametric scattering in semiconductor microcavities

In a pump-probe experiment, we have been able to control, with phase-locked probe pulses, the ultrafast nonlinear optical emission of a semiconductor microcavity, arising from polariton parametric amplification. This evidences the coherence of the polariton population near k=0, even for delays much longer than the pulse width. The control of a large population at k=0 is possible although the probe pulses are much weaker than the large polarization they control. With rising pump power the dynamics of the scattering get faster. Just above threshold the parametric scattering process shows unexpected long coherence times, whereas when pump power is risen the contrast decays due to a significant pump reservoir depletion. The weak pulses at normal incidence control the whole angular emission pattern of the microcavity.     

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.     

F-Continuous Graphs

For a nontrivial connected graph F, the F-degree of a vertex in a graph G is the number of copies of F in G containing . A graph G is F-continuous (or F-degree continuous) if the F-degrees of every two adjacent vertices of G differ by at most 1. All P₃-continuous graphs are determined. It is observed that if G is a nontrivial connected graph that is F-continuous for all nontrivial connected graphs F, then either G is regular or G is a path. In the case of a 2-connected graph F, however, there always exists a regular graph that is not F-continuous. It is also shown that for every graph H and every 2-connected graph F, there exists an F-continuous graph G containing H as an induced subgraph.     

Reduction of Nitrobenzene to Aniline with Carbon Monoxide and Water in the Presence of the PdCl2/Fe/I2 System

A study of modified catalyst systems composed of palladium or its chloride and a co-catalyst such as metallic Fe-powder, iodine, and pyridine was used in the reduction of nitrobenzene to aniline with carbon monoxide and water at 180°C and 2.5-4 MPa pressure. The reaction is complete in 2 h with a nitrobenzene conversion of 98-100% and a 100% selectivity with respect to aniline.