Redox and Antioxidant Modulation of Circadian Rhythms: Effects of Nitroxyl,N-Acetylcysteine and Glutathione

The circadian clock at the hypothalamic suprachiasmatic nucleus (SCN) entrains output rhythms to 24-h light cycles. To entrain by phase-advances, light signaling at the end of subjective night (circadian time 18, CT18) requires free radical nitric oxide (NO•) binding to soluble guanylate cyclase (sGC) heme group, activating the cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG). Phase-delays at CT14 seem to be independent of NO•, whose redox-related species were yet to be investigated. Here, the one-electron reduction of NO• nitroxyl was pharmacologically delivered by Angeli’s salt (AS) donor to assess its modulation on phase-resetting of locomotor rhythms in hamsters. Intracerebroventricular AS generated nitroxyl at the SCN, promoting phase-delays at CT14, but potentiated light-induced phase-advances at CT18. Glutathione/glutathione disulfide (GSH/GSSG) couple measured in SCN homogenates showed higher values at CT14 (i.e., more reduced) than at CT18 (oxidized). In addition, administration of antioxidants N-acetylcysteine (NAC) and GSH induced delays per se at CT14 but did not affect light-induced advances at CT18. Thus, the relative of NO• nitroxyl generates phase-delays in a reductive SCN environment, while an oxidative favors photic-advances. These data suggest that circadian phase-locking mechanisms should include redox SCN environment, generating relatives of NO•, as well as coupling with the molecular oscillator.     

Effect of 1-Hexene Comonomer on Polyethylene Particle Growth and Kinetic Profiles

Summary: The polymer growth and the microstructure of the final polymer are greatly affected by mass transfer, especially in the early stages of polymerization. In the present work, the catalytic system (nBuCp)₂ZrCl₂/MAO immobilized over SiO₂-Al₂O₃ has been tested in ethylene-1-hexene copolymerizations using different amounts of comonomer. The catalytic activity shows a positive comonomer effect up to 1-hexene concentration of 0.724 mol/L since larger amounts of 1-hexene lead to a decrease in the activity. Copolymer properties analyzed by ¹³C NMR, GPC, CRYSTAF and DSC point to the presence of important amorphous regions in the growing polymer chains as the 1-hexene concentration increases. In order to study the incorporation of 1-hexene during ethylene polymerization, several experiments were performed with 0.194 mol/L of 1-hexene, 5 bar of ethylene pressure and different polymerization times. The incorporation of 1-hexene decreases slightly at polymerization times above 20 minutes. From cross-sectioned SEM images it can be concluded that the presence of 1-hexene helps catalyst fragmentation which could be related with the filter effect proposed by Fink.     

Correlation between dipolar TSDC and AC dielectric spectroscopy at the PVDF glass transition

The α_a-mode (associated to the dynamic glass transition) in PVDF-α has been studied by Thermally Stimulated Depolarization Currents (TSDC) and Dielectric Spectroscopy (DS) techniques. The distribution of relaxation parameters, reorientation energies, characteristic temperature, and preexponential factors of the Vogel–Tammann–Fulcher relaxation times have been precisely determined by using the Simulated Annealing Direct Signal Analysis applied to a partially discharged TSDC α_a peak. This distribution has been used to predict the variation of the dielectric loss, ε″(ω, T), in the temperature and frequency range where the DS measurements were made on the same material. The simulated ε′(T, ω) for various ω, are compared to the experimental values. The width of the peak is always too low, due to the restricted distribution used for the generation of the curves. A relaxation map including the TSDC results is used to determine the relaxation time variation. In the limited frequency range where the AC DS experiments are performed (10² ≤ f ≤ 10⁵ Hz) a master curve is drawn and the exponents of the frequency dependence are found at low and high frequency; also, a fitting to the Havriliak–Negami distribution is successfully performed. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2483–2493, 1997     

Selenosulfides Tethered to gem-Dimethyl Esters: A Robust and Highly Versatile Framework for H2S Probe Development

Selenosulfides coupled to gem-dimethyl esters provide an exceptional platform for H₂S probe development. With the sulfur half being nonessential to its high reactivity and selectivity towards H₂S, we highlight the unique flexibility of our design by improving its biocompatibility and tissue specificity through structural modifications of its sulfide moiety.     

Flow-Injection Spectrophotometric Determination of Methimazole in Pharmaceuticals Using a Charge Transfer Complex Cu(I)‒Neocuproine

In this work an accurate, fast and high throughput flow procedure was developed in order to determine methimazole in pharmaceutical formulations. The method is based on reduction of Cu(II) to Cu(I) by methimazole in the presence of 2,9-dimethyl-1,10-phenanthroline (neocuproine), followed by the generating a yellow charge-transfer complex that was spectrophotometrically monitored at 455 nm. The methimazole analytical curve was linear in a concentration range from 4.0 × 10^–5 to 1.5 × 10^–4 M. The sample throughput was 90 h^–1 and the relative standard deviation was 0.3% for a methimazole solution. The average recovery was 99%. The developed method is economic due to reduced consumption of samples and reagents. Samples can be analyzed without special pretreatment or using of organic solvents.     

Influence of aging and crystallinity on the molecular motions in bisphenol-A polycarbonate

Thermally Stimulated Depolarization Current technique, Differential Scanning Calorimetry, and Dynamic Mechanical Analysis have been applied to amorphous and semicrystalline bisphenol-A polycarbonate with crystallinity degrees up to 21.8%, in a temperature interval covering the α and β relaxations. The secondary β transition is found to be the sum of three components whose variations in aged and annealed specimens have shown the cooperative character of the β₁ and β₂ modes, contrary to the localized nature of the β₃ component. A T_g decrease was observed by both TSDC and DSC as a function of X_c and has been related to the possible confinement of the mobile amorphous phase in regions whose sizes are smaller than the correlation lengths of the cooperative movements that characterize the motions occurring at T_g. The α relaxation intensity variations with crystallinity show the existence of an abundant rigid amorphous phase in the semicrystalline material. The relaxation parameters deduced from the Direct Signal Analysis of the α relaxation for the mobile amorphous phase do not show significant deviations from those found for the amorphous material. The existence of the rigid amorphous phase has been associated to the ductile-to-brittle transition experienced by the material at low crystallinity levels. © 1996 John Wiley & Sons, Inc.