Experimental and Computational Study of the Thermal Decomposition of 3‐Methyl‐3‐buten‐1‐ol in m‐Xylene Solution

An experimental study of the thermal decomposition of a β‐hydroxy alkene, 3‐methyl‐3‐buten‐1‐ol, in m‐xylene solution, has been carried out at five different temperatures in the range of 513.15–563.15 K. The temperature dependence of the rate constants for the decomposition of this compound in the corresponding Arrhenius equation is given by ln k (s^?1) = (25.65 ± 1.52) ? (17,944 ± 814) (kJ·mol^?1)·T^?1. A computational study has been carried out at the M05–2X/6–31+G(d,p) level of theory to calculate the rate constants and the activation parameters by the classical transition state theory. There is a good agreement between the experimental and calculated rate constants and activation Gibbs energies. The bonding characteristics of reactant, transition state, and products have been investigated by the natural bond orbital analysis, which provides the natural atomic charges and the Wiberg bond indices. Based on the results obtained, the mechanism proposed is a one‐step process proceeding through a six‐membered cyclic transition state, being a concerted and slightly asynchronous process. The results have been compared with those obtained previously by us (Struct Chem 2013, 24, 1811–1816) for the thermal decomposition of 3‐buten‐1‐ol, in m‐xylene solution. We can conclude that in the compound studied in this work, 3‐methyl‐3‐buten‐1‐ol, the effect of substitution at position 3 by a weakly activating CH₃ group is the stabilization of the transition state formed in the reaction and therefore a small increase in the rate of thermal decomposition.     

Structural and Kinetic Aspects of Blood Plasma Protein Adsorption on the Surface of Hydrophobic Polymers

Abstract

Due to the wide use of polymers in medicine, researchers are required to solve a very important problem–to understand the interaction between materials of nonphysiological origin and the surrounding biological liquids, and tissues, particularly blood.     

Superoxide dismutase targets NO from GSNO to Cysbeta93 of oxyhemoglobin in concentrated but not dilute solutions of the protein

The role of hemoglobin (Hb) in transmitting the vasodilatory property of NO throughout the vascular system is of much current interest. NO exchange between Hb and low-molecular-weight nitrosothiols such as S-nitrosoglutathione (GSNO) has been speculated and reported in vitro. Previously, we reported that NO delivery from GSNO to Cysbeta93 of human oxyHb is prevented in the presence of the Cu chelators, neocuproine, and DTPA.(1) In the present work, 5 mM solutions of commercial human Hb were found by ICP-MS to contain approximately 20 microM Cu and Zn, suggesting the presence of Cu,Zn-superoxide dismutase (CuZnSOD), which was confirmed by Western blotting. SOD activity measurements were consistent with the presence of approximately 20 microM CuZnSOD monomer in 5 mM Hb solutions, which is the physiological concentrations of these proteins in the red blood cell. Incubation of 3.75 mM oxyHb (15 mM heme; 7.5 mM Cysbeta93) with 3.75 or 7.5 mM GSNO gave rise to 50% or 100% S-nitrosation, respectively, of Cysbeta93 as monitored by FTIR nu(SH) absorption, whereas excess GSNO over Cysbeta93 converted oxyHb to metHb due to the reaction, oxyHb + NO<==>metHb + NO(3)(-). Removal of CuZnSOD by anion-exchange chromatography yielded an oxyHb sample that was unreactive toward GSNO, and replacement with bovine CuZnSOD restored reactivity. Addition of 1 microM GSNO (Cysbeta93/GSNO = 1) to solutions diluted 10(4)-fold from physiological concentrations of oxyHb and CuZnSOD resulted largely in metHb formation. Thus, this work reports the following key findings: CuZnSOD is an efficient catalyst of NO transfer between GSNO and Cysbeta93 of oxyHb; metHb is not detected in oxyHb/GSNO incubates containing close to the physiological concentration (5 mM) of Hb and CuZnSOD when the Cysbeta93/GSNO molar ratio is 0.5 to 1.0, but metHb is detected when the total Hb concentration is low micromolar. These results suggest that erythrocyte CuZnSOD may play a critical role in preserving the biological activity of NO by targeting it from GSNO to Cysbeta93 of oxyHb rather than to its oxyheme.     

Electron paramagnetic resonance of Er doped in YVO4: hyperfine parameters

X-band (9.60 GHz) electron paramagnetic resonance (EPR) spectra of the Er³⁺ Kramers ion substituting for the Y³⁺ ion in yttrium vanadate (YVO₄) single crystal were recorded at liquid-helium temperatures. Fine and hyperfine EPR transitions were observed for the ¹⁶⁶Er (zero nuclear magnetic moment) and ¹⁶⁷Er (I=7/2) isotopes, respectively. The values of the elements of the anisotropic ²- and ò-tensors of the ¹⁶⁷Er³⁺ ion, and those of the ² tensor for the ¹⁶⁶Er ion, were estimated. The admixture of crystal-field wave functions in the ground-state wave function of Er³⁺ were determined using the experimental g-values.     

Preferential suppression of high-energy upconverted emissions of Tm3+ by Dy3+ ions in Tm3+/Dy3+/Yb3+-doped LiYF4 colloidal nanocrystals

The intensity of high energy UV and blue upconverted emissions of Tm(3+) ions in Tm(3+)/Yb(3+) co-doped LiYF(4) colloidal nanocrystals was selectively reduced compared to the NIR emission at 802 nm. This was achieved by doping a small amount of Dy(3+) ions into the host matrix.     

Intermittency driven by band-limited noise

Nonlinear systems driven by band-limited noise exhibit intermittent dynamics over a wide frequency domain, as revealed by high-pass filtering the system response at a cut-on frequency much higher than the noise cut-off frequency. The statistics of the stationary intermittency thus developed is investigated in detail by analogue simulation of a simple monostable system, the overdamped quartic oscillator, in the limit of strong nonlinearity. The mathematical interpretation of our results is provided in terms of a statistically refined singular-perturbation argument, which explains the occurrence of an intermittent burst in the high-pass filtered signal with the close coincidence of a signal inflection point with a noise zero-crossing. Our interest focuses on a characteristic frequency domain, where the intermittent phenomenon is sensitive to the nonlinear nature of the system, only, irrespective of the driving noise statistics (inertial range).