Studying of the critical exponents around the glass transition in bulk polymerization of ethyl methacrylate by using fluorescence techniques

The glass transition during bulk polymerization was studied in free-radical crosslinking copolymerization (FCC) of ethyl methacrylate (EMA), using both the steady-state fluorescence (SSF) and the fast transient fluorescence (FTRF) techniques. Pyrene (Py) was used as a fluorescence probe. Changes in the viscosity of the pregel solutions due to gel formation dramatically enhance the fluorescent yield of Py molecules. The reaction time at which the Py intensity and lifetime exhibit a sudden increase corresponds to the reaction time at which the rate of polymerization becomes maximum resulting from the gel effect. This effect is used to study the gelation of EMA, as a function of time, at various crosslinker concentrations and different temperatures. The results were interpreted in the view of percolation theory. The gel fraction, β and weight average degree of polymerization, γ exponents β?=?0.37?±?0.01, γ?=?1.71?±?0.04 and β?=?0.36?±?0.002, γ?=?1.687?±?0.01 are found in agreement with percolation results for SSF and FTRF measurements, respectively.     

Delayed myelination in a rhizomelic chondrodysplasia punctata case: MR spectroscopy findings

Rhizomelic chondrodysplasia punctata is a member of genetic peroxisomal disorders. Delayed myelination, which is probably related to the inadequacy of plasmalogens biosynthesis, is an important feature of this disorder. Direct assessment of neuropathologic aspects of RCDP syndrome such as neuronal degeneration and delayed myelination is possible with MR spectroscopy.In this report, MR spectroscopy findings (decreased Cho/Cr and increased Ins-Gly/Cr ratios and increased levels of mobile lipids) of a rhizomelic chondrodysplasia punctata case supporting delayed myelination are presented. This is the second report of MR spectroscopy examination of the specific brain metabolic changes associated with rhizomelic chondrodysplasia punctata.     

Proton MR spectroscopy features of normal appearing white matter in neurofibromatosis type 1

To determine whether differences exist between neurofibromatosis type 1 (NF1) patients with or without focal lesions and healthy normal volunteers in the metabolite ratios of normal appearing white matter, 27 patients with NF1 (with parenchymal lesion, MR positive, n: 17; without parenchymal lesions, MR negative, n: 10) and 20 healthy volunteers underwent MRI and short TE (31 ms) proton MR spectroscopy (MRS). In 17 patients with parenchymal lesions, 61 focal lesions were detected by MRI. MRS was performed from normal appearing frontal and posterior parietal white matter (FWM and PWM) in NF1 and from control groups. NAA/Cr, Cho/Cr and MI/Cr ratios were calculated. Significant increase in Cho/Cr and MI/Cr ratios were found in FWM and PWM in MR negative and positive groups when compared to control group. NAA/Cr ratio in MR positive group was significantly decreased in FWM compared to control group. There were no significant differences between FWM and PWM in all metabolite ratios of MR negative group. MI/Cr ratio in MR positive group was significantly elevated in PWM compared to FWM. Metabolite changes detected by MRS could indicate demyelination and gliosis in normal appearing white matter in all NF1 patients, and additionally neuroaxonal damage in the FWM of NF1 patients with focal lesions. For that reason, in the clinical evaluation and follow-up of these patients MRS features of normal appearing white matter should be considered in addition to focal lesions.     

Composite matrices from group rings,composite G-codes and constructions of self-dual codes

Designs, Codes and Cryptography - In this work, we define composite matrices which are derived from group rings. We extend the idea of G-codes to composite G-codes. We show that these codes are...     

Steklov convexification and a trajectory method for global optimization of multivariate quartic polynomials

Mathematical Programming - The Steklov function $$\mu _f(\cdot ,t)$$ is defined to average a continuous function f at each point of its domain by using a window of size given by $$t>0$$ . It...     

Synthesis,characterization and biological evaluation of N-substituted triazinane-2-thiones and theoretical–experimental mechanism of condensation reaction

The synthesis of triazinthions and their reactions with some nucleophilic reagents have been investigated during this scientific study. Thus, thiourea with a single component has been synthesized as a result of concomitant reactions of aldehyde and amines trials. The structure of the synthesized compounds was confirmed by ¹H, ¹³C NMR spectroscopy methods. The inhibitory effects of novel N-substituted triazinane-2-thione derivatives on acetylcholinesterase (AChE) activity were performed according to the spectrophotometric method of Ellman et al. These novel N-substituted triazinane-2-thiones derivatives were effective inhibitors of the α-glycosidase, cytosolic carbonic anhydrase I and II isoforms (hCA I and II), and Acetylcholinesterase (AChE) enzymes with K_i values in the range of 1.01 ± 0.28 to 2.12 ± 0.37 nm for α-glycosidase, 13.44 ± 4.39 to 74.98 ± 6.25 nm for hCA I, 10.41 ± 4.8 to 72.6 ± 17.66 nm for hCA II, 36.82 ± 9.95 to 108.48 ± 1.17 nm for AChE, and 624.62 ± 100.34 to 1124.16 ± 205.14 nm for α-glycosidase, respectively.     

The Reactivity of Ambident Nucleophiles: Marcus Theory or Hard and Soft Acids and Bases Principle?

The model reactions CH₃X + (NH—CH=O)M ➔ CH₃—NH—NH═O or NH═CH—O—CH₃ + MX (M = none, Li, Na, K, Ag, Cu; X = F, Cl, Br) are investigated to demonstrate the feasibility of Marcus theory and the hard and soft acids and bases (HSAB) principle in predicting the reactivity of ambident nucleophiles. The delocalization indices (DI) are defined in the framework of the quantum theory of atoms in molecules (QT-AIM), and are used as the scale of softness in the HSAB principle. To react with the ambident nucleophile NH═CH—O⁻, the carbocation H₃C⁺ from CH₃X (F, Cl, Br) is actually a borderline acid according to the DI values of the forming C…N and C…O bonds in the transition states (between 0.25 and 0.49), while the counter ions are divided into three groups according to the DI values of weak interactions involving M (M…X, M…N, and M…O): group I (M = none, and Me₄N) basically show zero DI values; group II species (M = Li, Na, and K) have noticeable DI values but the magnitudes are usually less than 0.15; and group III species (M = Ag and Cu(I)) have significant DI values (0.30–0.61). On a relative basis, H₃C⁺ is a soft acid with respect to group I and group II counter ions, and a hard acid with respect to group III counter ions. Therefore, N-regioselectivity is found in the presence of group I and group II counter ions (M = Me₄N, Li, Na, K), while O-regioselectivity is observed in the presence of the group III counter ions (M = Ag, and Cu(I)). The hardness of atoms, groups, and molecules is also calculated with new functions that depend on ionization potential (I) and electron affinity (A) and use the atomic charges obtained from localization indices (LI), so that the regioselectivity is explained by the atomic hardness of reactive nitrogen atoms in the transition states according to the maximum hardness principle (MHP). The exact Marcus equation is derived from the simple harmonic potential energy parabola, so that the concepts of activation free energy, intrinsic activation barrier, and reaction energy are completely connected. The required intrinsic activation barriers can be either estimated from ab initio calculations on reactant, transition state, and product of the model reactions, or calculated from identity reactions. The counter ions stabilize the reactant through bridging N- and O-site of reactant of identity reactions, so that the intrinsic barriers for the salts are higher than those for free ambident anions, which is explained by the increased reorganization parameter Δr. The proper application of Marcus theory should quantitatively consider all three terms of Marcus equation, and reliably represent the results with potential energy parabolas for reactants and all products. For the model reactions, both Marcus theory and HSAB principle/MHP principle predict the N-regioselectivity when M = none, Me₄N, Li, Na, K, and the O-regioselectivity when M = Ag and Cu(I). © 2019 Wiley Periodicals, Inc.     

The synthesis,characterization and effect of molar mass distribution on solid-state degradation kinetics of oligo(orcinol)

Journal of Thermal Analysis and Calorimetry - In this study, the oxidative polymerization of orcinol monohydrate using different oxidants such as NaOCl, H2O2, and air was investigated....