Dynamic scaling approach to glass formation

Experimental data for the temperature dependence of relaxation times are used to argue that the dynamic scaling form, with relaxation time diverging at the critical temperature T(c) as (T-T(c))(-nuz), is superior to the classical Vogel form. This observation leads us to propose that glass formation can be described by a simple mean-field limit of a phase transition. The order parameter is the fraction of all space that has sufficient free volume to allow substantial motion, and grows logarithmically above T(c). Diffusion of this free volume creates random walk clusters that have cooperatively rearranged. We show that the distribution of cooperatively moving clusters must have a Fisher exponent tau=2. Dynamic scaling predicts a power law for the relaxation modulus G(t) approximately t(-2/z), where z is the dynamic critical exponent relating the relaxation time of a cluster to its size. Andrade creep, universally observed for all glass-forming materials, suggests z=6. Experimental data on the temperature dependence of viscosity and relaxation time of glass-forming liquids suggest that the exponent nu describing the correlation length divergence in this simple scaling picture is not always universal. Polymers appear to universally have nuz=9 (making nu=3 / 2). However, other glass-formers have unphysically large values of nuz, suggesting that the availability of free volume is a necessary, but not sufficient, condition for motion in these liquids. Such considerations lead us to assert that nuz=9 is in fact universal for all glass- forming liquids, but an energetic barrier to motion must also be overcome for strong glasses.     

Synthesis of dihydropyridines and pyridines from imines and alkynes via C-H activation

A convenient one-pot C-H alkenylation/electrocyclization/aromatization sequence has been developed for the synthesis of highly substituted pyridine derivatives from alkynes and alpha,beta-unsaturated N-benzyl aldimines and ketimines that proceeds through dihydropyridine intermediates. A new class of ligands for C-H activation was developed, providing broader scope for the alkenylation step than could be achieved with previously reported ligands. Substantial information was obtained about the mechanism of the reaction. This included the isolation of a C-H activated complex and its structure determination by X-ray analysis; in addition, kinetic simulations using the Copasi software were employed to determine rate constants for this transformation, implicating facile C-H oxidative addition and slow reductive elimination steps.     

Immobilization of Rhodococcus AJ270 and Useof Entrapped Biocatalyst for the Productionof Acrylic Acid

Summary.  Rhodococcus AJ270 is adsorbed by Dowex 1 at 15.4  mg dry weight per g resin with maximum amidase specific activity observed at lower loadings. Bacteria form a monolayer on the resin surface, and adsorption is complete within 2 min. AJ270 can be entrapped in agar and agarose gels (optimum loading: 20 mg dry weight bacteria per cm³ gel). Adsorption and entrapment improve amidase thermal stability 3–4 fold, and entrapment shifts the pH optimum from 8 to 7. Adsorbed and free bacteria show similar values for K _m and V _max, but entrapped bacteria have higher K _m values. Compared with bacteria adsorbed to Dowex, the activity per cm³ of matrix of agar-entrapped AJ270 is eight-fold higher. In stirred-tank reactors, exposure to acrylic acid reduces the amidase activity of the biocatalyst in the hydrolysis of acrylamide. In column reactors, entrapped AJ270 suffers little reduction in amidase activity against 0.25 M acrylamide over 22 h continuous operation. Received November 18, 1999. Accepted December 14, 1999     

Scaling analysis of the temperature dependence of intrinsic viscosity

The scaling predictions for the temperature dependence of the intrinsic viscosity of flexible polymers are briefly reviewed. When the predictions are fit to a power law over a fixed range of chain length, a relation between the exponent and prefactor of the Mark–Houwink–Sakurada equation emerges. In comparing with the experimental data compilation of Rai and Rosen, we conclude that real polymer systems are nowhere near the true good solvent limit, even when the exponent matches the good solvent prediction. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 1989–1991, 1997     

Polyelectrolyte conductivity

Using the de Gennes scaling model for the configuration of a polyelectrolyte chain in semidilute solution, we construct a simple model of AC conductivity for semidilute solutions of strongly charged polyelectrolytes without added salt. We compare the predictions of this model with literature data and new data on two polyelectrolytes with very different affinities for water. The sodium salt of sulfonated polystyrene in water is a hydrophobic polyelectrolyte (the uncharged monomer does not dissolve in water), where the chain is locally collapsed. The sodium salt of poly(2-acrylamido-2-methylpropanesulfonate), is a much more hydrophilic polyelectrolyte, making the chain quite expanded locally. The model describes the conductivity of both cases reasonably for concentrations below 10⁻² M (mol of monomer per liter). Deviations between experiment and theory at higher concentrations lead us to conclude that counterion condensation decreases as concentration is increased. This is qualitatively consistent with the experimental observation that the dielectric constant of the polyelectrolyte solution increases as polyelectrolyte is added. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2951–2960, 1997     

Buffer Standards for the Physiological pH of the Zwitterionic Compound, ACES, from 5 to 55 °C

The values of the second dissociation constant, pK ₂, and related thermodynamic quantities of [N-(2-acetamido)-2-aminoethanesulfonic acid] (ACES) have already been reported over the temperature range 5 to 55 °C including 37 °C. This paper reports the pa _H values of four chloride ion free buffer solutions and eight buffer solutions with I=0.16 mol⋅kg⁻¹, matching closely that of the physiological sample. Conventional pa _H values for all twelve buffer solutions from 5 to 55 °C are reported. The residual liquid-junction potential correction for two widely used temperatures, 25 and 37 °C, has been made. The flowing-junction calomel cell method has been utilized to measure E _j , the liquid-junction potential. The operational pH values for four buffer solutions at 25 and 37 °C are calculated using the physiological phosphate buffer standard based on the NBS/NIST convention. These solutions are recommended as pH standards in the pH range of 6.8 to 7.2 for physiological fluids.     

Evolution of morphology,segmental dynamics,and conductivity in ionic liquid swollen short side chain perfluorosulfonate ionomer membranes

We investigate the morphology, segmental dynamics, and conductivity of 1‐ethyl‐3‐methylimidazolium trifluoromethanesulfonate (EMI‐Tf) swollen short side chain perfluorosulfonate ionomer (Aquivion) over a broad uptake range using small angle X‐ray scattering (SAXS), dielectric relaxation spectroscopy, and transient current measurement. The SAXS data indicate that the absorbed EMI‐Tf is mainly bounded in the ionic region of Aquivion. At low uptakes, EMI‐Tf acts as an effective plasticizer lowering the cluster T_g and markedly shifting the segmental relaxation to a high frequency; however, at high uptakes, the additional EMI‐Tf acts like a filler instead. A time–domain model was employed to quantify the conductivity of these membranes containing two mobile ion species, that is, cations and anions. The conductivity of both neat EMI‐Tf and EMI‐Tf swollen membranes exhibits Vogel‐Fulcher‐Tamman relation, revealing different activation parameters for ionic conduction. Furthermore, membranes containing different EMI‐Tf uptakes have similar conductivity over the reduced T_g/T axis and also follow Debye‐Stokes‐Einstein relation. Therefore, despite the abrupt change in conductivity near the critical uptake (29 wt %), both cluster T_g and segmental motion remain the key factors for the ionic conduction in these EMI‐Tf swollen membranes. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1273–1280     

Zur Bestimmung des Phosphors in Roheisen, Stahl und Eisenerzen

Ohne Zusammenfassung     

Conversion of methyl ketones and methyl sulfones into α-deutero-α,α-difluoromethyl ketones and α-deutero-α,α-difluoromethyl sulfones in three synthetic steps

Deuterodifluoromethyl ketones and sulfones were assembled in three synthetic steps from methyl ketones and sulfones, respectively. The key synthetic transformation is the deuteration of the difluorocarbanion generated by the release of trifluoroacetate from highly α-fluorinated gem-diols. High levels of deuterium on the “CF₂D” group were routinely observed. This strategy is mild and versatile and it can be applied to both ketones and sulfones without additional concerns of over- or under-fluorination. Additional examples address issues of over-deuteration when compounds with other acidic protons are subjected to the reaction conditions. This process not only demonstrates a new method to install a “CF₂D” group but also extends the scope of trifluoroacetate release to sulfones.