Study of bulk chain coupling reactions. II. Reaction between bisoxazolones and amine-terminated polyether: Synthesis of polyether-block-polyamides

The bulk reactions between 2,2′-bis(4,4-dimethyl-5(4H)-oxazolone) ( B3 ) or 2,2′-(1,2-ethylene)-bis(4,4-dimethyl-5(4H)-oxazolone) ( B4 ) and amine-terminated polyether (Jeffamine ED-900) have been studied by SEC, and ¹H-and ¹³C-NMR and the resulting polymers were characterized by DSC and TGA. These chain coupling reactions have been applied to the synthesis of polyether-block-polyamides, starting from mixtures of amineterminated polyether and polyamide-12. High molar mass block copolymers were synthesized in the bulk within 1 h at 200°C and under atmospheric pressure, instead of several hours at 240°C under vacuum for the usual reaction between dicarboxy polyamides and dihydroxy polyethers. No other side reactions than the formation of a very small amount of 2-imidazolin-5-ones has been found. The DSC studies of block copolymers show the existence of a phase separation between the soft (polyether) and hard (polyamide) blocks. © 1993 John Wiley & Sons, Inc.     

Viscosities and thermodynamics of viscous flow of some binary mixtures at different temperatures

Viscosities of three non-electrolyte binary mixtures have been determined at different temperatures over the complete concentration range. Excess molar viscosities and excess molar energies of activation for viscous flow for n-butylamine + dichloromethane, n-butylamine + chloroform and n-butylamine + carbon tetrachloride systems at 20°C, 25°C, 30°C and 35°C were calculated. Thermodynamic effect parameters of activation were also calculated. The predictive abilities of some equations for viscosities of mixtures were examined.Presented at the XV Jornadas sobre Investigación en Ciencias de la Ingeneriía Química y Química Aplicada, Neuquén, 1989, R. Argentina.     

Bioorthogonal Enzymatic Activation of Caged Compounds

Engineered cytochrome P450 monooxygenase variants are reported as highly active and selective catalysts for the bioorthogonal uncaging of propargylic and benzylic ether protected substrates, including uncaging in living E. coli. observed selectivity is supported by induced‐fit docking and molecular dynamics simulations. This proof‐of‐principle study points towards the utility of bioorthogonal enzyme/protecting group pairs for applications in the life sciences.     

Employing Taylor and Heisenberg subfilter viscosities to simulate turbulent statistics in LES models

A turbulent subfilter viscosity for Large Eddy Simulation (LES) based on the Taylor statistical diffusion theory is proposed. This viscosity is described in terms of a velocity variance and a time scale, both associated to the inertial subrange. This new subfilter viscosity contains a cutoff wavenumber k_c, presenting an identical form (differing by a constant) to the Heisenberg subfilter viscosity. Therefore, both subfilter viscosities are described in terms of a sharp division between large and small wavenumbers of a turbulent flow and, henceforth, Taylor and Heisenberg subfilter viscosities are in agreement with the sharp Fourier filtering operation, frequently employed in LES models. Turbulent statistics of different orders, generated from atmospheric boundary layer simulations employing both Taylor and Heisenberg subfilter viscosities have been compared with observations and results provided by other simulations. The comparison shows that the LES model utilizing the approaches of Taylor and Heisenberg reproduces these turbulent statistics correctly in different vertical regions of a planetary convective boundary layer (CBL).     

Measurements of the Kolmogorov constant from laboratory and geophysical wind data

Turbulent wind data measured in the atmospheric surface layer and wind tunnels are used to estimate the Kolmogorov constant C_k. The analysis discusses distinct procedures to obtain the mean energy dissipation rate and C_k. We find that for our datasets the most reliable method is the third-order structure function one. The value found for the skewness of longitudinal velocity differences is in accordance with a multifractal approach recently proposed. Despite the limitations of the data discussed in the paper, the results point to a value of C_k independent of the Reynolds number.     

Site‐Resolved Observation of Vibrational Energy Transfer Using a Genetically Encoded Ultrafast Heater

Allosteric information transfer in proteins has been linked to distinct vibrational energy transfer (VET) pathways in a number of theoretical studies. Experimental evidence for such pathways, however, is sparse because site‐selective injection of vibrational energy into a protein, that is, localized heating, is required for their investigation. Here, we solved this problem by the site‐specific incorporation of the non‐canonical amino acid β‐(1‐azulenyl)‐l ‐alanine (AzAla) through genetic code expansion. As an exception to Kasha's rule, AzAla undergoes ultrafast internal conversion and heating after S₁ excitation while upon S₂ excitation, it serves as a fluorescent label. We equipped PDZ3, a protein interaction domain of postsynaptic density protein 95, with this ultrafast heater at two distinct positions. We indeed observed VET from the incorporation sites in the protein to a bound peptide ligand on the picosecond timescale by ultrafast IR spectroscopy. This approach based on genetically encoded AzAla paves the way for detailed studies of VET and its role in a wide range of proteins.     

Density functional study of neutral allopurinol tautomeric forms

Optimized structures and total molecular energy density functional theory calculations for the 14 possible neutral allopurinol tautomers give the decreasing stability order for the three most stable forms. Several molecular and electronic structure properties, the stabilities in oxidation and reduction processes, the tautomeric equilibrium constants, and the IR vibrational spectra were obtained for these. Those properties corresponding to the ketonic forms are discussed and compared with the theoretical ones for the two most stable species of the isomer hypoxanthine. A noticeable agreement is found between the predicted properties and the experimental behavior known up to date for both isomers. ©1999 John Wiley & Sons, Inc. J Comput Chem 20: 200–206, 1999     

Determination of methanol in o,o-dimethyldithiophosphoric acid (DMDTPA) of technical grade by UV/vis spectrophotometry and by HPLC

Two procedures are proposed in this work for the determination of methanol impurities in o,o-dimethyldithiophosphoric acid (DMDTPA). To avoid possible interferences from the main component, DMDTPA was precipitated in the form of insoluble lead complex. Free Pb(II) ions were eliminated with sulfuric acid and methanol was oxidized to formaldehyde with potassium permanganate in methanesulfonic acid medium. Finally, the excess of oxidizing agent was neutralized with saturated sodium oxalate. The above pretreatment procedure was identical for spectrophotometric assay and for chromatographic determination. In the first case, the solution obtained was treated with Nash reagent to form 3,5-diacetyl-1,4-dihydrolutidine (λ_max = 415 nm). In the calibration range 0.1-1.0% (methanol in DMDTPA), the analytical figures of merit were: R² = 0.9993, quantification limit 0.02% methanol in DMDTPA coefficient of variance (n = 5) for 0.1% and 0.4% methanol respectively 6.7% and 2.4%. Recoveries obtained in the sample fortified with 0.1, 0.2, 0.4% of methanol (in DMDTPA) were in the range 99-105%. For chromatographic procedure, formaldehyde was derivatized with 2,4-dinitrophenylhydrazine and separation was achieved on Luna C18(2) column using the isocratic elution with acetonitrile-water (70:30, v/v) and spectrophotometric detection at 360 nm. In the calibration range 0.05-0.25% (methanol in DMDTPA), R² was always higher than 0.999, the quantification limit was 0.004% and the recoveries in these same fortified samples in the range 98-101%. No statistically significant differences were observed between the results obtained in the analysis of technical grade DMDTPA by the two procedures (ANOVA, p < 0.05)     

Isotachophoresis of proteins

The analytical separation of proteins by isotachophoresis (ITP) was achieved in a short electrophoretic path and with a resolution comparable to that of isoelectric focusing by the appropriate selection of (1) a mixture of ampholytes as spacers to generate linear gradients of electrophoretic mobility and (2) the counter ions chosen to buffer the complete pH gradient generated. This ITP technique is exemplified by the analysis of plasma proteins in agarose gels. Up to 46 samples in the same gel plate were analysed. The resolution was such that at least 30 clear and discrete bands per sample could be observed after staining with Coomassie Brilliant Blue. The resolving power of ITP could be further increased for the study of a particular protein or zone by the selection of suitable spacers and counter ions.     

Analytical speciation of chromium in in-vitro cultures of chromate-resistant filamentous fungi

In this work, different analytical speciation schemes have been used to study the reduction of Cr(VI) by a chromate-resistant strain of filamentous fungi Ed8 (Aspergillus sp), indigenous to contaminated industrial wastes. As demonstrated previously, this strain has the capability to reduce chromate present in the growth medium without its accumulation in the biomass, yet the reduced chromium end-products have not been characterized. Liquid growth medium, initially containing 50 mg L(-1) Cr(VI), was analyzed for Cr(III)/Cr(VI) and for total Cr at different time intervals (0-24 h) after inoculation with fungi. Three hyphenated procedures, based on the Cr(III)-EDTA formation and species separation by anion-exchange or ion-pairing reversed-phase chromatography with ICP-MS or DAD detection were used. The results obtained for Cr(VI) in each case were consistent, demonstrating efficient reduction of chromate during 24 h of Ed8 growth. However, pre-column complexation with EDTA did not ensure complete recovery of the reduced forms of chromium in the above procedures. An alternative speciation scheme, based on extraction of Cr(VI)-benzyltributylammonium bromide (BTAB) ion pairs into chloroform and subsequent determination of residual chromium by ICP-MS has provided evidence on the effective conversion of chromate into reduced chromium species in the growth medium. The results indicate the feasibility of using Ed8 strain for chromate bioremediation purposes. Analytically it can be concluded that speciation of chromium in biological systems should not be limited to its two most common oxidation states, because the actual reduced chromium species are not converted quantitatively to Cr(III)-EDTA.