Dark cure studies of cationic photopolymerizations of epoxides: Characterization of kinetic rate constants at high conversions

The effective propagation rate constant (k_p; averaged over all the propagating active centers) was characterized for solvent‐free cationic photopolymerizations of phenyl glycidyl ether over the entire range of conversions, including the high conversion regime in which mass transfer limitations become important. The profile for the k_p as a function of conversion was found to exhibit a constant plateau value at low to intermediate conversions, followed by a monotonic increase above a threshold value of conversion. To explain this trend, it is proposed that at high conversion the diffusional mobility of the photoinitiator counterion is reduced whereas the mobility of the cationic active center remains high because of reactive diffusion. Therefore, with increasing conversion, the average distance between the active centers and counterions may increase, resulting in an increase in the propagation rate constant. The profiles for the k_p values were investigated as a function of the temperature, photoinitiator anion, and photoinitiator concentration. As the photoinitiator concentration was increased, the plateau value of the effective propagation rate constant decreased whereas the threshold conversion increased. All of the experimental trends are consistent with the proposed increase in ion separation at high conversions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4409–4416, 2004     

Efficient synthesis of 1,4-dihydronaphthalenelignans from 5-methylene-4-substituted-2(5H)-furanones and a concise synthesis of solafuranone

A short synthetic strategy for synthesis of lignan analogues involving 5-methylene-4-substituted-2(5H)-furanones as the key intermediates has been developed. Various lignans including the natural product solafuranone and analogues of dihydrotaiwanin C and deoxydehydropodophyllotoxin were synthesized in good yields.     

Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation

Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe₄₀Ni₄₀B₂₀ and Fe₄₀Ni₃₈Mo₄B₁₈ metallic glass ribbons. 90 MeV ¹²⁷I beam was used for the irradiations. Irradiation doses were 5×10¹³ and 7.5×10¹³ ions/cm². The relative intensity ratios D ₂₃ of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy.     

Supramolecular assemblies of a naturally derived sophorolipid

Acidic sophorolipid (SL) molecules derived from yeasts represent a novel type of asymmetrical bolaamphiphiles due to their unique structural features that include an asymmetrical polar head size (disaccharide vs COOH), a kinked hydrophobic core (cis-9-octadecenoic chain), and a non-amide polar-nonpolar linkage. Light microscopy, small- and wide-angle X-ray scattering, FT-IR spectroscopy, and dynamic laser light scattering were used to investigate the supramolecular structures of the self-assembled aggregates of SL molecules at different pH values. In acidic conditions (pH < 5.5), giant twisted and helical ribbons of 5-11 microm width and several hundreds of micrometers length were observed for the first time. Increase in solution pH values slowed ribbon formation, decreased ribbon yield, and increased the helicity and entanglements of the giant ribbons. An interdigitated lamellar packing model of acidic SL-COOH molecules with a long period of 2.78 nm, stabilized by both the strong hydrophobic association between the cis-9-octadecenoic chains and strong disaccharide-disaccharide hydrogen bonding, is proposed. The neutralization of SL-COOH in water to SL-COONa produced clear solutions with the formation of short-range ordered aggregates. At concentrations below 1.0 mg/mL, the size of self-assembled aggregates increased as the concentration increased. At concentrations above 1.0 mg/mL, narrowly distributed micellar aggregates with a constant hydrodynamic radius (R(h)) of about 100 nm are formed. The large micelles show strong angular dependence with the fast mode appearing at scattering angle theta >/= 60 degrees.     

Interfacing gradient elution ion-exchange chromatography and low-angle laser light-scattering photometry for analysis of proteins.

Molecular weights (MWs) of different proteins were determined by interfacing gradient elution ion-exchange chromatography and low-angle laser light-scattering photometry (IEC-LALLS). A high-performance strong cation-exchange column was used to elute proteins using fast (5 min) and conventional (15-30 min) gradients. The eluted proteins were characterized on-line by determining their MWs using LALLS. The specific refractive index (RI) increment (dn/dc) and the RI of the solvent used over the gradient range were determined off-line and used to calculate the absolute weight-average MWs. Four proteins, ribonuclease A, alpha-chymotrypsinogen A, trypsinogen and beta-lactoglobulin A (beta-LACT) were studied. Accurate MWs were obtained for all the proteins using fast and conventional gradients, except for beta-LACT, which aggregated as a function of the gradient employed. The degree of aggregation of beta-LACT increased as the rapidity of the gradient was increased over a fixed gradient range. This study indicated that it is possible to separate and characterize proteins rapidly using IEC-LALLS.     

Development of a pH titration method for the simultaneous determination of uranium,nitrate and free-acid in the feed solution of the sol-gel process of nuclear fuel fabrication

pH titration curves generated by slow addition of alkali to solutions containing varying concentrations of uranyl nitrate and nitric acid were studied using an autotitrator linked to a personal computer. A procedure with multiple choice of equations has been developed for the estimation of free acid, nitrate and uranium in pure uranyl nitrate solution by a single titration. The technique provides a simple single-step method with required accuracy and precision for the simultaneous estimation of the three quantities in the uranyl nitrate feed solution of the sol-gel process for making UO₃ microspheres. The relative standard deviations in the determination of uranium and nitrate were ±0.82% and ±1.52%, respectively, in 15 determinations.     

Rapid quantitative capillary zone electrophoresis method for monitoring the micro-heterogeneity of an intact recombinant glycoprotein

A simple high-resolution capillary zone electrophoresis (CZE) method capable of rapidly assessing the micro-heterogeneity of a 24 kDa molecular weight glycoprotein, has been developed. Separation is carried out using a bare silica capillary at a pH of 2.5 in a commercially available electrophoresis buffer system composed of triethanolamine and phosphoric acid. Over 30 peaks were detected within a run time of 15 min using a 27 cm capillary and approximately 60 peaks were detected using a 77 cm capillary. Although most of the peaks arise from differences in the oligosaccharide structures present on the one glycosylation site on this molecule, other forms of micro-heterogeneity due to the presence of the nonglycosylated form of this glycoprotein and various types of chemical degradation, e.g., deamidation, are also responsible for the multitude of peaks observed. Although the exact chemical identity of each peak in the resulting electropherogram of this glycoprotein is not known, useful information can be obtained for assessing comparability, stability, and batch consistency. Factors impacting the resolution, precision, accuracy, and robustness of the assay are also discussed along with inherent advantages and limitations associated with measuring the micro-heterogeneity of intact glycoproteins.     

Photocatalysed eosin Y mediated C(sp3)-H alkylation of amine substrates via direct HAT

A visible light promoted, photoredox catalysed, green one-pot approach for the alkylation of amine substrates with sp² carbon has been developed. This eosin Y based organic transformations, can behave as an effective direct hydrogen-atom transfer catalyst for coupling reaction. The proposed strategy includes simple procedure which can make adduct product with sp² carbon. This eosin Y based photocatalytic hydrogen-atom transfer strategy may hold great potential for diverse functionalization of a wide range of native CH bonds in an economical and sustainable manner.     

Proline-catalyzed asymmetric aldol reactions of tetrahydro-4H-thiopyran-4-one with aldehydes

Proline-catalyzed enantioselective direct intermolecular aldol reactions of tetrahydro-4H-thiopyran-4-one with various aldehydes give anti adducts with high diastereo- and enantioselectivities in moderate to excellent yields. With the aromatic aldehydes best results were obtained in wet DMF whereas dry DMSO generally was superior with the aliphatic aldehydes. Desulfurization of the adducts with Raney Ni provides products equivalent to aldols from 3-pentanone with potential applications in polypropionate synthesis.     

DNA polymerase template interactions probed by degenerate isosteric nucleobase analogs

The development of novel artificial nucleobases and detailed X-ray crystal structures for primer/template/DNA polymerase complexes provide opportunities to assess DNA-protein interactions that dictate specificity. Recent results have shown that base pair shape recognition in the context of DNA polymerase must be considered a significant component. The isosteric azole carboxamide nucleobases (compounds 1-5; ) differ only in the number and placement of nitrogen atoms within a common shape and therefore present unique electronic distributions that are shown to dictate the selectivity of template-directed nucleotide incorporation by DNA polymerases. The results demonstrate how nucleoside triphosphate substrate selection by DNA polymerase is a complex phenomenon involving electrostatic interactions in addition to hydrogen bonding and shape recognition. These azole nucleobase analogs offer unique molecular tools for probing nonbonded interactions dictating substrate selection and fidelity of DNA polymerases.