Structure of unsaturated polyester resins crosslinked with styrene as studied by raman spectroscopy

An unsaturated polyester resin and the styrene-crosslinked polyester were studied with laser Raman spectroscopy. Following the polyesterification reaction, Raman measurements showed that the polyester contained 55% fumarate and 45% maleate unsaturation. Additionally, the glycol fragment was indicated to exist as the gauche isomer. The 1213 cm^?1 line is assigned to the glycol-ester linkage and can be measured to follow the conversion to polymer. After the crosslinking reaction, styrene was found to copolymerize preferentially with the fumarate unsaturation. There was no evidence of forming long-chain polystyrene crosslinks. Our results indicate that, after crosslinking, 41% of the fumarates have reacted with styrene and there is an average of two styrene molecules in each link.     

Stereoinversion of Unactivated Alcohols by Tethered Sulfonamides

The direct, catalytic substitution of unactivated alcohols remains an undeveloped area of organic synthesis. Moreover, catalytic activation of this difficult electrophile with predictable stereo‐outcomes presents an even more formidable challenge. Described herein is a simple iron‐based catalyst system which provides the mild, direct conversion of secondary and tertiary alcohols to sulfonamides. Starting from enantioenriched alcohols, the intramolecular variant proceeds with stereoinversion to produce enantioenriched 2‐ and 2,2‐subsituted pyrrolidines and indolines, without prior derivatization of the alcohol or solvolytic conditions.     

Stop-consonant voicing and intraoral pressure contours in women and children

Previous authors have established that stop consonant voicing is more limited in young children than adults, and have ascribed this to immature vocal-tract pressure management. Physical development relevant to speech aerodynamics continues into adolescence, suggesting that consonant voicing development may also persist into the school-age years. This study explored the relationship between stop consonant voicing and intraoral pressure contours in women, 5 year olds, and 10 year olds. Productions of intervocalic /p b/ were recorded from eight speakers at each age. Measures were made of stop consonant voicing and delta, a measure designed to characterize the time course of intraoral pressure increase in stops, following Muller and Brown [Speech and Language: Advances in Basic Research and Practice, edited by N. Lass (Academic, Madison, 1980), Vol. 4, pp. 318-389]. Age effects for stop consonant voicing and delta were not statistically significant, but correlations between delta and stop voicing were less often significant and sometimes reversed in the children, providing some evidence of immature aerodynamic control. The current data, as well as those of Muller and Brown, also show that the delta measure may yield some paradoxical values, indicating that more work is needed on methods of assessing time-varying characteristics of intraoral pressure.     

LC–ELISA as a contribution to the assessment of matrix effects with environmental water samples in an immunoassay for estrone (E1)

Accreditation and Quality Assurance - Estrone (E1), a metabolite of the estrogenic hormones 17β-estradiol (β-E2) and 17α-estradiol (α-E2), is itself a potent estrogen which can...     

Establishing effective simulation protocols for beta- and alpha/beta-peptides. II. Molecular mechanical (MM) model for a cyclic beta-residue

All-atom molecular mechanical (MM) force field parameters are developed for a cyclic beta-amino acid, amino-cyclo-pentane-carboxylic acid (ACPC), using a multi-objective evolutionary algorithm. The MM model is benchmarked using several short, ACPC-containing alpha/beta-peptides in water and methanol with SCC-DFTB (self consistent charge-density functional tight binding)/MM simulations as the reference. Satisfactory agreements are found between the MM and SCC-DFTB/MM results regarding the distribution of key dihedral angles for the tetra-alpha/beta-peptide in water. For the octa-alpha/beta-peptide in methanol, the MM and SCC-DFTB/MM simulations predict the 11- and 14/15-helical form as the more stable conformation, respectively; however, the two helical forms are very close in energy (2-4 kcal/mol) at both theoretical levels, which is also the conclusion from recent NMR experiments. As the first application, the MM model is applied to an alpha/beta-pentadeca-peptide in water with both explicit and implicit solvent models. The stability of the peptide is sensitive to the starting configuration in the explicit solvent simulations due to their limited length ( approximately 10-40 ns). Multiple ( approximately 20 x 20 ns) implicit solvent simulations consistently show that the 14/15-helix is the predominant conformation of this peptide, although substantially different conformations are also accessible. The calculated nuclear Overhauser effect (NOE) values averaged over different trajectories are consistent with experimental data, which emphasizes the importance of considering conformational heterogeneity in such comparisons for highly dynamical peptides.     

Conformational Effects of Regioisomeric Substitution on the Catalytic Activity of Copper/Calix[8]arene C−S Coupling

Functionalization of the phenolic rim of p-tert-butylcalix[8]arene with phenanthroline to create a cavity leads to formation of two regioisomers. Substitution of positions 1 and 5 produces the known C_2v-symmetric regioisomer 1,5-(2,9-dimethyl-1,10-phenanthroyl)-p-tert-butylcalix[8]arene ( L^1,5 ), while substitution of positions 1 and 4 produces the C_s-symmetric regioisomer 1,4-(2,9-dimethyl-1,10-phenanthroyl)-p-tert-butylcalix[8]arene ( L^1,4 ) described herein. [ Cu(L^1,4)I ] was synthesized from L^1,4 and CuI in good yield and characterized spectroscopically. To evaluate the effect of its cavity on catalysis, Ullmann-type C−S coupling was chosen as proof-of-concept. Selected aryl halides were used, and the results compared with the previously reported Cu(I)/ L^1,5 system. Only highly activated aryl halides generate the C−S coupling product in moderate yields with the Cu(I)/ L^1,4 system. To shed light on these observations, detailed computational investigations were carried out, revealing the influence of the calix[8]arene macrocyclic morphology on the accessible conformations. The L^1,4 regioisomer undergoes a deformation that does not occur with L^1,5 , resulting in an exposed catalytic center, presumably the cause of the low activity of the former system. The 1,4-connectivity was confirmed in the solid-state structure of the byproduct [ Cu(L^1,4 − H) (CH₃CN)₂] that features Cu(I) coordinated inside a cleft defined by the macrocyclic framework.     

Studying anomalous diffusion in a liquid crystal/ polymer system using fast FTIR imaging

The diffusion of liquid crystal 4‐n‐pentyl‐4′‐cyanobiphenyl (5CB) into a poly(butyl methacrylate) (PBMA) matrix has been studied using fast FTIR imaging. The concentration profiles were obtained as a function of time at several temperatures above and below the nematic to isotropic transition temperature (T_NI) of 5CB and the T_g of PBMA. The time‐dependent progression of the diffusion front position, when fitted to a power law model, exhibited exponential values between 0.40 and 0.52. This, along with the observed progression of a sharp 5CB‐diffusion front into the PBMA matrix, indicates the presence of an anomalous diffusion process. It was shown that fast FTIR was able to correctly identify the diffusion process as anomalous, whereas a simple mass uptake analysis would have led to the conclusion that the process proceeded according to Fick's second law. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2261–2268, 1999