Preparation of ‘click’ hydrogels from polyaspartamide derivatives

Lately, copper‐assisted azide–alkyne cycloaddition (CuAAC) has become a very interesting tool for synthesizing biocompatible polymer‐based materials such as hydrogels or microgels, which can be used as biomaterials for tissue engineering and drug delivery. Novel poly(2‐hydroxyethyl aspartamide)s (PHEAs) functionalized with pendent acetylene or azide groups were prepared from polysuccinimide, which is the thermal polycondensation product of aspartic acid, through successful ring‐opening reactions using propargylamine, 1‐azido‐2‐aminoethane and ethanolamine. The composition of the prepared copolymers was analyzed using ¹H NMR spectroscopy. Clickable PHEA derivatives were crosslinked by mixing together in water with a catalyst system of Cu(I) and N, N, N′, N′, N″‐pentamethyldiethylenetriamine, a type of Huisgen's 1,3‐dipolar azide‐alkyne cycloaddition. The reaction of the polymers resulted in a chemoselective coupling between alkynyl and azido functional groups with multiple formation of triazole crosslinks to give hydrogels. The triazole linkages in the hydrogels are highly stable and may also play a role in swelling behavior. PHEA‐based hydrogels were also obtained by the crosslinking of azide‐ or alkyne‐modified PHEA with a small‐molecule crosslinker. The hydrogels prepared using these two methods were characterized by their degree of swelling and the morphology of the hydrogels was confirmed using scanning electron microscopy. The approach we describe here presents a promising alternative to common chemical hydrogel preparation techniques, and these hydrogels seem to possess structures having potential for a variety of industrial and biomedical applications. © 2012 Society of Chemical Industry     

Fabrication of long lengths of low-loss IR transmitting As40S(60-x)Sex glass fibers

Teflon clad and As₄₀S₆₀ glass clad As₄₀ S₅₅Se₅ fibers transmitting in the 1-6 μm wavelength region have been fabricated in lengths of about 50 m and with minimum losses of 0.098 and 0.65 dB/m, respectively. Short lengths of the Teflon clad fiber possessed a minimum loss of 0.047 dB/m. While current fiber losses are dominated by extrinsic scattering and absorption, the calculated theoretical minimum loss is estimated to be 3.6 dB/km at 5.3 μm and is limited by the contribution from the weak absorption tail. Improvements in the purification and processing of the glasses into the optical fibers are required to reduce the losses further     

New telechelic polymers and sequential copolymers by polyfunctional initiator-transfer agents (inifers)

Summary The unsaturated aliphatic dichlorides cis and trans Cl(CH₃)₂C-CH=CH-C(CH₃)₂Cl in conjunction with BCl₃ have been found to be excellent binifers and yield tert.-Cl capped polyisobutylenes PIB in CH₃Cl at –30°C. Intramolecular cyclization is absent and terminal chlorine functionality is F_n = 2.0±0.1. The normalized inifer constants have been determined: ^CItrans = 1.05, and ^CIcis = 3.8 and 1.05, respectively, for the first and second allylic chlorines in the cis isomer. The inequality of the chlorines have been analyzed. The cis and trans isomers have identical relative termination constants (k_t/k_p = 6×10^–3). The structure of the PIBs obtained has been analyzed by a variety of techniques. Model experiments with isobutylene/Cl-(CH₃)₂C-CH=CH-C(CH₃)₂Cl = 2/1 in the presence of BCl₃ gave the expected trans Cl(CH₃)₂CCH₂-(CH₃)₂C-CH=CH-C(CH₃)₂-CH₂C(CH₃)₂ -Cl. The end groups of polymers have been quantitated. The central position of the -CH=CH- residue in polymers has been demonstrated by molecular weight determinations i.e., the M_n of PIB has decreased by a factor of two after oxidative cleavage. The uniform distribution of -CH=CH-group across all polymeric species has also been established.     

On using deterministic functions to reduce randomness in probabilistic algorithms

We show the existence of nonuniform schemes for the following sampling problem: Given a sample space with n points, an unknown set of size n/2, and s random points, it is possible to generate deterministically from them s + k points such that the probability of not hitting the unknown set is exponentially smaller in k than 2^−s. Tight bounds are given for the quality of such schemes. Explicit, uniform versions of these schemes could be used for efficiently reducing the error probability of randomized algorithms. A survey of known constructions (whose quality is very far from the existential result) is included.     

Sex chromosome meiotic drive systems in Drosophila melanogaster I. Abnormal spermatid development in males with a heterochromatin-deficient X chromosome (sc-4sc-8)

The meiotic drive chracteristics of the In(1)sc-4Lsc-8R/Y system have been examined by genetic analysis and by light and electron microscopy. sc-4sc8-/Y males show a direct correlation between nondisjunction frequency and meiotic drive. Temperature-shift experiments reveal that the temperature-sensitive period for nondisjunction is at meiosis, whereas that for meiotic drive has both meiotic and post-meiotic components. Cytological analyses in the light and electron microscopes reveal failures in spermiogenesis in the tests of sc-4sc-8 males. The extent of abnormal spermatid development increases as nondisjunction becomes more extreme.     

Effects of adsorption-desorption processes on the response time and accuracy of photoacoustic detection of ammonia

A distributed-feedback (DFB) diode laser radiating at 1.53 mum was used for photoacoustic detection of ammonia molecules in the gas phase under flow conditions. The influence of the adsorption-desorption processes that occur at the cell and tube walls on the measured gas concentration was studied. Dramatic differences in the adsorption behavior of a metal and a polypropylene cell are demonstrated. Simulations of the gas flow and adsorption-desorption processes yield the conditions that must be fulfilled for accurate concentration measurements in trace-gas analysis of polar molecules.