Poly(alkyl α-bromoacrylate)s. III. Tacticity analysis from 19 mHz 13C-NMR spectroscopy

Polymer tacticity was determined by 19 mHz ¹³C-NMR spectroscopy for isotactic, atactic, and syndiotactic samples of six poly(alkyl α-bromoacrylate)s. Included in this series were the methyl, ethyl, n-propyl, i-propyl, n-butyl, and n-pentyl esters. Complete assignments for the 10 pentad peaks of the carbonyl carbon resonance were achieved for all but the i-propyl ester while a complete analysis of tetrad tacticity from the backbone methylene carbon resonance was possible for all but the methyl ester. The tetrad values calculated from the experimentally determined pentad contents were found to agree with the experimental tetrad values. As a result of insufficient peak separation of the quaternary carbon resonance, complete pentad assignments were possible in only a few instances. The polymerization reaction mechanisms were discussed in terms of the propagation statistics calculated from the experimentally determined tetrads and pentads. Both the atactic and syndiotactic polymers that were synthesized by free radical techniques displayed Bernoullian or random statistics while the stereochemical statistics of the isotactic polymers synthesized by a modified Grignard complex were more consistent with nonrandom or first-order Markovian statistics.     

Crystallization-induced reactions of copolymers. II. Cis-trans isomerization of 1,4-poly-1,3-butadiene

The cis-trans photoisomerization reaction of 1,4-polybutadiene was carried out below the melting points on films of polymers containing high trans-1,4 contents. Under the proper conditions of temperature and polymer composition, the reaction was observed to undergo an anti-equilibrium behavior, which was attributed to an irreversible crystallization of repeating units after isomerization from cis to trans structure. As a result, the trans composition passed through a minimum with reaction time while crystallinity increased throughout the reaction, and unexpectedly the β crystalline form was observed well below the α–β transition temperature. The composition–time behavior observed was rationalized on the basis of incorporation of trans units into crystalline regions on the lamellar fold surfaces and discussed within the framework of the proposed requirements for crystallization-induced reactions of copolymers.     

Kinetics of polymerization initiated by Mn3+–substrate redox system. I

The kinetics and mechanism of polymerization of acrylamide (AM) initiated by manganese (III) acetate (MTA)–diglycolic acid (DGA) redox system in aqueous sulfuric acid were studied in the temperature range 20-35°C. The overall rates of polymerization and the disappearance of Mn³⁺ and the kinetic chain lengths of polyacrylamide were determined. The polymerization reaction is initiated by the organic free radical arising from the Mn³⁺–diglycolic acid reaction and the termination is by the metal ions. The rate of polymerization of acrylamide was found to be proportional to the first power of monomer and diglycolic acid and independent of manganese(III) acetate. The various rate parameters were evaluated.     

Styrene polymerization with some new macro or macromonomeric azoinitiators having peg units

Several new macroinitiators and macromerinitiators (macroinimers) were synthesized and evaluated for the bulk polymerization of sytrene at 60°C. Macroinitiators were prepared from the reaction of 4,4′-dicyano-4,4′ azovaleryl chloride ( 1 ) with poly(ethylene glycol) (PEG) with a M_ω of 400 and with either benzoyl chloride, acetyl chloride, phenyl isocyanate, or poly(ethylene glycol) oleyl ether. Macromer initiators were also prepared from the reaction of 1 with PEG having M_ω values of 200, 400, 600, 1000, or 1500 and with 4-vinylbenzyl chloride. The bulk polymerization of styrene by macroinimers gave crosslinked styrene-PEG block copolymers, while the polymerization by macroinitiators gave soluble copolymers. The molecular weights of the styrene-PEG block copolymers obtained with macroinitiators having either oleyl, benzoyl, or phenyl urethane end groups were 22000–29000 g/mol. DSC measurements showed that the crosslinked block copolymers had crystalline PEG units with melting transitions ranging from 11–37°C. © 1994 John Wiley & Sons, Inc.     

A portable absorption-fluorometer for detection of organic substances in fluids

Using the method of multipath-saturation fluorescence, which considers both fluorescent as well as nonfluorescent substances, the total absorption coefficient can be determined with high sensitivity. This new fluorescence method is appropriate, e.g. for in-situ applications. Thus a portable absorption-fluorometer has been constructed. The main part of the device is a multireflection cell based on a design of Herriott with a 1 cm quartz-cuvette. Two pairs of spherical dielectric mirrors are used to realize the multireflection of the excitation radiation in the UV and blue spectral range. The combination of a cylindrical and a convace mirror leads to a long pathway of the excitation radiation and, thus, to a full absorption by the fluid. A first experiment has been performed with drinking water samples defined polluted by non-fluorescent p-nitrophenol and 2-nitroaniline. Based on the method of multipath-saturation fluorescence a good correlation to the substance concentration was achieved, whereas the conventional absorption failed.     

Single transverse-spin asymmetry in very forward and very backward neutral particle production for polarized proton collisions at

In the 2001–2002 running period of the Relativistic Heavy Ion Collider (RHIC), transversely polarized protons were accelerated to 100 GeV for the first time, with collisions at . We present results from this run for single transverse-spin asymmetries for inclusive production of neutral pions, photons and neutrons of the energy region 20–100 GeV for forward and backward production for angles between 0.3 mrad and 2.2 mrad with respect to the polarized proton direction. An asymmetry of was observed for forward neutron production, where the errors are statistical and systematic, and the scale error is from the beam polarization uncertainty. The forward photon and π⁰, and backward neutron, photon, and π⁰ asymmetries were consistent with zero. The large neutron asymmetry indicates a strong interference between a spin–flip amplitude, such as one pion exchange which dominates lower energy neutron production, and remaining spin–non-flip amplitudes such as reggeon exchange.     

Photoisomerization in proteorhodopsin mutant D97N

The first steps of the photocycle of the D97N mutant of proteorhodopsin (PR) have been investigated by means of ultrafast transient absorption spectroscopy. A comparison with the primary dynamics of native PR and D85N mutant of bacteriorhodopsin is given. Upon photoexcitation of the covalently bound all-trans retinal the excited state decays biexponentially with time constants of 1.4 and 20 ps via a conical intersection, resulting in a 13-cis isomerized retinal. Neither of the two-deactivation channels is significantly preferred. The dynamics is slowed down in comparison with native PR at pH 9 and reaction rates are even lower than for native PR at pH 6, where the primary proton acceptor (Asp97) is protonated. Therefore, the ultrafast isomerization is not only controlled by the charge distribution within the retinal binding pocket. This study shows that in addition to direct electrostatics other effects have to be taken into account to explain the catalytic function of Asp97 in PR on the ultrafast isomerization reaction. This may include sterical interactions and/or bound water molecules within the retinal binding pocket.     

Nanomagnetic sponges for the cleaning of works of art

This letter reports the synthesis and characterization of functionalized magnetic nanoparticles associated with chemical gels and their application to the conservation of cultural heritage. Magnetic nanoparticles, which are associated with acrylamide ethylene oxide polymers, produce a sponge that can be loaded with oil-in-water microemulsions, forming a magnetically responsive gel-like system and acting as a permanent hydrogel. The magnetic gel-like system can be used for specific applications in detergents or in the release of the loaded material. The system can be magnetically manipulated and cleaned from the loaded materials and then dried and reused for a different application. We report an important application of this new nanomagnetic responsive material in the field of cultural heritage conservation.     

A practical synthesis of (3R,4R)-N-tert-butoxycarbonyl-4-hydroxymethylpyrrolidin-3-ol

The title compound (+)-, required for production of transition state analogue inhibitors of enzymes involved in T-cell-dependent disorders, was synthesized in five steps. A 1,3-dipolar cycloaddition of the nitrone formed from formaldehyde and N-benzylhydroxylamine to diethyl maleate gave the racemic cis-isoxazolidine (+/-)-. Reduction of the N-O bond of this compound gave pyrrolidone (+/-)- in excellent yield. A very efficient enzymic resolution of this racemic product led to the title enantiomer (+)-. This route employs only one chromatographic purification.     

A metabonomic study of strain- and age-related differences in the Zucker rat

Ultra-performance liquid chromatography (UPLC) coupled to orthogonal acceleration time-of-flight mass spectrometry (oa-TOFMS) in positive electrospray ionization mode was used to obtain metabolite profiles for urine obtained from three strains of Zucker rat. These were the Zucker lean, the Zucker (fa/fa) obese and the Zucker lean/(fa) cross. Clear age- and strain-related differences were noted with the leptin-deficient (fa/fa) obese animal showing significant differences from both the other Zucker rat strains with respect to metabolite profiles.