Effect of the addition of a nonionic surfactant on the complex poly(asparagine)--cationic surfactant

Poly(asparagine) (pAsn) at 0.1wt % in the presence of dodecyltrimethylammonium bromide (DTAB) and pentaoxyethylene octyl ether (C(8)E(5)) at 1:1 molar ratio leads to the formation of mixed DTAB/C(8)E(5) micelle-like aggregates onto the polypeptide as a total surfactant critical association concentration (cac) is reached, as revealed by surface tension measurements and NMR chemical shifts. Two-dimensional nuclear Overhauser enhancement spectroscopy (NOESY) capable of revealing spatial relationships among proximal protons has been performed on the pAsn-DTAB-C(8)E(5)-water system to study structural details of the surfactant-polypeptide aggregates. NOESY cross-peaks at sample temperature of 298.15 K indicate that the polypeptide interacts with the DTAB/C(8)E(5) micelle-like aggregates. The NOE intermolecular effects also show direct interactions between surfactant and polypeptide in the pAsn-DTAB-water system, whereas no interaction has been revealed in the pAsn-C(8)E(5)-water system. Furthermore, the experimental evidence suggest that the DTAB-polypeptide complex is mainly driven by the polar attraction between the two molecules.     

Fast neutron activation analysis: High resolution gamma spectroscopy

The purpose of this study was to demonstrate the versatility of combining the use of high resolution, Ge(Li) γ-detectors with the techniques of fast neutron activation analysis. A compilation of γ-ray spectra are presented for irradiation of 30 elements with 14.8 MeV neutrons under standard conditions and the origin of all major photopeaks is determined.     

Novel search for heavy nu mixing from the beta+ decay of 38mK confined in an atom trap

A new technique, full neutrino momentum reconstruction, is used to set limits on the admixture of heavy neutrinos into the electron neutrino. We measure coincidences between nuclear recoils and positrons from the beta decay of trapped radioactive atoms and deduce the neutrino momentum. A search for peaks in the reconstructed recoil time-of-flight spectrum as a function of positron energy is performed. The admixture upper limits range from 4 x 10(-3) to 2 x 10(-2) and are the best direct limits for neutrinos (as opposed to antineutrinos) for the mass region of 0.7 to 3.5 MeV.     

Beta–neutrino correlation experiments on laser trapped 38mK, 37K

Laser trapping and cooling techniques are now being applied to the study of nuclear β-decay at several labs. A magneto-optical trap (MOT) provides a localized source of atoms suspended in space, so the low-energy recoiling nuclei can freely escape and be detected in coincidence with the β. This allows reconstruction of the neutrino momentum, and the deduction of the β-v correlation in a more direct fashion than previously possible. In addition, the nuclei can be polarized by atomic techniques, opening a new class of spin correlation measurements to test the degree to which parity is maximally violated in the weak interaction. Our present experiment has detected several hundred thousand recoil-β⁺ coincidences from the 0⁺ → 0⁺ pure Fermi decay of ^38mK, produced at the on-line isotope separators TISOL and ISAC at TRIUMF. Our goal is to set constraints on non-Standard Model scalar bosons competitive with high-energy colliders and more conventional β-v correlation experiments. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phosphido‐diphosphine pincer group 3 complexes as efficient initiators for lactide polymerization

New Group 3 metal complexes of the type [LM(CH₂SiMe₃)₂(THF)_n] supported by tridentate phosphido‐diphosphine ligands [(o‐C₆H₄PR₂) ₂ PH; L1‐H : R = iPr; L2‐H : R = Ph] have been synthesized by reaction of L1‐H and L2‐H with [M(CH₂SiMe₃)₃(THF)₂)] (M = Y and Sc). All the new complexes [(o‐C₆H₄PR₂) ₂ PM(CH₂SiMe₃)₂(THF)_n] [M = Y, R = iPr (1), R = Ph (2); M = Sc, R = iPr (3), R = Ph (4)] were studied as initiators for the ring opening polymerization of lactide. The yttrium complexes ( 1 and 2 ) exhibited high activity and good polymerization control, shown by the linear fits in the plot of number‐averaged molecular weight (M_n) versus the percentage conversion and versus the monomer/initiator ratio and by the low polydispersity index values. Interestingly, very good molar‐mass control was observed even when L ‐Lactide was polymerized in the absence of solvent at 130 °C. A good molar‐mass control but lower activities were observed in the polymerization reaction of lactide promoted by the analogous scandium complexes 3 and 4 . © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1374–1382, 2010     

Phosphido‐diphosphine pincer aluminum complexes as catalysts for ring opening polymerization of cyclic esters

New aluminum alkyl complexes, supported by o‐phenylene‐derived phosphido diphosphine pro‐ligands [Ph‐PPP]‐H and [ⁱPr‐PPP]‐H ([Ph‐PPP]‐H = bis(2‐diphenylphosphinophenyl)phosphine; [ⁱPr‐PPP]‐H = bis(2‐diisopropylphosphinophenyl)phosphine) are reported. Compounds [Ph‐PPP]AlMe₂ ( 1 ), [ⁱPr‐PPP]AlMe₂ ( 2 ), and [Ph‐PPP]AlⁱBu₂ ( 3 ) have been synthesized by reaction of the pro‐ligand with the appropriate trialkyl aluminum precursor and have been characterized by ¹H, ¹³C and ³¹P NMR spectroscopy. The solution NMR data and theoretical calculations suggest for all complexes trigonal bipyramidal structures with C_2v symmetry in which the phosphido diphosphine ligand acts as a κ³ coordinated ligand. All complexes promote the ring‐opening polymerization of ε‐caprolactone, L‐ and rac‐lactide. Polyesters with controlled molecular parameters (M_n, end groups) and low polydispersities are obtained. Upon addition of isopropanol, efficient binary catalytic systems for the immortal ring‐opening polymerization of the cyclic esters are produced. Preliminary investigations show the ability of these complexes to promote copolymerization of l ‐lactide and ?‐caprolactone to achieve copolymers whose microstructures are depending on the structure of the catalyst. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 49–60