Mid-infrared spectroscopy of protected peptides in the gas phase: a probe of the backbone conformation

Infrared/UV hole-burning spectroscopy is performed on individual conformers of the protected dipeptide Z-Aib-Pro-NHMe. The extended IR range probed in this study allows one to elucidate both the H-bonding motif (5-7 microm) as well as the backbone structure (7-10 microm). Comparison with DFT calculations shows that the backbone is locally constrained to an alpha-conformation by Aib and to a gamma-turn by Pro. The gamma-turn motif observed here is intriguing since the condensed phase structure is known to be a beta-turn. This is the first actual observation of such a discrepancy, and it emphasizes the subtle balance between intra- and intermolecular forces, which is responsible for the relative stability of the different secondary structure motifs.     

Fluorescence spectroscopic study on complexation of uranium(VI) by glucose: a comparison of room and low temperature measurements

Cryogenic techniques are currently used in scanning tunnelling microscopy (STM) and single molecule spectroscopy. Recently such cryogenic devices have also been adapted to time resolved laser-induced fluorescence spectroscopy (TRLFS) systems applied to uranium(VI). In our study, we interpret TRLFS results obtained for the uranyl(VI) glucose system at room temperature (RT) and under cryogenic conditions of 153 K (cryo-TRLFS). A uranyl(VI) glucose complex was only identified by cryo-TRLFS measurements at pH 5 and not by RT measurements. The uranyl(VI) glucose complex was characterized by five emission bands at 499.0, 512.1, 525.2, 541.7, and 559.3 nm and a fluorescence lifetime of 20.9 ± 2.9 μs. The uranyl(VI) glucose complex formation constant was calculated for the first time to be logß_I=0.1 M = 15.25 ± 0.96. Cryo-TRLFS investigation opens up new possibilities for the determination of complex formation constants since interfering quenching effects often encounter at RT are suppressed by measurements at cryogenic conditions.     

Modification of Particle Filled Polymers with High Energy Electrons Under In-Stationary Conditions of Melt Mixing

Summary: Polymer modification with high energy electrons is well-established in polymer industry and used for degradation, cross-linking, grafting, curing, and polymerization. These applications use local and temporal precise input of energy in order to generate excited atoms or molecules and ions for subsequent molecule changes via radical induced chemical reactions. In the present study, high energy electrons have been used to modify polyolefine (polyethylene and polypropylene) systems in presence of a grafting agent under stationary and in-stationary conditions. Polymer modification with high energy electrons under stationary conditions characterizes a process where required absorbed dose is applied to polymers in solid state and at room temperature. Polymer modification with high energy electrons under in-stationary conditions is a novel process where required absorbed dose is applied in molten state during melt mixing process. In this novel process, the penetration depth of electrons is limited to a part of mixing volume. The total mixing volume is modified due to the change of polymer mass within the penetration depth of electrons during mixing process. A 1.5 MeV electron accelerator has been directly coupled to a banbury mixing chamber in order to study this novel process. In comparison to the stationary process, the main differences are working at higher temperature, absence of any crystallinity, intensive macromolecular mobility as well as intensive mixing during dose application. The influence of both processes on mechanical properties and flame resistance of polymer composites is discussed.     

A new Fenchel dual problem in vector optimization

We introduce a new Fenchel dual for vector optimization problems inspired by the form of the Fenchel dual attached to the scalarized primal multiobjective problem. For the vector primal-dual pair we prove weak and strong duality. Furthermore, we recall two other Fenchel-type dual problems introduced in the past in the literature, in the vector case, and make a comparison among all three duals. Moreover, we show that their sets of maximal elements are equal.     

Monte Carlo Simulation of Polymer Reactions at Interfaces

Adhesion of immiscible polymers during two‐component injection moulding may be improved by transreactions of properly functionalised components. We performed MC simulations based on the three‐dimensional coarse‐grained bond fluctuation model (BFM) including a thermal interaction potential in with energy to characterise the behaviour of several selected types of chemical reactions, which are governed by activation energies of E_A = 0, 1, 3 and 5 k_BT. The consumption of reactive monomers for all the reactions in the time interval below the Rouse time τ_R exhibits a typical crossover from a kinetic‐controlled to a diffusion‐controlled behaviour and can be described by a bimolecular kinetic ansatz.

     

trans‐(2‐Methyl­thio­benzoato‐O)phenylbis­(tri­phenyl­phosphine)­palladium(II), two conformational isomers

The title compound, trans‐[Pd(C₆H₅)(C₈H₇O₂S)(C₁₈H₁₅P)₂], crystallizes in two modifications differing only in the orientation of the 2‐methyl­thio­benzoato ligand. In both cases, this ligand binds to the metal centre via one O atom in a monodentate fashion. The only significant difference is a rotation about the C(Ph)—COO bond, with O—C—C—C torsion angles having values of 6.3 (7) and 157.3 (3)° in the two isomeric forms.     

The effect of a cluster on a chemical reaction: a quasiclassical trajectory study

We have calculated product rotational state distributions for the D + H₂ reaction trapped in the center of icosahedral argon cluster at various cluster temperatures. All the degrees of freedom are treated classically in the present calculations. The rotational state distributions exhibit considerable dependence on the cluster environment and its temperature as compared with those obtained in the gas phase reaction.