Infrared Intensity Studies in Fluorinated Macromolecules

Summary: Functionalized perfluoropolyethers are investigated by infrared spectroscopy with the aim to give a quantitative estimate of the carboxylic acid groups species; since hydrogen bonded moieties have been observed, also the relative distribution of the associated species has been determined. The study is based both on measured and on theoretically predicted infrared intensities, as obtained by density functional theory (DFT) calculations on model systems.     

Nanocomposite TiN films with embedded MoS2 inorganic fullerenes produced by combining supersonic cluster beam deposition with cathodic arc reactive evaporation

We report the production and characterization of nanocomposite thin films consisting of a titanium nitride matrix with embedded molybdenum disulphide fullerene-like nanoparticles. This was achieved by combining a cluster source generating a pulsed supersonic beam of MoS₂ clusters with an industrial cathodic arc reactive evaporation apparatus used for TiN deposition. Cluster-assembled films show the presence of MoS₂ nanocages and nanostructures and the survival of such structures dispersed in the TiN matrix in the co-deposited samples. Nanotribological characterization by atomic force microscopy shows that the presence of MoS₂ nanoparticles even in very low concentration modifies the behaviour of the TiN matrix. PACS 62.20.Qp; 62.23.Pq; 68.55.-a; 81.07.-b     

Probing the chemical reactivity of free titanium clusters by x-ray absorption spectroscopy

Synchrotron radiation-based experimental techniques are largely employed for the characterization of the reactivity of finite size systems; in particular, x-ray absorption spectroscopy (XAS) is a suitable tool to shed light on the local electronic structure and chemical status of atoms in nano-objects, as it is very sensitive to the local bonding environment of the probed site. In supported clusters intrinsic properties and reactivity are largely distorted and obscured by the changes imposed by the growth procedure and by the influence of the substrate, so the attainability of experiments on free clusters reacting with species in the gas phase is a primary goal in the development of cluster science. In this paper we report a proof of principle of the applicability of gas phase XAS technique to titanium and titanium oxide, hydride and hydrate systems. Experiments are performed by coupling a pulsed microplasma cluster source (PMCS) with a third generation synchrotron light source, and measuring the intensity of the electron yield coming from the interaction of VUV photons with the clusters seeded in a supersonic beam.     

Structural Determinants of the Specific Activities of an L-Amino Acid Oxidase from Pseudoalteromonas luteoviolacea CPMOR-1 with Broad Substrate Specificity

The Pseudoalteromonas luteoviolacea strain CPMOR-1 expresses a flavin adenine dinucleotide (FAD)-dependent L-amino acid oxidase (LAAO) with broad substrate specificity. Steady-state kinetic analysis of its reactivity towards the 20 proteinogenic amino acids showed some activity to all except proline. The relative specific activity for amino acid substrates was not correlated only with K_m or k_cat values, since the two parameters often varied independently of each other. Variation in K_m was attributed to the differential binding affinity. Variation in k_cat was attributed to differential positioning of the bound substrate relative to FAD that decreased the reaction rate. A structural model of this LAAO was compared with structures of other FAD-dependent LAAOs that have different substrate specificities: an LAAO from snake venom that prefers aromatic amino acid substrates and a fungal LAAO that is specific for lysine. While the amino acid sequences of these LAAOs are not very similar, their overall structures are comparable. The differential activity towards specific amino acids was correlated with specific residues in the active sites of these LAAOs. Residues in the active site that interact with the amino and carboxyl groups attached to the α-carbon of the substrate amino acid are conserved in all of the LAAOs. Residues that interact with the side chains of the amino acid substrates show variation. This provides insight into the structural determinants of the LAAOs that dictate their different substrate preferences. These results are of interest for harnessing these enzymes for possible applications in biotechnology, such as deracemization.     

Testing Newtonian gravity in space

We propose to measure the universal constant of gravity G in space by means of a small scale planetary system in geosynchronous orbit; test particle satellites of different nuclear composition and with different distances from the central mass would allow one to check possible variations with material and distance. With current technology G can be measured with a relative accuracy of 10⁻⁵ or better depending on the capability of controlling some perturbations which act at the level of 10⁻⁶ (i.e. ≈ 10⁻¹¹ cm s⁻²; however, particular dynamical configurations mutuated from celestial mechanics should allow detection of differential effects with composition and distance (if any) to at least 10⁻⁶. Distance variations will be detected only if acting on a distance scale of 10 m.     

含1,2二取代的苯并咪唑配体的Zn(Ⅱ)络合物上化学固定CO_2转化为环状碳酸酯（英文）

合成了一种新的Zn(Ⅱ)配合物ZnCl_2(L1)_2](1)(L1为2-(2-噻吩)-1-(2-噻吩甲基)-1H-苯并咪唑),并采用NMR和IR光谱、元素分析、ESI-HRMS光谱测定和热重分析等对它进行了表征,其分子结构也由单晶X射线衍射确定.络合物1含有单核四面体Zn(Ⅱ)单元,即所谓的锁定的几何结构,这源自分子中存在弱的分子间S···p和p-p配体间相互作用.通过简易的合成路线即可制得苯并咪唑配体及其与Zn(Ⅱ)配合物.采用CO_2与环氧化物耦合生成环状碳酸酯反应考察了1的催化活性,以及反应条件的影响.该配合物在无溶剂条件下可高效催化多种环氧化物的转化,具有较好的转化率,TONs和TOFs.     

Methyl branching in polyethylene from homopolymerization of ethylene with N‐arylcyano‐β‐diketiminate methallyl nickel‐B(C6F5)3

N‐Arylcyano‐β‐diketiminate methallyl nickel complexes activated with B(C₆F₅)₃ were used in the polymerization of ethylene. The microstructure analysis of obtained polyethylene (PE) was done by differential scanning calorimetry and ¹³C nuclear magnetic resonance (NMR). The branched polymer structures produced by these catalysts were attributed to one step isomerization mechanism of the catalyst along the polymer chain. The ortho or para position of the cyano group with co‐ordinated B(C₆F₅)₃ in both methallyl nickel catalysts influenced the polymer molecular weight, branching, and consequently melting and crystallization temperatures. NMR spectroscopic studies showed predominantly the formation of methyl branches in the obtained PE. Catalysts under study gave linear low‐density PEs with good crystallinities at temperatures of reaction between 50 °C and 70 °C at moderate pressures (12.3 atm). A propylene–ethylene copolymer produced by the metallocene catalyst had the same concentration of branches as the PE synthesized from methallyl nickel/B(C₆F₅)₃. Comparing the two polyolefins with the same degree of branching, it was observed that the polymer obtained with the nickel catalyst proved to be twice more crystalline and had greater T_m. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 452–458     

Asymmetrical response of semiconductor lasers in optical systems

The symmetry of the optical outputs of a semiconductor laser diode having front and rear facets with equal reflectivity is destroyed by the injection of a reflected signal, even of weak intensity, from one side: this asymmetry must be taken into account when designing laser packages and integrated circuits. A systematic experimental investigation is presented. Moreover, the behaviour of the system, i.e., the appearance of certain asymmetrical features together with the survival of the symmetry of other features, can be accounted for on the basis of a microscopic model, providing a link between the optical outputs from the two facets.Italtel-Advanced Technology Laboratory Cascino Castelletto, CLTB-20019 Settimo Milanese, Italy. Consorzio Milano Ricerche Via Cicognara, 7-20129 Milano, Italy. Physics Department, University of Milan, Via Celoria, 16-20133 Milano, Italy. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 99, No. 3, pp. 364–369, June, 1994.