The Arsenic Oxide Trichloride Dimer

The crystal structure and Raman spectrum of AsOCl₃ reveals that in the solid state it consists of double oxygen bridged dimers with a trigonal bipyramidal structure environment around the arsenic atoms. (a = 804.3(2), b = 613.1(2), c = 1019.7(2) pm, β = 111.99(2)°, space group P2₁/c, Z = 4). In solution of CH₂Cl₂ it is monomeric, as evidenced by Raman spectroscopy. These findings are supported by ab initio and density functional calculations.     

The Resting State Makes the Difference: The Influence of the Anchor Group in the ROMP of Norbornene Derivatives

Summary: A model study with four norbornene derivatives with different groups connecting a functional unit to the norbornene reveals that the “anchor groups” influence the polymerisation rate constants of ring opening metathesis (ROM) polymerisations. Consequently, polydispersities and molecular weights are affected. The observed effects are explained by different tendencies of the anchor groups to coordinate to the ruthenium centre during the resting state of the propagation.

A functionalised monomer where F is the functional unit, S is a spacer, A is an anchor group and P is the polymerisable group.     

Hybrid polymer inorganic materials prepared from ternary microemulsions

The microemulsion system containing vinyl acetate (Vac), silane derivatives tetraethoxysilane (TEOS), methacryloxypropyltrimethoxysilane (MPTS), vinyltriethoxysilane (VTES), methyltriethoxysilane (MeTES), octyltriethoxysilane (OTES), nonylphenol etoxylated with 25 mol of ethylene oxyde (NPEO₂₅) and water was studied. It was established that the probability of microemulsion formation increases with surfactant concentration. The microenviroment of the solubilization of the VAc and of silane derivatives in the aggregates of NPEO₂₅ was affected by their polarity. Hybrid materials were obtained by sol-gel reaction of silane derivatives combined with free-radical polymerization of VAc. The change of the glass transition temperature and of thermal stability of the polymer chains in the presence of the inorganic one proved the formation of simultaneous polymer inorganic hybrids.     

Kinetics and mechanism of the reaction of CF3 radicals with NO2

The reaction of CF₃ with NO₂ was studied at 296 ± 2K using two different absolute techniques. Absolute rate constants of (1.6 ± 0.3) × 10⁻¹¹ and (2.1 _−0.3⁺⁰⁷) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ were derived by IR fluorescence and UV absorption spectroscopy, respectively. The reaction proceeds via two reaction channels: CF₃ + NO₂ → CF₂O + FNO, (70 ± 12)% and CF₃ + NO₂ → CF₃O + NO, (30 ± 12)%. An upper limit of 11% for formation of other reaction products was determined. The overall rate constant was within the uncertainty independent of total pressure between 0.4 to 760 torr. © 1996 John Wiley & Sons, Inc.     

A Robust Protocol for Entropy Measurement in Mesoscopic Circuits

Previous measurements utilizing Maxwell relations to measure change in entropy, S, demonstrated remarkable accuracy in measuring the spin-1/2 entropy of electrons in a weakly coupled quantum dot. However, these previous measurements relied upon prior knowledge of the charge transition lineshape. This had the benefit of making the quantitative determination of entropy independent of scale factors in the measurement itself but at the cost of limiting the applicability of the approach to simple systems. To measure the entropy of more exotic mesoscopic systems, a more flexible analysis technique may be employed; however, doing so requires a precise calibration of the measurement. Here, we give details on the necessary improvements made to the original experimental approach and highlight some of the common challenges (along with strategies to overcome them) that other groups may face when attempting this type of measurement.     

Utilization of deuterium labelling and 13C NMR spectroscopy in the investigation of the condensation of 1-Methyl-5-nitroimidazole-2-aldehyde and 2-Amino-4-methylpyrimidine

The product obtained condensing l-methyl-5-nitroimidazole-2-aldehyde with 2-amino-4-trideuteriomethyl-pyrimidine and showing total deuterium incorporation at one of the olefinic carbons and partial deuterium incorporation para to the amino group, served to assign ¹³C and ¹H resonances in the condensation products 3. The nature of the species undergoing condensation has been inferred from labelling experiments and from ¹H and ¹³C nmr spectra of precursors and products in dimethylsulfoxide and trifluoroacetic acid.     

Amperometric Detection and Quantification of 8‐Hydroxy‐2′‐deoxyguanosine (8‐OHdG) Using Dendrimer Modified Electrodes

8‐Hydroxy‐2′‐deoxyguanosine (8‐OHdG) detection by high performance liquid chromatography (HPLC) with amperometric detection was studied using a Au electrode modified with different dendrimer based thin films. Gold electrode is thiol‐modified, forming self‐assembled monolayers on which different generation PAMAM dendrimers with terminal functional groups ? COOH and ? NH₂ have been attached using peptidic bonds. Results obtained in synthetic samples show low limits of detection and quantification for 8‐OHdG (1.2×10^?9 and 3.7×10^?9 M respectively), with matrix interference elimination, thus avoiding sample pretreatment. Best results are obtained with electrodes modified with aliphatic amino thiols and 3.5 and 4.5 generation carboxylated dendrimers (Au/AET/DG^3.5 and Au/AET/DG^4.5), demonstrating that these materials constitute a good alternative for 8‐OHdG determination in biological fluids.     

Modelling Protein Plasticity: The Example of Frataxin and Its Variants

Frataxin (FXN) is a protein involved in storage and delivery of iron in the mitochondria. Single-point mutations in the FXN gene lead to reduced production of functional frataxin, with the consequent dyshomeostasis of iron. FXN variants are at the basis of neurological impairment (the Friedreich’s ataxia) and several types of cancer. By using altruistic metadynamics in conjunction with the maximal constrained entropy principle, we estimate the change of free energy in the protein unfolding of frataxin and of some of its pathological mutants. The sampled configurations highlight differences between the wild-type and mutated sequences in the stability of the folded state. In partial agreement with thermodynamic experiments, where most of the analyzed variants are characterized by lower thermal stability compared to wild type, the D104G variant is found with a stability comparable to the wild-type sequence and a lower water-accessible surface area. These observations, obtained with the new approach we propose in our work, point to a functional switch, affected by single-point mutations, of frataxin from iron storage to iron release. The method is suitable to investigate wide structural changes in proteins in general, after a proper tuning of the chosen collective variable used to perform the transition.