Evaluation of Ptitsyn-Eizner λ parameter in dilute solutions of poly(N-vinylcarbazole) and its variation in conformational transitions of poly(methyl methacrylate)

The Ptitsyn-Eizner λ flexibility parameter for poly(N-vinylcarbozole) solutions under theta conditions has been found to be 6.31, demonstrating the rigidity imparted to the polymer chain by the carbazole group. A study has been made of the variation of this parameter with solvent and temperature. A study has been made of the variation of λ in a conformational transition of poly(methyl methacrylate).     

Construction and analytical application of a biosensor based on stearic acid-graphite powder modified with sweet potato tissue in organic solvents

A biosensor based on stearic acid-graphite powder modified with sweet potato (Ipomoea batatas (L.) Lam.) tissue as peroxidase source was constructed and applied in organic solvents. Several parameters were studied to evaluate the performance of this biosensor such as stearic acid-graphite powder and tissue composition, type and concentration of supporting electrolyte, organic solvents, water/organic solvent ratio (% v/v) and hydrogen peroxide concentration. After selection of the best conditions, the biosensor was applied for the determination of hydroquinone in cosmetic creams in methanol. At the peroxidase electrode hydroquinone is oxidized in the presence of hydrogen peroxide and the radical formed was reduced back electrochemically at -180 mV vs Ag/AgCl (3.0 mol L(-1) KCl). The reduction current obtained was proportional to the concentration of hydroquinone from 6.2 x 10(-5) to 1.5 x 10(-3) mol L(-1) (r = 0.9990) with a detection limit of 8.5 x 10(-6) mol L(-1). The recovery of hydroquinone from two samples ranged from 98.8 to 104.1% and an RSD lower than 1.0% for a solution containing 7.3 x 10(-4) mol L(-1) hydroquinone and 1.0 x 10(-3) mol L(-1) hydrogen peroxide in 0.10 mol L(-1) tetrabutylammonium bromide methanol-phosphate buffer solution (95:5% v/v) (n = 10) was obtained.     

Reactions oftrans-[Mo(CNMe)2(PMe2Ph)4] andmer-[W(CNMe)3(PMe2Ph)3] complexes with methanol and with mineral acids to give amines,ammonia and hydrocarbons

Summary Treatment oftrans-[Mo(CNMe)₂(PMe₂Ph)₄] andme-[W(CNMe)₃(PMe₂Ph)₃] with sulphuric or hydrochloric acids in methanol or ethanol, or in methanol alone, under irradiation, gives methylamine, ammonia and hydrocarbons (mainly methane). The complex [W₂(CNMe)₄(-CNHMe)₂(PMe₂Ph)₄]²⁺ cation has been obtained by the treatment ofmer-[W(CNMe)₃(PMe₂Ph₃] with H₂SO₄ or [Et₂OH][BF₄] and gives methylamine, ammonia and methane on further acid treatment.     

Ni(III) vs. Ni(II)-thiyl radical: charge-delocalisation in a binuclear Ni(III)Ni(II)-dithiolate complex

Multi-frequency EPR spectroscopy on 61Ni-labelled samples of [Ni2(L)]3+ confirms extensive charge-delocalisation between the Ni(III) centre and thiolate donors in the Ni(II)Ni(III) complex.     

Tailoring the cavities of hydrogen-bonded amphidynamic crystals using weak contacts: towards faster molecular machines

This work describes the use of C–H⋯F–C contacts in the solid-state from the stator towards the rotator to fine-tune their internal motion, by constructing a set of interactions that generate close-fitting cavities in three supramolecular rotors 1–3I. The crystal structures of these rotors, determined by synchrotron radiation experiments at different temperatures, show the presence of such C–H⋯F–C contacts between extended carbazole stators featuring fluorinated phenyl rings and the 1,4-diazabicyclo[2.2.2]octane (DABCO) rotator. According to the ²H NMR results, using deuterated samples, and periodic density functional theory computations, the rotators experience fast angular displacements (preferentially 120° jumps) due to their low rotational activation energies (E_a = 0.8–2.0 kcal mol⁻¹). The higher rotational barrier for 1 (2.0 kcal mol⁻¹) is associated with a larger number of weak C–H⋯F–C contacts generated by the stators. This strategy offers the possibility to explore the correlation among weak intermolecular forces, cavity shape, and internal dynamics, which has strong implications in the design of future fine-tuned amphidynamic crystals.

This work describes the use of C–H⋯F–C contacts in the solid-state from the stator towards the rotator to fine-tune their internal motion, by constructing a set of interactions that generate close-fitting cavities in three supramolecular rotors 1–3I.     

Gamma-radiolysis of quinoline in 2-propanol solution

In the last twenty years the ionizing effects on matter of⁶⁰Co γ-rays have been widely discussed. However, regarding organic compounds, mainly aromatic ones, results are scarce, particularly those obtained in alcoholic solution. γ-Radiation is used mainly in industry and medicine, particularly for sterilization of surgical materials. In this work we studied the chemical and radiolytic stability of products by radiation from quinoline in isopropanol solution. Doses were from 2×10⁴ to 3×10⁵ Gy and the samples concentration was 1∶1 by volume. We have observed significant effects for high radiation doses. Lower doses effected the solvent with the production of long polymeric hydrocarbons. Products formed were characterized by capillary gas chromatography coupled to a mass-selective detector (GC/MSD). We have used a fused silica capillary column 25 m long, 0.2 mm in internal diameter, covered by a 0.33 μm thick film of crosslinked 5% phenyl methyl silicone.     

Reconstruction of the free energy in the metastable region using the path ensemble

By quenching into the metastable region of the three-dimensional Ising model, we investigate the paths that the magnetization (energy) takes as a function of time. We accumulate the magnetization (energy) paths into time-dependent distributions from which we reconstruct the free energy as a function of the magnetic field, temperature, and system size. From the reconstructed free energy, we obtain the free-energy barrier that is associated with the transition from a metastable state to the stable equilibrium state. Although mean-field theory predicts a sharp transition between the metastable and the unstable region where the free-energy barrier is zero, the results for the nearest-neighbor Ising model show that the free-energy barrier does not go to zero.     

Flow injection spectrophotometric method for chloride determination in natural waters using Hg(SCN)(2) immobilized in epoxy resin

A flow injection (FI) spectrophotometric method was proposed for the determination of chloride ion in natural waters. The determination of chloride was carried out by reaction with Hg(SCN)₂ immobilized in an epoxy resin bead in a solid-phase reactor (SPR) and the thiocyanate ions released were determined spectrophotometrically at 480 nm after complexing reaction with Fe(III). The analytical curve for chloride was linear in the concentration range from 5.6 × 10⁻⁵ to 2.2 × 10⁻⁴ mol l⁻¹ with a detection limit of 1.4 × 10⁻⁵ mol l⁻¹. The relative standard deviation (R.S.D.) was 2.2% for a solution containing 2.2 × 10⁻⁴ mol l⁻¹ (n = 10). The simple manifold allows a routine analytical frequency of 100 determinations per hour. The main advantage of the developed method is the 400% reduction of the Hg waste solution generated when compared to conventional methods for chloride determination based on the same spectrophotometric reaction.     

Unprecedented single-pot synthesis of nitrile-derived ketoimino platinum(II) complexes by ring opening of Delta4-1,2,4-oxadiazolines

[PtCl2(RCN)2] (1a R=CH2CO2Me, 1b R=CH2Cl) prepared upon EtCN replacement at [PtCl2(EtCN)2] by the appropriate organonitrile, react with a cyclic nitrone -O-+N=CHCH2CH2C(Me)2, under mild conditions, to give, in an unprecedented single-pot synthesis involving spontaneous N-O bond cleavage, the ketoimino complexes trans-[PtCl2[RC(=O)N=CN(H)C(Me)2-CH2CH2]2 (2a, 2b) with two (pyrrolidin-2-ylidene)amino ligands. The analogous 2c (R=Et) and 2d (R=Ph) are formed by treatment with H2, in the absence of any added catalyst, of the Delta4-1,2,4-oxadiazoline complexes trans-[PtCl2[N=C(R)ONC(Me)2CH2CH2CH]2] (3a R=Et, 3b R=Ph) derived from the [2 + 3]-cycloaddition of the cyclic nitrone with the appropriate organonitrile complex of type 1. The compounds were characterized by elemental analyses, IR, 1H, (13C and 195Pt NMR spectroscopies, FAB mass spectrometry and X-ray structure analyses for 2a and 2d.