A rotation-torsion-vibration treatment with three-dimensional internal coordinate approach and additional FTIR spectral assignments for the CH3-bending fundamentals of methanol

A theoretical model has been developed to account for certain features of both newly observed and previously reported CH₃-bending subbands between 1450 and 1570 cm⁻¹ in the high-resolution Fourier transform infrared spectrum of CH₃OH [Can. J. Phys. 79 (2001) 435]. The features include (i) an apparent inversion of the rotationless E-A torsional splitting with respect to the ground state, i.e., the A state located above the E state, (ii) a pronounced upward slope in the K-reduced torsion-vibration energy pattern for the subband origins, and (iii) unexpected A₁/A₂ inversion of the K=2A and K=3AJ-rotational levels that led to ambiguity in identifying the vibrational mode as or . The model is an effective internal coordinate Hamiltonian constructed in G₆ molecular symmetry with the CH₃-bends coupled to each other and to torsion and including a- and γ-type Coriolis coupling. With this model, 33 out of 36 experimental upper-state K-term values for newly assigned , and ν₁₀ subbands plus previous ν₄ subbands have together been fitted successfully, employing 9 adjustable parameters and 17 fixed parameters to give a standard deviation of 0.14 cm⁻¹. The P_γ Coriolis term appears to be the leading cause of the upward shift in the K-reduced energies. When J-dependence is introduced via a rotational Hamiltonian including b- and c-type Coriolis terms in addition to molecular asymmetry, the observed A₁/A₂ inversion of the K=2A and 3A rotational levels can also be reproduced. Predictions using the fitted K-rotation-torsion-vibration Hamiltonian show an interesting Coriolis-induced crossover and mixing of the ν₅ and ν₁₀ torsion-vibration energy patterns. These predictions played a role in identifying two of the new ν₅ subbands in the crossing region, thereby helping to validate the model.     

Effects of different composition ratio on the dielectric relaxation and dynamic mechanical properties of poly(ω‐dodecalactam‐co‐ε‐caprolactam‐co‐propylene oxide) copolymers

The molecular dynamics of new poly (ω‐dodecalactam‐co‐ε‐caprolactam‐co‐propylene oxide) copolymers (DL/CL/PAC) has been investigated by using dynamic mechanical thermal analysis (DMTA) and dielectric relaxation spectroscopy (DRS) measurements. The copolymers were synthesized via anionic polymerization of relevant lactams activated with carbamoyl derivatives of telechelic hydroxyl terminated polypropylene oxide with isophorone diisocyanate (PAC). The calorimetric, X‐ray diffraction, and DMTA measurements were performed to recognize the influence of the composition ratio and the type of PAC on the physical, thermal, and mechanical properties of the synthesized copolymers. The DRS was used to study the frequency dependence of the dielectric permittivity of some isotherms from ?110 to 145 °C. Copolymerization of ε‐caprolactam with about 10 wt % ω‐dodecalactam results in a copolymer that has lower water absorption, a melting point close to that of polyamide 6 and has a high enough degree of crystallinity in respect to high storage modulus. Five dielectric relaxations have been observed in the dielectric spectra, three at lower temperature and two at higher temperature. The copolymers have two glass transition temperatures for polyamide segments and polyether blocks, indicating microphase separation in the copolymers. Other studies directed toward molecular dynamics of polyamide DL/CL/PAC copolymers have not been reported. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

A novel carbon/chitosan paste electrode for electrochemical detection of normetanephrine in the urine

Normetanephrine is a marker for pheochromocytoma, a rare catecholamine-secreting and neuroendocrine tumor, that arises from sympathetic and parasympathetic paraganglia. In this work, a novel carbon/chitosan electrode paste was used for sensitive voltammetric determination of normetanephrine and dopamine in the presence of ascorbic acid and uric acid. The modified electrode has shown an increase in the effective area of up to 68%, well-separated oxidation peaks, and an excellent electrocatalytic activity. The electrochemical response characteristics were investigated by cyclic and differential pulse voltammetry. Interestingly, high sensitivity and selectivity in the linear range of normetanephrine, dopamine, ascorbic acid, and uric acid concentrations were observed. The present method was applied in the urine sample and satisfactory results were obtained showing that this electrode is very suitable in pharmaceutical and clinical preparations.     

Structural characteristics and cyclic voltammetric behaviour of Sonogel-Carbon tyrosinase biosensors. A detailed comparative study of three immobilization matrixes

Structural characteristics an cyclic voltammetry of three amperommetric biosensors based on immobilization of tyrosinase on a Sonogel-Carbon electrode for detection of phenols are described. Cyclic voltammetry was applied to study the electrochemical behaviour of the electrode and the electrochemical reaction on the electrode surface. Scanning electron microscopy, X-ray energy dispersive spectroscopy and atomic force microscopy were used for the structure characterization of the electrode surface, enzyme film and polymers coatings. The influence of additive-protective polymers, such as polyethylene glycol and perfluorinated-Nafion ion-exchanger on the surface of the biosensor were explored.     

Voltammetric determination of trace mercury at a sonogel-carbon electrode modified with poly-3-methylthiophene

The sonogel-carbon electrode is a new class of sol-gel electrode that exhibit favourable mechanics and electrics properties to be used as electrochemical sensor. In this paper, a modified sonogel-carbon electrode is proposed to determine mercury at trace levels. The modified electrode is obtained by electropolymerization of 3-methylthiophene on the surface of a bare sonogel-carbon electrode. This electrode shows high selectivity and sensitivity and linear response towards Hg(II), with a detection limit of 1.4 × 10⁻³ mg l⁻¹. The electrode is reusable by a simple chemical cleaning procedure. No deterioration was observed in the electrode response during at least 1 week of successive measurements.     

Sonogel-carbon electrode based on hemin for detection of superoxide

The Sonogel electrode was immersed in hemin solution to obtain the hemin-Sonogel-modified electrode by cyclic voltammetry (CV). It was applied to detect superoxide radicals produced by xanthine oxidase catalyzed hypoxanthine oxidation. The characterization of hemin-Sonogel was modified by impedance and CV.     

Cyclic voltammetric studies of the antipsychotic chlorpromazine using an alkylthiol/phospholipid-modified gold electrode

Self-assembled monolayers of alkanethiols on gold have been reported to be highly stable for voltammetry experiments in aqueous electrolyte. In this work a gold electrode has been modified by first depositing one layer of an alkylthiol (S-C₁₈) and then coating by phospholipid multilayers. Voltammetric oxidation of the antipsychotic chlorpromazine at this two-step modified electrode was followed by means of cyclic voltammetry measurements. The results give important information concerning the behaviour of the pharmacological agent at the lipid-water interface. Measurements made using the pre-concentration method allow good sensitivity improvement after 5 min accumulation time. The ability of chlorpromazine to penetrate inside the phospholipid multilayers has also been investigated under different conditions such as the nature of the phospholipid and the pH of the medium. The accumulation process seems to be closely related to the charge carried by the phospholipid and by the molecule, while the incorporation process seems to be independent of the charge carried by the phospholipid and dependent of the degree of fluidity of their hydrocarbon chains. We found through this work that the acid-base equilibrium of chlorpromazine together with its amphiphilic properties (as compared with the results of similar studies on phenothiazine) could be responsible for governing the principal aspects of the drug's behaviour toward biological membranes. Received: 6 January 1997 / Accepted: 27 February 1997     

Electrochemically aided solid phase microextraction: conducting polymer film material applicable for cationic analytes

The cation uptake and release properties of a poly(pyrrole-sulfated β-cyclodextrin) (PPy-SβCD) film electrode have been investigated under both open circuit and controlled potential conditions for prospective applications in electrochemically aided solid-phase microextraction (EA SPME). The EDAX and ion chromatography results show that the K⁺ and Na⁺ cation uptake is enhanced if a small negative potential is applied to the electrode in the range where PPy is in its neutral form. These cations are released rapidly from the film if the applied potential is switched to the value at which PPy is converted to its positively charged form, i.e., oxidized state. The cation ingress and egress mechanism is affected both by the cation exchange at the negative sulfate moiety on the cyclodextrin sites and electrostatic interactions generated by the applied potential. The electrochemical "switching" capability increases the speed of the cation uptake and release, presumably due to electro migration, as compared to the open circuit ion exchange which is controlled solely by diffusion. Our preliminary fundamental results show that the PPy-SβCD film is suitable for the future design of EA SPME devices. Electronic Publication     

A frequency domain inversion method applied to propagation models in unconsolidated granular materials

The measurement setup consists of a water filled tank within which a smaller Plexiglas tank containing a known sediment is placed. This provides a Plexiglas-sediment-Plexiglas configuration, which is then used in conjunction with transducers and a pulser-receiver for a transmission and reflection experiment. The aim of this work is to find some physical parameters of the sediment from these measurements. A general viscoelastic model that considers losses due to absorption and dispersion along the propagation of the wave through the sediments is proposed. A rational transfer function is used to model the viscoelastic modulus of the bulk sediments, and comparisons with constant Q viscoelastic modelling and Biot modelling are performed. The estimation of the model parameters is elaborated using a maximum likelihood estimator in the frequency domain.