Photometric and amperometric flow-injection determination of triazolam and clotiazepam

Triazolam and clotiazepam can be determined by flow-injection analysis with photometric and amperometric detection. With photometric detection, the signals are a linear function of the drug concentration from 3 to 55muM (lambda = 228 nm) for triazolam and from 31 to 502muM (lambda = 390 nm) and from 6 to 125muM (lambda = 260 nm) for clotiazepam. FIA systems with amperometric detection allow the determination of these drugs in the range 6-116muM (triazolam) and 16-162muM (clotiazepam).     

Dipole moment and rovibrational intensities in the electronic ground state of NH3: bridging the gap between ab initio theory and spectroscopic experiment

We report theoretical values for the transition moments of an extensive set of vibrational bands in the electronic ground state of (14)NH(3). For selected bands, we have further made detailed simulations of the rotational structure. The calculations are carried out by means of recently developed computational procedures for describing the nuclear motion and are based on a high-level ab initio potential energy surface, and high-level dipole moment surfaces, for the electronic ground state of NH(3). The reported theoretical intensity values are compared to, and found to agree very well with, corresponding experimental results. It is believed that the computational method, in conjunction with high-quality ab initio potential energy and dipole moment surfaces, can simulate rotation-vibration spectra of XY(3) pyramidal molecules prior to observation with sufficient accuracy to facilitate the observation of these spectra. By degrading the accuracy of selected elements of the calculations, we have also investigated the influence of customary approximations on the computed intensity values.     

A MOF@COF Composite with Enhanced Uptake through Interfacial Pore Generation

Herein, we describe a new class of porous composites comprising metal–organic framework (MOF) crystals confined in single spherical matrices made of packed covalent‐organic framework (COF) nanocrystals. These MOF@COF composites are synthesized through a two‐step method of spray‐drying and subsequent amorphous (imine‐based polymer)‐to‐crystalline (imine‐based COF) transformation. This transformation around the MOF crystals generates micro‐ and mesopores at the MOF/COF interface that provide far superior porosity compared to that of the constituent MOF and COF components added together. We report that water sorption in these new pores occurs within the same pressure window as in the COF pores. Our new MOF@COF composites, with their additional pores at the MOF/COF interface, should have implications for the development of new composites.     

Nitrogen regulation of Saccharomyces cerevisiae invertase

The regulation of extracellular enzymes is of great biotechnological interest. We studied the regulatory role of the URE 2 gene on the periplasmic invertase of Saccharomyces cerevisiae, because its periplasmic asparaginase is regulated by the URE2/GLN3 system. Enzymatic activity was measured in the isogenic strains P40-1B, the ure2 mutant P40-3C, and the P40-3C strain transformed with the pIC-CS plasmid carrying the URE2 gene. The assays were performed using midlog and stationary phase cells and nitrogen-starved cells from these growth phases. During exponential growth, the level of invertase in both wild-type and ure 2 mutant cells was comparable. However, the invertase activity in ure2 mutant cells from stationary phase was sixfold lower than in the wild-type cells. When P40-3C cells were transformed with the pIC-CS plasmid, the wild-type phenotype was restored. On nitrogen starvation in the presence of sucrose, the invertase activity in wild-type cells from midlog phase decreased three times, whereas in stationary cells, the activity decreased eight times. However, invertase activity doubled in ure 2 mutant cells from both phases. When these cells were trans-formed with the aforementioned plasmid, the wild-type phenotype was restored, although a significant invertase decrease in stationary cells was not observed. These results suggested that the URE2 protein plays a role in invertase activity.     

Comparison between phase space structures in coupled Morse systems and in various su(2) approximations

While Hamiltonians written in terms of position and momentum provide a transparent picture of the motion of a system, Hamiltonians written in terms of Lie algebras are easier to handle quantum mechanically. Therefore we are interested to know how to transform one into the other. Since the exact transformation often leads to complicated expressions, we look for approximations which preserve the essential features. As basic criterion we look for the degree of equality of the classical phase space structures. We illustrate our ideas for the case of two coupled Morse systems and its approximation in terms of the Lie algebra su(2), which is relevant to anharmonic models of molecular spectroscopy. (c) 2001 American Institute of Physics.     

Determination of a Potential Energy Surface for CO2 Using Generalized Internal Vibrational Coordinates

A potential energy surface for CO2 is determined from experimental data using generalized internal vibrational coordinates. These coordinates are defined as two arbitrary distances and the angle between them and depend on two external parameters, which can be properly optimized. An optimal generalized internal coordinate system is obtained for CO2 by minimizing unconverged vibrational energies with respect to the external parameters. The optimal coordinates are shown to be superior to previously derived normal hyperspherical coordinates for this molecule. A nonlinear least-squares fit of the potential energy surface of CO2 to observed vibrational frequencies is made by using the optimal internal coordinates and fully variational calculations. The potential function is represented by a fourth-order Morse-cosine expansion and its quality is checked by computing highly excited vibrational transition frequencies which were not included in the fit. Copyright 1999 Academic Press.     

Insights on the photomagnetism in copper octacyanomolybdates

High level ab initio calculations on the photoinduced high-spin molecule [Mo(CN)(2)(CN-Cu(tris(2-aminoethyl)amine)(6)](8+) are reported. The calculations indicate that the mechanism of the photoinduced transformation from a paramagnetic to a ferromagnetic state involves a local Mo d-d transition followed by the deformation of the coordination sphere from dodecahedron to square antiprism. Subsequently, Mo loses a ligand and becomes seven coordinated in a pentagonal bipyramid coordination. The resulting Mo(IV)(S = 1) ion interacts ferromagnetically with the five remaining Cu(II) ions through the cyanide bridges. The estimated coupling is about +50 K and the resulting magnetic susceptibility curve resembles the experimental one taking into account that part of the sample is magnetically deactivated during the measurement. The calculated potential energy profile along the linear interpolated reaction coordinate shows a small barrier for the reverse reaction in agreement with the thermal reversibility of the photoinduced state. Moreover, we find that the reverse reaction can be induced by light.     

CCSD(T) study of dimethyl-ether infrared and Raman spectra

CCSD(T) state-of-the-art ab initio calculations are used to determine a vibrationally corrected three-dimensional potential energy surface of dimethyl-ether depending on the two methyl torsions and the COC bending angle. The surface is employed to obtain variationally the lowest vibrational energies that can be populated at very low temperatures. The interactions between the bending and the torsional coordinates are responsible for the displacements of the torsional overtone bands and several combination bands. The effect of these interactions on the potential parameters is analyzed. Second order perturbation theory is used as a help for the understanding of many spectroscopic parameters and to obtain anharmonic fundamentals for the 3N - 9 neglected modes as well as the rotational parameters. To evaluate the surface accuracy and to verify previous assignments, the calculated vibrational levels are compared with experimental data corresponding to the most abundant isotopologue. The surface has been empirically adjusted for understanding the origin of small divergences between ab initio calculations and experimental data. Our calculations confirm previous assignments and show the importance of including the COC bending degree of freedom for computing with a higher accuracy the excited torsional term values through the Fermi interaction. Besides, this work shows a possible lack of accuracy of some available experimental transition frequencies and proposes a new assignment for a transition line. As an example, the transition 100 → 120 has been computed at 445.93 cm(-1), which is consistent with the observed transition frequency in the Raman spectrum at 450.5 cm(-1).