Pulsed electrochemical detection of penicillins using three and four step waveforms

Aided by the construction of a custom potentiostat, a series of different PAD waveforms were compared to find the optimum detector for penicillin oxidation. The waveforms included standard 3-step direct and indirect PAD in addition to reverse-PAD and 4-step PAD. Two new waveforms, the indirect reverse-PAD and the 4-step indirect PAD were examined in the study. Under the solvent conditions of the study (0.01M acetate buffer, pH 4.6) the indirect waveforms yielded the best detectability for penicillin G while the reverse-PAD waveforms yielded the worst performance. The 4-step PAD methods did not improve detectability when compared to the 3-step types, but they did provide output peak profiles with better shapes and less tailing. Although indirect waveforms gave better detectability than direct detection in the 0.01M acetate buffer solution, the limits of detection for each were found to be differing functions of ionic strength. At higher acetate concentrations, direct PAD was more favorable than indirect detection.     

关于Hirota-Satsuma系统初值问题的局部和整体适定性

本文利用ＫＤＶ方程所对应的线性方程解所具有的光滑效应及压缩映像原理,得到了Ｈｉｒｏｔａ－Ｓａｔｓｕｍａ系统初值问题的局部和整体适定性结果．     

Overlapping B3Π0u ← X1Σ g/+ and 1Π1u ← X1Σ g/+ non-radiative characteristic of Br2 vapour in the wavelength region 505–541 nm

The vibronic vapour phase photoacoustic spectrum of Br₂ in the wavelength region 505–541 nm (19796–18480 cm⁻¹) has been recorded using microphone as well as pump-probe method. Discrete vibronic bands superimposed on a monotonically increasing continuum background towards the dissociation limit results from the overlapping B ³Π _0u ^/+ ← X ¹Σ _g ^/+ and ¹Π_1u ← X ¹Σ _g ^/+ electronic transitions. Vibronic bands originating from υ″=0 have been used to estimate the relative rate of non-radiative relaxation as a function of the excited state B ³Π_0u vibrational quantum number υ′. A comparison with the optical absorption spectroscopy of Br₂ leads to the identification of three broad spectral regions between 505 and 541 nm (19796 and 18480 cm⁻¹) on the basis of different non-radiative relaxation processes.     

Properties of nearly one-electron molecules. II. Application to the Rydberg spectrum of CaF

The ab initio K matrix method described in the preceding paper (Part I) is applied to the Rydberg electronic structure of calcium monofluoride. The spectroscopic quantum defects for the 2Sigma+, 2Pi, 2Delta, and 2Phi states of CaF are computed using the effective potential of Arif et al. [M. Arif, Ch. Jungen, and A. L. Roche, J. Chem. Phys. 106, 4102 (1997)]. Satisfactory agreement with the experimental values is obtained. The eigenquantum defects obtained from the reaction matrix for the CaF++e- system are found to be strongly energy dependent. The analysis shows that the main features of the energy-dependent structure in the eigenphases are a consequence of a broad molecular shape resonance. Partial-l (orbital angular momentum) characters of two interacting collision eigenchannels vary rapidly as a function of increasing collision energy. This prominent variation leads to interference structure in the intensities for transitions into the ionization continuum, manifesting nodal points in the total ionization cross section in the continuum above the shape resonance. The usefulness of this structure in the ionization cross section as a direct probe of the l-character of the bound state is discussed. In addition, ab initio results for the photoelectron angular distribution and the anisotropy parameter are presented. These computed results are susceptible to direct experimental verification.     

Properties of nearly one-electron molecules. I. An iterative Green function approach to calculating the reaction matrix

An ab initio R-matrix method for determining the molecular reaction matrix of scattering theory is introduced. The method makes use of a principal-value Green function to compute the collision channel wave functions for the scattered electron, in combination with the Kohn variational scheme for the evaluation of R-matrix eigenvalues on a spherical boundary surface at short range. This technique permits the size of the bounded volume in the variational calculation to be reduced, making the computations fast and efficient. The reaction matrix is determined in a form that minimizes its energy dependence. Thus the procedure does not require modification or an increase in the computational effort to study the electronic structure and dynamics in Rydberg molecules with extremely polar ion cores. The analysis is specialized to examine the bound-state and free-electron scattering properties of nearly one-electron molecular systems, which are characterized by a Rydberg/scattering electron incident on a closed-shell ion core. However, it is shown that the treatment is compatible with all-electron/ab initio representations of open-shell and nonlinear polyatomic ion cores, emphasizing its generality. The introduced approach is used to calculate the electronic spectrum of the calcium monofluoride molecule, which has the extremely polar (Ca+2F-)+e- closed-shell ion-core configuration. The calculation utilizes an effective single-electron potential determined by M. Arif, C. Jungen, and A. L. Roche [J. Chem. Phys. 106, 4102 (1997)] previously. Close agreement with experimental data is obtained. The results demonstrate the practical utility of this method as a viable alternative to the standard variational approaches.     

Broad shape resonance effects in CaF Rydberg states

Results of ab initio R-matrix calculations [S. N. Altunata et al., J. Chem. Phys. 123, 084319 (2005)] indicate the presence of a broad shape resonance in electron-CaF(+) scattering for the (2)Sigma(+) electronic symmetry near the ionization threshold. The properties of this shape resonance are analyzed using the adiabatic partial-wave expansion of the scattered electron wave function introduced by Le Dourneuf et al. [J. Phys. B 15, L685 (1982)]. The qualitative aspects of the shape resonance are explained by an adiabatic approximation on the electronic motion. Mulliken's rule for the structure of the Rydberg state wave functions [R. S. Mulliken, J. Am. Chem. Soc. 86, 3183 (1964)] specifies that, except for an (n*)(-32) amplitude scale factor, every excited state wave function within one Rydberg series is built on an innermost lobe that remains invariant in shape and nodal position as a function of the excitation energy. Mulliken's rule implies a weak energy dependence of the quantum defects for an unperturbed molecular Rydberg series, which is given by the Rydberg-Ritz formula. This zero-order picture is violated by a single (2)Sigma(+) CaF Rydberg series at all Rydberg state energies (n*=5-->infinity, more so with increasing n*) below the ionization threshold, under the broad width of the shape resonance. Such a violation is diagnostic of a global "scarring" of the Rydberg spectrum, which is distinct from the more familiar local level perturbations.     

Analytical calculations of molecular integrals for multielectron R-matrix methods

Closed-form analytical expressions for one- and two-electron integrals between Cartesian Gaussians over a finite spherical region of space are developed for use in ab initio molecular scattering calculations. In contrast with some previous approaches, the necessary integrals are formulated solely in terms of finite summations involving standard functions. The molecular integrals evaluated over the finite region of space are computed by subtracting the contributions outside the region from the integrals over all space. The latter integrals can be efficiently and accurately obtained from existing bound-state algorithms. Our approach incorporates molecular scattering calculations into current quantum chemistry programs and facilitates the unification of bound- and continuum-state calculations for both diatomic and polyatomic molecules. Multidimensional Monte Carlo numerical integrations validate the high accuracy of our closed form results for the two-electron integrals.     

A new salicin derivative from the stem bark of Populus davidiana

Phytochemical study on the BuOH-soluble fraction of the stem bark of Populus davidiana resulted in the isolation of a new salicin derivative(1),named davidianoside.The structure was elucidated on the basis of extensive physicochemical and spectroscopic analyses.     

Effect of doping Ca on polaron hopping in LaSr2Mn2O7

From the transport studies in the bilayer manganites LaSr_2−x Ca _x Mn₂O₇, we have found the variable-range hopping model proposed by Viret et al to be inadequate to describe the transport of charge in these materials. The polarons appear to hop to their nearest neighbors with an activation energy, which in part is dependent on the magnetic interactions in the lattice.