Real-space measurement of the potential distribution inside organic semiconductors

We demonstrate that the soft nature of organic semiconductors can be exploited to directly measure the potential distribution inside such an organic layer by scanning-tunneling microscope (STM) based spectroscopy. Keeping the STM feedback system active while reducing the tip-sample bias forces the tip to penetrate the organic layer. From an analysis of the injection and bulk transport processes it follows that the tip height versus bias trace obtained in this way directly reflects the potential distribution in the organic layer.     

Search for new heavy particles in the WZ0 final state in pp collisions at square root[s] = 1.8 TeV

We present the first general search for new heavy particles, X, which decay via X --> WZ0 --> e(nu)+jj as a function of M(X) and Gamma(X) in pp collisions at square root[s] = 1.8 TeV. No evidence is found for production of X in 110 pb(-1) of data collected by the Collider Detector at Fermilab. General cross section limits are set at the 95% C.L. as a function of mass and width of the new particle. The results are further interpreted as mass limits on the production of new heavy charged vector bosons which decay via W' --> WZ0 in an extended gauge model as a function of the width, Gamma(W'), and mixing factor between the W' and the standard model W bosons.     

Longitudinal focusing and cooling of a molecular beam

A neutral polar molecule experiences a force in an inhomogeneous electric field. This electric field can be designed such that a beam of polar molecules is exposed to a harmonic potential in the forward direction. In this potential the longitudinal phase-space distribution of the ensemble of molecules is rotated uniformly. This property is used to longitudinally focus a pulsed beam of ammonia molecules and to produce a beam with a longitudinal velocity spread of 0.76 m/s, corresponding to a temperature of 250 mu K.     

Structure determination of gas-phase niobium and tantalum carbide nanocrystals via infrared spectroscopy

Niobium and tantalum carbide clusters have been isolated in the gas phase and irradiated with intense tunable infrared (IR) light. Stable neutral clusters are selectively ionized and subsequently detected in a mass spectrometer. By tuning the IR frequency, infrared multiphoton absorption spectra are obtained for a whole range of clusters. These mass-selective IR spectra lead to insights into the structures of small niobium and tantalum carbide clusters and nanocrystals.     

Diffuse-reflectance spectroscopy from 500 to 1060 nm by correction for inhomogeneously distributed absorbers

Diffuse-reflectance spectroscopy for measurement of the absorption and scattering coefficients of biological tissue produces reliable results for wavelengths from 650 to 1050 nm. Implicitly, this approach assumes homogeneously distributed absorbers. A correction factor is introduced for inhomogeneous distribution of blood concentrated in discrete cylindrical vessels. This factor extends the applicability of diffusion theory to lower wavelengths. We present measurements of in vivo optical properties in the wavelength range 500-1060 nm.     

Speciation of arsenic in coarse and fine urban aerosols using sequential extraction combined with liquid chromatography and atomic fluorescence detection

An analytical procedure for speciation of As in urban aerosol samples was developed. The aerosols were collected by sequential filtration through membrane filters. Part of each filter was investigated by INAA for the total amount of As. Another part of the filters was treated by a sequential extraction procedure to differentiate between water-extractable, phosphate-extractable and refractory chemical forms. Water-extractable forms were further differentiated into anionic As species by HPLC-HGAFS. Extractability of As into water exhibited a clear dependency on the aerosol size fraction (12% in coarse fraction and 50% in fine fraction). Dependency of the phosphate extractable As on the aerosol size fraction seems not to be significant (10-15% in both size fractions). The remaining amount, i.e., about 78% of the coarse As and about 40% of the fine As was considered to be refractory or environmentally immobile As. Water-extractable As forms could only be attributed to arsenate.     

Amperometric biosensor based on D-aminoacid oxidase for the R-perindopril assay

A new amperometric biosensor based on D-aminoacid oxidase is described for the assay of R-perindopril. R-perindopril can be determined in the 400-20 nmol/L concentration range; the detection limit is 10 nmol/L. The selectivity was checked with S-perindopril, D- and L-proline, and polyvinylpyrrolidone. The main interfering species was D-proline. An automated system for the assay of R-perindopril based on the concept of flow injection with an amperometric biosensor (based on D-aminoacid oxidase) as detector is also described. The system is suitable for the on-line monitoring of R-perindopril at a sampling rate of 72 samples/h, in the linear range: 100 nmol/L -20 nmol/L with an RSD better than 0.09% (n = 10).     

Catalysis of the addition of benzenethiol to 2-cyclohexen-1-ones by uranyl-salophen complexes: a catalytic metallocleft with high substrate specificity

The base induced addition of benzenethiol to 2-cyclohexen-1-one and its 4,4-, 5,5- and 6,6-dimethyl derivatives is catalysed by a salophen-uranyl based metallocleft 2 in chloroform solution with high turnover efficiency and low product inhibition. Analysis of rate data coupled with equilibrium measurements for complexation of the catalyst with the enone reactants and addition products shows that the catalytic mechanism involves the three main steps typical of single-substrate enzymatic processes, namely substrate binding and recognition, transformation of the bound substrate, and release of the reaction product. Unlike the reference salophen-uranyl 1, catalyst 2 is endowed with a structured binding site responsible for a high degree of substrate specificity among the investigated enones, due to recognition of their shape and size.     

Optimization of capillary electrophoretic separation of several inhibitors of the angiotensin-converting enzyme

Capillary electrophoretic separation of eight inhibitors of the angiotensin-converting enzyme, viz., enalapril, lisinopril, quinapril, fosinopril, perindopril, ramipril, benazepril and cilazapril, was investigated with respect to the following parameters: pH of the running buffer, organic modifiers and surfactants. The most critical parameter is the pH of the running buffer. The addition of sodium dodecyl sulfate had a negative influence on the peak symmetry, and selectivity was not improved. The separation of the eight compounds can be performed by means of two phosphate buffers (each 100 mM) at pH 7.0 and pH 6.25, respectively. This combination is necessary for the selective identification of structurally related substances because of their similar pKa values.