LOVASTATIN POTENTIATES THE PHOTOCYTOTOXIC EFFECT OF PHOTOFRIN II DELIVERED TO HT29 HUMAN COLONIC ADENOCARCINOMA CELLS BY LOW DENSITY LIPOPROTEIN

A 24 h preculture of HT29–18human colonic adenocarcinoma cells with the sterol synthesis inhibitor lovastatin at concentrations of 0.1-0.5 μM markedly increased the photocytotoxic effect of photofrin II delivered to cells by low density lipoproteins. Under the same conditions, LDL binding and photofrin II (PII) uptake by HT29 cells increased about 1.8-fold and 1.5-fold, respectively. These results suggest that hydroxymethylglutaryl-coenzyme A reductase inhibitors could be useful for potentiating the photodynamic therapy of tumors by PII.     

Comparison of several spray chambers operating at very low liquid flow rates in inductively coupled plasma atomic emission spectrometry

Four different spray chambers were evaluated in ICP-AES at very low liquid flow rates: a double-pass (Scott type), a conventional cyclonic, and two low-volume cyclonic-type spray chambers (i.e., Cinnabar and Genie). A glass concentric pneumatic micro nebulizer (Atom Mist) was used in conjunction with all four chambers. The liquid flow rate was varied from 10 to 160 microL min(-1). The conventional cyclonic spray chamber gave rise to coarser tertiary aerosols, higher analyte and solvent transport rates, higher sensitivity and lower limits of detection than the remaining ones. The low-volume spray chambers afforded analytical figures of merit similar to the double-pass one, despite their very different designs. However, these spray chambers exhibited shorter wash-out times. The matrix effects were significant only for the double-pass. This fact allowed the analysis of reference samples by employing aqueous standards at a minimum level of sample consumption. The recoveries obtained for the cyclonic spray chambers and several certified samples were close to 100%, being always lower in the case of the double-pass spray chamber.     

Tandem mobility mass spectrometry study of electrosprayed tetraheptyl ammonium bromide clusters

Multiply charged electrospray ions from concentrated solutions of Heptyl4N+Br- (designated A+B- hereafter) in formamide are analyzed mass spectrometrically (MS) following mobility selection in ambient air in a differential mobility analyzer (DMA). Most of the sharp mobility peaks seen are identified as (AB)(n)A+ clusters, with 0 < or = n < ot = 5. One anomalously abundant and mobile ion is identified as NH4+(AB)4. Six ions in the (AB)n(A+)2 series are also identified, completing and correcting earlier mobility data for singly and doubly charged ions up to masses of almost 9000 Da. The more mobile of two broad humps seen in the mobility spectrum includes m/z values approximately from 2500 up to 12,000 Da. It is formed primarily by multiply charged (AB)n(A+)z clusters with multiple ammonium bromide adducts. Because of overlapping of many peaks of different m/z and charge state z, only a few individual species can be identified by MS alone in this highly congested region. However, the spectral simplification brought about by mobility selection upstream of the MS reveals a series of broad modulations in m/z space, with all ions resolved in the second, third, ...sixth modulation being in charge states z = 2, 3, ...6, respectively. Extrapolation of this trend beyond the sixth wave fixes the ion charge state (in some cases up to z = 15) and mass (beyond m = 175,000 u). This wavy structure had been previously observed and explained in terms of ion evaporation kinetics from volatile drops, though without mass identification. All observations indicate that the clusters are formed as charged residues, but their charge state is fixed by the Iribarne-Thomson ion evaporation mechanism. Consequently, the measured curve of cluster diameter versus z yields the two parameters governing ion evaporation kinetics. Clusters with z > 1 and electrical mobility Z > 0.495 cm2/V/s are metastable and evaporate a singly charged cluster, probably (AB)2A+, between the DMA and the MS. Plotting the electrical mobilities Z of the clusters in the form (z/Z)1/2 versus m(1/3) (both proportional to cluster diameter) collapse the data for all cluster sizes and charge states into one single straight line for Z below 0.495 cm2/V/s. This linear relation reveals a uniform apparent cluster density of 0.935 g/cm3 and an effective hard-sphere diameter of the air molecules of 0.44 nm. An anomalous mobility increase is observed at diameters below 3 nm.     

Study and determination of the pesticide Imidacloprid by square wave adsorptive stripping voltammetry

The kinetics of the reaction between double stranded DNA (dsDNA) and formamide is monitored at the single DNA molecule level. We find that stretching of the DNA leads to an accelerated reaction rate and to a shift in the final equilibrium concentrations. The larger the stretching force, the faster the reaction and the larger the denatured fraction of the product DNA. The single molecule kinetics is obtained from the change in the contour length of the DNA which, in turn, is measured using optical tweezers on a microbead-single DNA molecule-cover slip construct.     

Kinetics of small ion evaporation from the charge and mass distribution of multiply charged clusters in electrosprays

The distribution of charge z and radii R in clusters electrosprayed from formamide solutions of tetraheptylammonium bromide was investigated by selecting those within a narrow range of electrical mobilities Z(1) in a first differential mobility analyzer (DMA), reducing their charge to unity by passage through a neutralizing chamber containing a radioactive (alpha) source, and measuring the mobilities Z(z) of the resulting discrete set of singly charged clusters in a second DMA. After correcting for the polarization contribution to cluster drag, the tandem DMA data yield the range of radii present at detectable levels for each charge state up to z = 9. Because small ion evaporation from electrospray drops leads to charge loss when a drop reaches a certain critical radius R(crit)(z), the measured maximum and minimum cluster radii associated with a given z can be used to infer the activation energy Delta for ion evaporation as a function of drop charge and curvature. These results confirm the Iribarne-Thomson ion-evaporation mechanism, and support earlier theoretical expressions for the functional form of Delta(z,R). The different phenomenon of ion evaporation from metastable multiply charged dry clusters is also observed at characteristic times of 1 s. Its activation energy is estimated as approximately 0.3 eV larger than for ion evaporation from the drops. This new process complicates the interpretation of the present measurements in terms of ion evaporation from liquid surfaces, but introduces no radical change in the picture. It helps understand why salt clusters with more than two or three charges are harder to see in mass spectrometers than in mobility studies under ambient conditions. Copyright 2000 John Wiley & Sons, Ltd.     

Charge-induced unfolding of multiply charged polyethylene glycol ions

The electrical mobility of mass-selected single poly(ethylene glycol) (PEG) chains of mass m (<14 kDalton) and charge state z (+1 to +5) reveals a near-spherical shape above a critical mass m(z) approximately z(2). The abrupt unfolding observed at m < m(z) shows that the polymer molecules behave as liquid drops upon reaching the Rayleigh limit, with an apparent surface energy of 0.026 N/m at ion diameters from 1.7 to 3.2 nm. Other nonspherical shape families with structures independent of charge, and with charge-dependent stability domains, are observed. Highly charged ions adopt approximately linear highly stretched configurations where the mobility depends only on m/z, independently of z. An operational definition of the surface energy of a single long chain molecule that is computable and agrees with the measured surface energy is provided.     

Selective extraction and determination of multiclass pesticide residues in post-harvest French beans by low-pressure gas chromatography/tandem mass spectrometry

A selective and reliable extraction procedure was developed and validated to determine multiclass pesticide residues in lyophilized agricultural plants by low-pressure gas chromatography coupled with tandem mass spectrometry. The method is based on a rapid and simple extraction of the lyophilized sample with dichloromethane. The results were compared with those obtained by using fresh and naturally dried samples. Slightly better recoveries and precision values were obtained for the lyophilized samples. The application of the proposed methodology was tested by analyzing French bean plants from an agricultural area of Almería (Spain). The availability of this methodology, which is capable of detecting a high number of analytes in a single analysis, has priority in analyses for a large number of pesticides used on individual commodities.     

Chemical correlation of mortonins A,C and D sesquiterpenoids from mortonia genus

The structures of mortonins A (1), C (2a) and D (3) were previously deduced from chemical transformations and spectral data. The LAH reductions of mortonin A, mortonin C and their derivatives are discussed. Structure 2a, previously proposed for mortonin C, is proved by single crystal X-ray diffraction study. The transformation of Mortonin C (2a) into Mortonin A (1) and Mortonin D (3), proves the structure and stereochemistry proposed for all of them.