Optimization of a liquid chromatographic separation for the simultaneous determination of four anthracyclines and their respective 13-S-dihydro metabolites

The optimization of a liquid chromatographic separation of four anthracyclines (doxorubicin, epirubicin, daunorubicin and idarubicin) and their respective 13-S-dihydro metabolites (doxorubicinol, epirubicinol, daunorubicinol and idarubicinol) is described. Inclusion of epidaunorubicin in the assay allows internal standardization. Potential chromatographic interference of aglycones (doxorubicinone, daunorubicinone, idarubicinone, doxorubicinolone, daunorubicinolone and idarubicinolone) was investigated and tackled. The analyses were performed on a C18 RP column and gradient elutions were performed with a mixture of 0.1% formic acid in water and 0.1% formic acid in ACN. The analytes were measured by fluorescence detection with an excitation wavelength of 480 nm and emission wavelength of 555 nm, respectively. The separation will potentially allow a broad field of applications, ranging from therapeutic drug monitoring and kinetic studies in cancer patients to monitoring hospital personnel and effluents.     

Separation of purine and pyrimidine bases by ion chromatography with direct conductivity detection

A simple, rapid and accurate method for the simultaneous determination of four purine and pyrimidine bases (cytosine, 5-methylcytosine, adenine and N6-methyladenine) has been developed. The quantitative determination of these bases was accomplished by ion chromatography (IC) with direct conductivity detection (CD) based on their ionization in acidic medium without chemical suppression. The recovery of cytosine, 5-methylcytosine, and adenine in calf thymus DNA was more than 98% (n=3) and the relative standard deviation (RSD, n=5) less than 2.4%. In a single chromatographic run, the four bases could be separated and determined in less than 10 min. The detection limits were found to be 0.05 microg/mL for cytosine, 0.08 microg/mL for 5-methylcytosine, 0.07 microg/mL for adenine, and 0.07 microg/mL for N6-methyladenine. Linear ranges were 0.2-95.1 microg/mL for cytosine (r2=0.9996), 0.3-196.6 microg/mL for 5-methylcytosine (r2=0.9994), 0.3-105.5 microg/mL for adenine (r2=0.9998), and 0.3-159.1 microg/mL for N6-methyladenine (r2=0.9999). With the proposed method, purine and pyrimidine bases could be successfully detected in calf thymus DNA. We also determined these bases in calf thymus DNA using RP-HPLC. Compared to RP-HPLC, the IC method offers advantages such as high selectivity and simple mobile phase.     

Characterization of organosulfates from the photooxidation of isoprene and unsaturated fatty acids in ambient aerosol using liquid chromatography/(-) electrospray ionization mass spectrometry

In the present study, we have characterized in detail the MS(2) and MS(3) fragmentation behaviors, using electrospray ionization (ESI) in the negative ion mode, of previously identified sulfated isoprene secondary organic aerosol compounds, including 2-methyltetrols, 2-methylglyceric acid, 2-methyltetrol mononitrate derivatives, glyoxal and methylglyoxal. A major fragmentation pathway for the deprotonated molecules of the sulfate esters of 2-methyltetrols and 2-methylglyceric acid and of the sulfate derivatives of glyoxal and methylglyoxal is the formation of the bisulfate [HSO(4)](-) anion, while the deprotonated sulfate esters of 2-methyltetrol mononitrate derivatives preferentially fragment through loss of nitric acid. Rational interpretation of MS(2), MS(3) and accurate mass data led to the structural characterization of unknown polar compounds in K-puszta fine aerosol as organosulfate derivatives of photooxidation products of unsaturated fatty acids, i.e. 2-hydroxy-1,4-butanedialdehyde, 4,5- and 2,3-dihydroxypentanoic acids, and 2-hydroxyglutaric acid, and of alpha-pinene, i.e. 3-hydroxyglutaric acid. The deprotonated molecules of the sulfated hydroxyacids, 2-methylglyceric acid, 4,5- and 2,3-dihydroxypentanoic acid, and 2- and 3-hydroxyglutaric acids, showed in addition to the [HSO(4)](-) ion (m/z 97) neutral losses of water, CO(2) and/or SO(3), features that are characteristic of humic-like substances. The polar organosulfates characterized in the present work are of climatic relevance because they may contribute to the hydrophilic properties of fine ambient aerosol. In addition, these compounds probably serve as ambient tracer compounds for the occurrence of secondary organic aerosol formation under acidic conditions.     

Cationic Si−H−Si Bridges in Polysilanes: Their Detection and Targeted Formation in Stable Ion Studies

The ionization of 1,1‐dihydridocyclopentasilane 7 has been found to yield the cyclic polysilanylsilyl cation 8 instead of the expected hydrogen‐substituted silylium ion 6 . The silyl cation 8 is stabilized by the formation of an intramolecular Si?H?Si bridge, which also provides the thermodynamic driving force for its formation. In general, the preference for the formation of Si?H?Si bridges can be used to scavenge and identify transient intermediates in the Lewis acid induced rearrangement of polysilanes. The validity of this concept has been demonstrated for one central step in this chemistry, the ring‐contraction reaction of cyclohexasilanes to form silylcyclopentasilanes.     

High-density targeting of a viral multifunctional nanoplatform to a pathogenic, biofilm-forming bacterium

Nanomedicine directed at diagnosis and treatment of infections can benefit from innovations that have substantially increased the variety of available multifunctional nanoplatforms. Here, we targeted a spherical, icosahedral viral nanoplatform to a pathogenic, biofilm-forming bacterium, Staphylococcus aureus. Density of binding mediated through specific protein-ligand interactions exceeded the density expected for a planar, hexagonally close-packed array. A multifunctionalized viral protein cage was used to load imaging agents (fluorophore and MRI contrast agent) onto cells. The fluorescence-imaging capability allowed for direct observation of penetration of the nanoplatform into an S. aureus biofilm. These results demonstrate that multifunctional nanoplatforms based on protein cage architectures have significant potential as tools for both diagnosis and targeted treatment of recalcitrant bacterial infections.     

The influence of surface states on in-plane-gated structures

A model for in-plane-gated structures is proposed, taking into account surface currents and surface charges. The lateral band structures and barrier heights are calculated self-consistently for different bias voltages utilizing this new model. Accumulated negative surface charges lead to a strongly increased depletion length at the positively biased side of the lateral barriers. Most of the applied bias drops in this depleted region and does not affect the barrier height. We have found good agreement between these theoretical results and experimentally determined barrier heights and depletion lengths obtained from temperature-dependent current measurements and optical-beam-induced current measurements.     

Effect of Chain Length on the Adsorption Behavior of n-Alkanes in Ferrierite

¹³ C NMR spectroscopy and computer simulations have shown that the chain length of hydrocarbons has a surprising effect on where these molecules reside in the zeolite FER. Propane and butane can access the entire two-dimensional channel structure, while hexane only the one-dimensional substructure. This difference has important consequences for the catalytic activity and explains some of the experimental observations.     

Synthetic Activators of Cell Migration Designed by Constructive Machine Learning

Constructive machine learning aims to create examples from its learned domain which are likely to exhibit similar properties. Here, a recurrent neural network was trained with the chemical structures of known cell-migration modulators. This machine learning model was used to generate new molecules that mimic the training compounds. Two top-scoring designs were synthesized, and tested for functional activity in a phenotypic spheroid cell migration assay. These computationally generated small molecules significantly increased the migration of medulloblastoma cells. The results further corroborate the applicability of constructive machine learning to the de novo design of druglike molecules with desired properties.