DNA-protein cross-linking: model systems for pyrimidine-aromatic amino acid cross-linking

[reaction: see text] We have synthesized simple model systems to explore the possibility of photo-cross-linking between the pyrimidine bases and the side chains of the aromatic amino acids. Thymine/phenylalanine and thymine/tyrosine models gave cross-links, and thymine/tryptophan models gave complex mixtures; the cytosine/phenylalanine model was unreactive. The quantum yields for the model cross-linking reactions were 18-46 times smaller than those for thymine dimer formation. Biphotonic excitation contributes little to the yield of these reactions.     

Determination of the collisionally activated dissociation of a substituted indole by orthogonal acceleration quadrupole time-of-flight mass spectrometry

The use of orthogonal acceleration quadrupole time-of-flight (Q-TOF) mass spectrometry to determine the collisionally activated dissociation (CAD) of a test compound 1-(3-[5-[1,2,4-triazol-4-yl]-1H-indol-3-yl]propyl)-4-(2-[3-fluorophenyl]ethyl)piperazine is described. At unit-mass resolution the identity of many ions is ambiguous because of the complexity of the resulting product ion spectrum. Using the high resolution capabilities of the Q-TOF instrument, exact masses for each fragment were determined. These data were used to infer molecular formulas for each fragment through software interpretation and, by further applying chemical intuition, the majority of ions were fully assigned. Additionally, by utilizing in-source fragmentation at high cone voltage, analyses of second-generation products allowed derivation of a consistent sequential fragmentation pathway. This study clearly demonstrates the power of Q-TOF mass spectrometry to elucidate complex product ion spectra.     

Physical quantification of the biological effectiveness of ionizing radiations

The role, and limitations, of the fundamental physical quantities used in our current system of dosimetry for the protection of individuals against the hazardous effects of ionizing radiation is discussed briefly. A major limitation is the inability to correlate biological data, in a unified way, as a function of linear energy transfer with the consequent necessity for quality factors. From consideration of the various interaction processes undergone by charged particles in the equilibrium slowing down spectra generated by the incident radiation field, it is shown that good correlation of biological effects, for all radiation types, can be achieved in terms of linear primary ionization. The implication is that delta-ray effects play at most a very minor role, at moderate fluences, and that, consequently, the absorbed dose is an unsuitable parameter for describing radiation effects. Structure in the radiosensitive targets is observed to have a critical dimension of about 2 nm. It occurs only when double-stranded DNA is present and the magnitude of the inactivation probability is consistent with double-stranded breaks being the significant lesion. Calculation is made of the yield of lesions as a function of the mean free path for primary ionization. Differential spectra of radiation quality are obtained for monoenergetic electrons (0.2 keV to 30 MeV); for characteristic X-rays from carbon, aluminium, neon, potassium, copper, silver, and tungsten; for 50 kV X-rays, 250 kV X-rays, ²⁴¹Am, ¹³⁷Cs, and ⁶⁰Co gamma rays; and for neutrons with energies between 0.1 and 50 MeV. Damage by electrons is shown to be predominant at the ends of their tracks between 50 and 200 eV, whereas this is not so for the proton recoil spectrum generated by neutrons above 1 MeV. Proposals are made for a unified system of dosimetry that is independent of radiation type and that obviates the need for quality factors. The method is thought to be of general applicability to irradiations by nuclides incorporated into mammalian cells, by ingested emitters, and by external sources.     

Implementation of enhanced correlation maps in near infrared chemical images: Application in pharmaceutical research

Recent developments in Hyperspectral Imaging equipment have made possible the use of this analytical technique for fast scanning of sample surfaces. This technique has turned out to be especially useful in Pharmacy, where information about the distribution of the components in the surface of a tablet can be obtained. One particular application of Hyperspectral Chemical Imaging is the search for singularities inside pharmaceutical tablets, e.g. coating defects. Nevertheless, one problem has to be faced: how to analyze a sample without any previous knowledge about it, or having only the minimum information about the tablet.In this work a new methodology, based on correlation coefficients, is introduced to obtain valuable information about one Hyperspectral Image (detection of defects, punctual contaminants, etc.) without any previous knowledge. The methodology combines Principal Component Analysis (PCA), correlation coefficient between one specific pixel included in the image and the rest of the image; and a new enhanced contrast function to obtain more selective chemical and spatial information about the image. To illustrate the applicability of the proposed methodology, real tablets of ibuprofen have been studied.The proposed methodology is presented as a control technique to detect batch variability, defects in final tablets and punctual contaminants, being a potential supplementary tool for quality controls. In addition, the usefulness of the proposed methodology is not exclusive to NIR-CI devices, but to any hyperspectral and multivariate image system.     

Ferritin and metallothionein: dangerous liaisons

Ferritin (Ft) interaction with the Zn-complexes of mammalian MT1, MT2 and MT3 metallothioneins (MT) leads to simultaneous Fe(II) and Zn(II) release.     

Generation of supercontinuum radiation in conventional single-mode fibre and its application to broadband absorption spectroscopy

High-pulse-energy supercontinuum radiation with a width exceeding 900 nm in the near-infrared spectral region has been generated in conventional single-mode fibre. The fibre was pumped at 1064 nm which is in the normal dispersion regime, resulting in predominantly red-shifted spectral broadening. Supercontinuum pulse energies exceeding 450 nJ were obtained. The use of conventional fibre allows for inexpensive generation of near-infrared supercontinuum radiation, featuring high pulse energies and good spatial beam quality. This supercontinuum radiation was used to acquire high-resolution (15 pm) broadband absorption spectra of H₂O, C₂H₂ and C₂H₄ in the near-infrared spectral region (1340–1700 nm), using an optical spectrum analyser for detection. H₂O spectra were also recorded at high repetition rates, by dispersing the supercontinuum pulses and detecting the transmitted signal in the time domain. A spectral resolution of 38 pm was obtained employing the dispersed supercontinuum pulses, which is comparable to the H₂O line widths at ambient conditions. PACS 07.07.Df; 42.62.Fi; 42.79.Nv; 42.81.-i     

Ferritin as a photocatalyst and scaffold for gold nanoparticle synthesis

The ferrihydrite mineral core of ferritin is a semi-conductor capable of catalyzing oxidation/reduction reactions. This report shows that ferritin can photoreduce AuCl₄ ⁻ to form gold nanoparticles (AuNPs). An important goal was to identify innocent reaction conditions that prevented formation of AuNPs unless the sample was illuminated in the presence of ferritin. TRIS buffer satisfied this requirement and produced AuNPs with spherical morphology with diameters of 5.7 ± 1.6 nm and a surface plasmon resonance (SPR) peak at 530 nm. Size-exclusion chromatography of the AuNP–ferritin reaction mixture produced two fractions containing both ferritin and AuNPs. TEM analysis of the fraction close to where native ferritin normally elutes showed that AuNPs form inside ferritin. The other peak eluted at a volume indicating a particle size much larger than ferritin. TEM analysis revealed AuNPs adjacent to ferritin molecules suggesting that a dimeric ferritin–AuNP species forms. We propose that the ferritin protein shell acts as a nucleation site for AuNP formation leading to the AuNP-ferritin dimeric species. Ferrihydrite nanoparticles (~10 nm diameter) were unable to produce soluble AuNPs under identical conditions unless apo ferritin was present indicating that the ferritin protein shell was essential for stabilizing AuNPs in aqueous solution.     

Polymerization of ethylene catalyzed by diethylaluminum chloride and titanium (III) acetylacetonate

Catalysts for the polymerization of ethylene were prepared from titanium (III) acetylacetonate and diethylaluminum chloride. Titanium (III) acetylacetonate is of interest because it is soluble in hydrocarbon solvents used as polymerization media. As its oxidation product oxobisacetylacetonatotitanium (IV) is also hydrocarbon-soluble, this system provides a vehicle for studying the effects of a change in valence on catalyst activity without an accompanying change of state, as occurs with titanium halides. Relatively high molar ratios (>20:1) of aluminum alkyl to titanium compound were required to give active catalysts. Precipitates generally formed in the catalyst mixtures, although dilute catalyst solutions in which no precipitate was visible still initiated polymerization. Catalyst mixtures were observed to undergo certain changes on standing. Light-scattering studies indicated an increase in catalyst particle size, and a gas identified as ethane was evolved. These changes were accompanied by a reduction in activity of the catalyst. Parallel polymerization tests were run for a comparison of catalysts prepared from titanium(III) acetylacetonate and catalysts prepared from oxobisacetylacetonatotitanium(IV). There was essentially no difference in yield or properties of polymer prepared using the two catalyst systems. The evidence suggests that both the trivalent and tetravalent titanium compounds yield the same catalytic intermediate when reacting with diethylaluminum chloride.