KINETIC ANALYSIS OF THE PHOTOREACTION (365 nm) BETWEEN PSORALEN AND DNA

Abstract— Psoralen complexed with DNA under irradiation at 365 nm forms monofunctional and bifunctional adducts with pyrimidine bases of DNA. while the fraction of psoralen which remains free in the aqueous solution forms photodimer and photooxidation products. We havc studied the photoreaction betwecn psoralen and DNA from a kinetic point of view. Only some products of this photoreaction could be measured quantitatively. Thus. in order to present a picture of the overall photoreaction. we have represented this by a mathematical model consisting of a system of seven differential equations. Utilizing all the experimental data that it was possible to obtain. we were able to estimate rate constants for formation of all photoproducts. From the general picture thus obtained. we conclude that monofunctional adducts are formed in a four to one ratio to bifunctional adducts. Among the monofunctional photoproducts. 3,4-cycloadducts occur with a higher yield than 4',5'-cycloadducts. The combined rate constant of formation of photodimer and photooxidation products of psoralen is small. indicating that they are marginal by-products relative to the cycloadducts formed in the photoreactions with DNA.     

Structural and optical characterizations of rare earth pentaphosphates LnP5O14 (Ln = La, Gd) synthesized by the sol–gel process

The sol–gel chemistry route has successfully been used to prepare samples of LnP₅O₁₄ (Ln = La, Gd) pentaphosphates from lanthanides chlorides and phosphorous pentoxide dissolved in isopropanol. Crystallized powders of single phase were obtained after calcination of gels at 350 °C. The structural characterizations of materials were investigated by means of X-ray diffraction as well as infrared and Raman spectroscopies, whereas their thermal behavior has been studied by differential thermal analyse and thermogravimetric analyses. Powders morphology was analyzed by means of scanning electron microscopy and laser granulometry. The photoluminescence properties of the Eu³⁺ ions in sol–gel derived LaP₅O₁₄ and GdP₅O₁₄ samples were investigated and compared with homologous samples synthesized by the conventional solid state reaction.     

How to handle nanomaterials? The re-entry of individuals into the philosophy of chemistry

In this paper we will argue that the categories of physical individuals and chemical stuff are not sufficient to face the chemical ontology if nanomaterials are taken into account. From a perspective that considers ontological questions and wonders which the items involved in science are, we will argue that the domain of nanoscience must be considered as populated by entities that are neither individuals, as those of physics, nor stuff, as those items of macro-chemistry. This discussion, in virtue of the analysis of the nature of nanomaterials, leads to propose a proper ontological category for nanoparticles: nanoindividuals. Nanomaterials are sorts of individuals, but they are different from physical individuals and from chemical stuff. We will also claim to contribute to the growing field of the philosophy of chemistry, especially regarding discussions that manifest not only epistemological but also ontological issues. In this scenario, the field on nanoscience is particularly challenging.     

Metal-ligand solution equilibria studied by electrospray ionization mass spectrometry: effect of instrumental parameters

Electrospray ionization mass spectrometry (ESI-MS) is being increasingly employed in the study of metal-ligand equilibria in aqueous solution. In the present work, the ESI-MS spectral changes due to different settings of the following instrumental parameters are analyzed: the solution flow rate (F(S)), the nebulizer gas flow rate (F(G)), the sprayer potential (E), and the temperature of the entrance capillary (T). Twenty-eight spectra were obtained for each of six samples containing aluminum(III) and 2,3-dihydroxypyridine at various pH, in the absence or in the presence of a buffer and of sodium ions. Among the considered instrumental parameters, T produced the largest effects on the ionic intensities. F(S) and F(G) affected the ESI-MS spectra to a lower extent than T. In the investigated conditions E had the weakest effects on the spectra.The correlations observed between the ionic intensities and these instrumental parameters were interpreted considering the presence of three kinds of perturbations occurring in the ESI-MS ion source: formation of some dimers in the droplets, different transfer efficiencies from the droplets to the gas phase for different complexes (according to their surface activity), and subsequent partial thermal decomposition of the dimers and of one of the monomeric complexes in the gas phase. Our results show that the evaluation of the effects produced in the ESI-MS spectra by a change of instrumental parameters can allow to identify the perturbations occurring when metal-ligand solutions are studied by ESI-MS.     

Mechanistic investigation on 2-aza-spiro[4,5]decan-3-one formation from 1-(aminomethyl)cyclohexylacetic acid (gabapentin)

The intramolecular cyclization of the amino acid gabapentin has been studied in the pH range 2.24-11.15 at 80 °C in buffered solutions and constant ionic strength, and monitoring the progress of the process by fluorimetric method and proton NMR spectroscopy. From the profile of log k₀ versus pH two different acid-base equilibria are involved. The maximum rate is observed above pH 9.80 and the minimum rate has been measured between pH 5.15 and 6.21. The pK_a1 and pK_a2 have been determined by potentiometric titration to be 3.72 and 9.37, respectively. The buffer effect and the solvent kinetic isotopic effect suggest that the reaction is subject to general acid and general base catalysis. The process is sensitive to the gabapentin concentration (pH 10.45) and the pseudo-first order rate constant decrease with increasing the reagent concentration above 5.50×10⁻² M.     

Smoothness of holonomy covers for singular foliations and essential isotropy

Given a singular foliation, we attach an “essential isotropy” group to each of its leaves, and show that its discreteness is the integrability obstruction of a natural Lie algebroid over the leaf. We show that a condition ensuring discreteness is the local surjectivity of a transversal exponential map associated with the maximal ideal of vector fields prescribed to be tangent to the foliation. The essential isotropy group is also shown to control the smoothness of the holonomy cover of the leaf (the associated fiber of the holonomy groupoid), as well as the smoothness of the associated isotropy group. Namely, the (topological) closeness of the essential isotropy group is a necessary and sufficient condition for the holonomy cover to be a smooth (finite-dimensional) manifold and the isotropy group to be a Lie group. These results are useful towards understanding the normal form of a singular foliation around a compact leaf. At the end of this article we briefly outline work of ours on this normal form, to be presented in a subsequent paper.     

Synthesis of the syn and anti isomer of 1,4,5,8,9,12-hexahydro-2,3,6,7,10,11-hexamethylidene-1,4:5,8:9,12-trimethano triphenylene and Diels-Alder reactivity of the syn isomer

The title compounds, new members in the class of tris-annelated benzenes with [2.2.1] bicyclic rings, were obtained in high yields by coupling of 2-bromo-3-trimethyltin-5,6-dimethylenenorborn-2-ene with copper(I) 2-thiophenecarboxylate (CuTC). The syn isomer was reacted with 3 equiv. of the dienophiles TCNE, DMAD, PTAD and norbornadiene to afford the corresponding cycloadducts.     

Development of a method for simultaneous analysis of PCDDs, PCDFs, PCBs, PBDEs, PCNs and PAHs in Antarctic air

The development of a unique analytical method for the determination of five classes of persistent organic pollutants (POPs) in atmospheric gas and the particle phase through gas chromatography coupled to high-resolution mass spectrometry is presented. Every step of the pre-analytical and analytical optimization process is described. Great effort was put into simplifying the traditional techniques, with reference to EPA and literature methods. Automated instruments were used for sample extraction and cleanup in order to enhance repeatability and reduce contamination risks. Unlike most common approaches, no separation of the analytes was performed before the GC analysis in order to avoid sample fractionation and to save time and materials. This allowed low instrumental and method detection limits (pg to sub-pg) to be achieved. Accuracy and precision were tested by fortifying the matrix and analysing standard reference materials (NIST SRM 1649b Urban Dust and 2585 Organic Contaminants in House Dust). The method was applied to five samples from Terra Nova Bay, Antarctica. Concentrations of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs), polychlorinated biphenyls (PCBs), polychlorinated naphthalenes (PCNs), polybrominated diphenyl ethers (PBDEs) and polycyclic aromatic hydrocarbons (PAHs) are presented. Lighter compounds dominate the distribution and are mainly present in the gaseous phase. The observed pattern may be attributable to long-range transport. Results are in general agreement with literature data, where available.     

On the geometry of prequantization spaces

Given a Poisson (or more generally Dirac) manifold P$P$, there are two approaches to its geometric quantization: one involves a circle bundle Q$Q$ over P$P$ endowed with a Jacobi (or Jacobi–Dirac) structure; the other one involves a circle bundle with a (pre)contact groupoid structure over the (pre)symplectic groupoid of P$P$. We study the relation between these two prequantization spaces. We show that the circle bundle over the (pre)symplectic groupoid of P$P$ is obtained from the Lie groupoid of Q$Q$ via an S¹$S^1$ reduction that preserves both the Lie groupoid and the geometric structures.