PIXE analysis of human stones: Comparison with data from ICP-AES

25 human stone samples previously analyzed by inductively coupled plasma atomic emission spectroscopy /ICP-AES/ and the IAEA Animal Bone Standard Reference Material were used to evaluate trace element analysis by PIXE. Bombardment with 4 MeV protons was used for the determination of Mn, Fe, Cu, Pb, Br, Rb, Sr as well as Ca. PIXE and ICP-AES data gave correlation factors better than 0.97 for the elements Ca, Fe, Zn, Sr and Pb.     

THE PHOTOSENSITIZED FORMATION AND REACTION OF SINGLET OXYGEN, O2*(1Δ), IN AQUEOUS MICELLAR SYSTEMS

Abstract— Oxygenated aqueous solutions of methylene blue containing dispersions of sodium dodecyl sulphate micelles with solubilised diphenyl isobenzofuran were irradiated with red light and the rate of loss of furan was followed over several min. The results are consistent with a mechanism in which singlet oxygen is produced by energy transfer from methylene blue triplet in the aqueous phase, and then diffuses to and penetrates the interior of the micelles where it reacts with the furan. The competition between this process and the natural decay of the excited oxygen has been examined and a β-value of 9.7 times 10^-5 M determined which is comparable to that for the same reaction in homogeneous solvents. A model of the system is proposed and its kinetic features discussed.     

FLASH PHOTOLYSIS STUDIES OF HEMATO-AND COPRO-PORPHYRINS IN HOMOGENEOUS AND MICROHETEROGENEOUS AQUEOUS DISPERSIONS

This paper describes an experimental study of the photo properties of the triplet (T,) states of hematoporphyrin (HP) and coproporphyrin (CP), particularly in relation to their medium dependence and reactivity towards oxygen. Triplet-triplet absorption spectra of HP and CP have been determined in aqueous buffer at pH = 7.4 and in water-methanol and water-formamide mixtures. The spectra corrected for ground state contributions show major absorption peaks near 400 nm and lesser peaks near 500 nm. Extinction coefficient measurements have been made and their dependences on solvent composition investigated. Natural lifetimes of the T₁ states of HP and CP and the bimolecular quenching constants with oxygen have been determined. The quantum yields of T₁ formation are ca. 0.6 in buffer rising to 0.8 and higher in predominantly organic media. Incorporation of the porphyrins into micellar phases similarly causes φ_T, to increase. Quantum efficiencies of O^?₂ and O₂(^lΔ_g) formation have been determined for HP in buffer, some binary mixtures and micellar dispersions. Superoxide yields are low and may result from photo-ionization processes. O₂(^lΔ_g) yields are large but appear to have an unexpected dependence on the medium.     

Physicochemical Investigations on the Interaction of Surfactants and Salts with Polyvinylpyrrolidone in Aqueous Medium

Microcalorimetric investigations have been carried out onthe interaction of the surfactants sodium cholate, sodium deoxycholate, tetradecyltrimethylammonium bromide, cetyl(hexadecyl)trimethylammonium bromide, and p-tert-octylphenoxy polyoxy-ethylene ether (Triton X-100) and the salts potassium iodide, sodium benzoate, sodium bromide, and sodium salicylate with the neutral polymer polyvinylpyrrolidone (PVP). The enthalpy of dilution of the surfactants has been measured in the absence and presence of the polymer and the results are compared to determine the effect of PVP on the micellization of the surfactants and the energetics of the process. As well, the micellization activity of the surfactants in the presence of the polymer has been studied by conductometric and fluorimetric methods. The enthalpy of dilution of the salts has been measured to provide an understanding of the nature and magnitude of their interaction with PVP. Copyright 2001 Academic Press.     

Effect of Photosensitizer Delivery System and Irradiation Parameters on the Efficiency of Photodynamic Therapy of B16 Pigmented Melanoma in Mice

Abstract— Previous studies (Biolo et al., Photochem. Photobiol. 59, 362-365, 1994) showed that liposome-delivered Si(IV)-na-phthalocyanine (SiNc) photosensitizes B16 pigmented melanoma subcutaneously transplanted in C57 mice to the action of 776 nm light. However, the efficacy of the phototreatment was limited by a lack of selectivity of tumor targeting by SiNc as well as by incomplete necrosis of the neoplastic mass. The present investigations show that the use of a different delivery system (Cremophor emulsion vs liposomes of dipalmitoylphosphatidylcholine) causes no significant increase in the selectivity of tumor targeting for three injected doses of SiNc (0.5, 1, 2 mg/kg). However, upon 776 nm light irradiation (300 mW/cm²; 520 J/cm²), the delay in the rate of tumor growth was maximal (7-8 days) for the highest naphthalocyanine dose. On the other hand, a remarkable improvement in the tumor response was obtained by inducing an intratumoral temperature increase to 44°C immediately after PDT. The thermal effect appeared to be due to photoexcitation of melanin by 776 nm light (550 mW/cm²; 520 J/cm²) and subsequent partial conversion of absorbed energy into heat.     

Clustering files of chemical structures using the fuzzy k-means clustering method

This paper evaluates the use of the fuzzy k-means clustering method for the clustering of files of 2D chemical structures. Simulated property prediction experiments with the Starlist file of logP values demonstrate that use of the fuzzy k-means method can, in some cases, yield results that are superior to those obtained with the conventional k-means method and with Ward's clustering method. Clustering of several small sets of agrochemical compounds demonstrate the ability of the fuzzy k-means method to highlight multicluster membership and to identify outlier compounds, although the former can be difficult to interpret in some cases.     

Structural and spectroscopic study of reactions between chelating zinc-binding groups and mimics of the matrix metalloproteinase and disintegrin metalloprotease catalytic sites: the coordination chemistry of metalloprotease inhibition

To understand the coordination chemistry of zinc-binding groups (ZBGs) with catalytic zinc centers in matrix metalloproteinases (MMPs) and disintegrin metalloproteases (ADAMs), we have undertaken a model compound study centered around tris(3,5-methylphenypyrazolyl)hydroboratozinc(II) hydroxide and aqua complexes ([Tp(Ph,Me)ZnOH] and [Tp(Ph,Me)Zn(OH2)]+, respectively, wherein (Tp(Ph,Me))- = hydrotris(3,5-methylphenylpyrazolyl)borate) and the products of their reactions with a class of chelating Schiff's base ligands. The results show that the protic ligands, HL (HL = N-propyl-1-(5-methyl-2-imidazolyl)methanimine (5-Me-4-ImHPr), N-propyl-1-(4-imidazolyl)methanimine (4-ImHPr), and N-propyl-1-(2-imidazolyl)methanimine (2-ImHPr)), react with [Tp(Ph,Me)ZnOH] and give products with the general formula [Tp(Ph,Me)ZnL], whereas reactions with neutral aprotic ligands, L' (L' = N-propyl-1-(1-methyl-2-imidazolyl)methanimine (1-Me-2-ImPr) and N-propyl-1-(2-thiazolyl)methanimine (2-TaPr)), yield the corresponding [Tp(Ph,Me)ZnL]+ complexes. Although the phenol group of N-propyl-1-(2-hydroxyphenyl)methanimine (2-HOPhPr) is protic, this ligand forms a cationic four-coordinate complex containing an intraligand hydrogen bond. The solid-state structures of these complexes were determined by single-crystal X-ray diffraction, and the results showed that the protic ligands form five-membered chelates of the Zn2+ ion. All ligands displace the aqua ligand in [Tp(Ph,Me)Zn(OH2)]+ to yield complexes having 1H NMR spectra consistent with the formation of five membered chelates. The 1H resonance frequencies of the chelating ligands typically shift upfield upon coordination to the zinc center, due to ring current effects from the pendant phenyl groups of the (Tp(Ph,Me))- ligand. Thus, the 1H NMR spectra provide a convenient and sensitive means of tracking the solution reactions by titration. The resulting series of spectra showed that the stabilities of the chelates in solution depend on the propensity of the ligands to deprotonate upon chelation of the zinc center. The behaviors of these bidentate ZBGs provide insight into the structural and electronic factors that contribute to the stabilities of inhibited MMPs and ADAMs and suggest that the proton acidity of the coordinated ZBG may be a crucial criterion for inhibitor design.     

Cation-pi interactions with a model for the side chain of tryptophan: structures and absolute binding energies of alkali metal cation-indole complexes

Threshold collision-induced dissociation techniques are employed to determine bond dissociation energies (BDEs) of mono- and bis-complexes of alkali metal cations, Li+, Na+, K+, Rb+, and Cs+, with indole, C8H7N. The primary and lowest energy dissociation pathway in all cases is endothermic loss of an intact indole ligand. Sequential loss of a second indole ligand is observed at elevated energies for the bis-complexes. Density functional theory calculations at the B3LYP/6-31G level of theory are used to determine the structures, vibrational frequencies, and rotational constants of these complexes. Theoretical BDEs are determined from single point energy calculations at the MP2(full)/6-311+G(2d,2p) level using the B3LYP/6-31G* geometries. The agreement between theory and experiment is very good for all complexes except Li+ (C8H7N), where theory underestimates the strength of the binding. The trends in the BDEs of these alkali metal cation-indole complexes are compared with the analogous benzene and naphthalene complexes to examine the influence of the extended pi network and heteroatom on the strength of the cation-pi interaction. The Na+ and K+ binding affinities of benzene, phenol, and indole are also compared to those of the aromatic amino acids, phenylalanine, tyrosine, and tryptophan to elucidate the factors that contribute to the binding in complexes to the aromatic amino acids. The nature of the binding and trends in the BDEs of cation-pi complexes between alkali metal cations and benzene, phenol, and indole are examined to help understand nature's preference for engaging tryptophan over phenylalanine and tyrosine in cation-pi interactions in biological systems.