A Study of the Uptake of Toluidine Blue O by Porphyromonas gingivalis and the Mechanism of Lethal Photosensitization

The purpose of the study was to determine the distribution of the photosensitizer toluidine blue O (TBO) within Porphyromonas gingivalis and the possible mechanism(s) involved in the lethal photosensitization of this organism. The distribution of TBO was determined by incubating P. gingivalis with tritiated TBO (³H-TBO) and fractionating the cells into outer membrane (OM), plasma membrane (PM), cytoplasmic proteins, other cytoplasmic constituents and DNA. The percentage of TBO in each of the fractions was found to be, 86.7, 5.4, 1.9, 5.7 and 0.3%, respectively. The involvement of cytotoxic species in the lethal photosensitization induced by light from a helium-neon (HeNe) laser and TBO was investigated by using deuterium oxide (D₂O), which prolongs the lifetime of singlet oxygen, and the free radical and singlet oxygen scavenger L-tryptophan. There were 9.0 log₁₀ and 2 log₁₀ reductions in the presence of D₂O and H₂O (saline solutions), respectively, at a light dose of 0.44 J (energy density = 0.22 J/cm²), suggesting the involvement of singlet oxygen. Decreased kills were attained in the presence of increasing concentrations of L-tryptophan. The effect of lethal photosensitization on whole cell proteins was determined by measuring tryptophan fluorescence, which decreased by 30% using 4.3 J (energy density = 4.3 J/ cm²) of light. Effects on the OM and PM proteins were determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. There was evidence of change in the molecular masses of several PM proteins and OM proteins compared to controls. There was evidence of damage to the DNA obtained from irradiated cells. Scanning electron microscopic studies showed that there was coaggre-gation of P. gingivalis cells when sensitized and then exposed to laser light. These results suggest that lethal photosensitization of P. gingivalis may involve changes in OM and/or PM proteins and DNA damage mediated by singlet oxygen.     

Effect of Dosimetric and Physiological Factors on the Lethal Photosensitization of Porphyromonas gingivalis in vitro

The aims of this study were to (1) determine the effect of dosimetric and physiological factors on the lethal photosensitization of Porphyromonas gingivalis using tolui-dine blue O (TBO) and light from a helium/neon (HeNe) laser; (2) determine the influence of sensitizer concentration, preirradiation time, serum and growth phase on sensitizer uptake by P. gingivalis. The dosimetric factors studied were concentration of TBO, light dose and preirradiation time. The physiological factors were presence of serum, pH and bacterial growth phase. Sensitizer uptake by P. gingivalis under various conditions was determined using tritiated TBO (³H-TBO). In the presence of TBO, a light dose-dependent increase in kill was attained (100% kill at 4.4 J). There was no significant effect on the numbers killed when TBO was increased from 12.5 to 50 µg/mL. An increase in preirradiation time gave slightly increased kills. High kills were achieved at all three pH (6.8–8.0). Although kills were substantial in the presence of serum, they were significantly less than those obtained in the presence of saline. Cells in all three growth phases were susceptible to lethal photosensitization, although stationary phase cells were slightly less susceptible. Maximum uptake of TBO occurred within 60 s and uptake in serum was less than in saline. The uptake by the log phase cells was greater at lower concentrations of sensitizer (50 µg/mL), compared to the other two phases.     

Synthesis of ferrites: Thermal analysis of some transition metal tris(maleato)ferrates(III)

Thermal analysis of some transition metal ferrimaleate precursors, M₃[Fe(mal)₃]₂·xH₂O (M=Mn, Co, Ni, Cu) has been studied in static air atmosphere from ambient to 600°C. Various physico-chemical techniques, i.e. TG, DTG, DTA, XRD, IR, Mössbauer spectrometry, have been employed to characterize both the intermediates and final products. After dehydration the anhydrous precursors undergo decomposition to yield an iron(II) intermediate, M[Fe^II(mal)₂] (M=Mn, Co, Ni, Cu) in the temperature range 160-275°C. A subsequent oxidative decomposition of iron(II) species leads to the formation of -Fe₂O₃ and MO in the successive stages. Finally a solid-state reaction occurs between the oxides above 400°C resulting in the formation of transition metal ferrites, MFe₂O₄. The ferrites have been obtained at much lower temperature and in less time than in the conventional ceramic method.This revised version was published online in November 2005 with corrections to the Cover Date.     

Metal-Doped Barium Sulphate Nanoparticles Decorated with Gelatin as Antibacterial Agents

Journal of Cluster Science - Nanoparticles are gaining a new impetus in the field of medicine because of their potential to overcome core problems of drug efficacy. Amongst inorganic nanoparticles,...     

One‐pot Regioselective Synthesis of Novel 1‐N‐Methyl‐spiro[2,3′]oxindole‐spiro[3,3″]‐1″‐N‐arylpyrrolidine‐2″,5″‐dione‐4‐arylpyrrolidines through Multicomponent 1,3‐Dipolar Cycloaddition Reaction of Azomethine Ylide

An atom economic and facile synthesis of novel dispiro–oxindole–pyrrolidines has been achieved via a three‐component tandem cycloaddition of azomethine ylide generated in situ from isatin and sarcosine by decarboxylative condensation with N‐aryl‐3‐benzylidene‐pyrrolidine‐2,5‐dione derivatives as dipolarophiles. The salient features of synthetic procedure are characterized by the mild reaction conditions, high yields, high regioselectivity and stereoselectivity, one‐pot procedure, and operational simplicity. This regioselectivity was assumed to be under the influence of π–π stacking interactions between the aromatic rings of azomethine ylide and N‐aryl‐3‐benzylidene‐pyrrolidine‐2,5‐diones that further control the exo–endo selectivity of the reaction 1,3‐dipolar cycloaddition. The regiochemistry and structures of the cycloadducts were determined with spectroscopic data.     

The synergistic co‐operation of N—H…O=P hydrogen bonds and C—H…OX weak intermolecular interactions (X is =P or —C) in the (CH3O)2P(O)(NH–NHC6F5) amidophosphoester: a combined X‐ray crystallographic and theoretical study

The asymmetric unit of O,O′‐dimethyl [(2,3,4,5,6‐pentafluorophenyl)hydrazinyl]phosphonate, C₈H₈F₅N₂O₃P, is composed of two symmetry‐independent molecules with significant differences in the orientations of the C₆F₅ and OMe groups. In the crystal structure, a one‐dimensional assembly is mediated from classical N—H…O hydrogen bonds, which includes R₂²(8), D(2) and some higher‐order graph‐set motifs. By also considering weak C—H…O=P and C—H…O—C intermolecular interactions, a two‐dimensional network extends along the ab plane. The strengths of the hydrogen bonds were evaluated using quantum chemical calculations with the GAUSSIAN09 software package at the B3LYP/6‐311G(d,p) level of theory. The LP(O) to σ*(NH) and σ*(CH) charge‐transfer interactions were examined according to second‐order perturbation theory in natural bond orbital (NBO) methodology. The hydrogen‐bonded clusters of molecules, including N—H…O and C—H…O interactions, were constructed as input files for the calculations and the strengths of the hydrogen bonds are as follows: N—H…O [R₂²(8)] > N—H…O [D(2)] > C—H…O. The decomposed fingerprint plots show that the contribution portions of the F…H/H…F contacts in both molecules are the largest.     

Link quandles are residually finite

Monatshefte für Mathematik - Residual finiteness is known to be an important property of groups appearing in combinatorial group theory and low dimensional topology. In a recent work (Bardakov...     

Preparation of magnesium and calcium ferrites from the thermolysis of M3[Fe(cit)2]2·xH2O precursors

Magnesium and calcium ferrites have been prepared from the thermolysis of M₃[Fe(C₆H₅O₇)₂]₂·xH₂0 (M=Mg, Ca) precursors. Thermal decomposition of the precursors has been studied employing various physico-chemical techniques, i.e., TG-DSC, XRD, IR and Mössbauer spectroscopy. After dehydration the anhydrous precursors undergo an abrupt oxidative pyrolysis to yield α-Fe₂O₃ and a metastable acetone-dicarboxylate intermediate. A subsequent exothermic decomposition leads to the formation of MgO and CaCO₃ from the respective intermediates. Finally ferrite is formed as a result of solid state reaction between MO/MCO₃ and α-Fe₂O₃. Nanosized ferrites of the stoichiometry MgFe₂O₄ and Ca₂Fe₂O₅ have been obtained from magnesium and calcium bis(citrato) ferrates(III). The temperature of ferrite formation is much lower than possible in conventional ceramic method. The results have been compared with the respective oxalate and maleate precursors.     

The thermolysis of zinc bis(citrato)ferrate(III) dodecahydrate

The thermolysis of zinc bis(citrato)ferrate(III)dodehydrate has been investigated from ambient temperature to 600 °C using various physico-chemical techniques, i.e., simultaneous TG-DTG-DTA, XRD, Mössbauer and I.R. spectroscopy. After dehydration at 200 °C, the anhydrous complex undergoes oxidative decomposition to yield -Fe₂O₃ and ZnO at 350 °C. Subsequently, the cations remix to yield fine particles of zinc ferrite, ZnFe₂O₄ as a result of solid state reaction between -Fe₂O₃ and ZnO at a temperature (450 °C) much lower than for ceramic method.