Phototoxic effect of visible light on Porphyromonas gingivalis and Fusobacterium nucleatum: an in vitro study

The antibacterial effect of visible light irradiation combined with photosensitizers has been reported. The objective of this was to test the effect of visible light irradiation without photosensitizers on the viability of oral microorganisms. Strains of Porphyromonas gingivalis, Fusobacterium nucleatum, Streptococcus mutans and Streptococcus faecalis in suspension or grown on agar were exposed to visible light at wavelengths of 400-500 nm. These wavelengths are used to photopolymerize composite resins widely used for dental restoration. Three photocuring light sources, quartz-tungsten-halogen lamp, light-emitting diode and plasma-arc, at power densities between 260 and 1300 mW/cm2 were used for up to 3 min. Bacterial samples were also exposed to a near-infrared diode laser (wavelength, 830 nm), using identical irradiation parameters for comparison. The results show that blue light sources exert a phototoxic effect on P. gingivalis and F. nucleatum. The minimal inhibitory dose for P. gingivalis and F. nucleatum was 16-62 J/cm2, a value significantly lower than that for S. mutans and S. faecalis (159-212 J/cm2). Near-infrared diode laser irradiation did not affect any of the bacteria tested. Our results suggest that visible light sources without exogenous photosensitizers have a phototoxic effect mainly on Gram-negative periodontal pathogens.     

Effect of Groundwater Composition on Arsenic Detection by Bacterial Biosensors

A luminescent bacterial biosensor was used to quantify bioavailable arsenic in artificial groundwater. Its light production above the background emission was proportional to the arsenite concentration in the toxicologically relevant range of 0 to 0.5 μM. Effects of the inorganic solutes phosphate, Fe(II) and silicate on the biosensor signal were studied. Phosphate at a concentration of 0.25 g L⁻¹ phosphate slightly stimulated the light emission, but much less than toxicologically relevant concentrations of the much stronger inducer arsenite. No effect of phosphate was oberved in the presence of arsenite. Freshly prepared sodium silicate solution at a concentration of 10 mg L⁻¹ Si reduced the arsenite-induced light production by roughly 37%, which can be explained by transient polymerization leading to sequestration of some arsenic. After three days of incubation, silicate did not have this effect anymore, probably because depolymerization occurred. In the presence of 0.4 mg L⁻¹ Fe(II), the arsenite-induced light emission was reduced by up to 90%, probably due to iron oxidation followed by arsenite adsorption on the less soluble Fe(III) possibly along with some oxidation to the stronger adsorbing As(V). Addition of 100 μM EDTA was capable of releasing all arsenic from the precipitate and to transform it into the biologically measurable, dissolved state. The biosensor also proved valuable for monitoring the effectiveness of an arsenic removal procedure based on water filtration through a mixture of sand and iron granules.     

Das Verhalten des 2,4,6-Tri-tert.butylphenyllithiums gegenüber Halogensilanen. Bildung und Umwandlung des Trichlorsilyllithiums,LiSiCl3

The Behaviour of 2,4,6-Tri-tert.butylphenyllithium towards Halosilanes. Formation and Conversion of Trichlorosilyllithium, LiSiCl₃ Trichlorosilyllithium, LiSiCl₃ 2 , is formed as the result of a fast metal halogen exchange reaction at ?78°C in THF between 2,4,6-tri-tert.butylphenyllithium 1 or mesityllithium and bromotrichlorosilane. Also the interaction of 1 with trichlorosilane gives 2 after partial deprotonation of HSiCl₃. 2 is not isolated; it's existence in the THF solution is proved by protonation or deuteration, resp., and by identification of the HSiCl₃ or DSiCl₃ formed that way by means of ¹H-NMR or infrared spectroscopy. Attempts to react 2 with various electrophiles failed; also efforts to trapp dichlorosilylene, the expected decomposition product of 2 , by isoprene, were unsuccessful. Studies of the thermal decomposition of LiSiCl₃–THF solutions led to the identification of polychloropolysilanes and of insertion products of SiCl₂ in tetrahydrofuran.     

Trapping of random walks on the line

Several features of the trapping of random walks on a one-dimensional lattice are analyzed. The results of this investigation are as follows: (1) The correction term to the known asymptotic form for the survival probability ton steps is O(( ₂n)^–1/3), where =–ln(1–c), andc is the trap concentration. (2) The short time form for the survival probability is found to be exp[–a(c)n ^1/2], wherea(c) is given in Eq. (21). (3) The mean-square displacement of a surviving random walker is found to go liken ^2/3for largen. (4) When the distribution of trap-free regions is changed so that very large regions are much rarer than for ideally random trap placement the asymptotic survival probability changes its dependence onn. One such model is studied.     

Structures of the Intermediate Complexes in Friedel-Crafts Acylations

Addition compounds of Lewis acids MX_n and acyl halides R? COX occur as intermediates in Friedel-Crafts acylations. IR and NMR studies on these intermediates have indicated the probable existence of structural isomers. In X-ray structural analysis, it is possible to distinguish two forms, i.e. the molecular form, in which the compounds are present as donor-acceptor complexes R? CXO→MX_n, and the ionic form, in which they can be formulated as oxocarbenium salts [R? CO]⁺[MX_n+1]^?. The compounds of the donor-acceptor type R? CXO→MX_n are characterized by the formation of a coordinate oxygen-metal bond; the transfer of electrons from the oxygen to the metal of the acceptor is always due to a weak donor-acceptor interaction. The positive charge of the aryloxocarbenium ions is partly delocalized over the aromatic nucleus. The positive charge in alkyloxocarbenium ions, on the other hand, is essentially localized on the carbon atom of the carbonyl group, as is confirmed by electron density distribution calculations.     

Die Glykoside der Samen von Dregea volubilis (L.) BENTH. ex HOOK. 2. Mitt. Isolierung weiterer Drevogenine Glykoside und Aglykone, 277. Mitteilung

A total of fifteen substances were identified through thin-layer chromatography, after mild acid hydrolysis of the chloroform extract from the seeds of Dregea volubilis (L.) BENTH . ex HOOK . Of these fifteen substances, eight (B, D, P, O; U, V, H and T) were isolated in crystalline form. Two of these were identical with the known genins drevogenin B (B) and drevogenin D (D). Drevogenin P (P) and the unknown substance O (probably a genin) were isolated for the first time. U proved to be identical with D -cymarose, V with the biose U1 obtained from Asclepias lilacina, and H with (+)-methyl-pachybioside. T was not investigated (probably a sugar derivative).     

A theory of pseudo-differential boundary value problems with discontinuous conditions I

Summary The paper deals with mixed boundary value problems and transmission problems for elliptic differential and pseudo-differential operators. These problems are considered as elements of an algebra (where is the considered domain, x=, YX a submanifold of codimension 1, where the conditions have a jump, and x is a certain compactification of X/Y), the elements of which are described on a symbolic level. By means of additional conditions (of trace and potential type, with respect to Y) a given mixed problem is extended to an operator, and the Fredholm property of is established under an ellipticity condition, the parametrix is constructed on symbolic level and ind is expressed. In the second part the authors also study classes of special cases, namely differential operators of second and higher order with mixed boundary conditions for dim 2, where explicit index expressions are derived.     

Über metall-alkyl- und -aryl-verbindungen: XVII. Die kristallstruktur des kaliumhydridotrimethylaluminats,K[AlH(CH3)3]

K[AlH(CH₃)₃] is formed by decomposition of K[Al(CH₃)₃SiH₃] in diethyl ether. The compound crystallizes in the orthorhombic space group Cmca with the lattice parameters a = 9.647, b = 17.332, c = 7.711 Å. There are eight formula units in the unit cell. Analogously to K[Al(CH₃)₄] the hydrido compound contains isolated anions with a tetrahedral coordination of aluminium by hydrogen and three methyl groups.