"SUNLIGHT"-INDUCED MAMMALIAN CELL KILLING: A COMPARATIVE STUDY OF ULTRAVIOLET AND NEAR-ULTRAVIOLET INACTIVATION

Abstract— We have examined the relationship between the survival curves obtained with UV light (254 nm) and those obtained with a near-UV sburce (Westinghouse Sun Lamps, FS20) simulating sunlight for cultured Chinese hamster cells, C3H mouse cells, and HeLa cells. In no case do the "sunlight" survival curves have the same shape as the UV survival curves. Also, the combined lethal effects of UV and near-UV, sunlight-like exposures are not entirely additive. Hence, we conclude that (1) the cell-killing photolesions induced by these radiations are at most only partly the same, and (2) in view of (I), caution should be exercised in predicting near UV-induced dose-dependencies of other end points based upon observations with UV.     

DNA SINGLE-STRAND LESIONS DUE TO ''SUNLIGHT'' AND UV LIGHT: A COMPARISON OF THEIR INDUCTION IN CHINESE HAMSTER AND HUMAN CELLS, AND THEIR FATE IN CHINESE HAMSTER CELLS

Abstract— It has been shown that the lethal properties of germicidal UV light (254 nm) and sunlight-simulating near UV light are qualitatively different (Elkind et al ., 1978). Further to compare these two radiations, the induction of single-strand DNA breaks (i.e. frank breaks plus alkali-labile lesions) was measured in two cell lines. Equal numbers of breaks in Chinese hamster cells require a dose of UV 5.5% of a near UV dose but in HeLa cells a UV dose of 7.6% of a near-UV dose is required. The rate of break production by these radiations is about 1/10-th of that due to X-rays when a comparison is made on an equal killing dose basis. The inventory of breaks in Chinese hamster cells was also followed and was found to be characteristically different for UV compared to near UV light. These data indicate that significant differences exist, at a molecular level, in the effects produced by ultraviolet and sunlight-simulating light, and further emphasize the need for caution in attempting to extrapolate from observed molecular or biological effects due to the former to those to be expected from the latter.     

Flocculation of colloidal clay by bacterial polysaccharides: effect of macromolecule charge and structure

The molecular mechanism of montmorillonite flocculation by bacterial polysaccharides was investigated, with special emphasis on the effect of carboxylic charges in the macromolecules on the mechanisms of interaction with the clay surface. An indirect way to quantify the energy of interaction was used, by comparing the flocculation ability of variously acidic polysaccharides. Data on tensile strength of aggregates in diluted suspension were collected by timed size measurements in the domain 0.1-600 microm, using laser diffraction. The flow behavior of settled aggregates was studied by rheology measurements. Flocculation of colloidal clay suspension by polysaccharides requires cancelling of the electrostatic repulsions by salts, which allows approach of clay surfaces close enough to be bridged by adsorbing macromolecules. The amount of acidic charges of the polysaccharides, and especially their location in the molecular structure, governs the bridging mechanism and the resulting tensile strength of the aggregates. The exposure of carboxylate groups located on side chains strongly promotes flocculation. In turn, charges located on the backbone of the polysaccharide are less accessible to interaction, and the flocculation ability of such polysaccharides is lowered. Measurements at different pH indicate that adsorption of acidic polysaccharides occurs via electrostatic interactions on the amphoteric edge surface of clay platelets, whereas neutral polysaccharides rather adsorb via weak interactions. Increased tensile strength in diluted aggregates due to strong surface interactions results in proportionally increased viscosity of the concentrated aggregates.     

Interaction of monovalent and divalent counterions with some carboxylic polysaccharides

Eleven samples of carboxylic polysaccharides were studied. The activity coefficients γ have been measured for monovalent (Na⁺) and divalent (Ca²⁺) counterions. There is no specific influence of the structure of the chain on γ values. Agreement with theoretical values confirms the rigidity of the chain; for low charge density, the theoretical treatment seems to be incorrect. Selectivity is discussed in term of selectivity coefficient K and free energy of exchange ΔG; ΔG is linearly related to the charge density but K which characterizes the competition of the two counterions is sensitive to the nature of the chain. The carboxymethylamyloses present a larger selectivity whose origin is not discussed here. The last point treated is the intrinsic constant of dissociation of polyacids. The pK₀ values are practically independent of the nature of the polyelectrolyte and of the charge density; the values are close to the pK₀ of monomeric unit and are not affected by the position of ? COOH in the anhydroglucose ring.     

Conformational and stereoelectronic control in ring-transformations of cis-4,5-dialkoxytetrahydropurine-2,6,8-triones

Divergent acid-catalysed ring-openings of 4,5-dimethoxytetrahydropurine-2,6,8-triones 2 at position 4, yielding 1-(5-methoxyhydantoin-5-carbonyl)ureas 4 (R⁷ = Me) or 5-methoxy-5-ureido-2,4,6-pyrimidinetriones 5 (R⁷ = H), can be rationalized by assuming a preference for one of two conformational isomers of the cis-fused system, associated with the N-substitution effects. Intramolecular transamidation 5 → 4 presumably occurs via a bicyclic acid aminal type intermediate 3 , heretofore misassigned as the reaction product. A curious base-catalysed rearrangement was encountered with the 5 (R¹ = R³ = Me, R⁷ = H) cases, which afforded 5-methoxy-1,5-bis(methylaminocarbonyl)hydantoins 7 . Remarkable stability of the conformationally rigid propellane type 4,5-ethylenedioxytetrahydropurine-2,6,8-triones 9 toward acids, shows that the mode of ring-opening at position 4 is controlled by powerful Stereoelectronic factors. However, an alternative ring-opening at the 1,6-bond has occurred on heating aqueous solutions of 9a (R⁷ = H); the ensuing decarboxylative rearrangement leads to 1,3-dimethylallantoin ( 12 ) and its precursor, 1-(2-hydroxyethoxy)-2,4-dimethyl-3,7-dioxo-2,4,6,8-tetraazabicyclo[3.3.0]octane( 11 ).     

Stabilization effect of single-walled carbon nanotubes on the functioning of photosynthetic reaction centers

The interaction between single-walled carbon nanotubes and photosynthetic reaction centers purified from purple bacterium Rhodobacter sphaeroides R-26 has been investigated. Atomic force microscopy studies provide evidence that reaction center protein can be attached effectively to the nanotubes. The typical diameter of the nanotube is 1-4 nm and 15 +/- 2 nm without and with the reaction centers, respectively. Light-induced absorption change measurements indicate the stabilization of the P+(Q(A)Q(B))- charge pair, which is formed after single saturating light excitation after the attachment to nanotubes. The separation of light-induced charges is followed by slow reorganization of the protein structure. The stabilization effect of light-initiated charges by the carbon nanotubes opens a possible direction of several applications, the most promising being in energy conversion and storage devices.     

Logarithmic Intertwining Operators and Vertex Operators

This is the first in a series of papers where we study logarithmic intertwining operators for various vertex subalgebras of Heisenberg and lattice vertex algebras. In this paper we examine logarithmic intertwining operators associated with rank one Heisenberg vertex operator algebra M(1) _a , of central charge 1 − 12a ². We classify these operators in terms of depth and provide explicit constructions in all cases. Our intertwining operators resemble puncture operators appearing in quantum Liouville field theory. Furthermore, for a = 0 we focus on the vertex operator subalgebra L(1, 0) of M(1)₀ and obtain logarithmic intertwining operators among indecomposable Virasoro algebra modules. In particular, we construct explicitly a family of hidden logarithmic intertwining operators, i.e., those that operate among two ordinary and one genuine logarithmic L(1, 0)-module.