Sorption of three types of dissolved organic matter (DOM; i.e., humic acid, peptone and alpha-phenylalanine) by a mutiwalled carbon nanotube (MWNT40) and sorption of phenanthrene (Phen), naphthalene (Naph), and 1-naphthol (1-Naph) by the original and DOM-coated MWNT40 were examined. Sorption data of Phen, Naph, and 1-Naph by all sorbents were fitted with Freundlich and Polanyi models. MWNT40 had nonlinear isotherms for all DOMs examined. Sorption of DOMs by MWNT40 followed the order peptone > humic acid > alpha-phenylalanine. The humic acid used in this study had much lower sorption for Phen, Naph, and 1-Naph than MWNT40, but its coating did not make striking changes on sorption of these compounds by MWNT40, suggesting that humic acid coating dramatically altered the physical form and surface properties of MWNT40. Peptone coating made the strongest suppression on sorption of Phen, Naph, and 1-Naph by MWNT40 among the three DOMs used, due to its highest sorption on MWNT40, thus causing a great reduction in accessibility of sorption sites. Polanyi modeling results showed that reduction in the maximum volume sorption capacity (Q0) of MWNT40 induced by DOM coating followed the order Phen < Naph < 1-Naph. 1-Naph was less hydrophobic than Phen and Naph but it had much higher sorbed volume (V(m)) than Phen and Naph at individual RT In(S(w)/C(e))/V(s)points for all sorbents. The correlation curve for the Polanyi model was applicable for sorption of aromatic compounds of similar structure by the original and DOM-coated carbon nanotubes.

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Endonuclease V is a deoxyinosine 3'-endonuclease which initiates removal of inosine from damaged DNA. A thermostable endonuclease V from the hyperthermophilic bacterium Thermotoga maritima has been cloned and expressed in Escherichia coli. The DNA recognition and reaction mechanisms were probed with both double-stranded and single-stranded oligonucleotide substrates which contained inosine, abasic site (AP site), uracil, or mismatches. Gel mobility shift and kinetic analyses indicate that the enzyme remains bound to the cleaved inosine product. This slow product release may be required in vivo to ensure an orderly process of repairing deaminated DNA. When the enzyme is in excess, the primary nicked products experience a second nicking event on the complementary strand, leading to a double-stranded break. Cleavage at AP sites suggests that the enzyme may use a combination of base contacts and local distortion for recognition. The weak binding to uracil sites may preclude the enzyme from playing a significant role in repair of such sites, which may be occupied by uracil-specific DNA glycosylases. Analysis of cleavage patterns of all 12 natural mismatched base pairs suggests that purine bases are preferrentially cleaved, showing a general hierarchy of A = G > T > C. A model accounting for the recognition and strand nicking mechanism of endonuclease V is presented.