Mechanistic study on demulsification of water-in-diluted bitumen emulsions by ethylcellulose.

In our previous study, ethylcellulose (EC), an effective, nontoxic, and biodegradable natural polymer, was found effective in dewatering water-in-diluted bitumen emulsions. In this study, the demulsification mechanism of water-in-diluted bitumen emulsions by EC is investigated. In situ experiments using a micropipet apparatus provided direct evidence on both flocculation and coalescence of water droplets in diluted bitumen by EC. The addition of EC was found to decrease naphtha-diluted bitumen-water interfacial tension significantly. At the molecular level, AFM imaging revealed disruption of the continuous interfacial films formed from surface-active components of bitumen by EC. Our study clearly indicates that the demulsification by EC is through both flocculation and coalescence of water droplets, attained by competitive adsorption of EC at the oil-water interface and disruption of the original protective interfacial films formed from the surface-active components of bitumen.

Patterning of cantilevers with inverted dip-pen nanolithography: efforts toward combinatorial AFM.

We report patterning of AFM cantilevers by inverted dip-pen nanolithography, thereby markedly enhancing the development of combinatorial AFM as a high-throughput force-measuring instrument capable of determining interactions between opposing libraries of biomolecules.

Dissimilar mispair-recognition spectra of Arabidopsis DNA-mismatch-repair proteins MSH2*MSH6 (MutSalpha) and MSH2*MSH7 (MutSgamma).

Besides orthologs of other eukaryotic mismatch-repair (MMR) proteins, plants encode MSH7, a paralog of MSH6. The Arabidopsis thaliana recognition heterodimers AtMSH2*MSH6 (AtMutSalpha) and AtMSH2*MSH3 (AtMutSbeta) were previously found to bind the same subsets of mismatches as their counterparts in other eukaryotes--respectively, base-base mismatches and single extra nucleotides, loopouts of extra nucleotides (one or more) only--but AtMSH2*MSH7 (AtMutSgamma) bound well only to a G/T mismatch. To test hypotheses that MSH7 might be specialized for G/T, or for base mismatches in 5-methylcytosine contexts, we compared binding of AtMutSalpha and AtMutSgamma to a series of mismatched DNA oligoduplexes, relative to their (roughly similar) binding to G/T DNA. AtMutSgamma bound G/G, G/A, A/A and especially C/A mispairs as well or better than G/T, in contrast to MutSalpha, for which G/T was clearly the best base mismatch. The presence of 5-methylcytosine adjacent to or in a mispair generally lowered binding by both heterodimers, with no systematic difference between the two. Alignment of protein sequences reveals the absence in MSH7 of the clamp domains that in bacterial MutS proteins--and by inference MSH6 proteins--non-specifically bind the backbone of mismatched DNA, raising new questions as to how clamp domains enhance mismatch recognition. Plants must rigorously suppress mutation during mitotic division of meristematic cells that eventually give rise to gametes and may also use MMR proteins to antagonize homeologous recombination. The MSH6 versus MSH7 divergence may reflect specializations for particular mismatches and/or sequence contexts, so as to increase both DNA-replication and meiotic-recombination fidelity, or dedication of MSH6 to the former and MSH7 to the latter, consistent with genetic evidence from wheat.