The Experts below are selected from a list of 30 Experts worldwide ranked by ideXlab platform
Ronald Paul Gee - One of the best experts on this subject based on the ideXlab platform.
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emulsion polymerization of dimethylcyclosiloxane in cationic emulsion mechanism study utilizing two phase liquid liquid Reaction kinetics
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2015Co-Authors: Ronald Paul GeeAbstract:Abstract Dimethylcyclosiloxane emulsion polymerization (EP) was studied using heterogeneous two phase liquid–liquid kinetic theory combined with particle size measurements during Reaction. A typical octamethylcyclotetrasiloxane EP was found to have a Reaction Half-Life of about 1400 sec; much greater than the time (less than about 10 sec) for the cyclosiloxane to diffuse through the droplet surface into the aqueous phase. Previously published research proposing a mechanism where the cyclosiloxane EP begins by opening the cyclosiloxane ring at the droplet surface appears improbable because a Reaction Half-Life less than a few seconds would be required. The aqueous solubility of D4, D5 and D6 was determined as a function of temperature. Most significantly; the rate of Reaction of these cyclosiloxanes in EP was then determined to be a linear function of their aqueous solubility at the Reaction temperature. Dimethylcyclosiloxane EP was determined to fully conform to the four characteristics of two phase heterogeneous liquid–liquid Reaction kinetics wherein the Reaction occurs in the aqueous phase. The kinetic rate equation was developed and the effect of cyclosiloxane mass transfer limitations on Reaction rate was shown. (The influence of mass transfer limitations can give an erroneous appearance that Reaction occurs at the droplet surface.) Evidence is presented that polymerization of cyclosiloxane in micelles is not favorable. The mechanism of cyclosiloxane emulsion polymerization was concluded to be coagulative homogeneous nucleation in the aqueous phase.
Alexander C Drohat - One of the best experts on this subject based on the ideXlab platform.
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defining the impact of sumoylation on substrate binding and catalysis by thymine dna glycosylase
Nucleic Acids Research, 2018Co-Authors: Christopher T Coey, Alexander C DrohatAbstract:: Thymine DNA glycosylase (TDG) excises thymine from mutagenic G·T mispairs generated by deamination of 5-methylcytosine (mC) and it removes two mC derivatives, 5-formylcytosine (fC) and 5-carboxylcytosine (caC), in a multistep pathway for DNA demethylation. TDG is modified by small ubiquitin-like modifier (SUMO) proteins, but the impact of sumoylation on TDG activity is poorly defined and the functions of TDG sumoylation remain unclear. We determined the effect of TDG sumoylation, by SUMO-1 or SUMO-2, on substrate binding and catalytic parameters. Single turnover experiments reveal that sumoylation dramatically impairs TDG base-excision activity, such that G·T activity is reduced by ≥45-fold and fC and caC are excised slowly, with a Reaction Half-Life of ≥9 min (37°C). Fluorescence anisotropy studies reveal that unmodified TDG binds tightly to G·fC and G·caC substrates, with dissociation constants in the low nanomolar range. While sumoylation of TDG weakens substrate binding, the residual affinity is substantial and is comparable to that of biochemically-characterized readers of fC and caC. Our findings raise the possibility that sumoylation enables TDG to function, at least transiently, as reader of fC and caC. Notably, sumoylation could potentially facilitate TDG recruitment of other proteins, including transcription factors or epigenetic regulators, to these sites in DNA.
Rajendra Rathore - One of the best experts on this subject based on the ideXlab platform.
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From Wires to Cables: Attempted Synthesis of 1,3,5-Trifluorenylcyclohexane as a Platform for Molecular Cables
2016Co-Authors: Marat R. Talipov, Sameh H. Abdelwahed, Khushabu Thakur, Scott A. Reid, Rajendra RathoreAbstract:Multiple molecular wires braided together in a single assembly, termed as molecular cable, are promising next-generation materials for effective long-range charge transport. As an example of the platform for constructing molecular cables, 1,3,5-trifluorenylcyclohexane (TFC) and its difluorenyl analogues (DFCs) were systematically investigated both experimentally (X-ray crystallography) and theoretically (DFT calculations). Although the syntheses of DFCs were successfully achieved, the synthesis of TFC, which involved a similar intramolecular Friedel–Crafts cyclization as the last step, was unsuccessful. An exhaustive study of the conformational landscape of cyclohexane ring of TFC and DFCs revealed that TFC is a moderately strained molecule (∼17 kcal/mol), and computational studies of the Reaction profile show that this steric strain, present in the transition state, is responsible for the unusually high (∼5 years) Reaction Half-Life. A successful synthesis of TFC will require that the steric strain is introduced in multiple steps, and such alternative strategies are being currently explored
Marat R. Talipov - One of the best experts on this subject based on the ideXlab platform.
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From Wires to Cables: Attempted Synthesis of 1,3,5-Trifluorenylcyclohexane as a Platform for Molecular Cables
2016Co-Authors: Marat R. Talipov, Sameh H. Abdelwahed, Khushabu Thakur, Scott A. Reid, Rajendra RathoreAbstract:Multiple molecular wires braided together in a single assembly, termed as molecular cable, are promising next-generation materials for effective long-range charge transport. As an example of the platform for constructing molecular cables, 1,3,5-trifluorenylcyclohexane (TFC) and its difluorenyl analogues (DFCs) were systematically investigated both experimentally (X-ray crystallography) and theoretically (DFT calculations). Although the syntheses of DFCs were successfully achieved, the synthesis of TFC, which involved a similar intramolecular Friedel–Crafts cyclization as the last step, was unsuccessful. An exhaustive study of the conformational landscape of cyclohexane ring of TFC and DFCs revealed that TFC is a moderately strained molecule (∼17 kcal/mol), and computational studies of the Reaction profile show that this steric strain, present in the transition state, is responsible for the unusually high (∼5 years) Reaction Half-Life. A successful synthesis of TFC will require that the steric strain is introduced in multiple steps, and such alternative strategies are being currently explored
Christopher T Coey - One of the best experts on this subject based on the ideXlab platform.
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defining the impact of sumoylation on substrate binding and catalysis by thymine dna glycosylase
Nucleic Acids Research, 2018Co-Authors: Christopher T Coey, Alexander C DrohatAbstract:: Thymine DNA glycosylase (TDG) excises thymine from mutagenic G·T mispairs generated by deamination of 5-methylcytosine (mC) and it removes two mC derivatives, 5-formylcytosine (fC) and 5-carboxylcytosine (caC), in a multistep pathway for DNA demethylation. TDG is modified by small ubiquitin-like modifier (SUMO) proteins, but the impact of sumoylation on TDG activity is poorly defined and the functions of TDG sumoylation remain unclear. We determined the effect of TDG sumoylation, by SUMO-1 or SUMO-2, on substrate binding and catalytic parameters. Single turnover experiments reveal that sumoylation dramatically impairs TDG base-excision activity, such that G·T activity is reduced by ≥45-fold and fC and caC are excised slowly, with a Reaction Half-Life of ≥9 min (37°C). Fluorescence anisotropy studies reveal that unmodified TDG binds tightly to G·fC and G·caC substrates, with dissociation constants in the low nanomolar range. While sumoylation of TDG weakens substrate binding, the residual affinity is substantial and is comparable to that of biochemically-characterized readers of fC and caC. Our findings raise the possibility that sumoylation enables TDG to function, at least transiently, as reader of fC and caC. Notably, sumoylation could potentially facilitate TDG recruitment of other proteins, including transcription factors or epigenetic regulators, to these sites in DNA.
