This is a report on the kinetics of the destruction and formation processes of the 6-thioguanine self-assembled monolayer (6TG SAM) on a mercury electrode from acid solutions by chronoamperometry. The destruction of the 6TG SAM that has been previously formed under open circuit potential conditions is carried out by stepping the potential from an initial value where the chemisorbed layer is stable up to potentials where the molecules are no longer chemisorbed. The destruction of the SAM has been described by a model that involves three types of contributions: (i) a Langmuir-type adsorption process, (ii) a 2D nucleation mechanism followed by a growth controlled by surface diffusion, and (iii) a 2D nucleation mechanism followed by a growth at a constant rate. The nonlinear fit of the experimental transients by using this procedure allows the quantitative determination of the individual contributions to the overall process. The kinetics of the formation process is studied under electrochemical conditions. The chronoamperometric experiment allows us to monitor the early stages of 6TG SAM formation. The implications of the physisorbed state at low potentials in the type of monolayer formation and destruction processes as well as the influence of temperature are also discussed.
Download full-text PDF |
Source |
|---|---|
| http://dx.doi.org/10.1021/jp046642g | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Comparison of three methods for measuring thiopurine methyltransferase activity in red blood cells and human leukemia cells.
J Chromatogr B Analyt Technol Biomed Life Sci
November 2013
Department of Medicine, Clinical Pharmacology Unit, Karolinska Institutet, Karolinska University Hospital, SE-171 76 Stockholm, Sweden. Electronic address:
Thiopurine efficacy is partly reflected by the genetic polymorphism of the thiopurine methyltransferase (TPMT) enzyme, which is responsible for variation in the metabolism, toxicity and therapeutic efficacy of the thiopurines azathioprine (AZA), 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG). Determination of TPMT activity before administration of thiopurines is thus crucial for individualized dosing in order to prevent toxicity in TPMT deficient individuals. These individuals must be treated with markedly lower (eg, 5-10% of the standard) doses of the prescribed medications.
View Article and Find Full Text PDFThe effect of thiopurine drugs on DNA methylation in relation to TPMT expression.
Biochem Pharmacol
October 2008
Leukaemia Research Group, Northern Institute for Cancer Research, Newcastle University, Newcastle upon Tyne NE2 4HH, UK.
The thiopurine drugs 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG) are well-established agents for the treatment of leukaemia but their main modes of action are controversial. Thiopurine methyltransferase (TPMT) metabolises thiopurine drugs and influences their cytotoxic activity. TPMT, like DNA methyltransferases (DNMTs), transfers methyl groups from S-adenosylmethionine (SAM) and generates S-adenosylhomocysteine (SAH).
View Article and Find Full Text PDFFormation and dissolution processes of the 6-thioguanine (6TG) self-assembled monolayer. A kinetic study.
J Phys Chem B
February 2005
Departamento de Química Física y Termodinamica Aplicada, Universidad de Córdoba, Campus de Rabanales, Ed. Marie Curie, E-14071 Córdoba, Spain.
This is a report on the kinetics of the destruction and formation processes of the 6-thioguanine self-assembled monolayer (6TG SAM) on a mercury electrode from acid solutions by chronoamperometry. The destruction of the 6TG SAM that has been previously formed under open circuit potential conditions is carried out by stepping the potential from an initial value where the chemisorbed layer is stable up to potentials where the molecules are no longer chemisorbed. The destruction of the SAM has been described by a model that involves three types of contributions: (i) a Langmuir-type adsorption process, (ii) a 2D nucleation mechanism followed by a growth controlled by surface diffusion, and (iii) a 2D nucleation mechanism followed by a growth at a constant rate.
View Article and Find Full Text PDFInhibition of thiopurine S-methyltransferase activity by impurities in commercially available substrates: a factor for differing results of TPMT measurements.
Eur J Clin Pharmacol
June 1999
Department of Pharmacology, Lübeck Medical University, Germany.
Objectives: Thiopurine S-methyltransferase (TPMT) activity, when measured in red blood cells (RBC) with a recently published TPMT activity assay using 6-thioguanine (6-TG) as substrate, could not be reproduced in another laboratory. We investigated factors which could influence the results of the TPMT activity measurement.
Methods: We tested twelve 6-TG and four 6-mercaptopurine (6-MP) compounds from different suppliers as substrates and determined the enzyme kinetic parameters Km and Vmax.
Thiopurine S-methyltransferase activity in human erythrocytes: a new HPLC method using 6-thioguanine as substrate.
Eur J Clin Pharmacol
May 1998
Department of Pharmacology, Lübeck Medical University, Germany.
Objectives: To develop a non-radioactive assay to measure thiopurine S-methyltransferase (TPMT) activity. The assay was used to study the distribution of TPMT activity in a healthy German population.
Methods: The assay is based on the conversion of 6-thioguanine (6-TG) to 6-methylthioguanine (6-MTG) using non-radiolabelled S-adenosyl-L-methionine (SAM) as the methyl donor.
Want AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!