The organization of chiral self-assembled monolayers (SAMs) composed of a thiol deriv. of phenylalanine on a hanging mercury drop electrode (HMDE) has been studied. Comparing the excess of surface coverage of homo and heterochiral monolayers reveals that the latter are more densely packed. This was also supported by examn. the differential capacitance and the electrochem. behavior of an outer-sphere redox couple at surfaces covered by homochiral monolayers vs. monolayers based on the racemic mixt. [on SciFinder(R)]

A highly specific and sensitive electrode for the detn. of ultra-low levels of Hg and an anal. system based on such electrode are described. The electrode is a glassy C electrode spin-coated with a monolayer of a highly sensitive reagent for the detection of Hg. The anal. method based on the use of this type of electrode is a voltammetric method. Concns. of the order of as low as ∼2 × 10-12 Mol Hg can be detected and measured. The reagent is 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]hexacosane. [on SciFinder(R)]

The deposition of gold patterns on indium-tin-oxide (ITO) with the scanning electrochem. microscope (SECM) has been accomplished by the controlled dissoln. of a gold microelectrode. The continuous anodic dissoln. of gold at the microelectrode in the presence of bromide while maintaining the potential of the ITO const. resulted in the deposition of microcryst. structures of gold. The unique advantages of the SECM made it possible to suggest a mechanism for the process based on the structures as well as the parameters that control the deposition process. [on SciFinder(R)]

The etching of silicon has been studied by the scanning electrochem. microscope (SECM) technique. Etching has been accomplished in acidic fluoride solns. by electrogenerating a strong oxidant, i.e. bromine in this case, at an ultramicroelectrode which was held closely above a silicon 〈111〉 wafer. The parameters that affect the process and control the efficiency of the silicon etching were examd. A detailed mechanism of the process, which was derived from the unique advantages of the SECM and is in agreement with previous reports, is proposed. [on SciFinder(R)]

A detailed study of the Cd(II)/Cd(Hg) system in 2-mercaptoacetic acid, H2MA, solns. was carried out in 1 M NaClO4 at pH 4.8-12.0. The electrochem. behavior of 2-mercaptoacetic acid at a dropping mercury electrode was studied as well. Since all complexes that are formed in the soln. undergo a reversible two-electron redn., math. anal. of the data, provided the compn. of the various complexes. The stability consts. of the following complexes: Cd(SCH2CO2)34-, Cd(SCH2CO2)22-, Cd(SCH2CO2), CdH(SCH2CO2)33-, CdH2(SCH2CO2)32-, CdH(SCH2CO2)2-, CdH2(SCH2CO2)2 and CdH(SCH2CO2)+ were detd. and their degree of formation as a function of pH were estd. The protonation consts. of the ligand were calcd. The H2MA forms extremely stable bidentate complexes with cadmium ions. The formation of the various complexes as a function of pH reveals that at pH 10.7-12.0 the complex Cd(SCH2CO2)34- predominates, whereas at pH 4.8-6.0 the complexes CdH2(SCH2CO2)2 and CdH(SCH2CO2)+ are dominant. At pH 6.1-10.6 different protonated and unprotonated complexes, composed of one to three ligands, coexist. [on SciFinder(R)]

Selective electrodes are electrochem. probes which are sensitive toward specific species. Most of these probes can be divided into two categories, i.e. potentiometric and voltammetric, based on the nature of the measurement. The major challenge is designing a selective electrode is introducing selectivity. The ultimate limit of their selectivity should make it possible to det. the levels of the analyte in unpolluted sea water. Through this manuscript two different approaches have been used as a means of developing voltammetric selective electrodes for heavy metals. The first concept involves the application of electrodes modified with crown ethers analogs. A selective electrode for gold ions was assembled by attaching an aza crown ether onto a glassy carbon surface. On the other hand an extremely sensitive electrode for mercury ions was developed based on a cryptand. Levels of mercury lower than 1 ppt could easily be detected using this probe. The electrode has been successfully applied for studying the release of mercury from dental amalgam. The second approach involves the formation of self-assembled monolayers with high affinity toward specific species. As an example, a selective electrode for cadmium ions is described. The electrode is made of ω-mercaptocarboxylic acid, HS(CH2)nCO2H, monolayers on mercury or gold surfaces. The detection limit of this electrode is 4 x 20̅12 M which is less than 1 ppt. The electrodes have been carefully studied and the parameters that govern their sensitivity as well as selectivity were optimized. Our major conclusion from this research is that very selective and sensitive probes can be developed by architecturing the solid-liq. interface at the mol. level. [on SciFinder(R)]