Effect of chloride ions on the adsorption of 3-mercapto-1-propanesulfonic acid and bis(3-sulfopropyl)-disulfide on a Au(111) surface.

In situ scanning tunneling microscopy (STM) and cyclic voltammetry (CV) were used to study the adsorption of 3-mercapto-1-propanesulfonic acid (MPS) and bis(3-sulfopropyl)-disulfide (SPS) on Au(111) electrode in a HClO(4) aqueous solution. Chloride ions were introduced into the electrolyte solution, and their effect on the adsorption behavior of MPS and SPS was investigated. The CV results show that SPS and MPS molecules preferentially adsorb on the Au(111) surface compared to chloride ions, and furthermore, chloride ion can induce the adsorption of thiol molecules on the Au(111) surface. In the absence of chloride, no adsorption phase of SPS (or MPS) adlayer can be imaged by STM at low potentials. Raising electrode potential leads to the appearance of disordered adsorption phase at ca. 0.4 V (vs RHE) and ordered adlattices at ca. 0.8 V. In the presence of chloride, ordered adsorption structures of SPS and MPS appear at a lower potential (0.2 V), implying the enhancement effect of chloride to the thiol adsorption. It is inferred that the presence of chloride ions triggers a more positively charged gold surface, enhancing the reaction rate of thiol adsorption. Furthermore, the presence of chloride also leads to a decrease in the thiol-electrolyte interaction, due to the high solvation effect of chloride ions, which promotes the adsorption of SPS and MPS onto the Au surface. With further elevation of electrode potential, electrostatic interaction leads to coadsorption of chloride ions into the adlayer, as well as orientation changes of the ad-molecules. As a result, the ordered adlattice was disrupted and disappeared at ca. 0.5 V.

Synthesis and characterizations of new lysine-based biodegradable cationic poly(urethane-co-ester) and study on self-assembled nanoparticles with DNA.

To improve the self-assembly efficiency of nanoparticles with DNA, we synthesized lysine-based poly(urethane-co-ester) PMMD (6) and polyester PDMA (8) bearing ester linkages in the backbone and tertiary amines in the side chain. Both poly(urethane-co-ester) PMMD (6) and polyester PDMA (8), readily self-assembled with plasmid DNA (pCMV-beta-gal) in HEPES buffer, were characterized by dynamic light scattering and zeta-potential. The results reveal that PMMD (6) and PDMA (8) were able to self-assemble particles with DNA and yield complexes with positive charges of 80-115 nm and 170-180 nm in size at mass ratios (W/W) of 2/1 and 20/1, respectively. The degradation studies indicate that the half-life of PMMD (6) in the HEPES buffer was 20 h at pH 7.4. Titration studies were performed to determine the buffering capacities of the polymers. In addition, the COS-7 cell viabilities in the presence of PMMD/DNA, PDMA/DNA, and PEI/DNA were studied. The results indicate that PMMD (6) is an attractive cationic poly(urethane-co-ester) for gene delivery and an interesting candidate for further study.

3-Mercapto-1-propanesulfonic acid and Bis(3-sulfopropyl) disulfide adsorbed on Au(111): in situ scanning tunneling microscopy and electrochemical studies.

3-Mercapto-1-propanesulfonic acid (MPS) and bis(3-sulfopropyl) disulfide (SPS) adsorbed on a Au(111) electrode were studied by using in situ scanning tunneling microscopy (STM). Although the adsorptions of MPS and SPS are known to be oxidative and reductive, respectively, on an Au(111) electrode, these two admolecules behave similarly in terms of phase evolution, surface coverage, potential for stripping, and characteristics of cyclic voltammetry. However, different adsorption mechanisms of these molecules result in different structures. Raising electrode potential causes more MPS and SPS molecules to adsorb, yielding ordered adlattices between 0.67 and 0.8 V (vs reversible hydrogen electrode). The ordered adlattices of MPS and SPS appear as striped and netlike structures with molecules adsorbed parallel to the Au(111) surface. Switching potential to 0.9 V or more positive still does not result in upright molecular orientation, possibly inhibited by electrostatic interaction between the end group of -SO(3)(-) and the Au(111) electrode. Lowering the potential to 0.4 V disrupted the ordered adlayer. Stripping voltammetric experiments show that MPS and SPS admolecules are desorbed from Au(111) at the same potential, suggesting that these molecules are both adsorbed via their sulfur headgroups. The S-S bond in SPS is likely broken upon its adsorption on Au(111).