Although the desirability of developing synthetic molecular machine systems that can function on surfaces is widely recognized, to date the only well-characterized examples of electrochemically switchable rotaxane-based molecular shuttles which can do so are based on the tetracationic viologen macrocycle pioneered by Stoddart. Here, we report on a [2]rotaxane which features succinamide and naphthalene diimide hydrogen-bonding stations for a benzylic amide macrocycle that can shuttle and switch its net position both in solution and in a monolayer. Three oxidation states of the naphthalene diimide unit can be accessed electrochemically in solution, each one with a different binding affinity for the macrocycle and, hence, corresponding to a different distribution of the rings between the two stations in the molecular shuttle. Cyclic voltammetry experiments show the switching to be both reversible and cyclable and allow quantification of the translational isomer ratios (thermodynamics) and shuttling dynamics (kinetics) for their interconversion in each state. Overall, the binding affinity of the naphthalene diimide station can be changed by 6 orders of magnitude over the three states. Unlike previous electrochemically active amide-based molecular shuttles, the reduction potential of the naphthalene diimide unit is sufficiently positive (-0.68 V) for the process to be compatible with operation in self-assembled monolayers on gold. Incorporating pyridine units into the macrocycle allowed attachment of the shuttles to an acid-terminated self-assembled monolayer of alkane thiols on gold. The molecular shuttle monolayers were characterized by X-ray photoelectron spectroscopy and their electrochemical behavior probed by electrochemical impedance spectroscopy and double-potential step chronoamperometry, which demonstrated that the redox-switched shuttling was maintained in this environment, occurring on the millisecond time scale.

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Three state redox-active molecular shuttle that switches in solution and on a surface.

1,4-Benzenedimethanethiol (HS−CH2−C6H4−CH2−SH, BDMT) adsorbs dissociatively on silver and gold surfaces yielding self-assembled monolayers with the thiolate structure. Whereas the molecule adsorbs flat on silver as a result of the loss of two thiol protons, it adsorbs with the molecular plane perpendicular to the gold surface with the loss of one thiol proton. This is manifested by the presence of the ring C−H and S−H stretches and the S−C−H bend for the Au monolayer and the absence of these for the Ag monolayer in the surface-enhanced Raman spectra. The difference in adsorbate geometry is presumably due to the changes in interaction and not to differences in the lattice constants of the two surfaces, which is rather small. In both cases, metal−adsorbate π bonding is weak, resulting in only small shifts in the ring modes. BDMT monolayers are more stable than alkanethiol monolayers and desorb only at a fairly high temperature of 423 K in air, whereas alkanethiols desorb below 373 K. An increase in temperat...

http://www.dstuns.iitm.ac.in/listpdf/62.pdf?origin=publication_detail

Self-assembled Monolayers of 1,4-Benzenedimethanethiol on Polycrystalline Silver and Gold Films: An Investigation of Structure, Stability, Dynamics, and Reactivity

This comprehensive literature review covers recent studies on patterning neuronal cells by topographical modifications on material surfaces targeted for neural prostheses. We explore different materials that are used as the candidate surface for neuronal cell adhesion. Cell–material interactions are identified in both cases where the material surface was in direct contact with cells and where the materials were coated to facilitate cell adhesion. Commonly used coating materials and coating methods are discussed. The existing hypotheses behind mechanism of the response of neuronal cells to a specific topography are presented briefly. A few selected important studies have been presented to show the range of techniques employed and the extent of the research area. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2010

A comprehensive review of surface modification for neural cell adhesion and patterning

Self-assembled monolayers (SAMs) have been the preferred material systems to investigate specific properties in several disciplines for nearly 15 years. Advances in various techniques and their application to the study of SAMs have dramatically improved our understanding of these systems. Adaptation of this molecular architecture into three dimensions in the form of monolayer-protected clusters enabled the use of bulk techniques for the study of monolayers. Here we review recent developments in the structural properties and temperature-induced phase transitions of both these SAM structures. While alkanethiols on Au (111) and Ag (111) are taken as archetypal systems to discuss the properties of SAMs on two-dimensional surfaces, their assemblies on Au and Ag cluster surfaces are taken as examples for SAMs on three-dimensional surfaces. A comparison of these two SAMs is provided.

http://www.dstuns.iitm.ac.in/listpdf/108.pdf

Current understanding of the structure, phase transitions and dynamics of self-assembled monolayers on two- and three-dimensional surfaces

http://www.dstuns.iitm.ac.in/listpdf/67.pdf

V Bindu

Papers

Characterisation of alkanethiol (CnH2n + 1SH, n = 3, 4, 6, 8,10,12 and 18) self assembled monolayers by X-ray photoelectron spectroscopy