Smectite clays as solid supports for immobilization of beta-glucosidase:Synthesis, characterization, and biochemical properties

Nanomaterials as solid supports can improve the efficiency of immobilized enzymes by reducing diffusional limitation as well as by increasing the surface area per mass unit and therefore improving enzyme loading. In this work, beta-glucosidase from almonds was immobilized on two smectite nanoclays. The resulting hybrid biocatalysts were characterized by a combination of powder X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric. analysis, differential thermal analysis, and infrared spectroscopy. Biochemical studies showed an improved thermostability of the immobilized enzyme as well as enhanced performance at higher temperatures and in a wider pH range

Experimental and theoretical study of the adsorption of fumaramide [2]rotaxane on Au(111) and Ag(111) surfaces

Thin films of fumaramide [2] rotaxane, a mechanically interlocked molecule composed of a macrocycle and a thread in a "bead and thread" configuration, were prepared by vapor deposition on both Ag(111) and Au(111) substrates. X-ray photoelectron spectroscopy (XPS) and high-resolution electron-energy-loss spectroscopy were used to characterize monolayer and bulklike multilayer films. XPS determination of the relative amounts of carbon, nitrogen, and oxygen indicates that the molecule adsorbs intact. On both metal surfaces, molecules in the first adsorbed layer show an additional component in the C 1s XPS line attributed to chemisorption via amide groups. Molecular-dynamics simulation indicates that the molecule orients two of its eight phenyl rings, one from the macrocycle and one from the thread, in a parallel bonding geometry with respect to the metal surfaces, leaving three amide groups very close to the substrate. In the case of fumaramide [2]rotaxane adsorption on Au(111), the presence of certain out-of-plane phenyl ring and Au-O vibrational modes points to such bonding and a preferential molecular orientation. The theoretical and experimental results imply that the three-dimensional intermolecular configuration permits chemisorption at low coverage to be driven by interactions between the three amide functions of fumaramide [2]rotaxane and the Ag(111) or Au(111) surface. (c) 2005 American Institute of Physics.</p

Macroscopic transport by synthetic molecular machines

Nature uses molecular motors and machines in virtually every significant biological process, but demonstrating that simpler artificial structures operating through the same gross mechanisms can be interfaced with—and perform physical tasks in—the macroscopic world represents a significant hurdle for molecular nanotechnology. Here we describe a wholly synthetic molecular system that converts an external energy source (light) into biased brownian motion to transport a macroscopic cargo and do measurable work. The millimetre-scale directional transport of a liquid on a surface is achieved by using the biased brownian motion of stimuli-responsive rotaxanes (‘molecular shuttles’) to expose or conceal fluoroalkane residues and thereby modify surface tension. The collective operation of a monolayer of the molecular shuttles is sufficient to power the movement of a microlitre droplet of diiodomethane up a twelve-degree incline.

Characterization by X-ray Photoemission Spectroscopy of the Open and Closed Forms of a Dithienylethene Switch in Thin Films

Dithienylethene-based molecular switches have been extensively studied in solution and are considered excellent candidates in the design of molecular-based electronic devices. However, for most foreseeable applications they have to be integrated in the solid state, namely as building blocks in bottom-up approaches to prepare functional and addressable surfaces. Here we present a study of the electronic structure and chemical nature of dithienylethene switch thin films on Au(111) by X-ray photoemission spectroscopy, which proves to be a powerful technique to distinguish between the “open” and “closed” forms of the switch and gives information on the interactions between molecules and substrate. We explored the switching behavior of thin films when irradiated with UV and visible light. It is demonstrated that, despite the quenching effect that can be induced by the metal substrate, dithienylethenes can reversibly switch from open to closed form in thin solid films deposited on metal surfaces. We also showed that illumination of the closed form of dithienylethene with visible light induces not only the switching process in molecules isolated from the metal surface but also chemisorption of dithienylethene molecules that are in contact with Au(111). These results provide rationalization of the phenomena that take place while switching dithienylethenes at metal surfaces.

Synthetic light-activated molecular switches and motors on surfaces

Recent advances in synthetic methods and analysis techniques provide a basis for the construction and characterization of organized arrays of molecular switches and motors on surfaces. Among them, molecular systems that can be controlled by light are particularly promising because of their ease of addressability, fast response times and the compatibility of light with a wide range of condensed phases. The aim of this contribution is to highlight selected recent advances in building functional monolayers of light-activated molecules. Special focus is given to monolayers of molecules whose collective switching properties have been harnessed to produce macroscopic effects. The design, structure, and function of monolayers composed of bistable photochromic switches, which can control chirality, wettability, conductivity and self-assembly are described. A recent report on the successful demonstration of light-driven rotary motors functioning while grafted on gold surfaces will also be discussed, followed by a brief conclusion.

Rotaxane functionalized acid-terminated self-assembled siloxane monolayers on non-conducting surfaces - XPS, AFM and TRF

Mechanically interlocked molecules such as rotaxanes are fascinating for their potential in molecular-scale devices. Rotaxane, stimuli-responsive "molecular shuttles" are molecules where a macrocyclic 'bead' is locked onto a linear "thread" by bulky "stoppers". Large amplitude motion of the macrocycle can be induced by external stimuli (e.g. light, electrons, heat, pH, polarity of the environment etc.). While the solution chemistry of rotaxanes has been explored extensively, the study of the surface chemistry of these species has been limited to a few examples. Here we report detailed direct information on the surface morphology and the packing of rotaxane on self-assembled monolayer on quartz and silicon oxide/Si(110) followed by the photophysical studies.</p

Rotaxane Functionalized Acid-Terminated Self-Assembled Siloxane Monolayers on Non-Conducting Surfaces - XPS, AFM and TRF

Mechanically interlocked molecules such as rotaxanes are fascinating for their potential in molecular-scale devices. Rotaxane, stimuli-responsive “molecular shuttles” are molecules where a macrocyclic ‘bead’ is locked onto a linear “thread” by bulky “stoppers”. Large amplitude motion of the macrocycle can be induced by external stimuli (e.g. light, electrons, heat, pH, polarity of the environment etc.). While the solution chemistry of rotaxanes has been explored extensively, the study of the surface chemistry of these species has been limited to a few examples. Here we report detailed direct information on the surface morphology and the packing of rotaxane on self-assembled monolayer on quartz and silicon oxide/Si(110) followed by the photophysical studies.