Probe molecules, adsorbed, confinement

The physical properties of probe molecules adsorbed in the confined space of porous materials are known to vary in dependence of structural constraints on molecular motion. Detailed investigations of adsorption geometries are possible, when well-defined sites and loadings exist. This was the case for the adsorption of strongly interacting probe molecules, such as pyridine, on SiOH groups in the... 

The dynamics of the molecules adsorbed in confined geometry is one of the most common and important research subject which has received much attention in the past few decades. Owing to the large polarizability and the chemical inert nature of the monoatomic xenon, the l29Xe NMR chemical shift is very sensitive to its environment and thus provides an ideal probe for the investigation of the structure of porous materials [1]. There have been numerous publications in this area since the pioneering works by Ito and Fraissard [2] and by Ripmeester [3], and several reviews have been attributed to related subjects [4-7]. Recent developments of the mesoporous MCM-41 materials [8] have also drawn intense attention due... 

Recently, Pcs organized on surface have been used as molecular probes for the determination of quantum confined effects [207], CoPc molecules form ordered self-assembled monolayers (SAM) on the top of Pb(lll) thin films grown on a Si( 111) substrate with the Pc units lying flat on the surface, as revealed by atomically resolved STM. A close analysis of the STM data revealed that the Pc molecules adsorb and self-assemble on the surface following a thickness-dependent adsorption pattern, which is ultimately related to the quantum size effects of the metal surface. 

In other words, the medium-specific contribution is not easily measured or quantified for probe molecules in interaction with solid surfaces. Moreover, in the case of microporous solids, the short-distance interactions known as "confinement effects" are even more difficult to evaluate. In all comparisons of experimental data one should be aware that the reactivity of probe base molecules is largely influenced by the size of adsorbates and micropore dimensions. As a result, the acidity scales based on the free energy of proton transfer to a specific base are expected to depend on the choice of reference base. This fact has been confirmed experimentally, as calorimetric heats of adsorption of various bases on, e.g., zeolites, depend on the base chosen. For example, a ZH zeolite may be a stronger acid... 

The application of total internal reflection fluorescence spectroscopy (TIRF) by this laboratory to the study of protein adsorption at solid-liquid interfaces is reviewed. TIRF has been used to determine adsorption isotherms and adsorption rates from single-and multi-component protein solutions. Initial adsorption rates of BSA can be explained qualitatively by the properties of the adsorbing surface. Most recently, a TIRF study using monoclonal antibodies to probe the conformation of adsorbed sperm whale myoglobin (Mb) elucidated two aspects of the Mb adsorption process 1) Mb adsorbs in a non-random manner. 2) Conformational changes of adsorbed Mb, if they occur, are minor and confined to local regions of the molecule. Fluorescence energy transfer and proteolytic enzyme techniques, when coupled with TIRF, can characterize, respectively, the conformation and orientation of adsorbed Mb. 

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