Catalysis molecular probes

As far as we know, this is the first molecular probe that includes two different types of reporter units activated upon on a specific stimulus. The other option to achieve dual detection would be to use two separate probes. However, in this case there could be a problem of competitive catalysis (circumstances in which the Km of the two substrate is not identical). In our probe, 6-aminoquinoline and 4-nitrophenol, detected by fluorescence and absorbance spectroscopy, respectively, were used as reporter units. Due to the synthetic flexibility of our approach, other reporter molecules with different types of functional groups, like amine or hydroxyl, can be linked to our molecular probe. The two assays must be orthogonal to each other, in order to prevent disturbances in the detection measurement. Another advantage of the probe is the aqueous solubility... 

In conclusion the experimental support given by the use of molecular probes to the molecular approach to chemisorption considered as a localized interaction of chemisorbed molecules with metal atoms on the surface of metals or metal oxides [2, 5] was at the origin of the development of a more precise experimental identification of surface species involved in some aspects of heterogeneous catalysis. 

The development of new catalytic materials needs to be complemented with detailed studies of the surface chemistry of catalysis at the molecular level in order to better define the requirements for the catalytic active sites. The wide array of modem spectroscopies available to surface scientists today is ideally suited for this task (see Surfaces). Surface science studies on catalysis typically probe reaction intermediates on model metal samples under well controlled conditions. This kind of study is traditionally carried out in ultrahigh vacuum (UHV) systems such as that shown in Figure 10. Single crystals or other well-defined metal surfaces are cleaned and characterized in situ by physical and chemical means, and then probed using a battery of surface sensitive techniqnes snch as photoelectron (XPS and UPS), electron energy loss (ELS... 

The probe molecules of greatest historical interest in catalysis are the Hammett indicators [13]. The difficulty of making reliable visual or spectrophotometric observations of the state of protonation of these species on solids is well known. We have recently carried out the first NMR studies of Hanunett indicators on solid acids [ 14]. This was also the occasion of the first detailed collaboration between the authors of this article, and theoretical methods proved to strongly compliment the NMR experiments. The Hanunett story is told after first reviewing the application of theoretical chemistry to such problems. Central to the application of any physical method in chemistry is the process of modeling the relationship between the observables and molecular structure. However often one does this, it is rarely an exact process. One can rationalize almost any trend in isotropic chemical shift as a function of some variation in molecular structure - after the fact, but the quantitative prediction of such trends in advance defies intuition in most nontrivial cases. Even though the NMR spectrum is a function... 

In catalysis, infrared (IR) spectroscopy is commonly used to characterize specific adsorbates. Because of the localized nature and particular chemical specificity of molecular vibrations, IR spectra are quite rich in information, and can be used to extract or infer both structural and compositional information on the adsorbate itself as well as on its coordination on the surface of the catalyst. In some instances, IR spectroscopy is also suitable for the direct characterization of solids, especially if they can be probed in the far-IR region (10-200 cm ) [74-76],... 

Here we report the synthesis and catalytic application of a new porous clay heterostructure material derived from synthetic saponite as the layered host. Saponite is a tetrahedrally charged smectite clay wherein the aluminum substitutes for silicon in the tetrahedral sheet of the 2 1 layer lattice structure. In alumina - pillared form saponite is an effective solid acid catalyst [8-10], but its catalytic utility is limited in part by a pore structure in the micropore domain. The PCH form of saponite should be much more accessible for large molecule catalysis. Accordingly, Friedel-Crafts alkylation of bulky 2, 4-di-tert-butylphenol (DBP) (molecular size (A) 9.5x6.1x4.4) with cinnamyl alcohol to produce 6,8-di-tert-butyl-2, 3-dihydro[4H] benzopyran (molecular size (A) 13.5x7.9x 4.9) was used as a probe reaction for SAP-PCH. This large substrate reaction also was selected in part because only mesoporous molecular sieves are known to provide the accessible acid sites for catalysis [11]. Conventional zeolites and pillared clays are poor catalysts for this reaction because the reagents cannot readily access the small micropores. 

The amino acid sequences of numerous transport proteins have been elucidated during the last 10 years. As with conventional enzymes, molecular biological techniques now make it possible to modify individual amino acid residues in the proteins and thus to probe the roles these residues play in catalysis of facilitated diffusion or active transport. 

Zamaraev and Thomas provide a concise summary of work done with a family of classic catalytic test reactions—dehydration of butyl alcohols—to probe the workings of acidic molecular sieve catalysts. This chapter echoes some of the themes stated by Pines and Manassen, who wrote about alcohol dehydration reactions catalyzed by solid acids in the 1966 volume of Advances in Catalysis. 

CONTENTS Preface, C. Allen Bush. Thermodynamic Solvent Isotope Effects and Molecular Hydrophobicity, Terrence G. Oas and Eric J. Toone. Membrane Interactions of Hemolytic and Antibacterial Peptides, Karl Lohner and Richard M. Epand. Spin-Labeled Metabolite Analogs as Probes of Enzyme Structure, Chakravarthy Narasimhan and Henry M. Miziorko. Current Perspectives on the Mechanism of Catalysis by the Enzyme Enolase, John M. Brewer and Lukasz Leb-ioda. Protein-DNA Interactions The Papillomavirus E2 Proteins as a Model System, Rashmi S. Hedge. NMR-Based Structure Determination for Unlabeled RNA and DNA, Philip N. Borer, Lucia Pappalardo, Deborah J. Kenwood, and Istvan Pelczer. Evolution of Mononuclear to Binuclear CuA An EPR Study, William E. Antholine. Index. 

Although IRES has been used to follow surface reactions under conditions close to those typical of heterogeneous catalysis (2), the data chosen for presentation at this symposium deal mainly with the use of IRES as a probe of molecular interactions and local molecular geometry at high surface coverages, matters of interest in unravelling the fundamentals of heterogeneous catalysis. 

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