Molecular-level probe

Measurements of the chemical composition of an aqueous solution phase are interpreted commonly to provide experimental evidence for either adsorption or surface precipitation mechanisms in sorption processes. The conceptual aspects of these measurements vis-a-vis their usefulness in distinguishing adsorption from precipitation phenomena are reviewed critically. It is concluded that the inherently macroscopic, indirect nature of the data produced by such measurements limit their applicability to determine sorption mechanisms in a fundamental way. Surface spectroscopy (optical or magnetic resonance), although not a fully developed experimental technique for aqueous colloidal systems, appears to offer the best hope for a truly molecular-level probe of the interfacial region that can discriminate among the structures that arise there from diverse chemical conditions. 

Lee CK, Beiermatm BA, Silberstein MN, Wang J, Moore JS, Sottos NR, Braim PV (2013) Exploiting force sensitive spiropyrans as molecular level probes. Macromolecules 46 3746-3752... 

The development of scanning probe microscopies and x-ray reflectivity (see Chapter VIII) has allowed molecular-level characterization of the structure of the electrode surface after electrochemical reactions [145]. In particular, the important role of adsorbates in determining the state of an electrode surface is illustrated by scanning tunneling microscopic (STM) images of gold (III) surfaces in the presence and absence of chloride ions [153]. Electrodeposition of one metal on another can also be measured via x-ray diffraction [154]. 

Over 40 different types of polypeptide toxins have been found in marine animals (i). Many of these toxins are exquisitely selective in their actions, affecting a single process or receptor at minute concentrations. So far the sea anemone and gastropod Conus) toxins have attracted the most attention as molecular probes of ion channels. In this chapter, we discuss several approaches which are being used to investigate, at the molecular level, the interactions of the sea anemone neurotoxic polypeptides with sodium channels. 

Much of the pioneering work which led to the discovery of efficient catalysts for modern Industrial catalytic processes was performed at a time when advanced analytical Instrumentation was not available. Insights Into catalytic phenomena were achieved through gas adsorption, molecular reaction probes, and macroscopic kinetic measurements. Although Sabatier postulated the existence of unstable reaction Intermediates at the turn of this century. It was not until the 1950 s that such species were actually observed on solid surfaces by Elschens and co-workers (2.) using Infrared spectroscopy. Today, scientists have the luxury of using a multitude of sophisticated surface analytical techniques to study catalytic phenomena on a molecular level. Nevertheless, kinetic measurements using chemically specific probe molecules are still the... 

Through the use of pump-probe techniques pioneered by Zewail and coworkers,62 it is becoming possible to identify the detailed mechanisms of reactions at the molecular level and follow the actual course of a reaction. The study of ammonia clusters has provided an example of what can be accomplished using these techniques. 

Infrared spectroscopy has been widely used for the qualitative and quantitative characterization of polymorphic and pseudopolymorphic compounds of pharmaceutical interest. Since solid state IR can be used to probe the nature of (pseudo)polymorphism on the molecular level, this method is particularly useful in instances where full crystallographic characterization of (pseudo)poly-morphism was not found to be possible. Recently, a significant number of publications have appeared that discuss where a multidisciplinary, spectroscopic... 

XAS provides a powerful probe of both physical and electronic structure of an element within a sample, and has the ability to determine the molecular level speciation of As, Mo and Se over the concentration range of 50 pg/g to several weight percent (typical of mine tailings solids) (Brown et al. 1998) at the micron to mm scale. 

The distance scale associated within the glass transition is related to the method used. For example, thermal and mechanical techniques provide macroscopic views of the glass transition, whereas spectroscopy techniques yield a molecular-level view. Thus, it is not surprising to find that molecular-level techniques, such as NMR, may result in lower Tg values compared to those obtained using a macroscopic technique, such as DSC. Both Tg values are correct, but not necessarily equal, given the different points of view the two methods are probing. 

Since Avnir and Pfeifer s pioneer works83"86 regarding the characterization of the surface irregularity at the molecular level by applying the fractal theory of surface science, the molecular probe method using gas adsorption has played an important role in the determination of surface fractal dimension of the porous and particulate materials. 

Dendrimers have precise compositional and constitutional aspects, but they can exhibit many possible conformations. Thus, they lack long-range order in the condensed phase, which makes it inappropriate to characterize the molecular-level structure of dendrimers by X-ray diffraction analysis. However, there have been many studies performed using indirect spectroscopic methods to characterize dendrimer structures, such as studies using photophysical and photochemical probes by UV-Vis and fluorescence spectroscopy, as well as studies using spin probes by EPR spectroscopy. 

In situ hybridization (ISH) consists of the application of hybridization techniques to intact cells which demonstrate genetic information within a morphologic context. This technology takes advantage of the hybridization properties of nucleic acids and offers a distinct technique to directly analyze sequence information in intact tissues. In essence, it combines cytogenetic techniques with molecular biology to probe gene alterations at molecular levels. Development of... 

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