Electron molecular probes

Materials. The nearly monodisperse atactic PMMA, which was used for the electron beam lithography and fluorescence spectroscopy studies, was obtained from Pressure Chemical. It has a weight average molecular weight (Mw) of 188,100 and Mw/Mn< 1.08. Pyrenedodecanoic acid (PDA) used in the fluorescence studies was obtained from Molecular Probes and used as supplied. Spectroscopic grade benzene purchased from J.T. Baker was used as the spreading solvent in the PMMA and PMMA/PDA solutions. 

Over the years, there have been numerous reports of oxidase preparations that contain polypeptide components, additional to those described above. As yet no molecular probes are available for these, and so their true association with the oxidase is unconfirmed. There are many reports in the literature describing the role of ubiquinone as an electron transfer component of the oxidase, but its involvement is controversial. Quinones (ubiquinone-10) have reportedly been detected in some neutrophil membrane preparations, but other reports have shown that neither plasma membranes, specific granules nor most oxidase preparations contain appreciable amounts of quinone, although some is found in either tertiary granules or mitochondria. Still other reports suggest that ubiquinone, flavoprotein and cytochrome b are present in active oxidase preparations. Thus, the role of ubiquinone and other quinones in oxidase activity is in doubt, but the available evidence weighs against their involvement. Indeed, the refinement of the cell-free activation system described above obviates the requirement for any other redox carriers for oxidase function. 

Figure 5.22. Structures and electronic spectra of Fura-2 and Indo-l (a) excitation spectra of Fura-2 (b) emission spectra of Indo-l, in increasing concentrations of free calcium (from molecular probes).

High resolution NMR parameters are reeognized as invaluable probes to detect fine details of the electronic molecular structure of different types of compounds when adequate combinations of theoretical and experimental approaches are adopted. Pioneer works of Professor Oddershede on the study of high resolution NMR parameters are very well recognized in the literature [1-6], For this reason and for this occasion, the authors thought it pertinent to present a contribution... 

Our interest in SERS stemmed from our research activities concerned with establishing connections between the molecular structure of electrode interfaces and electrochemical reactivity. A current objective of our group is to employ SERS as a molecular probe of adsorbate-surface interactions to systems of relevance to electrochemical processes, and to examine the interfacial molecular changes brought about by electrochemical reactions. The combination of SERS and conventional electrochemical techniques can in principle yield a detailed picture of interfacial processes since the latter provides a sensitive monitor of the electron transfer and electronic redistributions associated with the surface molecular changes probed by the former. Although few such applications of SERS have been reported so far the approaches appear to have considerable promise. 

Recent advances in the development of non-invasive, in situ spectroscopic scanned-probe and microscopy techniques have been applied successfully to study mineral particles in aqueous suspension (Hawthorne, 1988 Hochella and White, 1990). In situ spectroscopic methods often utilise molecular probes that have diagnostic properties sensitive to changes in short-range molecular environments. At the particle-solution interface, the molecular environment around a probe species is perturbed, and the diagnostic properties of the probe, which can be either optical or magnetic, then report back on surface molecular structure. Examples of in situ probe approaches that have been used fruitfully include electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spin-probe studies perturbed vibrational probe (Raman and Fourier-transform IR) studies and X-ray absorption (Hawthorne, 1988 Hochella and White, 1990 Charletand Manceau, 1993 Johnston et al., 1993). 

A prototypical example of a molecular probe used extensively to study the mineral adsorbent-solution interface is the ESR spin-probe, Cu2+ (Sposito, 1993), whose spectroscopic properties are sensitive to changes in coordination environment. Since water does not interfere significantly with Cu11 ESR spectra, they may be recorded in situ for colloidal suspensions. Detailed, molecular-level information about coordination and orientation of both inner- and outer-sphere Cu2+ surface complexes has resulted from ESR studies of both phyllosilicates and metal oxyhydroxides. In addition, ESR techniques have been combined with closely related spectroscopic methods, like electron-spin-echo envelope modulation (ESEEM) and electron-nuclear double resonance (ENDOR), to provide complementary information about transition metal ion behaviour at mineral surfaces (Sposito, 1993). The level of sophistication and sensitivity of these kinds of surface speciation studies is increasing continually, such that the heterogeneous colloidal particles in soils can be investigated ever more accurately. 

Several simple relations have been proposed for the determination of the fractal dimensions from the results of such experiments as gas molecular probe method, transmission electron microscopy (TEM), small-angle X-ray scattering, neutron scattering, and laser light scattering.63,66,113 116 Among those techniques, gas molecular probe method and image analysis method have been widely used for the calculation of the surface... 

The unimolecular micellar characteristics of this poly(ammonium carboxylate) 156 were demonstrated 179 by UV analysis of guest molecules, such as pinacyanol chloride, phenol blue, and naphthalene combined with fluorescence lifetime decay experiments employing diphenylhexatriene as a molecular probe. The monodispersity, or absence of intermolecular aggregation, and molecular size were determined by electron microscopy. 

The proposed structure for ECR-1 was solved by accumulating evidence from many "traditional" sources, such as the synthesis phase relationships, powder x-ray diffraction (PXD) and electron diffraction (ED), molecular probe sorption, infra-red analysis (IR) and electron microscopy (EM). Initial unsuccessful models were based on extended merlinoite frameworks, followed by modifications based on mordenite. The observation of crystal overgrowths of mazzite in high resolution lattice images was the key to recognizing the compatibility of mordenite and mazzite structural layers, and that intimate intergrowth of the two structures was possible. 

Despite many advances in analytical methods in recent years, the structural characterization of materials that only occur as microcrystals less than about 30 l in diameter remains difficult and laborious. High resolution electron microscopy in the lattice imaging mode is by far the most powerful tool in giving the direct evidence of structural details essential for modelling clues, as has been demonstrated in the cases of recent zeolite structure solutions of theta-l/ZSM-23 (26) and beta (27), in addition to ECR-1. X-ray diffraction methods provide the essential confirmatory data, and sorption molecular probing and various well established spectroscopic methods are useful ancillary tools. 

The success of the method prompted the design of an Automatic Molecular Probe apparatus for the collection of retention data 82). At a preset cycle time a mixture of solute and noninteracting marker was iiqected into the carrier gas and the output of the GC detector was fed to an electronic peak detector. The temperature in the oven was programmed linearly and recorded with a thermocouple. Upon conversion into digital form, a printout of net retention time and temperature was obtained. Retention diagrams have been obtained with this apparatus for high and low density polyethylene 82, 83). 

The basic principles of ESR spectroscopy were reviewed lucidly in the context of surface speciation applications by McBride (33, 56). A comprehensive introduction oriented toward the use of ESR methods in mineral geochemistry was published by Calas (57). Senesi (58) did the same for organic geochemistry. Fundamentally, ESR spectroscopy detects chemical species with unpaired electrons. With respect to adsorbed metals, investigation is limited to to paramagnetic transition elements in certain oxidation states [e.g., V(IV), Cr(III), Mn(II), Fe(III), and Cu(II)], either as principal surface species or as in situ molecular probes of surface environments. 

Some essential discoveries concerning the organization of the adsorbed layer derive from the various spectroscopic measurements [38-46]. Here considerable experimental evidence is consistent with the postulate that ionic surfactants form localized aggregates on the solid surface. Microscopic properties like polarity and viscosity as well as aggregation number of such adsorbate microstructures for different regions in the adsorption isotherm of the sodium dedecyl sulfate/water/alumina system were determined by fluorescence decay (FDS) and electron spin resonance (ESR) spectroscopic methods. Two types of molecular probes incorporated in the solid-liquid interface under in situ equilibrium conditions... 

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