Choice of probes

The probes to be used in fluorescence polarization experiments should fulfil as far as possible the following requirements  

2 Intramolecular excimer fluorescence for probing the mobility of bulk polymers 

DIPHANT, and 5 x 106 s 1 for pyrene-based bifluorophores (whose lifetimes are of the order of 200 ns). 

The correlation time tc of the motions involved in intramolecular excimer formation is defined as the reciprocal of the rate constant ki for this process. Its temperature dependence can be interpreted in terms of the WLF equationb) for polymers at temperatures ranging from the glass transition temperature Tg to roughly Tg +100°  

This investigation shows that it is indeed possible to study the flexibility of polymer chains in polymer matrices by means of excimer-forming probes and that the rotational mobility of these probes reflect the glass transition relaxation phenomena of the polymer host matrix, in agreement with the appropriate WLF equation. 

I 8 Microviscosity, fiuidity, molecular mobility. Estimation by means of fluorescent probes 

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The choice of probe molecule for acidity determination is largely dictated by the sensitivity of the nuclei, and the high sensitivity of P nuclei has been exploited to quantify acidity in zeolites. The use of phosphorus containing bases as probe molecules to measure solid acidity circumvents insensitivity problems associated with (1.1% abundance) and N (0.4% abundance) in bases such as ammonia. 

Probes can be differently labeled with hapten labels, for example carboxyfluorescein (6-FAM), digoxigenin (DIG) and biotin can be bound to LNA oligos. The choice of probe label depends on experimental design and the techniques available in the laboratory. The hapten label provides a template for crucial signal amplification since the FITC label on the oligo itself is not sufficient to allow detection in standard epifluorescence. In this study, the fluorescence signal was obtained with the TSA-FITC substrate, which allowed detection of miR-21 and miR-205. 

All test solutions, except otherwise mentioned, were degassed by hree freeze-pump-thaw cycles with a vacuum line operated under 10 torr pressure. Problems of background fluorescence originating from sulfonates themselves could be adequately minimized by proper choice of probe/sulfonate ratios. The excitation wavelength was set at 340 nm. Emission spectra were obtained in constant energy mode. The spectral resolution was 3 nm. 

Choice of Probes. The sequence chosen for analysis will be determined by the nature of the evolutionary comparison to be carried out. Examples of probe DNAs used for examining populational and species level comparisons, as well as for higher level systematics, are described by Dowling et a/.38 Table II provides some of die cloned sequences (or techniques to obtain them)45-75 that have the potential to be useful in evolutionary studies. The list is not meant to be comprehensive but representative there... 

NISH technology has four elements (1) choice of probe/reporter and probe labeling, (2) pretreatment of cells/tissues, (3) denaturation/hybrid-ization, and (4) detection of signal. 

It is clear from previous discussions that fiber-optic probe designs differ substantially in sensitivity, background interference, acceptable fiber length, size, and fragility, not to mention cost. As always, the choice of probe depends on the requirements of the application, so there is no best design. Nevertheless, it is useful to address some general comparisons of probe performance. 

Probe Detection. There are a number of different protocols for the detection of hybridized probe and these are summarized in Table 2. The choice of detection system will be dictated by your choice of probe label, (biotin or dig), and whether you are carrying out single or double hybridizations. For single hybridizations with biotin-labeled probes, we favor the avidin-detection protocol (see Subheading 3.8.1.), and for double hybridizations with biotin- and dig-labeled probes simultaneously, the avidin/anti-dig protocol (see Subheading 3.8.3.). 

Due to the use of a single light source, the choice of probes is rather limited. When two probes are combined, the technique becomes cumbersome and loses its advantage of speed. Therefore, extension of the instrument with a second or even a third light source would open the possibility for a whole range of new applications. For example, if a viability probe and a probe for the detection of a specific species could be combined, detailed studies on the physiological behaviour of bacteria in a complex community would be facilitated. 

It should be pointed out that the choice of probe molecule is very important in the measurement of acid site concentrations. In TPD-TGA ammonia and... 

W e hope that this review wiU be helpful for the planning of experiments, choice of probe molecules, and interpretation of the results, not only for beginners but also for the experienced scientists in the field. 

D. Choice of Probe Labels for Fluorescence in Situ Hybridization... 

Advances in fluorescence and electron spin resonance (ESR) spectroscopies have enabled the use of organic fluorescent probes for in situ characterizations of molecular environments. The utility of fluorescence methods in such studies arises from the fact that the fluorescence and ESR responses of numerous probes are highly dependent on the environment, so that specific information can be obtained by appropriate choice of probes. Fluorescence responses that have been shown to depend on a micellar environment include excitation and emission, fluorescence polarization, and quenching (or sensitization). These responses have been, in turn, related to molecular properties such as polarity, viscosity, diffusion, solute partitioning, and aggregation numbers. 

In the determination of acidity by microcalorimetry, several factors play an important role, such as the adsorption temperature, the pretreatment temperature, and the choice of probe molecule. Other factors, more specific to zeolites, are the topology, the Si/Al ratio, the chemical composition, and the modifications to which the samples have been subjected. These various factors will be examined in what follows, for the various famihes of studied zeolites. However, the main two factors are the zeohte structure and the framework aluminum content. Most of the studies described herein are summarized as reference tables in a review by Cardona-Martinez et al. [5]. 

For examination of mixing behavior, light sheet visualization is important, particularly in multiple-impeller systems, to help the experimentahst think about suitable points of addition to study a mixing system, possible choice of feed location, and an initial estimate of suitable probe locations for mixing time experiments. Further tests should be performed to provide more detailed information on suitable choices of probe location. 

Adsorption is an exothermic process and when a reactive molecule interacts with the surface of the solid heat is evolved. This heat is related to the energy of the bonds formed between the adsorbed species and the adsorbent and hence to the nature of the bonds and to the chemical reactivity of the surface. From a number of techniques used to study this interaction only a few provide information about the strength of chemisorption itself. The determination of the differential heats evolved, by a suitable microcalorimeter, when known amounts of gas probe molecules are adsorbed on catalytic surface is the most suitable and accurate method which allows the determination of the number, strength and energy distribution of the adsorption sites [4-12]. The effective use of this technique in heterogeneous catalysis depends on choice of probe molecule, since the nature of the probe determines which surface property is going to be investigated. 

A comprehensive analysis of the hterature on the choice of probes for constructing polarity scales led om group to consider the molecular structure of 2-aniino-7-nitrofluo-... 

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