Micropolarity, probe

A) tracts, whereas conformation of the probe changed in the presence of an RNA poly(A)tract (alteration on the micropolarity around a pyrenecarboxamide chromo-phore caused by hybridization with the targeted RNA) and a much higher fluorescence was observed. 

Berezin MY, Lee H, Akers W, Achilefu S (2007) Near infrared dyes as lifetime solvato-chromic probes for micropolarity measurements of biological systems. Biophysical J 93 2892-2899... 

Less frequently used at present is electron spin resonance spectroscopy, which is based on the use of spin probes as model componnds or covalent spin labeling of drugs. Microviscosity and micropolarity of the molecnlar environment of the probe can be derived from electron spin resonance spectra. Moreover, the spectra allow us to differentiate isotropic and anisotropic movements, which result from the incorporation of the probe into liposomal structures. Quantitative distribution of the spin probes between the internal lipid layer, the snrfactant, and the external water phase is to be determined noninvasively. On the basis of the chemical degradation of drugs released from the lipid compartment, agents with reductive features (e.g., ascorbic acid) allow us to measure the exchange rate of the drugs between lipophilic compartments and the water phase [27,28]. 

The polarity within a surfactant assembly will be quite different from that of the bulk solution. It is useful to know the micropolarity of these assem-bhes for such applications where different substrates are compartmentalized inside these surfactants. The micropolarity of the surfactant assembhes can be determined using any fluorescence probe whose emission characteristics change with solvent polarity. The emissions of the probe are measured in solvents of known polarities and the polarity of the surfactant assembhes is determined by comparison. 

Pyrene carboxaldehyde and a series of pyrene carboxylic acids were found useful as fluorescence probes in describing the constitution of inverted micelles of certain calcium alkarylsulfonates in hydrocarbon media. 1-Pyrene carboxaldehyde is a convenient probe for studying the particle sizes of micelles in the region of lOOA. A series of graded probes, pyrene carboxylic acids with varying alkyl chain length, have been used to determine internal fluidity and micro-polarity as a function of distance from the polar core of these Inverted micelles. Pyrene exclmer to monomer fluorescence intensity ratio and fluorescene lifetime provided the means of measurement of internal fluidity and micropolarity, respectively. 

The present study demonstrates the utility of the above probe in describing the constitution of aggregates of certain alkarylsulfonates in hydrocarbon media. It also demonstrates the use of the probe technique in measuring the micropolarity of these same aggregates as a function of distance from the polar core. The micro-viscosity of inverted or normal micelles in the past has been estimated only as an average value of either the polar or non-polar regions (6). 

A kinetic study of the photosensitized oxidation of tryptophan-alkyl esters in Triton X-100 micellar solutions has been carried out by Criado et al. [24], The results obtained are presented in Table 6. These data show an important decrease in the relevance of the photo-oxidative pathway in the esterified compounds in the presence of the micelles. The magnitude of the effect seems to be extremely sensitive to the location of the probe, increasing as the length of the ester hydrocarbon chain increases. These results are interpreted in terms of the competition between the local oxygen concentration and the solvent micropolarity effect that... 

The micropolarity around the dendrophane core is reduced with increasing dendrimer generation. In the third generation material the polarity is roughly equivalent to that of ethanol, as measured by the fluorescent polarity probe 6 (p-toluidino) naphthalene-2-sulfonate (closely related to ANS). 

The principle advantage of the physical labeling method is the possibility of receiving direct information about the structure, mobility and local micropolarity of certain parts of a molecular object of any molecular mass. Developments in synthetic chemistry, biochemistry and site-directed mutagenesis have provided researchers with a wide assortment of labels and probes, and have paved the way for the specific modification of protein function groups, including enzyme active sites. 

Other aromatic amines with TICT-active amino groups include naphthyl-amines like DMANCN, which shows a well-separated dual fluorescence, and DANCA or related dyes which are used as fluorescence probes (sensing micropolarity) in biological investigations. In the latter case, only one (red-shifted) band (or two strongly overlapping bands) can be seen. 

As a fluorescence probe, a TICT compound possesses several merits. It can probe both microviscosity and micropolarity and furthermore, the mode of molecular motion necessary to the TICT phenomenon is well defined and limited to the rotation around a particular bond. This is a difference from intramolecular exciplex or excimer formation in which multiple modes of bond rotation and bending are compounded [7]. Fluorescence polarization studies also can not be free from ambiguity of the mode of rotation [8]. 

Electron spin resonance (ESR) is, as is NMR, a noninvasive method that does not require dilution of the sample. Paramagnetic spin probes are used as model drugs to investigate SLN dispersions. A large variety of spin probes is commercially available. The corresponding ESR spectra give information about the microviscosity and micropolarity. ESR permits the direct, repeatable, and noninvasive characterization of the distribution of the spin probe between the aqueous and the lipid phases. Experimental results demonstrate that storage-induced crystallization of SLN leads to an expulsion of the probe out of the lipid into the aqueous phase [43], Furthermore,... 

Since the dynamics of the twisted intramolecular charge transfer (TICT) process is very sensitive to the polarity of the medium, the local polarity of an organized medium may also be determined from the rate of the HCT process. For TNS, which is nearly nonfluorescent in water ((j)f = 10 and Xf = 60 ps), the emission quantum yield and lifetime increases nearly 50 times on binding to cyclodextrins and more than 500 times on binding to a neutral micelle, TX -100 [86]. Such a dramatic increase in the emission intensity and lifetime arises because of the marked reduction of the nonradiative HCT process inside the less polar microenvironment of the cyclodextrins and the micelle. Determination of the micropolarities of various organized assemblies using TICT probes has been surveyed quite extensively in several recent reviews [5b-d,f,86]. Therefore, in this chapter we will focus only on some selected works not covered in the earlier reviews. 

NMR Tis) reach their minimum value. The Wo-dependence of water pool polarity (often designated micropolarity) has been investigated using solubilizated which have solvent-sensitive UV-VIS absorption spectra [59, 60] and/or solvent-sensitive fluorescent lifetimes and quantum yields [61, 62]. Fluorescence polarization decay has been used to assess microviscosities. In such studies, it is important to determine by an independent technique the solubilizate s location within the reverse micelle, so that one is certain that the probe molecule is indeed located within the water pool rather than adsorbed at the interface (i. e. at the micelle boundary). At low Wq, contact between probe and interface is of course unavoidable. Even molecules which are quite soluble in water, such as phenols, are found to bind at the interface... 

As expected, water pool microviscosity decreased and micropolarity increases as Wq increases. With some probes, bulk water values are not obtained until Wq is much greater than 10 these may be cases where the probe reports on interfacial water as well as on the free bulk water in the pool. Indeed, the fluorescence polarization measurements of Zinsli [55] using l-amino-naphthalene-4-sulfonic acid (a water pool probe) and 2-(N-tetradecyl)amino-naphthalene-6-sulfonic acid (an interfacial probe) and the pKa measurements of Sunamoto and co-workers [56] on excited state pyranine have been interpreted in terms of a radially inhomogeneous microviscosity and micropolarity, with a viscous boundary layer of hydration water (type I) at the pool periphery and an inner core of water (type II) whose properties rapidly approach those of ordinary bulk water as Wq increases. 

Another remarkable property of the pyrene fluorescence is that a change of polarity in the vicinity of molecular pyrene leads to a dramatic modification of the intensity of the 0-0 vibronic band (/i peak), without affecting the intensity of the /j peak. The /1//3 ratio of the pyrene emission spectrum is therefore an extensively used probe parameter to determine the micropolarity of the environment in which it resides. 

Furthermore, using methyl orange (MO) and methylene blue (MB) as absorption probes, the micropolarity of the microemulsion system was investigated by UV-Vis spectroscopy [11]. The results demonstrated that micropolarity increased with the addition of IL only before the IL pools were formed. Once the IL was saturated for the solubilizing ability of the EO units and began to form cores of the microemulsions, the micropolarity became relatively constant. 

The absorption spectra can explore the effect of water content on the micropolarity of IL microemulsion [38]. Formation of water pools of Triton X-100/[bmim][BF ]/ water microemulsion was confirmed by riboflavin using methyl orange (MO) as probe the absorption spectra of MO in the microemulsion with different water contents are shown in Figure 18.3a [39]. The results suggested that when the water content is in the range of 0-5%, the absorption maximum of MO was red-shifted from 430 to 433nm (Rg. 18.3b) [39], Therefore, the micropolarity of bulk... 

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