Microenvironments

Talley C E and Dunn R C 1999 Single molecules as probes of lipid membrane microenvironments J. Chem. Phys. B 103 10 214-20... 

Inclusion compounds open up a wide area of applications (1,2,17—28). An important aspect in this connection is the specific microenvironment created by the host enclosure of the guest which exerts an influence on the physical, spectroscopic, chemical, and other properties of the guest. 

Mass-action model of surfactant micelle formation was used for development of the conceptual retention model in micellar liquid chromatography. The retention model is based upon the analysis of changing of the sorbat microenvironment in going from mobile phase (micellar surfactant solution, containing organic solvent-modifier) to stationary phase (the surfactant covered surface of the alkyl bonded silica gel) according to equation ... 

The model was tested by the micellar liquid chromatography separ ation of the five rarbornicin derivatives and four ethers of hydroxybenzoic acid. Micellar mobile phases were made with the sodium dodecylsulfate and 1-pentanol or isopentanol as modifier. In all cases the negative signs of the coefficients x and y indicate that at transition of the sorbat from the mobile on the stationar y phase the number of surfactant monomers as well as the number of modifier molecules increases in its microenvironment. 

Sulfate reducers. Active sulfate reducers are found in anaerobic environments. These environments may be highly localized, such as inside a tubercle or beneath a spotty deposit. A thin, fairly regular biofilm is difficult to perceive in such microenvironments. 

Exposure assessment techniques now attempt to include as many as possible of the locations in which individuals now spend time. The concept involves identification of microenvironments which are important for potential exposure. For example, exposure to CO would include time spent in commuting, parking garages, in residences with gas stoves, as well as time spent outdoors. This approach classifies time spent in these microenvironments and the typical concentrations of CO in these locations. 

The Modeling Engine in THERdbASE has the following model groups 1) Population Distributions, 2) Location/Activity Patterns, 3) Food Consumption Patterns, 4) Agent Releases Characteristics, 5) Microenvironment Agent Concentrations, 6) Macroenvironment Agent Concentrations, 7) Exposure Patterns and Scenarios, 8) Dose Patterns, and 9) Risk Assessment. 

Orlova et al. (2003) theoretically studied the mechanism of the firefly bioluminescence reaction on the basis of the hybrid density functional theory. According to their conclusion, changes in the color of light emission by rotating the two rings on the 2-2 axis is unlikely, whereas the participation of the enol-forms of oxyluciferin in bioluminescence is plausible but not essential to explain the multicolor emission. They predicted that the color of the bioluminescence depends on the polarization of the oxyluciferin molecule (at its OH and O-termini) in the microenvironment of the luciferase active site the... 

It is now believed from studies on the natural photosynthetic systems that microenvironments for the photoinduced ET reaction play an important role in the suppression of the back ET [1-3]. As such reaction environments, molecular assembly systems such as micelles [4], liposomes [5], microemulsions [6-8] and colloids [9] have been extensively investigated. In them, the presence of microscopically heterogeneous phases and interfacial electrostatic potential is the key to the ET rate control. 

The polyelectrolyte covalently functionalized with reactive groups may be viewed as an enzyme-like functional polymer or as a molecular reaction system in the sense that it has both reactive centers and reaction rate-controlling microenvironments bound together on the same macromolecule. 

In the following chapters, we will concern ourselves with the nature of the interfacial microenvironments of some polyelectrolytes whose functionality controls photoinduced ET. Emphasis will be placed on the local electrostatic potential and also on the microphase structure of some amphiphilic polyelectrolytes in aqueous solution. 

A merocyanine dye, l-ethyl-4-(2-(4-hydroxyphenyl)ethenyl)pyridinium bromide (M-Mc, 2), exhibits a large spectral change according to the acid-base equilibrium [40, 41]. The equilibrium is affected by the local electrostatic potential and the polarity of the microenvironment around the dye. Hence, this dye is useful as a sensitive optical probe for the interfacial potential and polarity when it is covalently attached to the polyelectrolyte backbone. 

This finding may be rationalized for the following reasons. The total length of the Me pendant moiety from the cylinder axis is approximately 15 A when the dye moiety is stretched out from the polymer main chain. Since the dye moiety is linked to the main chain via a flexible chemical bond, it may be able to reside at any distance between 3 and 15 A from the cylinder axis. Thus, on average the Me residues would experience the polyanion microenvironment at a distance of about 10 A. 

Morishima et al. [30, 50-54, 73-76] have made extensive investigations on photoinduced ET, using polycyclic aromatic chromophores covalently attached to polyelectrolytes. They were the first to show that the polyeletrolyte molecular surface provides an unusual microenvironment which greatly changes the rate of photoinduced ET and the fate of the charged photoproducts. 

The microphase structure of amphiphilic polyelectrolytes in aqueous solution provides photoinduced ET with an interesting microenvironment, where a photoactive chromophore and a donor or acceptor can be held apart at different locations. Photoinduced ET in such separated donor-acceptor systems allows an efficient charge separation to be achieved. 

Bierie B, Moses HL (2006) Tumour microenvironment TGF 3 the molecular Jekyll and Hyde of cancer. Nat Rev Cancer 6 506-520... 

Vaupel P, Kallinowski F, Okunieff P (1989) Blood flow, oxygen and nutrient supply, and metabolic microenvironment of human tumors a review. Cancer Res 49 6449-6465... 

The immobilization procedure may alter the behavior of the enzyme (compared to its behavior in homogeneous solution). For example, the apparent parameters of an enzyme-catalyzed reaction (optimum temperature or pH, maximum velocity, etc.) may all be changed when an enzyme is immobilized. Improved stability may also accrue from the minimization of enzyme unfolding associated with the immobilization step. Overall, careful engineering of the enzyme microenvironment (on the surface) can be used to greatly enhance the sensor performance. More information on enzyme immobilization schemes can be found in several reviews (7,8). 

As discussed and demonstrated in the previous chapters, the catalytic effect of several classes of enzymes can be attributed to electrostatic stabilization of the transition state by the surrounding active site. Apparently, enzymes can create microenvironments which complement by their electrostatic potential the changes in charges during the corresponding reactions. This provides a simple and effective way of reducing the activation energies in enzymatic reactions. 

In a more general application, thermoluminescence is used to study mechanisms of defect annealing in crystals. Electron holes and traps, crystal defects, and color-centers are generated in crystals by isotope or X-ray irradiation at low temperatures. Thermoluminescent emission during the warmup can be interpreted in terms of the microenvironments around the various radiation induced defects and the dynamics of the annealing process (117-118). ... 

Thus, In the microenvironment, calibration standards have different requirements than standards that are used to relate the Instrument signal to compound concentration. Standards used to calibrate the response of a mlcrospectrofluorometer for day-to-day or Instrument-to-lnstrument comparisons must not photobleach. Conversely, a standard used to quantify the concentration of an analyte In a sample must photobleach In a manner Identical to that of the sample. 

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