Electrical microenvironment

Considerable progress has been made within the last decade in elucidating the effects of the microenvironment (such as electric charge, dielectric constant and lipophilic or hydrophilic nature) and of external and internal diffusion on the kinetics of immobilized enzymes (7). Taking these factors into consideration, quantitative expressions have been derived for the kinetic behavior of relatively simple enzyme systems. In all of these derivations the immobilized enzymes were treated as simple heterogeneous catalysts. 

Fluorescence is also a powerful tool for investigating the structure and dynamics of matter or living systems at a molecular or supramolecular level. Polymers, solutions of surfactants, solid surfaces, biological membranes, proteins, nucleic acids and living cells are well-known examples of systems in which estimates of local parameters such as polarity, fluidity, order, molecular mobility and electrical potential is possible by means of fluorescent molecules playing the role of probes. The latter can be intrinsic or introduced on purpose. The high sensitivity of fluo-rimetric methods in conjunction with the specificity of the response of probes to their microenvironment contribute towards the success of this approach. Another factor is the ability of probes to provide information on dynamics of fast phenomena and/or the structural parameters of the system under study. 

Dopant orientation during and following electric field-induced poling can be studied continuously and in real time in order to examine the microenvironment surrounding the dopants in terms of the polymer relaxations and the applied corona field. In the results presented below, the SHG of 4-dimethylamino-4 -nitrostilbene (DANS) dispersed in polystyrene (PS) or poly(methyl methacrylate) (PMMA) matrices has been examined in corona poled films as a function of temperature in order to understand the effect of thermal conditions on the temporal stability of the dopant orientation. 

Since these interfaces are usually constructed of charged detergents a diffuse electrical double layer is produced and the interfacial boundary can be characterized by a surface potential. Consequently, electrostatic as well as hydrophilic and hydrophobic interactions of the interfacial system can be designed. In this report we will review our achievements in organizing photosensitized electron transfer reactions in different microenvironments such as bilayer membranes and water-in-oil microemulsions.In addition, a novel solid-liquid interface, provided by colloidal Si02 particles in an aqueous medium will be discussed as a means of controlling photosensitized electron transfer reactions. 

The usefulness of the micelle as a model colloid for studying many problems of general interest in colloid science has been pointed out.7 Micellar systems have proved to be very useful for studying the factors involved in hydrophobic and electrical interactions and for posing and answering many questions regarding the microenvironments encountered in interfacial systems of other kinds and membranes.712 Various spectroscopic methods are particularly useful. The use of micelles as model systems for membranes or some aspects of enzymes has very important biological implications.1315... 

Smaller environments can exist even within one of these microenvironments. For example, within one piece of wood associated with metal, there can be regions of an electric field that would cause hydrolytic or alkaline degradation of cellulose or lignin. 

Several important cell types are sensitive to the electrical characteristics of the cellular microenvironment. Neurons, cardiac myocytes, and retinal cells all generate and can be stimulated with electrical impulses. Because of the importance of these cell types, various methods have been devised to record or stimulate electrical activity within cells cultured in vitro. Traditionally, the electrical activity of cells has been recorded or stimulated by simply placing electrodes in the... 

Microfabrication technology has provided a plethora of tools and methods to engineer the position and microenvironment of cells in vitro. The unprecedented level of control over the mechanical, chemical, and electrical nature of the cellular microenvironment allows investigation of questions not addressable with conventional tools and methods. The unique insight into normal and abnormal cell behavior afforded by microfabricated tools and methods may one day lead to cures for injuries and diseases, and the ability to direct cell growth and behavior for tissue engineering or industrial applications. 

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