Biological electrolytes

Added salts can encourage the aggregation of ions to micelles, salting out . This is of considerable importance in biological electrolytes, such as bile salts and phospholipids. 

Silver-silver chloride electrodes require Cl" ions for proper operation. When used in biological electrolytes, they have a sufficient supply of Cl" ions available. If they are used as skin-surface electrodes in such applications as EEG or EKG recording, it is necessary to use a wetting solution or paste which contains Cl" ions. 

A major advance in force measurement was the development by Tabor, Win-terton and Israelachvili of a surface force apparatus (SFA) involving crossed cylinders coated with molecularly smooth cleaved mica sheets [11, 28]. A current version of an apparatus is shown in Fig. VI-4 from Ref. 29. The separation between surfaces is measured interferometrically to a precision of 0.1 nm the surfaces are driven together with piezoelectric transducers. The combination of a stiff double-cantilever spring with one of a number of measuring leaf springs provides force resolution down to 10 dyn (10 N). Since its development, several groups have used the SFA to measure the retarded and unretarded dispersion forces, electrostatic repulsions in a variety of electrolytes, structural and solvation forces (see below), and numerous studies of polymeric and biological systems. 

Biological Corrosion The metabohc activity of microorganisms can either directly or indirectly cause deterioration of a metal by corrosion processes. Such activity can (1) produce a corrosive environment, (2) create electrolytic-concentration cells on the metal surface, (3) alter the resistance of surface films, (4) have an influence on the rate of anodic or cathodic reaction, and (5) alter the environment composition. 

The Henderson-Hasselbalch equation provides a general solution to the quantitative treatment of acid-base equilibria in biological systems. Table 2.4 gives the acid dissociation constants and values for some weak electrolytes of biochemical interest. 

A biologically important point is revealed by the basic shape of the titration curves of weak electrolytes in the region of the pK, pH remains relatively unaffected as increments of OH (or H ) are added. The weak acid and its conjugate base are acting as a buffer. 

Otherwise it has been shown that the accumulation of electrolytes by many cells runs at the expense of cellular energy and is in no sense an equilibrium condition 113) and that the use of equilibrium thermodynamic equations (e.g., the Nemst-equation) is not allowed in systems with appreciable leaks which indicate a kinetic steady-state 114). In addition, a superposition of partial current-voltage curves was used to explain the excitability of biological membranes112 . In interdisciplinary research the adaptation of a successful theory developed in a neighboring discipline may be beneficial, thus an attempt will be made here, to use the mixed potential model for ion-selective membranes also in the context of biomembrane surfaces. 

Background current, 21, 65 Background subtraction, 40, 106 Bacteria electrode, 182 Band microelectrodes, 130, 135 Beryllium, 82 Bienzyme electrodes, 175 Biocatalytic devices, 172 Biological recognition, 171 Biosensors, 50, 171 Bipotentiostat, 106 Blood electrolyte, 165 Boltzmann equation, 19 Brain analysis, 40, 116 Butler-Volmer equation, 14... 

Analysis of environmental samples is similar to that of biological samples. The most common methods of analyses are GC coupled to MS, ECD, a Hall s electrolytic conductivity detector (HECD), or a flame-ionization detector (FID). Preconcentration of samples is usually done by sorption on a solid sorbent for air and by the purge-and-trap method for liquid and solid matrices. Alternatively, headspace above liquid and... 

An example of amperometric methods used for analytical purposes is the sensor proposed in 1953 by Leland C. Clark, Jr. for determining the concentration of dissolved molecular oxygen in aqueous solutions (chiefly biological fluids). A schematic of the sensor is shown in Fig. 23.1. A cylindrical cap (1) houses the platinum or other indicator electrode (2), the cylindrical auxiliary electrode (3), and an electrolyte (e.g., KCl) solution (4). The internal solution is separated by the polymer... 

From an electrochemical viewpoint, biological systems are highly branched circuits consisting of ionic conductors of aqueous electrolyte solutions and highly selective membranes. These circuits lack metallic conductors, but it has been found relatively recently that they contain sections that behave like electronic conductors (i.e., sections in which electrons can be transferred over macroscopic distances, owing to a peculiar relay-type mechanism). 

All biological systems contain aqueous electrolyte solutions. These solutions consist of strong electrolytes (inorganic salts) as well as various organic substances with acidic or basic functional groups which usually behave as weak electrolytes. The solutions are often gel-like in their consistency because of the polyelectrolytes, proteins, and other macromolecules contained in them. The pH values of biological solutions as a rule are between 6.7 and 7.6. 

Many important processes such as electrochemical reactions, biological processes and corrosion take place at solid/liquid interfaces. To understand precisely the mechanism of these processes at solid/liquid interfaces, information on the structures of molecules at the electrode/electrolyte interface, including short-lived intermediates and solvent, is essential. Determination of the interfacial structures of the intermediate and solvent is, however, difficult by conventional surface vibrational techniques because the number of molecules at the interfaces is far less than the number of bulk molecules. 

Interfacial water molecules play important roles in many physical, chemical and biological processes. A molecular-level understanding of the structural arrangement of water molecules at electrode/electrolyte solution interfaces is one of the most important issues in electrochemistry. The presence of oriented water molecules, induced by interactions between water dipoles and electrode and by the strong electric field within the double layer has been proposed [39-41]. It has also been proposed that water molecules are present at electrode surfaces in the form of clusters [42, 43]. Despite the numerous studies on the structure of water at metal electrode surfaces using various techniques such as surface enhanced Raman spectroscopy [44, 45], surface infrared spectroscopy [46, 47[, surface enhanced infrared spectroscopy [7, 8] and X-ray diffraction [48, 49[, the exact nature of the structure of water at an electrode/solution interface is still not fully understood. 

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