A physicochemical properties

These few examples are of course a small and arbitrarily chosen set of methods for the calculation of log P values. Nevertheless, it is hoped that they demonstrate some basic principles in the prediction of a physicochemical property. 

Flotation or froth flotation is a physicochemical property-based separation process. It is widely utilised in the area of mineral processing also known as ore dressing and mineral beneftciation for mineral concentration. In addition to the mining and metallurgical industries, flotation also finds appHcations in sewage treatment, water purification, bitumen recovery from tar sands, and coal desulfurization. Nearly one biUion tons of ore are treated by this process aimuaHy in the world. Phosphate rock, precious metals, lead, zinc, copper, molybdenum, and tin-containing ores as well as coal are treated routinely by this process some flotation plants treat 200,000 tons of ore per day (see Mineral recovery and processing). Various aspects of flotation theory and practice have been treated in books and reviews (1 9). 

According to USP Chapter (1088) the term IVIVC refers to the establishment of a rational stochastical relationship between a biological property, or a parameter derived from a biological property produced by a dosage form, and a physicochemical property or characteristic of the same dosage... 

In order to study a physicochemical property of a dendritic molecule which does not involve either the creation of a cavity in the solvent or the change in its shape, we chose as representative a property that could be studied by a spectroscopic technique such as the molecular tumbling phenomena. Such phenomena occur both... 

On the other hand toluene (4) and 5-methoxy-indole (5) would not be considered very similar from a conventional point of view, yet their hemolytic activity is the same (logl/C = 1.93, where C is the minimal molar concentration which causes 100% hemolysis in rabbit erythrocytes l)). Obviously, topological similarity or dissimilarily is not always a factor which is relevant for biological activity. In the present example the relevant feature is a physicochemical property of the compounds, i.e. lipophilicity as expressed by the octanol/water partition coefficient... 

In order to calculate a physicochemical property, the structure of a molecule must be entered in some manner into an algorithm. Chemical structure notations for input of molecules into calculation software are described in Chapter 2, Section VII and may be considered as either being a 2D string, a 2D representation of the structure, or (very occasionally) a 3D representation of the structure. Of this variety of methods, the simplicity and elegance of the 2D linear molecular representation known as the Simplified Molecular Line Entry System (SMILES) stands out. Many of the packages that calculate physicochemical descriptors use the SMILES chemical notation system, or some variant of it, as the means of structure input. The use of SMILES is well described in Chapter 2, Section VII.B, and by Weininger (1988). There is also an excellent tutorial on the use of SMILES at www.daylight.com/dayhtml/smiles/smiles-intro.html. 

Structure-activity relationships (SARs) and quantitative structure-activity relationships (QSARs), referred to collectively as QSARs, can be used for the prediction of physicochemical properties, environmental fate parameters (e.g., accumulation and biodegradation), human health effects, and ecotoxicological effects. A SAR is a (qualitative) association between a chemical substructure and the potential of a chemical containing the substructure to exhibit a certain physical or biological effect. A QS AR is a mathematical model that relates a quantitative measure of chemical structure (e.g., a physicochemical property) to a physical property or to a biological effect (e.g., a toxicological endpoint). 

Henglein, A. Physicochemical properties of small metal particles in solution Microelectrode reactions, chemisorption, composite metal particles, and the atom-to-metal transition, J. Phys. Chem. 1993, 97, 5457. 

For the purposes of the present article, a physicochemical property is taken to be one which has been measured quantitatively. These properties may conveniently be divided into three classes. 

The descriptors used for pairwise distance measurements can be continuous, as in a physicochemical property, or binary e.g., the presence or absence of a specific substructure). For continuous chemical spaces, nearly all metrics are based on the generalized Minkowski metric given in (1), where % represents the Mi feature of the ith molecule, k is the total number of features, and r the order of the metric. 

Recent trend in biosensor manufacturing is to use synthetic procedures to incorporate a label indicative of a change in a physicochemical property upon binding to biomolecule. An example is the preparation of a novel, fluorescently active, carboxylic acid derivative of 2-pyridylazo compounds (PAR) [186]. 

Jenner MR, Smithson A. Physicochemical properties of the sweetner sucralose. J Food Sci 1989 54(6) 1646-1649. 

Pogliani, L. (1996a). A Strategy for Molecular Modeling of a Physicochemical Property Using a Linear Combination of Connectivity Indexes. Croat.Chem.Acta, 69,95-109. 

SEL/SHN3] Selivanova, N. M., Shneider, V. A., Physicochemical properties of selenates X. Heat of formation of beryllium selenate, Zh. Fiz. Khim., 35, (1961), 574-579, in Russian, English translation in [6ISEL/SHN4]. Cited on pages 393,463, 648. 

Acceptance criteria for accuracy and precision of standards and QCs must be determined during method validation, and are analogous to acceptance criteria for chromatographic methods. IAs may not be as inherently precise as chemical methods, because IAs measure a reaction rather than a physicochemical property of the analyte. In cases where internal standards are not used for recovery correction, two to three replicate assays may be conducted on a single sample to improve precision. Despite all of the available mathematical transformations, it is important to remember that this is not a linear system and caution must be used as the concentrations approach either the upper or lower end of the standard curve. For example, variability becomes too large to be acceptable as the B/B0 value goes beyond <0.1 or >0.9 for most limited reagent assays. 

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