Water molecular properties

The input file for an STO-3G calculation of the bond distances, energies, and other molecular properties of the isolated water molecule in the gaseous state at 0 kelvins is... 

The dipole moment p. is a molecular property defined as the product of charge (usually just a fraction of the electronic change, of course) and distance between the centers of positive and negative charge in the molecule. The dipole moment is usually expressed in debyes (D), where 1 D = 1(T esu in SI units 1 D = 3.3356 X 10 ° C-m. so, for example, the dipole moment of water is 1.84 D or 6.14 in units of 10 C-m. Again a rough correspondence is seen between this property of a molecule and its polarity, though e and p. are not precisely correlated. 

Given the diversity of different SCRF models, and the fact that solvation energies in water may range from a few kcal/mol for say ethane to perhaps 100 kcal/mol for an ion, it is difficult to evaluate just how accurately continuum methods may in principle be able to represent solvation. It seems clear, however, that molecular shaped cavities must be employed, the electiostatic polarization needs a description either in terms of atomic charges or quite high-order multipoles, and cavity and dispersion terms must be included. Properly parameterized, such models appear to be able to give absolute values with an accuracy of a few kcal/mol." Molecular properties are in many cases also sensitive to the environment, but a detailed discussion of this is outside the scope of this book. ... 

In both variants of the approach, i) and ii), the ligands detected in a NMR screen would be subjected to further modifications, and become larger during the design process. The properties of the compound library need to fulfill therefore a number of NMR-specific requirements. The compounds need to be soluble in water, their molecular properties should not exceed half the number that is defined in the Lipinski rules for molecular... 

Kier and coworkers found that the molecular connectivity-index and such molecular properties as polarizability, molecular volume," and partition coefficients between water and octanol"" show very good correlation. Because all of these properties could be correlated with biological activity. 

C14-0055. Mercury, water, and bromine are liquids at J — 298 K, P = 1 bar. Their molar entropies are in the sequence H2 O < Hg < BT2. Using molecular properties, explain why bromine has more entropy than mercuiy but water has the least entropy of these three. 

The SPARC (Sparc Performs Automated Reasoning in Chemistry) approach was introduced in the 1990s by Karickhoff, Carreira, Hilal and their colleagues [16-18]. This method uses LSER [19] to estimate perturbed molecular orbitals [20] to describe quantum effects such as charge distribuhon and delocalizahon, and polarizability of molecules followed by quanhtative structure-activity relationship (QSAR) studies to correlate structure with molecular properties. SPARC describes Gibbs energy of a given process (e.g. solvation in water) as a sum of ... 

The coefficients Co, nnd C2 (denoted as mq, ai, and aj in Ref. 33) are influenced by various molecular properties of the solvent and an ion, including their electron-donating or accepting abilities. Hence, these coefficients are specific to the ion. Nevertheless, they may be considered as common to a family of ions such as the polyanions whose surface atoms, directly interacting with solvents, are oxygens. This is the case for hydrated cations or anions whose surfaces are composed of some water molecules that interact with outer water molecules in the W phase or with organic solvents in the O phase. 

Lipophilicity is a molecular property expressing the relative affinity of solutes for an aqueous phase and an organic, water-immiscible solvent. As such, lipophilicity encodes most of the intermolecular forces that can take place between a solute and a solvent, and represents the affinity of a molecule for a lipophilic environment. This parameter is commonly measured by its distribution behavior in a biphasic system, described by the partition coefficient of the species X, P. Thermodynamically, is defined as a constant relating the activity of a solute in two immiscible phases at equilibrium [111,112]. By convention, P is given with the organic phase as numerator, so that a positive value for log P reflects a preference for the lipid phase ... 

There are two pathways by which a drug molecule can cross the epithelial cell the transcellular pathway, which requires the drug to permeate the cell membranes, and the paracellular pathway, in which diffusion occurs through water-filled pores of the tight junctions between the cells. Both the passive and the active transport processes may contribute to the permeability of drugs via the transcellular pathway. These transport pathways are distinctly different, and the molecular properties that influence drug transport by these routes are also different (Fig. 

Kamlet, M. J., Doherty, R. M., Abboud, J. L., Abraham, M. H., Taet, R. W., Linear solvation energy relationships 36. Molecular properties governing solubilities of organic nonelectrolytes in water, J. Pharm. Sci. 1986, 75, 338-349. 

Many groups have discussed the correlation between solubility and molecular properties [14-19], and the octanol/water partition coefficient, the molecular volume and surface area, the boiling point and charge distribution in the molecules are well-documented molecular descriptors that correlate strongly with experimental solubility. 

Dickhut, R.M., Miller, K.E., Andren, A.W. (1994) Evaluation of total molecular surface area for predicting air water partitioning properties of hydrophobic aromatic chemicals. Chemosphere 29, 283-297. 

The background theory that underlies the FEP method as well as the molecular mechanics force fields that relate molecular structure to energy are reviewed in section one of the book. Section two describes the use of free energy calculations for determining molecular properties of ligands, including solvation, as calculated using both implicit and explicit water... 

It has also been shown [254] that a commercial petroleum sulfonate surfactant which consists of a diverse admixture of monomers does not exhibit behavior typically associated with micelle formation (i.e., a sharp inflection of solvent properties as the concentration of surfactant reaches CMC). These surfactants exhibit gradual change in solvent behavior with added surfactant. This gradual solubility enhancement indicates that micelle formation is a gradual process instead of a single event (i. e., CMC does not exist as a unique point, rather it is a continuous function of molecular properties). This type of surfactant can represent humic material in water, and may indicate that DHS form molecular aggregates in solution, which comprise an important third phase in the aqueous environment. This phase can affect an increase in the apparent solubility of very hydrophobic chemicals. 

Five organic solvents [acetonitrile, methanol, tetrahydrofuran (THF), acetone, and dimethylformamide], which are homogeneously miscible with water, have been used as modifiers to study the relationship of the selectivity of the solvent to the molecular properties of analytes. The polar interaction... 

Normal-phase liquid chromatography is thus a steric-selective separation method. The molecular properties of steric isomers are not easily obtained and the molecular properties of optical isomers estimated by computational chemical calculation are the same. Therefore, the development of prediction methods for retention times in normal-phase liquid chromatography is difficult compared with reversed-phase liquid chromatography, where the hydrophobicity of the molecule is the predominant determinant of retention differences. When the molecular structure is known, the separation conditions in normal-phase LC can be estimated from Table 1.1, and from the solvent selectivity. A small-scale thin-layer liquid chromatographic separation is often a good tool to find a suitable eluent. When a silica gel column is used, the formation of a monolayer of water on the surface of the silica gel is an important technique. A water-saturated very non-polar solvent should be used as the base solvent, such as water-saturated w-hexane or isooctane. 

A quantitative analysis of the structure-retention relationship can be derived by using the relative solubility of solutes in water. One parameter is the partition coefficient, log P, of the analyte measured as the octanol-water partition distribution. In early work, reversed-phase liquid chromatography was used to measure log P values for drug design. Log P values were later used to predict the retention times in reversed-phase liquid chromatography.The calculation of the molecular properties can be performed with the aid of computational chemical calculations. In this chapter, examples of these quantitative structure-retention relationships are described. 

To determine the molecular properties influencing the diffusion process they investigated the relationship between experimental stratum corneum-water partition coefficients and permeability data for 45 compounds. Rearrangement of the logarithmic form of Eq. 4 led to... 

Taft RW, Abraham MW, Doherty RM, Kamlet MJ (1985) The molecular properties governing solubilities of organic molecules in water. Nature 315 384-386. 

Based on their molecular properties as well as the properties of the solvent, each inorganic or organic contaminant exhibits an adsorption isotherm that corresponds to one of the isotherm classifications just described. Figure 5.1 illustrates these isotherms for different organic contaminants, adsorbed either from water or hexane solution on kaolinite, attapulgite, montmorillonite, and a red Mediterranean soil (Yaron et al. 1996). These isotherms may be used to deduce the adsorption mechanism. 

Independent of the molecular properties of contaminants, the subsurface solid phase constituents are a major factor that control the adsorption process. Both the mineral and organic components of the solid phases interact differentially with ionic and nonionic pollutants, and in all cases, environmental factors, such as temperature, subsurface water content, and chemistry, affect the mechanism, extent, and rate of contaminant adsorption. 

The solubility of contaminants in subsurface water is controlled by (1) the molecular properties of the contaminant, (2) the porous media solid phase composition, and (3) the chemistry of the aqueous solution. The presence of potential cosolvents or other chemicals in water also affects contaminant solubility. A number of relevant examples selected from the literature are presented here to illustrate various solubility and dissolution processes. 

Overall, dissolution in the electrolyte solutions of all studied compounds led to substantial decreases in their concentrations in the original crude oil. However, the rate of decrease was different for each compound, in accordance with the molecular properties. Bennett and Larter (1997) note that, in comparison with the original crude oil, the concentration of phenol decreased relative to cresol. The change in phenol content relative to cresol is highlighted by measuring the ratio (phenol/o- -i-m- + p- cresol), which shows that the reduction of more hydrophilic phenol relative to cresol is in accord with their relative dissolution in water. 

All surfactants have a common molecular similarity. A portion of the molecule has a long nonpolar chain, frequently a hydrocarbon chain, that promotes oil solubility but water insolubility (the hydrophobic portion— water hating). Another part of the molecule promotes oil insoluble and water soluble properties (the hydrophilic portion—water loving). 

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