Structure quantitative methods

There is also a quantitative method of measuring acidities. All protons can be given a number that quantifies exactly how acidic they are. This value is called p/fa- It is impossible to figure out the exact pA"a by just looking at a structure. The p/fa must be determined empirically through experimentation. Many professors require that you know some general p/fa s for certain classes of compounds (for instance, all alcoholic protons, RO-H, will have the same ballpark p/fa)- Most textbooks will have a chart that you can memorize. Your instructor will tell you if you are expected to memorize this chart. Either way, you should know what the numbers mean. 

SEC-FTIR yields the average polymer structure as a function of molecular mass, but no information on the distribution of the chemical composition within a certain size fraction. SEC-FTIR is mainly used to provide information on MW, MWD, CCD, and functional groups for different applications and different materials, including polyolefins and polyolefin copolymers [703-705]. Quantitative methods have been developed [704]. Torabi et al. [705] have described a procedure for quantitative evaporative FUR detection for the evaluation of polymer composition across the SEC chromatogram, involving a post-SEC treatment, internal calibration and PLS prediction applied to the second derivative of the absorbance spectrum. 

Our band shape methods have made use of the principal component method of factor analysis (Pancoska etal., 1979 Malinowski, 1991) to characterize the protein spectra in terms of a relatively small number of coefficients (loadings) (Pancoska et al., 1994 1995 Baumruk et al., 1996). This approach is similar, in its initial stages, to various methods (Selcon, Variselect, etc.) that have been used for determining protein secondary structure from ECD data (Hennessey and Johnson, 1981 Provencher and Glockner, 1981 Johnson, 1988 Pancoska and Keiderling, 1991 Sreerama and Woody, 1993, 1994 Venyaminov and Yang, 1996). At this point, one can say these traditional quantitative methods have had little impact upon structural studies of denatured proteins. 

For the establishment of a preparation method for LB films with well-defined noncentrosymmetric structure, quantitative evaluation of noncentrosymmetric molecular orientation is essential. The linear Stark effect, which is observed only in noncentrosymmetric materials, is expected to be helpful for the characterization of noncentrosymmetric molecular orientation in LB films [5], In this section, we describe the quantitative evaluation of noncentrosymmetric molecular orientation in LB films by the linear Stark effect measurement. 

Classical chemo metric methods, such as the Quantitative Structure Activity Relationships, QSAR, can be used to relate the chemical characteristics of a molecule to its structure. QSAR methods have been widely used in the pharmaceutical field for drug design, but they are also very useful for many other... 

Molecular fluorescence involves the emission of radiation as excited electrons return to the ground state. The wavelengths of the radiation emitted are different from those absorbed and are useful in the identification of a molecule. The intensity of the emitted radiation can be used in quantitative methods and the wavelength of maximum emission can be used qualitatively. A considerable number of compounds demonstrate fluorescence and it provides the basis of a very sensitive method of quantitation. Fluorescent compounds often contain multiple conjugated bond systems with the associated delocalized pi electrons, and the presence of electron-donating groups, such as amine and hydroxyl, increase the possibility of fluorescence. Most molecules that fluoresce have rigid, planar structures. 

Traube s rule accommodates the balance between hydrophobicity and hydro-philicity. It has been extended somewhat and formalized with the development of quantitative methods to estimate the surface area of molecules based on their structures [19, 237]. The molecular surface area approach suggests that the number of water molecules that can be packed around the solute molecule plays an important role in the theoretical calculation of the thermodynamic properties of the solution. Hence, the molecular surface area of the solute is an important parameter in the theory. In compounds other than simple normal alkanes, the functional groups will tend to be more or less polar and thus relatively compatible with the polar water matrix [227,240]. Hence, the total surface area of the molecule can be subdivided into functional group surface area and hydro carbonaceous surface area . These quantities maybe determined for simple compounds as an additive function of constituent groups with subtractions made for the areas where intramolecular contact is made and thus no external surface is presented. 

Weibel ER, Gomez DM (1962) Architecture of the human lung. Use of quantitative methods establishes fundamental relations between size and number of lung structures. Science 137(3530) 577-585. 

This series of volumes, established by Victor Gold in 1963, aims to bring before a wide readership among the chemical community substantial, authoritative and considered reviews of areas of chemistry in which quantitative methods are used in the study of the structures of organic compounds and their relation to physical and chemical properties. 

It is critical when performing quantitative GC/MS procedures that appropriate internal standards are employed to account for variations in extraction efficiency, derivatization, injection volume, and matrix effects. For isotope dilution (ID) GC/MS analyses, it is crucial to select an appropriate internal standard. Ideally, the internal standard should have the same physical and chemical properties as the analyte of interest, but will be separated by mass. The best internal standards are nonradioactive stable isotopic analogs of the compounds of interest, differing by at least 3, and preferably by 4 or 5, atomic mass units. The only property that distinguishes the analyte from the internal standard in ID is a very small difference in mass, which is readily discerned by the mass spectrometer. Isotopic dilution procedures are among the most accurate and precise quantitative methods available to analytical chemists. It cannot be emphasized too strongly that internal standards of the same basic structure compensate for matrix effects in MS. Therefore, in the ID method, there is an absolute reference (i.e., the response factors of the analyte and the internal standard are considered to be identical Pickup and McPherson, 1976). 

The structure-activity relationships of thyroid hormones and related structural analogs have been studied using both qualitative and quantitative methods, including the Hansch correlation. The structural requirements for receptor binding, and therefore hormone activity, are ... 

ILs have been used in the CE-electrochemiluminescence (ECL) method to determine bioactive constituents in Chinese traditional medicine [58]. CE/Tris(2,2-bipyridyl) ruthenium(II) (Ru(bpy)3 +) ECL, CE-ECL, with an IL detection system was established to determine bioactive constituents in Chinese traditional medicine opium poppy, which contains large amounts of coexistent substances. Running buffer containing 25 mM borax-8 mM [C2CiIm][BF4] (pH 9.18) was used, which resulted in significant changes in separation selectivity and obvious enhancement in ECL intensities for those alkaloids with similar structures. Quantitative analysis of four alkaloids was... 

Any study of the polymerization kinetics of a bisbenzocyclobutene monomer is complicated by the lack of understanding of the resulting polymer s structure and the fact that as the polymerization proceeds, the reaction mixture crosslinks and vitrifies. This vitrification limits somewhat the number of quantitative methods which can be used to study the bisbenzocyclobutene polymerization kinetics. Some techniques are however useful under these constraints and good kinetic results have been obtained by both infrared and thermal analysis methods. 

Infrared spectroscopy, before its present expansion as a quantitative method, was always used as a semi-empirical method for structural analysis. This application stems from the extension of the above rules to organic polyatomic molecules. 

It should be mentioned that there are other types of network architectures that can be used, but the feed-forward structure is shown here due to its relative simplicity and high relevance to quantitative method building. 

In contrast to the qualitative methods described above, the quantitative methods of molecular structure determination aim at finding the... 

After several decades of research, fundamental aspects of the chemical composition and structure of marine organic matter remain elusive. Advances in the chemical characterization of marine organic matter are, in large part, dependent on the development of quantitative methods for its concentration and isolation from seawater. Each of the major methods currently used for the isolation of marine DOM recovers around one-third of the DOM in seawater (solid-phase extractions, using XAD resins or C18 adsorbents, and ultrafiltration). A coupled reverse osmosis-electrodi-alysis method has recently been used to recover an average of 75% 12% of marine DOM from 16 seawater samples however, the method has emerged too recently to have been well tested at this time. 

Significant efforts have been made to assemble teratogenic data basses with peer-reviewed evaluations (ref. 1). New avenues for the SAR studies have been opened, such as quantitative methods for structural superposition of molecules and for superposition of their reactivity characteristics (ref. 2). Emphasis has been placed on the electrostatic properties of the molecules, such as the molecular electrostatic potential, the electric fields, and the polarizability terms calculated from perturbation expansions (ref. 2). Computer-assisted multivariate SAR which deals with many variables simultaneously has been advanced (ref. 3). 

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