Correlations between structure and

Correlations between structure and mass spectra were established on the basis of multivariate analysis of the spectra, database searching, or the development of knowledge-based systems, some including explicit management of chemical reactions. 

Another important correlation between structure and properties in the pteridine series is seen in the solubilities, to which insufficient attention has been paid in general. Introduction of an amino group into pteridine (1) lowers the solubility in all solvents despite the fact... 

G. Gompper, M. Schick. Correlation between structural and interfacial properties of amphiphilic systems. Phys Rev Lett 65 1116-1119, 1990. 

The concept of electrostatic complimentarity is somewhat meaningless without the ability to estimate its contribution to AAg. Thus, it is quite significant that the electrostatic contribution to AAthat should be evaluated by rigorous FEP methods can be estimated with a given enzyme-substrate structure by rather simple electrostatic models (e.g., the PDLD model). It is also significant that calculated electrostatic contributions to A A g seem to account for its observed value (at least for the enzymes studied in this book). This indicates that simple calculations of electrostatic free energy can provide the correlation between structure and catalytic activity (Ref. 10). 

In view of the arguments presented in this chapter, as well as in previous chapters, it seems that electrostatic effects are the most important factors in enzyme catalysis. Entropic factors might also be important in some cases but cannot contribute to the increase of kcJKM. Furthermore, as much as the correlation between structure and catalysis is concerned, it seems that the complimentarity between the electrostatic potential of the enzyme and the change in charges during the reaction will remain the best correlator. Finally, even in cases where the source of the catalytic activity of a given enzyme is hard to elucidate, it is expected that the methods presented in this book will provide the crucial ability to examine different hypothesis in a reliable way. 

Kim and Somorjai have associated the different tacticity of the polymer with the variation of adsorption sites for the two systems as titrated by mesitylene TPD experiments. As discussed above, the TiCl >,/Au system shows just one mesitylene desorption peak which was associated with desorption from low coordinated sites, while the TiCl c/MgClx exhibits two peaks assigned to regular and low coordinated sites, respectively [23]. Based on this coincidence, Kim and Somorjai claim that isotactic polymer is produced at the low-coordinated site while atactic polymer is produced at the regular surface site. One has to bear in mind, however, that a variety of assumptions enter this interpretation, which may or may not be vahd. Nonetheless it is an interesting and important observation which should be confirmed by further experiments, e.g., structural investigations of the activated catalyst. From these experiments it is clear that the degree of tacticity depends on catalyst preparation and most probably on the surface structure of the catalyst however, the atomistic correlation between structure and tacticity remains to be clarified. 

These spectroscopic and theoretical developments have stimulated the recent advances on electron-transfer dynamics at ITIES. In addition to the correlation between structure and dynamics of charge transfer, fundamental problems in connection with the energetics of ET reactions remain to be fully addressed. We shall consider these problems primarily before discussing kinetic aspects in full detail. 

In another series of experiments [149] the correlation between structure and dynamics was investigated on dilute solutions of 12-arm PS star systems (Mw = 14.9 104 g/mol) in d-tetrahydrofurane, where either only one or all 12 arms were protonated (labelled). 

It is quite difficult to predict or design a novel small molecule with desired photophysical properties because a direct correlation between structures and photophysical... 

Myelin in situ has a water content of about 40%. The dry mass of both CNS and PNS myelin is characterized by a high proportion of lipid (70-85%) and, consequently, a low proportion of protein (15-30%). By comparison, most biological membranes have a higher ratio of proteins to lipids. The currently accepted view of membrane structure is that of a lipid bilayer with integral membrane proteins embedded in the bilayer and other extrinsic proteins attached to one surface or the other by weaker linkages. Proteins and lipids are asymmetrically distributed in this bilayer, with only partial asymmetry of the lipids. The proposed molecular architecture of the layered membranes of compact myelin fits such a concept (Fig. 4-11). Models of compact myelin are based on data from electron microscopy, immunostaining, X-ray diffraction, surface probes studies, structural abnormalities in mutant mice, correlations between structure and composition in various species, and predictions of protein structure from sequencing information [4]. 

Aluminum-deficient Y zeolites. The properties of aluminum-deficient Y zeolites, including ultrastable zeolites, have been reviewed in several papers (9,33-35). During the last several years, new techniques have been applied to study these materials. This led to a better understanding of their structural characteristics and of the correlations between structure and properties. We shall discuss the structure and properties of aluminum-deficient Y zeolites, with the emphasis on more recently published results. 

This section considers recent attempts to extrapolate from observed structures to the experimentally unattainable transition state structures for bond making and breaking reactions. (Transition state structures for conformational changes are experimentally observable in the crystal in favourable cases, as described in Section 3, pages 135-136.) The approach builds on the regular correlations between structure and reactivity, particularly the linear correlations with bond length described in the previous section. 

Despite its simplicity, the statistical method has been quite successful in predicting the effect of various chemical variables on network formation (cf. e.g. [29, 30, 34-37]). Since the internal structure of the gel can be characterized to a certain degree by the statistical method (e.g. average size of dangling chains and weight fraction of material in them), these methods offer a basis for correlations between structure and viscoelastic properties. 

Minerals Metallurgical Processing, 2(4) 206 - 211 Nagaraj, D. R., et al., 1982. Copper depresants correlation between structure and activity. 112 SME-AIME Annual Meeting, 89 - 93... 

Carlucci MJ, Pujol CA, Ciancia M, Noseda MD, Matulewicz MC, Damonte EB, Cerezo AS (1997) Antiherpetic and anticoagulant properties of carrageenans from the red seaweed Gigartina skottsbergii and their cyclized derivatives correlation between structure and biological activity. Int J Biol Macromol 20 97-105... 

The wide variation in structure, ranging from complex steroids to the inert monatomic gas xenon, led to several theories of anesthetic action. The mechanism by which inhalation anesthetics manifest their effect is not exactly known. Since they do not belong to one chemical class of compounds, the correlations between structure and activity are also not known. Inhalation anesthetics are nonspecific and therefore there are not specific antagonists. Interaction of inhalation anesthetics with cellular structures can only be described as van der Waals interactions. There are a number of hypotheses that have been advanced to explain the action of inhalation anesthetics however, none of them can adequately describe the entire spectrum of effects caused by inhalation anesthetics. 

The most important tool in the arsenal of the product innovators is the ability to make predictions on which structure would lead to what properties, as well as what structure modifications would lead to what property modifications. The reverse research from a given set of properties to material that has these properties is even more important in creating new products and in modifying existing products. In most cases of molecular properties, it is more realistic to depend on empirical correlations between structure and properties. Forward and reverse searches are currently only available for simple physical-chemical properties, such as boiling points and densities such a facility is still not available for biological properties, such as narcotic and antibiotic activities. The development of such search engines would have a tremendous impact on the productivity of product innovators. 

Processes for two-electron reductions, two sequential one-electron reductions with a radical anion intermediate, and reactions of dianions with unreduced parents to give radical anions were observed. Structural reorganization is occasionally observed, particularly in the case of Fe(CO)2 and Fe(CO)3 complexes (26). There appears to be little correlation between structure and electrochemical behavior. In general, the presence of metal-metal bonds in the substrate appears to correlate well with the ability to yield a stable radical anion on reduction. The lack of a metal-metal bond correlates, although poorly, with the ability to form radical cations (25). At present, the predictability of results from reduction in metal-carbonyl complexes is very low. The area remains one in which a great deal more work is needed. 

Pereira, M. S., Melo, F. R., and Mourao, P. A. (2002a). Is there a correlation between structure and anticoagulant action of sulfated galactans and sulfated fucans Glycobiology 12, 573-580. 

Of the clusters with more than six metal atoms, the structures [75] of Os2(CO)2j (757, 284) and Rh2(CO)igj2 (79) can be rationalized in terms of skeletal electron-pair counting. For the clusters with six 38), nine (57), and eleven (59) gold atoms the rules have to be modified in order to agree with the observed structures, the main assumption being that one orbital per gold atom remains empty (55). For clusters of 8 to 15 metal atoms there is no correlation between structures and electron counts yet. 

Smith, W. W., Ludwig, M. L., Pattridge, K. A., Tsemoglou, D., Petsko, G. A. Crystallographic Studies of Flavodoxins Some correlation between structure and redox potential. In Frontiers of Biol. Energetics, Vol. II (Dutton, P. L., Leigh, J. S. Scarpa, A. eds.) pp. 957-964. New York, San Francisco, London, Academic Press 1978... 

Ultraviolet absorption spectra of 1,2,4-thiadiazoles have been determined in increasing numbers in recent years, but the information so far available does not provide any broad correlation between structure and absorption characteristics.122... 

Structural analysis from electronic spectra yields little information because of their relative simplicity. In the 1940s, however, before the advent of more powerful identification techniques, UV/VIS visible spectroscopy was used for structural identification. The study of a great number of spectra of various molecules has revealed correlations between structures and the positions of absorption maxima. The most widely known empirical rules, due to Woodward, Fieser and Scott, involve unsaturated carbonyls, dienes and steroids. Using incremental tables based on various factors and structural features, it is possible to predict the position of the n —> n absorption bands in these conjugated systems (Table 11.3). Agreement between the calculated values and the experimentally determined position of absorption bands is usually good, as can been seen by the following four examples ... 

Correlation between structure and composition of zeolites and their activity, stability, and selectivity for selected model reactions. 

Correlations between structure and catalytic activity have been described for carbonium-ion type reactions (1). Much effort was also spent to establish a correlation between structural and compositional factors and the activity for redox type reactions (1, 9-12). Transition metal ions in zeolites were shown to be active in the oxidation and hydrogenation of hydrocarbons. In this connection various techniques were used to locate the cations in the framework of the faujasite-type zeolites (13-20). These ions migrate upon thermal treatment or by the adsorption of various substances. Thus, methods are needed to determine the location of the cations under reaction conditions. 

Knocking characteristics of pure hydrocarbons and observed correlations between structure and knock have been summarized by Lovell (117). Work of American Petroleum Institute Project 45 (2, 3) represents a large fraction of this information. The reasons for these relationships have not been as adequately reviewed. 

Compactness or centralization in a molecule results in increased knock rating. Kobayashi and Mibashan have used this observation to develop empirical quantitative correlations between structure and knock. 

Since steric effects can change catalysis (e.g., the above mentioned trypsin case), one may still argue that such effects do influence the correlation between structure and function. However, this case is not so relevant to structure-function correlation since the steric effects establish new structure and the activity associated with this structure is the main subject of our... 

Balaban, A. T., et al., Correlation Between Structure and Normal Boiling Points of Haloalkanes C1-C4 Using Neural Networks. J. Chem. Inf. Comput. Sci., 1994 34, 1118-1121. 

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