Molecular identity

Many different approaches to QSAR have been developed since Hansch s seminal work. These include both two-dimensional (2D) and 3D QSAR methods. The major differences among these methods can be analyzed from two viewpoints (1) the strucmral parameters that are used to characterize molecular identities and (2) the mathematical procedure that is employed to obtain the quantitative relationship between a biological activity and the structural parameters. 

It is well to add that most of the compounds of carbon condense to molecular liquids and solids. Their melting points are generally low (below about 300°C) and many carbon compounds boil below 100°C. The similar chemistry of the liquid and solid phases shows the retention of the molecular identities. 

Water-Soluble Exotoxins. In this area, we enter into the slightly muddy waters of the lower molecular weight compounds which elicit toxic responses in susceptible host insects. Without reference to molecular identity, it is possible to sift through the various reports on the effects of bacillus-produced soluble exotoxins and recognize three possible types of material which are produced under appropriate conditions by specific strains of bacilli ... 

While the molecular identity of the capacitative Ca2+ entry channel is not known, a candidate is a homolog of the Drosophila mutant trp. This photoreceptor mutant is incapable of maintaining a sustained photoreceptor potential. This phenotype could be mimicked by the calcium entry blocker lanthanum, and it was suggested that the related defect is a failure of Ca2+ entry. 

As noted in the Introduction, a central focus of our current interests in both surface Raman and infrared spectroscopies is directed towards their utilization in reactive electrochemical systems (3-6). An important virtue of in-situ vibrational spectroscopies for this purpose is that they can yield information on the molecular identity (as well as detailed physical state) of electrogenerated species, and hence can provide considerable mechanistic information for multistep electrode processes. We have recently discussed several facets of such applications in a conference paper for "Surface Vibrations V" (6b). 

There is retention of the molecular identity of H atoms during reaction. The two H atoms used for hydrogenation of a reactant molecule originate from the same hydrogen molecule. 

Indeed, in the world of tomorrow we can expect new aspects of polymer solids to extend the conventional and successful structure ideas of this century. These, of course, were the recognition as molecular identities of the chains of repeating chemical monomers. The circumstances of those entities have resulted in interesting concepts of solubilities, viscosity, and other mechanics, and especially thermodynamic limitations m mutual solubility or comparability of polymer mixtures. But we have known for decades that even homogeneous regular chain polymers such as Carothers polyesters and polyamides formed solids with manifold imperfections and irregularities, such as order-disorder crystal configurations.(22,23)... 

In this level, the fundamental tasks required to convert the raw materials into the final product are identified. All tasks are related to property differences. Siirola (1996) has presented the following hierarchy of property differences molecular identity, amount, composition, phase, temperature/pressure, form. This list of tasks is not very well suited for food properties. Common tasks for food processes are decontamination (e.g. pasteurization and sterilization) and structure formation (e.g. emulsification, size reduction of dispersed phase in an emulsion, crystallization, interfacial adsorption/desorption). 

As used in the act, the term chemical substance means any organic or inorganic substance of a particular molecular identity, including any combination of such substances occurring in whole or in part as a result of a chemical reaction or occurring in nature and any element or uncombined radical. Items not considered chemical substances are listed in the definition section of the act. The term mixture means any combination of two or more chemical substances if the combination does not occur in nature and is not, in whole or in part, the result of a chemical reaction except that such term does include any combination that occurs, in whole or in part, as a result of a chemical reaction if none of the chemical substances comprising the combination is a new chemical substance and if the combination could have been manufactured for commercial purposes without a chemical reaction at the time the chemical substances comprising the combination were combined. 

Labastie MC, Cortes F, Romeo PH, Dulac C and Peault B (1998). Molecular identity of hematopoietic precursor cells emerging in the human embryo. Blood 92 3624-3635. 

Understandably, research focuses on discrete substances with unique molecular identity. We tend to take this for granted, but large-scale (industrial) synthesis... 

Caterina, M.J. and Julius, D. Sense and specificity a molecular identity for nociceptors, Curr. Op. Neurobiol. 1999, 9, 525-530. 

Infrared spectroscopy can provide a great deal of information on molecular identity and orientation at the electrode surface [51-53]. Molecular vibrational modes can also be sensitive to the presence of ionic species and variations in electrode potential [51,52]. In situ reflectance measurements in the infrared spectrum engender the same considerations of polarization and incident angles as in UV/visible reflectance. However, since water and other solvents employed in electrochemistry are strong IR absorbers, there is the additional problem of reduced throughput. This problem is alleviated with thin-layer spectroelectro-chemical cells [53]. 

Although both Raman and IR can be used to determine molecular identity or quantify the presence of an analyte, there are critical differences in the way that they can be applied. The extremely strong absorption of OH in the mid-IR makes any measurement difficult in the presence of water - a ubiquitous material in most biological samples. Subtle spectral differences that may be apparent in the Raman spectrum tend to be obscured by the overwhelming water absorption. This is shown in Fig. 1.3 for a solution of lactose in water ... 

SGZ (Seri et al. 2001). Our findings appear to differ from these results, and the reason could be that species variations may exist between monkeys and rodents with regard to the molecular identity of SGZ progenitors. 

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