Universal descriptors

Only a limited number of reliable prediction tools are currently available for photoinduced toxicity. This is not surprising since establishing phototoxic potential is a complex task. Phototoxicity can be the consequence of various mechanisms such as photogeneration of reactive oxygen species, production of toxic photoproducts or sensitization of DNA damage by energy transfer. In addition, so far, there are no available universal descriptors (indicators) to predict the photodynamic potency of chemicals. 

Arguably, the most important aspects of quality management for PAT are the concepts of quantitative process performance characterization using process capability indices as universal descriptors, which form the basis of the measure and analyze portions of the DMAIC model. Process capability indices consider simultaneously both process variability and process specifications to determine whether... 

Figure 3.2.2 The free energy diagram of oxygen evolution on 110 facets of rutile RuC>2 at three different potentials V - 0 V versus the RHE the equilibrium potential, Ee, U - 1.23 V and the smallest potential where all reaction steps are downhill, AGOER, U- 1.60 V. The 3.2 eV difference between OH and HOO is shown by the arrow on the right the smaller arrow to the left indicates the universal descriptor for OER.

In another study Senese et al. [126] reported later on the derivation and validation of a potential set of universal descriptors referred to as 4D-fingerprints. One of the elusive goals in the field of cheminformatics and molecular modeling has been to generate descriptors that once calculated for a molecule may be used in a wide variety of applications. The assumption inherent in the generation of such descriptors is that such universal descriptors are generated free from external constraints, thus they are independent of the dataset in which they were employed. 

In another preliminary evaluation of the use of the 6-dimensional eigenvalues from the LDM as universal descriptors we looked at building a model of the inhibitive properties of heterocyclic diazoles for acidic iron corrosion [96]. Table 3.5 shows the computed eigenvalues and corrosion inhibitor efficiencies (CIE %) for a set of diazoles reported by Babic-Samardzija et al. [96]. 

The BCUT descriptors (Buiden-CAS-University of Texas eigenvalues) [52], are commonly used, are eigenvalue-based, and include 3D information also. 

B and W J Howe 1991. Computer Design of Bioactive Molecules - A Method for Receptor-Based Novo Ligand Design. Proteins Structure, Function and Genetics 11 314-328. i H L 1965. The Generation of a Unique Machine Description for Chemical Structures - A hnique Developed at Chemical Abstracts Service. Journal of Chemical Documentation 5 107-113. J 1995. Computer-aided Estimation of Symthetic Accessibility. PhD thesis. University of Leeds, itan R, N Bauman, J S Dixon and R Venkataraghavan 1987. Topological Torsion A New )lecular Descriptor for SAR Applications. Comparison with Other Descriptors. Journal of emical Information and Computer Science 27 82-85. 

From the Old Dominion University survey it is clear that the students perceptions of Willy s actions in the Admiral Sugar Processing Plant incident shifted dramatically from pre-9/11 to post-9/11. For example, when asked to select the best pre-9/11 descriptor to describe Willy, crazy and insane ranked high however, after 9/11, the students perception shifted away from crazy and insane to terrorist. Likewise, the students pre-9/11 responses on Willy s actions ranked high in madness however, his actions post-9/11 overwhelmingly were described as terrorism . 

Sun H (2004) A Universal Molecular Descriptor System for Prediction of LogP, LogS, LogBB, and Absorption. J Chem Inf Comput Sci 44 748-757. 

For example, the descriptor set used in MOE, distributed by Chemical Computing Group, 125 University St., Suite 1600, Montreal, Quebec, Canada H3B 3x3, www.chemcomp.com. 

Breneman, C., Bennett, Bi, J., Song, M., and Embrechts, M. (2002) New electron density-derived descriptors and machine learning techniques for computational ADME and molecular design. MidAtlantic Computational Chemistry Meeting, Princeton University, Princeton, NJ. 

Age is both an observable and a universal demographic descriptor. It is frequently a substitute or proxy variable for physical fitness, activity levels, interests and previous travel experiences. 

In general, the rules pay a close attention to transparency when the model and the results are presented. Not only well described data, but also an unambiguous algorithm must allow everybody to be able to repeat the modeling. Therefore, the model cannot be reported as a black box, but all necessary details on the mathematical method, descriptors, etc. should be given in the report [15,16]. Currently, the universal... 

A.R. Katritzky et al., CODESSA PRO. Comprehensive DEscriptors for Structural and Statistical Analysis, University of Florida, USA, 2001-2005. http //www.codessa-pro.com. Accessed June 2007... 

An alternative to dimension reduction is the use of composite and uncorrelated descriptors that are suitable for the design of information-rich yet low-dimensional chemical spaces. An elegant example is presented by the popular BCUT (Burden-CAS-University of Texas) descriptors (Pearlman and Smith 1998). BCUTs are a set of uncorrelated descriptors that combine information about molecular connectivity, inter-molecular distances, and other molecular properties. BCUT spaces used for many applications are typically only six-dimensional and can frequently be further reduced to 3D representations for visualization purposes by identifying those BCUT axes around which most compounds map. 

Other techniques, such as fight scattering and sedimentation, are also sensitive to particle shape. The direct observation of particles by a scanning electron microscope and distribution measurements by image analysis would appear to overcome many of the problems associated with the various other techniques, but problems of describing irregularly shaped particles remain. A universal particle size descriptor has not yet been developed. The technique adopted and the results obtained are most useful when empirical correlations with the end use can be made. 

Micellane series registered trademark (University of South Florida) descriptor of the all-hydrocarbon based dendrimers MRI magnetic resonance imaging NBS N-bromosuccinimide... 

Also important to the validation process of QSARs is vertical validation. In this instance, quantitatively similar QSARs are developed with similar descriptors but using data for a different toxic endpoint. For example, the investigation of Karabunarliev et al. (1996b) modeled acute aquatic toxicity data for the fathead minnow Pimephales promelas. The compounds considered in the analysis were confined to substituted benzenes, and descriptors limited to log Kow and Amjx. The fish toxicity QSAR (log [LQ,]-1 = 0.62 log K, + 9.17 A - 3.21 n = 122 R2 = 0.83 i = 0.16 F = 292) of Karabunarliev et al. (1996b) was very similar in terms of slope, intercept, and statistical fit to the QSAR presented in Equation 12.2. The fact that different endpoints provide very similar QSARs indicates that the QSAR is valid across protocols. This shows the universality of the model. 

Burden, CAS, and University of Texas (BCUT) descriptors are well suited and widely used to describe diversity of a chemical population in a low dimensional Euclidian space and they allow for fast cell-based diversity selection algorithms (Pearlman and Smith, 1998). The DiverseSolutions... 

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