Biomedical subjects

Ilie Fishtik

Publications and source records attributed to Ilie Fishtik.

7 recordsLinked to original sources

PubMed2006

Group additivity methods without group values.

The conventional group additivity (GA) formalism may be identically reduced to a stoichiometric and thermochemical analysis of a special class of reactions referred to as GA reactions, that is, reactions that preserve the type and number of groups. Within this approach, the performance (error) of a GA scheme is determined by the stoichiometry and enthalpy changes of the GA reactions. That is, the lower the enthalpy changes of the GA reactions, the better the performance of a GA scheme. Ideally, an exact GA scheme would imply any conceivable GA reaction to be precisely thermoneutral, that is, have a zero enthalpy change. A somewhat surprising result is that, additionally, the performance of GA methods is influenced by a purely stoichiometric factor of GA reactions. These findings do not improve the performance of a given GA scheme. Rather, it is an interpretation that leads to a deeper understanding of the performance of a GA scheme and may be used in designing more accurate GA schemes.

Journal Article↗

PubMed2006

Integrating process safety with molecular modeling-based risk assessment of chemicals within the REACH regulatory framework: benefits and future challenges.

Registration, evaluation and authorization of chemicals (REACH) represents a recent regulatory initiative by the European union commission to protect human health and the environment from potentially hazardous chemicals. Under REACH, all stakeholders must submit (thermo)physical, thermochemical, and toxicological data for certain chemicals. The commission's impact assessment studies estimate that the costs of REACH will be approximately 3-5 billion Euros. The present study advocates the systematic incorporation of computational chemistry and computer-assisted chemical risk assessment methods into REACH to reduce regulatory compliance costs. Currently powerful computer-aided ab initio techniques can be used to generate predictions of key properties of broad classes of chemicals, without resorting to costly experimentation and potentially hazardous testing. These data could be integrated into a centralized IT decision and compliance support system, and stored in a retrievable, easily communicable manner should new regulatory and/or production requirements necessitate the introduction of different uses of chemicals under different conditions. For illustration purposes, ab initio calculations are performed on heterocyclic nitrogen-containing compounds which currently serve as high energy density materials in the chemical industry. Since investigations of these compounds are still in their infancy, stability studies are imperative regarding their safe handling and storage, as well as registration under REACH.

Chemical Industry↗

PubMed2006

Thermodynamic stability relations in redox systems.

Graphical stability relations in redox systems known as Pourbaix diagrams are analyzed employing the concept of overall stability of chemical species in multiple chemical reaction systems recently developed by us (Fishtik, I. J. Phys. Chem. B 2005, 109, 3851). The overall stability approach provides a simple and systematic algorithm for generating thermodynamically and stoichiometrically consistent Pourbaix diagrams that are referred to as overall Pourbaix diagrams. The conditions under which the conventional Pourbaix diagrams coincide with the overall Pourbaix diagrams are also discussed.

Algorithms↗

PubMed2005

Phase stability relations in invariant systems.

Except for the trivial case of one-component systems, the conventional Schreinemakers phase stability analysis in invariant systems is shown to be thermodynamically and stoichiometrically inconsistent in that the partition of the stability relations into contributions coming from univariant subsystems is formulated only qualitatively. Although the stability relations in invariant systems are essentially additive (i.e., the stability relations in invariant system may be partitioned into a sum contributions coming from univariant subsystems), the quantitative form of this partition has never been considered. On the basis of a new approach to the stability of chemical species in multiple chemical reaction systems that has been recently developed by us (Fishtik, I. J. Phys. Chem. B, 2005, 109, 3851), we show how the stability relations in invariant systems may be uniquely partitioned into contributions coming from univariant reactions. This finding provides a simple algorithm for the construction of various types of thermodynamically consistent stability diagrams.

Journal Article↗

PubMed2005

Thermodynamic stability of chemical species in multiple reaction systems.

A general thermodynamic and stoichiometric method, recently developed by us to study subtle forms of stability/instability relations among chemical species, such as resonance and strain energies (Fishtik, I.; Datta, R. J. Phys. Chem. A 2004, 108, 5727-5739), is extended to stability relations in multiple chemical reaction systems. Namely, a new definition as well as a new algorithm of evaluation of the stabilities of chemical species, referred to as the overall stabilities, is proposed. It is further shown that the overall stabilities may be partitioned into a sum of contributions associated with a complete set of stoichiometrically unique response reactions (RERs). This finding reveals that the conventional stability analysis is stoichiometrically and thermodynamically inconsistent in that it involves only a part of RERs.

Journal Article↗

PubMed2005

Reaction route graphs. III. Non-minimal kinetic mechanisms.

The concept of reaction route (RR) graphs introduced recently by us for kinetic mechanisms that produce minimal graphs is extended to the problem of non-minimal kinetic mechanisms for the case of a single overall reaction (OR). A RR graph is said to be minimal if all of the stoichiometric numbers in all direct RRs of the mechanism are equal to +/-1 and non-minimal if at least one stoichiometric number in a direct RR is non-unity, e.g., equal to +/-2. For a given mechanism, four unique topological characteristics of RR graphs are defined and enumerated, namely, direct full routes (FRs), empty routes (ERs), intermediate nodes (INs), and terminal nodes (TNs). These are further utilized to construct the RR graphs. One algorithm involves viewing each IN as a central node in a RR sub-graph. As a result, the construction and enumeration of RR graphs are reduced to the problem of balancing the peripheral nodes in the RR sub-graphs according to the list of FRs, ERs, INs, and TNs. An alternate method involves using an independent set of RRs to draw the RR graph while satisfying the INs and TNs. Three examples are presented to illustrate the application of non-minimal RR graph theory.

Journal Article↗

PubMedDate not supplied

A stoichiometric approach to quantitative structure-property relationships (QSPR).

An unusual analogy between the quantitative structure-property relationships (QSPR), stoichiometry, chemical thermodynamics, and kinetics is presented. Namely, the conventional ordinary least-squares (OLS) QSPR analysis is modified so as to explicitly minimize the residuals of the species subject to a set of linear relations among the residuals. The ways the linear relations among the residuals are visualized and defined totally resemble the formalism of chemical stoichiometry and, therefore, were called isostructural reactions. It is further proved that the residuals may be uniquely partitioned into a sum of contributions associated with a set of isostructural reactions that have the same properties as the response reactions (RERs) previously deduced by us from chemical thermodynamics and kinetics. This finding is shown to be a useful tool for a deeper understanding of the QSPR. In particular, the isostructural RERs approach may be effectively used to detect the outliers.

Journal Article↗