Valence molecular connectivity model in the prediction of compartmental distribution of selected aromatic pollutants

Abstract

Bu çalışmada Çizit Kuramının bir parçası olarak son yıllarda özellikle farmasötik kimya dalında yapı-etki ilişkilerinin incelenmesinde yaygın olarak kullanılan Valans Moleküler Ko- nektivite İndeks' lerine bağlı matametiksel bir modelin ge liştirilmesi amaçlanmıştır. Bu model yardamı ile Polisiklik Aromatik Hidrokarbonlar (PAH), Alkilbenzenler, Poliklorine Siklik Aromatik Hidrokarbonlar (PCB) ve Halojen Substitüye Benzenlerin çevredeki denge dağılımlarının hesaplanması ve böylece bu kimyasalların çevrenin çeşitli kom- partmanlarında (hava, toprak, su, biota, asılı madde ve sedi ment) hangi bağıl konsantrasyonlara ulaşacakları hesaplanmıştır. Son yıllarda atık olarak çevreye giren ve sağlığı tehdit eden çeşitli maddelerin çevredeki dağlımının sudaki çözünürlükleri, buhar basınçları ve oktanol-su oranı katsayıları gibi fiziko- kimyasal bazı özelikleri kullanılarak hesaplanması OECD Çevre Analiz Grubu tarafından ele alınmış ve bu amaçla Mackay tara fından geliştirilen maddenin bir fazdan kaçınım yatkınlığı il-XIV kesine dayalı `fugasite Modeli` esas olarak belirlenmiştir. Bu çalışma ile geliştirilen matamatiksel modelin bu konuya katkısı ise, sözkonusu dağılımı, yukarıda sözü edilen ve ö- zellikle çevre bilimlerinin ilgi alanına giren büyük mole küller için literatürde bulunması zor olan birçok fizikn- kimyasal parametreye gereksinim olmadan hesaplayabilme ko laylığını sağlamasıdır. Sözü edilen dört aromatik grup üzerinde yapılan detaylı bir istatistik! inceleme sonucu elde edilen veriler OECD tara fından benimsenen fugasite modeli ile elde edilen verilerle karşılaştırıldığında modelin yüksek bir korrelasyonla çalış tığı gözlenmiş ve bu tür hesapların yapılabilmesi için sade ce moleküler geometri ve moleküler ağırlığın yeterli olacağı kanıtlanmıştır.

The main purpose of this work is to develop a mathematical model based on the Valance Molecular Connectivity theory which is initiated as an extension of graph theory having its roots especially in structure-activity studies concer ning drug-design and toxicity prediction in pharmaceutical chemistry, to evaluate the compartmental distribution of various aromatic pollutants in the environment. During the last decade concerns have been expressed as to the `best way` to assess the potential hazards posed by ex posure to chemical substances. In response to these concerns, the chemical group of OECD initiated a hazard assessment pro ject to examine the available methods for hazard assessment of chemicals. The main purpose being to determine how infor mation on the ultimate fate and effects of a chemical can be derived from the set of premarket data, the group accepted four models for the estimation of exposure potentials ofchemicals within environmental compartments of major concern. All of the four models accepted by OECD chemical group was based on the concept of fugacity and essentially needed the following data ? molecular weight. water solubility. vapor pressure. soil sorption constant. ocfcanol-water partition coefficient However, the availability and precission of the set of data proposed, especially for chemicals which have rather large and complicated structures was a drawback of these models. Hence, a reasonable model to evaluate this distribution quan titatively without needing such hard-to-gather data would have been a remarkable advance in prediction of environmental ha zards that are going to be caused by unknown chemicals irrespective of size and conformation. In this work a new mathematical model (VMCI) based only onXI the topological characteristics of molecules is developed in order to evaluate the distribution of chemicals within various compartments of the environment such as air, soil, water, biota, suspended solids and sediment. The Valance Molecular Connectivity Index, which is the basis of this new model is known to correlate significantly with a number of structure dependent physicochemical properties, and by this work it has now been shown to have a high degree of correlation also with water solubilities, vapor pressures and partition coefficients hence with the partitioning pro perties of molecules. As a result, by comparing the two completely different methods of evaluation (VMCI and Level I Fugacity Models) this work proved that it is possible to predict the compartmental dis tribution of any aromatic compound guantitatively within a high accuracy just by considering the molecular geometry. The superiority of this model compared to fugacity dependentXll models accepted by OECD lies in the fact that it does not require the physical data such as solubility, vapor pressu re or partition coefficient. Relevantly another superiority comes out to be the ability to stay as accurate when even very complicated molecules are investigated while for fuga- city dependent models accuracy diminishes due the difficul ties in obtaining the experimental data.