AcknowledgmentsThe authors would like to thank Mr. M. Malaekeh for his assistance in flow cytometry. This work was supported by Grants (no. 910238) from Research Affairs of Mashhad University of Medical Sciences as a part of Pharm. D. thesis.
Polycyclic aromatic therefore hydrocarbons (PAHs) are very stable organic lipophilic pollutants principally produced during incomplete combustion processes, often exhibiting high levels of toxicity, mutagenicity, and carcinogenicity to humans and/or other living creatures [1�C5]. Since PAHs are ubiquitous contaminants, there is much interest in searching practical strategies for their identification and removal from environments. Generally, alkylated derivatives are found in prevalence in the environmental samples of PAHs [6�C8].
Dimethylnaphthalenes (DMNs) are substituted PAHs of great environmental interest [9�C15]. DMNs can exist as ten isomeric forms (Figure 1): 1,2-DMN, 1,3-DMN, 1,4-DMN, 1,5-DMN, 1,6-DMN, 1,7-DMN, 1,8-DMN, 2,3-DMN, 2,6-DMN, and 2,7-DMN. It has been previously recognized that the enzymatic biodegradation of DMNs in aqueous media is strongly affected by the specific position of the methyl substituents [12]. Indeed the first-order biomass-normalized rate coefficient (kb) of DMNs varies within one order of magnitude, the ��,��-disubstituted isomers showing the maximum kb values along the series [12]. Therefore, the detection of the DMN isomers in the environmental mixtures is of fundamental importance from environmental and biochemical viewpoints.
On the basis of experimental and theoretical investigations, the active site of the enzyme which controls the biodegradative mechanism is mainly characterized by hydrophobic residues [12, 13], involving contributions from dispersive and/or inductive forces in enzyme-substrate complex formation. This result has been corroborated by recent computational studies on the electronic polarizabilities (��) [14, 16] and Raman spectra [15] of alkylated-naphthalenes, the average polarizabilities [14], and summation of the Raman activities [15] of DMNs being found to be linearly related to the experimental kb values. However, although the average polarizabilities (��) of DMNs regularly increase in the order ��(��,��-DMNs) < ��(��,��-DMNs) < ��(��,��-DMNs), they slightly vary among the ten isomers (up to 3.5%). Thus, the average polarizability is little useful to discriminate unambiguously the DMN isomers.
A physicochemical property much more affected by the structural features is the electronic first-order hyperpolarizability (��) and the related nonlinear optical (NLO) properties Second Harmonic Generation (SHG) and Electro-Optical Pockels Effect (EOPE) [17�C32]. SHG measurements are currently employed for the structural identification GSK-3 of biomolecules such as peptides and proteins [28�C32].