Applications of FTIR spectroscopy in environmental studies supported by two dimensional correlation analysis

Abstract

In this paper, we report the joint use of FTIR spectroscopy and two dimensional correlation analysis (2DCORR) applied to the identification of the aggregation pathways of natural organic matter (i.e. humic substance) extracted from marine sediments and in the second case of study, to the comparison of the molecular modifications caused by the actions of different pollutants on a marine algae used as biomarker of environmental quality. In the first application, the extractable humic substance (HS) from sediments was ultra-filtered to obtain seven sub-fractions of HS with molecular weight (mw) < 1kDa and > 100kDa. After the examination of FTIR spectra of each sediment samples, 2DCORR was applied to examine the molecular mechanism of the aggregation process. This approach allows to differentiate the role played by carbohydrates, lipids and proteins during the evolution of the aggregation process. Carbohydrates are significant in any phase of the aggregation while proteins though significant in any phase of the aggregation seem to play a role strictly related to polymerisation reaction with carbohydrates. Lipids play a completely different role in the aggregation process with respect to carbohydrates and proteins because they are significant only in sub-fractions of HS with mw < 1 kDa and mw > 5 kDa, so suggesting that their role is the so called cross-linking action (i.e. bridge among lower mw aggregate), already observed in the aggregation of terrestrial HS. In the second application of FTIR spectroscopy and 2DCORR, the acetone extracts of Dunaliella tertiolecta prepared according to the ISO standard protocol for toxicity test, were examined in presence of several inorganic and organic pollutants to study the molecular modifications caused by pollutant actions in algal cells. This approach allows to differentiate the molecular mechanisms of toxic action for the observed pollutants. Heavy metals such as Hg, Zn, Cr (VI) and Cu cause modifications of carbohydrate lipid and nucleic acid contents and structural modifications (i.e. inter and intra molecular hydrogen bonds) of these biomolecules simultaneously. Glycols compounds cause modifications of carbohydrates lipids and nucleic acids contents and structural modifications too as observed for heavy metals but without an evident simultaneity between the two types of modification. At last, surfactants cause modifications of carbohydrates lipids and nucleic acid contents only. These experimental results suggest that the use of FTIR spectroscopy with 2DCORR analysis is a potential tool for evaluating toxic effects in the study of environmental quality of marine samples.