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

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.