Protein-like Fluorescence Peaks Research Articles

Characterization of photobleaching of chromophoric dissolved organic matter in Xiamen Bay by excitation emission matrix spectroscopy

Fluorescence excitation-emission matrix spectroscopy (EEMs) was applied to study the photobleaching of chromophoric dissolved organic matter (CDOM) in two surface water samples from Xiamen Bay exposed to natural sunlight between 10:00-16:00 during September 12-18, 2007. Both samples were collected from the lower and middle salinity areas in Jiulong Estuary of Xiamen Bay, and then filtered by 0.2 microm polycarbonate filters before the photobleaching incubation experiment. The results showed that three humic-like (C, A, M) and two protein-like (T, B) fluorescence peaks were observed in both samples, and the photobleaching didn't cause obvious shift of the positions of these fluorescence peaks. The fluorescence intensities of the five peaks decreased with the increase in irradiation time and peak C demonstrated the fastest photobleaching rate. The photobleaching rate of low salinity sample was higher than that of middle salinity sample, consistent with its higher content of chromophores. All the five fluorophores could be distinguished into labile and refractory components based on their photobleaching dynamics. The increase in the intensity ratios of peak T and C (IT/IC) and peak T and C (IA/IC) after irradiation suggested that photobleaching can cause obvious change of the properties of dissolved organic matter in seawater, and it may partly account for the dominance of the protein-like fluorescence relative to the humic-like fluorescence in coastal area. The results suggest that EEMs was a useful tool to trace the transformation and removal processes of terrestrial CDOM entering the coastal regions. Keywords Chromophoric dissolved organic matter (CDOM); Photobleaching; Excitation-emission matrix spectroscopy

Characterization of Fluorophores Released from Three Kinds of Lake Phytoplankton Using Gel Chromatography and Fluorescence Spectrophotometry

Three kinds of phytoplankton were cultivated, and the contribution of dissolved organic matter (DOM) released from the phytoplankton was examined to clarify the cause of organic pollution of Lake Biwa. Microcystis aeruginosa, Staurastrum dorcidentiferum, and Cryptomonas ovata were evaluated with regard to cultivation. A significant peak (M(w): <3000 Da) was mainly detected in the algal DOM released from plankton during cultivation by gel chromatography with a fluorescence detector (E(x) = 340 nm, E(m) = 435 nm). Since this peak corresponds to a peak with lower molecular weight in three peaks detected in the surface water of Lake Biwa, it can be concluded that the algal DOM released from the plankton during cultivation makes a considerable contribution to the refractory organic matter in Lake Biwa. Three fluorescence maxima were observed in the cultivation of three kinds of phytoplankton: two fulvic-like fluorescence peaks (A and B) and a protein-like fluorescence peak (C). These peaks became larger as their cell counts of plankton increased. As for the fractionations of algal DOM using DAX-8, the ratio of hydrophilic DOM is fairly high in DOM produced by three kinds of phytoplankton. The order of the amount of algal DOM per cell volume during cultivation was Cryptomonas ovata > Microcystis aeruginosa > Staurastrum dorcidentiferum. These results suggest that the increase of the refractory organic matter in Lake Biwa may be attributed to a change of the predominant phytoplankton.

Characterization of Dissolved Organic Matter Released from Microcystis aeruginosa

The contribution of dissolved organic matter (DOM) released from phytoplankton (Microcystis aeruginosa) during cultivation and biodegradation was examined to clarify the causes of the organic pollution of Lake Biwa. Two peaks, peak 2 (retention time (RT) = 32 min) and peak 3 (RT = 35 min), were detected in the algal DOM released from Microcystis aeruginosa during cultivation and biodegradation by gel chromatography with a fluorescence detector (Ex = 340 nm, Em = 435 nm). As these peaks correspond with the peaks detected in the surface water of Lake Biwa, one can conclude that the algal DOM released from Microcystis aeruginosa during cultivation and biodegradation makes a considerable contribution to the refractory organic matter in Lake Biwa. Three fluorescence maxima were observed in the cultivation of Microcystis aeruginosa: a fulvic-like fluorescence peak (peak A) with Ex/Em values of 320/430 nm, a protein-like fluorescence peak (peak C) with Ex/Em values of 280/360 nm, and another peak with Ex/Em values of 240/370 nm. The fluorescence material of peak C has a larger MW than that of peak A. The algal-derived DOM from Microcystis aeruginosa has similar fluorescence to fulvic acid of soil origin but exhibits mainly hydrophilic characteristics. In the biodegradation of Microcystis aeruginosa, a fulvic-like fluorescence peak (peak B) with Ex/Em values of 250/440 nm and a peak with Ex/Em values of 320/380 nm were observed.

Relationship between fluorescence characteristics and molecular weight distribution of natural dissolved organic matter in Lake Hongfeng and Lake Baihua, China

Dissolved organic matter (DOM) is one of the most interesting and difficult problems in recent years due to its important functions in the ecological and environmental system and the complexity of its chemical composition and structure. It is well accepted that fluorescence characteristics and molecular weight distribution are two important parameters in the DOM characterization. However, the relationship between them is still unknown. In this study, fluorescence and molecular weight distribution of DOM in Lake Hongfeng, Lake Baihua and their rivers, and their relationship were investigated using the combination of fluorescence spectroscopy and high-performance size exclusion chromatography (HPSEC) with on-line UV absorbance and fluorescence detectors. The results show that there were two obvious humic-like fluorescence peaks (Peaks A and B) in DOM from lake water. But there was another obvious protein-like fluorescence peak (Peak C) in DOM from river water. The humic-like fluorescence material consisted of DOM fraction with smaller molecular weight, ranging from 1.0 to 3.0 kDa, while the protein-like fluorescence material mainly consisted of DOM fraction with MW larger than 2.0 kDa. The calculation of MW using HPSEC was related to the UV absorbance wavelength chosen.

Monitoring of COD as an organic indicator in waste water and treated effluent by fluorescence excitation-emission (FEEM) matrix characterization

The fluorescence excitation-emission matrices (FEEM) of domestic waste water, treated effluent of a waste water treatment plant and receiving river water were analyzed to select wavelengths for the monitoring of organic contents as COD. Excitation/emission wavelengths of 220/350 nm and 270/350 nm for protein-like fluorescence and 240/450 nm and 340/450 nm for humic-like fluorescence were suggested as fluorescence peak emitting wavelength pairs, respectively. Without any pre-treatment, the protein-like fluorescence peaks showed better correlation between COD values and fluorescence intensities than the humic-like fluorescence peaks. No enhanced correlation was observed by removing the suspended solids from the samples using filtration. However, statistical multiple regression methods, using the fluorescence intensities from each peak and the light scattering intensity at 633 nm as variables, resulted in an enhanced correlation, with r2 > 0.9 for the measured and predicted COD values.

Molecular mass distribution and fluorescence characteristics of dissolved organic ligands for copper(II) in Lake Biwa, Japan

Molecular mass distribution and fluorescence characteristics of organic ligands for copper(II) in freshwater were, for the first time, investigated using ultrafiltration, immobilized metal ion affinity chromatography (IMAC) and three-dimensional excitation-emission matrix spectroscopy (3DEEM). Two types of humic-like fluorescence (Peaks A and B) were found in all molecular ligand fractions, while an additional type of protein-like fluorescence (Peak C) was only observed in the 0.1 μm-GF/F molecular ligand fractions. The Ex/Em maxima of Peak A in the <5 kDa and 0.1 μm-GF/F molecular ligand fractions were blue-shifted (shift towards the shorter wavelength) relative to that in the 5 kDa–0.1 μm fractions. Contributions of total organic ligands were 1.6–4.0% of the bulk dissolved organic matter (DOM) in the original water, as determined by UV absorbance. In the molecular mass distribution of organic ligands, the relative contribution of the fraction with the <5 kDa molecular masses was dominant (67–79%), while 17–30% of the total organic ligands were in the 5 kDa–0.1 μm fraction, leaving 3–6% in the 0.1 μm–GF/F fraction. Fluorescence at the longer excitation wavelength was more heavily weighted in the lower molecular organic ligands relative to that at the shorter excitation wavelength. The binding affinity of organic ligands increased with their molecular weight. These results have significance for further understanding the nature of organic ligands and their biogeochemical role in the aquatic environment.