Elucidating Environmental Micro-interface Behaviors By Vibrational Spectroscopy

The environmental micro-interfaces connect different media and are involved in a variety of micro-scale biological,biochemical and physicochemical reactions,and have many unique properties compared to homogeneous systems.It is of great environmental significance to understand the reaction processes at these micro-interfaces at the molecular level.This dissertation focuses on the exploring the physicochemical properties and related environmental behaviors of the typical biological and abiotic micro-interfaces in the environment with integrated various molecular spectroscopic techniques with chemometric methods.The main research contents and results are as follows:1.Investigation into the biological micro-interfaces by three-dimensional Raman mapping.Biofilms,which are formed by microorganisms and their extracellular polymer substances,are typical biological micro-interfaces in the environment Cognition of the chemical composition and their architecture in the biofilm matrix contributes to better understanding of its environmental behaviors and the development of targeted control strategies.Herein,the chemical composition and corresponding spatial structure of two typical biofilms developed by Pseudomonas ssp.were probed by three-dimensional Raman mapping combined with non-negative matrix factorization(NMF)analysis.The results show that cells,proteins,and glycolipids were the main chemical components in the "mushroom-like" structure of the mature Pseudomonas aeruginosa biofilm,while in the Pseudomonas putida biofilm,the main components were bacteria,polyhydroxyalkanoates(PHA)and proteins.The spatial distribution of these components within the biofilm was heterogeneous and might be related to the surrounding microenvironment and their physiological functions.In addition,the method does not require a priori knowledge of the samples and is thus particularly suitable for the non-targeted exploration into the complex biological micro-interfaces.2.Exploration into the development of the Escherichia coli biofilm matrix by three-dimensional Raman mapping.The formation of biofilm is a complex and dynamic process that contributes many emergent properties to microorganisms and enable their survival in unfavorable conditions.Therefore,it is essential to study the development process of biofilm.Three-dimensional Raman mapping integrated with NMF analysis was used to investigate the main chemical components of the E.coli biofilm matrix with distinct growth stages.Also,the corresponding spatial distribution of each component was visualized and quantified.The results show that at the stage of irreversible attachment and early development,there were mainly bacteria and proteins in the biofilm.When the biofilm became mature,a great amount of polyhydroxybutyrate appeared,which might facilitate the gene transfer.In addition,the spatial distribution of these components was also heterogeneous,the proteins were mainly located in the upper layers of the biofilm,and the amount of polyhydroxybutyrate was relatively higher in the bottom region of the biofilm.This method provides a comprehensive picture of the spatiotemporal changes of the biofilm matrix at a molecular level,and also reveals the close relationship between the chemical composition and the corresponding spatial structure of the biofilm matrix.3.Three-dimensional Raman mapping analysis of the biofilm changes during disinfection.The large amount of biofilms present in water distribution systems has seriously affected human health.Free chlorine and monochloramine are the most commonly used secondary disinfectants,but they have shown the limited control over biofilms.With the three-dimensional Raman mapping combined with NMF analysis,bacteria PHA and proteins were revealed to be existed in the mature P.putida biofilm matrix,and PHA was mainly distributed in the middle and lower layers of the biofilm.After dosing chlorine,the biofilm spatial structure was destroyed and rebuilt within one week.In contrast,monochloramine showed less impact on the biofilm matrix,but its thickness was reduced significantly after one week’s dosing.The NMF analysis reveals the different metabolic pathways when the P.putida biofilm faced with the two disinfectants.The dose of free chlorine led to the increased amount of PHA in the upper layers of the reconstructed biofilm.However,when facing up to the monochloramine,P.putida produced more glycogen,and few PHA was monitored.Moreover,the amount of proteins also increased to provide a barrier and decreased the penetration of the two disinfectants.The results indicate the different resistance strategies of the P.putida biofilm to the disinfectants monochloramine and free chlorine and suggest that the alternating dose of mutiple disinfectants might more effectively control the biofilm development4.Spectral analysis of the interaction of dissolved organic matter(DOM)with long-chain ionic liquids(ILs).The supramolecular polymer DOM is ubiquitous in the environment,and a variety of chemically active functional groups are contained to provide a micro-interface for the adsorption of organic pollutants.The interaction between long-chain ILs and DOM was studied by synchronous fluorescence spectroscopy,Fourier transform infrared spectroscopy(FTIR),dynamic light scattering and zeta potential technique.Two-dimensional correlation spectroscopy(2DCOS),hetero-2DCOS,and perturbation-correlation moving-window two-dimensional correlation spectroscopy were applied to analyze and integrate the information obtained by all the technologies.The results show that when the concentration of ILs was low,the interaction was mainly caused by the cation exchange of carboxyl groups in the humic acid-like component Meanwhile,due to the decrease in electrostatic repulsion and the increase in hydrophobicity,the DOM was loosely aggregated.When the ILs concentration was increased,the aromatic and carbonyl group participated in the adsorption via π-π and dipole-dipole interactions respectively,resulting in the destruction of intramolecular hydrogen bonds,and the DOM structure became much more compact due to the enhancement of hydrophobicity.This method gives a comprehensive understanding of the interaction between DOM and long-chain ILs,which helps to further evaluate the environmental behaviors of ILs.This integrated method exhibits a great potential in investigating the complex reactions on the environmental micro-interfaces.5.Infrared spectroscopy analysis of the conformational transition of proteins on the membrane interface.Proteins play a critical role in the irreversible membrane fouling,and the stiffness ofthe protein adsorption layer varies with the physicochemical properties ofp roteins and membranes.The attenuated total reflection infrared spectroscopy(ATR-FTTR)was used herein to probe the adsorption process of two model proteins,i.e.,lysozyme and bovine serum albumin(BSA),on three different membranes in-situ and online.The multivariate curve resolution-alternating least squares and 2DOCS analysis were integrated to analyze the ATR-FTIR spectra,Which contained the conformational information of the proteins.BSA was found to be unfolded and aggregated at the interface of relatively hydrophobic membranes;however,at the interface of the hydrophilic membrane,BSA was unfolded and formed a new α-helix structure,and the extended chain structure increased continuously.Lysozyme was aggregated on all the three membrane surfaces,with the transformation from a tight a-helix conformation to a more open β-sheet structure.The hydrophobic polyvinylidene fluoride membrane induced the unfolding of lysozyme at the initial stage of adsorption This work reveals the interaction mechanisms between various proteins and membranes at a molecular level,and the results are crucial for the development of new membrane technology and membrane anti-fouling strategies.