Heat-induced changes in soil water-extractable organic matter characterized using fluorescence and FTIR spectroscopies coupled with dimensionality reduction methods

[Abstract:] Water extractable organic matter (WEOM) is a very mobile and reactive soil OM fraction, critical in the translocation of carbon (C) from soils to other environmental compartments. Transformations of WEOM due to soil heating can have implications not only at a local scale, but in places far away from the location of the event. However, their accurate characterization is costly when analyzing a large number of samples. The objectives of this work were to identify common patterns for the changes in WEOM caused by the heating of various soil types using a combination of spectroscopic and dimensionality reduction techniques. Six soils from Spain, Kenya and Israel were collected at depths 0–10 cm and analysed before and after heating in air to temperatures of 300 and 600 °C. Fluorescence EEMs were measured in soil–water extracts containing WEOM, and decomposed using parallel factor (PARAFAC) analysis. The FTIR spectra were measured in freeze-dried extracts and further analysed using non-negative matrix factorization (NMF). Total organic C and SUVA254 values of the extracts experienced changes with the heating treatments that were soil dependant. Four PARAFAC and three NMF components were sufficient to characterize WEOM changes in all soils, which showed common thermal transformation patterns irrespective of their origin and properties. Thermal transformation of fluorescent WEOM led to the increase in the proportion of a component with an emission maximum at Ex 300/Em 392 nm, and to a lower extent one with the emission maximum at Ex 300/Em 426 nm. Concomitantly, the proportion of components with emission maxima at longer excitation wavelengths was reduced. These changes occurred at the lowest heating temperature and were maintained at 600 °C, and they seem to indicate a depletion of fluorescent components more conjugated, bigger in size, and an enrichment in smaller ones. The NMF components obtained from FTIR spectra showed an increase of the proportion of compounds with Csingle bondO bonds, more oxidized. No correlations were found between the components obtained with each method, thus indicating that the information obtained from the fluorescence EEMs-PARAFAC analysis and the NMF decomposition of FTIR spectra is complementary. It can be concluded that there is a common pattern of WEOM changes induced by thermal soil transformations irrespective of the origin and properties of the soils studied, and that the combination of different spectroscopic techniques coupled with dimensionality reduction methods can be used as a simple and low-cost method to fingerprint changes in WEOM composition, in general, and those caused by soil heating, in particular

Interactions of water with human serum albumin suspended in water-organic mixtures

Calorimetric enthalpy changes on suspending a partially hydrated preparation of human serum albumin (HSA) in various water-organic mixtures are discussed together with the water sorption isotherms. Experimental data indicate that suspending the HSA preparation is accompanied mainly by two processes. The first is water desorption-sorption which superficially obeys the Langmuir model. The influence of the medium on the thermodynamic parameters of water sorption can be described approximately by thermodynamic data on the solvation of water at infinite dilution. The second effect is a non-sorption process attributed tentatively to rupture of protein-protein contacts in the HSA preparation on suspending it. Depending on the nature of the solvent and its water content, such transformation of the HSA preparation can result in deviations from the Langmuir isotherm of water sorption by the suspended protein. This transformation is accompanied by the corresponding increase in the accessible surface area of the protein preparation and a significant enthalpy change. Experimental data cast doubt on the validity of the traditional opinion that the significant increase in water sorption by proteins at high water activities results from the various kinds of water-water interaction on the protein surface. It appears that the imposition of the transformation of the protein preparation on water sorption-desorption can determine both the calorimetric profile and thermodynamic data on suspending the protein preparation in various solvents

Thermodynamics of water binding by human serum albumin suspended in acetonitrile

Heat effects resulting from the introduction of solid human serum albumin (HSA) into various water-acetonitrile mixtures were measured calorimetrically at 298 K. The amount of water bound to the suspended HSA as a function of the water content of the solvent was also determined. Introducing HSA into water-acetonitrile mixtures involves water binding according to the Langmuir isotherm with an adsorption constant Kc = 1.0 ± 0.1 M-1, enthalpy Δh = -9.0 ± 1.5 kJ mol-1 and entropy ΔS = -30 ± 6 J mol-1 K-1. Placing HSA in the solvent has an additional heat effect of 46 ± 19 J g-1, which is attributed to an unknown transformation of the protein preparation. © 1995

Effect of chain length on interactions of aliphatic alcohols with suspended human serum albumin

Enthalpy changes on the immersion of human serum albumin (HSA) into n-butanol, n-propanol, ethanol and methanol containing different amounts of water have been measured calorimetrically at 25°C. Water sorption isotherms on HSA were also determined in water-n-butanol and water-ethanol mixtures. From comparison of the calorimetric and sorption data, it was concluded that there is a significant enthalpy change on the HSA immersion into methanol and ethanol even under conditions where there is no change in the quantity of adsorbed water. No similar contribution was found in the n-butanol based suspensions. Water monolayer capacity evaluated from the Langmuir model decreases also significantly when going from ethanol to n-butanol. Considering this non water sorption contribution, values of the monolayer capacity and the shape of the experimental dependences, it was inferred that a relatively small change of the solvent molecule structure (from n-propanol to ethanol) affects strongly the interactions of the protein with the solvent

Heat effects and water sorption by human serum albumin on its suspension in water-dimethyl sulphoxide mixtures

The heat effects on suspending solid human serum albumin (HSA) in various water-dimethyl sulphoxide (DMSO) mixtures were measured calorimetrically at 298 K. The isotherm of the water sorption for HSA suspended in the water-DMSO mixtures was also measured. The recording of the calorimetric heat effects exhibits endothermic and exothermic peaks. The endothermic heat effects were estimated graphically from the calorimetric curves. These values are shown to obey the Langmuir isotherm of the water sorption. The quasi-thermodynamic constant of water adsorption (1.2 ± 0.3 M-1) and the monolayer formation energy (-20.1 ± 1.0 J g-1) were estimated from the calorimetric data with the Langmuir model. The adsorption constant (0.16 ± 0.08 M-1) was evaluated from fitting the water sorption isotherm by the Langmuir model also. There is a divergence between the latter constant and the adsorption constant obtained from the calorimetric data. It appears that the processes accompanying the exothermic heat evolution influence the HSA's ability to bind water. The surface area of the water monolayer was also calculated from the fitting of the water sorption isotherm. It essentially exceeds the recognised values for proteins estimated from the data for water vapour sorption. The aqueous solubility of the protein after the exposure of the HSA preparation in the water-DMSO mixtures is also essentially decreased. Hence, changes in the protein-protein interactions of a diverse nature might accompany the exothermic heat evolution on suspending HSA in water-DMSO mixtures. © 1995

Effect of solvent composition on DSC exothermic peak of human serum albumin suspended in pyridkne-n-hexane mixtures

Human serum albumin (HSA) immersed in pyridine-n-hexane mixtures was analyzed using differential scanning calorimetry (DSC). State of the solid HSA in organic solvent mixtures is the non-equilibrium state which is seen as the exothermic peak on the DSC curves. The enthalpy change corresponding to this exothermic peak approaches zero when going from pure pyridine to pure n-hexane. Dependence of the enthalpy change on the pyridine concentration is suggestive that the non-equilibrium state of the immersed HSA results from the HSA-pyridine interactions 'frozen' at the lower temperature. Most likely the temperature-initiated exothermic peak observed on the DSC curves reflects the swelling of HSA by pyridine

Evaluation of the contribution to hydration of nonelectrolytes from the hydrophobic effect

A new method was suggested for estimating the hydrophobic effect of contributions to the Gibbs energies and enthalpies of hydration of hydrocarbons, inorganic gases and rare gases. In accordance with this method the hydrophobic effect contribution to the Gibbs energy was evaluated from the difference between the hydration Gibbs energy of a solute and the non hydrophobic contribution. To estimate the latter value, the known dependence connecting the Gibbs energies of solvation of a solute in a number of aprotic solvents to the Hildebrand solubility parameter for these solvents was used. The non hydrophobic contribution to the Gibbs energy of hydration was calculated for various solutes from such dependences extended to water as solvent. The Hildebrand solubility parameter for water used in the calculation was corrected for the effect of association through hydrogen bonding. This correction was made by subtraction of the water self-association enthalpy from the enthalpy of vaporization of water. The evaluated Gibbs energies of the hydrophobic effect are positive for saturated hydrocarbons, inorganic gases and rare gases and linearly depend on the solute molecular refraction. The hydrophobic contribution to the hydration enthalpies of the solutes was calculated in the same manner as was made to calculate the hydrophobic contribution to Gibbs energies of hydration. Enthalpies of the hydrophobic effect for the solutes under study are negative. © 1995 Plenum Publishing Corporation

Calorimetric and infrared study of methyl iodide and some monosubstituted butyl halides. Does methyl iodide form hydrogen bonds as a proton donor?

The solution enthalpies of methyl iodide, n- and t-butyl chlorides, n- and t-butyl iodides in cyclohexane, carbon tetrachloride, acetone and dimethyl sulfoxide (DMSO) were measured calorimetrically and the transfer enthalpies of the solutes from cyclohexane were calculated. The comparative analysis of the transfer enthalpies shows no remarkable differences that could be attributed to specific interaction between the solvents and the solutes. In addition, the infrared (IR) spectra of the butyl halides dissolved in CCl 4 and deuterated DMSO, and the IR spectra of methyl iodide in CCl 4., deuterated acetonitrile, acetone and DMSO, were investigated. Significant enhancement of the CH 3 stretching band intensity was observed for methyl iodide solutions when going from carbon tetrachloride to H-bond-acceptor solvents. This enhancement can be ascribed to the hydrogen bonding of methyl iodide with the solvents. Meanwhile, no IR spectroscopic evidence of such hydrogen bonding was observed when the solutions of n- and t-butyl halides in organic solvents were considered. A possible reason for the disagreement between the IR and calorimetric measurements is discussed

Hydrogen bonds formed by methyl groups of acetonitrile: Infrared and calorimetric study

Solutions of acetonitrile (I) in tetrachloromethane and deuteratred solvents (S) (benzene, acctonitrile, acetone and dimethylsulphoxide) have been studied by IR absorption spectra. The observed solvent effect on the IR spectrum of I was explained in terms of the existence of complexes with hydrogen bonding of the type NCCH3...solvent (S). The strength of the hydrogen bonding was characterized by enthalpies of specific interactions of I with solvents ΔHI/S int(sp). The values ΔHI/S int(sp) were determined both by IR spectroscopy and calorimetry and were found to be within the range 0.3-1.5 kcal mol-1. © 1993

Fluorescence spectroscopy for wastewater monitoring: A review

© 2016. Wastewater quality is usually assessed using physical, chemical and microbiological tests, which are not suitable for online monitoring, provide unreliable results, or use hazardous chemicals. Hence, there is an urgent need to find a rapid and effective method for the evaluation of water quality in natural and engineered systems and for providing an early warning of pollution events. Fluorescence spectroscopy has been shown to be a valuable technique to characterize and monitor wastewater in surface waters for tracking sources of pollution, and in treatment works for process control and optimization. This paper reviews the current progress in applying fluorescence to assess wastewater quality. Studies have shown that, in general, wastewater presents higher fluorescence intensity compared to natural waters for the components associated with peak T (living and dead cellular material and their exudates) and peak C (microbially reprocessed organic matter). Furthermore, peak T fluorescence is significantly reduced after the biological treatment process and peak C is almost completely removed after the chlorination and reverse osmosis stages. Thus, simple fluorometers with appropriate wavelength selectivity, particularly for peaks T and C could be used for online monitoring in wastewater treatment works. This review also shows that care should be taken in any attempt to identify wastewater pollution sources due to potential overlapping fluorophores. Correlations between fluorescence intensity and water quality parameters such as biochemical oxygen demand (BOD) and total organic carbon (TOC) have been developed and dilution of samples, typically up to ×10, has been shown to be useful to limit inner filter effect. It has been concluded that the following research gaps need to be filled: lack of studies on the on-line application of fluorescence spectroscopy in wastewater treatment works and lack of data processing tools suitable for rapid correction and extraction of data contained in fluorescence excitation-emission matrices (EEMs) for real-time studies