The role of electrostatic interactions on the rejection of organic solutes in aqueous solutions with nanofiltration

The effects of electrostatic interactions on the rejection of organic solutes with nanofiltration membranes were investigated. For two different membranes, the rejection of selected organic acids, positively and negatively charged pharmaceuticals and neutral pharmaceuticals was investigated at different feed water chemistries (different ionic strengths and pH conditions, with and without the presence of NOM and divalent cations). It was concluded that for negatively charged membranes, electrostatic repulsion leads to an increase of the rejection of negatively charged solutes and electrostatic attraction leads to a decrease of the rejection of positively charged solutes, compared to neutral solutes. Neutral and positively charged solutes engage in hydrophobic interactions with negatively charged membranes, whereas negatively charged solutes do not engage in hydrophobic interactions since they cannot approach the membrane surface. This provides proof for the theory of an increased concentration of positively charged organic solutes and a decreased concentration of negatively charged organic solutes at the membrane surface compared to the bulk fluid. This concept may be denoted as “charge concentration polarisation”. The concept was further used as a modelling tool to predict the effects of electrostatic interactions on the rejection of trace organic solutes.     

Optimised determinations of water in ethanol by encoded photometric near-infrared spectroscopy: a special case of sequential standard addition calibration

A special limiting case of sequential standard addition calibration (S-SAC) has been applied to measurement of the water content of ethanol using encoded photometric near infrared spectroscopy. The method has shown good comparability with certified reference materials and to measurements made by Karl Fischer titration. The technique is quick and easy to use and should have application in high throughput and process measurement, for instance in biofuels analysis at port-of-entry or in bio-refineries. The characteristics of this limiting case of S-SAC have been fully described, and the corrections required to the value obtained by extrapolation to avoid bias have been calculated. The precision of the S-SAC procedure has been studied, and proposals have been made to optimise this with respect to the analytical precision. The technique should be applicable for the measurement of water in ethanol mass fractions of up to 0.1 g g⁻¹ with an expanded uncertainty of less than 2% (relative).     

Characterisation of hydrogen bond perturbations in aqueous systems using aquaphotomics and multivariate curve resolution-alternating least squares

Aquaphotomics is a new discipline that provides a framework for understanding changes in the structure of water caused by various perturbations, such as variations in temperature or the addition of solutes, using near infrared spectroscopy (NIRS). One of the main purposes of aquaphotomics is to identify water bands as main coordinates of future absorbance patterns to be used as biomarkers. These bands appear as consequence of perturbations in the NIR spectra. Curve resolution techniques may help to resolve and find new water bands or confirm already known bands. The aim of this study is to investigate the application of multivariate curve resolution-alternating least squares (MCR-ALS) to characterise the effects of various perturbations on the NIR spectra of water in terms of hydrogen bonding. For this purpose, the perturbations created by temperature change and the addition of four solutions of different ionic strength and Lewis acidity were studied (NaCl, KCl, MgCl₂ and AlCl₃, with concentrations ranging from 0.2 to 1 mol L⁻¹ in steps of 0.2 mol L⁻¹). Transmission spectra of all salt solutions and pure water were obtained at temperatures ranging from 28 to 45 °C. We have found that three distinct components with varying temperature dependence are present in water perturbed by temperature. The salt solutions studied exhibited similar trends with respect to the temperature perturbation, while the peak locations of their MCR-ALS pure components varied according to the ionic strength of the salt used.     

Solid water at room temperature?

Previously, we have shown that water adjacent to many hydrophilic substances excludes colloidal and molecular solutes. It was labelled “exclusion zone” (EZ) or “fourth phase” water. A salient feature is its characteristic light absorbance at or near 270 nm. In this study, EZ water formed against three chemically distinct surfaces, Nafion, ghee, and Whatman-5 filter paper was extracted, characterized by UV–Visible absorbance spectroscopy, and solidified either by lyophilizing or evaporation in an oven. The resulting highly stable solid was dissolved in water and confirmed as EZ water by its characteristic absorbance at 270–280 nm. We used mass spectroscopy to verify the absence of ionizable contaminants that could reproduce the characteristic “signature EZ” spectra in the three liquid preparations, or in the solids formed from desiccated EZ water that had been reconstituted in deionized water. Hence, a solid form of EZ water may, indeed, exist at room temperature.     

Thermal signature of hydrophobic hydration dynamics

Hydrophobic hydration, the perturbation of the aqueous solvent near an apolar solute or interface, is a fundamental ingredient in many chemical and biological processes. Both bulk water and aqueous solutions of apolar solutes behave anomalously at low temperatures for reasons that are not fully understood. Here, we use (2)H NMR relaxation to characterize the rotational dynamics in hydrophobic hydration shells over a wide temperature range, extending down to 243 K. We examine four partly hydrophobic solutes: the peptides N-acetyl-glycine-N'-methylamide and N-acetyl-leucine-N'-methylamide, and the osmolytes trimethylamine N-oxide and tetramethylurea. For all four solutes, we find that water rotates with lower activation energy in the hydration shell than in bulk water below 255 +/- 2 K. At still lower temperatures, water rotation is predicted to be faster in the shell than in bulk. We rationalize this behavior in terms of the geometric constraints imposed by the solute. These findings reverse the classical "iceberg" view of hydrophobic hydration by indicating that hydrophobic hydration water is less ice-like than bulk water. Our results also challenge the "structural temperature" concept. The two investigated osmolytes have opposite effects on protein stability but have virtually the same effect on water dynamics, suggesting that they do not act indirectly via solvent perturbations. The NMR-derived picture of hydrophobic hydration dynamics differs substantially from views emerging from recent quasielastic neutron scattering and pump-probe infrared spectroscopy studies of the same solutes. We discuss the possible reasons for these discrepancies.     

Raman spectroscopy of archaeological and ancient resins: problems with database construction for applications in conservation and historical provenancing

The adoption of Raman spectroscopy as a screening technique for the presence of organic resins on diverse substrates is now being advocated for the first pass non-destructive examination of potential sites for limited sampling using other analytical techniques. The characterisation of ancient resins in art work and specimens recovered from archaeological excavations is critically dependent upon the analytical capability of Raman spectroscopy using different wavelengths of excitation from the visible to the near infrared and the interpretation of the data illustrates the advantages and limitations of the technique. Resin specimens from art works and artefacts span a period of about 7000 years of recorded history and the influence of factors such as the environmental degradation, burial deposition, reaction with associated substrates and mineral pigments on the observed Raman spectra have been assessed. The key molecular Raman spectral features that are definitive for the discrimination between contemporary resins are considered in respect of these factors and thereby illustrative of the difficulties posed for the creation of a Raman spectral database of ancient resins, in contrast with the extensive and definitive literature equivalents that are available for their mineral pigment and organic dye analogues.     

Biomolecular hydration dynamics probed with 2D-IR spectroscopy: From dilute solution to a macromolecular crowd

Although it is well known that water is essential for biological function, it has been a challenge to determine how water behaves near biomacromolecular interfaces, and what role water plays in influencing the dynamics of the biochemical machinery. By adopting a vibrational labeling strategy coupled with ultrafast two-dimensional infrared (2D-IR) spectroscopy, it has recently become possible to study hydration dynamics, site specifically at the surface of proteins and model membranes. We review our recent progress in measuring hydration dynamics in contexts ranging from small-molecule solutes to biomacromolecules in dilute, viscous, and crowded environments.     

磁场作用下葡萄糖近红外光谱检测技术研究

采用傅立叶变换红外光谱仪(FTIR)研究了磁场强度对葡萄糖溶液近红外光谱的影响,发现磁场作用下葡萄糖的近红外光谱吸收强度和部分峰位发生显著变化。分析了磁场对葡萄糖溶液近红外光谱吸收的影响机理。采用偏最小二乘回归法(PLS)建立了磁场作用下葡萄糖溶液的定量分析模型,使用验证集进行验证。研究结果表明,磁场对葡萄糖分子基团偶极矩产生诱导作用,使偶极矩增大,吸收增强;同时磁场作用下,葡萄糖分子趋于沿平行于磁场的方向排列,其基团振动频率(特征吸收峰)吸光度与浓度变化的线性关系得到极大的改善。该研究有助于提高葡萄糖分子吸收强度及其测量精度,为进一步提高血糖检测精度提供技术支持。     

Complete quality analysis of commercial surface-active products by Fourier-transform near infrared spectroscopy

Using proper calibration data Fourier-transform near infrared spectroscopy is used for developing multivariate calibrations for different analytical determinations routinely used in the surfactants industry. Four products were studied: oleyl-cetyl alcohol polyethoxylated, cocamidopropyl betaine (CAPB), sodium lauryl sulfate (SLS) and nonylphenol polyethoxylated (NPEO). Calibrations for major as well as very low concentrated compounds were achieved and every model was validated through linearity, bias, accuracy and precision tests, showing good results and the viability of NIR spectroscopy as a full quality control method for this products. Duplicate and complete analysis on a single sample takes at most 3 min, requiring neither sample preparation nor the use of reagents. The analytical reference procedures involved in this work represent the typical ones used in the industry and the NIR method shows good results in the analysis of components with weight concentrations less than 1%.     

A heuristic and parallel simulated annealing algorithm for variable selection in near‐infrared spectroscopy analysis

A new heuristic and parallel simulated annealing algorithm was proposed for variable selection in near‐infrared spectroscopy analysis. The algorithm employs a parallel mechanism to enhance the search efficiency, a heuristic mechanism to generate high‐quality candidate solutions, and the concept of Metropolis criterion to estimate accuracy of the candidate solutions. Several near‐infrared datasets have been evaluated under the proposed new algorithm, with partial least squares leading to improved analytical figures of merit upon wavelength selection. Improved robust and predictive regression models were obtained by the new algorithm. The method could also be helpful in other chemometric activities such as classification or quantitative structure‐activity relationship problems.     

Near‐infrared spectroscopy investigation of water effects on the cationic photopolymerization of vinyl ether systems

Real‐time Fourier transform near‐infrared spectroscopy has been used to monitor monomer and water concentrations simultaneously during cationic vinyl ether photopolymerization. The use of near‐infrared peak area methods allows the water content to be conveniently and nondestructively determined in any monomer or polymer for which the water peak has previously been calibrated by gravimetric analysis. Although the shape of the absorption band due to absorbed water in a monomer changes with the quantity of water, the integrated intensity from about 5350 to 4900 cm^?1 can be correlated directly to the water concentration, and this region is well removed from the vinyl‐based absorption at approximately 6190 cm^?1. This approach provides a highly informative, dynamic technique for examining the influence of moisture on polymerization reactions. Significant differences have been observed in the effects of absorbed water on the cationic photopolymerization kinetics of vinyl ether monomers with or without an ? OH group. Along with the rapid consumption of water coupled to vinyl ether polymerization, acid‐catalyzed hydrolysis reactions have also been spectroscopically observed, giving rise to the formation of aldehyde groups. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1985–1998, 2004     

Molecular view of water dynamics near model peptides

Incoherent quasi-elastic neutron scattering (QENS) has been used to measure the dynamics of water molecules in solutions of a model protein backbone, N-acetyl-glycine-methylamide (NAGMA), as a function of concentration, for comparison with results for water dynamics in aqueous solutions of the N-acetyl-leucine-methylamide (NALMA) hydrophobic peptide at comparable concentrations. From the analysis of the elastic incoherent structure factor, we find significant fractions of elastic intensity at high and low concentrations for both solutes, which corresponds to a greater population of protons with rotational time scales outside the experimental resolution (>13 ps). The higher-concentration solutions show a component of the elastic fraction that we propose is due to water motions that are strongly coupled to the solute motions, while for low-concentration solutions an additional component is activated due to dynamic coupling between inner and outer hydration layers. An important difference between the solute types at the highest concentration studied is found from stretched exponential fits to their experimental intermediate scattering functions, showing more pronounced anomalous diffusion signatures for NALMA, including a smaller stretched exponent beta and a longer structural relaxation time tau than those found for NAGMA. The more normal water diffusion exhibited near the hydrophilic NAGMA provides experimental support for an explanation of the origin of the anomalous diffusion behavior of NALMA as arising from frustrated interactions between water molecules when a chemical interface is formed upon addition of a hydrophobic side chain, inducing spatial heterogeneity in the hydration dynamics in the two types of regions of the NALMA peptide. We place our QENS measurements on model biological solutes in the context of other spectroscopic techniques and provide both confirming as well as complementary dynamic information that attempts to give a unifying molecular view of hydration dynamics signatures near peptides and proteins.     

A small molecular size system giving unexpected surface effects: alpha-Cyclodextrin + sodium dodecyl sulfate in water

Maximum drop volumes (MDV) and the resultant surface tension values (sigma) of alpha-cyclodextrin (alpha-CD) + sodium dodecyl sulfate (SDS) aqueous mixtures have been determined over a broad concentration range of both solutes at 283.15, 293.15, 303.15, 313.15, and 323.15 K. Drops significantly larger than those of pure water (up to approximately 25% larger) were observed at low temperatures for solutions with [alpha-CD]/[SDS] concentration ratios, approximately > 2, producing unexpectedly high surface tension values. Our results indicate that at certain solute concentration ratios and temperatures, the drop volume method provides wrong values for equilibrium surface tensions. This is due to the high viscoelasticity of the surface film whose effect is important even though the injection rate of the drops was slow and the solutes molecular sizes are small.     

近红外光谱分析技术的最新进展与展望

在过去的几十年,近红外光谱是发展最为迅速的分析技术之一。振动光谱基础理论、光谱仪器硬件和化学计量学是现代近红外光谱分析技术的3大支柱,近些年,近红外光谱技术在这3个方面均取得了显著进展。该文结合上述3个方面的应用研究情况,对近红外光谱分析技术的最新进展进行了综述,并对未来发展趋势进行了展望。     

Analytical techniques for characterization of organic molecular assemblies in molecular electronics devices

The analytical techniques used for the physical characterization of organic molecular electronic-based devices are surveyed and discussed. These protocols include methods that are used to probe molecular assemblies such as single wavelength ellipsometry, water contact angle goniometry, cyclic voltammetry, infrared spectroscopy, and X-ray photoelectron spectroscopy, and methods used to measure charge transport properties of devices such as scanning tunneling microscopy, and inelastic electron tunneling spectroscopy. Examples from our laboratory and the literature are given for each of these analytical techniques.     

Near infrared spectroscopy of stearic acid adsorbed on montmorillonite

The adsorption of stearic acid on both sodium montmorillonites and calcium montmorillonites has been studied by near infrared spectroscopy complimented with infrared spectroscopy. Upon adsorption of stearic acid on Ca–Mt additional near infrared bands are observed at 8236 cm^?1 and is assigned to an interaction of stearic acid with the water of hydration. Upon adsorption of the stearic acid on Na–Mt, the NIR bands are now observed at 5671, 5778, 5848 and 5912 cm^?1 and are assigned to the overtone and combination bands of the CH fundamentals. Additional bands at 4177, 4250, 4324, 4337, 4689 and 4809 cm^?1 are attributed to CH combination bands resulting from the adsorption of the stearic acid. Stearic acid is used as a model molecule for adsorption studies. The application of near infrared spectroscopy to the study of this adsorption proved most useful.     

Aquaphotomics Research of Cold Stress in Soybean Cultivars with Different Stress Tolerance Ability: Early Detection of Cold Stress Response

The development of non-destructive methods for early detection of cold stress of plants and the identification of cold-tolerant cultivars is highly needed in crop breeding programs. Current methods are either destructive, time-consuming or imprecise. In this study, soybean leaves’ spectra were acquired in the near infrared (NIR) range (588–1025 nm) from five cultivars genetically engineered to have different levels of cold stress tolerance. The spectra were acquired at the optimal growing temperature 27 °C and when the temperature was decreased to 22 °C. In this paper, we report the results of the aquaphotomics analysis performed with the objective of understanding the role of the water molecular system in the early cold stress response of all cultivars. The raw spectra and the results of Principal Component Analysis, Soft Independent Modeling of Class Analogies and aquagrams showed consistent evidence of huge differences in the NIR spectral profiles of all cultivars under normal and mild cold stress conditions. The SIMCA discrimination between the plants before and after stress was achieved with 100% accuracy. The interpretation of spectral patterns before and after cold stress revealed major changes in the water molecular structure of the soybean leaves, altered carbohydrate and oxidative metabolism. Specific water molecular structures in the leaves of soybean cultivars were found to be highly sensitive to the temperature, showing their crucial role in the cold stress response. The results also indicated the existence of differences in the cold stress response of different cultivars, which will be a topic of further research.     

Overview of Popular Techniques of Raman Spectroscopy and Their Potential in the Study of Plant Tissues

Raman spectroscopy is one of the main analytical techniques used in optical metrology. It is a vibration, marker-free technique that provides insight into the structure and composition of tissues and cells at the molecular level. Raman spectroscopy is an outstanding material identification technique. It provides spatial information of vibrations from complex biological samples which renders it a very accurate tool for the analysis of highly complex plant tissues. Raman spectra can be used as a fingerprint tool for a very wide range of compounds. Raman spectroscopy enables all the polymers that build the cell walls of plants to be tracked simultaneously; it facilitates the analysis of both the molecular composition and the molecular structure of cell walls. Due to its high sensitivity to even minute structural changes, this method is used for comparative tests. The introduction of new and improved Raman techniques by scientists as well as the constant technological development of the apparatus has resulted in an increased importance of Raman spectroscopy in the discovery and defining of tissues and the processes taking place in them.     

FT-IR microscopy characterization of sol–gel layers prior and after glucose oxidase immobilization for biosensing applications

Micro-Attenuated Total Reflection (ATR) Fourier Transform Infrared spectroscopy was used to investigate sol–gel layers for biosensing applications prior and after glucose oxidase (GOD) immobilization. The changes occurring in sol–gel infrared spectrum after GOD immobilization were clearly evidenced confirming the retaining of the enzyme activity. Moreover, micro-ATR experimental technique allowed us to investigate the spatial distribution of enzyme concentration. The non-destructive nature of our approach also enabled to monitor the time stability of sol–gel layers and of embedded GOD. The temporal evolution of some peaks in infrared spectra of these sol–gel layers was compared with absorption and steady-state fluorescence measurements. The results reported here confirm that micro-ATR infrared spectroscopy can be usefully employed for a non- or minimally invasive detailed characterization of supports for enzyme immobilization.     

Critical considerations for the accelerated ageing of high-density polyethylene potable water materials

Accelerated ageing conditions with chlorinated water were identified that minimize variations in solution chemistry and water sorption, and that also enable the interpretation of HDPE physical and chemical changes during 20 week (3884 h) immersion periods. Of the ten conditions tested, three conditions with an alkalinity concentration of 50 ppm as CaCO₃ at pH 6.5 and at 23 and 37 °C performed best. These three conditions exhibited stable pH, free available chlorine, and alkalinity concentration during 20 weeks of HDPE immersion with 72 h changes of ageing solution. HDPE was periodically characterized using differential scanning calorimetry, thermogravimetric analysis, tensile analysis, a density gradient column, moisture analysis, and optical and infrared spectroscopy. Formation of surface carbonyl bonds and gradual reductions in oxidation induction time were detected, as well as water sorption into HDPE. Ageing solution and water sorption monitoring recommendations from this work should be incorporated into accelerated ageing protocols and considered when characterizing aged PE drinking water pipe.