Aqueous solutions Fourier-transform infrared spectroscopy

Tejedor-Tejedor, M.L Yost, E.C. Anderson, M.C. (1990a) Characterization of benzoic acid and phenolic complexes at the goethite/ aqueous solution interface using cylindrical internal reflectance Fourier transform infrared spectroscopy. Part 5 Methodology. Langmuir 6 979-987... 

Durrani, C.M., Prystupa, D.A., Donald, A.M., and Clark, A.H. (1993). Phase diagram of mixtures of polymers in aqueous solution using Fourier transform infrared spectroscopy. Macromolecules, 26, 981-987. 

The secondary structure of proteins may also be assessed using vibrational spectroscopy, fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy both provide information on the secondary structure of proteins. The bulk of the literature using vibrational spectroscopy to study protein structure has involved the use of FTIR. Water produces vibrational bands that interfere with the bands associated with proteins. For this reason, most of the FTIR literature focuses on the use of this technique to assess structure in the solid state or in the presence of non-aqueous environments. Recently, differential FTIR has been used in which a water background is subtracted from the FTIR spectrum. This workaround is limited to solutions containing relatively high protein concentrations. 

Copolymers with sites for association in aqueous solutions were pre-pared by copolymerizing acrylamide with N-alkylacrylamides or with the ampholytic monomer pairs sodium 2-acrylamido 2 methylpro-panesulfonate (NaAMPS) and 2-acrylamido-2-methylpropane-dimethylammonium chloride (AMPDAC). The copolymers were characterized by elemental analysis, NMR and Fourier transform infrared spectroscopy, and lowhangle laser and quasielastic lightscattering measurements. Rheological properties were studied as a function of microstructure, molecular weight, polymer concentration, electrolyte concentration, and shear rate. On the basis of those results, a conceptual model that is based on microheterogeneous domain formation in aqueous solutions is proposed. 

Tejedor-Tejedor, M. I., Yost, E. C., and Anderson, M. A., Characterization of benzoic complexes at the goethite/aqueous solution interface using cylindrical internal reflection Fourier transform infrared spectroscopy. Part I. Methodology, Langmuir, 6, 980-987 (1990). 

Couzist, A., Gulari E. (1993). Adsorption of sodium laurate from its aqueous solution onto an alumina surface. A dynamic study of the surface-surfactant interaction using attenuated total reflection Fourier transform infrared spectroscopy, Langmuir Vol. 9, 3414-3421, 0743-7463. 

PAH has been studied in detail for its role in silicification under ambient conditions and at neutral pH. It was demonstrated that PAH can facilitate the formation of nanometer and micrometer-size spherical silica particles imder mild conditions from an aqueous solution of a silica precursor (Fig. 6). It was shown by energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) that the PAH was incorporated into the final silica structures. In the absence of PAH the reaction mixture gelled in 1 day. These results indicate that PAH may act as a catalyst as well as a template or structure-directing agent in silicification. In this context, the behavior of this system is consistent with how Tacke described the role(s) of macromolecules that facilitate silica formation via scaffolding (see section II). 

Ibuprofen is a nonsteroidal anti-inflammatoiy drug (NSAID) used for pain relief due to the anti-inflammatory effects [56], however this drug has low solubility in aqueous solutions [57, 58], which implies involvement in negative absorption by the body. Then researchers are using supercritical fluid technology to overcome these drawbacks. Antonov et al., [59] studied the solubility of ibuprofen in supercritical CO2 by fourier transform infrared spectroscopy, moreover ibuprofen was also studied in supercritical impregnation processes polymers [60, 61], in theoretical RESS process [62, 63] and experimentally for micronization of particles with reductions from 45 pm to 2.85 pm [64], and formation of even smaller nanoparticles by RESOLV [65]. Furthermore, Molnar et al., [66] studied the enantioseparation of racemic ibuprofen in SFE and realized that the system pressure of the extraction is directly related to resolution efficiency. 

Persson et al. (1991) used diffuse reflection infrared Fourier transform (DRIFT) spectroscopy to study the interactions between galena, pyrite sphalerite and ethyl xanthate. They provided the evidence that the DRIFT spectrum of oxidized galena treated with an aqueous solution of potassium ethyl xanthate is practically identical with that of solid lead (II) ethyl xanthate, which can be formed as the only detectable siuface species on oxidized galena. Dialkyl dixanthogen is formed as the only siuface species in the reaction between oxidized pyrite and aqueous solution of potassium alkyl xanthate. 

In this report we describe novel pressure tuning vibrational spectroscopic techniques that can be used to study aqueous surfactant solutions and discuss in some detail two examples of such studies with micellar solutions of anionic surfactants, one using Fourier transform infrared (FT-IR) and another using Raman spectroscopy. 

The use of infrared spectroscopy in the Earth and environmental sciences has been widespread for decades however, until development of the attenuated total reflectance (ATR) technique, the primary use was ex situ material characterization (Chen and Gardella, 1998 Tejedor-Tejedor et al., 1998 Degenhardt and McQuillan, 1999 Peak et al., 1999 Wijnja and Schulthess, 1999 Aral and Sparks, 2001 Kirwan et al., 2003). For the study of environmental systems, the strength of the ATR-Fourier transform infrared (FTIR) technique lies in its intrinsic surface sensitivity. Spectra are collected only from absorptions of an evanescent wave with a maximum penetration depth of several micrometers from the internal reflection element into the solution phase (Harrick, 1967). This short optical path length allows one to overcome any absorption due to an aqueous phase associated with the sample while maintaining a high sensitivity to species at the mineral-water interface (McQuillan, 2001). Therefore, ATR—FTIR represents a technique capable of performing in situ spectroscopic studies in real time. 

Fourier-transform infrared (FTIR) spectroscopy is particularly useful for probing the structures of membrane proteins [3, 23]. This technique can be used to study the secondary structures of proteins, both in their native environment as well as after reconstitution into model membranes. Myelin basic protein (MBP) is a major protein of the nervous system and has been studied by using FTIR spectroscopy in both aqueous solution and after reconstitution in myelin lipids [24]. The amide I band of MBP in D2O solution (deconvolved and curve-fitted) is... 

Raman spectroscopy is a vibrational spectroscopic technique which can be a useful probe of protein structure, since both intensity and frequency of vibrational motions of the amino acid side chains or polypeptide backbone are sensitive to chemical changes and the microenvironment around the functional groups. Thus, it can monitor changes related to tertiary structure as well as secondary structure of proteins. An important advantage of this technique is its versatility in application to samples which may be in solution or solid, clear or turbid, in aqueous or organic solvent. Since the concentration of proteins typically found in food systems is high, the classical dispersive method based on visible laser Raman spectroscopy, as well as the newer technique known as Fourier-transform Raman spectroscopy which utilizes near-infrared excitation, are more suitable to study food proteins (Li-Chan et aL, 1994). In contrast the technique based on ultraviolet excitation, known as resonance Raman spectroscopy, is more commonly used to study dilute protein solutions. 

The solubility of derivatives of CS has extended its utilization in noncovalent functionalization of CNTs to improve the properties of CNTs by making them individually dispersible. It has been reported that carboxymethyl CS was able to produce CNT dispersion in acidic media. On the other hand, PEG-functionalized carboxymethyl CS was found as an excellent candidate to produce highly effective debundUng and dispersion of CNTs in neutral aqueous solution [91], In an innovative method, the interaction between the functional groups of CS and CNTs was considered and the dispersibihty of CNTs was studied by Fourier transform infrared (FTIR) spectroscopy (Fig. 2.13). The authors found that the free electron pair of amine group of carboxymethyl CS and PEG-functionalized carboxymethyl CS plays a crucial role in dispersing CNTs via n-% interactions. 

Raman spectroscopy has been successfully employed to follow the kinetics of reactions at HTR Kessler et al. [197] studied the decomposition of tertiary butyl peroxypivalate in solution, obtaining the same activation energy as those which have been obtained by other conventional methods. Brill et al. have recently published an interesting series of articles [198-200] on the vibrational spectroscopy [Fourier transform infrared (FTIR) and Raman] of hydrothermal reactions, covering the decomposition of species such as urea, ammonium carbonate, cyanamide, or dicyandiamide. All of these works demonstrate the ability of vibrational spectroscopic techniques to obtain detailed information about the composition and evolution of aqueous systems in extreme conditions,... 

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