Raman Spectra Of Solutions Research Articles

Micro-Raman Spectroscopy and Univariate Analysis for Monitoring Disease Follow-Up

Micro-Raman spectroscopy is a very promising tool for medical applications, thanks to its sensitivity to subtle changes in the chemical and structural characteristics of biological specimens. To fully exploit these promises, building a method of data analysis properly suited for the case under study is crucial. Here, a linear or univariate approach using a R2 determination coefficient is proposed for discriminating Raman spectra even with small differences. The validity of the proposed approach has been tested using Raman spectra of high purity glucose solutions collected in the 600 to 1,600 cm−1 region and also from solutions with two known solutes at different concentrations. After this validation step, the proposed analysis has been applied to Raman spectra from oral human tissues affected by Pemphigus Vulgaris (PV), a rare life-threatening autoimmune disease, for monitoring disease follow-up. Raman spectra have been obtained in the wavenumber regions from 1,050 to 1,700 cm−1 and 2,700 to 3,200 cm−1 from tissues of patients at different stages of pathology (active PV, under therapy and PV in remission stage) as confirmed by histopathological and immunofluorescence analysis. Differences in the spectra depending on tissue illness stage have been detected at 1,150–1,250 cm−1 (amide III) and 1,420–1,450 cm−1 (CH3 deformation) regions and around 1,650 cm−1 (amide I) and 2,930 cm−1 (CH3 symmetric stretch). The analysis of tissue Raman spectra by the proposed univariate method has allowed us to effectively differentiate tissues at different stages of pathology.

Conformational and structural studies of isopropylamine from temperature dependent Raman spectra of xenon solutions and ab initio calculations

Author Institution: Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO 64110, USA

Surface-enhanced Raman spectroscopy of 4-tert -butylpyridine on a silver electrode

We report the observation of large surface-enhanced Raman scattering (SERS) (106) for 4-tert-butylpyridine molecules adsorbed on a silver electrode surface in an electrochemical cell with electrode potential set at − 0.5 V. A decrease in electrode potential to − 0.3 V was accompanied by a decrease in relative intensities of the vibrational modes. However, there were no changes in vibrational wavenumbers. Comparison of both normal solution Raman and SERS spectra shows very large enhancement of the intensities of a1, a2, and b2 modes at laser excitation of 488 nm. Enhancement of the non-totally symmetric modes indicates the presence of charge transfer as a contributor to the enhancement. Copyright © 2011 John Wiley & Sons, Ltd.

Hydroxide Hydrogen Bonding: Probing the Solvation Structure through Ultrafast Time Domain Raman Spectroscopy.

The mechanism of charge transport in aqueous media is critical in molecular, materials, and life sciences. The structure of the solvated hydroxide ion has been an area of some controversy. Polarization-resolved ultrafast time domain polarizability relaxation is used here to resolve the terahertz frequency Raman spectrum of hydroxide solutions. The measurements reveal the totally symmetric hydrogen-bond stretching (HO(-)···HOH) mode of the solvated hydroxide, permitting an experimental measurement of the bond force constant. The observed polarized Raman spectra are compared with those obtained from DFT calculations performed on HO(-)(H2O)n clusters. Good agreement between the observed frequency and the polarization dependence is found for the n = 3 or 4 clusters, particularly for those in which the solvating water molecules adopt a planar structure. The frequency of the symmetric stretch increases with concentration, consistent with an effect of ionic strength on either the H-bond or the structure of the cluster.

Manifestation of hydrogen bonds of aqueous ethanol solutions in the Raman scattering spectra

Spectra of Raman scattering of light by aqueous ethanol solutions in the range of concentrations from pure water to 96% alcohol are studied. For water, 25%, and 40% solutions of ethanol in water, as well as for 96% alcohol the Raman spectra are measured at temperatures from the freezing point to nearly the boiling point. The changes in the shape of the stretching OH band are interpreted in terms of strengthening or weakening of hydrogen bonds between the molecules in the solution. The strongest hydrogen bonding of hydroxyl groups is observed at the ethanol content from 20 to 25 volume percent, which is explained by formation of ethanol hydrates of a definite type at the mentioned concentrations of alcohol. This is confirmed by means of the method of multivariate curve resolution, used to analyse the Raman spectra of aqueous ethanol solutions. With growing temperature the weakening of hydrogen bonding occurs in all studied systems, which consists in reducing the number of OH groups, linked by strong hydrogen bonds.

Evaluation of the potential of surface enhancement Raman spectroscopy for detection of tricyclic psychotropic drugs. Case studies on imipramine and its metabolite

The potential use of surface Raman enhanced spectroscopy (SERS) for confirmatory identification and the semi-quantitative analysis of selected tricyclic antidepressants (TCAs) is examined utilizing a conventional silver colloid. Raman and SERS spectra of aqueous solutions of imipramine (Imi) and its metabolite, desipramine (Des), were recorded as the function of concentration using NIR excitation. A good linear correlation is observed for the dependence of the SERS signal at 684 cm(-1) (R(2) = 0.9997) on Imi concentration over the range of 0.75-7.5 μM. The limit of detection of imipramine in the silver colloidal solution is 0.98 μM. SERS spectra of Imi and Des were also recorded for blood plasma samples without prior purification as well as after the use of standard solid phase extraction. All spectra show the characteristic spectral profile of the molecules and moreover, stronger signal enhancement is observed for Imi in the "raw" samples as opposed to Imi extracted from a biological matrix.

Vibrational spectra and structural features of carbene analogs ElII(OCH2CH2NMe2)2 and ClElIIOCH2CH2NMe2 (ElII = Ge, Sn, Pb)

Vibrational spectra of compounds of divalent Group 14 elements ElII(OCH2CH2NMe2)2 with ElII = Ge (1), Sn (2), Pb (3) and ClElIIOCH2CH2NMe2 with ElII = Ge (4) and Sn (5) were measured for the first time and analyzed within the framework of DFT calclations. Monomeric compounds 1 and 2 whose molecules are stabilized only through intramolecular coordination were confirmed to be isostructural. Unlike 1 and 2, plumbylene 3 is a polymer in both solution and the crystalline state; the latter was confirmed by X-ray diffraction analysis. The νs C-N stretching frequency in the CH2NMe2 fragment was shown to decrease by 80–100 cm−1 owing to the formation of the coordination bond El←N. To elucidate the mechanism of a dynamic flip-flop process suggested earlier based on the broadening of some signals in the NMR spectra of compounds 1 and 4, the Raman spectra of solutions of compounds 1 and 2 in THF and Py were obtained. These experiments revealed no equilibrium with participation of a stable form with one coordination bond El←N cleaved along with the starting molecule. This is consistent with the results of the corresponding quantum chemical calculations of thermo-dynamic parameters. A somewhat different, more probable mechanism of the dynamic process was proposed, which involves an overturn of the CH2NMe2 fragment with cleavage of the El←N bond in the transition state only.

Structures of Vanadium(III)-Ethylenediamine-N,N′-diacetato-N,N′-di-3-propionato Complexes. Critical Role of pπ-dπ Donation in Determining the Coordination Number

Li[V(eddadp)]·3H(2)O (1a) and Cs[V(eddadp)]·2H(2)O (1b) were characterized by X-ray crystallography. 1a crystallizes in the monoclinic space group Cc with a = 11.467(7) Å, b = 13.398(8) Å, c = 12.529(8) Å, β = 114.85(4)°; V = 1746.7(2) Å(3), and Z = 4; 1b crystallizes in the monoclinic space group P2(1)/n with a = 10.265(5) Å, b = 11.673(6) Å, c = 15.507(8) Å, β = 104.29(2)°, V = 1800.6(2) Å(3), and Z = 4. The solution structure of 1 has been ascertained to be predominantly six-coordinated with a hexadentate eddadp which is based on a comparison of the electronic and Raman spectra of aqueous solutions of 1 with those in the solid state.

Temperature dependence of resonance Raman spectra of carotenoids

To understand the mechanism of the photoprotective and antioxidative functions of carotenoids, it is essential to have a profound knowledge of their excited electronic and vibronic states. In the present study we investigate the most powerful antioxidants: β-carotene and lutein by means of resonance Raman spectroscopy. The aim was to study in detail their Raman spectra in solution at room temperature and their changes as a function of temperature. To measure the spectra in their natural environment pyridine has been used as a solvent. It has been chosen because of its polarizability ( n = 1.5092) which is close to that of membrane lipids and proteins. The temperature dependence of the most intensive ν 1 band in the range from 77 K to 295 K at 514.5 nm excitation has been obtained. It was found that in pyridine the C C stretching frequency, its intensity, line shape, and line width are very sensitive to the temperature (the sensitivity being different for the two studied carotenoids). The observed linear temperature dependence of the C C stretching frequency is explained by a mechanism involving changes of the vibronic coupling and the extent of π-electron delocalization. The different behavior of the temperature-induced broadening of the ν 1 band and its intensity for the two studied carotenoids can be associated with the different nature of their solid matrices: glassy for β-carotene and crystalline-like for lutein, owing to their different chemical structures.

The pH dependent Raman spectroscopic study of caffeine

First of all the surface enhanced Raman spectroscopy (SERS) and normal Raman spectra of caffeine aqueous solution were obtained at different pH values. In order to obtain the detailed vibrational assignments of the Raman spectroscopy, the geometry of caffeine molecule was optimized by density functional theory (DFT) calculation. By comparing the SERS of caffeine with its normal spectra at different pH values; it is concluded that pH value can dramatically affect the SERS of caffeine, but barely affect the normal Raman spectrum of caffeine aqueous solution. It can essentially affect the reorientation of caffeine molecule to the Ag colloid surface, but cannot impact the vibration of functional groups and chemical bonds in caffeine molecule.

Semi-Quantitative Analysis of Gentian Violet by Surface-Enhanced Raman Spectroscopy Using Silver Colloids

The viability of the application of surface-enhanced Raman spectroscopy (SERS) to the semi-quantitative analysis of the triphenylmethane dye gentian violet was examined by using activated borohydride-reduced silver colloids. Raman and SERS spectra of aqueous solutions of gentian violet at different pH values were acquired for the first time and equally intense SERS signals were obtained at both acidic and alkaline pH values. Two maxima intensities observed in the pH profile revealed the presence of different ionization states of the dye. The pH conditions for SERS were optimized over the pH range 1 to 12 and the biggest enhancement for SERS of this charged dye was found to be at pH 2.0; thus, this condition was used for semi-quantitative analysis. A good linear correlation was observed for the dependence of the signal intensities of the SERS bands at 1620 cm(-1) (R = 0.999) and 1370 cm(-1) (R = 0.952) on dye concentration over the range 10(-6) to 10(-4) mol/L, using laser excitation at 514.5 nm. At concentrations of dye above 10(-2) mol/L, the concentration dependence of the SERS signals is nonlinear. This is explained as due to the precipitation of metallic silver as well as due to saturation caused by complete coverage of the SERS substrate. A series of intensities of the band at 1620 cm(-1) measured from dye molecules proved that the single-molecule limit of gentian violet is attained at the concentration of 10(-9) mol/L.

From Water Clustering to Osmotic Coefficients

Water activity is an important macroscopic property of aerosol particles and droplets in the atmosphere as well as aqueous solutions in many other fields of physical chemistry. This study focuses on relating water activity, described using osmotic coefficients, to the microscopic water structure in systems of atmospheric relevance, namely, aqueous solutions of each of the four electrolytes: NaCl, (NH(4))(2)SO(4), NH(4)Cl, and Na(2)SO(4). The osmotic coefficients of these compounds, as reported in literature based on thermodynamic measurements, decrease as a function of molality for dilute solutions and increase as a function of molality for concentrated solutions. At an intermediate molality, a minimum value of the osmotic coefficient is observed. We explain this behavior by describing osmotic coefficients as the product of two concentration-dependent effects: incomplete electrolyte dissociation and variations in the microphysical water structure. The degree of dissociation in electrolyte solutions can be obtained directly from literature or derived from reported pK values, and in this work the water structure is quantified using low-wavenumber Raman spectroscopy. We use the band at 180 cm(-1) in Raman spectra of aqueous electrolyte solutions, which has been assigned to the displacement of the central oxygen atom in a tetrahedral hydrogen bonding environment composed of five H(2)O units. The abundance of such translationally restricted water molecules is essential in describing the local microphysical structure of water, and the height of the band is used to estimate the amount of such translationally restricted water molecules in solution. We were able to qualitatively reproduce and explain literature values of osmotic coefficients for the four studied electrolytes. Our results indicate that the effect of electrolyte dissociation, which decreases as a function of molality, dominates in dilute solutions, whereas changes in water structure are more significant at higher concentrations.

Drop coating deposition Raman spectroscopy of fluorescein isothiocyanate labeled protein.

Using bovine serum albumin (BSA) as the model protein, normal Raman spectra of fluorescein isothiocyanate (FITC) conjugated protein were systematically studied for the first time using both solution and the drop coating deposition Raman (DCDR) sampling techniques. The FITC-BSA Raman spectra are dominated by the FITC Raman features that are strongly pH dependent. Current DCDR detection sensitivity obtained with a 10:1 FITC-BSA conjugate is 45 fmol in terms of total protein consumption and ∼15 attomol at laser probed volume. Unlike the FITC-BSA solution Raman spectra, where the FITC Raman features are photostable, concurrent FITC fluorescence and Raman photobleaching is observed in the DCDR spectra of FITC-BSA. While the FITC Raman photobleaching follows a single exponential decay function with a time constant independent of the FITC labeling ratio, the fluorescence background photobleaching is much more complicated and it depends strongly on the FITC labeling ratio and sample conditions. Mechanistically, the FITC Raman photobleaching is believed to be due to photochemical reaction of the FITC molecules in the electronically excited state. The FITC fluorescence photobleaching involves both concentration quenching and photochemical quenching, and the latter may involve a photochemical intermediate that is fluorescence inactive but Raman active.

ChemInform Abstract: Spectroelectrochemical Study of Iodide, Iodate and Periodate on a Silver Electrode in Alkaline Aqueous Solution.

Abstract The electrochemical oxidation of iodide on a silver electrode in 0.1 M NaOH and 5.0 × 10−4M iodide aqueous solution was monitored by in situ Raman spectroscopy. The chemical oxidation of iodide by AgO has been confirmed by in situ and ex situ Raman spectroscopy. The surface Raman spectra of a silver electrode in an alkaline working solution containing iodate and periodate indicated that the product of iodide oxidation was periodate. The spectroscopic data have been supplemented with cyclic voltammetry measurements. The adsorbed species is proposed to be a silver(I) dihydrogen orthoperiodate salt, Ag3H2IO6, based on the Raman spectra of aqueous periodate solution at various pH values and by comparing the surface spectra with the normal Raman spectra of silver(I) di- and trihydrogen orthoperiodate salts.

DFT studies of Al–O Raman vibrational frequencies for aquated aluminium species

Raman frequency calculations of Al ( H 2 O ) 6 3 + and Al ( OH ) 4 - species in different models were carried out with density functional theory (DFT). Gas-phase model (GP), polarizable continuum model (PCM), supermolecule model (SM) and supermolecule-polarizable continuum model (SM-PCM) were considered and frequencies over the wavenumber range from 0 to 1000 cm −1 were discussed. The calculated frequencies of the two species in SM-PCM model are in fair agreement with the observed frequencies in aqueous solution and the average deviation is 6 cm −1. Based on the results of Al ( H 2 O ) 6 3 + and Al ( OH ) 4 - , the DFT method and the SM-PCM model were used to study the Al–O Raman bands for some other monomeric and dimeric aluminiums. The monomeric aluminiums Al(OH) 2+, Al ( OH ) 2 + and Al ( OH ) 6 3 - as well as the dimer Al 2 O ( OH ) 6 2 - were included. As a result, we predict the main Al–O skeleton vibrations of Al ( OH ) ( H 2 O ) 5 2 + at 685 cm −1, trans- Al ( OH ) 2 ( H 2 O ) 4 + at 542 cm −1, Al ( OH ) 6 3 - at 510 cm −1 and Al 2 O ( OH ) 6 2 - at 510 and 699 cm −1 respectively in Raman spectra of aqueous solution. It can also be concluded that the calculated frequencies of Al 2 O ( OH ) 6 2 - are close to the experimental values and the existence of Al ( OH ) 6 3 - in aluminate solution cannot be ruled out.

Raman and Infrared Spectroscopic Investigation of Speciation in BeSO4(aq)

Measurements have been made of the Raman spectra of aqueous solutions of Be(ClO4)2, BeCl2, (NH4)2SO4 and BeSO4 to 50 cm−1. In some cases low concentrations (0.000770 mol⋅kg−1) have been used and two temperatures (23 and 40 °C) were studied. In BeSO4(aq), the ν 1- $\mathrm{SO}_{4}^{2-}$ mode at 980 cm−1 broadens with increasing concentration and shifts to higher wavenumbers. At the same time, a band at 1014 cm−1 is detectable with this mode being assigned to [BeOSO3], an inner-sphere complex (ISC). Confirmation of this assignment is provided by the simultaneous appearance of stretching bands for the $\mathrm{Be}^{2+}\mbox{-}\mathrm{OSO}_{3}^{2-}$ bond of the complex at 240 cm−1 and for the BeO4 skeleton mode of the [(H2O)3BeOSO3] unit at 498 cm−1. The ISC concentration increases with higher temperatures. The similarity of the $\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-}$ Raman bands for BeSO4 in H2O and D2O is further strong evidence for formation of an ISC. After subtraction of the ISC component at 1014 cm−1, the $\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-}$ band in BeSO4(aq) showed systematic differences from that in (NH4)2SO4(aq). This is consistent with a $\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-}$ mode at 982.7 cm−1 that can be assigned to the occurrence of an outer-sphere complex ion (OSCs). These observations are shown to be in agreement with results derived from previous relaxation measurements. Infrared spectroscopic data show features that are also consistent with a beryllium sulfato complex such as the appearance of a broad and weak $\nu_{1}\mbox{-}\mathrm{SO}_{4}^{2-}$ mode at ∼1014 cm−1, normally infrared forbidden, and a broad and asymmetric $\nu_{3}\mbox{-}\mathrm{SO}_{4}^{2-}$ band contour which could be fitted with four band components (including $\nu_{3}\mbox{-}\mathrm{SO}_{4}^{2-}(\mathrm{aq})$ ). The formation of ISCs in BeSO4(aq) is much more pronounced than in the similar MgSO4(aq) system studied recently.

Liquid cell with plasmon lenses for surface enhanced Raman spectroscopy

High-fidelity surface enhanced Raman spectra (SERS) of Rhodamine 6G and 2-mercaptopyrimidine liquid solutions are measured using a microfluidic delivery system constructed on a flat silver substrate. Microscopic plasmon lenses patterned in the silver film focus surface plasmons into a subwavelength spot which yields the light amplification required for SERS. The system provides an efficiency similar to traditional colloidal substrates, and allows multiple sample loading. We find that the main contribution to the spectra comes from the molecules directly attached to the silver surface, which gives strong evidence for the chemical enhancement of SERS.

Experimental study of the system H 3BO 3–NaF–SiO 2-H 2O at 350–800 °C and 1–2 kbar by the method of synthetic fluid inclusions

The phase state of fluid in the system H 3BO 3–NaF–SiO 2–H 2O was studied at 350–800 °C and 1–2 kbar by the method of synthetic fluid inclusions. The increase in the solubility of quartz and the high reciprocal solubility of H 3BO 3 and NaF in water fluid at high temperatures are due to the formation of complexes containing B, F, Si, and Na. At 800 °C and 2 kbar, both liquid and gas immiscible phases (viscous silicate-water-salt liquid and three water fluids with different contents of B and F) are dispersed within each other. The Raman spectra of aqueous solutions and viscous liquid show not only a peak of [B(OH) 3] 0 but also peaks of complexes [B(OH) 4] –, polyborates [B 4O 5(OH) 4] 2–, [B 3O 3(OH) 4] –, and [B 5O 6(OH) 4] –, and/or fluoroborates [B 3F 6O 3] 3–, [BF 2(OH) 2] –, [BF 3(OH)] –, and [BF 4] –. The high viscosity of nonfreezing fluid is due to the polymerization of complexes of polyborates and fluorine-substituted polyborates containing Si and Na. Solutions in fluid inclusions belong to P–Q type complicated by a metastable or stable immiscibility region. Metastable fluid equilibria transform into stable ones owing to the formation of new complexes at 800 ºC and 2 kbar as a result of the interaction of quartz with B-F-containing fluid. At high concentrations of F and B in natural fluids, complexes containing B, F, Si, and alkaline metals and silicate-water-salt dispersed phases might be produced and concentrate many elements, including ore-forming ones. Their transformation into vitreous masses or viscous liquids (gels, jellies) during cooling and the subsequent crystallization of these products at low temperatures (300–400 °C) should lead to the release of fluid enriched in the above elements.

The single donator-single acceptor hydrogen bonding structure in water probed by Raman spectroscopy

In this work, the Raman spectra of aqueous C(12)E(5) solutions are recorded and utilized to demonstrate the existence of single donator-single acceptor (DA) hydrogen bonding in water. From Raman OH stretching bands of aqueous C(12)E(5) solutions, the relative intensity of 3430 cm(-1) subband increases with C(12)E(5) concentrations. For confined water, the DA hydrogen bonding can be expected to be the important hydrogen bonding species. Therefore, the 3430 cm(-1) component can be ascribed to OH vibration engaged in DA hydrogen bonding. This is in agreement with our recent explanation on Raman OH stretching band of water. For water at ambient conditions, the double donor-double acceptor (DDAA) and DA should be the dominant hydrogen bonding species, the ratio of DDAA to DA can be approximately to be 0.75:1, and the mean hydrogen bonding can be determined to be 2.75.

Low-Frequency Isotropic Raman Spectra of Concentrated Aqueous KX (X: Cl, Br, NO3, and SCN) Solutions

Abstract Polarized Raman spectra for concentrated aqueous KX solutions (X: Cl, Br, NO3, and SCN) were measured in the frequency range of 30 ≤−1 in order to find the totally symmetric stretching vibrational mode of hydrated K+. The observed polarized peak intensities of the intermolecular vibrational mode at−1 in the isotropic spectra for KCl and KBr solutions exhibit systematic increase with increasing solute content. Polarized components at−1 were observed in the isotropic spectra for 5 mol % KNO3 and 7 mol % KSCN solutions, respectively. The position of these polarized peaks were found to shift to lower frequency by 7–15 cm−1 in D2O solutions, which is consistent with the expected value of the H/D isotopic shift calculated for the totally symmetric vibrational mode of the hydrated K+, K+(H2O)6.≤ 1000 cm= 160–180 cm= 166 and 167 cm