World Congress on Biosensors 2014

World Congress on Biosensors 2014
Biosensors 2014

Thursday, 10 May 2012

Just Published: Vibrational Spectroscopy


A new issue of this journal has just been published. To see abstracts of the papers it contains (with links through to the full papers) click here:
Vibrational Spectroscopy
Selected papers from the latest issue:

Thickness measurement of thin polymer films by total internal reflection Raman and attenuated total reflection infrared spectroscopy

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Antti O. Kivioja, Anna-Stiina Jääskeläinen, Ville Ahtee, Tapani Vuorinen
For the first time total internal reflection (TIR) Raman spectroscopy was utilized for thickness measurements of thin isotropic polystyrene films on polypropylene substrate. In the presented method, the band intensity ratios of polystyrene to polypropylene were defined from the spectra, and the film thicknesses in a range from 50nm to 350nm were calculated mathematically from these ratios. The quantitativeness of the method was validated by applying the same principle to attenuated total reflection infrared (ATR-IR) spectroscopy and comparing the results to values obtained by ellipsometry and a spin-coating model. The results showed that the novel and non-invasive TIR Raman method reveals the film thickness quantitatively, and the method is applicable for thin films on soft substrates with similar refractive indices.

Raman spectroscopic characterization of different regioisomers of monoacyl and diacyl chlorogenic acid

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Pinkie J. Eravuchira, Rasha M. El-Abassy, Sagar Deshpande, Marius F. Matei, Soni Mishra, Poonam Tandon, Nikolai Kuhnert, Arnulf Materny
We have investigated the Raman spectra of different regioisomeric forms of monoacyl and diacyl chlorogenic acids. Raman spectra of 3-caffeoylquinic acid, 4-caffeoylquinic acid, 5-caffeoylquinic, 3,4-di-O-caffeoylquinic acid, 3,5-di-O-caffeoylquinic acid, 4,5-di-O-caffeoylquinic acid, and a synthetic derivative of 3-feruloylqunic acid were recorded using visible Raman spectroscopic technique and vibrational bands are assigned. Additionally, a theoretical study of 5-caffeoylquinic acid was performed using Gaussian 03.

Improved assignment of vibrational modes in sum-frequency spectra in the CH stretch region for surface-bound C18 alkylsilanes

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Arthur D. Quast, Nathan C. Wilde, Sam S. Matthews, Scott T. Maughan, Steven L. Castle, James E. Patterson
Previous assignments of the CH stretching modes for surface-bound alkylsilanes in vibrationally resonant sum-frequency generation (VR-SFG) spectra have differed, leading to uncertainty in how to interpret vibrational spectra of these systems. In particular, the assignment of Fermi resonances, including which modes are coupled, has been unclear. To aid in these assignments, partially deuterated alkylsilanes were synthesized and characterized by FT-IR and VR-SFG. Density functional theory (DFT) calculations complement the spectroscopic investigation. Based on these results, we identify multiple contributions to the VR-SFG feature at ∼2950cm−1; this is primarily a Fermi resonance between the symmetric methyl stretch and symmetric methyl bending modes at 2945cm−1 with a high-frequency shoulder at ∼2960cm−1, assigned to the methyl antisymmetric stretch, and a small contribution from the antisymmetric stretch of the ω CH2 group at ∼2930cm−1. The feature at 2880cm−1 is assigned as the symmetric methyl stretch. Improved mode assignments will aid the interpretation of vibrational spectra with an aim toward developing a better understanding of the molecular basis of retention in liquid chromatography.

Determination of reduction degree of direct reduced iron via FT-IR spectroscopy

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Nesibe Dilmac, Sedat Yörük, Şahin M. Gülaboğlu
In this study, the applicability of FT-IR spectroscopy to determination of direct reduction degree of Attepe iron ore was examined. For that purpose, infrared spectra of all samples generated as the stack gas of the reduction reaction were recorded in a ZnSe windowed gas cell equipment at 2cm−1 resolution. Thus the variation of the stack gas composition with time was monitored. The degree of reduction for iron ores (R%), given as the ratio of removed oxygen amount during the reaction to the initial total oxygen content of ore, was estimated by both the FT-IR analysis of the stack gas and the volumetric analysis of the reduced iron ore samples. The results obtained by both gas and solid analyses were compared and a satisfactorily good agreement was observed. As a result, it is concluded that FT-IR Continuous Emission Monitoring (CEM) is a reliable, rapid and efficiently applicable analysis method for DR processes and for more other FT-IR traceable gas–solid reactions as well.

Raman spectral studies on 2′-hydroxyacetophenone in binary liquid mixtures

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
D. Yamini, V. Sasirekha, V. Ramakrishnan
Raman spectra of neat 2′-hydroxyacetophenone (2′-HAP) and its binary liquid mixtures in three different solvents of varying polarity in different volume fractions have been recorded. A complete Raman spectral analysis has been proposed for the neat 2′-HAP. Since carbonyl group plays a vital role in determining the physical and chemical properties of a molecule due to its high permanent dipole moment of strength, the behaviour of ν(CO), carbonyl stretching mode, in binary liquid mixtures has been investigated experimentally. The signatures in spectral wavenumber position and linewidth (full width at half maximum) have been discussed for neat as well as binary liquid mixtures in different volume ratio in terms of intramolecular and van der Waals interactions. The microviscosity and Onsager model have been used to describe the interactions between the solute and solvent molecules.

Replacement of H-bonded bridged water by transition metal ions in poly(1-vinylimidazole-co-methylmethacrylate) copolymers: A vibrational spectroscopy study using mid-FTIR, far-FTIR and ab initio calculations

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Markus Andersson Trojer, Anders Mårtensson, Magnus Nydén
A detailed structural analysis of the vibrational spectra of hydrophobic PVM (poly(1-vinylimidazole-co-methylmethacrylate)) copolymers PVM-4 (4wt% 1-VIm) and PVM-44 (44wt% 1-VIm) is provided with respect to bridging water and subsequent replacement by bridging transition metal ions. PVM-44 (44wt% 1-VIm) with a high fraction of 1-VIm forms water bridges as evident by the water bending vibration, which is shifted up to 1665cm−1. This band vanishes as transition metal ions are introduced and a new band at 952cm−1 appears which is ascribed as a δ(ring) band involving the entire [M(Im) n ]2+ unit. This fact is affirmed using ab initio calculations. The transition metal ions coordinate exclusively the imidazole groups. Although the imidazole associated water is replaced by transition metal ions, the amount of sorbed water for the very hydrophobic PVM-4 is increased as indicated by the ν(OH) region.

Quantitative surface plasmon spectroscopy: Determination of the infrared optical constants of living cells

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Alexander Zilbershtein, Michael Golosovsky, Vladislav Lirtsman, Benjamin Aroeti, Dan Davidov
Fourier transform infrared (FTIR) spectroscopy gives a great amount of information on the distribution of chemical components in biological objects, in particular cells, in a label-free manner. We report on the development of the spectroscopic technique that combines the surface plasmon resonance (SPR) and the FTIR. Our method is based on the original processing of SPR measurements at varying angles and wavelengths and yields the complex refractive index of the analyte in a broad wavelength region. Contrary to previous SPR studies which yielded information about refractive index variation only, our technique gives absolute optical constants of the examined medium. Using this approach, we studied living Madin Darby canine kidney (MDCK) epithelial cells cultured in their natural aqueous environment and measured their optical constants. We showed that our technique has the ability to distinguish absorption lines of certain chemical components of the cells, such as the absorption lines of a CH n bonds which are characteristic mostly for cell membrane lipids.

Raman spectroscopic evidence for the formation of B(OH)n(OR)3−n (n=0, 1, 2; R=CH3, C2H5 or CH(CH3)2) from boric acid in lower alcohol solutions

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Shigeru Yamauchi
Raman spectroscopy has been used to study the boron species in methanol, ethanol or 2-propanol solutions of boric acid. Raman bands are observed at about 814, 773, and 728cm−1 for methanol solutions of boric acid in the wavenumber range from 900 to 700cm−1. The three Raman bands were assigned on the assumption that boric acid reacts with methanol and produces methyl borates, B(OH)2(OCH3), B(OH)(OCH3)2, and B(OCH3)3, which are considered to have bands at 814, 773, and 728cm−1, respectively. For ethanol solutions of boric acid, Raman bands were detected at around 783, 754, and 726cm−1 and assigned to B(OH)2(OC2H5), B(OH)(OC2H5)2, and B(OC2H5)3, respectively. Moreover, Raman bands were sighted at about 788, 762, and 732cm−1 for 2-propanol solutions of boric acid and attributed to B(OH)2(OCH(CH3)2), B(OH)(OCH(CH3)2)2, and B(OCH(CH3)2)3, respectively.

Structural and IR and Raman spectral analysis of cyclo(His-Phe) dipeptide

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Sefa Celik, Aysen E. Ozel, Serda Kecel, Sevim Akyuz
A study was carried-out to measure and calculate infrared (4000–400cm−1) and Raman (3500–50cm−1) spectra of cyclo(His-Phe) dipeptide, which has anticancer activity. Conformational preferences of cyclo(His-Phe) dipeptide are investigated using theoretical conformational analysis followed by DFT calculations. The calculations of cyclo(His-Phe) dipeptide, as a function of side chain torsion angles, enable us to determine its energetically preferred conformations. The DFT calculations predict that the boat conformation is energetically more stable than the planar conformation. The dimeric forms of cyclo(His-Phe) dipeptide are constructed by bringing together two identical cyclo(His-Phe) monomers in possible configurations and three energetically favorable dimeric structures are obtained. The vibrational normal modes and associated wavenumbers, IR and Raman intensities of the global conformers of monomeric and dimeric units of cyclo(His-Phe) are calculated by DFT method at either both B3LYP/6-31G(d,p) and B3LYP/6-31++G(d,p) levels of theory (for monomer) or only at B3LYP/6-31G(d,p) level of theory (for dimeric unit). The total energy distributions (TED) of the vibrational modes are calculated by using the scaled quantum mechanical force field (SQM FF) method. Complete vibrational assignments of the observed spectra were performed by the aid of computed vibrational data. The cis amide II band is observed at 1481cm−1 in the Raman spectrum of solid cyclo(His-Phe), which is in agreement with previously reported Raman results for solid cyclic dipeptides, where the DKP ring adopts a boat conformation. The combination of the experimental and calculated spectra provide an insight into the structural and vibrational spectroscopic properties of cyclo(His-Phe) dipeptide. The energies of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of cyclo(His-Phe) are calculated by DFT method at B3LYP/6-31G(d,p) level of theory. HOMO is localized on histidine amino acid whereas LUMO is localized mostly on phenylalanine ring. The computed HOMO–LUMO energy gap corresponds to 6.3596eV (146.65kcal/mol).

The use of Raman spectroscopy to identify inorganic phases in iatrogenic pathological lesions of patients with malignant pleural mesothelioma

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
M. Musa, A. Croce, M. Allegrina, C. Rinaudo, E. Belluso, D. Bellis, F. Toffalorio, G. Veronesi
Thin sections of pleura and lung prepared for diagnosis of Malignant Mesothelioma (MM) in patients who underwent pleurodesis were analysed by micro-Raman spectroscopy. In the pleural tissue, visual inspection under an optical microscope attached to the Raman spectroscope revealed numerous acicular crystals and several rounded particles, micrometers in size. The laser beam of the spectrometer was focused on each of the inorganic phases in turn, revealing Raman spectra attributable to talc or to clinochlore on the acicular crystals and to phosphate phases on the rounded particles. In the lung tissue, optical inspection indicated the presence of asbestos bodies, identified by micro-Raman spectroscopy as crocidolite, “asbestos” mineral, the phase of the fibre inside the coating material. The identity of the inorganic phases as determined by Raman spectroscopy was confirmed by chemical analysis using a Scanning Electron Microscope equipped with an Energy Dispersive Spectrometer (SEM/EDS). Micro-Raman spectroscopy proved effective in identifying the inorganic phases present in thin sections prepared for medical diagnosis, allowing compounds introduced during treatment (talc or clinochlore) to be distinguished from those inhaled (asbestos) or crystallized during disease progression (phosphates).

Structure and microstructure of glasses from a NaCaPO4–SiO2–BPO4 system

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Maciej Sitarz, Katarzyna Bulat, Zbigniew Olejniczak
The present investigations are devoted to silicate–phosphate glasses of the NaCaPO4–SiO2–BPO4 system. Glasses belonging to this system are characterized by a glass phase separation phenomenon, i.e. occurrence of spherical amorphous inclusions dispersed in an amorphous matrix, which have been detected by SEM. SEM investigation has also shown that the introduction of boron ions into the structure of silicate–phosphate glasses leads to homogenization of their microstructure. Based on EDX analyses, it has been found that the introduction of boron ions results in an inversion of the matrix and chemical composition of inclusions. Structural investigations (middle infrared spectroscopy – MIR) of the obtained glasses as well as of the corresponding crystalline materials have shown that the glasses studied exhibit a domain composition. The structure of the domains is close to that of the corresponding crystalline phases. Spectroscopic investigations involving spectra decomposition into component bands have made it possible to establish the homogenising effect of boron ions on the structure of silicate–phosphate glasses. 11B MAS NMR research revealed that in the structure of the NaCaPO4–SiO2–BPO4 silicate–phosphate glasses boron ions show coordination numbers of 3 and 4. 29Si MAS NMR studies have shown the total separation of silicate and sodium–calcium–phosphate phases.

Infrared spectroscopic study of the model metal–ligand–antibody systems: What information on the structure and stability of systems can be obtained?

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Marie Reková, Pavel Matějka, Věra Jedináková-Křížová
In this study we investigated the possibility of using infrared spectroscopy for the characterization of the ligand (diethylenetriaminepentaacetic acid, DTPA) in various aqueous media (water and different buffers), the antibody (immunoglobulin G, IgG), the metal–ligand complexes (Y–DTPA and Lu–DTPA) and the metal–ligand–antibody conjugates (Y–DTPA–IgG and Lu–DTPA–IgG). The aim was to describe behaviour of individual components, and to find spectral markers of complexes and/or conjugates formation. The reason of the choice of Lu and Y was the potential use of their radionuclides to form radiopharmaceutical species for nuclear medicine. We performed kinetic measurements to describe the stability/instability of individual systems. Multivariate data analysis allowed finding out spectral regions related to different chemical processes. Hydrolysis effect of the diethylenetriaminepentaacetic acid dianhydride (cDTPAA) in water was confirmed in unbuffered aqueous solution. Nevertheless, the study of cDTPAA in various buffered media showed evident suppression of hydrolysis. Thus, appropriate buffers were selected as media for complexation reactions with Y and Lu. Characteristic marker bands of complexation were identified. Human IgG in phosphate buffer and its interaction with the metal–ligand complexes were studied. Observation of new bands, band shifts and intensity changes revealed formation of the metal–ligand–IgG conjugates together with a somewhat changed secondary structure of IgG. We demonstrated the possibility of vibrational spectroscopic monitoring of the preparation steps of the metal–ligand–antibody conjugates as potential radiopharmaceutical products.

Spectroscopic characterization of dragonfly wings common in Japan

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Akira Yoshihara, Atsushi Miyazaki, Toshiteru Maeda, Yoshika Imai, Takashi Itoh
A series of Fourier Transform infrared (FT-IR) absorption, X-ray diffraction (XRD), and Brillouin light scattering (BLS) studies on the wings of six species of dragonfly common in Japan, including the largest Anotogaster sieboldii and much smaller Lestes temporalis, was performed at room temperature. XRD and FT-IR results indicate that dragonfly wing is comprised of a randomly oriented microcrystalline or an amorphous-like α-chitin. We observed a pair of longitudinal acoustic (LA) phonon peaks and a broad quasi-elastic scattering peak in backscattering BLS spectra. LA phonon frequencies and full widths at half maximum were found to be 19.5±0.4GHz and 1.0±0.2GHz for the 488nm excitation and independent of their sizes and species.

Interaction of the C-terminal peptide from pigeon cytochrome C with silver nanoparticles. A Raman, SERS and theoretical study

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
C. Garrido, A.E. Aliaga, J.S. Gómez-Jeria, J.J. Cárcamo, E. Clavijo, M.M. Campos-Vallette
The Raman and surface-enhanced Raman scattering (SERS) spectra of the C-terminal peptide of pigeon cytochrome C (PCC87–104), were recorded. This peptide is widely used to study the immune response in vivo. Hydrophobicity and net charge parameters of PCC87–104, allowed prediction of the nature of its interaction with colloidal nanostructured silver surfaces. The SERS spectrum provided information about the organization and orientation of PCC87–104 on the surface of silver nanoparticles (AgNPs). The batch to batch reproducible SERS spectra were obtained by adding the colloidal AgNPs solution onto the dried analyte sample. On the basis of the SERS information and the analysis of the net charge of each amino acid residue in the peptide sequence, it is concluded that the interaction of the peptide and the AgNPs is mainly induced and oriented by the lysine residues. The spectroscopic results are supported by quantum chemical calculations, performed by using Extended Hückel theory for a model of PCC87–104 interacting with a silver surface.

Temperature evolution of Raman spectrum of iron phosphate glass

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
S. Chakraborty, A.K. Arora
Iron phosphate glass that has glass transition T g ∼782K, has been investigated between 81 and 873K using Raman spectroscopy. After correcting for the thermal population factor, the reduced spectra are analyzed to obtain the mode wavenumbers and their line widths. A total of nine modes were followed as a function of temperature. The temperature dependences of mode wavenumbers of nearly all the modes are found to show anomalies near T g. Below T g, the asymmetric stretching of Q1 tetrahedra of [P2O7]4− units and Q0 tetrahedra of [PO4]3− units at 1090 and 946cm−1, respectively, exhibit conventional anharmonic behavior, whereas the network vibration, iron polyhedral and PO4 network bending modes at 170, 306 and 420cm−1, respectively, show hardening suggesting stiffening of the force constants arising from structural relaxations. In addition, the 170cm−1 mode is also found to become sharp at elevated temperatures. As the reduced spectra represent the vibrational density of states, the changes in the intensities of the 750 and 946cm−1 mode also suggest redistribution of density of states due to structural relaxations.

From phonon confinement to phonon splitting in flat single nanostructures: A case of VO2@V2O5 core–shell nano-ribbons

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
B.W. Mwakikunga, M. Maaza, K.T. Hillie, C.J. Arendse, T. Malwela, E. Sideras-Haddad
Raman spectroscopy of the VO x nano-ribbons is discussed in the framework of the Richter (1981) equation for optical phonon confinement (a) as modified for thin films by Fauchet and Campbell (1986), (b) as presented by Kim and co-workers for slabs, (c) as explained by Eklund's group for surface phonons and (d) our own modification based on the transformation from the spherical coordinates in the Richter equation to Cartesian coordinates; the latter being in keeping with the ribbon geometry. The change of coordinates also influences the profiles of the phonon dispersion curves. Phonon splitting is ascribed to the bi-layer and core–shell geometries of the ribbons and this is used to calculate the ratio of the V5+ to V4+ to the value of 0.54±0.10. This is in perfect agreement with the V5+/V4+ ∼54.60% from X-ray photo-electron spectroscopy (XPS) measurements.

Dimeric structure and hydrogen bonds in 2-N-ethylamino-5-metyl-4-nitro-pyridine studied by XRD, IR and Raman methods and DFT calculations

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
J. Lorenc
The molecular structure of 2-N-ethylamino-5-methyl-4-nitropyridine (EN5MP) and its vibrational spectra have been analyzed in terms of quantum chemical DFT calculations (B3LYP/6-311++G(d,p) approaches) and related to the XRD data. The EN5MP crystal is triclinic and centrosymmetric and its unit-cell is built by asymmetric units consisting of two parallelly arranged formula units, 2[C8H11N3O2], of different conformations. In each of the two subunits the methyl carbons and N-atoms of the nitro group are coplanar with the pyridine ring, but the O-atoms are inclined from this plane in the opposite directions. Dimers are linked by intermolecular NH⋯N hydrogen bonds system. Properties of the NA H⋯NP interactions between the hydrogen atom of the pyridine ring NP and the hydrogen atom of the amino group NA have been characterized. Additionally the crystal structure is stabilized by a set of weak intermolecular CH⋯O interactions.

Analysis of human skin tissue by Raman microspectroscopy: Dealing with the background

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
F. Bonnier, S.M. Ali, P. Knief, H. Lambkin, K. Flynn, V. McDonagh, C. Healy, T.C. Lee, F.M. Lyng, H.J. Byrne
Raman microspectroscopy is widely used for molecular characterisation of tissue samples. Nevertheless, when working in vitro on tissue sections, the presence of a broad background to the spectra remains problematic and its removal requires advanced methods for pre-processing of the data. To date, research efforts have been primarily devoted to development of techniques of statistical analysis to extract the relevant information contained in the spectra. However, few attempts have been made to understand the origin of the background and to improve the protocols used for the collection of Raman spectra that could lead to the reduction or elimination of the background. It has been demonstrated that measurement at 785nm in water immersion significantly reduces the Raman background of both pure biochemical components and tissue sections, associating the background at 785nm with a scattering phenomenon rather than fluorescence. It is however of interest to probe the dependence of the observed background and any time evolution normally associated with photobleaching of fluorophores, under dry and immersed conditions, on the source wavelength. Using 785nm or 660nm as source, extended exposure of dried skin tissue sections to the laser results in a time dependent reduction of the background present in the Raman spectra. When working in water immersion, the overall background as well as the evolution over time is greatly reduced and the background is seen to stabilise after ∼20s exposure. Using 532nm or 473nm as source for the examination of dried tissue sections, visible photodamage of the sample limits the laser power usable for the collection of spectra to 5mW. Immersion of the tissue sections protects against photodamage and laser powers of up to 30mW can be used without any visible damage. Under these conditions, the background is significantly reduced and good quality Raman spectra can be recorded. By adapting the protocol usually used for the collection of Raman spectra, this study clearly demonstrates that other approaches rather than mathematical manipulation of the data can be used to deal with the intrinsic background commonly observable. Notably, the dependence of the background and its time evolution under prolonged exposure on sample environment potentially sheds light on its origin as due to sample morphology (scattering) rather than chemical content (fluorescence). Overall, the study demonstrates that, in addition to reduced background, the photostability of the samples is significantly enhanced in an immersion geometry.

Effect of comonomer ratio and ionic strength on the thermo-induced conformational changes in N-isopropylacrylamide based copolymers: An ATR-FTIR spectroscopic study

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Mihaela Avadanei, Ovidiu Avadanei, Gheorghe Fundueanu
The phase transition behavior of thermo-sensitive linear copolymers based on N-isopropylacrylamide (NIPAAm) and acrylamide (AAm) have been studied by means of ATR-FTIR spectroscopy. The temperature dependence was studied as a function of the NIPAAm:AAm molar ratio. The investigations were carried out in de-ionized water and in two different phosphate buffer systems (pH=7.4), containing mono- and/or divalent phosphate anions. Increasing the ratio of AAm in copolymer composition produced a shifting of the lower critical transition temperature (LCST) toward higher values, as well as a broadening of the phase transition domain, regardless the solvent type. Spectral decomposition of the amide I band area allowed investigating in a more detailed manner the thermal evolution of CO groups involved in various interactions. The results were compared with the dehydration process of methyl groups from isopropyl moieties. Due to the Hofmeister effect, the phase transition temperature of the copolymers was shifted toward lower values in phosphate buffer systems. The dependence of the amide I sub-bands on the temperature and the ionic strength suggests that there is a synergistic effect of mono- and divalent phosphate anions on the conformational changes of the studied copolymers.

Far-infrared spectroscopy analysis of linear and cyclic peptides, and lysozyme

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Tao Ding, Anton P.J. Middelberg, Thomas Huber, Robert J. Falconer
The far-infrared spectra of lysozyme, alanine-rich peptides and small cyclic helical peptides were studied. Both lysozyme and the alanine-rich peptides had a dome in the spectral background centred on 180–220cm−1 consistent with either structural collective modes or an ensemble of hydrogen bond vibrational modes associated with the peptide backbone. Molecular dynamics simulation of the alanine-rich peptide's infrared spectrum produced bands with similar positions to the experimental data and vibrational density of states simulation was able to attribute several of these bands to backbone and side chain vibrational modes. Evidence is presented that peaks at 333 and 375cm−1 are associated with alpha-helices in lysozyme and the alanine-rich peptides, and the peak at 445cm−1 is associated with beta-pleated sheet. Also, results suggest that peaks at 385, 402 and 470cm−1 are associated with the secondary structure of the cyclic helical peptide KARAD. This supports the hypothesis the low energy vibrational modes between 300 and 500cm−1 are diagnostic of the presence of secondary structures in (poly)peptides.

FT-IR spectroscopic analysis of kaolinite–microbial interactions

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Adrian Spence, Brian P. Kelleher
Soil microbial biomass is a primary source of soil organic carbon (SOC) and soil organic nitrogen (SON) and therefore plays a fundamental role in carbon and nitrogen cycling. However, little is known about the fate and transformation of the magnitude of microbial components in the soil. Here we employ Fourier Transform Infrared (FT-IR) spectroscopy and allied techniques to analyze kaolinite–microbial interactions to determine; the spatial distribution of organic structures on clay mineral surfaces, which organic structures preferentially associate with these surfaces, which may be accessible to microbial heterotrophs, and which are physically protected during decomposition. Results indicate that microbial biomass and microbial-derived OM adsorbed solely on the external surfaces of kaolinite and that these interactions are dominated by aliphatic structures. Similarly, aliphatic species remained dominant after acid hydrolysis, the possible harshest condition that such complexes will experience in the environment. This is consistent with the expectation of the preferential adsorption and stabilization off aliphatic lipids, in particular, polymethylenic lipids [(CH2) n ] by clay minerals. Protein and carbohydrate structures most likely from microbial exudate and cell wall components such as peptidoglycan also adsorbed strongly to kaolinite and are physically protected from acid hydrolysis.

Experimental and theoretical study of IR and Raman spectra of tetraoxa[8]circulenes

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Valentina A. Minaeva, Boris F. Minaev, Gleb V. Baryshnikov, Hans Ågren, Michael Pittelkow
The FTIR and Raman spectra of symmetrical derivatives of the tetraoxa[8]circulenes (D 4h symmetry) series have been detected and the experimental data have been interpreted by density functional theory (DFT). The equilibrium molecular geometry, harmonic vibrational frequencies, infrared intensities and Raman scattering activities of the studied tetraoxa[8]circulenes have been calculated by the DFT/B3LYP method with the 6–31G(d) basis set using the symmetry constrains. Comparison of the calculated vibrational spectra with the experimental data provides reliable assignments of all observed bands in FTIR and Raman spectra, including the low frequency region. Correlation diagrams with symmetry account of vibrational modes in the studied molecules and their constituents (benzene, naphthalene and furan) have been used and proven very useful in the force field and frequency analysis. The results of quantum-chemical calculations are in excellent agreement with all details of the experimental spectra.

Vibrational spectra, conformations, quantum chemical calculations and spectral assignments of 1-chloro-1-silacyclohexane

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Valdemaras Aleksa, Gamil A. Guirgis, Anne Horn, Peter Klaeboe, Richard J. Liberatore, Claus J. Nielsen
The infrared spectra of 1-chloro-1-silacyclohexane have been studied as a vapour and liquid at ambient temperature and as amorphous and annealed crystalline solids at 78K. Various infrared bands present in the vapour and liquid states vanished in the crystalline state upon cooling. Raman spectra of the liquid were recorded at 293K and polarization data obtained. Additional Raman spectra were recorded at various temperatures between 293 and 163K, and intensity changes with temperature of certain Raman bands were detected. A crystalline phase was observed around 140K, leading to spectral shifts and a number of vanishing bands. The compound exists in two conformers, equatorial (e) and axial (a) in the fluid phases, but only the a-conformer was present in the crystal. The experimental results suggest that the a-conformer has 2.8kJmol−1 lower enthalpy than e in the liquid, leading to 69% of the a conformer at 293K. B3LYP calculations with various basis sets and the G3 model chemistry gave conformational energy difference ΔE (e − a) in the range 0.4–1.4kJmol−1. Infrared and Raman intensities, polarization ratios and vibrational frequencies for the e and a conformers were calculated. The fundamental wavenumbers were also derived in the anharmonic approximation in B3LYP/cc-pVTZ calculations, a relative deviation of less than 2% between the observed and calculated wave numbers for the 48 modes of the e- and a-conformers was obtained.

Analysis of the packaging enclosing a counterfeit pharmaceutical tablet using Raman microscopy and two-dimensional correlation spectroscopy

10 May 2012, 10:38:04
Publication year: 2012
Source:Vibrational Spectroscopy, Volume 61
Kaho Kwok, Lynne S. Taylor
Counterfeit medicine is a serious global problem. Vibrational spectroscopy combined with chemometric methods can be used to combat the pharmaceutical counterfeit problem. In this study, packages containing counterfeit tablets were analyzed using Raman microscopy and two-dimensional correlation spectroscopy. Two color regions were analyzed and different chemical origins from the color region could be resolved by two-dimensional correlation spectroscopy. Univariate Raman images were used to show the spatial distribution of the chemical components and confirm the findings of two-dimensional correlation analysis. 

1 comment:

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