Structural Rearrangements of Carbonic Anhydrase Entrapped in Sol-Gel Magnetite Determined by ATR-FTIR Spectroscopy.

Enzymatically active nanocomposites are a perspective class of bioactive materials that finds their application in numerous fields of science and technology ranging from biosensors and therapeutic agents to industrial catalysts. Key properties of such systems are their stability and activity under various conditions, the problems that are addressed in any research devoted to this class of materials. Understanding the principles that govern these properties is critical to the development of the field, especially when it comes to a new class of bioactive systems. Recently, a new class of enzymatically doped magnetite-based sol-gel systems emerged and paved the way for a variety of potent bioactive magnetic materials with improved thermal stability. Such systems already showed themself as perspective industrial and therapeutic agents, but are still under intense investigation and many aspects are still unclear. Here we made a first attempt to describe the interaction of biomolecules with magnetite-based sol-gel materials and to investigate facets of protein structure rearrangements occurring within the pores of magnetite sol-gel matrix using ATR Fourier-transform infrared spectroscopy.

Comparative Electroanalytical Studies of Graphite Flake and Multilayer Graphene Paste Electrodes.

In this paper, the fabrication, surface characterisation and electrochemical properties of graphite flake (GFPE) and multilayer graphene (MLGPE) paste electrodes are described. The Raman investigations and scanning electron microscopy were used to analyze and compare structure of both carbon materials. The electroanalytical performance of both electrodes was examined and compared on the basis of the square-wave and cyclic voltammetric behavior of acetaminophen and model redox systems. Results of those studies revealed that GFPE has a larger electroactive surface area and better conductive properties, whilst MLGPE demonstrate better analytical characteristic in case of acetaminophen (AC) determination. AC determination was developed using square wave voltammetry (SWV) and square wave stripping voltammetry (SWSV). For both working electrodes, the process of accumulation enabled us to obtain an extended linear range and to lower the detection limit. In pharmaceutical formulations, AC was determined with good recovery.

A pure magnetite hydrogel: synthesis, properties and possible applications.

A magnetite-only hydrogel was prepared for the first time by weak base mediated gelation of stable magnetite hydrosols at room temperature. The hydrogel consists of 10 nm magnetite nanoparticles linked by interparticle Fe-O-Fe bonds and has the appearance of a dark-brown viscous thixotropic material. The water content in the hydrogel could be up to 93.6% by mass while volume fraction reaches 99%. The material shows excellent biocompatibility and minor cytotoxic effects at concentrations up to 207 µg mL-1. The gel shows excellent sorption capacity for heavy metal adsorption such as chrome and lead ions, which is 225% more than the adsorption capacity of magnetite nanoparticles. Due to thixotropic nature, the gel demonstrates mechanical stimuli-responsive release behavior with up to 98% release triggered by ultrasound irradiation. The material shows superparamagnetic behavior with a coercivity of 65 emu g-1 at 6000 Oe. The magnetite gels prepared could be used for the production of magnetite aerogels, magnetic drug delivery systems with controlled release and highly efficient sorbents for hydrometallurgy.

Dispersion related coupling effects in IR spectra on the example of water and Amide I bands.

We discuss coupling effects in infrared spectra which are caused by dispersion and local field effects. The first effect is instigated by changes of the refractive index due to absorption which have an impact on the strength of adjacent absorptions. The second effect is a consequence of the light-induced polarization of one molecule affecting neighboring ones. These coupling effects do not only effect band positions, but also influence relative intensities. They are particularly strong in case of overlapping bands and complicate their deconvolution by band fitting. We investigated the corresponding challenges for the HO-stretching vibrations in water and the Amide I band in proteins. Our findings show that the effects are significant and of high interest for protein and water structure determination. Especially, for the water stretching vibrations we conclude that it is of utmost importance to consider such coupling effects in quantum mechanical calculations of water spectra. Otherwise, progress in understanding band positions and profiles is likely to be hampered. Also, in case of the Amide I band we found a distinct impact of such coupling effects. Accordingly, we strongly recommend consideration of dispersion and local field effects to ensure the possibility of an accurate, quantitative determination of α-helix and ß-sheet structures.

Infrared refraction spectroscopy - Kramers-Kronig analysis revisited.

Since about 60 years, it is possible to determine the set of optical constants from reflectance measurements by the Kramers-Kronig relations. Unfortunately, the potential of the method seems to be limited in practice by the need to extend measured data into unknown regions by extrapolation, which is prone to error and leads to deviations from the true values in the known region depending on the method of extension. With the advent of infrared refraction spectroscopy, which uses reflectance measurements at normal or near normal incidence, the development of a fast method to determine the complex index of refraction function reliably for these cases has become an even more interesting goal. In this work, we introduce a way to perform a Kramers-Kronig analysis of such reflectance spectra without the need to extrapolate the measured data for higher wavenumbers beyond the measurement range. Furthermore, we introduce and compare very simple and reliable material-independent ways to extrapolate the measured data for lower wavenumbers. As a result, we devise fast and sufficiently accurate methods, which are easily implementable into existing spectrometer software, to extract quantitative spectral information from reflectance measurements at near normal incidence.

Detection of siloxane thin films on glass substrate using IR ratio-reflectance spectrum.

In case of thin films of siloxane obtained from different organo-silane derivatives (alkoxy and chloro) on soda lime silica glass substrates, IR-ATR and IR-SR could not detect the organic functional groups of the coating. This becomes even more problematic for the case of tetraethoxysilane (when fully hydrolyzed), the coating of which possesses the same functional groups as the glass substrate. In this work we propose to employ the so-called ratio-reflectance spectra in the v(Si-O) wavenumber region, where both glass and the siloxane coating give most prominent bands, important for the evaluation of the quality of coating formation and qualitative knowledge on its structure. We show that the reflectance-absorbance spectra obtained from the ratio-reflectance spectra are in direct connection to the structure of the siloxane network which depends not only on the chemical nature of the parent silane, but also on the dipping time and the solvent composition. Some characteristics of the reflectance-absorbance spectra, like the appearance of a two well defined bands at 1110 and 975 cm-1, can be correlated to the film morphology and bridging oxygen number. We support our conclusions using principal component analysis of reflectance spectra, contact angle, AFM and SEM measurements.

Dispersion analysis of polarized bulk reflectance spectra of potassium hydrogen succinate monocrystal.

Reflectance spectra may show very different and interesting shapes. The most interesting may be connected to Evans holes. Model calculations to reproduce this effect were done applying model dielectric function functions. When a weak oscillator appears within the frequency region of a strong one (i.e. between its TO and LO frequencies), its LO-mode frequency shifts towards higher wavenumbers. As a consequence, the oscillator strength of the corresponding weak mode becomes negative which produces a dip (Evans hole) in the reflectance spectrum. This model was successfully applied to analyze polarized reflectance spectra of potassium hydrogen succinate monocrystal in the ac crystal plane. The crystal symmetry was described by phenomenological model and by full symmetry consideration. The phenomenological approach applies the four-parametric model for dielectric function which allows good evaluation of asymmetric reflectance bands. A cosine dependence of oscillator strength on polarization angle was obtained for some bands, most likely due to small deviation of the crystal symmetry from orthorhombic. This is why the phenomenological approach provides good parameters for almost all phonon modes. The full symmetry consideration applies real description of dielectric tensor in the ac plane and the three-parameter model for dielectric function. This model could give very accurate directions of transition dipole moments, but cannot fit asymmetric bands well to measured reflectance. Both approaches describe all basic spectral features, the wide reflectance of asOH and the two Evans holes appearing on its shoulder.

Infrared Refraction Spectroscopy.

We suggest a new modality of infrared spectroscopy termed Infrared Refraction Spectroscopy, which is complimentary to absorption spectroscopy. The beauty of this new modality lies not only in its simplicity but also in the fact that it closes an important gap: It allows to quantitatively interpret reflectance spectra by simplest means. First, the refractive index spectrum is calculated from reflectance by neglecting absorption. The change of the refractive index is proportional to concentration, and the spectra with features similar to second derivative absorbance spectra can simply be computed by numerically deriving the refractive index spectra, something which can be easily carried out by standard spectra software packages. The peak values of the derived spectra indicate oscillator positions and are approximately proportional to the concentration in a similar way as absorbance is. In contrast to absorbance spectra, there are no baseline ambiguities for first derivative refractive index spectra, and in refractive index spectra, instead of integrating over a band area, a simple difference of two refractive index values before and after an absorption leads to a quantity that correlates perfectly linearly with concentration in the absence of local field effects.

Analysis of the polarized IR reflectance spectra of the monoclinic α-oxalic acid dihydrate.

In contrast to the extensive molecular and crystal structure investigations on oxalic acid dihydrate (C2H2O4·2H2O, α-POX) and its deuterated analogues (α-DOX), stands the absence of a complete vibrational spectra analysis. Such analysis is desirable in view of the proton dynamics in α-POX crystals. In this communication we report the room temperature polarized IR reflectance spectra of a single crystal of α-POX recorded from the ac crystal plane, and from the plane containing the b-crystallographic axis, with polarization along the axis. Dispersion analysis of the reflectance spectra of both Bu and Au symmetry type modes, using model dielectric and reflectance function valid for the monoclinic case, have been performed and the results are discussed. Some aspects of the obtained fit results for some of the spectral regions and the peculiar change of the reflectance function with polarization angle are also discussed in this work. A correlation between the crystal structure and measured spectra, together with the results of the performed dispersion analysis, gave answers to some of the problems concerned with the orientation of the transition dipole moments of the IR active modes. The assignment of modes is assisted by DFT calculations. Another aspect covered in this work is the model reflectance functions using different averaging theories that have been applied in obtaining the reflectance spectrum of a polycrystalline sample. The results of the comparison between these spectra and the recorded reflectance spectra from a polycrystalline sample were further discussed.

Polarized IR reflectance spectra of the monoclinic single crystal K2Ni(SO4)2.6H2O: dispersion analysis, dielectric and optical properties.

Polarized IR reflectance spectra of K2Ni(SO4)2.6H2O single crystal (belonging to the group of Tutton salts) were recorded at near-normal incidence. From the dispersion analysis performed on the spectra recorded from the ac crystal plane, mode parameters: transversal frequency, oscillator strength, attenuation constant and the orientation of the transition moment were determined. The polarized spectrum along the b crystallographic axis was also recorded and a dispersion analysis performed. Comparison between the spectroscopically obtained transition moment directions with those obtained from the structure data for various modes is discussed. All dielectric tensor component values were obtained for the whole mid-IR frequency range. Also, the real and the imaginary parts of the complex indexes of refraction for the waves with wave vector in the direction of the b crystallographic axis and in the ac plane (when the direction of the electric vector is oriented along the b axis) were found as functions of frequency.

Isosbestic-like point in the polarized reflectance spectra of monoclinic crystals--A quantitative approach.

If two overlapping bands originate from transition moments that are perpendicular and lie along the principal axes of the infinity frequency dielectric tensor, an isosbestic-like point (ILP) appears in the overlaid polarized IR reflectance spectra of single crystals. These conditions can also be met in principle in case of the reflectance from the ac-plane of a monoclinic crystal despite of the crystal's low symmetry. In order to determine the transition moment directions, diagonalization of the infinity frequency dielectric tensor should be performed. It is shown that a critical magnitude for the appearance of ILP is the angle of incidence. An increase of this angle leads to a transformation of the ILP to an isosbestic-like region, which eventually vanishes at higher incidence angles. Polarized reflectance spectra of gypsum (CaSO4.2H2O), recorded from the ac crystal face, were used to verify the theoretical results.

IR-ATR investigation of surface anisotropy in silicate glasses.

Several samples of flat soda-lime silicate glass were investigated by the Infrared Attenuated Total Reflection (IR-ATR) spectroscopy technique. The specular reflectance spectra together with the results of the performed dispersion analysis and the generated reflectance spectra, using Fresnel equations, suggest that the samples are isotropic. In contrast, spectra recorded by the ATR technique suggest an anisotropic structure on the surface of the specimen different from that in the bulk. This is established through differences in the s- and p-polarized IR-ATR spectra, which cannot be simply transformed into one another employing Fresnel formula for an isotropic case. It appears that this thin film having a structure different from the bulk is larger than the ATR effective penetration depth of the evanescent ray for each incidence angle above the critical one. The investigation suggests C2 symmetry of the SiO4 unit.

Inkjet fabrication of highly efficient luminescent Eu-doped ZrO2 nanostructures.

We have demonstrated for the first time an inkjet fabrication of highly efficient luminescent structures based on Eu-doped ZrO2 nanocrystals (3.4 ± 0.3 nm), with a refractive index close to the one of the bulk materials. The nanoparticles were synthesised using a nonhydrolytic method in benzyl alcohol where the particles were post treated using acetic acid, leading to the formation of a stable colloid. It was shown that the non-polar methyl group of the acetic acid is responsible for its penetration through the hydrophobic layer all the way through to the surface of the ZrO2, leading to the cleavage of the Zr-OCH2C6H5 bond and the formation of surface acetate species and a concomitant decomposition of the zirconia superlattice. Hereby we show a new and efficient universal ink production through a multi-step process - starting from solvothermal synthesis, dispersion of nanocrystals in water, and adaptation of the rheological parameters of the resulting sols. Eventually, we were able to obtain inks that we used for the production of optical coatings, monolayer luminescent-protected holography and anti-counterfeiting printing. These structures, obtained at room temperature through inkjet printing, present dense xerogel structures with high optical transparency, a high refractive index and more efficient luminescence compared with the non-homogeneous structures produced as a mixture of rare-earth elements and nanocrystals.

Generalized dispersion analysis of arbitrarily cut monoclinic crystals.

Dispersion analysis is applicable to arbitrarily cut monoclinic crystals of unknown orientation in order to find the symmetry axis. By this it is possible to differentiate between the transition moments oriented parallel and normal to the b-axis and to determine the dielectric tensor functions of those two principal directions. Dispersion analysis of arbitrarily cut monoclinic crystals is based on an extension of the evaluation scheme developed for arbitrarily cut orthorhombic crystals. We present dispersion analysis of monoclinic crystals exemplarily on spodumene (LiAl(SiO3)2) and yttrium orthosilicate (Y2SiO5).

Dispersion analysis of arbitrarily cut orthorhombic crystals.

We developed a measurement and evaluation scheme to perform dispersion analysis on arbitrarily cut orthorhombic crystals based on the schemes developed for triclinic and uniaxial crystals. As byproduct of dispersion analysis the orientations of the crystal axes are found. In contrast to the spectra of arbitrarily cut uniaxial crystals, where the fit routine has to separate two independent principal spectra, the spectra of arbitrarily cut orthorhombic crystals are a combination of three independent spectra and the evaluation scheme gets more complex. Dispersion analysis is exemplary performed on two different crystals, which show different spectral features and different levels of difficulties to evaluate. Neodymium gallate (NdGaO3) has broad overlapping reflections bands while topaz (Al2SiO4 [F, OH]2) has a quite high total number of infrared active bands.

Dispersion analysis with inverse dielectric function modelling.

We investigate how dispersion analysis can profit from the use of a Lorentz-type description of the inverse dielectric function. In particular at higher angles of incidence, reflectance spectra using p-polarized light are dominated by bands from modes that have their transition moments perpendicular to the surface. Accordingly, the spectra increasingly resemble inverse dielectric functions. A corresponding description can therefore eliminate the complex dependencies of the dispersion parameters, allow their determination and facilitate a more accurate description of the optical properties of single crystals.

A universal magnetic ferrofluid: Nanomagnetite stable hydrosol with no added dispersants and at neutral pH.

A facile method to produce highly stable magnetite magnetic fluid at neutral pH without any stabilizing agents, resulting in pure Fe3O4 nanoparticles dispersed in water is described. The hydrosol which consists of only two components - magnetite and water - behaves as a typical ferrofluid, that is, although it responds to a magnetic field, the magnetic particles cannot be phase-separated from the water by that field. No such pure magnetic fluid have been described before, making it a universal carrier which can be easily modified for any application in materials science and chemistry, and in particular for a range of applications where non-corrosivity, low viscosity, and mild conditions are needed, such as in most bioapplications and in nano electro-mechanical systems. Under optimal conditions the hydrosol is stable for at least three months.

Infrared reflectance spectra of some optically biaxial crystals: on the origin of isosbestic-like points in the polarized reflectance spectra.

An investigation of the IR polarized reflectance spectra of the orthorhombic K2SO4, KHSO4 and monoclinic CaSO4 x 2H2O, K2Ni(SO4)2 x 6H2O, (NH4)2Ni(SO4)2 x 6H2O was performed in order to explain the appearance of particular intersection points in their spectra. The analogy in the origin of the appearance of intersection points and the well-known isosbestic points in UV-vis and IR spectra was discussed. The reason for such an appearance was identified in the way that the individual reflectances (for radiation polarized along principal dielectric axes) sum up to give the reflectance under arbitrary polarization. This summation may also produce supplementary bands in the reflectance spectra, not predicted by the group theory. It was shown that relatively large LO-TO splitting is needed for the supplementary band(s) to appear, but also the overlapping region must be taken into account.

The IR reflectance spectra of the nu 3(SO4(2-)) and nu 4(SO4(2-)) band regions of some Tutton salts using polarized radiation: testing the model dielectric function.

The investigation of the vibrational bands of the SO(4)(2-) ions (in the nu(3) and nu(4) frequency regions) of six different Tutton salts was performed with specular IR reflectance spectroscopy using polarized radiation, on single crystal samples. The reflectance function under oblique incidence using dielectric model function as parameter (originally derived for optically uniaxial crystals) appeared to be readily applicable for the investigated monoclinic crystals. The frequencies of the transversal and longitudinal phonons were obtained by fitting of spectra recorded from (0 1 0), (0 0 1) and (1 0 0) crystal planes. Further, the symmetry types of all experimentally detected phonons were identified. Some of the results were further confirmed from IR absorption spectra recorded at liquid nitrogen temperature (LNT) of isomorphously isolated SO(4)(2-) ions into the corresponding selenate matrices.

A direct method of quantification of maximal chemisorption of 3-aminopropylsilyl groups on silica gel using DRIFT spectroscopy.

3-Aminopropylsilyl (APS) modified silica gel plays an important role as a precursor for further modifications, where APS acts as a spacer or bridging molecule. A monolayer of APS which is most suitable for this purpose was obtained in anhydrous conditions. The properties of the APS-modified silica gel depend on the amount of molecules chemisorbed on the surface. A direct quantitative method using Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy was proposed. The obtained results were further supported by elemental analysis. The conclusion was that the proposed methodology can be used for the quantification of APS groups chemisorbed on silica gel when the grafting chemical reaction was mainly irreversible.