Vassilis Gionis

On the structure of palygorskite by mid- and near-infrared spectroscopy

Abstract The OH-structural characteristics of an iron-rich palygorskite from Western Macedonia, Greece (Gr-1) and an aluminous palygorskite from Florida (PFl-1) were examined by combined Fourier-transform near-infrared reflectance (NIR) and mid-infrared attenuated total reflectance (ATR) spectroscopy. Analyses of samples heated from ambient to 130 °C allowed for the development of a self-consistent set of band assignments for the structural and surface OH and H2O species of both the hydrated and dehydrated forms. The inner octahedral sites of both samples are largely accounted for by dioctahedral AlAlOH, AlFe3+OH, and Fe3+Fe3+OH pairs. Band intensities for these pairs are consistent with variations in the concentration of octahedral Fe and Al in the two samples. In addition, both samples display a trace trioctahedral signature in NIR, which may be related to local trioctahedral domains, or the presence of sepiolite in trace amounts, or as intergrowths. A surface H2O species typical of the hydrated phase was identified via its NIR combination mode at 5317 cm-1. The desorption of this species by heating revealed distinct silanol groups with overtone and combination modes at 7255 and 4575 cm-1, respectively. Mg-coordinated and zeolitic H2O species are strongly coupled in the hydrated phase and give rise to NIR combination modes at 5190 and 5240 cm-1. The removal of zeolitic H2O causes the blue shift of the three dioctahedral OH overtones by ca. 20 cm-1 and the rearrangement of the coordinated H2O manifested by the growth of sharp combination modes at ca. 5215 and 5120 cm-1.

Octahedral cation distribution in palygorskite

Abstract The OH speciation of 18 palygorskite samples from various localities were evaluated by near infrared spectroscopy (NIR) and compared to the corresponding octahedral composition derived from independent, single-particle analytical electron microscopy (AEM). NIR gives evidence for dioctahedral-like (AlAlOH, AlFe3+OH, Fe3+Fe3+OH) and trioctahedral-like (Mg3OH) species. Therefore, palygorskite can be approximated by the formula yMg5 Si8O20(OH)2·(1 - y)[xMg2Fe2·(1 - x)Mg2Al2] Si8O20(OH)2, where x is the Fe content of the dioctahedral component, and y is the trioctahedral fraction. The values of x estimated from the NIR data are in excellent agreement with the Fe/(VIAl + Fe) ratio from AEM (R2 = 0.98, σ = 0.03), thus suggesting that all octahedral Al and Fe in palygorskite participate in M2M2OH (dioctahedral-like) arrangements. Furthermore, y values from AEM can be compared to NIR (R2 = 0.90 and σ = 0.05) after calibrating the relative intensity of the Mg3OH vs. (Al,Fe)2OH overtone bands using AEM data. The agreement between the spectroscopic and analytical data are excellent. The data show that Fe3+ for Al substitution varies continuously in the analyzed samples over a broad range (0 < x < 0.7), suggesting that fully ferric dioctahedral palygorskites (x = 1) may exist. On the other hand, the observed upper trioctahedral limit of y = 0.50 calls for the detailed structural comparison of Mg-rich palygorskite with sepiolite.

Use of NIR for structural characterization of urea–formaldehyde resins

Abstract In this paper, the effect of pH and temperature on the structure of urea–formaldehyde resins was studied. GPC, NMR and Raman measurements were performed to elucidate the structural characteristics of the resin systems. Fourier Transform Near Infrared (FT-NIR) spectroscopy via optical fibers was used to monitor the reaction progress in situ. It was found that the reactions of urea and formaldehyde at different temperatures and pH values result in resins with different structures and properties: Resins produced at high temperatures and acidic pH values exhibit higher degrees of condensation, presumably because of the development of more cross-linked structures.

COMBINED NEAR-INFRARED AND X-RAY DIFFRACTION INVESTIGATION OF THE OCTAHEDRAL SHEET COMPOSITION OF PALYGORSKITE

The octahedral composition of palygorskite in more than 300 samples from the Pefkaki deposit, W. Macedonia, Greece, has been studied by near-infrared (NIR) and X-ray diffraction (XRD), and evaluated according to the formula

Use of FT-NIR spectroscopy for on-line monitoring of formaldehyde-based resin synthesis

y{\rm{M}}{{\rm{g}}_5}{\rm{S}}{{\rm{i}}_8}{{\rm{O}}_{20}}{\left( {{\rm{OH}}} \right)_2} \cdot x{\rm{M}}{{\rm{g}}_2}{\rm{Fe}}_{\rm{2}}^{{\rm{III}}}{\rm{S}}{{\rm{i}}_8}{{\rm{O}}_{20}}{\left( {{\rm{OH}}} \right)_2} \cdot \left( {1 - x - y} \right)

Bis (Alkylthio) Tetrathiafulvalenes and a Few of Their Salts

yMg5Si8O20(OH)2⋅xMg2Fe2IIISi8O20(OH)2⋅(1−x−y) Mg2Al2Si8O20(OH)2. Included in the study were PFl-1 and several commercial palygorskites. Our analysis of 2nd derivative NIR spectra shows that the dioctahedral composition is adequately described by three sharp overtone bands representing AlAlOH, AlFeIIIOH and FeIIIFeIIIOH in M2 dioctahedral sites, and that the summed intensity of these bands is proportional to the amount of dioctahedral component present (1−y). The samples show large variations in the degree of dioctahedral FeIII-for-Al substitution with FeIII occupying up to 70% of the dioctahedral M2 sites. Ternary analysis shows that the distribution of dioctahedral Al and FeIII is not random, but displays a tendency towards homoionic pairing. An overtone band at 7214 cm−1 and several combination bands are indicative of a trioctahedral Mg3OH component (y), and their appearance correlates with a distinct palygorskite signature in thermogravimetric analysis. Nevertheless, these bands cannot be used reliably for the quantification of a trioctahedral palygorskite component due to their close similarity to those of sepiolite. To circumvent this problem, we have evaluated y indirectly by calculating the difference between 1−y and the total concentration of palygorskite determined by the normalized intensity of the d110 XRD peak of palygorskite at 10.4 Å. Using this methodology, we have found that the samples conform to a trioctahedral limit of y ≈ 0.55, although within this limit they display large variations in octahedral character. Finally, we extend the above methodology to PLS chemometrics and show how NIR can be used to determine palygorskite content routinely in multimineralic geological samples.

Amyloid‐like fibrils from an 18‐residue peptide analogue of a part of the central domain of the B‐family of silkmoth chorion proteins

A new method is being developed for the fast and reliable assessment of the pathway(s) followed during formaldehyde-based resin synthesis, both at laboratory and industrial scale. The method is based on Fourier transform Near Infrared (FT-NIR) chemometrics. No sample manipulation is necessary and the complete evaluation can be performed on- or off-line in less than 1 min. FT-NIR chemometrics were found to be valuable in providing a fast and consistent way of monitoring directly the effects of a change of resin formulation when evaluating new procedures at laboratory scale. Similarly, during industrial production, NIR will soon become a standard tool for ensuring reproducibility and improving overall quality. Measurements are performed on-line and deviations from the standard synthesis pathway can be detected early, allowing the necessary steps to be taken in order to return to the desired pathway. Furthermore, NIR methodologies have been developed to identify and check the conformity of raw materials and final products from urea and UFC solutions to laminated paper produced by impregnation with formaldehyde-based resins. This can prove particularly useful in applications (such as in laminated paper production) where the reproducibility of production and the effects of storage are both questionable and difficult to assess.

Complexation of Lysozyme with Poly(sodium(sulfamate-carboxylate)isoprene)

Abstract Some unsymmetrical bis(alkylthio) tetrathiafulvalenes (π-donors) and a number of their charge transfer complexes and cation radical salts of the type DmXn (where D=π-donor, X=TCNQ, I3, IBr2, PF6, CIO4) have been prepared and studied.

Preparation, structure and optical properties of [CH3SC(NH2)NH2]3PbI5, [CH3SC(NH2)NH2]4Pb2Br8and [CH3SC(NH2)NH2]3PbCl5·CH3SC(NH2)NH2Cl

Chorion is the major component of silkmoth eggshell. More than 95% of its dry mass consists of the A and B families of low molecular weight structural proteins, which have remarkable mechanical and chemical properties, and protect the oocyte and the developing embryo from the environment. We present data from negative staining, Congo red binding, X‐ray diffraction, Fourier transform‐Raman, attenuated total reflectance infrared spectroscopy and modelling studies of a synthetic peptide analogue of a part of the central domain of the B family of silkmoth chorion proteins, indicating that this peptide folds and self‐assembles, forming amyloid‐like fibrils. These results support further our proposal, based on experimental data from a synthetic peptide analogue of the central domain of the A family of chorion proteins, that silkmoth chorion is a natural, protective amyloid [Iconomidou et al., FEBS Lett. 479 (2000) 141–145].

Liquid Crystalline Organic Conductors: Studies in Crystalline and Mesomorphic Phase

The complexation between hen egg white lysozyme (HEWL) and a novel pH-sensitive and intrinsically hydrophobic polyelectrolyte poly(sodium(sulfamate-carboxylate)isoprene) (SCPI), was investigated by means of dynamic, static, and electrophoretic light scattering and isothermal titration calorimetry measurements. The complexation process was studied at both pH 7 and 3 (high and low charge density of the SCPI, respectively) and under low ionic strength conditions for two polyelectrolyte samples of different molecular weights. The solution behavior, structure, and effective charge of the formed complexes proved to be dependent on the pH, the [-]/[+] charge ratio, and the molecular weight of the polyelectrolyte. Increasing the ionic strength of the solution led to vast aggregation and eventually precipitation of the complexes. The interaction between HEWL and SCPI was found to be mainly electrostatic, associated with an exothermic enthalpy change. The structural investigation of the complexed protein by fluorescence, infrared, circular dichroism spectroscopic, and differential scanning calorimetric measurements revealed no signs of denaturation upon complexation.