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Kalampounias A.G.,University of Patras | Kalampounias A.G.,Institute of Chemical Engineering And High Temperature Chemical Processes
Journal of Physics and Chemistry of Solids | Year: 2012

In this paper we present the picosecond vibrational dynamics of a series of binary metaphosphate glasses, namely Na2OP2O5, MOP2O5 (M=Ba, Sr, Ca, Mg) and Al2O 33P2O5 by means of Raman spectroscopy. We studied the vibrational dephasing and vibrational frequency modulation by calculating time correlation functions of vibrational relaxation by fits in the frequency domain. The fitting method used enables one to model the real line profiles intermediate between Lorentzian and Gaussian by an analytical function, which has an analytical counterpart in the time domain. The symmetric stretching modes νs(PO2 -) and νs(POP) of the PO2 - entity of PØ2O2 - units and of POP bridges in metaphosphate arrangements have been investigated by Raman spectroscopy and we used them as probes of the dynamics of these glasses. The vibrational time correlation functions of both modes studied are rather adequately interpreted within the assumption of exponential modulation function in the context of KuboRothschield theory and indicate that the system experiences an intermediate dynamical regime that gets only slower with an increase in the ionic radius of the cation-modifier. We found that the vibrational correlation functions of all glasses studied comply with the Rothschild approach assuming that the environmental modulation is described by a stretched exponential decay. The evolution of the dispersion parameter α with increasing ionic radius of the cation indicates the deviation from the model simple liquid indicating the reduction of the coherence decay in the perturbation potential as a result of local short lived aggregates. The results are discussed in the framework of the current phenomenological status of the field. © 2011 Elsevier Ltd. All rights reserved.

Gialeli C.,University of Patras | Theocharis A.D.,University of Patras | Karamanos N.K.,University of Patras | Karamanos N.K.,Institute of Chemical Engineering And High Temperature Chemical Processes
FEBS Journal | Year: 2011

Matrix metalloproteinases (MMPs) consist of a multigene family of zinc-dependent extracellular matrix (ECM) remodeling endopeptidases implicated in pathological processes, such as carcinogenesis. In this regard, their activity plays a pivotal role in tumor growth and the multistep processes of invasion and metastasis, including proteolytic degradation of ECM, alteration of the cell-cell and cell-ECM interactions, migration and angiogenesis. The underlying premise of the current minireview is that MMPs are able to proteolytically process substrates in the extracellular milieu and, in so doing, promote tumor progression. However, certain members of the MMP family exert contradicting roles at different stages during cancer progression, depending among other factors on the tumor stage, tumor site, enzyme localization and substrate profile. MMPs are therefore amenable to therapeutic intervention by synthetic and natural inhibitors, providing perspectives for future studies. Multiple therapeutic agents, called matrix metalloproteinase inhibitors (MMPIs) have been developed to target MMPs, attempting to control their enzymatic activity. Even though clinical trials with these compounds do not show the expected results in most cases, the field of MMPIs is ongoing. This minireview critically evaluates the role of MMPs in relation to cancer progression, and highlights the challenges, as well as future prospects, for the design, development and efficacy of MMPIs. © 2010 The Authors Journal compilation.

Iatridi Z.,University of Patras | Tsitsilianis C.,University of Patras | Tsitsilianis C.,Institute of Chemical Engineering And High Temperature Chemical Processes
Chemical Communications | Year: 2011

We report on the association capability of a novel multisegmented, multiarm star terpolymer to form a diversity of pH-responsive amphoteric micellar nanostructured self-assemblies. © 2011 The Royal Society of Chemistry.

Kalampounias A.G.,University of Patras | Kalampounias A.G.,Institute of Chemical Engineering And High Temperature Chemical Processes
Bulletin of Materials Science | Year: 2011

IR and Raman spectroscopies have been utilized to study the structure and vibrational modes of sol-gelderived binary silicate glasses. The present study is motivated by the immense geological significance and focuses on the MO-SiO2 (M = Ca, Mg) binary systems in an effort to unveil the role of the CaO and MgO modifiers when incorporated to the 3D silica structure. Glasses in the composition range x = 0, 0·1, 0·2, 0·3 and 0·4 prepared by the sol-gel method were compared with the corresponding glasses formed by appropriate mixing of SiO2 and MO powders through melting and fast cooling. The vibrational spectra of the sol-gel-derived glasses have revealed considerable changes in relative intensities as a function of the MO mole fraction. These changes signify structural modifications on the silica network. The population of the Q3 species was found to increase for both modified silicate systems. The rate of increase is more pronounced in the CaO-SiO2 glasses. The extent of network depolymerization in the porous glass is higher at the same content of alkaline earth oxide compared to the bulk glass. The results are indicative of a more 'defective' nature of the sol-gel glasses compared to the corresponding melt-quenched ones. © Indian Academy of Sciences.

Tsilomelekis G.,Institute of Chemical Engineering And High Temperature Chemical Processes | Boghosian S.,Institute of Chemical Engineering And High Temperature Chemical Processes
Physical Chemistry Chemical Physics | Year: 2012

Supported molybdenum oxide catalysts on TiO 2 (anatase) with surface densities in the range of 1.8-17.0 Mo per nm 2 were studied at temperatures of 410-480 °C for unraveling the configuration and molecular structure of the deposited (MoO x) n species and examining their behavior for the ethane oxidative dehydrogenation (ODH). In situ Raman and in situ FTIR spectra under oxidizing conditions combined with 18O/ 16O isotope exchange studies provide the first sound evidence for mono-oxo configuration for the deposited (MoO x) n species on anatase. Isolated OMo(-O-) 3 tetra-coordinated species in C 3v-like symmetry prevail at all surface coverages with a low presence of associated (polymeric) species (probably penta-coordinated) evidenced at high coverages, below the approximate monolayer of 6 Mo per nm 2. A mechanistic scenario for 18O/ 16O isotope exchange and next-nearest-neighbor vibrational isotope effect is proposed at the molecular level to account for the pertinent spectral observations. Catalytic measurements for ethane ODH with simultaneous monitoring of operando Raman spectra were performed. The selectivity to ethylene increases with increasing surface density up to the monolayer coverage, where primary steps of ethane activation follow selective reaction pathways leading to ∼100% C 2H 4 selectivity. The operando Raman spectra and a quantitative exploitation of the relative normalized MoO band intensities for surface densities of 1.8-5.9 Mo per nm 2 and various residence times show that the terminal MoO sites are involved in non-selective reaction turnovers. Reaction routes follow primarily non-selective pathways at low coverage and selective pathways at high coverage. Trends in the initial rates of ethane consumption (apparent reactivity per Mo) as a function of Mo surface density are discussed on the basis of several factors. © 2012 the Owner Societies.

Tsilomelekis G.,Institute of Chemical Engineering And High Temperature Chemical Processes | Boghosian S.,Institute of Chemical Engineering And High Temperature Chemical Processes
Catalysis Science and Technology | Year: 2013

The article addresses the critical molecular structural issue of differentiating between the mono-oxo (MoO) and di-oxo [Mo(O)2] configurations as well as the most plausible structures for the oxo-molybdenum [(MoOx)n] sites (including aspects related to coordination number of Mo and extent of association/polymerization) deposited on typical catalyst supports such as γ-Al2O3, monoclinic ZrO2, TiO2-anatase and SiO2. The issue is of topical character and has been the subject of persistent post-2005 research endeavors comprising both theoretical (mainly DFT) work as well as careful experimental/spectroscopic studies (Raman, IR, DR-UV/Vis) that in some cases have also been combined with isotopic labeling experiments. The pertinent vibrational properties are discussed in relation to site configuration (mono-oxo vs. di-oxo), structure and extent of association/polymerization of dispersed oxomolybdates. Vibrational isotope effects and mechanisms for 18O/16O exchange at the molecular level are given special attention. This journal is © 2013 The Royal Society of Chemistry.

Donahue N.M.,Carnegie Mellon University | Kroll J.H.,Massachusetts Institute of Technology | Pandis S.N.,Carnegie Mellon University | Pandis S.N.,Institute of Chemical Engineering And High Temperature Chemical Processes | Robinson A.L.,Carnegie Mellon University
Atmospheric Chemistry and Physics | Year: 2012

We discuss the use of a two-dimensional volatility-oxidation space (2-D-VBS) to describe organic-aerosol chemical evolution. The space is built around two coordinates, volatility and the degree of oxidation, both of which can be constrained observationally or specified for known molecules. Earlier work presented the thermodynamics of organics forming the foundation of this 2-D-VBS, allowing us to define the average composition (C, H, and O) of organics, including organic aerosol (OA) based on volatility and oxidation state. Here we discuss how we can analyze experimental data, using the 2-D-VBS to gain fundamental insight into organic-aerosol chemistry. We first present a well-understood "traditional" secondary organic aerosol (SOA) system-SOA from α-pinene + ozone, and then turn to two examples of "non-traditional" SOA formation-SOA from wood smoke and dilute diesel-engine emissions. Finally, we discuss the broader implications of this analysis. © 2012 Author(s).

Tsakiroglou C.D.,Institute of Chemical Engineering And High Temperature Chemical Processes
AIChE Journal | Year: 2011

A method is suggested to compute the capillary pressure and relative permeability curves of heterogeneous porous media. The broad pore radius distribution (PRD) and throat radius distribution (TRD) are decomposed into relatively narrow component distribution functions which are used for the computer-aided construction of pore-and-throat networks. The quasi-static motion of menisci in pores and throats is tracked by accounting for capillary forces. The presence of fractal roughness along pore walls ensures the coexistence of both phases in pores. The calculation of the hydraulic conductance of each phase is based on the concept of constricted unit cell. Simulations in component pore networks constructed from narrow PRD and TRD produce a set of capillary pressure and relative permeability functions, the arithmetic averaging of which yields the corresponding functions for a heterogeneous synthetic pore network. This information is used by a dynamic simulator of drainage in permeability networks to predict experimental results of soil columns. © 2010 American Institute of Chemical Engineers (AIChE).

Tsakiroglou C.D.,Institute of Chemical Engineering And High Temperature Chemical Processes
Transport in Porous Media | Year: 2012

The immiscible displacement of a wetting fluid by a non-wetting one in heterogeneous porous media is modeled using a multi-scale network-type analysis: (1) The pressure-controlled immiscible displacement of water by oil in pore-and-throat networks (1st length scale ~ 1 mm) is simulated as a capillary-driven process. (2) The pressure-controlled immiscible displacement in uncorrelated cubic lattices (2nd length scale ~ 1 cm) is simulated as a site percolation process governed by capillary and gravity forces. At this scale, each node represents a network of the previous scale. (3) The rate-controlled immiscible displacement of water by oil in cubic networks (3rd length scale ~ 10 cm), where each node represents a lattice of the previous scale, is simulated by accounting for capillary, gravity, and viscous forces. The multi-scale approach along with the information concerning the pore structure properties of the porous medium can be employed to determine the transient responses of the pressure drop and axial distribution of water saturation, and estimate the effective (up-scaled) relative permeability functions. The method is demonstrated with application to data of highly heterogeneous soils. © 2011 Springer Science+Business Media B.V.

Yannopoulos S.N.,Institute of Chemical Engineering And High Temperature Chemical Processes | Kyriazis F.,Institute of Chemical Engineering And High Temperature Chemical Processes | Chochliouros I.P.,99 Technologies
Optics Letters | Year: 2011

Massive photoinduced short-and medium-range structural changes (photopolymerization) in As-S glasses are induced by near-bandgap light and studied by Raman scattering. Structural changes involve bond restructuring in sulfur-rich nanodomains of these nanoscale-phase-separated glasses. The spectral dependence of the photopolymerization effect demonstrates that various wavelengths can be used to optically change the structure of As-S glasses. The immense structural changes are relevant to recent findings about the role of bandgap light illumination for fabricating channel waveguides in noncrystalline arsenic sulfides. © 2011 Optical Society of America.

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