Development and characterization of an immobilized enzyme reactor based on glyceraldehyde-3-phosphate dehydrogenase for on-line enzymatic studies

The glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been extensively studied as a target for new drugs to be used in the treatment of various parasitic diseases. The standard approach to the determination of GAPDH activity utilizes solubilized free enzyme and is limited by the enzyme's low stability. In the current study the stability of GAPDH was significantly increased through the covalent immobilization of the enzyme on a wide-pore silica support containing glutaraldehyde (Glut-P). The optimal conditions for the immobilization were: 100 mg Glut-P stationary phase, approximately 150 microg of enzyme dissolved in pyrophosphate buffer (15 mM, pH 8.5). The mixture was gently agitated for 6 h at 4 degrees C. Under these conditions 91.3% of protein was immobilized on 100 mg of Glut-P support with retention of 2.97% of the initial enzymatic activity. The activity of the immobilized GAPDH was stable for over 30 days. The GAPDH-Glut-P stationary phase was packed into a glass column to produce a GAPDH immobilized enzyme reactor (GAPDH-IMER). The activity and kinetic parameters of the GAPDH-IMER were investigated and the results demonstrated that the enzyme retained its activity and sensitivity to the competitive inhibitor agaric acid.     

Vibrational dynamics of a glass forming liquid in nanoscopic confinement as probed by inelastic neutron scattering

In this article we present incoherent inelastic neutron scattering results, as a function of temperature, on the vibrational dynamics of a glass-forming liquid, namely propylene glycol, confined to the 26 Å pores of a controlled porous glass. The aim is to elucidate the effects induced by surface interactions (chemical traps) and geometrical restrictions (physical traps) on the fast microscopic dynamics of hydrogen-bonded liquids. The most prominent effect is the appearance of the ‘boson peak’ in the vibrational spectra. It is ascribed to an excess density of vibrational states due to quasilocalized collective atomic vibrations induced by confinement. A destructuring effect on the transient aggregates with the highest degree of connectivity, promoted by PG in the bulk phase, is hypothesized under confinement as a consequence of interactions, via hydrogen bond, between the hydroxyl groups (OH) of the PG molecule and the active silanol groups (Si–OH) on the surface of the porous glass.

Interfacial and/or finite-size effects are also found to give rise to a destructuring effect, under confinement, of the disordered Longitudinal Acoustic Mode, together with a broadening of the highest frequency torsional vibration and a stabilization, vs. T, of the internal CCO bending vibration.     

Simultaneous micellar electrokinetic chromatography and liquid chromatography of adriblastina and tarabine PFS Their application to some biological fluids

The current work presents analytical procedures for simultaneous determination of tarabine PFS and adriblastina by micellar electrokinetic chromatography (MEKC) and liquid chromatography (LC). For MEKC analysis, separations and identifications were accomplished using uncoated fused-silica capillary with hydrodynamic injections in the presence of 50mM borate/phophate pH 8.7 and 100mM SDS. The migration times of tarabine PFS and adriblastina were found to be 2.70 and 6.40min, respectively. Calibration curves were established for 10-300ng/mL (r=0.998) tarabine PFS and for 8-120microg/mL (r=0.999) adriblastina. For LC analysis, separations were performed on teicoplanin stationary phase with reversed mobile phase containing methanol:buffer pH 4.05 (20:80%, v/v) at 285nm. The retention times of tarabine PFS and adriblastina were 5.18 and 7.20min, respectively. Calibration curves were established for 3-90microg/mL (r=0.998) tarabine PFS and for 10-120microg/mL (r=0.999) adriblastina. Both MEKC and LC methods were applied for the simultaneous determination of analytes in urine samples.     

Analysis of human histone H4 by capillary electrophoresis in a pullulan-coated capillary,LC-ESI-MS and MALDI-TOF-MS

The object of the present study was the analysis of the human histone H4 (a core histone) in order to evaluate the state of its acetylation. Capillary electrophoresis (CE) using a pullulan-coated capillary provides a rapid and efficient approach to the separation of monoacetylated, diacetylated and triacetylated H4 isoforms from human cells. By using a simple running buffer of 100 mM triethanolamine-phosphate solution at pH 2.5 and exploiting the effectiveness of pullulan-based coverage in preventing adsorptive phenomena, the separation of the differently acetylated isoforms was achieved in less than 15 min with high efficiency and reproducibility. The proposed method was for the first time applied in the analysis of histone H4 fractions obtained from cell lines treated with different histone deacetylase (HDAC) inhibitors, used as potential anticancer drugs. Matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) analysis demonstrated that the acetylation occurred in the histone H4 tail, whereas the CE separation allowed for a fast determination of the percentages of H4 acetylated isoforms in real samples; the results were in agreement with those obtained from liquid chromatography electrospray ionisation mass spectrometry (LC-ESI-MS) analysis. Therefore, the proposed CE method is a useful complementary support to the hyphenated techniques for the rapid monitoring of the activity of HDAC inhibitors.     

Temperature-Dependent Dynamical Evolution in Coum/SBE-β-CD Inclusion Complexes Revealed by Two-Dimensional FTIR Correlation Spectroscopy (2D-COS)

A combination of Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR) and 2D correlation analysis (2D-COS) was applied here for the first time in order to investigate the temperature-dependent dynamical evolution occurring in a particular type of inclusion complex, based on sulfobutylether-β-cyclodextrin (SBE-β-CD) as hosting agent and Coumestrol (7,12-dihydorxcoumestane, Coum), a poorly-soluble active compound known for its anti-viral and anti-oxidant activity. For this purpose, synchronous and asynchronous 2D spectra were calculated in three different wavenumber regions (960–1320 cm⁻¹, 1580–1760 cm⁻¹ and 2780–3750 cm⁻¹) and over a temperature range between 250 K and 340 K. The resolution enhancement provided by the 2D-COS offers the possibility to extract the sequential order of events tracked by specific functional groups of the system, and allows, at the same time, the overcoming of some of the limits associated with conventional 1D FTIR-ATR analysis. Acquired information could be used, in principle, for the definition of an optimized procedure capable to provide high-performance T-sensitive drug carrier systems for different applications.     

Monolithic stationary phase coupled with coulometric detection: development of an ion-pair HPLC method for the analysis of quinone-bearing compounds

Memoquin, a recently discovered new drug candidate for the treatment of Alzheimer's disease (AD), is a compound able to interfere with different key targets of AD neurodegeneration. In the present work, the electroactivity of Memoquin, due to the presence of a quinone ring in the molecule, was exploited for the development of a sensitive and selective HPLC chromatographic method with coulometric detection system. For this purpose, a monolithic silica-based stationary phase (Chromolith C18) was coupled with ESA detector and under high flow rate condition (2 mL/min) gave an efficient coulometric detection without a significant backpressure. The monolithic stationary phase and the electrochemical detection were combined to obtain a very fast (less than 7 min) and sensitive analysis of the compound of interest. For this reason, the method was found suitable to determine Memoquin with very high sensitivity (LOD, 0.005 microg/mL; LOQ, 0.016 microg/mL), better than with UV and fluorescence detections, and selectivity resulting potentially suitable for its analysis in biological samples. Moreover, the HPLC method was employed for the separation of Memoquin from other quinone analogs (endowed with different substituent on the quinone ring and length of the lateral chain) and allowed the comparison of the electrochemical properties of the compounds of the series. In the optimized chromatographic conditions it was possible to separate each quinone and to evaluate the influence of the substituent of the quinone ring on the electrochemical properties of the molecule.     

Electrical Properties of Single Walled Carbon Nanotube Reinforced Polystyrene Composites

Composites of carbon nanotubes (CNT) in polymeric matrices have attracted considerable attention in the research communities due to their good electrical conductivity, high stiffness and high strength at relatively low CNT contents. Effective utilization of CNT in composites depends primarily on the ability to disperse them homogeneously throughout the polymer matrix, avoiding the formation of bundles due to van der Waals interactions existing between the nanotubes. In this work composites of polystyrene at various percentages of SWNT were fabricated using Latex Technology technique, a polymer type-independent method based on using a surfactant as a dispersing agent. An electrical characterization of SWNT composites was performed both in DC and AC modes. From the analysis of DC data a percolative behavior was found for the conductivity as function of SWNT content. The innovative contribution of this work consists in the modeling of the composite material upon its electrical properties. AC measurements and the analysis of impedance as function of angular frequency lead to the formulation of an equivalent circuit able to model the composite material in correspondence of the percolative threshold.     

Seebeck Effect in Silicon Semiconductors

An extended hydrodynamic model will be used for the coupled system of electrons and phonons. This system is formed by a set of balance equations derived from the Bloch-Boltzmann-Peierls (BBP) kinetic equations applying the moment method and solving the problem of the closure by means of the Maximum Entropy Principle of Extended Thermodynamics. By using this model with a suitable limit, thermoelectric effects in bulk silicon are investigated.     

Surface plasmon resonance, fluorescence, and circular dichroism studies for the characterization of the binding of BACE-1 inhibitors

The mechanism of action underlying β-secretase 1 (BACE-1) inhibition was characterized by a surface plasmon resonance (SPR) method using primary amino groups to immobilize OM99-2, a well-known highly potent peptidic BACE-1 inhibitor, on the carboxyl groups of the dextran layer of a sensor chip. The diluted BACE-1 was mixed with buffer or the test compound and the mixture was flushed through the chip. BACE-1 binding to the immobilized peptide inhibitor was quantified. This SPR method was used to identify BACE-1 inhibitor binding sites and the mechanism of action (competitive/noncompetitive) and to validate findings of fluorescence resonance energy transfer (FRET) inhibition studies. To support this, a multimethodological approach (circular dichroism and fluorescence spectroscopy) was applied in parallel to FRET inhibition studies to characterize the binding modes of peptidic and nonpeptidic BACE-1 inhibitors. Circular dichroism spectroscopy served to correlate the conformation of BACE-1 with enzymatic activity and to monitor secondary structure changes upon ligand binding. In a complementary approach, direct fluorescence spectroscopy was used to characterize different BACE-1 inhibitor binding sites. The influence of pH and inhibitors on BACE-1 secondary structure was also elucidated. This multimethodological approach was applied to identify binding modes of bis(7)-tacrine and myricetin in comparison with well-known peptidic inhibitors.