Non-enzymatic reactions involving vitamin B6: Spectroscopic investigations on the effect of pH and metal ions on the decyclization reactions of the pyridoxal-histamine cyclized Schiff base

The effect of pH and metal ions (Cu2+, Zn2+, Cd2+, Mn2+, Cr3+, Co3+, and Mg2+) on the decyclization reactions of pyridoxal-histamine cyclized Schiff base has been studied using electronic spectroscopy. The study reveals that the cyclization reaction is irreversible with respect to pH and metal ions. Interest in this work derives from the possible involvement of cyclization reactions in the inhibitory activity of a number of pyridoxal-dependent enzymes.

Adsorption and Unfolding of Lysozyme at a Polarized Aqueous-Organic Liquid Interface

The adsorption of proteins at the interface between two immiscible electrolyte solutions has been found to be key to their bioelectroactivity at such interfaces. Combined with interfacial complexation of organic phase anions by cationic proteins, this adsorption process may be exploited to achieve nanomolar protein detection. In this study, replica exchange molecular dynamics simulations have been performed to elucidate for the first time the molecular mechanism of adsorption and subsequent unfolding of hen egg white lysozyme at low pH at a polarized 1,2-dichloroethane/water interface. The unfolding of lysozyme was observed to occur as soon as it reaches the organic−aqueous interface,which resulted in a number of distinct orientations at the interface. In all cases, lysozyme interacted with the organic phase through regions rich in nonpolar amino acids, such that the side chains are directed toward the organic phase, whereas charged and polar residues were oriented toward the aqueous phase. By contrast, as expected, lysozyme in neat water at low pH does not exhibit significant structural changes. These findings demonstrate the key influence of the organic phase upon adsorption of lysozyme under the influence of an electric field, which results in the unfolding of its structure.

Platelet endothelial cell adhesion molecule 1 (PECAM-1) and its interactions with glycosaminoglycans: 2. Biochemical analyses

Platelet endothelial cell adhesion molecule 1 (PECAM-1) (CD31), a member of the immunoglobulin (Ig) superfamily of cell adhesion molecules with six Ig-like domains, has a range of functions, notably its contributions to leukocyte extravasation during inflammation and in maintaining vascular endothelial integrity. Although PECAM-1 is known to mediate cell adhesion by homophilic binding via domain 1, a number of PECAM-1 heterophilic ligands have been proposed. Here, the possibility that heparin and heparan sulfate (HS) are ligands for PECAM-1 was reinvestigated. The extracellular domain of PECAM-1 was expressed first as a fusion protein with the Fc region of human IgG1 fused to domain 6 and second with an N-terminal Flag tag on domain 1 (Flag-PECAM-1). Both proteins bound heparin immobilized on a biosensor chip in surface plasmon resonance (SPR) binding experiments. Binding was pH-sensitive but is easily measured at slightly acidic pH. A series of PECAM-1 domain deletions, prepared in both expression systems, were tested for heparin binding. This revealed that the main heparin-binding site required both domains 2 and 3. Flag-PECAM-1 and a Flag protein containing domains 1-3 bound HS on melanoma cell surfaces, but a Flag protein containing domains 1-2 did not. Heparin oligosaccharides inhibited Flag-PECAM-1 from binding immobilized heparin, with certain structures having greater inhibitory activity than others. Molecular modeling similarly identified the junction of domains 2 and 3 as the heparin-binding site and further revealed the importance of the iduronic acid conformation for binding. PECAM-1 does bind heparin/HS but by a site that is distinct from that required for homophilic binding.

The structure of glycosaminoglycans and their interactions with proteins

Glycosaminoglycans (GAGs) are important complex carbohydrates that participate in many biological processes through the regulation of their various protein partners. Biochemical, structural biology and molecular modelling approaches have assisted in understanding the molecular basis of such interactions, creating an opportunity to capitalize on the large structural diversity of GAGs in the discovery of new drugs. The complexity of GAG–protein interactions is in part due to the conformational flexibility and underlying sulphation patterns of GAGs, the role of metal ions and the effect of pH on the affinity of binding. Current understanding of the structure of GAGs and their interactions with proteins is here reviewed: the basic structures and functions of GAGs and their proteoglycans, their clinical significance, the three-dimensional features of GAGs, their interactions with proteins and the molecular modelling of heparin binding sites and GAG–protein interactions. This review focuses on some key aspects of GAG structure–function relationships using classical examples that illustrate the specificity of GAG–protein interactions, such as growth factors, anti-thrombin, cytokines and cell adhesion molecules. New approaches to the development of GAG mimetics as possible new glycotherapeutics are also briefly covered.

Prediction of heparin binding sites in bone morphogenetic proteins (BMPs)

Heparin is a glycosaminoglycan known to bind bone morphogenetic proteins (BMPs) and the growth and differentiation factors (GDFs) and has strong and variable effects on BMP osteogenic activity. In this paper we report our predictions of the likely heparin binding sites for BMP-2 and 14. The N-terminal sequences upstream of TGF-β-type cysteine-knot domains in BMP-2, 7 and 14 contain the basic residues arginine and lysine, which are key components of the heparin/HS-binding sites, with these residues being highly non-conserved. Importantly, evolutionary conserved surfaces on the beta sheets are required for interactions with receptors and antagonists. Furthermore, BMP-2 has electropositive surfaces on two sides compared to BMP-7 and BMP-14. Molecular docking simulations suggest the presence of high and low affinity binding sites in dimeric BMP-2. Histidines were found to play a role in the interactions of BMP-2 with heparin; however, a pKa analysis suggests that histidines are likely not protonated. This is indicative that interactions of BMP-2 with heparin do not require acidic pH. Taken together, non-conserved amino acid residues in the N-terminus and residues protruding from the beta sheet (not overlapping with the receptor binding sites and the dimeric interface) and not C-terminal are found to be important for heparin–BMP interactions.

Diabetic ketoacidosis and electroencephalographic changes in newly diagnosed pediatric patients

Objective: To document electroencephalogram (EEG) changes and their correlation with clinical parameters in a newly diagnosed pediatric cohort of type 1 diabetes mellitus (T1DM) patients with and without diabetic ketoacidosis (DKA) and to define their medium term utility and significance. Research design and methods: Prospective longitudinal study of children presenting with T1DM. EEGs were performed within 24 h of diagnosis, day 5, and at 6 months post-diagnosis and reviewed by a neurologist blinded to clinical status. Severity of encephalopathy was graded from 1 to 5 using the Aoki and Lombroso encephalopathy scale. Cognitive abilities were assessed using standardized tests of attention, memory, and intelligence. Results: Eighty eight children were recruited; 34 presented with DKA. Abnormal background slowing was more often observed in the first 24 h in children with DKA (p = 0.01). Encephalopathy scores on day 1 correlated with initial pH, CO2, HCO3, base excess, respiratory rate, heart rate, diastolic blood pressure, and IV fluid intake (all parameters p < 0.05). EEG scores at day 1 did not correlate with contemporaneous mental state or cognition in the medium term. Conclusions: DKA was associated with significant clinical and neurophysiologic signs of brain dysfunction at presentation. While EEG is sensitive to the detection of encephalopathy in newly diagnosed T1DM, it has limited use in identifying children at risk of later cognitive deficits.

Dependence of pH and surfactant effect in the synthesis of magnetite(Fe3O4) nanoparticles and its properties

Nanoparticles of Fe3O4 were synthesized by co-precipitation in an aqueous solution containing ferrous and ferric salts (1:2) at varying pH with ammonia as a base. It was found that the value of pH influences the reaction mechanism for the formation of Fe3O4. Furthermore, the addition of mercaptoethanol significantly reduced the crystalline size of Fe3O4 nanoparticles from 15.03 to 8.02 nm. X-ray diffraction (XRD) spectra revealed that the synthesized nanoparticles were epsilon-Fe2O3 or Fe3O4 phase. To further prove the composition of the product, as-prepared Fe3O4 were examined by X-rayphotoelectron spectroscopy (XPS). Magnetic properties of the obtained particles were determined by vibrating sample magnetometer (VSM). Further analysis of the X-ray studies shows that while maintaining a pH value of 6 and 9 in a solution containing iron salts II and III ions produces epsilon-Fe2O3. Whereas a pH value of 11 produces magnetite (Fe3O4) phase. All of these results show that the pH has a major role in the observed phase formation of (Fe3O4) nanoparticles.

Acidic pH and acidic enzymes in atherosclerosis

Atherosclerosis is an inflammatory disease characterized by accumulation of lipids and fibrous connective tissue in the arterial wall. Recently, it has been suggested that decrease in the pH of extracellular fluid of the arterial intima may enhance LDL accumulation by increasing binding of the LDL to matrix proteoglycans and also by making the plaque more favorable for acidic enzymes to be active. Many lysosomal acidic enzymes have been found in atherosclerotic plaques. In this thesis, we were able to induce secretion of lysosomal acidic cathepsin F from human monocyte-derived macrophages by stimulation with angiotensin II. We also showed that LDL pre-proteolyzed with cathepsin S was more prone to subsequent hydrolytic modifications by lipases. Especially acidic secretory sphingomyelinase was able to hydrolyze pre-proteolyzed LDL even at neutral pH. We also showed that the proteolyzed and lipolyzed LDL particles were able to bind more efficiently to human aortic proteoglycans. In addition, the role of extracellular acidic pH on the ability of macrophages to internalize LDL was studied. At acidic pH, the production of cell surface proteoglycans in macrophages was increased as well as the binding of native and modified LDL to cell surface proteoglycans. Furthermore, macrophages cultured at acidic pH showed increased internalization of modified and native LDL leading to foam cell formation. This thesis revealed various mechanisms by which acidic pH can increase LDL retention and accumulation in the arterial intima and has the potential to increase the progression of atherosclerosis.

RecA Protein of Mycobacterium tuberculosis Possesses pH-Dependent Homologous DNA Pairing and Strand Exchange Activities: Implications for Allele Exchange in Mycobacteria

To gain insights into inefficient allele exchange in mycobacteria, we compared homologous pairing and strand exchange reactions promoted by RecA protein of Mycobacterium tuberculosis to those of Escherichia coli RecA protein. The extent of single-stranded binding protein (SSB)-stimulated formation of joint molecules by MtRecA was similar to that of EcRecA over a wide range of pH values. In contrast, strand exchange promoted by MtRecA was inhibited around neutral pH due to the formation of DNA networks. At higher pH, MtRecA was able to overcome this constraint and, consequently, displayed optimal strand exchange activity. Order of addition experiments suggested that SSB, when added after MtRecA, was vital for strand exchange. Significantly, with shorter duplex DNA, MtRecA promoted efficient strand exchange without network formation in a pH-independent fashion. Increase in the length of duplex DNA led to incomplete strand exchange with concomitant rise in the formation of intermediates and networks in a pH-dependent manner. Treatment of purified networks with S1 nuclease liberated linear duplex DNA and products, consistent with a model in which the networks are formed by the invasion of hybrid DNA by the displaced linear single-stranded DNA. Titration of strand exchange reactions with ATP or salt distinguished a condition under which the formation of networks was blocked, but strand exchange was not significantly affected. We discuss how these results relate to inefficient allele exchange in mycobacteria.

Novel synthesis of superparamagnetic Ni-Co-B nanoparticles and their effect on superconductor properties of MgB2

A new procedure for the preparation of amorphous Ni-Co-B nanoparticles is reported, with a detailed investigation of their morphology by X-ray diffraction and transmission electron microscopy, as well as their magnetic properties. Many factors, such as chemical composition, anisotropy, size and shape of the particles, were controlled through chemical synthesis, resulting in the control of morphological and magnetic properties of the nanoparticles. Controlling pH values with ethylenediamine and using sodium dodecyl sulfate surfactant lowered the size of the nanoparticles to below 10 nm. Such a small structure and chemical disorder in nanocrystalline materials lead to magnetic properties that are different from those in their bulk-sized counterparts. The obtained nanoparticles can be used for different purposes, from pharmaceutical applications to implementations in different materials technology. The focus of this research is the synthesis of Ni-Co-B nanoparticles in a new way and studying the reaction of Ni-Co-B nanoparticles with Mg and B precursors and their effect on MgB2 properties. New nanostructures are formed in the reaction of Ni-Co-B nanoparticles with Mg: Mg2Ni, Co2Mg and possibly Mg2Co.

A Methanol-Tolerant Carbon-Supported Pt-Au Alloy Cathode Catalyst for Direct Methanol Fuel Cells and Its Evaluation by DFT

A Pt-Au alloy catalyst of varying compositions is prepared by codeposition of Pt and Au nanoparticles onto a carbon support to evaluate its electrocatalytic activity toward an oxygen reduction reaction (ORR) with methanol tolerance in direct methanol fuel cells. The optimum atomic weight ratio of Pt to Au in the carbon-supported Pt-Au alloy (Pt-Au/C) as established by cell polarization, linear-sweep voltammetry (LSV), and cyclic voltammetry (CV) studies is determined to be 2:1. A direct methanol fuel cell (DMFC) comprising a carbon-supported Pt-Au (2:1) alloy as the cathode catalyst delivers a peak power density of 120 mW/cm2 at 70 °C in contrast to the peak power density value of 80 mW/cm2 delivered by the DMFC with carbon-supported Pt catalyst operating under identical conditions. Density functional theory (DFT) calculations on a small model cluster reflect electron transfer from Pt to Au within the alloy to be responsible for the synergistic promotion of the oxygen-reduction reaction on a Pt-Au electrode.

Aqueous colloidal stability evaluated by zeta potential measurement and resultant TiO2 for superior photovoltaic performance

Controlling the morphological structure of titanium dioxide (TiO 2) is crucial for obtaining superior power conversion efficiency for dye-sensitized solar cells. Although the sol-gel-based process has been developed for this purpose, there has been limited success in resisting the aggregation of nanostructured TiO2, which could act as an obstacle for mass production. Herein, we report a simple approach to improve the efficiency of dye-sensitized solar cells (DSSC) by controlling the degree of aggregation and particle surface charge through zeta potential analysis. We found that different aqueous colloidal conditions, i.e., potential of hydrogen (pH), water/titanium alkoxide (titanium isopropoxide) ratio, and surface charge, obviously led to different particle sizes in the range of 10-500 nm. We have also shown that particles prepared under acidic conditions are more effective for DSSC application regarding the modification of surface charges to improve dye loading and electron injection rate properties. Power conversion efficiency of 6.54%, open-circuit voltage of 0.73 V, short-circuit current density of 15.32 mA/cm2, and fill factor of 0.73 were obtained using anatase TiO 2 optimized to 10-20 nm in size, as well as by the use of a compact TiO2 blocking layer.

Preparation of reticulated MAX-phase support with morphology-controllable nanostructured ceria coating for gas exhaust catalyst devices

Reticulated porous Ti3AlC2 ceramic, a member of the MAX-phase family (Mn+1AXn phases, where M is an early transition metal, A is an A-group element, and X is carbon and/or nitrogen), was prepared from the highly dispersed aqueous suspension by a replica template method. Through a cathodic electrogeneration method, nanocrystalline catalytic CeO2 coatings were deposited on the conductive porous Ti 3AlC2 supports. By adjusting the pH value and cathodic deposition current, coatings exhibiting nanocellar, nanosheets-like, or bubble-free morphologies can be obtained. This work expects to introduce a novel practically feasible material system and a catalytic coating preparation technique for gas exhaust catalyst devices.

Electrophoretic deposition of Ti3Si(Al)C2 from aqueous suspension

Ti3Si(Al)C2 films were electrophoretically deposited at 3 V on indium-tin-oxide (ITO) conductive glass from Ti3Si(Al) C2 aqueous suspension with 1 vol% solid loading at pH 9 in the absence of any dispersant. The surface morphology, cross section microstructure, and preferred orientation of the films were investigated by scanning electron microscopy and X-ray diffraction. The as-deposited Ti3Si(Al)C 2 films exhibited (00l) preferred orientation and the thickness can be controlled by the deposition-drying-deposition method. These results demonstrate that electrophoretic deposition is a simple and feasible method to prepare MAX-phases green films at room temperature.