A poly-Lys tag was fused to the Lucina pectinata hemoglobin I (HbI) coding sequence and purified using an efficient and fast process. HbI is a hemeprotein that binds hydrogen sulfide (H2S) with high affinity and it has been used to understand physiologically relevant reactions of this signaling molecule. The (Lys)6-tagged rHbI construct was expressed in E. coli and purified by immobilization on a cation exchange matrix, followed by size-exclusion chromatography. The identity, structure, and function of the (Lys)6-tagged rHbI were assessed by mass spectrometry, small and wide X-ray scattering, optical spectroscopy, and kinetic analysis. The scattering and spectroscopic results showed that the (Lys)6-tagged rHbI is structurally and functionally analogous to the native protein as well as to the (His)6-tagged rHbI. Kinetics studies with H2S indicated that the association (kon) and dissociation (koff) rate constants were 1.4 × 105/M/s and 0.1 × 10−3/s, respectively. This results confirmed that the (Lys)6-tagged rHbI binds H2S with the same high affinity as its homologue.

Inorganic surface modification was used to prepare Pt/Ru/Vulcan catalysts by coordinating a triruthenium cluster [ Ru3(CO)9(MeCN)3] on Pt nanoparticles. The method was used to provided a surface with catalytic activity for use in the direct methanol fuel cell. The cluster adsorptive process followed a Langmuir adsorption isotherm. The amount of Ru could be controlled by changing the experimental conditions of adsorption. The catalyst powder was characterized by energy-dispersive spectrocopy, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction, and electrochemical studies. The proposed methodology provides a way to place Ru atoms on a Pt surface while avoiding metal segregation. The optimum results were obtained with a catalyst that presented a Ru/Pt ratio of 0.07, as given by XPS analysis. The peak current for methanol oxidation in cyclic voltammetry scans was similar to that of commercial true alloy catalysts. On the basis of these results, some considerations about how ruthenium segregation interferes with methanol oxidation are addressed. IntroductionThe direct methanol fuel cell (DMFC) is an attractive power source for mobile applications as a result of the high energy density of methanol, the portability of liquid rather than gaseous fuels, and the existence of a similar infrastructure that could be used for methanol distribution. In addition to being safe and renewable, methanol is also a combustible that exerts a low negative impact on the environment. The DMFC requires a catalyst. A platinum/ruthenium catalyst is, at this time, the alternative of choice because it strongly overcomes CO surface contamination. To reduce the amount of the expensive noble metal required, there have been considerable efforts to increase the dispersion of the metal on the support matrix. Most often, the bimetallic alloy is dispersed on a carbon support. However, the morphology, crystallography, and chemical environment of the particles alter the electronic properties of the catalyst. As a consequence, different manufacturing processes and catalytic pretreatment may result in a catalyst with different activities in methanol oxidation. 1 The support material also influences catalytic activity. A common conductive support is Vulcan X-72, a carbon substrate with a graphitic character. The chemical characteristics of the support, its treatment, and cleanliness change the environmental conditions for the dispersion of the metal particles and their subsequent catalytic activity. This is principally due to problems of contamination such as platinum organosulfur poisoning. 2 Therefore, a considerable amount of the catalyst manufacturing process does not result in a real bimetallic alloy but in a bimetallic surface with a certain amount of metal segregation. [3][4][5]

The recombinant polyhistidine-tagged hemoglobin I ((His)6-rHbI) from the bivalve Lucina pectinata is an ideal biocomponent for a hydrogen sulfide (H2S) biosensor due to its high affinity for H2S. In this work, we immobilized (His)6-rHbI over a surface modified with gold nanoparticles functionalized with 3-mercaptopropionic acid complexed with nickel ion. The attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) analysis of the modified-gold electrode displays amide I and amide II bands characteristic of a primarily α-helix structure verifying the presence of (His)6-rHbI on the electrode surface. Also, X-ray photoelectron spectroscopy (XPS) results show a new peak after protein interaction corresponding to nitrogen and a calculated overlayer thickness of 5.3 nm. The functionality of the immobilized hemoprotein was established by direct current potential amperometry, using H2S as the analyte, validating its activity after immobilization. The current response to H2S concentrations was monitored over time giving a linear relationship from 30 to 700 nM with a corresponding sensitivity of 3.22 × 10−3 nA/nM. These results confirm that the analyzed gold nanostructured platform provides an efficient and strong link for polyhistidine-tag protein immobilization over gold and glassy carbon surfaces for a future biosensors development.

Highly ordered pyrolytic graphite (HOPG) surfaces were modified by the adsorption of Pd molecular precursors from solution. Two palladium-containing molecular precursors were studied, a mononuclear one and a trinuclear one, to compare their affinities and distributions at substrate surfaces. To obtain Pd nanoparticles, these neutral molecular precursors were reduced under a hydrogen atmosphere. Thermogravimetric analysis was carried out to establish the behavior of these precursors at various temperatures. Understanding the thermal stability of these compounds is very important to establish the appropriate conditions to form metallic Pd. The modified surface has been characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy; also, the reductive process was monitored by XPS. Remarkable differences were observed between the mononuclear and trinuclear compounds in terms of dispersion, particle size, and homogeneity. The preference of the trinuclear compound was to deposit at HOPG defects, in contrast to that of the mononuclear one, which was agglomeration on all surfaces. After the application of this technique, not only Pd nanoparticles but also Pd nanowires were obtained.

Nanostructures and nanoparticles of palladium assembled on highly ordered pyrolytic graphite (HOPG) by the adsorption of palladium molecular precursors (MPs), in dichloromethane solutions, have been prepared. Self-assemblies of palladium nanostructures on HOPG were characterized by scanning electron microscopy (SEM), Auger electron spectroscopy (AES), transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques. In this work, palladium rings had a wide variety of sizes in the nanometer range, and the ring/tube structures were preserved after a reductive process in which palladium metallic nanoparticles were formed. Noncircular structures were observed at HOPG defects and atomic step sites, as well. It is proposed that the observed ring formation of the palladium molecular precursors on HOPG substrates is related to the functional groups in the MPs, van der Waals interactions between particles and between particle-substrate, as well as the wetting properties of the solvent. In the present work, we illustrate several examples of the formation and characterization of palladium complex tubes and the resulting palladium rings, via the reduction process.