Theoretical study of CO adsorption on the Ni?Cu(110) system

The electronic influence of the matrix on several adsorption sites of the CO/Ni? Cu(110) system has been studied using a semiempirical molecular orbital calculation. A negative ligand effect of a copper matrix on monometallic nickel sites and a less important ligand effect of a nickel matrix on copper sites have been found and explained in base on the electronic structure. Bridge nickel–copper sites show an intermediate negative ligand effect within a Cu matrix. The results of the theoretical calculation are compared with the available experimental data.     

The effect of ruthenium(III) chloride on the formation of protonated parent ions in electrospray mass spectrometry

We report the use of RuCl3 as an "alkali metal sponge". This is a general and highly efficient method for generating protonated parent ions for a variety of compounds that usually do not show this ion in electrospray mass spectrometry. This technique is demonstrated to be highly useful in "cleaning up" spectra from multiply metallated ions, thereby substantially improving the signal-to-noise ratio.     

Mechanisms of Molecular Mobility of Oxygen and Nitrogen in Carbon Molecular Sieves

Molecular mobility of oxygen, O₂, and nitrogen, N₂, in Carbon Molecular Sieves, CMS, was investigated using the Frequency Response, FR, technique to identify mass-transfer mechanisms and related kinetic time constants. The FR data showed that O₂ mobility in four types of CMS was dominantly controlled by surmounting surface-barrier resistances, whereas the mobility of both O₂ and N₂ in pellets of a fifth CMS type obeyed the Fickian diffusion model. Temperature and pressure dependences of surface-barrier penetration time constants were obtained for O₂ and N₂ in several of those CMS materials. The kinetic time constants of surface-barrier penetration were related to Langmuir-type rate constants, which indicates that kinetic behavior of O₂ therein could also be interpreted in terms of a Langmuir-kinetics equation.     

Theoretical study of the thermolysis of beta-hydroxyl aldehydes

A mechanism involving a six-membered cyclic transition state where the hydrogen of the hydroxyl group interacts with the oxygen of the carbonyl group has been proposed previously to describe the thermolysis of many beta-hydroxyl compounds. In this paper, the proposed mechanism is studied for a series of beta-hydroxyl aldehydes. Rate constants and activation energies are reported as well as a study of the influence of tunneling on the reaction rates. The electron density at the ring critical points, population analyses by the theory of atoms in molecules (AIM) and the natural bond orbital (NBO) method, as well as atomic energy analyses are used to gain insight into this interesting mechanism and into the effects of substituents.     

New chemical evidence for the ability to generate radical molecular ions of polyenes from ESI and HR-MALDI mass spectrometry

We report here new chemical evidence for the generation of radical molecular ions of compounds with a conjugated pi-system (polyene) in ESI and HR-MALDI mass spectrometry. The oxidation potential of the neutral polyenes was calculated by cyclic-voltammetry and the results compared with those previously published for other complex conjugated compounds that have also been shown to form M*+ in ESI-MS. This study clearly demonstrates the correlation between the oxidation potential and the formation of the M*+ for the polyenes studied.     

Calorimetric and Raman investigation of cow’s milk lactoferrin

Lactoferrin (LF), a non-heme iron-binding protein of blood plasma and milk with antioxidant, cariostatic, anticarcinogenic, and anti-inflammatory properties, has been studied by differential scanning calorimetry (DSC) and Raman spectroscopy over a wide pH range (4.0–9.0). Using these two techniques, the modifications in the quantity of iron bounded in the cow’s milk LF and in the secondary structures, as a function of pH and heating, have been evaluated. DSC curves showed higher value of denaturation temperatures and enthalpy changes when LF was saturated with iron (holo-form) than when it was in its unsaturated form (apo-form). The denaturation curves of the protein solutions at pH ≥ 5.5 confirming that LF is a mix of apo- and holo-forms; on the contrary at pH 4.0, the holo-form is practically absent. Spectroscopic investigation showed that, as a function of pH, the content of α-helix increases up to pH 7.4, followed by a small decrease by further pH increase. The β-sheet percentage exhibits the opposite behavior, while the random-coil and turn structures do not change noticeably. In contrast, after heat-induced denaturation, strong variations were observed in the secondary structure, with an evident increase of β-sheet and decrease of the α-helix percentage. Finally, both thermal and spectroscopic analysis pointed out that the structure of cow’s milk LF is strictly sensible to pH variation and it has the highest thermal stability at physiological pH.     

Unusual coordination in a silver thionate complex. Synthesis,structural characterization and theoretical calculations of dinuclear and polynuclear silver(I) thiosaccharinates with pyridine and 1,10-phenanthroline

Treatment of Ag₆(tsac)₆ (tsac = thiosaccharinate anion) with pyridine (py) and 1,10-phenanthroline (o-phen) each affords two novel silver(I)-thiosaccharinate complexes: dinuclear [Ag₂(tsac)₂py] (1) and polynuclear [Ag(tsac)(o-phen)]_n (2). Both crystal structures have been determined by X-ray diffraction and spectroscopic structural analysis (IR and Raman, UV–Vis, ¹H and ¹³C NMR) have also been made for both compounds. Thermal stability analysis (TGA and DTA) of complex 1 are used to confirm the strength of the pyridine coordination to the silver ion. The molecular structure of complex 1 shows some astonishing characteristics. The two silver atoms are in different environments: one of them is surrounded by two S atoms, while the other completes its coordination sphere by three N atoms, two from the thiosaccharinate anions and the third from a pyridine molecule. The short Ag(1)–Ag(2) contact distance, 2.9681(8) Å, indicates an interaction between the two silver metal atoms exists. Complex 2 shows a thiosaccharinate molecule bridging two silver atoms through the exocyclic S atom while the o-phenanthroline ligand is coordinated as a bidentate N,N chelate, forming a polynuclear chain. Quantum chemical calculations confirm the argentophilic character of the Ag–Ag interaction in complex 1, and its structure and vibrational assignments were correlated and confirmed theoretically.     

Synthesis and fluorescence emission of neutral and anionic di- and tetra-carboranyl compounds

A new family of photoluminescent neutral and anionic di-carboranyl and tetra-carboranyl derivatives have been synthesized and characterized. The reaction of α,α'-bis(3,5-bis(bromomethyl)phenoxy-m-xylene with 4 equiv. of the monolithium salt of 1-Ph-1,2-C(2)B(10)H(11) or 1-Me-1,2-C(2)B(10)H(11) gives the neutral tetracarboranyl-functionalized aryl ether derivatives closo-1 and closo-2, respectively. The addition of the monolithium salt of 1-Ph-1,2-closo-C(2)B(10)H(11) to α,α,'-dibromo-m-xylene or 2,6-dibromomethyl-pyridine gives the corresponding di-carboranyl derivatives closo-3 and closo-4. These compounds, which contain four or two closo clusters, were degraded using the classical method, KOH in EtOH, affording the corresponding nido species, which were isolated as potassium or tetramethylammonium salts. All the compounds were characterized by IR, (1)H, (11)B and (13)C NMR spectroscopy, and the crystal structure of closo-3 was analysed by X-ray diffraction. The carboranyl fragments are bonded through CH(2) units to different organic moieties, and their influence on the photoluminescent properties of the final molecules has been studied. All the closo- and nido-carborane derivatives exhibit a blue emission under ultraviolet excitation at room temperature in different solvents. The fluorescence properties of these closo and nido-derivatives depend on the substituent (Ph or Me) bonded to the C(cluster), the solvent polarity, and the organic unit bearing the carborane clusters (benzene or pyridine). In the case of nido-derivatives, an important effect of the cation is also observed.     

Adsorption and spectroscopic characterization of lactoferrin on hydroxyapatite nanocrystals

Lactoferrin (LF), a well-characterized protein of blood plasma and milk with antioxidant, cariostatic, anticarcinogenic and anti-inflammatory properties, has been adsorbed onto biomimetic hydroxyapatite (HA) nanocrystals at two different pH values (7.4 and 9.0). The interaction was herein investigated by spectroscopic, thermal and microscopic techniques. The positive electrostatic surface potential of LF at pH 7.4 allows a strong surface interaction with the slightly negative HA nanocrystals and avoids the protein-protein interaction, leading to the formation of a coating protein monolayer. In contrast, at pH 9.0 the surface potential of LF is a mix of negative and positive zones favouring the protein-protein interaction and reducing the interaction with HA nanocrystals; as a result a double layer of coating protein was formed. These experimental findings are supported by the good fittings of the adsorption isotherms by different theoretical models according to Langmuir, Freundlich and Langmuir-Freundlich models. The nanosized HA does not appreciably affect the conformation of the adsorbed protein. In fact, using FT-Raman and FT-IR, we found that after adsorption the protein was only slightly unfolded with a small fraction of the α-helix structure being converted into turn, while the β-sheet content remained almost unchanged. The bioactive surface of HA functionalized with LF could be utilized to improve the material performance towards the biological environment for biomedical applications.     

Determination of atazanavir in human plasma by high-performance liquid chromatography with UV detection

A high-performance liquid chromatographic method for the determination of atazanavir (ATV) in human plasma is developed and validated. The method involves a rapid and simple solid-phase extraction (SPE) of ATV using Bond-elut C18 3 mL cartridge. The separation of ATV from internal standard and endogenous components is achieved using an isocratic elution on an octyl column and an UV detector set at 260 nm. The method is linear from 20 to 10,000 ng/mL (mean r2 = 0.9991, n = 10). The observed intra- and inter-day assay precision ranged from 2.2% to 14.7%[at the lower limit of quantitation (LOQ)], whereas accuracy varies between 1.0% and 14% (at LOQ). Mean drug recovery is 80.5% for ATV and 78.4% for IS. The method is found to be precise and accurate, practical enough for therapeutic drug monitoring in routine clinical practice and is applied for the assessment of 24-h ATV plasma concentration-time profiles in HIV-infected pregnant women.