Structure of CdS/SiO2 Nanocomposites: Influence of the Precursor and Cd Concentration

The influence of using TMOS or TEOS in the formation of CdS quantum dots in a silica matrix have been studied by X-ray absorption spectroscopy (XAS). The amount of Cd-S bonds have been monitored as a function of the nominal Cd concentration. The relative amount of CdS crystals depends on the precursor. The use of TEOS is not recommended because it gives a poor yield, especially for high Cd concentration. A discussion of the influence of CdS concentration in matrices from TMOS is carried out from structural models created from their pore volume distribution. The mean pore size becomes smaller and the size distribution more uniform when CdS concentration increases but the nanocrystals of low CdS nominal content present a more efficient quantum confinement.     

CONSEL, a least-squares program for estimating stability constants from polarographic data

This article describes CONSEL, a least-squares linear-regression program which, when applied to polarographic data, provides estimates of stability constants suitable for priming non-linear optimization programs. The use of CONSEL avoids the need for recourse to traditional graphical methods. The results of its application to three systems are presented.     

Photophysics and biological applications of the environment-sensitive fluorophore 6-N,N-dimethylamino-2,3-naphthalimide

We have synthesized a new environment-sensitive fluorophore, 6-N,N-dimethylamino-2,3-naphthalimide (6DMN). This chromophore exhibits valuable fluorescent properties as a biological probe with emission in the 500-600 nm range and a marked response to changes in the environment polarity. The 6DMN fluorescence is red-shifted in polar protic environments, with the maximum emission intensity shifting more than 100 nm from 491 nm in toluene to 592 nm in water. Additionally, the fluorescence quantum yield decreases more than 100-fold from chloroform (Phi = 0.225) to water (Phi = 0.002). The scope and applications of the 6DMN probe are expanded with the synthesis of an Fmoc-protected amino acid derivative (5), which contains the fluorophore. This unnatural amino acid has been introduced into several peptides, demonstrating that it can be manipulated under standard solid-phase peptide synthesis conditions. Peptides incorporating the new residue can be implemented for monitoring protein-protein interactions as exemplified in studies with Src homology 2 (SH2) phosphotyrosine binding domains. The designed peptides exhibit a significant increase in the quantum yield of the long wavelength fluorescence emission band (596 nm) upon binding to selected SH2 domains (e.g., Crk SH2, Abl SH2, and PI3K SH2). The peptides can be used as ratiometric sensors, since the short wavelength band (460 nm) was found almost invariable throughout the titrations.     

Influence of the clay and the nickel content in catalysts for vegetable oil hydrogenation

Nickel catalysts prepared using two different clays as support, natural bentonite and palygorskite, and with different nickel contents have been tested in the hydrogenation of a sunflower oil. The influence of the clays, and of the nickel-bentonite ratio on the activity, selectivity and trans-isomer formation was investigated. Previously it was establised that no diffusional limitations were controlling the rate. Bentonite with the highest nickel content was the most active and selective catalysts.     

On the surfactant-sensitized analytical reaction of titanium with bromopyrogallol red

A spectrophotometric investigation of the Ti(IV)-bromopyrogallol red chelate shows that marked changes occur in the presence of aqueous dispersions of cetylpyridinium bromide. The increase in the absorption and the bathochromic shifts are interpreted in terms of the interaction of the binary complex Ti(IV)-BPR with the surfactant in the micelles. Analytical parameters for the spectrophotometric determination of Ti(IV) with bromopyrogallol red and cetylpyridinium bromide have been worked out in detail and are given as well. In basis of the experimental results an attempt is made to extend this approach to the understanding of the sensitized-reactions mechanism.     

Study of the nitric oxide system in the rat cerebellum during aging

Background  

The cerebellum is the neural structure with the highest levels of nitric oxide, a neurotransmitter that has been proposed to play a key role in the brain aging, although knowledge concerning its contribution to cerebellar senescence is still unclear, due mainly to absence of integrative studies that jointly evaluate the main factors involved in its cell production and function. Consequently, in the present study, we investigate the expression, location, and activity of nitric oxide synthase isoenzymes; the protein nitration; and the production of nitric oxide in the cerebellum of adult and old rats.     

Isotope dilution GC-MS routine method for the determination of butyltin compounds in water

A standard GC-MS instrument with electron impact ionisation has been used to develop a fast, simple and reliable method for the simultaneous determination of monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) in water samples. Isotope dilution analysis (IDA) is used for the determination of species, taking advantage of a commercially available spike solution containing a mixture of MBT, DBT and TBT enriched in ¹¹⁹Sn. Method detection limits for 100-mL samples were between 0.18 and 0.25 ng L⁻¹ for the three butyltin compounds with typical RSD between 2 and 4% at levels between 100 and 10 ng L⁻¹, respectively. Recovery of tin species in spiked samples (natural water, wastewater and seawater) was quantitative. The stability of butyltin compounds in collected seawater samples was also studied. The addition of a 1% (v/v) glacial acetic acid preserved tin species in the samples for at least 5 days at room temperature. The IDA method was finally implemented in a routine testing laboratory and it was subsequently accredited by the Spanish National Accreditation Body according to the requirements of UNE-EN ISO/IEC 17025.