A detailed experimental and theoretical study of the femtosecond A-band photodissociation of CH(3)I

The real time photodissociation dynamics of CH(3)I from the A band has been studied experimentally and theoretically. Femtosecond pump-probe experiments in combination with velocity map imaging have been carried out to measure the reaction times (clocking) of the different (nonadiabatic) channels of this photodissociation reaction yielding ground and spin-orbit excited states of the I fragment and vibrationless and vibrationally excited (symmetric stretch and umbrella modes) CH(3) fragments. The measured reaction times have been rationalized by means of a wave packet calculation on the available ab initio potential energy surfaces for the system using a reduced dimensionality model. A 40 fs delay time has been found experimentally between the channels yielding vibrationless CH(3)(nu=0) and I((2)P(32)) and I(*)((2)P(12)) that is well reproduced by the calculations. However, the observed reduction in delay time between the I and I(*) channels when the CH(3) fragment appears with one or two quanta of vibrational excitation in the umbrella mode is not well accounted for by the theoretical model.     

Hemoabzymes different strategies for obtaining artificial hemoproteins based on antibodies

Besides existing models of chemical or biotechnological origin for hemoproteins like peroxidases and cytochromes P450, catalytic antibod ies (Abs) with a metalloporphyrin cofactor represent a promising alter native route to catalysts tailored for selective oxidation reactions. A brief overview of the literature shows that, until now, the first strategy for obtaining such artificial hemoproteins has been to produce antipor phyrin Abs, raised against various free-base, N-substituted, Sn-,Pd-,or Fe-porphyrins. Four of them exhibited, in the presence of the corre sponding Fe-porphyrin cofactor, a significant peroxidase activity, with k_cat/K_m values of 10² to 5 × 10³/M/s. This value remained low when com pared to that of peroxidases, probably because neither a proximal ligand of the Fe, nor amino acid residues participating in the catalysis of the heterolytic cleavage of the O—O bond of H₂O₂, have been induced in those Abs. This strategy has been shown to be insufficient for the elabo ration of effective models of cytochromes P450, because only one set of Abs, raised againstmeso-tetrakis(para-carboxyvinylphenyl)porphyrin, was reported to catalyze the nonstereoselective oxidation of styrene by iodosyl benzene using a Mn-porphyrin cofactor, and attempts to gener ate Abs having binding sites for both the substrate and the metallopor phyrin cofactor, using as a hapten a porphyrin covalently linked to the substrate, were not successful. A second strategy is then proposed, which involves the chemical labeling of antisubstrate Abs with a metallopor phyrin. As an example, preliminary results are presented on the covalent linkage of an Fe-porphyrin to an antiestradiol Ab, in order to obtain semisynthetic catalytic Abs able to catalyze the selective oxidation of steroids.     

Influence of iron oxide nanoparticles on the rheological properties of hybrid chitosan ferrogels

Magnetite nanoparticles have been successfully synthesized in the presence of chitosan using an in situ coprecipitation method in alkali media. This method allows obtaining chitosan ferrogels due to the simultaneous gelation of chitosan. The chitosan concentration has been varied and its effects on the particle synthesis investigated. It has been demonstrated that high chitosan concentrations prevents the formation of magnetite due to the slow diffusion of the alkali species through the viscous medium provided by chitosan, instead iron hydroxides are formed. The presence of magnetite nanoparticles increases the elastic modulus which results in a reinforcement of the chitosan ferrogels. This effect is counterbalanced by the disruption of hydrogen bonding responsible for the formation of chitosan hydrogels in alkali media.     

Comparative Study of HRP,a Peroxidase‐Mimicking DNAzyme,and ALP as Enzyme Labels in Developing Electrochemical Genosensors for Pathogenic Bacteria

A comparative evaluation of an electrochemical sandwich genoassay for pathogenic bacteria based on immobilized hairpin DNA probes and three different enzyme labels (horseradish peroxidase, alkaline phosphatase and a biomimetic peroxidase‐like DNAzyme) is reported. The natural enzymes were used as streptavidin conjugates, coupled to the surface duplex by using a biotin‐labeled signaling probe, whereas the DNAzyme was directly incorporated to the sequence of the signaling probe. HRP provides enhanced sensitivity although the choice of a catalytic reporter DNA sequence could simplify the assay.     

[Li(tmeda)2][cyclo-(P5But4)]: An unusual ion-separated lithium oligophosphanide

The reaction of lithium with Bu^tPCl₂ and PCl₃ in the ratio 12:4:1 in THF gave a product mixture comprising cyclo-(P₄Bu^t₄), Li₂(P₄Bu^t₄), and lithium tetra-tert-butylcyclopentaphosphanide Li[cyclo-(P₅Bu^t₄)] (1) among other phosphanides and phosphanes. Optimization of the reaction conditions and recrystallization from THF/TMEDA (TMEDA: Me₂NCH₂CH₂NMe₂) gave [Li(tmeda)₂][cyclo-(P₅Bu^t₄)] (1b) which was characterized by multinuclear NMR spectroscopy, mass spectrometry, IR spectroscopy, and elemental analysis. Single-crystal X-ray diffraction studies showed the presence of separated [Li(tmeda)₂]⁺ cations and [cyclo-(P₅Bu^t₄)]^? anions. 1b represents the first structure of a “naked” [cyclo-(P₅Bu^t₄)]^? anion.     

Mechanistic study on the palladium-catalyzed (3 + 2) intramolecular cycloaddition of alk-5-enylidenecyclopropanes

The intramolecular (3 + 2) cycloaddition of alkenylidenecyclopropanes to alkenes under palladium catalysis provides a practical and stereoselective entry into a variety of interesting bicycles. The reaction outcome and stereoselectivity of the process are somewhat dependent on the characteristics of the substrate and of the palladium ligand, which is not easy to justify on the basis of the current mechanistic understanding. We therefore decided to study the different mechanistic alternatives from a theoretical point of view. The energies of the reaction intermediates and transition states for different possible pathways have been explored at DFT level in a model system, and using PH(3) and P(OMe)(3) as ligands. The results obtained suggest that the most favourable reaction pathway involves an initial oxidative addition of Pd(0) at the distal position of the cyclopropane to afford a palladacyclobutane intermediate. The evolution of this intermediate into the final cycloadduct can occur following different paths, the most favorable depending on the configuration and substitution of the alkene cycloaddition partner, and the number of ancillary ligands coordinated to Pd. The computational results are consistent with the experimental observations and provide the basis for proposing which would be the operative mechanistic pathway in different cases. The results also allow us to explain the stereochemical divergences observed in some of the reactions.     

Highly homogeneous stereocontrolled construction of quaternary hydroxyesters by addition of dimethylzinc to α-ketoesters promoted by chiral perhydrobenzoxazines and B(OEt)3

A highly efficient enantioselective addition of Me(2)Zn to α-ketoesters, assisted by a chiral perhydro-1,3-benzoxazine ligand, is described. This novel catalytic system offers homogeneous elevated enantioselectivities in the preparation of α-hydroxyesters that bear a quaternary stereocenter, with a minor dependence on electronic and steric effects when aromatic, heteroaromatic, or aliphatic α-ketoesters are employed. The catalyst can be recovered and reused without loss of activity.     

MASPIT: three-hybrid trap for quantitative proteome fingerprinting of small molecule-protein interactions in mammalian cells

Organic small molecules generally act by perturbing the function of one or more cellular target proteins, the identification of which is essential to an understanding of the molecular basis of drug action. Here we describe the application of methotrexate-linked small molecule ligands to a mammalian three-hybrid interaction trap for proteome-wide identification of small molecule targets, quantification of the targeting potency of unmodified small molecules for such targets in intact cells, and screening for inhibitors of small molecule-protein interactions. During the course of this study we also identified the pyrido[2,3-d]pyrimidine PD173955, a known SRC kinase inhibitor, as a potent inhibitor of several ephrin receptor tyrosine kinases. This finding could perhaps be exploited in the design of inhibitors for this kinase subfamily, members of which have been implicated in the pathogenesis of various diseases, including cancer.     

Effects of Seed Roasting Temperature on Sesame Oil Fatty Acid Composition,Lignan, Sterol and Tocopherol Contents,Oxidative Stability and Antioxidant Potential for Food Applications

Roasting is a key step for preparing sesame oil that leads to important changes in its organoleptic properties and quality. In this study, white sesame seeds were roasted for 20 min in an electric oven at different temperatures (120, 150, 180, 210, 250 and 300 °C). The oils extracted from unroasted and roasted seeds were compared for their chemical composition: fatty acids (including trans isomers), phytosterols, lignans (sesamin and sesamolin), tocopherols and total phenolic compounds, as well as their oxidative stability and antiradical capacity. There were no obvious differences in the oil densities, refractive indexes or iodine values, but the saponification values were affected by temperature. Relevant primary and secondary lipid oxidation were observed at T > 250 °C, resulting in a higher p-anisidine value and K232 as well as K268 values. Roasting improved oil yield (from 33.5 to 62.6%), increased its induction period (from 5.5 to 10.5 h) and enhanced the total phenolic content (from 152 to 194 mg/100 g) and antiradical activity of the extracted oil. Depending on roasting temperature, a gradual decline was recorded in total amounts of phytosterols (up to 17.4%), γ-tocopherol (up to 10.6%), sesamolin (maximum of 27.5%) and sesamin (maximum of 12.5%). All the investigated oils presented a low quantity in triglyceride polymers, clearly below the maximum tolerated quantity according to the European regulation. The optimal roasting temperature for obtaining high nutritional grade oil within the permissible values was 210 °C. The unsaponifiable components (including lignans and sterols) extracted from roasted seeds have been shown to be natural additives to fresh meatball products to extend shelf life. The results of this study may help to boost the nutritional content of plant-based diets by allowing for the use of roasted sesame seed oil and its components.     

A Molecular Imprinted Polymer Sensor for Biomonitoring of Fenamiphos Pesticide Metabolite Fenamiphos Sulfoxide

A new electrochemical method for the identification and quantification of Fenamiphos pesticide's major metabolite in biological samples – Fenamiphos Sulphoxide ( FNX ) was developed. Computational calculations, Density Functional Theory (DFT) and semi-empirical models (PM3) were performed to determine the best monomer, pyrrole, and a ratio of 1 : 5 (template: monomer) was chosen for the fabrication of the FNX− MIP sensor obtained by electropolymerization. The FNX− MIP sensor responded well to increasing FNX concentrations (range of 1–30 μM). Limit of detection and quantification (LOD=0.183 μM, LOQ=0.601 μM), respectively, selectivity, and repeatability were also investigated for the developed method. The obtained percentage of recovery showed good agreement compared to reference values obtained from GC-MS, which was used as a reference method. The FXN− MIP sensor proved selective in the presence of potential interferents. The developed sensor was successfully applied for the determination of FNX in spiked plasma and urine matrixes with acceptable recovery rates. The proposed method also proved successful in detecting FNX prepared from the in vitro metabolism of FNP using liver microsomes to metabolize it.