Alejandro M. Granados

Distinctive Interactions of Oleic Acid Covered Magnetic Nanoparticles with Saturated and Unsaturated Phospholipids in Langmuir Monolayers

The growing number of innovations in nanomedicine and nanobiotechnology are posing new challenges in understanding the full spectrum of interactions between nanomateriales and biomolecules at nano-biointerfaces. Although considerable achievements have been accomplished by in vivo applications, many issues regarding the molecular nature of these interactions are far from being well-understood. In this work, we evaluate the interaction of hydrophobic magnetic nanoparticles (MNP) covered with a single layer of oleic acid with saturated and unsaturated phospholipids found in biomembranes through the use of Langmuir monolayers. We find distinctive interactions among the MNP with saturated and unsaturated phospholipids that are reflected by both, the compression isotherms and the surface topography of the films. The interaction between MNP and saturated lipids causes a noticeable reduction of the mean molecular area in the interfacial plane, while the interaction with unsaturated lipids promotes area expansion compared to the ideally mixed films. Moreover, when liquid expanded and liquid condensed phases of the phospholipid(s) coexist, the MNP preferably partition to the liquid-expanded phase, thus hindering the coalescence of the condensed domains with increasing surface pressure. In consequence organizational information on long-range order is attained. These results evidence the existence of a sensitive composition-dependent surface regulation given by phospholipid-nanoparticle interactions which enhance the biophysical relevance of understanding nanoparticle surface functionalization in relation to its interactions in biointerfaces constituted by defined types of biomolecules.

Effect of β-cyclodextrin on the hydrolisis of N-phenylphtalamide and N-adamantylphtalamide—a two-sided semiempirical approach

Complexes of β-cyclodextrin including N-phenylphtalamide, N-adamantylphtalamide or their respective intermediates occurring during intramolecular amide hydrolysis were calculated by means of the PM3 and molecular mechanics programs. Structural features of the complexes, energy changes and mutual interactions are comparatively analyzed in order to explain the behavior differences that were experimentally observed between the two-substrate families. Some convergence characteristics are also commented.

Insertion of Fischer carbene complexes into the carboncarbon bond. Ring expansion of a sulfur heterocycle from five- to six-membered

The reaction of 4-X-5-alkylthio-3H-1,2-dithiole-3-thione (1) with Fischer carbene complexes (2) gives, as a main product, cyclohexa dithiine derivatives due to insertion of the carbene ligand into the C3C4 bond of the heterocycle. The reaction takes place with 1 where the alkyl substituents in position 5 are ethyl, butyl, benzyl and dodecyl and the substituents in position 4 are H, O-Me, Ph and Cl. Complexes with Cr and W as metallic center were used, the Cr complexes were more reactive than the W derivatives.

E−Z Isomerization and Aggregation Phenomena of Dithiafulvenes in CHCl3

The physical-chemical properties of several 1,3-dithiafulvene (DTF) derivatives having a donor and acceptor group in the molecule were studied. The synthesis of these compounds produces selectively the E isomer, but when the compound is dissolved in CHCl(3) isomerization to the Z isomer takes place with a rate that depends on the substituents. The interconversion rate is slow on the NMR time scale; therefore, two separated signals are observed, and they are used to measure the rate constant of isomerization. The equilibrium constant is, in all cases, very close to 1, and this is coincident with the fact that theoretical calculations of the energy of the two isomers in the gas phase differ by less than 0.1 kcal/mol. The isomerization reaction is completely reversible, and the E isomer can be obtained in pure form by selective crystallization. The derivatives with thioalkyl groups have a strong tendency to aggregate in CDCl(3). The formation of the aggregates is evidenced from the changes in 1D (1)H NMR and DOSY spectra as a function of concentration. The compounds are highly delocalized, and this is reflected by the low activation energy for the isomerization.

Effects of the alkyl substituent in the π-donor heteroatom on the kinetic and thermodynamic acidities of Fischer thiocarbene complexes

Rate constants for the proton transfer reaction from Fischer thiocarbene complexes (CO)5MC(SR1)CH3 (M = Cr or W; R1 = n-butyl, isopropyl, tert-butyl, cyclohexyl) to OH– and various primary and secondary amines were determined in 50% acetonitrile–50% water at 25 °C. These measurements allowed the determination of the thermodynamic and kinetic acidities for these substrates. The results obtained show that there is a slight effect of the substituent on the thermodynamic acidity, which is governed by its hydrophobicity; whereas the effect on the kinetic acidity is more noticeable and is due to the steric effect of the substituent.

Effect of cyclodextrin on the intramolecular catalysis of aryl hydrogen phthalate ester hydrolysis

The kinetics of the hydrolysis of Z-phenyl hydrogen phthalate (Z = H, p-Me, m-Me, m-Cl and p-Cl) was studied in the presence of hydroxypropyl-β-cyclodextrin (HPCD) at pH 2.00, 3.00 and 12.00. In acid solutions these reactions involve two kinetic processes, which correspond to the formation and decomposition of phthalic anhydride. At pH 12 only the formation of phthalic anhydride could be measured because it decomposes very fast under these conditions. The rate constant for the formation of phthalic anhydride decreases as the HPCD concentration increases whereas the decomposition of phthalic anhydride is almost constant. The kinetic results are interpreted in terms of the formation of an inclusion complex of the neutral, KCDAH, or ionized substrate, KCDA, with HPCD. In all cases KCDAH > KCDA, so part of the observed inhibition is due to an increase in the amount of substrate in its unreactive neutral form. Comparison of the rate constants for the reaction of the complexed substrates with those in the bulk solution indicates that the transition state for the cyclodextrin-mediated reaction is less stabilised than the ionised substrate with values of ΔΔG ranging from 0.28 to 1.59 kcal mol−1 depending on the substituent on the aryl ring.

Cyclodextrin Effect on Intramolecular Catalysis

HPCD inhibits the hydrolysis reaction of monoamides and monoesters of phthalic and maleic acid at pH 2. The magnitude of inhibition depends on the leaving group. For some of the substrates, the reaction in the cavity is more than 100 times slower than that in solution.