Image-guided therapy using maghemite-MOF nanovectors

Advances in nanotechnology offer the possibility of tailored delivery of therapeutics with real-time imaging of disease. In this issue of Chem, Steunou and co-workers amalgamate the powerful MRI properties of ultra-small paramagnetic iron oxides with the excellent drug-delivery capabilities of metal-organic frameworks to produce theranostic nanoparticulate devices for cancer treatment and imaging

Nonviscous Modes of Viscoelastically Damped Vibrating Systems

Nonviscously damped vibrating systems are characterized by dissipative mechanisms depending on the time history of the response velocity, introduced in the physical models using convolution integrals involving hereditary kernel functions. One of the most used damping viscoelastic models is Biot’s model, whose hereditary functions are assumed to be exponential kernels. The free-motion equations of these types of nonviscous systems lead to a nonlinear eigenvalue problem enclosing certain number of the so-called nonviscous modes with nonoscillatory nature. Traditionally, the nonviscous modes (eigenvalues and eigenvectors) for nonproportional systems have been computed using the state-space approach, computationally expensive. This number of real eigenvalues is directly related to the rank of the damping matrices associated with the exponential kernels. The state-space approach has traditionally been used up to now as the only method to compute the nonviscous modes for nonproportionally damped systems. Motivated by this open problem, we propose in this chapter to describe the available numerical methods for classically damped systems and present the recent methods for nonclassically damped systems. It is shown that the problem of finding the nonviscous modes can be reduced to solve as a set of linear eigenvalue problems. The presented methods are compared through a numerical example

Lower bounds for the centered Hardy-Littlewood maximal operator on the real line

Let $10$ such that for each $f\in L^p(\mathbb{R})$, the centered Hardy-Littlewood maximal operator $M$ on $\mathbb{R}$ satisfies the lower bound $\|Mf\|_{L^p(\mathbb{R})}\ge (1+\varepsilon_p)\|f\|_{L^p(\mathbb{R})}$.Comment: accepted manuscrip

Kinetics and mechanism of gas-phase thermolysis using headspace-gas chromatographic analysis

Headspace gas chromatography is employed in order to study the thermal decomposition reaction of gaseous di-tert-butyl peroxide (DTBP) in the 130°C to 160°C temperature range and in the presence of n-hexane as the internal standard and nitrogen as the carrier gas. The reaction exclusively yields acetone and ethane as products. First-order kinetics are observed, including when the surface-to-volume ratio (S/V) of the Pyrex 20-mL vial employed as the reactor is increased by packing it with silanized glass wool. However, a small increase in the rate constant values is observed at each temperature, which supports a heterogeneous surface process in DTBP decomposition. The rate constant's dependence on the homogeneous unimolecular decomposition reaction corresponds to the O-O bond rupture of the DTBP molecule in a stepwise three-stage mechanism. Thus, the relevant question of the participation of a surface catalytic effect in the DTBP gas-phase thermolysis can easily be assessed through the procedure described in this work. In general, this is advantageous for the rapid investigation of the reaction kinetics of volatile compounds at different temperatures.Laboratorio de Estudio de Compuestos Orgánico

Solvent and substituent effects on the kinetics of thermolysis of cis-fused 1,2,4-trioxanes

The kinetics of the thermal decomposition reaction of cis-6-phenyl-5,6-(2- phenylpropyliden)-3,3-pentamethylene-1,2,4-trioxacyclohexane (Ia) were investigated in benzene and methanol solutions in the temperature and concentration ranges of 353.3-413.2 K and (1.1 - 13.1)×10-3 M, respectively. First-order rate constant values were obtained for up to at least ca. 20% conversions of that cyclic peroxide. The activation parameter values for the initial unimolecular homolysis of that molecule, results supported by the effect of the addition of di-tert-butyl-p-cresol as a free radical scavenger, indicate a stepwise reaction mechanism which is in keeping with the reaction products analysis. The corresponding activation parameters for the reaction of Ia in methanol (ΔH# = 20.2 ± 0.6 kcal mol-1; ΔS# = 0.1 ± 1.6 cal mol-1K-1; ΔG# = 20.2 ± 0.6 kcal mol-1 and in benzene (ΔH# = 15.4 ± 0.2 kcal mol-1; ΔS# = -13.2 ± 0.5 cal mol-1K-1; ΔG# = 20.5 ± 0.2 kcal mol-1 solutions are compared with values obtained for cis-6-phenyl-5,6-(2-phenylpropyliden)-3,3- tetramethylene-1,2,4-trioxacyclohexane (Ib) thermolysis in the same solvents. The thermolysis kinetics of Ia are less sensitive to solvent changes compared to the behaviour already reported for the analogous reactions of Ib. Because both molecules in solution are flexible structures due to their configurations, the relatively small solvent effect found on the former trioxane reaction is attributed to the extent of the chain of methylene groups attached on C-3 of the corresponding molecular rings. Furthermore, the pertinent substituent effect on the peroxidic bond strength of those molecules in solution was evaluated.Facultad de Ciencias Exacta

Solvent and substituent effects on the thermolysis of antimalarial fluorophenyl substituted 1,2.4-trioxanes

The kinetics and mechanism of the thermal decomposition reaction of cis-6-(4-fluoropheny1)-5,6-[2-(4-fluorophenyl)-propylidene]-3, 3-tetramethylene-1,2,4-trioxacyclo-hexane (I) were investigated separately in n-hexane and in methanol solutions over the temperature and concentration ranges of 393.2-443.2 K and 2.7-54 × 10-5 M, respectively. The values of the activation parameters for both reactions were compared with the corresponding ones for the thermolysis of cis-6-(4-fluorophenyl-5,6-[2-(4- fluorophenyl)-3-hydroxypropylidene]-3,3-tetramethylene-1,2,4-trioxacyclohexane (II), investigated in the same solvents and temperature range. Substituent and solvent effects on the initial homolytic rupture of the O-O peroxydic bonds of those molecules were evaluated.Facultad de Ciencias Exacta

Solvent and substituent effects on the thermolysis of antimalarial fluorophenyl substituted 1,2.4-trioxanes

The kinetics and mechanism of the thermal decomposition reaction of cis-6-(4-fluoropheny1)-5,6-[2-(4-fluorophenyl)-propylidene]-3, 3-tetramethylene-1,2,4-trioxacyclo-hexane (I) were investigated separately in n-hexane and in methanol solutions over the temperature and concentration ranges of 393.2-443.2 K and 2.7-54 × 10-5 M, respectively. The values of the activation parameters for both reactions were compared with the corresponding ones for the thermolysis of cis-6-(4-fluorophenyl-5,6-[2-(4- fluorophenyl)-3-hydroxypropylidene]-3,3-tetramethylene-1,2,4-trioxacyclohexane (II), investigated in the same solvents and temperature range. Substituent and solvent effects on the initial homolytic rupture of the O-O peroxydic bonds of those molecules were evaluated.Facultad de Ciencias Exacta

Transferencia de materia hacia la solución en la extracción de productos bioactivos de vegetales y su degradación en mezclas de solventes

A quantitative analytic evaluation of the extraction of the natural antimalarial drug artemisinin, in wild plants of Artemisia annua L., using mixtures of ethanol 70% (v/v)-water has ben carried out. This study has been performed in order to find a justification of the reduced recovery of that drug in their isolation processes previously reported, not corresponding to the values of its dosage in the fresh plant material. The results of this work could be useful to interpret similar situations in the isolation of plant natural products.Se ha realizado una evaluación analítica cuantitativa de la extracción de la droga antimalárica natural artemisinina, presente en plantas silvestres de Artemisia annua L., utilizando mezclas de etanol 70% (v/v) - agua. El objetivo ha sido encontrar una justificación de la reducida recuperación de esa droga en los procesos de su aislamiento ya indicados en la literatura y que conducen a la obtención de rendimientos que no corresponden con el dosaje inicial de la droga en el material vegetal fresco. Los resultados de este trabajo podrían ser de utilidad para interpretar situaciones análogas en el aislamiento de productos naturales provenientes de vegetales