Cesar A. Sierra

The generalized tanh-coth method to special types of the fifth-order KdV equation

Abstract In this paper we use a generalization of the well-known tanh–coth method to obtain new periodic and soliton solutions for several forms of the fifth-order KdV equation (fKdV). Three special cases that we consider here are the Caudrey–Dodd–Gibbon (CDG), the generalized Kaup–Kupershmidt (GKK) and the generalized Ito equations. New traveling wave solutions which include periodic and soliton solutions for three cases are formally derived.

Photoinduced energy transfer in bichromophoric pyrene-PPV oligomer systems: the role of flexible donor-acceptor bridges.

In this contribution, we report on the electronic energy transfer dynamics of bichromophoric systems incorporating two pyrene chromophores tethered by variable-length flexible alkyloxy chains to p-phenylenevinylene oligomers. These were studied using UV-vis absorption and both steady state and time-resolved fluorescence spectroscopy. Time-resolved emission measurements showed an efficient photoinduced energy transfer process in all the multichromophoric systems, which occurs on the time scale of tens of picoseconds after excitation at 265 nm. The energy transfer process is especially efficient in systems where the linker is formed by eight atoms (up to k(ET) ≈ 2.7 × 10(10) s(-1)), which, despite not being the shortest bridge studied, allows the approach of the donor and acceptor chromophores due to an appropriate number of flexible single bonds. Using Förster theory, we calculated the donor-acceptor distance in each triad from the experimental energy transfer rate, finding them to be in the range 8.8-10 Å.

ABCG2/BCRP: Specific and Nonspecific Modulators.

Multidrug resistance (MDR) in cancer cells is the development of resistance to a variety of structurally and functionally nonrelated anticancer drugs. This phenomenon has become a major obstacle to cancer chemotherapy seriously affecting the clinical outcome. MDR is associated with increased drug efflux from cells mediated by an energy‐dependent mechanism involving the ATP‐binding cassette (ABC) transporters, mainly P‐glycoprotein (ABCB1), the MDR‐associated protein‐1 (ABCC1), and the breast cancer resistance protein (ABCG2). The first two transporters have been widely studied already and reviews summarized the results. The ABCG2 protein has been a subject of intense study since its discovery as its overexpression has been detected in resistant cell lines in numerous types of human cancers. To date, a long list of modulators of ABCG2 exists and continues to increase. However, little is known about the clinical consequences of ABCG2 modulation. This makes the design of novel, potent, and nontoxic inhibitors of this efflux protein a major challenge to reverse MDR and thereby increase the success of chemotherapy. The aim of the present review is to describe and highlight specific and nonspecific modulators of ABCG2 reported to date based on the selectivity of the compounds, as many of them are effective against one or more ABC transport proteins.

Evaluation of sodium acetate trihydrate–urea DES as a benign reaction media for the Biginelli reaction. Unexpected synthesis of methylenebis(3-hydroxy-5,5-dimethylcyclohex-2-enones), hexahydroxanthene-1,8-diones and hexahydroacridine-1,8-diones

In this work, the low melting mixture sodium acetate trihydrate–urea was synthesized and the eutectic composition was determined and characterized using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The physical properties of the deep eutectic solvent (DES) such as viscosity, electrical conductivity, density, pH and refractive index were measured and analyzed as a function of temperature. To explore the use of this DES as a reaction media, the Biginelli one-pot reaction for the preparation of polyhydroquinoxaline derivatives was studied and unexpectedly methylenebis(3-hydroxy-5,5-dimethylcyclohex-2-enones) and hexahydroxanthene-1,8-diones were obtained when the reaction was performed at 60 °C, and hexahydroacridine-1,8-diones when the reaction was conducted at 100 °C. Our results showed that the nature of the obtained products can be tuned by increasing the temperature of the reaction.

Competitive One-Pot Reactions: Simultaneous Synthesis of Decahydroacridine-1,8-diones and 1,8-Dioxo-octahydroxanthenes and Photophysical Characterization

Abstract A simple and convenient one-pot method for simultaneously obtaining decahydroacridine-1,8-diones and 1,8-dioxo-octahydroxanthene derivatives is described. A high conversion yielding both products was obtained under the reaction conditions. To understand the optical behavior of the model compounds and their potential use as antenna moieties in bichromophoric systems, the photophysical properties of all samples were studied using ultraviolet–visible absorption and steady-state fluorescence spectroscopy in methanol solutions. For the case of the acridinediones, the fluorescence spectra were found to exhibit the typical emission profile of the locally excited state, whereas, contrary to previous published experimental results, reliable fluorescence emission spectra for the xanthenes derivatives could not be obtained. On the other hand, the poor quantum yields of the synthesized decahydroacridine-1,8-diones were explained based on the benzene-like substitution effect, which favors the intersystem crossing relaxation mechanism. [Supplementary materials are available for this article. Go to the publishers online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] GRAPHICAL ABSTRACT

New exact solutions for a generalization of the Korteweg-de Vries equation (KdV6)

The generalized tanh-coth method is used to construct periodic and soliton solutions for a new integrable system, which has been derived from an integrable sixth-order nonlinear wave equation (KdV6). The system is formed by two equations. One of the equations may be considered as a Korteweg-de Vries equation with a source and the second equation is a third-order linear differential equation.

High-Yield Synthesis of the Novel E,E-2,5-Dimethoxy-1,4-bis[2-(4-ethylcarboxylatestyril)]benzene by the Heck Reaction

Abstract The novel E,E-2,5-dimethoxy-1,4-bis[2-(4-ethylcarboxylatestyril)]benzene, 4, was obtained in good yield (92%), by the Heck cross-coupling reaction using Pd(dba)2 and P(OPh)3 like catalytic system. The high trans specificity of the product produced by the Heck reaction was confirmed by Fourier Transform–infrared and NMR. The methodology reported can be used as synthetic route for precursors to phenylenevinylene target systems with highly desired functional groups in their molecular structure, such as carboxylic, to build metal–organic frameworks and other applications within the supramolecular chemistry. Supplemental materials are available for this article. Go to the publishers online edition of Synthetic Communications® to view the free supplemental file. GRAPHICAL ABSTRACT

On a KdV equation with higher-order nonlinearity: Traveling wave solutions

Abstract In this work, the improved tanh–coth method is used to obtain wave solutions to a Korteweg–de Vries (KdV) equation with higher-order nonlinearity, from which the standard KdV and the modified Korteweg–de Vries (mKdV) equations with variable coefficients can be derived as particular cases. However, the model studied here include other important equations with applications in several fields of physical and nonlinear sciences. Periodic and soliton solutions are formally derived.

Oligo p-Phenylenevinylene Derivatives as Electron Transfer Matrices for UV-MALDI

AbstractPhenylenevinylene oligomers (PVs) have outstanding photophysical characteristics for applications in the growing field of organic electronics. Yet, PVs are also versatile molecules, the optical and physicochemical properties of which can be tuned by manipulation of their structure. We report the synthesis, photophysical, and MS characterization of eight PV derivatives with potential value as electron transfer (ET) matrices for UV-MALDI. UV-vis analysis show the presence of strong characteristic absorption bands in the UV region and molar absorptivities at 355 nm similar or higher than those of traditional proton (CHCA) and ET (DCTB) MALDI matrices. Most of the PVs exhibit non-radiative quantum yields (φ) above 0.5, indicating favorable thermal decay. Ionization potential values (IP) for PVs, calculated by the Electron Propagator Theory (EPT), range from 6.88 to 7.96 eV, making these oligomers good candidates as matrices for ET ionization. LDI analysis of PVs shows only the presence of radical cations (M+.) in positive ion mode and absence of clusters, adducts, or protonated species; in addition, M+. threshold energies for PVs are lower than for DCTB. We also tested the performance of four selected PVs as ET MALDI matrices for analytes ranging from porphyrins and phthalocyanines to polyaromatic compounds. Two of the four PVs show S/N enhancement of 1961% to 304% in comparison to LDI, and laser energy thresholds from 0.17 μJ to 0.47 μJ compared to 0.58 μJ for DCTB. The use of PV matrices also results in lower LODs (low fmol range) whereas LDI LODs range from pmol to nmol. Graphical Abstractᅟ

9-(4-Hydroxybutyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9- hexahydro-1H-xanthene-1,8(2H)-dione

The title compound 9-(4-hydroxybutyl)-3,3,6,6-tetramethyl-3,4,5,6,7,9-hexahydro-1H-xanthene-1,8(2H)-dione was synthesized in 72% yield through a simple, convenient and environmentally friendly one-pot reaction between dimedone and 3,4-dihydro-2H-pyran in aqueous citric acid. Additionally, a plausible reaction mechanism for the formation of the target xanthene is proposed.