Fabio S. Miranda

6-Aminocoumarin-naphthoquinone conjugates: design, synthesis, photophysical and electrochemical properties and DFT calculations

Quatro novos conjugados do tipo 6-aminocumarina-naftoquinona foram sintetizados e suas propriedades fotofisicas e eletroquimicas, investigadas. O composto 2-cloro-3-(2-oxo-2H-cromen6-ilamino)-1,4-naftoquinona 1 nao apresentou fluorescencia apreciavel, em comparacao com a 6-aminocumarina, 6-AC. Visando entender as razoes da extincao da fluorescencia neste composto, duas estrategias foram imaginadas. Primeiramente, o composto 1 foi metilado no nitrogenio para remover a interacao eletrostatica intramolecular N-H…O=C que mantem as duas unidades fixas. Entretanto, as propriedades de emissao do produto 2 nao se mostraram significantemente diferentes das do precursor 1. Como os calculos usando a teoria do funcional da densidade dependente do tempo (TD-DFT) dos compostos 1 e 2 indicaram que a supressao da fluorescencia relaciona-se ao carater aceptor no anel naftoquinonico, a segunda estrategia envolveu a substituicao do atomo de cloro na posicao 2 do nucleo naftoquinonico por diferentes grupos doadores de eletrons (compostos 3-5). Novamente nao houve mudancas apreciaveis nas propriedades de emissao. Para explicar estes resultados foram feitos calculos TD-DFT dos estados fundamental (S0) e excitado (S1) de todas as moleculas em solucao, os quais indicaram que o grupo fluorescente (6-AC) doa eletrons para o LUMO da naftoquinona, resultando em uma transferencia de eletron fotoinduzida oxidativa (oxidative-PET). Four novel 6-aminocoumarin-naphthoquinone conjugates were synthesized and their photophysical and electrochemical properties, investigated. 2-Chloro-3-(2-oxo-2H-chromen-6ylamino)-1,4-naphthoquinone 1 did not present appreciable fluorescence in solution in comparison with 6-aminocoumarin, 6-AC. In order to understand the reasons for the fluorescence quenching in this compound, two strategies were attempted. Firstly, compound 1 was N-methylated to remove the intramolecular N-H…O=C electrostatic interaction that maintained the two units fixed, but the emission properties of the product 2 were not significantly different from those of 1. Time-dependent density functional theory (TD-DFT) calculations of compounds 1 and 2 indicate that the fluorescence quenching is related to the electron acceptor character of the naphthoquinone ring. The second strategy, therefore, involved the substitution of the chlorine atom in position 2 of the naphthoquinone nucleus for different electron donor groups (compounds 3-5), but again the emission properties did not change significantly. To explain these experimental findings, TD-DFT calculations of the ground (S0) and excited (S1) states of all molecules in solution were carried out. The results suggest that the energy states in these conjugates are such that the fluorescent group (6-AC) donates electrons to the naphthoquinone LUMO resulting in an oxidative photoinduced electron transfer (oxidative-PET).

The effect of the molecular structures of dicyanomethylene compounds on their supramolecular assembly, photophysical and electrochemical properties

Two series of flexible dicyanomethylene compounds, specifically, class 1 and class 2 compounds, have been designed and synthesised. In class 1 compounds, the dicyanomethylene groups are separated by glycol chain spacers of different lengths, whereas, in class 2 compounds, the spacers are alkyl linkers of different lengths. The notion underlying the design of these compounds is that in class 1 molecules, the spacers contain donor oxygen atoms that could not only form hydrogen bonds during the course of crystal packing but also promote withdrawing effects that modify the photophysical and electrochemical properties of these molecules in solution; in contrast, these effects would be absent for class 2 molecules. However, this study revealed that, with respect to crystal packing, the size of the spacers and their even and odd numbers of atoms are more important than their chemical nature. All of the synthesised compounds exhibited blue emission in the solid state and in CH2Cl2 solutions. The photophysical and electrochemical properties of these compounds in solution were not significantly affected by the type and length of the spacer that was used in each molecule. In the solid state, however, the compound with the shortest spacer showed the highest Stokes shift. The electronic transitions for the synthesized compounds in solution were explained by density functional theory and time-dependent density functional theory calculations, which indicated that the methylene moieties control the properties of both classes of compounds and that the spacers do not conjugate with the end groups. These two series of flexible dicyanomethylene compounds could be utilised as molecular building blocks for the development of new solids with novel properties.

Polypyridyl Ruthenium Complexes: Novel DNA-Intercalating Agents against Human Breast Tumor

This paper describes a new series of four DNA-intercalating agents with promising anticancer activities, based on ruthenium(II) with the planar ligand dpqQX (dpqQX = dipyrido[3,2-a:2’,3’-c] quinoxaline[2,3-b]quinoxaline). The complexes identified as trans-[RuCl2(dppb)(dpqQX)], cis-[RuCl2(dppb)(dpqQX)], ct-[RuCl(CO)(dppb)(dpqQX)]PF6 and ct-[RuCl2(PPh3)2(dpqQX)] (dppb = 1,4-bis(diphenylphosphine)butane and PPh3 = triphenylphosphine) were characterized by P{H} nuclear magnetic resonance (NMR) and infrared spectroscopies, cyclic voltammetry, molar conductance measurements, elemental analysis, mass spectrometry and X-ray diffraction analysis for complex ct-[RuCl2(PPh3)2(dpqQX)]. Their in vitro cytotoxic activities against MDAMB-213 and MCF-7 breast cancer cells were evaluated and compared with normal L-929 cells. Low drug concentration at which 50% of the cells are viable relative to the control (IC50) values were obtained for all four complexes compared with a reference metallodrug, cisplatin. In addition, DNA affinity studies from titrations, as well as the images obtained by atomic force microscopy (AFM) involving pBR322 plasmid DNA, suggest interactions between the metal complexes and the DNA macromolecule, in which they act as intercalating agents. The intercalation of the complexes with DNA was confirmed by viscosity measurements.

Melt sonoquenching: an affective process to obtain new hybrid material and achieve enhanced electrochromic performances based on V2O5/2,4,5-tris(1-methyl- 4-pyridinium)-imidazolide tetrafluoroborate nanofibers

Hybrid electrochromic materials are a very important class of compounds, because they enable new and/or better optical and electrochemical properties to be unfolded. This paper reports the synthesis of the new V2O5.1.26H2O([C3N2(C6H7N)3])0.07 using the combination of two traditional methods, melting quenching and sonochemistry. The new material was characterized by several methods in order to verify the physical and chemical characteristics and its possible use as an electrochromic electrode. The organic guest provokes an interlayer spacing decrease of the inorganic matrix and the electrostatic interaction between the oxo groups of the V2O5 matrix and the pyridinium rings of the organic guest demonstrate a strong interaction. The new hybrid nanostructure presented good reversibility and cyclability during 50 cycles, electrochromic efficiency of 22 cm2 C-1 (410 nm) and 96 % color retention after 50 cycles of color changing.