Intramolecular Hydroamination of Selenoalkynes to 2-Selenylindoles in the Absence of Catalyst

In this work, a series of 2-chalcogenylindoles was synthesized by an efficient methodology, starting from chalcogenoalkynes, including a previously unreported tellurium indole derivative. For the first time, these 2-substituted chalcogenylindoles were obtained in the absence of metal catalyst or base, under thermal conditions only. In addition, the results described herein represent a methodology with inverse regioselectivity for the chalcogen functionalization of indoles.     

Static light scattering,ultraviolet–visible,and fluorescence spectroscopy from fluorescent methyl methacrylate/benzazole dye copolymers displaying an intramolecular proton‐transfer mechanism in the electronically excited state

The solution behavior of new copolymers of methyl methacrylate and benzazole dyes emitting fluorescence because of an intramolecular proton‐transfer mechanism in the electronically excited state has been investigated by static light scattering, fluorescence spectroscopy, ultraviolet–visible, and gel permeation chromatography. In the dilute regime, with tetrahydrofuran (THF) and chloroform as solvents, the copolymers behave as typical polydisperse linear chains in good solvents. The analysis of the osmotic modulus for concentrated solutions in THF (c ≥ 60 g L^?1) indicates the existence of an interchain association mechanism. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 341–350, 2003     

Iron Oxide Nanoparticles Labeled with an Excited‐State Intramolecular Proton Transfer Dye

Excited‐state intramolecular proton transfer (ESIPT) is a particularly well known reaction that has been very little studied in magnetic environments. In this work, we report on the photophysical behavior of a known ESIPT dye of the benzothiazole class, when in solution with uncoated superparamagnetic iron oxide nanoparticles, and when grafted to silica‐coated iron oxide nanoparticles. Uncoated iron oxide nanoparticles promoted the fluorescence quenching of the ESIPT dye, resulting from collisions during the lifetime of the excited state. The assembly of iron oxide nanoparticles with a shell of silica provided recovery of the ESIPT emission, due to the isolation promoted by the silica shell. The silica network gives protection against the fluorescence quenching of the dye, allowing the nanoparticles to act as a bimodal (optical and magnetic) imaging contrast agent with a large Stokes shift.     

Effects of Prenatal Exposure to Aflatoxin B1: A Review

Aflatoxins are mycotoxins produced as secondary fungal metabolites. Among them, aflatoxin B1 (AFB1) stands out due to its genotoxic and mutagenic potential, being a potent initiator of carcinogenesis. In this review, the outcomes from the published literature in the past 10 years on the effects of AFB1 pathophysiological mechanisms on embryological and fetal development are discussed. In several animal species, including humans, AFB1 has a teratogenic effect_, resulting in bone malformations, visceral anomalies, lesions in several organs, and behavioral and reproductive changes, in addition to low birth weight. The mutagenic capacity of AFB1 in prenatal life is greater than in adults, indicating that when exposure occurs in the womb, the risk of the development of neoplasms is higher. Studies conducted in humans indicate that the exposure to this mycotoxin during pregnancy is associated with low birth weight, decreased head circumference, and DNA hypermethylation. However, as the actual impacts on humans are still unclear, the importance of this issue cannot be overemphasized and studies on the matter are essential.     

Amphiphilic ESIPT benzoxazole derivatives as prospective fluorescent membrane probes

Fluorescent amphiphilic benzoxazole derivatives were synthesized and used to produce photoactive phosphatidylcholine (PC) liposomes by reserve-phase evaporation. The dyes absorbed in the UV region and were fluorescent in the blue-green region (determined by solvent polarity). The alkyl chain length seemed to play a fundamental role in the photophysics of the benzoxazole fluorophore in reverse liposomes, and despite the same ESIPT core and phospholipid building block, each amphiphilic dye had a particular emission profile related to the dye location in the liposome. The fluorescence emission spectra from dye 5 showed that its fluorophore experienced a polar environment, due to the single normal emission, while dyes 6–7 had (in part) a normal emission, and the main fluorescent band ascribed to the ESIPT emission indicated a more hydrophobic environment. Despite the complex fluorescent profiles, the benzoxazole derivatives could be successfully introduced into the reverse liposome structure due to the interaction between the alkyl chain and PC bilayer.     

The role of the sol–gel route on the interaction between rhodamine B and a silica matrix

A series of silica xerogels having rhodamine B (RhB) as a template and Ti centers were synthesized by distinct sol–gel routes, namely, acid-catalyzed, base-catalyzed, acid-catalyzed with base-catalyzed (two steps) hydrolytic routes and a FeCl₃-catalyzed non-hydrolytic route. The interaction of RhB with the prepared silica matrix was investigated by Fourier transform infrared spectroscopy, attenuated total reflectance, diffuse reflectance spectroscopy in the ultraviolet–visible region, Raman spectroscopy, mass spectrometry, X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and confocal microscopy. Raman spectroscopy suggested the presence of Ti–O and Si–O–Ti moieties within the silica matrix. Infrared band shifts provided insight into potential interaction sites. Taking into account the results from ART, XPS, PL and confocal microscopy, encapsulation of RhB preferentially occurs inside the silica network for acid 1, basic and two-steps routes, and the presence of Ti occurs on the surface of the silica occurs for acid 2, basic and two-steps routes. Also, we have shown that although the structural characteristics of the encapsulated and extracted systems are affected by the route, the molecular structure is conserved during and after the encapsulation process.     

Development of an electrochemical sensor for potassium ions based on KSr2Nb5O15 modified electrode

In the work described by this paper, we studied the development of a selective potassium ion sensor constituted of a carbon paste electrode modified (CPEM) with a novel KSr₂Nb₂O₁₅. The material KSr₂Nb₂O₁₅ is an oxide with the tetragonal tungsten bronze structure (TTB) type are in forefront both in the area of research as well as in industrial applications. The sensor response to potassium ions was linear in the concentration range 1.26 x 10^-5 at 1.62 x 10^-3 mol L^-1 (E (mV) = 32.7 + 51.1 log [K⁺]). The sensor based KSr₂Nb₂O₁₅, of the TTB-type presented very good potentiometric response, with a slope of 51.1 mV/dec (at 25 °C) and detection limit for the potassium ions of 7.27 x 10^-5 mol.L^-1.     

Synthesis and photophysical properties of novel succinimidyl benzazole derivatives, evaluated by Candida albicans ATCC 10231 fluorescent staining

New fluorescent succinimidyl benzazole derivatives were synthesised and successfully used to stain Candida albicans ATCC 10231 cells. The dyes were characterised by means of infrared, ¹³C and ¹H NMR spectroscopies and elemental analysis. UV-Vis and steady-state fluorescence in solution were also applied to characterise their photophysical behaviour. The novel dyes were fluorescent in the yellow-green region by a phototautomerism in the excited state (ESIPT) with a large Stokes shift (9065-10962 cm⁻¹). Dual fluorescence could also be observed depending on the solvent polarity. The present dyes were used as new probes by means of culture methodology or direct staining to study the micromorphology of Candida albicans.     

Synthesis of 2-arylbenzothiazoles via direct condensation between in situ generated 2-aminothiophenol from disulfide cleavage and carboxylic acids

In this work we describe a simple and efficient general methodology for 2-arylbenzothiazole preparation employing disulfides and carboxylic acids. The reaction is promoted by tributylphosphine that acts both in disulfide bond cleavage and as activating agent for coupling with carboxylic acids. The reaction scope was studied using bis(2-aminophenyl)disulfide and different carboxylic acids with donor/withdrawing substituents, which resulted in the desired 2-arylbenzothiazole with moderate to good yields. The method was tested with success in preparation of the amyloid probe 2-(4-aminophenyl)-6-methoxybenzothiazole that employed a substituted bis(2-aminophenyl)disulfide.     

New fluorescent monomers and polymers displaying an intramolecular proton‐transfer mechanism in the electronically excited state (ESIPT), 1. Synthesis of benzazolylvinylene derivatives and its copolymerization with methyl methacrylate (MMA)

Six new fluorescent monomers of the benzazole family were synthesized by the reaction of 2‐(5′‐amino‐2′‐hydroxyphenyl)benzazole derivatives and differently functionalized vinylene compounds. The radical copolymerization of the monomers with MMA results in transparent and fluorescent polymers with good optical and thermal properties. These monomers and copolymers emit fluorescence with a large Stokes shift due to the intramolecular proton‐transfer mechanism in the electronically excited state (ESIPT).