Leandra Franciscato Campo

Synthesis and spectroscopic characterisation of 2-(2'-hydroxyphenyl)benzazole isothiocyanates as new fluorescent probes for proteins

Abstract Three new benzazole isothiocyanate (BzITC) fluorescent dyes, 2-(5′-isothiocyanate-2′-hydroxyphenyl)benzoxazole, 2-(5′-isothiocyanate-2′-hydroxyphenyl)benzimidazole and 2-(5′-isothiocyanate-2′-hydroxyphenyl)oxazole[4,5-b]pyridine, were synthesised, purified until optical purity grade and characterised by elemental analysis, 1 H NMR , IR, UV–VIS and fluorescence spectroscopy. These dyes exhibit an intense fluorescence emission with a large Stokes shift due to an excited state intramolecular proton transfer (ESIPT) mechanism. The BzITCs were also studied for labelling three proteins (bovine serum albumin (BSA), concanavalin-A (con-A) and rabbit immunoglobulin G (rabbit IgG)) and the resulting conjugates presented good and stable fluorescence. A simple assay for detection of these proteins was reported here. The method is based on the direct fluorescence detection of protein-labelled with BzITC fluorophores after polyacrylamide gel electrophoresis and present potential use as fluorescent probes for proteins.

The first silica aerogels fluorescent by excited state intramolecular proton transfer mechanism (ESIPT)

Five silyl-functionalized benzazole dyes, fluorescent by excited state intramolecular proton transfer (ESIPT) mechanism, were synthesized by reaction of amino benzazole derivatives with 3-(triethoxysilyl)propyl isocyanate. Fluorescent silica gels were prepared and monolithic aerogels (d ≈ 0.18 g cm−3) were obtained via supercritical CO2 drying of the fluorescent gel. The photophysical behaviour of the dyes and fluorescent silica aerogels was investigated by UV–vis and steady-state fluorescence spectroscopy.

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).

Symmetrical and Asymmetrical Cyanine Dyes. Synthesis, Spectral Properties, and BSA Association Study

New cyanines were prepared by an efficient and practical route with satisfactory overall yield from low-cost starting materials. The photophysical behavior of the cyanines was investigated using UV-vis and steady-state fluorescence in solution, as well as their association with bovine serum albumin (BSA) in phosphate buffer solution (PBS). No cyanine aggregation was observed in organic solvents or in phosphate buffer solution. The alkyl chain length in the quaternized nitrogen was shown to be fundamental for BSA detection in PBS in these dyes.

Synthesis and thermal behavior of new liquid crystals arylaldoxime esters

We report the synthesis of a series of liquid-crystalline materials based on arylaldoxime esters and the characterization of these materials by 1H, 13C NMR, ATR/FT-IR spectroscopy and elemental analysis. The chemical stability and liquid-crystalline as well as photophysical properties of the compounds are described being dependent on the heating/cooling cycles. The changes in chemical stability and the liquid crystals properties of arylaldoxime esters were observed during these thermal cycles by IR analysis. All samples underwent a thermal degradation yielding the corresponding nitriles and carboxylic acid as evidenced by IR and 1H NMR spectra. Due to the decomposition process, information about the mesomorphic behaviour is lost. The UV-Vis absorption spectra in solution display three absorption bands between 230 and 340 nm. The fluorescence spectra exhibit a broad and structureless emission band located at 430 nm. Ab initio calculations were performed to obtain information on the molecular structure and properties of the title compounds.

Static Light Scattering from ESIPT Copolymers of Poly(methyl methacrylate) - Benzazole Dyes

Static Light Scattering (SLS) was used for characterization of the fluorescent ESIPT copolymers of PMMA - Benzazole dyes in solution with chloroform (CHCl 3 ) and tetrahydrofuran (THF) were studied. The results show that macromolecular parameters and copolymers architectures in solution are not changing in relation to those of PMMA. In this way, the incorporation of Benzazole dyes in PMMA does not affect the final polymer properties and conformations in the investigated dilution regime.

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.

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.

Comparative analysis of organic-chromophore-doped sol-gel films by poling optical polarimetry, ellipsometry, AFM, and Abeles-Hacskaylo characterization

We consider application of the in situ poling optical polarimetry method to guest-host systems consisting of a Corona-poled, sol-gel, porous silicate film matrix doped with Disperse Red 1 (DR1) chromophores. Refractive indices, and physical thicknesses are consistently determined by ex situ null ellipsometry, atomic force microscopy and Abeles- Hacskaylo characterization. Due to the pronounced poling- induced birefringence we found in the composite films, in opposition to previous approaches, we could not disregard it with respect to refractive index values. Even for the case of strong birefringence, this procedure and associated modeling allow estimation of electro-optic coefficients and second-order susceptibilities of poled dielectric films doped with DR1, or with other high hyperpolarizability chromophores.

Bromine-terminated azobenzene liquid crystals

ABSTRACT A series of liquid crystals (LCs) of bromine-terminated azobenzene were synthesised and characterised. The LCs were composed of an azobenzene core, an alkyl chain and a flexible spacer with a bromine atom at a remote position. Mesomorphic properties were dependent on both the alkyl chain length and the relative position of the bromine atom at the end of the spacer group. The nematic phase was favoured over the smectic A phase for alkyl chains with one and seven carbon atoms. However, the SmA mesophase was dominant for compounds with 10-carbon alkyl chains. The remote bromine atom in the spacer group favoured SmA for homologous with n-decyl chains and the nematic phase for n-heptyl and methyl groups. Molecular modelling showed that the azobenzene LCs tended to adopt the all trans-conformation in the gas phase as the number of carbon atoms increased. For short spacer groups, bent conformations contributed to the level population proportion of conformers. For the non-LC 5a, the gauche conformation became the most stable with a torsional angle of –68.9°. X-ray experiments showed a monolamellar SmA mesophase in an antiparallel arrangement. Absorption maxima at 360 and 440 nm were assigned to π–π* and n–π* transitions, respectively. Graphical Abstract