Lucinda V. Reis

Synthesis and Spectroscopic Characterisation of N-Alkyl Quaternary Ammonium Salts Typical Precursors of Cyanines

The synthesis and spectroscopic characterisation of some representative N-alkyl-substituted quaternary ammonium salts derived from benzothiazole, benzoxazole, benzo-selenazole, indole and quinoline are described. These heterocyclic salts, bearing an activated methyl group in the 2-position in relation to the nitrogen atom and N-methyl, -pentyl, -hexyl and -decyl chains, are typical precursors of cyanine dyes.

Some new symmetric rigidified triheterocyclic heptamethinecyanine dyes absorbing in the near infrared

Abstract Several new rigidified heptamethinecyanine dyes bearing different N -alkyl chains were readily prepared by a novel semi-catalyzed method, envisioning their potential usefulness for photodynamic therapy. All dyes displayed absorption within the so-called “phototherapeutic window”. In order to improve the structural versatility of the dyes, it was incorporated in the exocyclic conjugated bridge present in the polimethine chain a chlorine atom. In some cases the later underwent an unexpected in situ substitution by a third oxygenated heterocyclic group, depending on the solubility of the chloro dye in the reaction solvent. Two possible mechanisms for the formation of these triheterocyclic dyes are proposed. The full spectroscopic characterisation of all the cyanines synthesised is described.

Crystal structures of a benzoselenazole-derived squarylium cyanine dye and three derivatives substituted at the central squaric ring

The crystal structures of 4-[(3-hexylbenzoselenazol-3-ium-2-yl)methylidene]-2-[(3-hexyl-3H-benzoselenazol-2-ylidene)methyl]-3-oxocyclobut-1-en-1-olate and its analogues substituted at the squaric ring with O-methyl, NH-methyl and N,N-diethylamino groups have been determined using single crystal X-ray crystallography techniques. The unsubstituted squaraine dye is symmetrical and packs as a stepped ribbon array (via a C–H⋯O close interaction), which is in contrast to the slip-stacked arrangements observed in similar squaraine analogues. Each of the substituted analogues is asymmetric and pack in slightly differing slip-stacked charge-transfer columns. The NH-methyl analogue packs with a single water molecule per squaraine unit.

3,3-Sigmatropic Rearrangements Involving N−O Bond-Cleavage of Enehydroxylamine Derivatives

Enehydroxylamines, derived from carbocyclic and heterocyclic 1,3-dioxo compounds, react with a variety of unsaturated electrophiles to give, in good to excellent yields, substances that in general undergo 3,3-sigmatropic rearrangements either spontaneously or upon heating. In those cases in which such reactions failed, addition of sodium hydride was found to induce the transformation. A study of the rearrangement by use of deuterium-labelled compounds showed that no crossover occurs, indicating the intramolecular nature of the process. The method provides 2,3- or 3,4-disubstituted cyclohexenones, 5,6-disubstituted barbiturates and the corresponding fused pyrrole and imidazolinone derivatives. (© Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003)

Sesquiterpene lactones from Cynara humilis

Abstract The extract of the aerial parts of Cynara humilis gave, in addition to four known sesquiterpene lactones, three new guaianolides. The structure and stereochemistry of the new compounds were elucidated by high field NMR techniques and chemical transformations.

Enehydroxylamines as versatile compounds in 3,3-sigmatropic rearrangements

Abstract Enehydroxylamines react readily, in the presence of base, with electrophiles containing unsaturation to afford intermediates that, either spontaneously or upon heating, lead via a 3,3-sigmatropic rearrangement to α-substituted products.

Surface Photochemistry: 3,3′-Dialkylthia and Selenocarbocyanine Dyes Adsorbed onto Microcrystalline Cellulose

In this work, thia and selenocarbocyanines with n-alkyl chains of different length, namely with methyl, ethyl, propyl, hexyl and decyl substituents, were studied in homogeneous and heterogeneous media for comparison purposes. For both carbocyanine dyes adsorbed onto microcrystalline cellulose, a remarkable increase in the fluorescence quantum yields and lifetimes were detected, when compared with solution. Contrary to the solution behaviour, where the increase in the n-alkyl chains length increases to a certain extent the fluorescence emission ΦF and τF, on powdered solid samples a decrease of ΦF and τF was observed. The use of an integrating sphere enabled us to obtain absolute ΦF’s for all the powdered samples. The main difference for liquid homogeneous samples is that the increase of the alkyl chain strongly decreases the ΦF values, both for thiacarbocyanines and selenocarbocyanines. A lifetime distribution analysis for the fluorescence of these dyes adsorbed onto microcrystalline cellulose, evidenced location on the ordered and crystalline part of the substrate, as well as on the more disordered region where the lifetime is smaller. The increase of the n-alkyl chains length decreases the photoisomer emission for the dyes adsorbed onto microcrystalline cellulose, as detected for high fluences of the laser excitation, for most samples.

Protein purification by aminosquarylium cyanine dye-affinity chromatography

The most selective purification method for proteins and other biomolecules is affinity chromatography. This method is based on the unique biological-based specificity of the biomolecule-ligand interaction and commonly uses biological ligands. However, these ligands may present some drawbacks, mainly because of their cost and lability. Dye-affinity chromatography overcomes the limitations of biological ligands and is widely used owing to the low cost of synthetic dyes and to their resistance to biological and chemical degradation. In this work, immobilized aminosquarylium cyanine dyes are used in order to exploit affinity interactions with standard proteins such as lysozyme, α-chymotrypsin and trypsin. These studies evaluate the affinity interactions occurring between the immobilized ligand and the different proteins, as a reflection of the sum of several molecular interactions, namely ionic, hydrophobic and van der Waals, spread throughout the structure, in a defined spatial manner. The results show the possibility of using an aminosquarylium cyanine dye bearing a N-hexyl pendant chain, with a ligand density of 1.8 × 10(-2) mmol of dye/g of chromatographic support, to isolate lysozyme, α-chymotrypsin and trypsin from a mixture. The application of a decreasing ammonium sulfate gradient resulted in the recovery of lysozyme in the flowthrough. On the other hand, α-chymotrypsin and trypsin were retained, involving different interactions with the ligand. In conclusion, this study demonstrates the potential applicability of ligands such as aminosquarylium cyanine dyes for the separation and purification of proteins by affinity chromatography.

Synthesis, spectroscopic characterization and biological evaluation of unsymmetrical aminosquarylium cyanine dyes

New unsymmetrical aminosquarylium cyanine dyes were synthesized and their potential as photosensitizers evaluated. New dyes, derived from benzothiazole and quinoline, were prepared by nucleophilic substitution of the corresponding O-methylated, the key intermediate that was obtained by methylation with CF3SO3CH3 of the related zwitterionic unsymmetrical dye, with ammonia and methylamine, respectively. All three news dyes herein described displayed intense and narrow bands in the Vis/NIR region (693-714nm) and their singlet oxygen formation quantum yields ranged from 0.03 to 0.05. In vitro toxicity, in Caco-2 and HepG2 cells, indicated that dark toxicity was absent for concentrations up to 5µM (for the less active dye) or up to 1µM (for the two more active dyes). The three dyes present potential as photosensitizers, differing in irradiation conditions and period of incubation in the presence of irradiated dye. The less active dye needs a longer irradiation period to exhibit phototoxicity which is only evident after longer period of contact with cells (24h). However, the remaining two more active dyes produce higher phototoxicity, even at shorter incubation periods (1h), with shorter irradiation time (7min). Although in different extents, these dyes show promising in vitro results as photosensitizers.

Ethylenediamine-Derived Chromatographic Ligand to Separate BSA, Lysozyme, and RNase A

Chromatography has become an essential tool for the purification of proteins, since most purification schemes involve some forms of this methodology. Recently, using chromatographic matrices prepared from symmetrical aminosquarylium cyanine dyes immobilized on Sepharose via a central alkylamino residue, we were able to isolate lysozyme, α-chymotrypsin and trypsin from a mixture. Following this, we envisioned that the immobilization of an asymmetric squarylium dye bearing an N-carboxyethyl group in one of its ending nuclei, on ethylenediamine-activated Sepharose, through EDC/NHS amidation coupling, could enhance the ligand’s mobility and improve the interactions with the target proteins. The prepared support was found to separate an artificial mixture of BSA, lysozyme, and RNase A. Unexpectedly, the support prepared in the absence of the dye exhibited a separation performance similar to that of the dyed support, contrary to that observed in all previous studies using cyanine dyes as ligands for affinity chromatography, which prompted us to try to determine the structural molecular constitution of the matrix surface. A synthetic route to the final chromatographic support could be devised, which is believed to consist in the cyclization of two nearby ethylenediamine units, involving the inclusion of a succinimide-derived residue between them and the EDC-mediated Lossen rearrangement of an intermediary hydroxamic acid.