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- Polímeros fluorescentes para a detecção de metais tóxicosPublication . Fialho, Carina B.; Barata, Patrícia; Prata, José V.; Costa, Alexandra I.As reconhecidas capacidades dos calixarenos como receptores moleculares sintéticos, capazes de interagir e formar, selectivamente, complexos com espécies moleculares e iónicas, suscitaram o nosso interesse na sua incorporação em sistemas poliméricos conjugados, perspectivando a ocorrência da amplificação do sinal de transdução em processos de detecção de explosivos [1] e biomoléculas [2]. Na presente comunicação será apresentada a síntese, caracterização e aplicação sensorial a metais tóxicos de polímeros baseados em unidades de calix[4]arenos ditópicos e dietinil-9-propil-9H-carbazoles (CALIX-OCF-PPE-2,7-CBZeCALIX-OCF-PPE-3,6-CBZ).
- Metal ion recognition induced by calix[4]arene carbazole containing polymersPublication . D. Barata, Patrícia; Costa, Alexandra; Fialho, Carina B.; Prata, José VirgílioSensing and recognition of ions and neutral molecules via synthetic receptors are of current interest in supramolecular chemistry because of their significant importance in several areas, such as chemistry, biology and environment. Compared with small molecules, polymers-based sensors displayed several importante advantages like signal amplification. In this way, the incorporation of molecular receptors such as calixarenes with conjugated polymer backbones is expected to enhance the signaling events related to a host–guest interaction. The preorganized binding sites, easy derivatization and flexible three-dimensional steric structures make calixarenes ideal construction platforms for molecular design to generate fluorescente receptors. The use of calixarenes as supramolecular scaffolds for this type of architectures has been explored and the sensing abilities of resultant polymers toward metal and molecular ions established. Based on the high sensitivity shown by the non-polymeric analogue CALIX-OCP-CBZ (notshown), to toxic metal cations, we decide two extend the sensing study to polymer materials. Herein, we report the preliminar results of the chemosensing ability of a new bicyclic calix[4]arene-carbazole-polymer (CALIX-OCP-PPE-CBZ) towards the detection of toxic metals in fluid phase.
- Fostering protein-calixarene interactions: from molecular recognition to sensingPublication . Prata, José Virgílio; D. Barata, PatríciaTwo isomeric bis-calixarene-carbazole conjugates (CCC-1 and CCC-2) endowed with carboxylic acid functions at their lower rims have been found to display a high sensing ability (KSV up to 6 x 10(7) M-1) and selectivity toward cytochrome c, a multi-functional protein, in an aqueous-based medium. After targeting basic amino acid residues on the protein surface residing near the prosthetic heme group through electrostatic and hydrophobic interactions, a rapid photoinduced electron transfer ensues between the integrated transduction element (aryleneethynylene chromophore) of CCCs and the iron-oxidized heme of cytochrome c, enabling direct detection of the protein at nanomolar levels. Our results show that CCCs are capable of efficiently discriminating heme proteins (cytochrome c vs. myoglobin) and non-heme proteins (lysozyme) in an aqueous medium. Studies performed in two solvent systems (organic and aqueous) strongly suggest that in an organic medium a Forster-type resonance energy transfer is responsible for the observed reduction in CCCs emission upon contact with heme proteins while in an aqueous medium a specific photoinduced electron transfer mechanism prevails.
- Adsorption of myoglobin on calixarenes and biocatalysis in organic mediaPublication . Semedo, Magda C.; Karmali, Amin; Barata, Patrícia; Prata, José V.Derivatives of p-tert-butylcalix[4,6,8]arene carboxylic acids were used for selective adsorption of myoglobin.Amixtureofmyoglobin,laccaseandperoxidase wasusedforextractionwithcalixarenesandonlymyoglobin was selectively extracted to organic media. Myoglobin and Mb c–calixarene exhibited pseudoactivity of peroxidase in aqueous and organic media. This protein-calixarene complex exhibited the highest specific activity of 1.37 × 10−1 U.mg protein−1 at initial pH 6.5 of myoglobin aqueous solution. Apparent kinetic parameters (V max, K m, k cat and k cat/K m) for the pseudoperoxidase activity were determined in organic media for different initial pH values of myoglobin aqueous solution by Michaelis-Menten plot. The stability of this complex was studied for different initial pH values and t1/2 values were obtained in the range of 3.5–5.2 days. The extracted Mb c in organic media was recovered into fresh aqueous solutions at alkaline pH with a recovery of pseudoperoxidase activity of over 100%.
- Synthesis, structure, and optical properties of an alternating calix[4]arene-based meta-linked phenylene ethynylene copolymerPublication . D. Barata, Patrícia; Costa, Alexandra; Ferreira, Luis F. V.; Prata, José VirgílioNovel alternating copolymers comprising biscalix[4]arene-p-phenylene ethynylene and m-phenylene ethynylene units (CALIX-m-PPE) were synthesized using the Sonogashira-Hagihara cross-coupling polymerization. Good isolated yields (60-80%) were achieved for the polymers that show M-n ranging from 1.4 x 10(4) to 5.1 x 10(4) gmol(-1) (gel permeation chromatography analysis), depending on specific polymerization conditions. The structural analysis of CALIX-m-PPE was performed by H-1, C-13, C-13-H-1 heteronuclear single quantum correlation (HSQC), C-13-H-1 heteronuclear multiple bond correlation (HMBC), correlation spectroscopy (COSY), and nuclear overhauser effect spectroscopy (NOESY) in addition to Fourier transform-Infrared spectroscopy and microanalysis allowing its full characterization. Depending on the reaction setup, variable amounts (16-45%) of diyne units were found in polymers although their photophysical properties are essentially the same. It is demonstrated that CALIX-m-PPE does not form ground-or excited-state interchain interactions owing to the highly crowded environment of the main-chain imparted by both calix[4]arene side units which behave as insulators inhibiting main-chain pi-pi staking. It was also found that the luminescent properties of CALIX-m-PPE are markedly different from those of an all-p-linked phenylene ethynylene copolymer (CALIX-p-PPE) previously reported. The unexpected appearance of a low-energy emission band at 426 nm, in addition to the locally excited-state emission (365 nm), together with a quite low fluorescence quantum yield (Phi = 0.02) and a double-exponential decay dynamics led to the formulation of an intramolecular exciplex as the new emissive species.
- New entities for sensory chemistry based on calix[4]arene-carbazole conjugates: from synthesis to applicationsPublication . Barata, Patrícia; Prata, José VirgílioTwo new calix[4]arene-carbazole conjugates (CALIX-CBZs) comprising 2- and 3-ethynyl-substituted carbazole derivatives attached to a central bis-calix[4]arene-containing phenylene ring have been designed for fluorescence-based detection of high explosive materials and explosive markers in vapour phase. The title compounds were prepared in good isolated yields and structurally fully characterised. CALIX-CBZs are highly fluorescent compounds that largely preserve their deep blue luminescence in solid state with no notorious emissions from electronic aggregated states. The excellent optical properties exhibited by casted films of both materials, including their photochemical stability, suggested their potential use as solidstate sensors. Remarkable high and fast responses were in fact retrieved upon contact with saturated vapours of 2,4,6trinitrotoluene (TNT, a high explosive) and 2,4-dinitrotoluene (a common impurity in TNT batches, often used as its chemical marker), reaching near 80% of fluorescence quenching for the later on 30s of exposure. Experiments performed with nitroaliphatic compounds (nitromethane (NM), a liquid explosive and 2,3-dimethyl-2,3-dinitrobutane, an explosive taggant) also revealed a high level of sensitivity (up to near 40% fluorescence quenching in only 10s of exposure to NM). The quenching efficiencies were overall correlated with the extent and strength of CALIX-CBZs–analyte interactions, the vapour pressure of the analytes and the film thicknesses.
- Cooperative effects in the detection of a nitroaliphatic liquid explosive and na explosive taggant in the vapor phase by calix[4]arene-based carbazole-containing conjugated polymersPublication . D. Barata, Patrícia; Prata, José VirgílioTwo fluorescent molecular receptor based conjugated polymers were used in the detection of a nitroaliphatic liquid explosive (nitromethane) and an explosive taggant (2,3-dimethyl-2,3-dinitrobutane) in the vapor phase. Results have shown that thin films of both polymers display remarkably high sensitivity and selectivity toward these analytes. Very fast, reproducible, and reversible responses were found. The unique behavior of these supramolecular host systems is ascribed to cooperativity effects developed between the calix[4] arene hosts and the phenylene ethynylene-carbazolylene main chains. The calix[4]-arene hosts create a plethora of host-guest binding sites along the polymer backbone, either in their bowl-shaped cavities or between the outer walls of the cavity, to direct guests to the area of the transduction centers (main chain) at which favorable photoinduced electron transfer to the guest molecules occurs and leads to the observed fluorescence quenching. The high tridimensional porous nature of the polymers imparted by the bis-calixarene moieties concomitantly allows fast diffusion of guest molecules into the polymer thin films.
- Aryleneethynylene trimers bearing calix[4]arenes: synthesis, optical properties and self-assembling studiesPublication . Prata, José Virgílio; Barata, PatríciaNew homoditopic bis-calix[4]arene-carbazole conjugates, armed with hydrophilic carboxylic acid functions at their lower rims, are disclosed. Evidence for their self-association in solution was gathered from solvatochromic and thermochromic studies, as well as from gel-permeation chromatography analysis. Their ability to function as highly sensitive sensors toward polar electron-deficient aromatic compounds is demonstrated.
- Highly selective and sensitive detection of toxic metals by fluorescent Bicyclic Calix[4]arene-based sensorsPublication . D. Barata, Patrícia; Fialho, Carina B.; Prata, José Virgílio; Costa, Alexandra I.Development of fast and portable chemosensors for trace detection of toxic metals, in particular those which are mostly present in the environment due to natural phenomenon and human activities (e.g. cadmium, mercury and lead), is a challenging area of current research.1 Calixarenes are one of the most widespread scaffolds in host-guest chemistry because of their rigid structures, which make them perfect candidates for complexation studies with ions and neutral molecules. Metal ions commonly bind at the lower rim of the calixarene moiety. Host-guest interaction can be enhanced by proper choice of additional binding sites containing nitrogen, oxygen, sulfur or a combination of them, and specifically designed calixarene architectures. Exploring the inherent capabilities of certain fluorescent calixarene-based compounds for establishing strong host:guest interactions, several sensing materials have been developed and tested by us towards the detection of neutral molecular species.2. We report in this communication the chemosensing ability of CALIX-OCP-CBZ and CALIX-OCP (Scheme 1) towards the detection of toxic metals, either by using the sensing element in fluid phase or solid state.
- Novel bicyclic fluorescent calix[4]arene-based sensors for toxic metalsPublication . Costa, Alexandra; Fialho, Carina B.; Barata, Patrícia; Prata, José VirgílioCalix[4]arene has been widely exploited as the basic molecular framework for many fluorescent chemosensors in the construction of selective binding sites given its structural rigidity (particularly important when the recognition and reporting events are to be undertaken in fluid phase), various conformations, and facile introduction of fluorophores. Exploring the inherent capabilities of certain fluorescent calixarene scaffolds for establishing strong host:guest interactions, several sensing materials have been recently developed by us [1]. In the same line of research new bicyclic calix[4]arene-based fluorescent chemosensors containing amides as coordination sites (ionophore) and carbazole segments as fluorescent signaling moieties (CALIX-AMD-CBZ) are being developed and that are expected to have high ability toward the detection of metallic cations in solution. However its complex synthesis and characterization has led to the use of a similar compound based on narrow rim 1,3-oxacyclophane tethered calix[4]arene derivatives integrating the same fluorescent segments (CALIX-OCP-2-CBZ) [2] as fluorophore in the present communication. Herein we report the most significant photophysical properties and sensory capabilities of CALIX-OCP-2-CBZ towards divalent ions (Cd2+, Cu2+, Hg2+, Pb2+) by fluorescence spectroscopy in fluid phase.