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- Carbon dots from coffee grounds by a one-pot microwave-assisted methodPublication . Moraes, Bianca; Costa, Alexandra I.; Barata, Patrícia; Prata, José V.Carbon-based nanomaterials, particularly carbon dots (C-dots) have attracted the researchers interest due their excellent luminescence, photostability and biocompatibility, encouraging their use in several areas such as biomedicine, (bio)sensors, photocatalysis and optoelectronics. C-dots could be prepared by a variety of methods (top-down and bottom-up approaches), using a great diversity of carbon sources. Bottom-up processes based on the use of waste materials for producing C-dots are particularly attractive since an effective reduction of environmental impacts of those wastes may be foreseen, while high-valued nanomaterials can be simultaneously obtained. Coffee is one of the most consumed brews all over the world, generating large amounts of coffee waste, a source of a serious environmental problem due to the high content of organic matter such as caffeine, phenols, tannins, and sugars. Herein, we explore the valorization of coffee grounds generated from automatic and vending machines for production of C-dots through a one-pot monomode microwave-assisted method. Structural and photophysical characterization of the as-synthesized nanomaterials have been carried out, and their potential applications as sensing materials for pollutants and explosives (e.g. nitroanilines and nitroaromatics) were evaluated by fluorescence and absorption techniques.
- 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).
- Linear and crosslinked copolymers of p-tert-butylcalix[4]arene derivatives and styrene: new synthetic approaches to polymer-bound calix[4]arenesPublication . Mendes, Ana R.; Gregório, Carla C.; Barata, Patrícia; Costa, Alexandra I.; Prata, José V.As an extension of our previous studies concerning the free radical copolymerisation of 25,26,27-tripropoxy-28-(4-vinyl-benzyloxy)-p-tert-butylcalix[4]arene (3) with styrylic monomers, we report herein on the synthesis and characterisation of new terpolymers derived from 3, styrene and divinylbenzene, having nominal crosslinking degrees ranging from 4% to 40% wt. The terpolymers exhibited good thermal stabilities (DSC) and were prepared in good yields. Depending on the reaction conditions (dilution degree and aqueous phase to porogen ratio), materials with identical nominal crosslinking but otherwise differentiated morphologies and swelling abilities were obtained. In a related study, the radical polymerisation of styrene was carried out in the presence of a novel calix[4]arene derivative 4, bearing two distal benzyl–vinyl groups in the lower rim. It is shown that, albeit the presence of two phenolic groups within the calixarene moiety which could have functioned as inhibitors of the free radical polymerisation, the macrocycle was able to take part in the copolymerisation reaction, yielding new soluble and crosslinked polymers. In both cases, no pendant vinyl groups were found in the polymeric materials. The probable mechanisms underlying their formation are discussed.
- Carbon dots synthesis from coffee grounds, and sensing of nitroanilinesPublication . Moraes, Bianca; Costa, Alexandra I.; Barata, Patrícia; Prata, José V.Fluorescent carbon dots (C-dots) were directly synthesized by a sustainable and eco friendly one-pot microwave-assisted hydrothermal carbonization method from coffee grounds waste. The coffee grounds obtained from automatic coffee machines, after being heated at 190 °C for 1–4 h in the presence of nitrogen additives, furnished the desired carbon nanomaterials. Struc tural and photophysical properties of the as-synthesized nanomaterials were evaluated by FTIR, 1H NMR, UV-Vis, and fluorescence spectroscopies. The ability of the C-dots to behave as probes for isomeric nitroanilines (ortho-, meta- and para-nitroaniline) was explored through fluorimetric titra tion experiments. High sensitivities and selectivities were obtained for the detection of nitroanilines in aqueous media.
- 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%.
- Carbon dots from coffee grounds: synthesis, characterization, and detection of noxious nitroanilinesPublication . Costa, Alexandra I.; Barata, Patrícia; Moraes, Bianca; Prata, José V.Coffee ground (CG) waste is generated in huge amounts all over the world, constituting a serious environmental issue owing to its low biodegradability. Therefore, processes that simultaneously aim for its valorization while reducing its environmental impact are in great demand. In the current approach, blue luminescent carbon dots (C-dots) were produced in good chemical yields from CGs following hydrothermal carbonization methods under an extended set of reaction parameters. The remarkable fluorescent properties of the synthesized C-dots (quantum yields up to 0.18) allied to their excellent water dispersibility and photostability prompted their use for the first time as sensing elements for detection of noxious nitroanilines (NAs) in aqueous media. Very high levels of NA detection were achieved (e.g., limit of detection of 68 ppb for p-nitroaniline), being the regioisomeric selectivity attributed to its higher hyperpolarizability and dipole moment. Through ground-state and time-resolved fluorescence assays, a static fluorescence quenching mechanism was established. H-1 NMR titration data also strongly suggested the formation of ground-state complexes between C-dots and NAs.
- Fluorescent bis-calix[4]arene-carbazole conjugates: synthesis and inclusion complexation studies with fullerenes C-60 and C-70Publication . Barata, Patrícia; Costa, Alexandra I.; Costa, Sérgio; Prata, José V.Supramolecular chemistry has become a central theme in chemical and biological sciences over the last decades. Supramolecular structures are being increasingly used in biomedical applications, particularly in devices requiring specific stimuli-responsiveness. Fullerenes, and supramolecular assemblies thereof, have gained great visibility in biomedical sciences and engineering. Sensitive and selective methods are required for the study of their inclusion in complexes in various application fields. With this in mind, two new fluorescent bis-calix[4]arene-carbazole conjugates (4 and 5) have been designed. Herein, their synthesis and ability to behave as specific hosts for fullerenes C-60 and C-70 is described. The optical properties of the novel compounds and their complexes with C-60 and C-70 were thoroughly studied by UV-Vis and steady-state and time-resolved fluorescence spectroscopies. The association constants (K-a) for the complexation of C-60 and C-70 by 4 and 5 were determined by fluorescence techniques. A higher stability was found for the C-70@4 supramolecule (K-a = 5.6 x 10(4) M-1; Delta G = -6.48 kcal/mol). Evidence for the formation of true inclusion complexes between the host 4 and C-60/C-70 was obtained from NMR spectroscopy performed at low temperatures. The experimental findings were fully corroborated by density functional theory (DFT) models performed on the host-guest assemblies (C-60@4 and C-70@4).
- The synthesis of novel polymer-bound calix[4]arenesPublication . Barata, Patrícia; Costa, Alexandra I.; Granja, Paulo; Prata, José V.Two simple and efficient procedures for the synthesis of linear and cross-linked polymers containing hydrophobic and hydrophilic lower rim derivatives of p-tert-butylcalix[4]arenes are described. The target polymers were prepared either through the direct attachment of 25,26,27,28-tetrahydroxy-p-tert-butylcalix[4]arene (1), or its tripropoxy (2) and tetracarboxymethoxy (4) derivatives, to light cross-linked Merrifield's resins (1–2% DVB) or via radical addition copolymerisation of 25,26,27-tripropoxy-28-(4-vinyl-benzyloxy)-p-tert-butylcalix[4]arene (11) with styrene and a cross-linking agent.
- Comparative study of the copolymerization kinetics of mono and divinylbenzyl p-tert-butylcalix[4]arene derivatives and styrenePublication . Costa, Alexandra I.; Barata, Patrícia; Prata, José V.A study of the copolymerization kinetics of 25,27-bis(4-vinyl-benzyloxy)-26,28-dihydroxy-p-tert-butylcalix[4]arene (1) and 25,26,27-tripropoxy-28-(4-vinyl-benzyloxy)-p-tert-butylcalix[4]arene (2) with styrene (St) was undertaken. The radical copolymerizations were carried outin THF in thepresence ofbenzoyl peroxideat 758C for a certain period. Six molar feed ratios, ranging from 1:1 to 1:20 (1 or 2 to St), were used to calculate the reactivity parameters. The copolymer composition was determined by FT-IR spectroscopy using a Beer’s law plot obtained from the corresponding homopolymers. The reactivity ratio calculations were performed with the linearization methods of Fineman-Ross (F-R) and Kelen-Tu ¨do ¨s (K-T), assuming the validity of the so-called terminal model. In the copolymerization of the monoene 2, similar reactivity ratios were found for the comonomers (ca. 1.2; K-T). On the other hand, the reactivity ratios calculated for the copolymerization of 1 with St yielded rSt 5 0.67 and rcalix 5 3.0 (K-T method). The higher reactivity of monomer 1 as compared to styrene is discussed in connection with our previously postulated cyclocopolymerization route.
- Highly sensitive and selective fluorescent probes for Cu(II) detection based on calix[4]arene-oxacyclophane architecturesPublication . Costa, Alexandra I.; Barata, Patrícia; Fialho, Carina; Prata, José V.A new topological design of fluorescent probes for sensing copper ion is disclosed. The calix[4]arene-oxacyclophane (Calix-OCP) receptor, either wired-in-series in arylene-alt-ethynylene conjugated polymers or standing alone as a sole molecular probe, display a remarkable a_nity and selectivity for Cu(II). The unique recognition properties of Calix-OCP system toward copper cation stem from its pre-organised cyclic array of O-ligands at the calixarene narrow rim, which is kept in a conformational rigid arrangement by a tethered oxacyclophane sub-unit. The magnitude of the binding constants (Ka = 5.30 8.52 _ 104 M1) and the free energy changes for the inclusion complexation (DG = 27.0 28.1 kJmol1), retrieved from fluorimetric titration experiments, revealed a high sensitivity of Calix-OCP architectures for Cu(II) species. Formation of supramolecular inclusion complexes was evidenced from UV-Vis spectroscopy. The new Calix-OCP-conjugated polymers (polymers 4 and 5), synthesized in good yields by Sonogashira–Hagihara methodologies, exhibit high fluorescence quantum yields (_F = 0.59 0.65). Density functional theory (DFT) calculations were used to support the experimental findings. The fluorescence on–o_ behaviour of the sensing systems is tentatively explained by a photoinduced electron transfer mechanism.