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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).
- A solid-state fluorescence sensor for nitroaromatics and nitroanilines based on a conjugated Calix[4]arene polymerPublication . Prata, José V.; Costa, Alexandra I.; Teixeira, CarlosA new conjugated polymer possessing calix[4]arene-oxacyclophane units wired-in-series by phenyleneethynylene linkers was synthesized by a Sonogashira-Hagihara cross-coupling method in high yield. The polymer was structurally characterized by FTIR and 1H/13C/HSQC NMR techniques, and its average Mn (38.5 kDa) retrieved from GPC analysis. The polymer is highly emissive (ΦF =0.55) and exhibits a longer-than-usual excited-state lifetime (1.80 ns) for a phenyleneethynylene type polymer. Similar photo physical properties (absorption and fluorescence emission) were observed in solution and insolid-state. This stems from the presence of bulky calixarene moieties along the polymer chains which prevent interchain staking and the formation of ground-state aggregates and/or non-emissive exciplexes, both deleterious to solid-state materials envisioned for fluorescence sensing applications. Moreover, the intrinsic molecular recognition capabilities of its two rigid inner cavities (calixarene and cyclophane sub-units), allied with the high three-dimensionality of the macromolecule that creates additional interstitial voids around the molecular receptors, can boost its sensory responses towards specific analytes. A high sensitive response was observed in the detection of nitroaromatics and nitroanilines in neat vapour phases by casted films of the polymer. The largest sensitivitieswereobtainedfor2,4-dinitrotoluene (a taggant for the explosive TNT;>85% of fluorescence quenching upon 1 min exposure) and ortho-nitroaniline (90% of emission reduction in 30s).The sensory responses attained in solid-state are discussed on the basis of the electron affinities of the analytes and their electrostatic interactions with polymer films.
- 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.
- Finding value in wastewaters from the cork industry: carbon dots synthesis and fluorescence for hemeprotein detectionPublication . Alexandre, Marta R.; Costa, Alexandra I.; Berberan-Santos, Mario; Prata, José V.Valorisation of industrial low-value waste residues was preconized. Hence, carbon dots (C-dots) were synthesized from wastewaters of the cork industry—an abundant and a_ordable, but environmentally-problematic industrial e_uent. The carbon nanomaterials were structurally and morphologically characterised, and their photophysical properties were analysed by an ensemble of spectroscopy techniques. Afterwards, they were successfully applied as highly-sensitive fluorescence probes for the direct detection of haemproteins. Haemoglobin, cytochrome c and myoglobin were selected as specific targets owing to their relevant roles in living organisms, wherein their deficiencies or surpluses are associated with several medical conditions. For all of them, remarkable responses were achieved, allowing their detection at nanomolar levels. Steady-state and time-resolved fluorescence, ground-state UV–Vis absorption and electronic circular dichroism techniques were used to investigate the probable mechanisms behind the fluorescence turn-o_ of C-dots. Extensive experimental evidence points to a static quenching mechanism. Likewise, resonance energy transfer and collisional quenching have been discarded as excited-state deactivating mechanisms. It was additionally found that na oxidative, photoinduced electron transfer occurs for cytochrome c, the most electron-deficient protein Besides, C-dots prepared from citric acid/ethylenediamine were comparatively assayed for protein detection and the di_erences between the two types of nanomaterials highlighted.
- 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.
- 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.