Carbamazepine polymorphism: a re-visitation using Raman imaging

Raman imaging methods have appeared in the last years as a powerful approach to monitoring the quality of pharmaceutical compounds. Because polymorphism occurs in many crystalline pharmaceutical compounds, it is essential to monitor polymorphic transformations induced by different external stimulus, such as temperature changes, to which those compounds may be submitted. Raman imaging with k-means cluster analysis (CA) is used here as an essential technique to investigate structural and chemical transformations occurring in carbamazepine p-monoclinic (CBZ III) into carbamazepine triclinic (CBZ I) when submitted to temperatures near the melting point of CBZ III (178 °C) and CBZ I (193 °C). CBZ III commercial powder and laboratorial prepared CBZ I were analyzed by differential scanning calorimetry, powder X-ray diffraction and Raman spectroscopy with variable temperature. After thermal treatment, the resultant CBZ powder was evaluated by Raman imaging, in which all imaging data was analyzed using CA. Raman imaging allowed the identification of different polymorphs of CBZ (CBZ III and CBZ I) and iminostilbene (IMS), a degradation product of CBZ, in the treated samples, depending on the heating treatment method.publishe

Raman imaging studies on the stability of Paracetamol tablets under different storage conditions

The applicability of Raman imaging for pharmaceutics production ranges from the characterization of pharmaceutical formulations, kinetic processes in drug delivery to the rapid detection and identification of counterfeit drugs/contaminants. Acetaminophen (Paracetamol, APAP) is an analgesic and antipyretic drug and one of the most consumed medicines worldwide. On the other hand, the compound 4-aminophenol (4-AP) is a hydrolytic product of APAP with nephrotoxicity and teratogenic effects. In this work, we have explored for the first time Raman imaging methods to characterize the main components of commercial APAP tablets (APAP-tablets) and to inquire about the potential of this optical technique to identify 4-AP in APAP tablets, which have been previously spiked with such contaminant. The laboratorial treated APAP-tablet samples were subjected to different temperature, humidity and sunlight exposure conditions, mimicking storage conditions, and then the Raman spectra and images were collected to monitor changes that might occur in those conditions. Although the lower limit of detection of 4-AP in APAP-tablets is above the minimum levels established by Pharmacopoeias (0.005 %), this research demonstrates that Raman imaging still allows the detection of small amounts of the contaminant, thus opening perspectives for exploring this technique for characterizing APAP products.publishe

Gold loaded textile fibres as substrates for SERS detection

Spectroscopic methods based on surface-enhanced Raman scattering (SERS) are among the analytical tools most exploited in recent years for the detection of vestigial amounts of compounds with environmental and health relevance. In the last decades, SERS methods have been largely improved with the unprecedented progress in instrumentation and materials development in the scope of nanoscale science. The current developments in Raman instruments, in particular for Raman imaging, brought a new look on composites and its applications. The use of confocal microscopes allows high resolution Raman mapping with short measurement times, creating strongly improved Raman images in two and three dimensions. In this manuscript, we will present an overview of our own research on the development of malleable and easy-handled SERS substrates based on textile fibres for analytical detection. The strategies employed for the coating of the textile fibres with gold nanoparticles (NPs) will be described in detail. A final section will focus on the combination of Raman imaging and SERS for the development of substrates based on textile fibres and their application on the detection of water pollutants and biomolecules. A case study on the development of cotton swab fibres coated with Au NPs for SERS detection of L-lactate will be illustrated in more detail.publishe

Structure and photoactivity for hydrogen production of CdS nanorods modified with In, Ga, Ag-In and Ag-Ga and prepared by solvothermal method

This work studies the variation in the photocatalytic properties of CdS derived from the insertion of In, Ga, Ag-In and Ag-Ga in the CdS lattice through solvothermal methodology. Solvothermal synthesis of CdS-M photocatalysts has been succesful for the insertion of Ga3þ, In3þ, Ga3þ/Agþ and In3þ/Agþ into the hexagonal crystal lattice of one-dimensional CdS. The insertion of In, Ga, Ag-In and Ag-Ga modifies the band gap and the relative position of EVB. CdS modified with In3þ or Ga3þ shows an increase in the band gap and upshift in the relative position of the valence band energy which leads to a low efficiency hydrogen production. The co-addition of Agþ-In3þ or Agþ-Ga3þ favours the insertion of Agþ ions into the CdS lattice with narrower band gap. Of all the co-substituted photocatalysts, the CdS-AgGa was the only one that showed a higher photoactivity with respect to the CdS. The increase in the photoactivity of the CdS-AgGa photocatalyst is related to the band gap narrowing and downshift in the relative position of the valence band energy which enhance their visible light absorption and potential for oxidation. The CdS-AgGa photocatalyst shows small segregation of metallic Ag nanoparticles at the surface which also assist in the photoactivity of the sample.publishe

Colloidal dendritic nanostructures of gold and silver for SERS analysis of water pollutants

Surface-Enhanced Raman Scattering (SERS) using colloidal metal (Ag, Au) nanoparticles has been regarded as a powerful method for detecting organic pollutants at vestigial levels. Although less investi- gated, the controlled synthesis of binary nanostructures comprising two metals provides an alternative route to SERS platforms with tuned surface plasmon resonances. Here, we demonstrate that the use of dendrimers allows the formation of distinct combinations of Ag:Au nanostructures that are composed of smaller metal nanocrystals. Our research highlights the role of the dendrimer macromolecules as a multipurpose ligand in the generation of such hybrid nanostructure, including as a reducing agent, an effective long-term colloidal stabilizer and as a molecular glue for interconnecting the primary metal nanocrystals. Noteworthy, the dendrimer-based Ag:Au hybrid nanostructures are more SERS sensitive as compared to the corresponding colloidal blends or to the single-phase metals, as revealed by using molecular pesticides as analytes in spiked water samples. We suggest that the high SERS sensitivity of the hybrid nanostructures is due to interparticle plasmonic coupling occurring between the primary metal nanoparticle aggregates, whose arrangement is templated by the presence of the dendrimer macromolecules.publishe

Can contaminated waters or wastewater be alternative sources for technology-critical elements? The case of removal and recovery of lanthanides

Technology critical elements (TCE) are considered the vitamins of nowadays technology. Factors such as high demand, limited sources and geopolitical pressures, mining exploitation and its negative impact, point these elements as new emerging contaminants and highlight the importance for removal and recycling TCE from contaminated waters. This paper reports the synthesis, characterization and application of hybrid nanostructures to remove and recover lanthanides from water, promoting the recycling of these high value elements. The nanocomposite combines the interesting properties of graphite nanoplatelets, with the magnetic properties of magnetite, and exhibits good sorption properties towards La(III), Eu(III) and Tb(III). The sorption process was very sensitive to solution pH, evidencing that electrostatic interactions are the main binding mechanism involved. Removal efficiencies up to 80% were achieved at pH 8, using only 50 mg/L of nanocomposite. In ternary solution, occurred a preferential removal of Eu(III) and Tb(III). The equilibrium evidenced a rare but interesting behaviour, and as a proof-of-concept the recoveries and reutilization rates, at consecutive cycles, highlight the recyclability of the composite without loss of efficiency. This study evidences that surface charge and the number of active sites of the composite controls the removal process, providing new insights on the interactions between lanthanoids and magnetic-graphite-nanoplatelets.publishe

Colloidal nanomaterials for water quality improvement and monitoring

Water is the most important resource for all kind forms of live. It is a vital resource distributed unequally across different regions of the globe, with populations already living with water scarcity, a situation that is spreading due to the impact of climate change. The reversal of this tendency and the mitigation of its disastrous consequences is a global challenge posed to Humanity, with the scientific community assuming a major obligation for providing solutions based on scientific knowledge. This article reviews literature concerning the development of nanomaterials for water purification technologies, including collaborative scientific research carried out in our laboratory (nanoLAB@UA) framed by the general activities carried out at the CICECO-Aveiro Institute of Materials. Our research carried out in this specific context has been mainly focused on the synthesis and surface chemical modification of nanomaterials, typically of a colloidal nature, as well as on the evaluation of the relevant properties that arise from the envisaged applications of the materials. As such, the research reviewed here has been guided along three thematic lines: 1) magnetic nanosorbents for water treatment technologies, namely by using biocomposites and graphite-like nanoplatelets; 2) nanocomposites for photocatalysis (e.g., TiO2/Fe3O4 and POM supported graphene oxide photocatalysts; photoactive membranes) and 3) nanostructured substrates for contaminant detection using surface enhanced Raman scattering (SERS), namely polymers loaded with Ag/Au colloids and magneto-plasmonic nanostructures. This research is motivated by the firm believe that these nanomaterials have potential for contributing to the solution of environmental problems and, conversely, will not be part of the problem. Therefore, assessment of the impact of nanoengineered materials on eco-systems is important and research in this area has also been developed by collaborative projects involving experts in nanotoxicity. The above topics are reviewed here by presenting a brief conceptual framework together with illustrative case studies, in some cases with original research results, mainly focusing on the chemistry of the nanomaterials investigated for target applications. Finally, near-future developments in this research area are put in perspective, forecasting realistic solutions for the application of colloidal nanoparticles in water cleaning technologies.publishe

Defect concentration in nitrogen-doped graphene grown on Cu substrate: A thickness effect

Tuning the band-gap of graphene is a current need for real device applications. Copper (Cu) as a substrate plays a crucial role in graphene deposition. Here we report the fabrication of in-situ nitrogen (N) doped graphene via chemical vapor deposition (CVD) technique and the effect of Cu substrate thickness on the growth mechanism. The ratio of intensities of G and D peaks was used to evaluate the defect concentration based on local activation model associated with the distortion of the crystal lattice due to incorporation of nitrogen atoms into graphene lattice. The results suggest that Cu substrate of 20 µm in thickness exhibits higher defect density (1.86×1012 cm−2) as compared to both 10 and 25 µm thick substrates (1.23×1012 cm−2 and 3.09×1011 cm−2, respectively). Furthermore, High Resolution -X-ray Photoelectron Spectroscopy (HR-XPS) precisely affirms ~0.4 at% of nitrogen intercalations in graphene. Our results show that the substitutional type of nitrogen doping dominates over the pyridinic configuration. In addition, X-ray diffraction (XRD) shows all the XRD peaks associated with carbon. However, the peak at ~24° is suppressed by the substrate peaks (Cu). These results suggest that nitrogen atoms can be efficiently incorporated into the graphene using thinner copper substrates, rather than the standard 25 µm ones. This is important for tailoring the properties by graphene required for microelectronic applications. © 2017 Elsevier B.V

Polymer based silver nanocomposites as versatile solid film and aqueous emulsion SERS substrates

Nanocomposites containing Ag nanoparticles (average diameter similar to 11 nm) dispersed in poly(tertbutylacrylate) were prepared by in situ polymerization via miniemulsions and constitute active and versatile SERS substrates. The use of this synthetic strategy enables the dual use of the final composites as SERS substrates, both as aqueous emulsions and as cast films, shown here by several measurements using thiosalicylic acid as the testing analyte. The main advantage of these types of materials is related to the potential to scale up and the widespread use of handy substrates, using technology already available. This requires homogeneous composite substrates with SERS activity and this was demonstrated here by means of confocal Raman microscopy. Finally, a series of experiments were carried out on Ag/polymer nanocomposites submitted to temperature variations below and above the polymer glass transition temperature (T(g)) in order to conclude about the effect of temperature processing conditions on the composites' SERS activity.FCT- SFRH/BD/66460/2009FCT- SFRH/BPD/66407/2009FCT- PTDC/QUI/67712/ 2006RNME-Pole UA-FCT Project REDE/1509/RME/200