Versatility of Amide-Functionalized Co(II) and Ni(II) Coordination Polymers: From Thermochromic-Triggered Structural Transformations to Supercapacitors and Electrocatalysts for Water Splitting.

The new 2D coordination polymers (CPs) [M(L)2(H2O)2]n [M = CoII (1) and NiII (2); L = 4-(pyridin-3-ylcarbamoyl)benzoate] were synthesized from pyridyl amide-functionalized benzoic acid (HL). They were characterized by elemental, Fourier transform infrared, thermogravimetric, powder X-ray diffraction (PXRD), and single-crystal X-ray diffraction (XRD) structural analyses. Single-crystal XRD analysis revealed the presence of a 2D polymeric architecture, and topological analyses disclose a 2,4-connected binodal net. A thermochromic effect leads to the production of two new CPs, 1' and 2', by heating at ca. 220 °C, accompanied by a color change from orange to purple in the case of 1 and from blue to green in the case of 2. The transformation of 1 to 1' takes place through an intermediate (1a) with a different twist of the L- ligand, leading to the formation of a 1D polymeric architecture, as proven by single-crystal XRD analysis. The addition of water or keeping 1' or 2' in air for several days leads to regeneration of 1 or 2, respectively. The thermochromic-triggered structural transformations of 1 and 2 were further substantiated by PXRD and UV-vis ground-state diffuse-reflectance absorption studies. The supercapacitance ability of the CPs 1 and 2 and a Ni-Co composite (made from mixing the CPs 1 and 2) was investigated by electroanalytical techniques, such as cyclic voltammetry and electrochemical impedance spectroscopy. The CP 2 exhibits the highest specific capacity of 273.8 C g-1 at an applied current density of 1.5 A g-1. These newly developed CPs further act as electrocatalysts for the water-splitting reaction.

Influence of apple phytochemicals in ZnO nanoparticles formation, photoluminescence and biocompatibility for biomedical applications.

The new green-synthesised ZnO nanoparticles (NPs) using apple (var. Starking) phytochemicals present a great potential for bioimaging applications. These NPs, when compared with ZnO microparticles synthesised with pure phytochemicals (quercetin or sucrose), and water, revealed that sizes and shapes were widely dependent on the organic precursors used. Based on these findings, new insights into the synthesis of ZnO NPs using apple phytochemicals were presented. The photoluminescent properties, characterized by steady-state and time resolve photoluminescence measurements, revealed that besides the intense sharp near-UV band edge emission observed for all particles, with sub-nanosecond lifetime, a strong broad emission band peak at 2.20 eV was detected for microparticles, with longer decay times being associate to crystal defects. Additionally, the photoluminescent properties of ZnO particles, further explored by fluorescence lifetime imaging microscopy (FLIM), suggested adequacy for imaging applications. The cytotoxicity, evaluated in human dermal fibroblasts, proving the biosafety of ZnO NPs by an unaffected cellular viability, total mitochondrial activity and F-actin cytoskeleton organization, contrasted with some degree of cytotoxicity depicted for microparticles. The influence of the phytochemicals in ZnO cytotoxicity was discussed. To the authors' best knowledge this is the first report of ZnO NPs synthesised with apple extracts. The novelty of choosing a fruit widely used in the food industry will render affordable NPs through the concept of circular economy. The proved biosafety of these ZnO NPs together with their intrinsic photoluminescent properties, open perspectives for the development of cost-effective bioimaging materials with potential to be further directed into biomedical applications.

In vitro degradation of ZnO flowered coated Zn-Mg alloys in simulated physiological conditions.

Flowered coatings composed by ZnO crystals were successfully electrodeposited on Zn-Mg alloys. The distinct coatings morphologies were found to be dependent upon the solid interfaces distribution, with the smaller number of bigger flowers (ø 46µm) obtained on Zn-Mg alloy containing 1wt.% Mg (Zn-1Mg) contrasting with the higher number of smaller flowers (ø 38µm) achieved on Zn-Mg alloy with 2wt.% Mg (Zn-2Mg). To assess the in vitro behaviour of these novel resorbable materials, a detailed evaluation of the degradation behaviour, in simulated physiological conditions, was performed by electrochemical impedance spectroscopy (EIS). The opposite behaviours observed in the corrosion resistances resulted in the build-up of distinct corrosion layers. The products forming these layers, preferentially detected at the flowers, were identified and their spatial distribution disclosed by EDS and Raman spectroscopy techniques. The presence of smithsonite, simonkolleite, hydrozincite, skorpionite and hydroxyapatite were assigned to both corrosion layers. However the distinct spatial distributions depicted may impact the biocompatibility of these resorbable materials, with the bone analogue compounds (hydroxyapatite and skorpionite) depicted in-between the ZnO crystals and on the top corrosion layer of Zn-1Mg flowers clearly contrasting with the hindered layer formed at the interface of the substrate with the flowers on Zn-2Mg.

In vivo assessment of a new multifunctional coating architecture for improved Mg alloy biocompatibility.

Magnesium alloys are regarded as potential biodegradable load-bearing biomaterials for orthopedic applications due to their physico-chemical and biomechanical properties. However, their clinical applicability is restricted by their high degradation rate, which limits the physiological reconstruction of the neighbouring tissues. In this work, a multifunctional coating architecture was developed on an AZ31 alloy by conjoining an anodization process with the deposition of a polymeric-based layer consisting of polyether imine reinforced with hydroxyapatite nanoparticles, aiming at improved control of the corrosion activity and biological performance of the Mg substrate. Anodization and coating protocols were evaluated either independently or combined for corrosion resistance and biological behaviour, i.e. the irritation potential and angiogenic capability within a chicken chorioallantoic membrane assay, and bone tissue response following tibia implantation within a rabbit model. Electrochemical impedance spectroscopy (EIS) analysis showed that coated Mg constructs, particularly anodized plus coated with AZ31, exhibited excellent stability compared to the anodized alloy and, particularly, to the bare AZ31. Microtomographic evaluation of the implanted samples correlated with these degradation results. Mg constructs displayed a non-irritating behaviour, and were associated with high levels of vascular ingrowth. Bone ingrowth neighbouring the implanted constructs was observed for all samples, with coated and anodized plus coated samples presenting the highest bone formation. Gene expression analysis suggested that the enhanced bone tissue formation was associated with the boost in osteogenic activity through Runx2 upregulation, following the activation of PGC-1α/ERRα signaling. Overall, the developed multifunctional coatings appear to be a promising strategy to obtain safe and bioactive biodegradable Mg-based implants with potential applications within bone tissue.

In vitro corrosion behaviour and anti-Candida spp. activity of Zn coated with ZnO-nanostructured 'Anastacia' flowers.

Rejection and colonization by microbes are two problematic issues that often require the surgical removal of medical implants with increased risks for patients. In this work it is shown that functionalization of Zn surfaces with ZnO-nanostructured 'Anastacia' flowers (NAF) resulted in improved biomaterials that can potentially overcome these important drawbacks, which can further boost the use of Zn in biomedical implants. The in vitro degradation of NAF-coated Zn under simulated physiological conditions resulted in the formation of a biomimetic corrosion layer rich in a hydroxyapatite analogue that, being an important bone component, may potentially decrease implant rejection. Colonization of the NAF-coated Zn surface by Candida parapsilosis and Candida albicans, two of the more relevant microbial species colonizing medical devices, was significantly reduced on the NAF-coated Zn surface. The mechanism by which this colonization inhibition occurred was distinct since for C. parapsilosis cells this was attributed to reduced cell viability, while for C. albicans the reduced colonization was related to impaired biofilm formation. This ZnO-derived coating is an expeditious strategy to improve the resilience of Zn-based resorbable biomaterials towards Candida spp. colonization, paving the way for the design of bioactive ZnO-derived coatings with potential for clinical applications on bone.

Studies on the electrochemical growth of (Per)2[Au(mnt)2].

The first stages of the electrocrystallization of (Per)(2)[Au(mnt)(2)] salt from dichloromethane on gold, platinum, and highly orientated pyrolytic graphite (HOPG) were investigated by cyclic voltammetry, atomic force microscopy, and X-ray photoelectron spectroscopy in order to understand the determinant factors for nucleation and crystal growth. The crystal growth occurs from adsorbed films of dithiolate on gold or platinum and of perylene on HOPG, after homogeneous nucleation, and it is controlled by the low diffusion of the species toward the growing surface.