Lina Marcela Bolivar-Pineda

This study aimed to optimize the extraction process of pectin from cupuassu pod husk powder by microwave-assisted extraction method, using response surface methodology (RSM). The effects of three variables: irradiation time, pH and solvent ratio, as well as their interactions, were analyzed to determine the optimal extraction conditions with the best process yield. The results indicated that the optimum conditions were pH 1.8, irradiation time of 20 min and solvent ratio of 20 mL/g, to obtain 10.82% yield. Characterization of the extracted pectin showed that obtained pectin is classified as high methoxyl (HMP), which highlights its applicability in the food industry as a gelling, thickening, emulsifying and stabilizing agent in products that require the presence of high levels of soluble solids, such as sugar, and under acidic pH conditions. Key parameters such as equivalent weight of 741.55 ± 1.73 mg/mol, moisture of 9.8 ± 0.19% and ash content of 10.19 ± 0.25%, key characteristics to evaluate the properties of pectin, were also determined. Finally, fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), thermal analysis (TGA and DSC), and scanning electronic microscopy (SEM) revealed structural characterization, thermal stability and morphology of the obtained pectin.

Context: Lanthanide-based systems, such as nitride cluster fullerenes Ln₃N@C₈₀ and bipthalocyanines LnPc₂ (Pc = phthalocyanine ligand), are of interest for their magnetic, fluorescent and electronic properties. In this regard, we performed DFT characterization to investigate the changes in structure and electronic properties for noncovalently interacting lanthanide (Ln; where Ln = La, Ce, Gd and Lu) nitride cluster fullerenes and bisphthalocyanines to form Ln₃N@C₈₀ + LnPc₂ dyads. The optimized geometries, formation and frontier orbital energies, HOMO-LUMO plots, charge and spin of Ln and N(NCF) atoms, as well as spin density plots of the dyads were analyzed in comparison with those of isolated Ln₃N@C₈₀ and LnPc₂ components. In addition to LnPc₂ bending distortion, the noncovalent dyad formation alters the geometry of the encapsulated Ln₃N cluster, favoring more planar or pyramidal geometries, depending on the case. The HOMO and LUMO orbitals are found on bisphthalocyanines, being localized on the isoindole units, except for Ce₃N@C₈₀ + CePc₂ dyad, where the LUMO was found on the central metal of CePc₂. The HOMO-LUMO gap energy is lower for the dyads compared to isolated NCFs, being rather close to the gap energy of bisphthalocyanines. The changes in spin density distribution are evident in the dyads containing Ce and Gd atoms, contrary to their La and Lu-derived counterparts. The interaction of Ce₃N@C₈₀ and Gd₃N@C₈₀ with CePc₂ and GdPc₂, respectively, causes redistribution of the spin density, with changes in the orientation of spin-up and spin-down electrons in the encapsulated Ce₃N and Gd₃N clusters. Methods: The geometry optimization and electronic properties calculations based on density functional theory were performed using the DMol³ module of Material Studio 8.0 software package from Accelrys Inc. The computational parameters selected included the general gradient approximation functional PBE, combined with a long-range dispersion correction developed by Grimme (PBE-D2), the double numerical basis set (DN), equivalent to the 6-31G Pople-type basis set along with the DFT semiconductor pseudopotentials. To mitigate the self-consistent field convergence problems, the thermal smearing technique was applied, with a final very small value of 0.0001 Ha (equivalent to 31.6 K temperature), or Fermi orbital occupancy in some cases. Graphical

Rare earth bisphthalocyanines (MPc₂) are of particular interest because of their behavior as single-molecular magnets, which makes them suitable for applications in molecular spintronics, high-density data storage and quantum computation. Nevertheless, MPc₂ are not commercially available, and the synthesis routes are mainly focused on obtaining substituted phthalocyanines. Two preparation routes depend on the precursor: synthesis from phthalonitrile (PN) and the metalation of free or dilithium phthalocyanine (H₂Pc and Li₂Pc). In both options, byproducts such as free-base phthalocyanine and in the first route additional PN oligomers are generated, which influence the MPc₂ yield. There are three preparation methods for these routes: heating, microwave radiation and reflux. In this research, solvothermal synthesis was applied as a new approach to prepare yttrium, lanthanum, gadolinium and terbium unsubstituted bisphthalocyanines using Li₂Pc and the rare earth(III) acetylacetonates. Purification by sublimation gave high product yields compared to those reported, namely 68% for YPc₂, 43% for LaPc₂, 63% for GdPc₂ and 62% for TbPc₂, without any detectable presence of H₂Pc. Characterization by infrared, Raman, ultraviolet–visible and X-ray photoelectron spectroscopy as well as elemental analysis revealed the main featuresof the four bisphthalocyanines, indicating the success of the synthesis of the complexes.

Context: Molecular modeling of carbon nanotubes and lanthanide double-decker phthalocyanines hybrids is challenging due to the presence of 4f-electrons. In this paper, we analyzed the trends in structural changes and electronic properties when a lanthanide (La, Gd, and Lu) bisphthalocyanine molecule is adsorbed on the surface of two single-walled carbon nanotubes (SWCNTs) models: armchair and zigzag. The density functional theory (DFT) computations showed that the height of bisphthalocyanines complexes (LnPc₂) when adsorbed on a nanotube (LnPc₂+SWCNT) is the structural feature which is most affected by the nanotube model. The formation energy of the LnPc₂+SWCNT hybrid depends on the metal atom and the nanotube chirality. LaPc₂ and LuPc₂ bind stronger to the zigzag nanotube, while for GdPc₂, bonding to the armchair nanotube is the stronger one. The HOMO-LUMO gap energy (Egap) shows a correlation between the nature of lanthanide and the nanotube chirality. In the case of adsorption on armchair nanotube, E_gap tends to match the gap of isolated LnPc₂, whereas for adsorption on the zigzag nanotube, it is closer to the value for the isolated nanotube model. The spin density is localized on the phthalocyanines ligands (plus on Gd in the case of GdPc₂), when the bisphthalocyanine is adsorbed on the surface of the armchair nanotube. For bonding to zigzag nanotube (ZNT), it extends over both components, except for LaPc₂+ZNT, where spin density is found on the nanotube only. Method: All DFT calculations were carried out using the DMol³ module of Material Studio 8.0 software package from Accelrys Inc. The computational technique chosen was the general gradient approximation functional PBE in combination with a long-range dispersion correction developed by Grimme (PBE-D2), the double numerical basis set DN, and the DFT semi-core pseudopotentials.

This work reports the facile preparation of single‐walled carbon nanotubes (SWCNTs) noncovalently functionalized with 3d transition metal (II) phthalocyanines MPcs (M=Mn, Fe, Co and Ni) and their electrochemical evaluation towards the oxygen evolution reaction (OER) in alkaline media. The modification of SWCNTs with MPcs improved the potential required for the oxygen evolution reaction in 0.1 M and 1 M KOH by lowering the potential by approximately 120 mV in comparison with unmodified SWCNTs, at a current density of 10 mA cm⁻¹. The onset potential of the hybrids is close to the bulk Ni electrode in 1 M KOH and significantly outperforms Ni and Ir black electrodes in 0.1 M KOH solution. Nickel, cobalt and iron phthalocyanines showed auto‐activation during extended cyclic voltammetry and long‐term chronoamperometric measurements in both KOH concentrations. The excellent electrocatalytic activity of hybrids obtained and the straightforward method of their synthesis opens the possibility of exploring the proposed materials for applications in anion exchange membrane water electrolysis (AEMWE).

Unsubstituted phthalocyanines (both free-base, H2Pc, and many of its metal complexes) are among the most stable organic compounds. They can sublime without decomposition under reduced pressure and temperatures of up to 550 °C. This property was previously employed to design a novel approach to noncovalent functionalization of pristine single-walled carbon nanotubes (SWNTs) with 3d metal(II) phthalocyanine complexes. However, when we attempted to use the same sublimation protocol to prepare a SWNTs–H2Pc hybrid, an unexpected side effect of partial H2Pc pyrolysis was detected, phthalonitrile being a main decomposition product, under the conditions when H2Pc is supposed to be totally stable. By using density functional theory calculations, we offer an explanation for the thermal behavior of H2Pc based on its covalent attachment to the pentagonal-ring topological defects, which are very common in all graphene-derived carbon nanomaterials and capable of reacting with amines via nucleophilic addition process.