Unravelling the structure of chemisorbed CO2 species in mesoporous aminosilicas: a critical survey

Chemisorbent materials, based on porous aminosilicas, are among the most promising adsorbents for direct air capture applications, one of the key technologies to mitigate carbon emissions. Herein, a critical survey of all reported chemisorbed CO2 species, which may form in aminosilica surfaces, is performed by revisiting and providing new experimental proofs of assignment of the distinct CO2 species reported thus far in the literature, highlighting controversial assignments regarding the existence of chem- isorbed CO2 species still under debate. Models of carbamic acid, alkylammonium carbamate with different conformations and hydrogen bonding arrangements were ascertained using density functional theory (DFT) methods, mainly through the comparison of the experimental 13C and 15N NMR chemical shifts with those obtained computationally. CO2 models with variable number of amines and silanol groups were also evaluated to explain the effect of amine aggregation in CO2 speciation under confinement. In addition, other less commonly studied chemisorbed CO2 species (e.g., alkylammonium bicarbonate, ditethered carbamic acid and silylpropylcarbamate), largely due to the difficulty in obtaining spectroscopic identification for those, have also been investigated in great detail. The existence of either neutral or charged (alkylammonium siloxides) amine groups, prior to CO2 adsorption, is also addressed. This work extends the molecular-level understanding of chemisorbed CO2 species in amine-oxide hybrid surfaces showing the benefitof integrating spectroscopy and theoretical approaches.publishe

Interacções intermoleculares fracas em materiais funcionais avançados: um estudo espectroscópico e computacional

Doutoramento em QuímicaA utilização combinada de espectroscopia vibracional e de cálculos envolvendo a teoria do funcional de densidade (DFT) possibilita o estudo de ligações de hidrogénio em fase condensada, assim como a análise da estrutura molecular dos sistemas em estudo. Por um lado, a espectroscopia vibracional permite a detecção de associações moleculares, enquanto os métodos computacionais auxiliam na obtenção de informação referente aos mecanismos de associação, nomeadamente no que diz respeito à possível estrutura de dímeros e compostos de inclusão em ciclodextrinas e às energias de interacção e de inclusão. O estudo que originou a presente dissertação pretende contribuir para o reforço da aplicação de estudos espectroscópicos e computacionais na elucidação de diversos fenómenos químicos, com especial destaque para o papel desempenhado por interacções intermoleculares fracas na estrutura e propriedades de materiais moleculares. No âmbito desta tese foram investigados os seguintes tópicos: polimorfismo e pseudopolimorfismo em sólidos farmacêuticos, transições de fase em misturas binárias de ácidos gordos, inclusão em ciclodextrinas, interacção de compostos farmacêuticos com superfícies metálicas e formação de agregados de água em materiais híbridos orgânicos-inorgânicos. Os sistemas foram analisados utilizando a espectroscopia vibracional – particularmente a espectroscopia de difusão de Raman – como técnica fundamental. Para uma melhor caracterização de processos envolvendo transições de fase, foram efectuados estudos com variação de temperatura, variação de humidade relativa e substituição isotópica. O estudo da interacção com superfícies metálicas foi realizado por espectroscopia de Raman intensificada à superfície. Dada a complexidade dos sistemas em estudo, a informação obtida por espectroscopia vibracional foi complementada por resultados de cálculos mecânico-quânticos. Em particular, os cálculos DFT foram utilizados para a optimização de geometrias e previsão de frequências vibracionais de moléculas e associações moleculares, permitindo assim a análise e interpretação de espectros vibracionais e a caracterização da estrutura de materiais.The characterisation of hydrogen bonds in condensed phase and analysis of molecular structure for several systems is possible combining the use of vibrational spectroscopy and DFT calculations. While vibrational spectroscopic techniques allow the detection of molecular associations, computational methods help assemble information regarding association mechanisms, especially viable dimer structures and inclusion compounds in cyclodextrins (interaction and inclusion energies). The research work developed throughout the course of the present thesis aims to strengthen the application of spectroscopic and computational studies in the elucidation of several chemical phenomena, with special emphasis on the role of weak intermolecular interactions in the structure and properties of molecular materials. The following topics were explored: polymorphism and pseudopolymorphism in pharmaceutical solids, phase transitions in binary mixtures of fatty acids, inclusion compounds in cyclodextrins, interaction of pharmaceutical drugs with metal surfaces and formation of water clusters in hybrid organic-inorganic materials. The aforementioned systems were analysed using vibrational spectroscopy – mainly Raman spectroscopy – as a fundamental tool. In order to improve global understanding of processes involving phase transition, several studies were performed with temperature variation, relative humidity variation and isotopic substitution. The study of the interaction with metal surfaces was performed using surface-enhanced Raman spectroscopy. Due to the complexity of the systems, the information obtained from vibrational spectroscopy was complemented by results provided by mechanical-quantum methods. In particular, DFT calculations were used in order to optimise geometries and predict vibrational frequencies of molecules and molecular associations, promoting the analysis and interpretation of vibrational spectra and the structural characterisation of materials

O coração de Valverdinho

Esta dissertação pretende dar a conhecer mais um exemplo de arquitetura vernacular em território nacional, a aldeia de Valverdinho, esquecida no tempo e na memória, contribuindo para a valorização da herança construída de forma anónima. Inserido numa região afetada pelo despovoamento e pela desertificação ao longo das últimas décadas (na beira interior), o seu potencial tanto de valor natural como construído, merece ser preservado, recuperado e explorado, nas vertentes económicas, culturais e ambientais, podendo assim contribuir para o desenvolvimento da economia local, no combate à centralização do litoral e dos principais centros urbanos. Assim, a aldeia é o objeto de estudo nesta dissertação, no sentido de compreender e analisar, num contexto teórico e prático, os elementos arquitetónicos deste conjunto edificado. A partir de um levantamento fotográfico e topográfico, de uma análise in situ, e a partir de registos históricos e documentais, é elaborado uma análise morfológica do lugar e uma análise tipológica dos edifícios integrantes, compreendendo a sua génese, forma e função. Propõe-se também uma proposta com soluções adequadas para a sua revitalização e que preserve a memória do património construído.This dissertation intends to make known another example of vernacular architecture in national territory, the village of Valverdinho, forgotten in time and memory, contributing to the valorization of the anonymously built heritage. Located in a region affected by depopulation and desertification over the last decades (in the interior), its potential of both natural and built value, deserves to be preserved, recovered and exploited, in the economic, cultural and environmental aspects, to being able to contribute to the development of the local economy, in the fight against centralization of the coast and of the main urban centers. Therefore, the village is the object of study in this dissertation, in the sense of understanding and analyzing, in a theoretical and practical context, the architectural elements of this built set. From a photographic and topographic survey, from an in situ analysis, and from historical and documentary records, a morphological analysis of the place and a typological analysis of the integrating buildings are elaborated, including their genesis, form and function. It is also proposed a plan with appropriate solutions for its revitalization and that preserves the memory of the built heritage

Exploring Molecular Dynamics of Adsorbed CO2 Species in Amine-Modified Porous Silica by Solid-State NMR Relaxation

Previous studies on CO2 adsorbents have mainly addressed the identification and quantification of adsorbed CO2 species in amine-modified porous materials. Investigation of molecular motion of CO2 species in confinement has not been explored in depth yet. This work entails a comprehensive study of molecular dynamics of the different CO2 species chemi- and physisorbed at amine-modified silica materials through the determination of the rotating frame spin-lattice relaxation times (T 1ρ) by solid-state NMR. Rotational correlation times (τC) were also estimated using spin relaxation models based on the Bloch, Wangsness, and Redfield and the Bloembergen-Purcell-Pound theories. As expected, the τC values for the two physisorbed CO2 species are considerably shorter (32 and 20 μs) than for the three identified chemisorbed CO2 species (162, 62, and 123 μs). The differences in molecular dynamics between the different chemisorbed species correlate well with the structures previously proposed. In the case of the physisorbed CO2 species, the τC values of the CO2 species displaying faster molecular dynamics falls in the range of viscous liquids, whereas the species presenting slower dynamics exhibit T 1ρ and τC values compatible with a CO2 layer of weakly interacting molecules with the silica surface. The values for chemical shift anisotropy (CSA) and 1H-13C heteronuclear dipolar couplings have also been estimated from T 1ρ measurements, for each adsorbed CO2 species. The CSA tensor parameters obtained from fitting the relaxation data agree with the experimentally measured CSA values, thus showing that the theories are well suited to study CO2 dynamics in silica surfaces.publishe

Amnésia global transitória: uma síndrome enigmática

A amnésia global transitória (AGT) é uma síndrome clínica que cursa com incapacidade de formar novas memórias e que pode durar até 24 horas. Este estado de amnésia desaparece de forma gradual, sem qualquer tratamento e, aparentemente, sem deixar sequelas. Relativamente à sua etiologia, a AGT permanece como uma entidade mal compreendida. Nesta revisão será apresentada uma perspetiva atual acerca dos fatores de risco, desencadeantes, fisiopatologia e abordagem ao doente com AGT. Para a elaboração deste artigo revisão, foram selecionados 290 artigos através de uma pesquisa na PubMed com termo "Transient global amnesia". A pesquisa foi limitada a artigos escritos em inglês e publicados a partir de 2010. A estes foram acrescentados artigos da área frequentemente citados, ainda que não selecionados a partir da pesquisa inicial, que os autores consideraram relevantes. Os resultados deste estudo indicam que a incidência de AGT é semelhante entre os sexos feminino e masculino. Porém, o fator idade parece ser preponderante, dado estes episódios serem mais frequentes entre indivíduos acima dos 50 anos de idade. Foram também apontadas associações epidemiológicas a diversos fatores, tais como, história de enxaqueca, manobra de Valsalva a preceder o episódio e patologia psiquiátrica. Contudo, nenhum destes fatores está universalmente presente. A AGT permanece um diagnóstico essencialmente clínico. Os estudos de neuro-imagem poderão ser utilizados sobretudo em contexto de urgência, nomeadamente, para diagnóstico diferencial com patologia vascular, e em contexto de projetos de investigação. A fisiopatologia da AGT é tema de grande controvérsia e fonte de diversas hipóteses explicativas. A disfunção do hipocampo é globalmente reconhecida como mecanismo subjacente aos vários modelos conceptuais descritos. Devido ao curso autolimitado da AGT, a abordagem ao doente implica a vigilância clínica até à resolução dos sintomas e a sua explicação ao doente e familiares ou cuidadores. Em suma, a AGT é um fenómeno de caráter aparentemente benigno e recorrência rara. Para uma melhor abordagem a estes doentes e possível prevenção destes episódios, este estudo realça a necessidade de investigação adicional acerca da sua etiologia e eventuais efeitos a longo-prazo. Palavras-chave: Amnésia; Amnésia global transitória; Hipocampo; Memória; Cognição; Doenças cognitivasTransient global amnesia (TGA) is a clinical syndrome characterized by an inability to form new memories. This amnesic state can last up to 24 hours and gradually disappears without any treatment and with no sequels left. Concerning its etiology, TGA still remains poorly understood. In this review, an updated perspective regarding TGA risk factors, triggers, pathophysiology and patient management will be presented. For this review, 290 articles were selected. A PubMed literature research was conducted with the term "Transient global amnesia" and was limited to publications written in English since 2010. Additionally, relevant articles referenced in the initial database were also included. The results indicate that TGA incidence between genders is equivalent. However, the age of the individuals has shown to be a major risk factor since this condition affects predominantly people over 50 years old. Several other epidemiologic correlations to TGA were found such as migraine history, Valsalva maneuver preceding an episode and psychiatric disorders. Nevertheless, none of these factors is consistently present. The TGA diagnosis is essentially clinical. Neuroimaging studies may be used particularly in emergency department context for the differential diagnosis with vascular disease and for research projects. The TGA pathophysiology is a very controversial topic and has led to a vast diversity of explanatory hypothesis. Hippocampus dysfunction is globally recognized as the underlying mechanism to all the conceptual models described so far. Due to its self-limited course, patient management requires clinical vigilance until complete resolution of symptoms and providence of explanations to the patients and their family or care-givers. In conclusion, TGA is considered a benign entity with a low recurrence rate. In order to improve these patients management and to prevent future episodes, this study highlights that further investigation is needed concerning its etiology and potential long-term effects. Key words: Amnesia; Transient global amnesia; Hippocampus; Memory; Cognition; Cognitive disease

Moisture effect on the separation of CO2/CH4 mixtures with amine-functionalised porous silicas

The effect of minor amounts of water on the CO2 and CH4 adsorption on primary and secondary amine-functionalised mesoporous silicas (APTES@SBA-15 and DEAPTES@SBA15, respectively) was studied with a combination of high-pressure gas adsorption, solid state NMR of labelled 13CO2 and density functional theory (DFT) calculations. Known amounts of water were pre-adsorbed on the materials (0.047 to 0.157 mmol∙g−1) and the adsorption performance for CO2 and CH4 was compared to the performance of the dry samples. We observed that even when only minor amounts of water are present, the tertiary amine-functionalised material revealed a significant enhancement of the selectivity for CO2 (from ca. 5.8 to 208) while the one with primary amine maintained the same adsorption properties. This is related to the change in the adsorption mechanism in DEAPTES@SBA15 when water is present since water participates in the reaction of the tertiary amine with CO2 to produce bicarbonate (confirmed by NMR and DFT results). Such species was not observed in APTES@SBA-15 with water. From a broader perspective, the results presented in this work are relevant to confirm the suitability of this type of hybrid adsorbents in industrial applications related with CO2 adsorption, where minor amounts of water may be present in the process streams, such as during bio, landfill, or natural gas upgrading, or also in carbon capture applications.publishe

PAIN with and without PAR: variants for third-spin assisted heteronuclear polarization transfer

In this article, we describe third-spin assisted heteronuclear recoupling experiments, which play an increasingly important role in measuring long-range heteronuclear couplings, in particular 15N-13C, in proteins. In the proton-assisted insensitive nuclei cross polarization (PAIN-CP) experiment (de Paëpe et al. in J Chem Phys 134:095101, 2011), heteronuclear polarization transfer is always accompanied by homonuclear transfer of the proton-assisted recoupling (PAR) type. We present a phase-alternating experiment that promotes heteronuclear (e.g. 15N→13C) polarization transfer while simultaneously minimizing homonuclear (e.g.13C→13C) transfer (PAIN without PAR). This minimization of homonuclear polarization transfer is based on the principle of the resonant second-order transfer (RESORT) recoupling scheme where the passive proton spins are irradiated by a phase-alternating sequence and the modulation frequency is matched to an integer multiple of the spinning frequency. The similarities and differences between the PAIN-CP and this het-RESORT experiment are discussed her

Engineering phosphatidylinositol-4,5-bisphosphate model membranes enriched in endocytic cargo: a neutron reflectometry, AFM and QCM-D structural study

The combination of in vitro models of biological membranes based on solid-supported lipid bilayers (SLBs) and of surface sensitive techniques, such as neutron reflectometry (NR), atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D), is well suited to provide quantitative information about molecular level interactions and lipid spatial distributions. In this work, cellular plasma membranes have been mimicked by designing complex SLB, containing phosphatidylinositol 4,5-bisphosphate (PtdIns4,5P2) lipids as well as incorporating synthetic lipo-peptides that simulate the cytoplasmic tails of transmembrane proteins. The QCM-D results revealed that the adsorption and fusion kinetics of PtdIns4,5P2 are highly dependent of Mg2+. Additionally, it was shown that increasing concentrations of PtdIns4,5P2 leads to the formation of SLBs with higher homogeneity. The presence of PtdIns4,5P2 clusters was visualized by AFM. NR provided important insights about the structural organization of the various components within the SLB, highlighting that the leaflet symmetry of these SLBs is broken by the presence of CD4-derived cargo peptides. Finally, we foresee our study to be a starting point for more sophisticated in vitro models of biological membranes with the incorporation of inositol phospholipids and synthetic endocytic motifs.publishe

Potentiation of 5-fluorouracil encapsulated in zeolites as drug delivery systems for in vitro models of colorectal carcinoma

The studies of potentiation of 5-fluorouracil (5-FU), a traditional drug used in the treatment of several cancers, including colorectal (CRC), were carried out with zeolites Faujasite in the sodium form, with different particle sizes (NaY, 700nm and nanoNaY, 150nm) and Linde type L in the potassium form (LTL) with a particle size of 80nm. 5-FU was loaded into zeolites by liquid-phase adsorption. Characterization by spectroscopic techniques (FTIR, 1H NMR and 13C and 27Al solid-state MAS NMR), chemical analysis, thermal analysis (TGA), nitrogen adsorption isotherms and scanning electron microscopy (SEM), demonstrated the successful loading of 5-FU into the zeolite hosts. In vitro drug release studies (PBS buffer pH 7.4, 37°C) revealed the release of 80-90% of 5-FU in the first 10min. To ascertain the drug release kinetics, the release profiles were fitted to zero-order, first-order, Higuchi, Hixson-Crowell, Korsmeyer-Peppas and Weibull kinetic models. The in vitro dissolution from the drug delivery systems (DDS) was explained by the Weibull model. The DDS efficacy was evaluated using two human colorectal carcinoma cell lines, HCT-15 and RKO. Unloaded zeolites presented no toxicity to both cancer cells, while all DDS allowed an important potentiation of the 5-FU effect on the cell viability. Immunofluorescence studies provided evidence for zeolite-cell internalization.RA is recipient of fellowship SFRH/BI/51118/2010 from Fundacao para a Ciencia e a Tecnologia (FCT, Portugal). This work was supported by the FCT projects refs. PEst-C/QUI/UI0686/2011 and PEst-C/CTM/LA0011/2011 and the Centre of Chemistry and Life and Health Sciences Research Institute (University of Minho, Portugal). The NMR spectrometer is part of the National NMR Network (RNRMN), supported with funds from FCT/QREN (Quadro de Referencia Estrategico Nacional)

Water-Soluble Polymeric Carbon Nitride Colloidal Nanoparticles for Highly Selective Quasi-Homogeneous Photocatalysis

Heptazine‐based polymeric carbon nitrides (PCN) are promising photocatalysts for light‐driven redox transformations. However, their activity is hampered by low surface area resulting in low concentration of accessible active sites. Herein, we report a bottom‐up preparation of PCN nanoparticles with a narrow size distribution (ca. 10±3 nm), which are fully soluble in water showing no gelation or precipitation over several months. They allow photocatalysis to be carried out under quasi‐homogeneous conditions. The superior performance of water‐soluble PCN, compared to conventional solid PCN, is shown in photocatalytic H2O2 production via reduction of oxygen accompanied by highly selective photooxidation of 4‐methoxybenzyl alcohol and benzyl alcohol or lignocellulose‐derived feedstock (ethanol, glycerol, glucose). The dissolved photocatalyst can be easily recovered and re‐dissolved by simple modulation of the ionic strength of the medium, without any loss of activity and selectivity.This work was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Projektnummer 364549901—TRR 234 [Projects B6, B7, C3 and Z2] and BE 5102/3‐1. We acknowledge also support by Spanish MINECO (MAT2016‐78155‐C2‐1‐R) and Gobierno del Principado de Asturias (GRUPIN‐ID2018‐170), and the project CICECO‐Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. L.M., M.S., and M.I. also acknowledge the National NMR Network (PTNMR), partially supported by Infrastructure Project N° 022161, and FCT/MCTES for funding (Project PTDC/QEQ‐QAN/6373/2014). B.K. acknowledges the University of Iceland Research Fund for support through a PhD fellowship. Computational resources were provided by the state of Baden‐Württemberg through bwHPC and the German Science Foundation (DFG) under Grant No. INST 40/467‐1 FUGG. C.N. and A.T. acknowledge financial support of the DFG through the project TU 149/8‐2 “Towards photo‐active membranes for artificial photosynthesis” as well as the DFG through a research infrastructure grant INST 275/257‐1 FUGG. I.K. acknowledges the support of the Alexander von Humboldt Foundation through the Humboldt Research Fellowship.Peer reviewe