Dynamic Penetration Profile of Starch Betainate, Pluronics and PCC Coated Papers

Despite changes in optical and printing properties, the applied coating components on the paper surface have a significant impact on the surface chemistry of office paper. Depending on the use, such as ink penetration for printing and writing papers, an optimal hydrophobic and hydrophilic balance may be beneficial. In this study, several coating components including starch betainate, Pluronics, and precipitated calcium carbonate were employed to coat base paper (paper without any surface treatment). The influence of these components on water penetration was investigated using dynamic penetration. When compared to native starch coated papers, paper coated with starch betainate (a cationic starch ester) showed reduction in hydrophobicity and increased water penetration. Moreover, this effect was further enhanced with the use of Pluronics. Likewise, hydrophobicity decreased as the concentration of starch betainate, precipitated calcium carbonate and Pluronics increased. Furthermore, water penetrated even more quickly when the combination of these components compared with the individual component coatings. Keywords: hydrophobicity, PCC, Pluronics, starch betainate, water penetratio

A comparative study of reactivity and selectivity of chiral diamines and structurally analogous amino alcohol ligands in enantioselective alkylations with diethylzinc

A series of chiral delta-diamines and structurally analogous delta-amino alcohols derived from natural tartaric acid were synthesized and a comparative study of their activity and selectivity in the enantioselective alkylation of aromatic aldehydes was carried out. Our results show that in general the delta-diamines were found to be better chiral inducers than the corresponding delta-amino alcohols. The highest selectivity was observed when benzaldehyde was alkylated in the presence of the benzylic diamine, giving (R)-1-phenylpropanol with an ee of 42%. Copyright © 2008 John Wiley & Sons, Ltd

β-ketoenamine covalent organic frameworks—effects of functionalization on pollutant adsorption

Water pollution due to global economic activity is one of the greatest environmental concerns, and many efforts are currently being made toward developing materials capable of selectively and efficiently removing pollutants and contaminants. A series of β-ketoenamine covalent organic frameworks (COFs) have been synthesized, by reacting 1,3,5-triformylphloroglucinol (TFP) with different C2-functionalized and nonfunctionalized diamines, in order to evaluate the influence of wall functionalization and pore size on the adsorption capacity toward dye and heavy metal pollutants. The obtained COFs were characterized by different techniques. The adsorption of methylene blue (MB), which was used as a model for the adsorption of pharmaceuticals and dyes, was initially evaluated. Adsorption studies showed that –NO2 and –SO3H functional groups were favorable for MB adsorption, with TpBd(SO3H)2-COF [100%], prepared between TFP and 4,4′-diamine- [1,1′-biphenyl]-2,2′-disulfonic acid, achieving the highest adsorption capacity (166 ± 13 mg g−1). The adsorption of anionic pollutants was less effective and decreased, in general, with the increase in –SO3H and –NO2 group content. The effect of ionic interactions on the COF performance was further assessed by carrying out adsorption experiments involving metal ions. Isotherms showed that nonfunctionalized and functionalized COFs were better described by the Langmuir and Freundlich sorption models, respectively, confirming the influence of functionalization on surface heterogeneity. Sorption kinetics experiments were better adjusted according to a second-order rate equation, confirming the existence of surface chemical interactions in the adsorption process. These results confirm the influence of selective COF functionalization on adsorption processes and the role of functional groups on the adsorption selectivity, thus clearly demonstrating the potential of this new class of materials in the efficient and selective capture and removal of pollutants in aqueous solutions.This work was funded by the Coimbra Chemistry Centre (CQC), which is supported by the Fundação para a Ciência e a Tecnologia (FCT), Portugal, through the grants ref. UID/QUI/00313/2020 and ref. UI/BD/150809/2020, co-funded by COMPETE2020-UE

Desenvolvimento de novos catalisadores quirais para alquilação e redução

Tese de doutoramento em Química (Síntese Orgânica) apresentada à Fac. Ciências e Tecnologia de CoimbraO plano de trabalho que deu lugar a esta dissertação visava o desenvolvimento de novos catalisadores quirais adequados a processos catalíticos enantiosselectivos de alquilação e redução de aldeídos e cetonas. São processos que permitem obter álcoois secundários quirais (com ou sem aumento da cadeia carbonada), compostos com largo espectro de aplicação, nomeadamente como materiais de partida para a síntese de compostos biologicamente activos. A primeira parte deste trabalho dirigiu-se à concepção de estruturas e ao estabelecimento de sequências sintéticas simples adequadas à obtenção de novos catalisadores quirais, partindo de precursores de baixo custo. Concentrámo-nos portanto na exploração de compostos naturais quirais acessíveis, como o ácido (+)-canfórico, o ácido L-tartárico ou seus derivados, o ácido L-málico, etc. Sobre estes e outros compostos, como a D-pantolactona e o ácido L-citramálico, efectuámos modificações estruturais que conduzissem a ligandos com várias funcionalidades como diaminas, aminossulfonamidas, dissulfonamidas, dióis e aminoálcoois. Os ligandos desenvolvidos, alguns novos, outros já conhecidos, foram ensaiados em reacções de alquilação de aldeídos e na redução de cetonas. As alquilações foram efectuadas centrando-se na utilização de dietilzinco como reagente alquilante e benzaldeído como substrato modelo. Alguns dos ligandos, em função das suas características electrónicas, foram estudados na alquilação catalisada por um ácido de Lewis, Ti(O^i Pr)4. As condições de reacção (na presença ou ausência do reagente de titânio) foram optimizadas, nomeadamente no que respeita à temperatura e solvente. De entre os vários ligandos estudados as di-hidroxipirrolidinas (que são β-aminoálcoois) foram os que apresentaram melhores resultados na alquilação com dietilzinco e excessos enantioméricos que atingiram valores de 74%. O nosso melhor ligando foi ensaiado com outros substratos aromáticos, tendo-se verificado que grupos dadores de electrões no anel conduzem a ee da mesma ordem de grandeza dos obtidos com o benzaldeído e que grupos sacadores de electrões originam uma diminuição considerável do ee. Com o objectivo de obter melhores ee e esclarecer qual o efeito da presença do segundo grupo hidroxilo, das di-hidroxipirrolidinas, nas reacções de alquilação, estudou-se um conjunto de outros ligandos de estrutura análoga, com apenas um grupo hidroxilo. Neste conjunto incluíam-se ligandos derivados do ácido málico com diferentes substituintes no nitrogénio do anel pirrolidínico (grupos benzilo, naftilmetilo e1-feniletilo – de configuração R e S). Verificámos que os ee eram inferiores aos da di-hidroxipirrolidinas, o que nos permitiu concluir que a presença do segundo hidroxilo é importante para uma boa indução de quiralidade. Sintetizámos ainda dois novos ligandos com maior impedimento no anel da pirrolidina, um derivado da pantolactona, com dois grupos metilo no carbono 4 do anel, e outro derivado do ácido citramálico, com um grupo metilo no carbono 3, o mesmo que contém o grupo hidroxilo. Para o primeiro ligando o ee obtido é da mesma ordem de grandeza dos obtidos com os ligandos derivados do ácido málico e para o segundo o ee é inferior, o que revela que neste caso a introdução de maior impedimento não contribuiu para uma melhoria da indução de quiralidade. Já no final deste trabalho preparámos ainda uma di-hidroxipirrolidina com um dos grupos hidroxilo protegido com metoximetano e verificámos que o ee obtido é substancialmente inferior ao obtido com o mesmo ligando, sem este grupo protegido, evidenciando que a presença do segundo grupo hidroxilo é responsável pela melhor indução de quiralidade observada para as di-hidroxipirrolidinas. Os ligandos com características mais acídicas, como as dissulfonamidas e as aminossulfonamidas, foram ensaiados na alquilação do benzaldeído na presença de Ti(O^i Pr)4. Embora as conversões obtidas com alguns destes ligandos fossem bastante elevadas, eles não se revelaram eficientes na indução de quiralidade. As dissulfonamidas, aminossulfonamidas, diaminas e dióis sintetizados não são β-funcionalizados pelo que formam quelatos de 6, 7 ou 8 membros com o metal, pouco rígidos, o que pode explicar os resultados obtidos. Os ligandos sintetizados foram também ensaiados em reacções de hidrogenação por transferência de cetonas, utilizando isopropanol como dador de hidrogénio, KOH como base e [Ru(p-cimeno)Cl2]2 como precursor metálico. Os nossos ligandos revelaram-se pouco activos, pelo que as reacções foram efectuadas a 80 ºC. Apesar disso, as conversões foram baixas ou moderadas e nenhum dos sistemas se mostrou eficiente em termos da indução de quiralidade. Ao contrário do observado nas alquilação, as di-hidroxipirrolidinas revelaram-se ligandos menos eficientes do que a hidroxipirrolidinas, quando utilizados em processos de reduçãoThe workplan which gave rise to this dissertation was intended to develop new chiral catalysts appropriate for enantioselective catalytic processes, namely alkylation of aldehydes and reduction of ketones. These processes are important and useful means of obtaining chiral secondary alcohols (with and without an increase of the carbon chain), compounds with a vast spectrum of applications, namely, as starting materials for the synthesis of biologically active products. The first part of our work involved the design of specific structures and the establishment of appropriate simple synthetic sequences which would lead to new chiral catalysts, obtained from inexpensive chiral precursors. We concentrated our efforts on exploring easily accessible chiral natural products such as (+)-camphoric acid, L-tartaric acid and its derivatives, L-malic acid, and similar ones. Using these and other starting materials, such as D-pantolactone and L-citramalic acid, we carried out structural modifications that would produce ligands with a range of functionalities, namely, diamines, aminosulfonamides, disulfonamides diols and aminoalcohols. The resulting ligands, some new, others previously described, were tested in the enantioselective alkylation of aldehydes and in the enantioselective reduction of ketones. Alkylations were carried out with diethylzinc as the alkylating agent and benzaldehyde as the model substrate. Depending on their electronic characteristics, some of the ligands required a Lewis acid catalysis, the alkylation being carried out in the presence of Ti(O^i Pr)4. Reaction conditions (with and without titanium) were optimized with regard to both temperature and solvent. Of the ligands which were object of our studies, the dihydroxypyrrolidines, b-aminoalcohols, were those which presented the best results in the enantioselective alkylations with diethylzinc, enantiomeric excesses in these cases having reached 74%. Our most efficient ligand was further tested with other aromatic aldehyde substrates. The results allowed us to conclude that electron donating substituents on the aromatic ring lead ee similar to those obtained with benzaldehyde and that electron releasing substituents cause a considerable decrease in the ee. Seeking to obtain products with higher ee, and to elucidate the effect of the presence of the second hydroxyl group on the dihydroxypyrrolidines in the alkylations, another group of structurally similar ligands with only one hydroxyl was studied. Included in this group were malic acid derivatives having different substituents on the pyrrolidine nitrogen (benzyl, naphthylmethyl, and 1-phenylethyl of R and S absolute configuration). Results showed that the ee of the products were lower than those obtained with the dihydroxypyrrolidines, which allowed us to conclude that the presence of the second hydroxyl contributes to an efficient chiral induction. We synthesized yet two more new chiral ligands with greater steric hindrance on the pyrrolidine ring, a pantolactone derivative and a citramalic acid derivative: the former, with two methyl groups on C4 of the pyrrolidine ring and the latter with a methyl group on the carbinol carbon, C3, of the pyrrolidine ring. The first ligand gave ee of the same magnitude as the malic acid derived ligands while the second ligand gave lower ee, which reveals that in this case the introduction of steric crowding did not contribute to the improvement of chiral induction. Before concluding our studies, we prepared one last ligand, a dihydroxypyrrolidine having one of the hydroxyls protected with methyoxymethane. We found that the ee obtained with this new ligand is significantly lower than that which resulted when we used the identical ligand in which both hydroxyls are free. Once again this reveals that the presence of the second hydroxyl is responsible for the more efficient induction observed when the dihydroxypyrrolidines are used. Ligands with more acidic characteristics, disulfonamides and aminosulfonamides, were tested in the alkylation of benzaldehyde in the presence of Ti(O^i Pr)4. Although high conversions were observed with some of these ligands, they were not found to be efficient in inducing chirality. The disulfonamides, aminosulfonamides and diols which we synthesized are not β-functionalized, thus implying the formation of six, seven or eight membered flexible chelates with the metal, as opposed to the rigid five memebered chelates formed by the β-functionalized ligands. This difference is possibly the explanation for our results. All the synthesized ligands were tested in the enantioselective transfer reduction of ketones, using isopropanol as the hydrogen donor, KOH as the base and [Ru(p-cymene)Cl2]2 as the active catalyst precursor. Our ligands showed poor activity, requiring the reductions to be carried out at 80ºC. Nevertheless, conversions were low or moderate and no system tested showed an efficient induction of chirality in the product. Contrary to the alkylation reaction results, in the reductions the dihydroxypyrrolidines were found to be less efficient than the hydroxypyrrolidines

Association of antioxidant monophenolic compounds with β-cyclodextrin-functionalized cellulose and starch substrates

Polysaccharide substrates loaded with antioxidant and antimicrobial compounds, effectively protected by cyclodextrin moieties, can be a long-lasting solution to confer certain properties to fabrics, paper and other materials. β-Cyclodextrin was attached to α-cellulose, bleached pulp and starch by a two-step esterification with a tetracarboxylic acid. The resulting derivatives were characterized by spectroscopy, thermal degradation analysis and capability of phenolphthalein inclusion. The carriers, containing between 89 and 171 μmol of β-cyclodextrin per gram, were loaded with carvacrol, cuminaldehyde, cinnamaldehyde and hydroxytyrosol. From a stoichiometric addition, the percentage of compound retained ranged from 49% (hydroxytyrosol in pulp-cyclodextrin) to 92% (carvacrol in starch-cyclodextrin). Finally, the release rate to aqueous ethanol was measured over eight days and fitted to kinetic models. From the analysis of the mean dissolution time, it can be concluded that inserting β-cyclodextrin units enhanced the long-term holding of phenolic active compounds in carbohydrate matrices

ONE-POT DIASTEREOSELECTIVE SYNTHESIS OF CHIRAL TRICYCLIC l-CYSTEINE AND d-PENICILLAMINE DERIVATIVES: A LABORATORY EXPERIMENT

A one-pot diastereoselective synthesis of thiazolidine-ring fused systems derived from enantiomerically pure amino acids, L-cysteine or D-penicillamine, and achiral succindialdehyde is described as an experiment to be carried out by upper-division undergraduate students in a laboratory classroom. Reactions were performed under mild conditions, the products were isolated through simple experimental procedures and fully characterized. This study combines organic synthesis, determination of the purity of compounds (TLC analysis and melting point measurements), optical activity measurements as well as structural analysis (interpretation of 1D NMR and 2D NMR spectra). It offers a platform for the discussion of important organic chemistry concepts such as diastereoselectivity, kinetic control vs thermodynamic control and cyclization reactions via nucleophilic addition to imines/iminium cations

Síntese de fotoprotetores e sua imobilização em poli(metacrilato de metilo): um projeto integrado de química orgânica, química de polímeros e fotoquímica Sunscreen synthesis and their immobilisition on polymethylmethacrylate: an integrated project in organic chemistry, polymer chemistry and photochemistry

<abstract language="eng">Dibenzalacetone and other aldol condensation products are known sunscreens commonly used in cosmetics. This type of compounds can easily be prepared in an Organic Chemistry Lab by reaction of aldehydes with ketones in basic medium. These compounds can be incorporated in poly(methyl methacrylate) and used as UV light absorbers, for example in sunglasses. This project has the advantage of using inexpensive reagents which are readily available in Chemistry Laboratories. This experiment can also be a base starting point for discussions of organic, polymer and photochemistry topics

Enantioselective trimethylsilylcyanation of benzaldehyde using pyrrolidine-based chiral salen ligands

The in situ formed Ti(IV) complexes of several pyrrolidine-based chiral salen ligands derived from natural (L)-tartaric acid were evaluated as catalysts in the enantioselective trimethylsilylcyanation of benzaldehyde. The catalysts were found to be very active, producing the corresponding product, O-trimethylsilylmandelonitrile, in high yields (>94%) and enantioselectivities of up to 88%

Diazo-coupled porous organic polymers as efficient catalysts for metal-free Henry and Knoevenagel reactions

Owing to linkage and building block diversity, Porous Organic Polymers (POPs) are versatile materials with high potential in organic catalysis. Herein, nitrogen-rich POPs bearing –OH phenolic groups were synthesized via the diazo-coupling reactions between phloroglucinol and benzidine (PgBd-POP), and between 1,3,5-tris(4-aminophenyl) triazine and 4,4’-[1,1′ -biphenyl]-4,4′ -diylbis(diazene-2,1-diyl))diphenol (TAPT-Bd(PhOH)2-POP), under mild reaction conditions. The mesoporous polymers exhibited a BET surface area of 276 ± 4 m2 g 1 and 1.94 ± 0.06 m2 g 1, and chemical stability up to 315 ◦C and 330 ◦C, respectively. Both POPs were used as catalysts in metal-free Henry and Knoevenagel condensation reactions between aromatic aldehydes and nitromethane and ethyl cyanoacetate, respectively, under mild conditions. PgBd-POP showed a remarkable efficiency of up to 99% conversion and >99% selectivity, for the Henry nitroaldol reaction between 4-nitrobenzaldehyde and nitromethane, after only 1 h at room temperature, whereas TAPT-Bd(PhOH)2-POP generally exhibited the highest catalytic activity towards the Knoevenagel reaction, with up to 99% conversion for the condensation of 4-nitrobenzaldehyde with ethyl cyanoacetate, after 1 h at room temperature. These results confirm the potential of this class of porous materials as green catalysts for organic reactions.We would like to thank Coimbra Chemistry Center (CQC), supported by the Portuguese Agency for Scientific Research, Fundaçao para a Ciencia e a Tecnologia (FCT) through grant ref. UI/BD/150809/2020, co-funded by COMPETE2020-UE, for supporting this work, and the UCNMR facility for providing the NMR data (www.nmrccc.uc.pt)

Micro-/Nanofibrillated Cellulose-Based Coating Formulations: A Solution for Improving Paper Printing Quality

The use of micro-/nanofibrillated celluloses (M/NFCs) is often considered for the enhancement of paper properties, while it is still challenging to use them in lower weight gain coatings. This work explores how they might be used on the paper surface to improve the printing quality. In this regard, M/NFCs were produced using different pre-treatment methods, including mechanical (m-MFC), enzymatic (e-MFC), TEMPO-mediated oxidation (t-NFC) and cationization (c-NFC), and uniform coating formulations were developed through the cooking of starch and M/NFCs simultaneously. The formulations, at 6–8% of total solid concentration, were applied to the paper surface by roll coating, resulting in a dry coating weight of 1.5 to 3 g/m2. Besides M/NFCs, other components such as starch betainate (a cationic starch ester; SB), Pluronics® (a triblock co-polymer), precipitated calcium carbonate (PCC) and betaine hydrochloride (BetHCl) were also used in the M/NFC-based coating formulations to observe their combined influence on the printing quality. The presence of M/NFCs improved the paper printing quality, which was further enhanced by the increase in cationic charge density due to the presence of BetHCl/SB, and also by Pluronics®. The cationic charge of c-NFC was also found to be effective for improving the gamut area and optical density of coated papers, whereas whiteness was often reduced due to the quenching of the brightening agent. BetHCl, on the other hand, improved the printing quality of the coated papers, even though it was more effective when combined with M/NFCs, PCC and Pluronics®, and also helped to retain paper whiteness.This work was carried out under the Project inpactus -innovative products and technologies from eucalyptus, Project N.º 21874 funded by Portugal 2020 through European Regional Development Fund (ERDF) in the frame of COMPETE 2020 nº246/AXIS II/2017. Authors would like to thank the Coimbra Chemical Centre, which is supported by the Fundação para a Ciência e a Tecnologia (FCT), through the projects UID/QUI/00313/2020 and COMPETE. Authors would also like to thank the CIEPQPF-Strategic Research Centre Project UIDB/00102/2020, funded by the Fundação para a Ciência e Tecnologia (FCT). M.S. acknowledges the PhD grant BDE 03|POCI-01-0247-FEDER-021874. R.A. acknowledges the post-doc grant BPD 02|POCI-01-0247-FEDER-021874