António Pereira

Antimicrobial Activity of Chitosan Derivatives Containing N-Quaternized Moieties in Its Backbone: A Review

Chitosan, which is derived from a deacetylation reaction of chitin, has attractive antimicrobial activity. However, chitosan applications as a biocide are only effective in acidic medium due to its low solubility in neutral and basic conditions. Also, the positive charges carried by the protonated amine groups of chitosan (in acidic conditions) that are the driving force for its solubilization are also associated with its antimicrobial activity. Therefore, chemical modifications of chitosan are required to enhance its solubility and broaden the spectrum of its applications, including as biocide. Quaternization on the nitrogen atom of chitosan is the most used route to render water-soluble chitosan-derivatives, especially at physiological pH conditions. Recent reports in the literature demonstrate that such chitosan-derivatives present excellent antimicrobial activity due to permanent positive charge on nitrogen atoms side-bonded to the polymer backbone. This review presents some relevant work regarding the use of quaternized chitosan-derivatives obtained by different synthetic paths in applications as antimicrobial agents.

Convenient Synthesis of 3-Vinyl and 3-Styryl Coumarins

A variety of 2-hydroxy aldehydes on reaction with 3-butenoic acid afford in a one-pot reaction the corresponding 3-vinylcoumarins. As expected, extension of the delocalized π-electron system accomplished by Heck coupling reactions with aryl halides results in an increased fluorescence of the compounds whose applicability is yet to be established.

New indole alkaloids from Sarcocephalus latifolius.

Abstract Phytochemical investigation of the root extract of Sarcocephalus latifolius has led to the isolation of the new indole alkaloids 21-O-methylstrictosamide aglycone and 21-O-ethylstrictosamide aglycone, together with strictosamide, angustine, nauclefine, angustidine, angustoline, 19-O-ethylangustoline, naucleidinal, 19-epi-naucleidinal, quinovic acid-3β-O-β-D-fucopyranoside, quinovic acid-3β-O-α-L-rhamnopyranoside, scopoletin, and β-sitosterol. Strictosamide displayed moderate antiplasmodial activity against Plasmodium falciparum.

Fast dye removal from water by starch-based nanocomposites.

Robust and efficient methylene blue (MB) adsorbent was prepared based on starch/cellulose nanowhiskers hydrogel composite. Maximum MB adsorption capacity of ∼2050mgperg of dried hydrogel was obtained with the composite at 5wt.% of cellulose nanowhiskers and at pH 5. Adsorption capacity varied from 1450mg/g to 2050mg/g with increasing the initial MB concentration from 1500mg/L to 2500mg/L, respectively. For all the concentrations studied ca. 90% of MB was removed by the adsorbent. Optimal conditions were obtained at pH⩾5 due to the generation of negatively charged groups (COO(-)) in the adsorbent, which can strongly interact with the positive charges from MB. The main advantage of this system over other reported adsorbents, besides the fact of being synthesized from biodegradable polymers (starch and cellulose), is its fast adsorption kinetics that follows the pseudo-second order model, which is based on chimisorption phenomenon. Saturation condition was reached as fast as 1h of experiments owing to the formation of an adsorbed MB monolayer as suggested by the Langmuir isotherm model. Desorption experiments showed 60wt.% of MB loaded can be removed from the adsorbent by immersing it in a pH 1 solution, showing its feasibility to be reused. Therefore, starch/cellulose nanowhiskers hydrogel composite presents outstanding capacity to be employed in the remediation of MB contaminated wastewaters.

Cellulose nanowhiskers improve the methylene blue adsorption capacity of chitosan- g -poly(acrylic acid) hydrogel

Cellulose nanowhiskers (CNWs, 90% crystalline) were used to enhance the adsorption capacity of chitosan-g-poly(acrylic acid) hydrogel. The composites up to 20w/w-% CNWs showed improved adsorption capacity towards methylene blue (MB) as compared to the pristine hydrogel. At 5w/w-% CNWs the composite presented the highest adsorption capacity (1968mg/g). The maximum removal of MB (>98% of initial concentration 2000mg/L) was achieved quickly (60min) at room temperature, pH 6, and at low ionic strength (0.1M). Adsorption mechanism was explained with the Langmuir type I model suggesting the formation of a MB monolayer on the adsorbent surface. The interaction between the adsorbent and MB molecules was explained by chemisorption, as suggested by the pseudo-second-order kinetic model. Desorption experiments showed that 75% of loaded-MB could be recovered from the adsorbent by its immersion in a pH 1 solution. Additional experiments showed the post-utilized composite could be regenerated and reused for at least 5 consecutive adsorption/desorption cycles with minimum efficiency loss (∼2%).

Effects of strictosamide on mouse brain and kidney Na+,K+-ATPase and Mg2+-ATPase activities

Present study reports on the general bioactivity of strictosamide and on its effects on Na(+),K(+)-ATPase and Mg(2+)-ATPase activities of Charles River male mouse. Strictosamide is the main glycoalkaloid of Sarcocephalus latifolius (Rubiaceae) leaves and roots, used as medicinal plant in folk medicine. In this work, we studied the in vitro effects of various concentrations of strictosamide (0.25, 0.5, 1 or 2 mg/mL) and the in vivo effects of single doses (50, 100 or 200 mg/kg, i.p.) of this compound on kidney and brain Na(+),K(+)-ATPase and Mg(2+)-ATPase activities. Results of general study showed that strictosamide is slightly toxic to Charles River mouse (LD(50)=723.17 mg/kg), producing CNS depression and kidney toxicity, but the exact mechanism of these effects could not be defined. Strictosamide inhibited the in vitro and in vivo Mg(2+)-ATPase activity on kidney but had nonsignificant effect on brain. Furthermore, strictosamide had nonsignificant in vitro and in vivo effect on kidney Na(+),K(+)-ATPase activity but produced an in vivo increase of Na(+),K(+)-ATPase activity of brain, these findings suggesting that strictosamine may be related to the induction of alpha(2) isoform of Na(+),K(+)-ATPase and may account for the folk use of Sarcocephalus latifolius root infusion on hypertension.

Characterisation of a sugar fraction from Sarcocephalus latifolius stem bark extract

Abstract The stem bark extract of the medicinal plant Sarcocephalus latifolius was analysed for its qualitative and quantitative carbohydrate content. Preparative high-performance liquid chromatography (HPLC) of the benzoylated sugar fraction, led to the isolation of d -fructose derivatives 1,2,3,4,6-penta- O -benzoyl-α- d -fructofuranose, 1,2,3,4,6-penta- O -benzoyl-β- d -fructofuranose, 1,2,3,4,5-penta- O -benzoyl-β- d -fructopyranose, and 1,3,4,5-tetra- O -benzoyl-β- d -fructopyranose, in addition to α- and β- d -pyranose forms of glucose, xylose, and arabinose perbenzoates, glycerol and d -erythriol perbenzoates, and an inseparable mixture of methyl 1,3,4,6-tetra- O -benzoyl-α,β- d -fructofuranoside, whose occurrence has never been previously reported from a natural source. The corresponding structures and conformations were fully characterised by extensive one and two-dimensional nuclear magnetic resonance (NMR) experiments. Quantification of the natural free sugars in the extract was achieved by HPLC using refractive-index detection.

Gaining insight into the photophysical properties of a coumarin STP ester with potential for bioconjugation

The photophysical properties of a coumarin 392 4-sulfotetrafluorophenyl ester, C392STP (sodium (E/Z)-4-(4-(2-(6,7-dimethoxycoumarin-3-yl)vinyl)-benzoyl)-2,3,5,6-tetrafluoro-benzenesulfonate), an amine reactive coumarin with potential for bioconjungation, have been studied in different solvents. When increasing the solvent polarity, strong red shifts (31 to 56 nm on going from dioxane to DMSO and PBS, respectively) were observed in the emission spectra while there were minor changes in the absorption spectra. It was found that in addition to non-specific solute–solvent interactions, in protic solvents specific interactions such as hydrogen-bonding occurred. The photophysical behaviour of coumarin also pointed to an increase of the polarity of the molecule upon excitation. The molar absorption coefficient, e385 = 1.03 × 104 M−1 cm−1, and brightness, e × Φ = 1.18 × 103 M−1 cm−1, of the coumarin ester were found to be moderate in PBS even if the fluorescence quantum yield (Φ = 0.115) was found to be relatively low. The large Stokes shifts (Δλ = λem − λabs was found to increase from 74 nm in dioxane to 136 nm in PBS), photostability and pH insensitivity are characteristics that turn C392STP into a promising fluorescent dye with potential applications in different fields.

Tortoiseshell or Polymer? Spectroscopic Analysis to Redefine a Purported Tortoiseshell Box with Gold Decorations as a Plastic Box with Brass.

The study and preservation of museum collections requires complete knowledge and understanding of constituent materials that can be natural, synthetic, or semi-synthetic polymers. In former times, objects were incorporated in museum collections and classified solely by their appearance. New studies, prompted by severe degradation processes or conservation-restoration actions, help shed light on the materiality of objects that can contradict the original information or assumptions. The selected case study presented here is of a box dating from the beginning of the 20th century that belongs to the Portuguese National Ancient Art Museum. Museum curators classified it as a tortoiseshell box decorated with gold applications solely on the basis of visual inspection and the information provided by the donor. This box has visible signs of degradation with white veils, initially assumed to be the result of biological degradation of a proteinaceous matrix. This paper presents the methodological rationale behind this study and proposes a totally non-invasive methodology for the identification of polymeric materials in museum artifacts. The analysis of surface leachates using 1H and 13C nuclear magnetic resonance (NMR) complemented by in situ attenuated total reflection infrared spectroscopy (ATR FT-IR) allowed for full characterization of the object s substratum. The NMR technique unequivocally identified a great number of additives and ATR FT-IR provided information about the polymer structure and while also confirming the presence of additives. The pressure applied during ATR FT-IR spectroscopy did not cause any physical change in the structure of the material at the level of the surface (e.g., color, texture, brightness, etc.). In this study, variable pressure scanning electron microscopy (VP-SEM-EDS) was also used to obtain the elemental composition of the metallic decorations. Additionally, microbiologic and enzymatic assays were performed in order to identify the possible biofilm composition and understand the role of microorganisms in the biodeterioration process. Using these methodologies, the box was correctly identified as being made of cellulose acetate plastic with brass decorations and the white film was identified as being composed mainly of polymer exudates, namely sulphonamides and triphenyl phosphate.

An Evaluation Of Parchments' Degradation A Hybrid Approach.

Parchment stands for a multifaceted material made from animal skin, which has been used for centuries as a writing support or as bookbinding. Due to the historic value of objects made of parchment, understanding their degradation and their condition is of utmost importance to archives, libraries and museums, i.e., the assessment of parchment degradation is mandatory, although it is hard to do with traditional methodologies and tools for problem solving. Hence, in this work we will focus on the development of a hybrid decision support system, in terms of its knowledge representation and reasoning procedures, under a formal framework based on Logic Programming, complemented with an approach to computing centered on Artificial Neural Networks, to evaluate Parchment Degradation and the respective Degree-of-Confidence that one has on such a happening.