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Understanding chemical models can be challenging for many university students studying chemistry. This study analysed students' understanding of molecular structures using the Lewis structure as a model, and examined what hinders their understanding. We conducted pre- and post-tests to analyse students' conceptions and changes in them. The measures contained multiple-choice questions and drawing tasks testing their understanding of concepts, such as polarity, geometry, charge or formal charge and expanded octet. The pre-test revealed a lack of knowledge and several misconceptions in students' prior knowledge. For example, the concept of polarity was well-known, but the combination of polarity and geometry appeared to be difficult. For some students, the representation of molecules was intuitive and lacking a systematic approach. Certain students used mnemonics and draw ball-and-stick models connected to surficial representations. After the chemistry courses, the conceptions and drawings had generally changed, and the level of the students' knowledge increased markedly. Although, fewer ball-and-stick models were drawn in the post-test, some students still used them. The main result was that students who drew ball-and-stick models in the pre-test were less capable of drawing the correct Lewis structures with electrons in the post-test. In addition, heuristics seem to hinder learning and some concepts, such as resonance, remained difficult. This is probably due to the fact that understanding molecular structures requires systemic understanding, where several matters must be understood at the same time. Our study highlights that the understanding of molecular structures requires conceptual change related to several sub-concepts.

Anthelmintic resistance in gastrointestinal nematodes produces substantial challenges to agriculture, and new strategies for nematode control in livestock animals are called for. Natural compounds, including tannins, with proven anthelmintic activity could be a functional option as structurally diverse complementary compounds to be used alongside commercial anthelmintics. However, the dual use of two anthelmintic components requires an understanding of the pharmacological effects of the combination, while information concerning the interactions between plant-based polyphenols and commercial anthelmintics is scarce. We studied the direct interactions of proanthocyanidins (PAs, syn. condensed tannins) and a commercial anthelmintic thiabendazole, as a model substance of benzimidazoles, by isothermal titration calorimetry (ITC). Our results show evidence of a direct interaction of an exothermic nature with observed enthalpy changes ranging from 0 to −30 kJ/mol. The strength of the interaction between PAs and thiabendazole is mediated by structural characteristics of the PAs with the strongest positive correlation originating from the presence of galloyl groups and the increased degree of polymerization. [ABSTRACT FROM AUTHOR]

Previous studies have illustrated that different bioactive legume fodders containing condensed tannins might represent one of the options for integrated sustainable control of gastrointestinal nematodes (GIN) in ruminants, which may help address the worldwide development of resistance to synthetic anthelmintics. More recently, impetus has been given to assess the potential antiparasitic activity of less conventional resources, represented by different agro-industrial by-products (AIBPs). This review presents in vitro and in vivo results obtained with a range of tannin-containing AIBPs of various geographical and botanical origins, namely AIBP of nuts, temperate and tropical barks, carob, coffee and cocoa. They tend to confirm the “proof of concept” for their antiparasitic effects and also for other aspects of ruminant production in an agro-ecological context. Socio-economic aspects of the exploitation of such non-conventional resources are also discussed as potential models of the circular economy, by using waste. The different modes of use of these resources are presented in this review, as well as strengths, weaknesses, opportunities, and threats (SWOT) analyses to illustrate the advantages and limitations of on-farm use.

Food, feed and beverage processing brings tannins into contact with macromolecules, such as proteins and polysaccharides, leading to different chemical and physical interactions. The interactions of tannins with proteins are well known but less is known about the affinity of tannins to polysaccharides. We used bacterial cellulose from nata de coco as a model compound to investigate how tannins and cellulose interact by adsorption measurements using UPLC-DAD. We also explored how the structure of tannins influences these interactions. The model tannins included nine individual structurally different hydrolysable tannins (HTs) and eight well-defined proanthocyanidin (PA) fractions with different monomeric units, mean degree of polymerization and both A- and B-type linkages. Tannins were found to have both strong and weak interactions with bacterial cellulose, depending on the exact structure of the tannin. For HTs, the main structural features affecting the interactions were the structural flexibility of the HT molecule and the number of free galloyl groups. For PAs, prodelphinidins were found to have a higher affinity to cellulose than procyanidins. Similarly to HTs, the presence of free galloyl groups in galloylated PAs and the flexibility of the PA molecule led to a stronger interaction. Adsorption measurements by UPLC-DAD proved to be a sensitive and rapid tool to evaluate the affinity of tannins to cellulose. [ABSTRACT FROM AUTHOR]

Context:Terminaliais used in folk medicine for the treatment of various diseases. Objective: The objective of this study is to investigate the hepatonephro protective activity of a polyphenol-rich fraction (TMEF) obtained fromTerminalia muelleriBenth. (Combretaceae) against CCl4-induced toxicity in mice. Materials and methods: TMEF was administered (100, 200, and 400 mg/kg/d) for 5 d. CCl4was administered at the end of the experiment. Hepatic and renal biomarkers were measured in the serum. Glutathione (GSH), superoxide dismutase (SOD), and malondialdehyde (MDA) were estimated in the liver and kidney tissues. The active constituents of TMEF were identified by HPLC–PDA–ESI/MS/MS. Results: TMEF is rich in ellagitannins, galloyl esters, phenolic acids, and flavone-C-glucosides. TMEF pretreatment significantly (p < 0.001) inhibited the CCl4-induced increase in ALT (17, 43, and 53%), AST (20, 46, and 58%), ALP (20, 48, and 56%), LDH (21, 47, and 58%), hepatic MDA (23, 49, and 54%), renal MDA (22, 35, and 52%), creatinine (48, 66, and 91%), uric acid (16, 34, and 59%), urea (22, 39, and 59%), and cholesterol (20, 27, and 46%). Furthermore, TMEF administration significantly (p < 0.001) increased hepatic GSH (15, 51, and 79%), renal GSH (23, 45, and 73%), hepatic SOD (9, 52, and 95%), renal SOD (39, 66, and 85%) and protein levels (17, 24, and 29%) at the tested doses of TMEF, respectively. Pretreatment with TMEF preserved the hepatic architecture and protected from ballooning degeneration, liver necrosis, renal inflammation, and degeneration of the kidney tubules. Conclusion: TMEF has a marked hepato-nephro protective effect. [ABSTRACT FROM PUBLISHER]

Footnote k states that "k = Tripeptide containing Arg, Glu and Val; or Arg, Asp and Leu or Ile; or Gln, Gln and Lys or a tetrapeptide containing Ala, Ala, Asp and Lys; or Ala, Gln, Gly and Lys or a pentapeptide containing Ala, Ala, Gly, Gly and Lys". However, it should be "k = Tripeptide containing Arg, Glu and Val; or Arg, Asp and Leu or Ile; or Gln, Gln and Lys or a tetrapeptide containing Ala, Ala, Asn and Lys; or Ala, Gln, Gly and Lys or a pentapeptide containing Ala, Ala, Gly, Gly and Lys". However, it should be "n = Tripeptide containing Ala, Glu and Val; or Glu, Gly and Leu or Ile; or Pro, Thr and Thr; or Ala, Asp and Leu or Ile; or an acetylated tripeptide containing Gly, Ser and Leu or Ile; or Gly, Thr and Val; or the methyl ester of a tripeptide containing Ala, Asp and Val or Asp, Gly and Leu or Ile". [Extracted from the article]

In a previous study, the total ethanol extract of Bauhinia hookeri showed a significant hepatoprotective effect in CCl4-induced toxicity model in mice. However, the active components responsible for the activity were not identified. Therefore, this study was undertaken to determine if the activity of B. hookeri extract is due to its flavonoid content. The hepatoprotective activity of B. hookeri flavonoids was determined by measuring the activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in the culture medium of HepG2 cells challenged with CCl4. The lipid peroxidation and antioxidant parameters, superoxide dismutase (SOD) and glutathione (GSH) were estimated in the cell lysates. The isolated flavonoids were identified by mass, UV and NMR spectral data. This study revealed that B. hookeri flavonoid fraction and its pure compounds (kaempferol 3-O-β-D-glucoside, quercetin 3-O-β-D-glucoside and catechin 3-O-α-L-rhamnoside) possess a promising hepatoprotective activity as evidenced from the normalized levels of ALT and AST. This was attributed partly to their potent antioxidant activity as demonstrated by the increased GSH levels, SOD activity and reduced lipid peroxidation. The whole flavonoid fraction showed the highest cytoprotective activity and was more effective than silymarin. This study highlights a promising natural hepatoprotective remedy derived from B. hookeri. [ABSTRACT FROM AUTHOR]