Knowledge of the structure-property-function relationship of humic substances (HSs) is key for understanding their role in soil. Despite progress, studies on this topic are still under discussion. We analyzed 37 humic fractions with respect to their isotopic composition, structural characteristics, and properties responsible for stimulating plant root parameters. We showed that regardless of the source of origin of the carbon (C3 or C4), soil-extracted HSs and humic acids (HAs) are structurally similar to each other. The more labile and functionalized HS fraction is responsible for root emission, whereas the more recalcitrant and less functionalized HA fraction is related to root growth. Labile structures promote root stimulation at lower concentrations, while recalcitrant structures require higher concentrations to promote a similar stimulus. These findings show that lability and recalcitrance, which are derived properties of humic fractions, are related to the type and intensity of their bioactivity. In summary, the comparison of humic fractions allowed a better understanding of the relationship between the source of origin of plant carbon and the structure, properties, and type and intensity of the bioactivity of HSs in plants. In this study, scientific concepts are unified and the basis for the agronomic use of HSs is established.

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The structural identity of humic substances (HS) in the soil is a highly debated issue in the soil sciences. Although the complexity and structural characteristics that determine the functions of HS justify their further study, there is enough scientific evidence explaining the presence of these compounds as a group of structures that are formed by humification and have unique chemical characteristics. This review presents scientific information that follows the structure-property-function relationship with the objective of better explaining the nature of HS. On the basis of the spectroscopic characterization of a number of humic acids, together with the use of chemometric techniques, it is shown that, although the sources of origin are different, HS have a unique structural pattern that is different from that of any other group of soil compounds. From this structural pattern, it is possible to understand how fragments with greater lability in HS can reach root surfaces and interact with the cell membrane, regulate oxidative metabolism, and stimulate root growth in plants. Lability and recalcitrance are properties arising from the characteristics and suprastructural organization of HS and can define the type and intensity of the bioactivity of HS in plants. In this review, we demonstrate that there are methods for studying HS by which a deeper understanding of the functions of these substances on the basis of their chemical properties is possible. Therefore, the understanding of this complex system allows the connection of the scientific elements that justify the existence of these compounds in the soil.

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This research might aid in the discrimination of honey floral origin, by using simple analytical methods in association with multivariate analysis, which could also show a great difference among floral honeys and artificial honey, indicating a possible way to help with the identification of artificial honeys.

Foram avaliadas as atividades antioxidantes e o conteúdo de polifenóis de cinco méis silvestres e quatro de laranjeira, bem como de seus extratos fenólicos. A identificação e quantificação das substâncias fenólicas foram realizadas por HPLC-DAD (cromatografia líquida de alta eficiência com detecção por arranjo de diodos). A atividade sequestradora de radicais livres, determinada por 2,2-difenil-1-picrilhidrazil (DPPH •) e expressa como CE 50 , variou de 10,81 a 52,64 mg mL-1 para mel e de 6,17 a 52,87 mg mL-1 para extrato. A atividade antioxidante dos extratos foi também determinada pelos métodos com 2,2'-azinobis-(3-etil-benzotiazolino-6-ácido sulfônico) sal diamônio (ABTS) e poder antioxidante de redução do ferro (FRAP), e os resultados variaram de 46,53 a 383,49 mmol TE 100 g-1 e de 34,99 a 408,14 mol Fe(II) 100 g-1 , respectivamente. Também foram avaliados os teores de fenóis totais e flavonóides pelos métodos de Folin-Denis e complexação com cloreto de alumínio, respectivamente. A atividade antioxidante e o teor de fenóis totais mostraram-se altamente correlacionáveis. The antioxidant activities and total polyphenolic content of five multifloral and four orange blossom Brazilian honey samples and their phenolic extracts were investigated. Identification and quantification of phenolic compounds were carried out by HPLC-DAD (high-performance liquid chromatography with diode-array detection). The radical scavenging activities, determined with 2,2-diphenyl-1-picrylhydrazyl (DPPH •) and expressed as EC 50 , ranged from 10.81 to 52.64 mg mL-1 for honey and 6.17 to 52.87 mg mL-1 for the extracts. The extract antioxidant activities were also determined by 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) and ferric reducing antioxidant power (FRAP) assays, and the results varied from 46.53 to 383.49 mmol TE 100 g-1 and 34.99 to 408.14 mol Fe(II) 100 g-1 , respectively. It was also evaluated the total phenolic and flavonoid contents by the Folin-Denis and aluminum chloride methods, respectively. Antioxidant activities and total phenolic contents were found to be highly correlated.

Abstract:The work reported herein describes the synthesis and the assessment of the trypanocidal activity of thirteen new 1,2,4-triazole-3-thiones obtained from natural piperine, the main constituent of the dry fruits of Piper nigrum. It is part of a research program aiming to use abundant and easily available natural products as starting materials for the design and synthesis of new molecules potentially useful as antiparasitic drugs. The variously substituted triazole derivatives were synthesized from the natural amide in four steps with the use of microwave irradiation on overall yields ranging from 32% to 51%. The cyclohexyl substituted derivative showed the best trypanocidal profile on proliferative forms of Trypanosoma cruzi (Y strain), with IC 50 s = 18.3 and 8.87 μM against epimastigotes and amastigotes, respectively.