There is a trend of development of analytical methodologies and technologies that allow in situ analysis, producing accurate information in real time, at low cost, using homemade experiments and devices to increase interest in scientific knowledge with a constructive approach in an interdisciplinary perspective in Chemistry Education. In this context, a photometric-chemometric method of analysis was developed to measure the pH of solutions using easily accessible and low-cost material based on the use of natural pigments found in red cabbage (Brassica oleracea L.). Calibrations and determinations were performed by RGB measurements of pigment coloration in solution at different pH values using the free app Photometrix, converted to HSV, YCbCr and YUV color spaces and processed by Partial Least Squares regression (PLS). The best PLS model found was HSV with mean central scale obtained pH measurements with RMSEP 0.98, R2 0.97 and bias close to zero. In addition, experimental data were statistically validated. Analyzes of predicted pH from three independents experiments revealed high recoveries (95-103%) and low relative standard deviations. Thus, the PhotoMetrix app was viable for colorimetric pH determinations using the low-cost photometric pH meter sensor and a smartphone, improving accessibility and applicability in Chemistry Education.

The Amazonian Rubiaceae species Uncaria guianensis (UG) is locally used as anti-inflammatory, antitumor, antidiabetic, anti-ulcers, and others. The phenolic content of its leaves is characterized by the great predominance of the flavonoid kaempferol-3,7-O-(α)-L-dirhamnoside (kaempferitrin). The present study quantitatively evaluates the kaempferitrin content in the leaves and branches of cultivated and wild UG specimens collected in different locations of the Brazilian Amazon rainforest by employing high-performance liquid chromatography coupled to a diode array detector (HPLC-DAD). Besides, the understanding of the polyphenol profile performed by electron spray ionization is deepened by tandem mass spectrometry analysis (ESI-MS/MS), using a previously approached leaf UG extract, and the flavonoid quercetin-3,7-O-(α)-L-dirhamnoside was first isolated from UG. All samples showed quite similar qualitative polyphenol profiles. Kaempferitrin in UG ranged from 1.1 to 1.9 mg 100 mg-1 for dry leaves of adult wild plants, 0.3 to 0.7 mg 100 mg-1 for dry leaves of cultivated young plants and 0.00 to 0.04 mg 100 mg-1 for dry branches of adult wild plants. Besides suggesting the distribution of kaempferitrin in the species, these results reinforce this flavonol as a suitable chemical marker for UG leaves and the products derived from them.

The leaf MeOH extract of Psychotria leiocarpa (Rubiaceae) showed in vitro non-cytotoxic and anti-dengue virus serotype 2 (DENV2) activity in human hepatocarcinoma cell lineage (HepG2). A one-step and cost-effective reversed-phase solid-phase extraction method based on high-performance liquid chromatography (HPLC) parameters allowed the isolation, directly from this bioactive extract, of the monoterpene indole alkaloids: N-glucopyranosyl vincosamide (1), vincosamide (2) and strictosidinic acid (3). The chemical structures were characterized based on 1D and 2D nuclear magnetic resonance (NMR), UV and high-resolution mass spectra (HRMS). The methodology has also allowed yielding a polyphenolic-rich fraction that was analyzed by high-performance liquid chromatography coupled to diode array detection and electrospray ionization tandem mass spectrometry (HPLC-DAD-ESI-MS/MS) revealing two flavonol triglycosides (4, 5) and three caffeoylquinic acid isomers (6-8). Compound 3 is reported for the first time in P. leiocarpa and all the phenolic compounds (4-8) are described for the first time in the genus Psychotria. Compounds 1-3 showed to be non-cytotoxic and anti-dengue active towards DENV2, highlighting vincosamide (2).

Uncaria tomentosa (Willd.) DC. e U. guianensis (Aubl.) Gmel., conhecidas como unha-de-gato, são trepadeiras lenhosas nativas das florestas tropicais amazônica e central-americana. As espécies contêm, em diferentes proporções, alcalóides indólicos e oxindólicos, triterpenóides glicosilados, esteróides e proantocianidinas. U. tomentosa é quimicamente identificada pelo perfil e conteúdo de alcalóides oxindólicos, ao passo que U. guianensis não possui um marcador químico efetivo. Nesse trabalho descreve-se o isolamento de canferol-3,7-O-(α)-dirramnosídeo (canferitrina) pela primeira vez em espécies do gênero Uncaria. A triagem para essa substância em folhas, galhos ou cascas das duas espécies por CCD e CLAE-DAD-EM demonstrou a presença de canferitrina apenas nas folhas e galhos de U. guianensis, numa proporção cerca de trinta e seis vezes maior nas folhas do que nos galhos. Estes resultados revelaram a seletividade da U. guianensis em produzir o flavonóide glicosilado, sugerindo esta substância como um marcador químico potencial para a espécie.

Uncaria tomentosa (Willd.) DC. and U. guianensis (Aubl.) Gmel., known as cat's claw, are large woody vines native to the Amazonian and Central American rainforests. The species contain, in different proportions, indole and oxindole alkaloids, triterpenoid glycosides, sterols and proanthocyanidins. U. tomentosa can be chemically identified by its oxindole alkaloid profile and content, whereas U. guianensis has no satisfactorily established chemical markers. This work describes, for the first time, the isolation of kaempferol-3,7-O-(α)-dirhamnoside (kaempferitrin) in Uncaria species. Screening for this compound in leaves, stems or bark of both species through TLC and HPLC-DAD-MS showed the presence of kaempferitrin only in the leaves and stems of U. guianensis, at a ratio almost thirty six times greater in the leaves than in the stems. These results reveal the selectivity of U. guianensis to produce this bioactive flavonoid glycoside, and suggest this compound as a potential chemical marker for the species.