Espectros de duas formas de lignina obtidos por ressonância magnética nuclear

Abstract

Resumo O conteúdo de lignina pode ser útil na estimativa da digestão da fibra de plantas forrageiras. A determinação quantitativa da lignina pelo método espectrofotométrico pressupõe a existência de um padrão de referência satisfatório. O objetivo deste trabalho foi avaliar, por meio da ressonância magné-tica nuclear (RMN), duas ligninas, uma extraída com brometo de acetila (LBrAc) e outra com solução ácida de dioxano (LDiox), para utilização como padrão de referência em análises espectrofotométricas. A ressonância de próton acusou altos teores de carboidratos contaminantes nas amostras de LBrAc. Como a cromatografia líquida já havia indicado menor presença de carboidratos contaminantes na LDiox, os espectros por ressonância de carbono, mais rica em detalhes do que a espectroscopia anterior, porém mais demorada, foram realizados somente nas ligninas LDiox. Este espectro revelou picos típicos, comuns à maioria das ligninas. Os achados da RMN foram condizentes com a análise química, a qual identificou que o carboidrato da parede celular que acompanha a LBrAc seria possivelmente a celulose, ao passo que a pequena contaminação da LDiox teria origem nas pentosanas. A LDiox pode ser considerada melhor padrão de referência para as análises espectrofotométricas do que a LBrAc.Termos para indexação: brometo de acetila, carboidrato, dioxano, parede celular, espectrometria. Nuclear magnetic resonance spectra of two types of ligninAbstract Lignin content can be useful to estimate fiber digestion of forage plants. Quantitative determination of lignin by the spectrophotometric method presumes an efficient standard. The objective of this work was to evaluate, by the nuclear magnetic resonance (NMR), two lignins, one extracted with acetyl bromide (AcBrL) and another with acidic dioxane solution (DL), as standards in spectrophotometric analysis. Proton resonance revealed high presence of carbohydrates in the AcBrL residues. Because liquid chromatograph had already shown low contamination with carbohydrates in the DL samples, only carbon resonance, which is lengthier, but richer in details than proton resonance, was run on these lignin samples. The carbon resonance revealed typical peaks common to most lignins. NMR findings were harmonious with wet chemistry which revealed that the cell wall carbohydrates attached to AcBrL would possibly be cellulose whereas in the DL, the small carbohydrate components would come from pentosans. DL can be considered a better standard to the spectrophotometric analysis than AcBrL.

Bioactivity of Chemically Transformed Humic Matter from Vermicompost on Plant Root Growth

“…CP/MAS 13 C NMR. The carbon distribution in the original HS and derivatives was revealed by CPMAS 13 C NMR spectra.…”

“…Acid Hydrolysis by Dioxane in 2 M HCl (D6). The HS (300 mg) were submitted to acidolysis with 20 mL of a dioxane solution containing 2 M HCl for 30 min under reflux at 60 °C and N 2 atmosphere (13). After recovery of supernatant by centrifugation (30 min, 6500g), the residue was washed three times with 10 mL of dioxane.…”

“…Solid-State NMR Spectroscopy ( 13 C CPMAS-NMR). Cross-polarization magic angle spinning (CPMAS) 13 C NMR spectra were acquired with a Bruker AVANCE 300 NMR spectrometer, equipped with a 4 mm widebore MAS probe, operating at a 13 C resonating frequency of 75.475 MHz. Samples (100-200 mg) were packed in 4 mm zirconia rotors with Kel-F caps and were spun at 13 ( 1 kHz.…”

“…The aim of this study was to evaluate the influence of chemical modifications of humic structure on root stimulation. The HS were evaluated by elemental composition, HPSEC, CP-MAS 13 NMR, and DOSY 1 H NMR spectroscopies, and their bioactivities were monitored by following the morphological and biochemical traits of Arabidopsis (Arabidopsis thaliana Heynh), tomato (Solanum lycopersicum L.), and maize (Zea mays L.).…”

Modificações estruturais da lignina causada por fungos

“…Os carbonos da cadeia alifática são identificados com as letras gregas α, que corresponde ao carbono ligado ao anel benzílico, β e γ, seguindo na ordem sequencial. Os carbonos da cadeia alifática são unidos por ligações éter (C-O-C) e carbono-carbono (C-C) (SARKANEN;ERGERT, 1971;FUKUSHIMA;HATFIELD, 2003;MUNK et al, 2015).…”