Toward Understanding of Bio-Oil Aging: Accelerated Aging of Bio-Oil Fractions

Pyrolysis bio-oil from biomass is a promising intermediate for producing transportation fuels and platform chemicals. However, its instability, often called aging, has been identified as a critical hurdle that prevents bio-oil from being commercialized. The objective of this research is to explore the bio-oil aging mechanism by an accelerated aging test of fractionated bio-oil produced from loblolly pine. When water soluble (WS), ether insoluble (EIS), and pyrolytic lignin (PL) fractions were aged separately, the increased molecular weight (Mw) was observed with increasing aging temperature and the presence of acids. WS and EIS fractions had high Mw brown solids formed after aging. Adjusting the pH of WS and EIS fractions from 2.5 to 7.0 significantly reduced the tendency of a Mw increase. Similar Mw rise was also observed on a PL fraction with an elevated temperature and acid addition. Formaldehyde was found to react with the PL fraction in the presence of any acid catalysts tested, i.e., 8-fold Mw increase in acetic acid environment, while other bio-oil aldehydes did not significantly promote lignin condensation. To better understand bio-oil stability, a potential bio-oil aging pattern was proposed, suggesting that bio-oil can be aged within or between its fractions

Thermal and Storage Stability of Bio-Oil from Pyrolysis of Torrefied Wood

The objective of this paper is to investigate the biomass torrefaction effect on bio-oil stability by comparing the physicochemical and compositional properties of aged bio-oils. Two aging methods, accelerated aging (held at 80 °C for 24 h) and long-term natural aging (12-month storage at 25 °C), were employed to produce aged bio-oils for such comparison. The results indicate that bio-oils made from heat-treated wood had similar aging behavior in terms of increase of water content, acid content, molecular weight, and viscosity. The increase rate, however, was found to be different and dependent on the aging method. The accelerated method found parallel water and total acidity number (TAN) increments between raw and torrefaction bio-oils, while the natural aging method found torrefaction bio-oils, especially those made from heavily treated wood, had much slower water and acid accumulation than that of raw bio-oil. As a negative effect, both methods identified the viscosity of torrefaction bio-oils increased more significantly than that of raw bio-oil, while their molecular weights were unexpectedly lower. The correlation study showed that bio-oil viscosity is more tied to the content of bio-oil–water insoluble fraction rather than its average molecular weight. In addition, the characterization of aged bio-oils using NMR, GC/MS, and solvent fractionation indicated that torrefaction bio-oils had less compositional alternation after accelerated aging than the raw bio-oil. Also, they were more stable during the first 6 months of storage at room temperature. During the long-term storage, the raw bio-oil completely phase-separated after 6 months. However, two distinct torrefaction bio-oils (LP-280T and LP-330T) had enhanced phase stability, as a stable uniform oil phase without gum formation can be maintained during the entire 12-month storage

New Ustilaginoidins from Rice False Smut Balls Caused by Villosiclava virens and Their Phytotoxic and Cytotoxic Activities

Ustilaginoidins are a class of bis-naphtho-γ-pyrones, typically produced by Villosiclava virens, the pathogen of the rice false smut (RFS), which has been one of the most destructive rice fungal diseases. Previously, we found that ustilaginoidins identified from the culture of V. virens on rice medium were less polar than those reported from the RFS balls in general. In this study, we reinvestigated the high-performance liquid chromatography with diode array detection and high-resolution mass spectrometry (HPLC–DAD–HRMS) profile of the ethyl acetate (EtOAc) extract of the RFS balls and found several interesting peaks that correspond to new ustilaginoidins. As a result, eight new and polar congeners, named ustilaginoidins Q–T (<b>1</b>–<b>4</b>), 2,3-dihydroustilaginoidin T (<b>5</b>), and ustilaginoidins U–W (<b>6</b>–<b>8</b>), were isolated. In addition, 17 known ustilaginoidins, including ustilaginoidins K–N (<b>9</b>–<b>12</b>), ustilaginoidin P (<b>13</b>), ustilaginoidin E₁ (<b>14</b>), isochaetochromin B₂ (<b>15</b>), and ustilaginoidins A–J (<b>16</b>–<b>25</b>), were re-isolated. The structures of the new compounds were elucidated by comprehensive analysis of the spectroscopic data. Ustilaginoidins Q (<b>1</b>) and R (<b>2</b>) feature an uncommon 2-hydroxypropyl-substituted skeleton and biogenetically incorporate one more acetate unit than common ustilaginoidins. Ustilaginoidin W (<b>8</b>) is a rare formate-containing bis-naphtho-γ-pyrone. Ustilaginoidins R (<b>2</b>), U (<b>6</b>), B (<b>17</b>), and I (<b>24</b>) showed moderate inhibitory activities toward the radicle or germ elongation of rice seeds. Ustilaginoidins R (<b>2</b>), S (<b>3</b>), V (<b>7</b>), W (<b>8</b>), B (<b>17</b>), C (<b>18</b>), and H–J (<b>23</b>–<b>25</b>) were cytotoxic to the tested human cancer cell lines (HCT116, NCI-H1650, BGC823, Daoy, and HepG2), with IC₅₀ values in the range of 4.06–44.1 μM

Bioactive Bis-naphtho-γ-pyrones from Rice False Smut Pathogen Ustilaginoidea virens

Ustilaginoidins were bis-naphtho-γ-pyrones mycotoxins possessing an a<i>R</i> configuration of the chiral axis previously reported from the false smut balls of rice infected by the fungal pathogen Ustilaginoidea virens. To investigate the chemical diversity of these metabolites and their bioactivities, we fermented this fungus on solid rice media, which afforded the isolation of 13 ustilaginoidins, including seven new compounds, namely ustilaginoidins K–P, <b>1</b>–<b>6</b>, and E₁, <b>7</b>, together with the known ustilaginoidins A, <b>8</b>, D, <b>9</b>, E, <b>10</b>, F, <b>11</b>, and G, <b>12</b>, and isochaetochromin B₂, <b>13</b>. The structures of the new compounds were elucidated by using (1D, 2D) NMR, high-resolution mass spectrometry, UV, and circular dichroism, as well as by comparison with the literature data. A plausible biosynthesis pathway was proposed for these dimeric polyketides. The isolated compounds were evaluated for their antibacterial, cytotoxic, and radicle elongation inhibitory activities. Ustilaginoidins K, <b>1</b> and L, <b>2</b> showed cytotoxic activities on the A2780 human ovarian cancer cell line with IC₅₀ values of 4.18 and 7.26 μM, respectively. Ustilaginoidins N, <b>4</b>, D, <b>9</b>, E, <b>10</b>, and G, <b>12</b> were active against the tested pathogenic bacteria with MIC values in the range of 16–64 μg/mL. Ustilaginoidins O, <b>5</b>, E, <b>10</b>, and F, <b>11</b>, and isochaetochromin B_2, <b>13</b> displayed moderate inhibitory activity on the radicle elongation of rice seeds