Periodic Grain Boundaries Formed by Thermal Reconstruction of Polycrystalline Graphene Film

Grain boundaries consisting of dislocation cores arranged in a periodic manner have well-defined structures and peculiar properties and can be potentially applied as conducting circuits, plasmon reflectors and phase retarders. Pentagon-heptagon (5–7) pairs or pentagon-octagon-pentagon (5–8–5) carbon rings are known to exist in graphene grain boundaries. However, there are few systematic experimental studies on the formation, structure and distribution of periodic grain boundaries in graphene. Herein, scanning tunneling microscopy (STM) was applied to study periodic grain boundaries in monolayer graphene grown on a weakly interacting Cu(111) crystal. The periodic grain boundaries are formed after the thermal reconstruction of aperiodic boundaries, their structures agree well with the prediction of the coincident-site-lattice (CSL) theory. Periodic grain boundaries in quasi-freestanding graphene give sharp local density of states (LDOS) peaks in the tunneling spectra as opposed to the broad peaks of the aperiodic boundaries. This suggests that grain boundaries with high structural quality can introduce well-defined electronic states in graphene and modify its electronic properties

Hepatoprotective Activity and Mechanisms of Prenylated Stilbenoids

Dietary prenylated stilbenoids, found in various food sources, offer multiple health benefits, including liver protection. However, the underlying mechanisms of hepatoprotection remain unclear. In this study, we synthesized 13 natural prenylated stilbenoids and examined their hepatoprotective activities, with silent mating type information regulation 2 homologue-1 (SIRT1) as the primary target for screening. Among all of the prenylated stilbenoids tested, 4-C-geranyl oxyresveratrol demonstrated superior performance. It activated SIRT1 activity more effectively than resveratrol, a well-known SIRT1 activator. To further investigate the mechanism of liver protection, two in vitro models were used: the palmitic acid-induced lipid accumulation model and the H2O2-induced apoptosis model. Our findings suggested that 4-C-geranyl oxyresveratrol mitigated lipid accumulation through the SIRT1-PGC1α pathway, reduced apoptosis via the SIRT1-p53-p21 pathway, and exerted antioxidant effects through the SIRT1-Nrf2 pathway. These findings provide new insights into the chemical basis of the health benefits of prenylated stilbenoids and their potential use as functional food additives

The PC#1 series and sample depth over the common reliable period 1560–2011.

<p>a) PC#1 series extracted from the four residual chronologies; b) PC#1 series (blue curve) extracted from the four standard chronologies and the corresponding 11-year low-pass filtered series (red heavy curve) with the 95% confidence levels (red thin curve).</p

Correlations between climate data and the four residual chronologies over their common periods.

<p>a) correlations with monthly temperature; b) correlations with monthly minimum temperature; c) correlations with monthly maximum temperature; d) correlations with monthly precipitation; e) correlations with monthly PDSI; f) correlations with monthly relative humidity. The horizontal dashed lines indicate the p = 0.05 significant level.</p

General characteristics of the four “standard” tree-ring chronologies.

<p>MSL is the mean segment length; AGR is the average growth rate; MRR is the missing-ring rate; SD is the standard deviation; MS is the mean sensitivity; AC1 is the first order autocorrelation; PC#1 is the variance explained by the first principal component; SNR is the signal-to-noise ratio; EPS is the expressed population signal; EPS >0.85 indicates the year and number of trees with EPS exceeding 0.85; R1 is the all-series Rbar; R2 is the within-trees Rbar; R3 is the among-trees Rbar.</p

Response function results between climate data and the four chronologies over their common periods.

<p>The detailed panels (a), (b), (c), (d), (e) and (f) follow the order in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0069065#pone-0069065-g002" target="_blank">Figure 2</a>. Response functions significant at the 0.05 level are marked with an asterisk.</p

Comparison of low-frequency variability in four STD chronologies at different elevations and the composite chronology during 1110–2011.

<p>Comparison of low-frequency variability in four STD chronologies at different elevations and the composite chronology during 1110–2011.</p

Comparison of altitude-related effects on standardized tree ring series (a) and residual tree ring series (b), which separately constitute the STD and RES chronologies during six typical periods (three high-value periods and three low-value periods).

<p>Euclidean distance is defined as the distance between each TRW series (50-dimensional vectors) and the mean TRW series (50-dimensional vector) of all the TRW series in the given periods. Both the elevation (m) and Euclidean distance are transformed to Z scores. R(1204–1253): high precipitation during 1204–1254; P(1254–1303):low precipitation during 1254–1303; SE: standard error; RSS: residual sum of squares; Prob>F: the probability that the null hypothesis for the full model is true (i.e., that all of the regression coefficients are zero).</p

Correlation coefficient matrix between the four STD (upper right corner) and RES (lower left corner) chronologies and the composite chronology during 1956–2011 and 1110–2011.

<p>All the values are significant at the p = 0.01 level.</p

Plant Prenylflavonoids and Prenyltransferases Related to their Biosynthesis

As the most widely distributed phenolic compounds in the plant kingdom, flavonoids play an integral role in plant reproduction and defense. Also, they represent many important quality traits of edible plants like color and antioxidants, and have a variety of biological activities beneficial to human health. To diversify the functions of synthesized flavonoids, plants have evolved various enzymes to perform structural modifications on different flavonoid backbones. One of these modifications is prenylation, which refers to the attachment of an isoprenoid moiety, most commonly a prenyl (C5) group. Numerous structure-activity analyses of prenylflavonoids have shown that isopentenyl substitutions at specific sites can significantly expand and enhance their chemical properties, bioactivities and potential health benefits. This review summarizes prenylflavonoids reported so far in all plant species and highlights the current knowledge on naturally occurring prenyltransferases from different biological sources that can act on plant flavonoids to synthesize prenylflavonoids. Most of them have strict flavonoid substrate- and regio-specificities, and they provide a valuable gene repository to facilitate the efficient scale-up production of flavonoids with specific prenylation patterns in cell factories. To truly achieve this goal, it is necessary to explore more diversified natural prenyltransferases, and to optimize the bioreactors system such as pathway regulation and modular co-culture engineering in the future.</p