Two new cyclopeptides, named arenariphilin A ( 1 ) and arenariphilin B ( 2 ), were isolated from the whole plants of Arenaria oreophila. Their structures were determined as cyclo‐(Thr‐Gly) ( 1 ) and cyclo‐(Ser1‐Gly ‐Ser2‐Ile ‐Phe1‐Phe2) ( 2 ) on the basis of spectral data, especially by 2D‐NMR. 相似文献
N,N,N‐trimethylchitosan (TMC) was prepared by reacting purified chitosan with iodomethane, in the presence of sodium hydroxide, water and sodium iodide, at room temperature. The reaction medium was N‐methyl‐2‐pyrrolidone. Different samples of TMC were obtained by adding to the reaction medium a fixed volume (5.5 mL) of aqueous NaOH solutions at different concentrations (15, 20, 30 and 40 wt.‐%) and carrying out the reactions for 9 or 24 h. The features observed in the 1H and 13C NMR spectra of these chitosan derivatives, in respect of the chemical shift, number and relative intensity of the signals, depended strongly on the excess of NaOH and H3CI added to the reaction medium, but when the lowest excess was employed, the characteristics of the derivative were not affected by the reaction time to the same extent. The average degree of quaternization of these N‐methylated derivatives of chitosan ranged from 10.5% to 44.8%, according to the reaction conditions. Increasing the excess of NaOH, in reactions carried out for 9 h, resulted in TMC samples with progressively higher content of trimethylated sites however, the reaction yields were correspondingly lower and O‐alkylation was favored in these cases.
1H NMR spectrum of sample [AX]24h dissolved in D2O (Cp = 10 g/L). 相似文献
The frontier of nitric oxide biology has gradually shifted from mechanism elucidation to biomanipulation, e.g. cell-proliferation promotion, cell-apoptosis induction, and lifespan modulation. This warrants biocompatible nitric oxide (NO) donating materials, whose NO release is not only controlled by a bioorthogonal trigger, but also self-calibrated allowing real-time monitoring and hence an onset/offset of the NO release. Additionally, the dose of NO release should be facilely adjusted in a large dynamic range; flux and the dose are critical to the biological outcome of NO treatment. Via self-assembly of a PEGylated small-molecule NO donor, we developed novel NO-donating nanoparticles (PEG-NORM), which meet all the aforementioned criteria. We showcased that a low flux of NO induced cell proliferation, while a high flux induced cell oxidative stress and, ultimately, death. Notably, PEG-NORM was capable of efficiently modulating the lifespan of C. elegans. The average lifespan of C. elegans could be fine-tuned to be as short as 15.87 ± 0.29 days with a high dose of NO, or as long as 21.13 ± 0.41 days with a low dose of NO, compared to an average life-span of 18.87 ± 0.46 days. Thus, PEG-NORM has broad potential in cell manipulation and life-span modulation and could drive the advancement of NO biology and medicine.Schematic illustration of modulating the longevity of the C. elegans by PEG-NORM nanoparticles.相似文献
Dynamic equilibrium between the folded and unfolded conformations of single stranded DNA hairpin molecules containing polythymine hairpin loops was investigated using simultaneous two-beam fluorescence cross-correlation spectroscopy and single beam autocorrelation spectroscopy. The hairpins were end-labeled with a fluorescent dye and a quencher, such that folding and unfolding of the DNA hairpin primary structure caused the dye fluorescence to fluctuate on the same characteristic time scale as the folding and unfolding reaction. These fluctuations were observed as the molecules flowed sequentially between two spatially offset, microscopic detection volumes. Cross-correlation analysis of fluorescence from the two detection volumes revealed the translational diffusion and flow properties of the hairpins, as well as the average molecular occupancy of the two volumes. Autocorrelation analysis of the fluorescence from the individual detection volumes revealed the kinetics of hairpin folding and unfolding, with the parameters relating to diffusion, flow, and molecular occupancy constrained to the values determined from the cross-correlation analysis. This allowed unambiguous characterization of the folding and unfolding kinetics, without the need to determine the hydrodynamic properties by analyzing a separate control sample. The analysis revealed nonexponential relaxation kinetics and DNA size-dependent folding times characteristic of dynamic heterogeneity in the DNA hairpin-forming mechanism. 相似文献
4,4′‐Bipyridyl N,N′‐dioxide crystallizes with 3‐hydroxy‐2‐naphthoic acid to give a centrosymmetric three‐component adduct, C10H8N2O2·2C11H8O3, which is engineered into a two‐dimensional layer structure by two kinds of π–π interactions. Weak C—H⋯O interactions further link the two‐dimensional structure into a three‐dimensional structure. 相似文献