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991.
分子识别指导下的有机分子设计、合成和组装——世纪交替时代的有机化学 总被引:3,自引:2,他引:1
在21世纪即将来临之际,有机化学将面临生命科学、环境科学和材料科学越来越多的挑战。本文回顾了在分子识别指导下的有机分子的设计、合成和组装这个新领域的诞生和发展,认为这个领域将成为新世纪有机化学发展的一个重要方向。它的发展和应用不仅使得有机化学可能较好地面对新挑战,同时能推动有机合成化学自身的发展。 相似文献
992.
993.
Host–guest complexations of a twisted cucurbit[15]uril with some paraquat derivatives and bispyridinium salts in aqueous solution are investigated by nuclear magnetic resonance, UV–vis spectrometry and isothermal titration calorimetry. These complexations are mainly enthalpy-driven. 相似文献
994.
995.
Laura Díaz-Casado Israel Serrano-Chacón Dr. Laura Montalvillo-Jiménez Francisco Corzana Agatha Bastida Dr. Andrés G. Santana Prof. Dr. Carlos González Dr. Juan Luis Asensio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(20):6204-6212
Targeting the interface between DNA quadruplex and duplex regions by small molecules holds significant promise in both therapeutics and nanotechnology. Herein, a new pharmacophore is reported, which selectively binds with high affinity to quadruplex–duplex junctions, while presenting a poorer affinity for G-quadruplex or duplex DNA alone. Ligands complying with the reported pharmacophore exhibit a significant affinity and selectivity for quadruplex–duplex junctions, including the one observed in the HIV-1 LTR-III sequence. The structure of the complex between a quadruplex–duplex junction with a ligand of this family has been determined by NMR methods. According to these data, the remarkable selectivity of this structural motif for quadruplex–duplex junctions is achieved through an unprecedented interaction mode so far unexploited in medicinal and biological chemistry: the insertion of a benzylic ammonium moiety into the centre of the partially exposed G-tetrad at the interface with the duplex. Further decoration of the described scaffolds with additional fragments opens up the road to the development of selective ligands for G-quadruplex-forming regions of the genome. 相似文献
996.
常用的梅尔倒谱系数结合高斯混合模型(MFCC+GMM)方法的鸟鸣声识别技术难适应噪声环境,模型难以收敛,且计算复杂度高。该文提出一种融合声纹信息的能量谱图的鸟类识别方法(VPS-BR),该方法利用鸟类鸣声在能量谱图上所表现的多维差异性,定量识别鸣声声纹特征。通过对分贝能量进行颜色映射得到能量谱图,提取其视觉特征所表达的声学特征,分析归纳得到鸟类特有鸣声模式。在特征提取步骤中,选用识别速度快的局部二值模式、识别鲁棒性高的方向梯度直方图两个参数表征鸟鸣声谱图的边缘声纹;在识别步骤中,用局部二值模式和方向梯度直方图两种特征分别与支持向量机、K最近邻和随机森林3种分类器算法进行两两组合构建识别模型测试。对15种原始带噪鸟类鸣声数据集进行交叉验证,VPS-BR模型的平均识别率比MFCC+GMM组合模型高出11.3%,方向梯度直方图特征与K最近邻分类器的组合模型识别率达90.5%,表现出较好的抗噪性能和识别性能。最后针对样本数据集缺乏问题,使用生成对抗网络进行图像增强,进一步将识别率提升1.48%。 相似文献
997.
随着信息技术的发展,数字技术越来越多地应用于民族文化数字化保护,民族服饰的数字化及分类问题也日益受关注。相比一般服饰,少数民族服饰具有更多的细节特征信息,对其进行分类识别具有很大挑战。选用卷积神经网络DenseNet-BC作为基础网络结构,设计并使用了多尺度密集连接单元,用不同大小的卷积提取不同尺度的特征信息,以提高网络的学习能力;此外,为进一步提高网络的鲁棒性,提出一种局部和全局注意力机制方法进行分类识别。实验结果表明,改进的DenseNet-BC模型对少数民族服饰的识别准确率达95.18%,较ResNet-18、ResNet-34和DenseNet模型的识别准确率分别提升了3.84%、2.27%和1.18%。改进的DenseNet-BC模型具有更好的特征提取能力,能够提取更多的细节特征信息,一定程度上解决了普通模型提取特征尺度单一、特征丰富度低的问题。 相似文献
998.
Xiao-Hui Pan Dr. Min Chen Dr. Shuo-Hui Cao Zi-Qian Xu Zhao Li Prof. Yao-Qun Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(69):17331-17335
Different cell membrane domains play different roles in many cell processes, and the discrimination of these domains is of considerable importance for the elucidation of cellular functions. However, the strategies available for distinguishing these cell membrane domains are limited. A novel technique called plasmon coupling enhanced micro-spectroscopy and imaging to discriminate basal and lateral membrane domains of a single cell combines the application of an additional plasmonic silver film for surface plasmon (SP) excitation to selectively excite and enhance the basal membranes in the near-field with directional enhanced microscopic imaging and spectroscopy. The SP and critical evanescent fields are induced upon excitation through a silver-coated semitransparent coverslip at the surface plasmon resonance and critical angles, respectively. The basal and lateral membrane domains located within the SP and critical evanescent fields can be selectively excited and distinguished by adjusting the incident angle of laser irradiation. Moreover, the brighter images and more intense spectra of membrane-targeting fluorescence-Raman probes under directional excitation than in conventional EPI mode allow clear identification of the membrane domains. 相似文献
999.
Anion binding to a receptor based on stiff-stilbene, which is equipped with a urea hydrogen bond donating group and a phosphate or phosphinate hydrogen bond accepting group, can be controlled by light. In one photoaddressable state (E isomer) the urea binding site is available for binding, while in the other (Z isomer) it is blocked because of an intramolecular interaction with its hydrogen bond accepting motif. This intramolecular interaction is supported by DFT calculations and 1H NMR titrations reveal a significantly lower anion binding strength for the state in which anion binding is blocked. Furthermore, the molecular switching process has been studied in detail by UV/Vis and NMR spectroscopy. The presented approach opens up new opportunities toward the development of photoresponsive anion receptors. 相似文献
1000.
Peiwen Zhang Yiran Li Xiaofei Yu Prof. Dr. Huangxian Ju Prof. Dr. Lin Ding 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(44):10505-10510
Precision cell-selective surface glycan remodeling is of vital importance for modulation of cell surface dynamics, tissue-specific imaging, and immunotherapy, but remains an unsolved challenge. Herein, we report a switchable enzymatic accessibility (SEA) strategy for highly specific editing of carbohydrate moieties of interest on the target cell surface. We demonstrate the blocking of enzyme in the inaccessible state with a metal-organic framework (MOF) cage and instantaneous switching to the accessible state through disassembly of MOF. We further show that this level of SEA regulation enables initial guided enzyme delivery to the target cell surface for subsequent cell-specific glycan remodeling, thus providing a temporally and spatially controlled tool for tuning the glycosylation architectures. Terminal galactose/N-acetylgalactosamine (Gal/GalNAc) remodeling and terminal sialic acid (Sia) desialylation have been precisely achieved on target cells even with other cell lines in close spatial proximity. The SEA protocol features a modular and generically adaptable design, a very short protocol duration (ca. 30 min or shorter), and a very high spatial resolving power (ability to differentiate immediately neighboring cell lines). 相似文献