A zinc(Ⅱ) MOF based on secondary building units of infinite wavy-shaped chain exhibiting obvious luminescent sense effects

A new metal-organic framework (MOF),{[Zn_7 (BPS)_4 (OH)_6 (H_2O)_2]·5 H_2O]_n}(1), (H_2 BPS=4,4′-bibenzoic acid-2,2′-sulfone), based on a wavy and infinite chain-shaped secondary building units, has been synthesized under solvothermal conditions and characterized by single crystal X-ray diffraction and further confirmed by PXRD, TGA and IR spectrum. The solid-state emission spectra reveal that compound 1 presents strong luminescence emission bands at room temperature. The fluorescent properties of compound 1 in diverse organic solvents indicated that 1 has palpable luminescent sense effects for DMF and DMAC.     

Parameter settings in a compact laser-nitriding system for titanium composed of a focused pulsed Nd:YAG laser and nitrogen gas blow

The aim of the present study was to form a nitride layer on a titanium (Ti) substrate through a compact laser-nitriding system comprising a focused pulsed Nd:YAG laser and nitrogen gas blow. To obtain a high-quality layer, the effects of pulse frequency and gas flow rate on the surface characteristics were investigated by using plasma emission analysis as well as X-ray analyses. Optical emission spectra from the laser-induced plasma mainly consisted of ionic Ti lines, and their intensities when the pulse frequency was 15 Hz were much higher than those for 8 Hz. Similarly, the reflections from the δ-TiN phase in the X-ray diffraction (XRD) pattern were enhanced when using 15 Hz. On the other hand, the flow rate of nitrogen gas blow had a significant effect on the thickness of the thin oxide layer that formed above the nitride layer. Using a lower flow rate resulted in the formation of a thicker oxide layer. The higher pulse frequency and the faster flow rate were beneficial for obtaining a higher-quality layer because of the enhancement of nitridation and the suppression of oxidation, respectively.     

Cu2+ Effects on Beta-Amyloid Oligomerisation Monitored by the Fluorescence of Intrinsic Tyrosine

A non-invasive intrinsic fluorescence sensing of the early stages of Alzheimer's beta amyloid peptide aggregation in the presence of copper ions is reported. By using time-resolved fluorescence techniques the formation of beta amyloid-copper complexes and the accelerated peptide aggregation are demonstrated. The shifts in the emission spectral peaks indicate that the peptides exhibit different aggregation pathways than in the absence of copper.     

Revealing and comparing different excited-state intramolecular proton transfer processes for 3-(4-dimethylamino-phenyl)-1-(4-fluoro-2-hydroxy-phenyl)-propenone and 3-(4-dimethylamino-phenyl)-1-(4-fluoro-2-hydroxy-phenyl)-3-hydroxy-propenon

Two novel 2′-hydroxychalcone derivatives (i.e., M1 and M2) are explored in this work. We mainly focus on investigating the effects of photoexcitation on hydrogen bonds and on the excited-state intramolecular proton transfer (ESIPT) process. On the basis of calculations of electrostatic potential surface and intramolecular interactions, we verify the formation of hydrogen bond O1 H2···O3 in both S₀ and S₁ states. Exploring the ultraviolet–visible spectra in the liquid phase, our simulated results reappear in the experimental phenomenon. Analyzing molecular geometry and infrared stretching vibrational spectra, we confirm O1 H2···O3 is strengthened for both M1 and M2 in the S₁ state. We further confirm that charge redistribution facilitates ESIPT tendency. Constructing potential energy curves, we find the ultrafast ESIPT behavior for M1, which is because of the deficiency of side hydroxyl moiety comparing with M2. This work makes a reasonable affiliation of the ESIPT mechanism for M1 and M2. We wish this paper could facilitate understanding these two novel systems and promote their applications.     

Accurate theoretical prediction of optical properties of BODIPY dyes

Boron-dipyrromethene dyes (BODIPY) are of great interest nowadays mostly due to their valuable optical properties. Nevertheless, no systematic research of the optical property dependence on the structure of dyes has been performed yet. In this work, analysis of the available quantum-chemical methods for BODIPY optical property calculations has been carried out. The accuracy of eight DFT functionals has been studied. The solvation effects upon excitation have been considered within two schemes. The methods that predict the absorption and emission spectra of BODIPY derivatives with high accuracy have been proposed. Using the suggested methods, the influence of nature of substituents and their position in the BODIPY core on the optical spectra of the dyes has been studied. A complex pattern of red- and blue-shifts in optical spectra in dependence of nature and position of substituents has been revealed. The results of this work provide the way for efficient design of BODIPY derivatives with desired optical properties.     

Gas-phase 21Ne NMR studies and the nuclear magnetic dipole moment of neon-21

Gas-phase ²¹Ne nuclear magnetic resonance spectra were measured at the natural abundance of ²¹Ne isotope for samples consisting of pressurized neon up to 60 bar at room temperature and applying the magnetic field of the strength B₀ = 11.7574 T. It showed that the nuclear magnetic resonance frequency is linearly dependent on the density of gaseous neon. The resonance frequency was extrapolated to the zero-density point, and it permitted the determination of the ²¹Ne nuclear magnetic moment, μ(²¹Ne) = 0.6617774(10) μ_N. The present value of μ(²¹Ne) is not influenced by the bulk magnetic susceptibility of neon and interactions between neon atoms; therefore, it is more precise and reliable than the previous result obtained for μ(²¹Ne).     

基于红外光谱聚类分析的纳滤膜污染动态发展行为研究

污水再生利用是解决水资源短缺问题的有效对策。纳滤技术由于能够生产高质量的再生水，成为污水深度处理、再生利用的有效方法之一。然而，在纳滤过程中存在复杂的、动态的膜污染现象，会导致产水通量、产水质量下降等问题。研究膜污染动态发展的行为，对于膜污染的分阶段针对性控制具有重要意义。有机物是污染层动态发展过程的重要指示性成分，红外光谱是表征污染层发展过程中表面有机物官能团变化情况的重要手段。但由于红外光谱中峰的数量多，系列样品之间峰强度的差别较小（尤其是当膜污染过程中的采样间隔较小时），利用直观观察不易甄别不同样品间的谱图差异及其变化趋势，在此水平上难以对膜污染阶段进行准确识别、对各阶段特征进行有说服力的分类概括。为探索膜污染的动态发展过程，本研究将傅里叶变换红外光谱与统计学聚类分析相结合，对膜污染过程中不同时间点的膜样本进行红外光谱分析，再对红外光谱数据进行一系列预处理和系统聚类分析，从而客观解读膜污染动态发展过程中系列样品红外光谱分阶段变化规律。考虑到类别间距离度量方法、红外吸收峰强度标准化、峰之间自相关性、峰与样本之间交互作用等因素的影响，研究采用对应分析对红外数据进行预处理，提取各样本在主要维度上的得分，随后基于标准化欧式距离对各样本进行聚类。在为期一个月的城市污水深度处理纳滤试验过程中，由于污染物在膜表面累积，纳滤膜发生了较为严重的污染。通过对13个不同时间点的膜样本进行红外光谱聚类发现，膜污染可清晰划分为如下阶段：空白膜、阶段Ⅰ（3 h～8 d）、阶段Ⅱ（10～15 d）和阶段Ⅲ（20～30 d）。采用红外聚类，得到膜表面X射线光电子能谱（XPS）和三磷酸腺苷（ATP）含量分析等方法的交互验证。结果表明，随着膜污染的发展，膜表面有机物成分与共存微生物量发生协同变化，各阶段大致特征为：阶段Ⅰ各类有机污染物初步覆盖，微生物开始富集；阶段Ⅱ多糖类污染物比例上升，微生物的富集趋于稳定；阶段Ⅲ整体污染趋于成熟，有机污染物氢键特征更加明显。该研究通过对红外数据进行聚类分析，能够灵敏地探测各红外图谱之间的差别，有助于对红外光谱规律的深度挖掘，为膜污染阶段的识别和划分提供了一种客观、自动、可量化的辅助性方法，并且有助于归纳出不同阶段的污染层特征，可作为膜污染时序特征的侦查手段。此外，除了膜污染的研究，在材料、吸附等领域，只要有一系列变化的红外光谱，均可尝试采用红外光谱聚类分析方法，获取基于红外特征的定类信息或分阶段规律。     

利用带无标签数据的双支持向量机对恒星光谱分类

恒星光谱分类是天文技术与方法领域一直关注的热点问题之一。随着观测设备持续运行和不断改进，人类获得的光谱数量与日俱增。这些海量光谱为人工处理带来了极大挑战。鉴于此，研究人员开始关注数据挖掘算法，并尝试对这些光谱进行数据挖掘。近年来，神经网络、自组织映射、关联规则等数据挖掘方法广泛应用于恒星光谱分类。在这些方法中，支持向量机(SVM)以其强大的学习能力和高效的分类性能而备受推崇。SVM的基本思想是试图在两类样本之间找到一个最优分类面将两类分开。SVM在求解时，通过将其最优化问题转化为具有(QP)形式的凸问题，进而得到全局最优解。尽管该方法在实际应用中表现优良，但为了进一步提高其分类能力，有的学者提出双支持向量机(TSVM)。该方法通过构造两个非平行的分类面将两类分开，每一类靠近某个分类面，而远离另一个分类面。TSVM的计算效率较之传统SVM提高近4倍，因此，自TSVM提出后便受到研究人员的持续关注，并出现若干改进算法。在恒星光谱分类中，一般分类算法都是根据历史观测光谱来建立分类模型，其中最关键的是对光谱进行人工标注，这项工作极为繁琐，且容易犯错。如何利用已标记的光谱以及部分无标签的光谱来建立分类模型显得尤为重要。因此，提出带无标签数据的双支持向量机(TSVMUD)用以实现对恒星光谱智能分类的目的。该方法首先将光谱分为训练数据集和测试数据集两部分；然后，在训练集上进行学习，得到分类依据；最后利用分类依据对测试集上的光谱进行验证。继承了双支持向量机的优势，更重要的是，在训练集上学习分类模型过程中，不仅考虑有标记的训练样本，也考虑部分未标记的样本。一方面提高了学习效率，另一方面得到更优的分类模型。在SDSS DR8恒星光谱数据集上的比较实验表明，与支持向量机SVM、双支持向量机TSVM以及K近邻(KNN)等传统分类方法相比，带无标签数据的双支持向量机TSVMUD具有更优的分类能力。然而，该方法亦存在一定的局限性，其中一大难题是其无法处理海量光谱数据。该工作将借鉴海量数据随机采样思想，利用大数据处理技术，来对所提方法在大数据环境下的适应性展开进一步研究。