Methods of hexagonal boron nitride exfoliation and its functionalization: covalent and non-covalent approaches

The exfoliation of two-dimensional (2D) hexagonal boron nitride nanosheets (h-BNNSs) from bulk hexagonal boron nitride (h-BN) materials has received intense interest owing to their fascinating physical, chemical, and biological properties. Numerous exfoliation techniques offer scalable approaches for harvesting single-layer or few-layer h-BNNSs. Their structure is very comparable to graphite, and they have numerous significant applications owing to their superb thermal, electrical, optical, and mechanical performance. Exfoliation from bulk stacked h-BN is the most cost-effective way to obtain large quantities of few layer h-BN. Herein, numerous methods have been discussed to achieve the exfoliation of h-BN, each with advantages and disadvantages. Herein, we describe the existing exfoliation methods used to fabricate single-layer materials. Besides exfoliation methods, various functionalization methods, such as covalent, non-covalent, and Lewis acid–base approaches, including physical and chemical methods, are extensively described for the preparation of several h-BNNS derivatives. Moreover, the unique and potent characteristics of functionalized h-BNNSs, like enhanced solubility in water, improved thermal conductivity, stability, and excellent biocompatibility, lead to certain extensive applications in the areas of biomedical science, electronics, novel polymeric composites, and UV photodetectors, and these are also highlighted.

Synthesis methods for the exfoliation of BNNSs and BNNS functionalization methods are reviewed.     

The influence of erythrocyte shape on suspension viscosities

Erythrocyte shape changes are known to occur in vivo and can readily be induced in vitro. We have analysed the influence of increasing stomatocytosis produced by 0-0.64 mmol l-1 chlorpromazine and increasing echinocytosis induced with 0-120 mmol l-1 salicylate or 0-8 mmol l-1 2,4-dinitrophenol on suspension viscosities. The morphological index of each sample was determined and related to the suspension viscosity. It was found that the viscosity was increased by echinocytosis in dextran-free solutions, where no aggregation occurred. The viscosity could be normalized by retransforming echinocytes into discocytes. Under conditions with erythrocyte aggregation (suspension with 4 g dl-1 dextran 70, low shear rate: 0.1 s-1) a small degree of echinocytosis produced the highest viscosity, whereas at higher degrees of echinocytosis the ability to aggregate was reduced and the viscosity was similar to that of discocytes or stomatocytes. Erythrocytes incubated in hypotonic medium (constant cell number/volume) had a higher viscosity than cells in iso- or hypertonic medium. Severely hypotonic medium led to sphering of erythrocytes which reduced the ability of these cells to aggregate and hence decreased the viscosity of suspensions with dextran at low shear rate. The results indicate that discocytes have the lowest viscosity and thus the best oxygen transport efficiency and that iso- to hypertonicity provides a lower viscosity and better oxygen transport efficiency than hypotonicity. These results may contribute to the understanding of blood flow in health and disease.     

The iliolumbar ligament: its influence on stability of the sacroiliac joint

STUDY DESIGN: In human specimens the influence of the iliolumbar ligament on sacroiliac joint stability was tested during incremental moments applied to the sacroiliac joints. OBJECTIVES: To assess whether the iliolumbar ligament is able to restrict sacroiliac joint mobility in embalmed cadavers. BACKGROUND: Firstly, the sacroiliac joint can play an important role in non-specific low back pain; hence, its mobility and stability are of special interest. Secondly, the iliolumbar ligament is considered to be an important source of chronic low back pain. Data on a functional relation between the iliolumbar ligament and sacroiliac joint mobility are lacking. METHODS: In 12 human specimens an incremental moment was applied to the sacroiliac joint to induce rotation in the sagittal plane. After the assessment of the relationship between rotation angle and moment in the intact situation, specific parts of the iliolumbar ligaments were transected. After each partial transection the measurements were repeated. RESULTS: Sacroiliac joint mobility in the sagittal plane was significantly increased after a total cut of both iliolumbar ligaments. This increase was in particular due to the transection of a specific part of the iliolumbar ligament, the ventral band. CONCLUSIONS: The main conclusions are: (a) the iliolumbar ligaments restrict sacroiliac joint sagittal mobility; (b) the ventral band of the iliolumbar ligament contributes most to this restriction. RELEVANCE: In embalmed human cadavers, the mobility of the sacroiliac joint increases after sequential cutting of specific parts of the iliolumbar ligaments. It can be expected that severance of this ligament during surgery will lead to increase of mobility and hence loss of stability of the sacroiliac joint. As a consequence adjacent structures will be affected. This may well be a cause of pain in patients with failed back surgery.     

The effects of Fe-doping on MnO2: phase transitions,defect structures and its influence on electrical properties

The composition of Mn_1−xFe_xO₂ (x = 0–0.15) was synthesized by a hydrothermal method at 140 °C for 5 hours of reaction time. Investigations were carried out including XRD, FTIR, Raman spectroscopy, FESEM, and TEM for crystallographic phase analysis. Furthermore, XPS and XAS were used to analyze the oxidation states of Mn and dopant Fe in the octahedron sites. For electrical characterizations, an impedance analyzer was used to explore the conductivity and dielectric properties. It was discovered that the undoped MnO₂ possessed an α-MnO₂ structure performing (2 × 2) tunnel permitting K⁺ insertion and had a nanorod morphology. The Fe ion that was doped into MnO₂ caused a phase transformation from α-MnO₂ to Ramsdellite R-MnO₂ after x = 0.15 was reached and the tunnel dimension changed to (2 × 1). Furthermore, this caused increased micro-strain and oxygen vacancies. An oxidation state analysis of Mn and substituted Fe in the octahedron sites found mixed 3+ and 4+ states. Electrical characterization revealed that the conductivity of Fe-doped MnO₂ is potentially electron influenced by the oxidation state of the cations in the octahedron sites, the micro-strain, the dislocation density, and the movement of K⁺ ions in the tunnel.

Phase transformation from initially α-MnO₂ to R-MnO₂ due to Fe-doping cause modification of interatomic distances affects to the electrical properties.     

影响磁珠共价偶联效率的因素分析

目的研究不同条件下Dynabeads M-280 Tosylactivated磁珠与牛血清白蛋白(BSA)的偶联效率,探讨其影响因素。方法分别取Dynabeads M-280 Tosylactivated磁珠与BSA混合,在不同的pH条件、不同的硫酸铵浓度和不同的BSA浓度下37℃振荡孵育18 h,然后置于磁力架上静置2～3 min分离上清液。应用Bradford蛋白定量法对偶联前后的上清液进行蛋白定量分析,计算不同条件下的偶联效率。结果当缓冲液pH值为9.5时偶联效率为1.12μgBSA/mg磁珠,pH值为7.4时偶联效率为0.41μg BSA/mg磁珠;当反应体系中硫酸铵终浓度为1.2 mol/L时偶联效率为9.5μg BSA/mg磁珠,硫酸铵浓度为0.8 mol/L时偶联效率为8μg BSA/mg磁珠;当偶联的BSA终浓度为0.4 mol/L时偶联效率为9.5μg BSA/mg磁珠,BSA浓度为0.6 mol/L时偶联效率为13μg BSA/mg磁珠。结论缓冲液pH值、硫酸铵浓度和BSA的浓度会影响Dynabeads M-280 Tosylactivated磁珠与BSA的偶联效率,该偶联过程在pH9.5、1.2 mol/L硫酸铵浓度和0.6 mol/L BSA的条件下进行较为适合。     

The influence of gas saturation on microbubble stability

Accurate acoustic characterisation is an essential component of any experimental investigation concerning the use and development of microbubble contrast agents. It is of increasing importance as applications such as therapy and molecular and quantitative imaging are investigated. Such characterisation is generally conducted in the laboratory in the form of bulk acoustic studies or optical observation of single bubbles using high speed photography in a water tank containing "out-gassed" water. The approach is widely used in acoustics to prevent inaccurate measurements being made due to the presence of gas bubbles settling on instrumentation, however, the term is often used to cover a range of water preparation techniques and the final gas content of the water is not usually stated. This technical note demonstrates the influence of gas content on the stability of microbubble contrast agents and concludes that characterisation should always be conducted in equilibrated, gas-saturated water to ensure accurate and repeatable measurements are made.     

Effect of clarithromycin on sputum production and its rheological properties in chronic respiratory tract infections.

Macrolide antibiotics possess a variety of actions other than antimicrobial activities. To determine the effects of long-term administration of clarithromycin (CAM) on the amount and physical properties of sputum in patients with clinical conditions associated with excessive airway secretions, we conducted the present study in a parallel, double-blind, placebo-controlled fashion. Patients were divided into two groups: the first group (n = 16) received CAM (100 mg, twice a day) for 8 weeks, and the second group (n = 15) received placebo. In evaluating airway secretion, the daily amount of expectorated sputum, solid composition, viscoelastic properties (including elastic modulus and dynamic viscosity), and sputum microbiology were assessed. CAM decreased sputum production from 51 +/- 6 to 24 +/- 3 g/day after treatment, whereas placebo had no effect. The bacterial density and sputum flora were unaltered. In the group receiving CAM, the percent solid composition and elastic modulus increased from 2.44% +/- 0.29% to 3.01% +/- 0.20% and 66 +/- 7 to 87 +/- 8 dyne/cm2 (P < 0.05), respectively, but the dynamic viscosity remained unchanged. These results suggest that long-term treatment with CAM reduces the amount of sputum production, probably by inhibiting airway secretions, and increases sputum elasticity.     

Methodology of studying the rheological properties of the gastric mucus and its diagnostic informativeness

Rotation viscosimetry, a simple and easily reproducible method, has been employed in studies of the gastric mucus rheologic characteristics. Examinations of 66 patients with peptic ulcers and of 17 normal subjects have demonstrated a high diagnostic value of the reduction of the elasticity range and of the effective viscosity of the native gastric mucus.     

Characterization of endogenous antioxidant attributes and its influence on thermal stability of canola oil

Difference in thermal stability of two commercially available canola oils prepared by either expeller-extraction (EE) or solvent-extraction (SE) method was investigated. After 5 days consecutive deep-fry, content of oxidized-triacylglycerols (oxTAGs) in SE oil increased by 250.0% compared to its original status. However, 62.5% increase of oxTAGs in EE oil occurred, indicating that EE oil exhibits superior thermal stability to SE oil. Antioxidant capacity of EE oil was highly retained and loss rate of tocopherols in EE oil was much slower than in SE oil during deep-fry. Lipidomics showed that although there was no significant difference in molecular profile of either triacylglycerols or diacylglycerols between two oils, EE oil was characterized with 19 times higher phosphatidylcholine contents than SE oil. Considering no difference in antioxidant capacity between the two oils in their original status, it is proposed that synergetic mechanism is simultaneously initiated by antioxidant compounds and phosphatidylcholines, which plays key roles for maintaining better thermo-stability of vegetable oil during deep-fry.

Difference in thermal stability of two commercially available canola oils prepared by either expeller-extraction (EE) or solvent-extraction (SE) method was investigated.     

The influence of gut microbiota on the rheological characterization of soy hull polysaccharide and mucin interactions

Nutrients reach the body through the food delivery system, interacting with intestinal mucus and gut microbiota for effective absorption. The purpose of this study was to investigate the possible interactions between soluble soy hull polysaccharide (SSHP), gut microbiota and mucin. The digestive environment of the porcine intestinal mucus was simulated, and the changes of the SSHP–mucin mixed system were monitored by shear rheology, interface measurement, scanning electron microscopy, particle size distribution, and microbial sequencing. First, based on scanning electron microscopy and particle size distribution, it was shown that the gut microbiota undergoes glycolysis in different mucus. The apparent viscosity and viscoelastic properties of the mucus during fermentation were then determined using shear rheology. Compared with the control and microwave-assisted citric acid extraction of soy hull polysaccharide (MCSP), the viscosity of microwave-assisted oxalic acid extraction of soy hull polysaccharide (MOSP) increased significantly (p < 0.05) at 24 h, and the thixotropy of all samples increased. The adsorption properties of mucin at the air–liquid interface were analyzed by the interfacial tension technique. As the fermentation time increased, the adsorption performance of the SSHP mucus increased, the interfacial tension decreased, and the expansion modulus increased. Moreover, according to high-throughput 16S rDNA sequencing analysis, the gut microbiota community structure changed significantly after ingestion of MCSP and MOSP, and the abundances of Bifidobacteriaceae and Lactobacillaceae increased to varying degrees. In summary, polysaccharides can be used by the intestinal flora to increase the viscosity and thixotropy of the mucus system, to increase the interfacial strength, and promote the proliferation of intestinal probiotics. This study provides useful insights for the potential application of SSHP.

SSHP increased the viscoelasticity of the interfacial film and reduced the interfacial tension at the air–water interface by interacting with mucin. SSHP increased the ratio of Proteobacteria and Firmicutes and promoted the growth of probiotics.     

含锶生物填料制备与牙科树脂的机械性能

背景:复合树脂是口腔临床常用的充填和黏结材料,其中大量的无机填料对复合树脂的机械和生物学性能有着重要的影响,纳米含锶磷灰石作为复合树脂添加物的研究尚未见报道.目的:观察含锶量和分散剂对纳米含锶磷灰石制备的影响,以及含锶填料对牙科复合树脂机械性能的影响.方法:以氯化锶、硝酸钙、磷酸二氢铵为原料水热法制备纳米含锶磷灰石粉末,采用X射线衍射、红外光谱、透射电镜观察其结构和表面特征,并观察硅烷化处理的含锶填料对复合树脂挠曲强度和压缩强度的影响.结果与结论:成功制备了低结晶性的针状纳米含锶磷灰石,纳米含锶填料添加比为60%时复合树脂的综合力学性能最好,其挠曲强度和压缩强度分别为(92.459±3.285)MPa和(150.573±4.706)MPa.提示纳米含锶填料的加入能改善牙科复合树脂的机械性能.     

Effect of non-covalent self-dimerization on the spectroscopic and electrochemical properties of mixed Cu(i) complexes

A series of six new Cu(i) complexes with ([Cu(N-{4-R}pyridine-2-yl-methanimine)(PPh₃)Br]) formulation, where R corresponds to a donor or acceptor p-substituent, have been synthesized and were used to study self-association effects on their structural and electrochemical properties. X-ray diffraction results showed that in all complexes the packing is organized from a dimer generated by supramolecular π stacking and hydrogen bonding. ¹H-NMR experiments at several concentrations showed that all complexes undergo a fast-self-association monomer–dimer equilibrium in solution, while changes in resonance frequency towards the high or low field in specific protons of the imine ligand allow establishing that dimers have similar structures to those found in the crystal. The thermodynamic parameters for this self-association process were calculated from dimerization constants determined by VT-¹H-NMR experiments for several concentrations at different temperatures. The values for K_D (4.0 to 70.0 M⁻¹ range), ΔH (−1.4 to −2.6 kcal mol⁻¹ range), ΔS (−0.2 to 2.1 cal mol⁻¹ K⁻¹ range), and ΔG₂₉₈ (−0.8 to −2.0 kcal mol⁻¹ range) are of the same order and indicate that the self-dimerization process is enthalpically driven for all complexes. The electrochemical profile of the complexes shows two redox Cu(ii)/Cu(i) processes whose relative intensities are sensitive to concentration changes, indicating that both species are in chemical equilibrium, with the monomer and the dimer having different electrochemical characteristics. We associate this behaviour with the structural lability of the Cu(i) centre that allows the monomeric molecules to reorder conformationally to achieve a more adequate assembly in the non-covalent dimer. As expected, structural properties in the solid and in solution, as well as their electrochemical properties, are not correlated with the electronic parameters usually used to evaluate R substituent effects. This confirms that the properties of the Cu(i) complexes are usually more influenced by steric effects than by the inductive effects of substituents of the ligands. In fact, the results obtained showed the importance of non-covalent intermolecular interactions in the structuring of the coordination geometry around the Cu centre and in the coordinative stability to avoid dissociative equilibria.

Organized crystal packing from non-covalent dimers and the self-dimerization in solution of Cu(NN′)(PPh₃)Br] were characterized. Differences in Cu(ii)/Cu(i) potentials between the monomer and dimer are modulated by the non-covalent interactions.     

镁合金AZ31B材料表性与成骨细胞的黏附

背景：镁合金对成骨细胞的生物学行为及早期黏附是否有影响尚不明确.目的：分析镁合金 AZ31B 的表性,并评价其对成骨细胞黏附的影响.方法：采用扫描电镜及能谱分析明确镁合金 AZ31B 的表面形态及元素组成.以蛋白吸附实验检测镁合金 AZ31B 与钛合金对蛋白的吸附能力.将镁合金 AZ31B 与钛合金分别与小鼠前成骨细胞 MC3T3-El共培养于24孔板内,观察培养2,6,24 h 的细胞黏附情况.结果与结论：扫描电镜可见镁合金 AZ31B 表面较为粗糙,有利于细胞在其表面的黏附.能谱分析结果表明镁合金 AZ31B 的主要元素有镁、铝、锌,其中镁约占96%,铝约占3%,锌约占1%,另有一些其他元素,含量较少.镁合金 AZ31B 与钛合金的蛋白吸附率差异无显著性意义.培养2 h 时,镁合金 AZ31B 与钛合金上的细胞黏附率差异无显著性意义;培养6,24 h,镁合金 AZ31B 上的细胞黏附率显著低于钛合金上的细胞黏附率（P 〈0.01）.培养于镁合金表面的成骨细胞贴壁展开,形态不规则,大多呈梭形,有较多突起,部分细胞间突起相互连接.表明镁合金 AZ31B 具有良好的细胞黏附性,适合于成骨细胞的早期黏附.     

The effect of solid content on the rheological properties and microstructures of a Li-ion battery cathode slurry

The development of new materials and the understanding of the microstructure formation of electrodes have become increasingly important for improving Li-ion battery performance. In this study, we investigate the effect of solid content on the rheological properties of and the microstructures in the cathode slurry prepared from Ni-rich materials. With long-chain structures, PVDF molecules can change their configurations when they come into contact with the solid particles in slurries, and their bridging function can change with the solid content in the slurry. Below the optimum content, particle sedimentation easily takes place. Above the optimum content, excessive yield stress is created in the slurry, and this stress is not conducive to homogeneous distribution of the components. The rheological properties of the slurries vary greatly under different solid contents. We investigated the uniformity and stability of the slurry prepared from Ni-rich materials and found that the most suitable solid content of the slurry lies in the range from 63.9% to 66.3%. Our work might assist in the production of high-performance Li-ion batteries that are made using an electrode slurry.

There are three main situations in which the uniformity and microstructure of the slurry change with the solid content.     

可活化细胞穿膜肽的设计及修饰高分子载体pHPMA的作用检测

目的 合成一种可活化细胞穿膜肽ACPP,并初步探索其穿膜活性及其对高分子聚合物pHPMA的共价修饰作用。方 法通过化学合成的方法合成可活化细胞穿膜肽ACPP,通过免疫荧光法检测细胞内mmp2蛋白的表达;通过荧光显微镜观察鉴定ACPP的穿膜活性。通过化学修饰法合成接合物pc-Ad.egfp 及ACPP-pc-Ad.egfp。通过荧光显微镜观察及动态光散射法初步鉴定接合物的合成,通过荧光显微镜观察鉴定接合物ACPP-pc-Ad.egfp 亚细胞分布。结果成功合成了可活化细胞穿膜肽ACPP;ACPP具有肿瘤靶向性穿膜活性;通过ACPP修饰高分子聚合物pHPMA合成了ACPP-pc-Ad.egfp;经荧光显微镜观察证实ACPP-pc-Ad.egfp 具有较强的感染细胞的能力,并由ACPP介导大分子进行非内吞性跨膜运输。结论成功合成了ACPP,ACPP 具有肿瘤靶向性穿膜活性,并成功修饰高分子聚合物pHPMA。     

不同保存温度对精浆天门冬氨酸氨基转移酶活性和稳定性的影响

目的探讨不同保存温度对精浆天门冬氨酸氨基转移酶(AST)活性和稳定性的影响。方法将10份精浆样本分别保存在室温、4、-20、-80℃等4种不同温度条件下,分别于第1、2、3、5、7、9天测定精浆AST,观察其活性和稳定性的变化。结果在-20℃和-80℃温度条件下精浆AST活性的天间比较差异无统计学意义(P>0.05);在4℃温度条件下精浆AST活性的天间比较差异无统计学(P>0.05),但精浆AST活性从第5天开始呈上升趋势;在室温条件下精浆AST活性从第3天开始比较差异有统计学意义(P<0.05),从第2天开始呈下降趋势。结论在-20℃和-80℃温度条件下精浆AST的活性比较稳定。     

Construction of a flexible covalent organic framework based on triazine units with interesting photoluminescent properties for sensitive and selective detection of picric acid

Highly emissive two-dimensional (2D) covalent organic frameworks (COFs) have rarely been reported due to the challenge of inhibiting the aggregation-caused quenching (ACQ) caused by π–π stacking between layers. To address this issue, the use of flexible building units is a promising strategy. However, currently reported flexible 2D COFs generally exhibit poor crystallinity, low surface area, etc. and the mechanism of the excellent fluorescence performance for the flexible 2D COFs still needs to be further explored. In this article, a novel flexible 2D COF (DTZ-COF) was synthesized using two π-electron deficient triazine monomers rather than the commonly used one π-electron rich fused aromatic ring under solvothermal conditions. Fortunately, DTZ-COF exhibits excellent crystallinity and high surface area (1276.5131 m² g⁻¹ and 2087.5502 m² g⁻¹ for Brunauer–Emmett–Teller (BET) and Langmuir surface area, respectively), which are rarely observed in previously reported flexible 2D COFs. The increased Lewis basic sites endow DTZ-COF with certain advantages in the separation of CO₂ and N₂. The comparison between flexible DTZ-COF and a non-flexible 2D COF (TPT-TPT-COF) with a similar framework suggests that the introduction of flexible building units can indeed improve the photoluminescence (PL) efficiency. The π-electron deficient DTZ-COF has excellent fluorescence performance and exhibits unique solvent responsiveness, such as fluorescence enhancement in aromatic solvents, and fluorescence quenching in alcohol and water. As a chemical sensor for detection of picric acid (2,4,6-trinitrophenol, TNP), the efficient fluorescence quenching involving both static and dynamic behaviors ensures high selectivity and sensitivity (ppb level).

Construction of a novel two-dimensional covalent organic framework with excellent photoluminescence performance using flexible building blocks.     

Construction of a simple crosslinking system and its influence on the poling efficiency and oriental stability of organic electro-optic materials

A new fluorinated polycarbonate was synthesized by solution polymerization of bisphenol AF, anthracen-9-ylmethyl-4,4-bis(4-hydroxyphenyl)pentanoate with triphosgene. This new polycarbonate was used as a host polymer. A traditional chromophore with a D–π–A structure was modified by bisphenol A acrylate affording chromophore A. The large modified group can not only effectively avoid the dipole interaction between chromophores, but also endow the chromophores with the properties of attaching and crosslinking with a host polymer through in situ Diels–Alder “click chemistry” reactions. Such properties can improve both the poling efficiency and the thermal stability of organic electro-optic (EO) polymers. The thermodynamic properties of the crosslinking system showed that the glass transition temperature rose with the increase of the chromophore content. The EO polymer showed a large EO coefficient of about 78.9 pm V⁻¹ at a wavelength of 1310 nm and an excellent long-term stability of about 89% with respect to its initial value and it can be kept after 300 h of heating at 80 °C.

A new fluorinated polycarbonate was synthesized by solution polymerization of bisphenol AF, anthracen-9-ylmethyl-4,4-bis(4-hydroxyphenyl)pentanoate with triphosgene.