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141.
We aimed to evaluate the inhibitory effect and mechanism of plantaricin YKX on S. aureus. The mode of action of plantaricin YKX against the cells of S. aureus indicated that plantaricin YKX was able to cause the leakage of cellular content and damage the structure of the cell membranes. Additionally, plantaricin YKX was also able to inhibit the formation of S. aureus biofilms. As the concentration of plantaricin YKX reached 3/4 MIC, the percentage of biofilm formation inhibition was over 50%. Fluorescent dye labeling combined with fluorescence microscopy confirmed the results. Finally, the effect of plantaricin YKX on the AI-2/LuxS QS system was investigated. Molecular docking predicted that the binding energy of AI-2 and plantaricin YKX was −4.7 kcal/mol and the binding energy of bacteriocin and luxS protein was −183.701 kcal/mol. The expression of the luxS gene increased significantly after being cocultured with plantaricin YKX, suggesting that plantaricin YKX can affect the QS system of S. aureus.  相似文献   
142.
Mulberry extract has been proven to have the effect of resisting alcohol damage, but its mechanism is still unclear. In this study, the composition of mulberry ethanol extract (MBE) was identified by LC-MS/MS and the main components of MBE were ascertained by measuring. Gastric mucosal epithelial (GES-1) cells were used to elucidate the mechanism of MBE and rutin (the central part of MBE) helped protect against alcohol damage. The results revealed that phenolics accounted for the majority of MBE, accounting for 308.6 mg/g gallic acid equivalents and 108 substances were identified, including 37 flavonoids and 50 non-flavonoids. The treatment of 400 μg/mL MBE and 320 μM rutin reduced early cell apoptosis and the content of intracellular reactive oxygen species, malondialdehyde and increased glutathione. The qPCR results indicated that the MBE inhibits the expression of genes in the mitogen-activated protein kinase (MAPK) pathway, including p38, JNK, ERK and caspase-3; rutin inhibits the expression of p38 and caspase-3. Overall, MBE was able to reduce the oxidative stress of GES-1 cells and regulated apoptosis-related genes of the MAPK pathway. This study provides information for developing anti-ethanol injury drugs or functional foods.  相似文献   
143.
Domain adaptation aims to learn a classifier for a target domain task by using related labeled data from the source domain. Because source domain data and target domain task may be mismatched, there is an uncertainty of source domain data with respect to the target domain task. Ignoring the uncertainty may lead to models with unreliable and suboptimal classification results for the target domain task. However, most previous works focus on reducing the gap in data distribution between the source and target domains. They do not consider the uncertainty of source domain data about the target domain task and cannot apply the uncertainty to learn an adaptive classifier. Aimed at this problem, we revisit the domain adaptation from source domain data uncertainty based on evidence theory and thereby devise an adaptive classifier with the uncertainty measure. Based on evidence theory, we first design an evidence net to estimate the uncertainty of source domain data about the target domain task. Second, we design a general loss function with the uncertainty measure for the adaptive classifier and extend the loss function to support vector machine. Finally, numerical experiments on simulation datasets and real-world applications are given to comprehensively demonstrate the effectiveness of the adaptive classifier with the uncertainty measure.  相似文献   
144.
To establish the analytic conditions for examining the aroma quality of vanilla pods, we compared different extraction methods and identified a suitable option. We utilized headspace solid-phase microextraction (HS-SPME), steam distillation (SD), simultaneous steam distillation (SDE) and alcoholic extraction combined with gas chromatography (GC) and gas chromatography–mass spectrometry (GC-MS) to identify volatile components of vanilla pods. A total of 84 volatile compounds were identified in this experiment, of which SDE could identify the most volatile compounds, with a total of 51 species, followed by HS-SPME, with a total of 28 species. Ten volatile compounds were identified by extraction with a minimum of 35% alcohol. HS-SPME extraction provided the highest total aroma peak areas, and the peak areas of aldehydes, furans, alcohols, monoterpenes and phenols compounds were several times higher than those of the other extraction methods. The results showed that the two technologies, SDE and HS-SPME, could be used together to facilitate analysis of vanilla pod aroma.  相似文献   
145.
新型含氮螯合树脂的制备及其吸附性能   总被引:1,自引:0,他引:1  
陈兴娟  申颖 《合成化学》2008,16(1):24-27
以三甘醇和苯磺酰氯为原料,二乙烯三胺为交联剂合成了新型含氮螯合树脂(5),其结构经IR表征.讨论了Ni2 浓度和pH对5吸附容量的影响.动力学研究表明,5对Ni2 的吸附速率符合鲛岛公式.  相似文献   
146.
Near-infrared (NIR) light-emitting materials show excellent potential applications in the fields of military technology, bioimaging, optical communication, organic light-emitting diodes (OLEDs), etc. Recently, thermally activated delayed fluorescence (TADF) emitters have made historic developments in the field of OLEDs. These metal-free materials are more attractive because of efficient reverse intersystem crossing processes which result in promising high efficiencies in OLEDs. However, the development of NIR TADF emitters has progressed at a relatively slower pace which could be ascribed to the difficult promotion of external quantum efficiencies. Thus, increasing attention has been paid to NIR TADF emitters. In this review, the recent progress of NIR TADF emitters has been summarized along with their molecular design strategies and photophysical properties, as well as electroluminescence performance data of their OLEDs, respectively.

This review presents the recent progress of NIR TADF emitters along with their molecular design strategies and photophysical properties, as well as the electroluminescence performance data of the emitters and their OLEDs.  相似文献   
147.
Extended polymeric structures based on redox-active species are of great interest in emerging technologies related to energy conversion and storage. However, redox-active monomers tend to inhibit radical polymerisation processes and hence, increase polydispersity and reduce the average molecular weight of the resultant polymers. Here, we demonstrate that styrenic viologens, which do not undergo radical polymerisation effectively on their own, can be readily copolymerised in the presence of cucurbit[n]uril (CB[n]) macrocycles. The presented strategy relies on pre-encapsulation of the viologen monomers within the molecular cavities of the CB[n] macrocycle. Upon polymerisation, the molecular weight of the resultant polymer was found to be an order of magnitude higher and the polydispersity reduced 5-fold. The mechanism responsible for this enhancement was unveiled through comprehensive spectroscopic and electrochemical studies. A combination of solubilisation/stabilisation of reduced viologen species as well as protection of the parent viologens against reduction gives rise to the higher molar masses and reduced polydispersities. The presented study highlights the potential of CB[n]-based host–guest chemistry to control both the redox behavior of monomers as well as the kinetics of their radical polymerisation, which will open up new opportunities across myriad fields.

Extended polymeric structures based on redox-active species are of great interest in emerging technologies related to energy conversion and storage.

Polyviologens are redox-active polymers based on N-substituted bipyridinium derivatives which have emerged as promising materials for energy conversion and storage.1–5 Their physicochemical properties can be adjusted through copolymerisation of the redox-active viologen monomers.6–8 The resultant materials are stable, water soluble and exhibit fast electron transfer kinetics. Polyviologens have been commonly fabricated through step-growth polymerisation in linear and dendritic architectures,9–13 as supramolecular polymers,14–16 networks,6,17,18 and covalent organic frameworks.19,20 Alternatively, anionic/cationic or metathesis-based polymerisations are used to avoid interference of radical-stabilising monomers with the radical initiators, however, these techniques are highly water- and/or oxygen-sensitive.21,22 When free-radical polymerisation (FRP) is conducted in the presence of viologen species, its reduction can cause a depletion of active radicals and thus disruption of the polymerisation process. Despite varying solvents, comonomers and initiator loadings, the direct FRP of viologen-containing monomers remains therefore limited to molar masses of 30 kDa.23–25 Accessing higher molar masses has been possible via post-polymerisation modification,26–28 which has impacted the electrochemical properties of the resultant materials.29,30 Alternative strategies to access higher molar masses of redox-active polymers and control their polymerisation are highly desirable.Incorporation of cucurbit[n]uril (CB[n]) macrocycles have lead to a variety of functional materials through host–guest chemistry.31–34 Moreover, the redox chemistry of viologens can be modulated through complexation with CB[n].35–38 Specifically, CB[n] (n = 7, 8) can tune the redox potential of pristine viologens and efficiently sequester monoreduced viologen radical cations, avoiding precipitation in aqueous environments. Further to this, we recently demonstrated that the viologen radical cation is stabilised by −20 kcal mol−1 when encapsulated in CB[7].39Consequently, we envisioned that incorporating CB[n]s as additives prior to polymerisation could (i) overcome current limits in accessible molar masses, (ii) increase control over FRP of viologen-based monomers through encapsulation and (iii) enable separation of radical species avoiding aggregation.Here, we demonstrate a new approach to control FRP of redox-active monomers leading to high molar masses and decreased dispersity of the resultant polymers. In absence of CB[n], co-polymerisation of the N-styryl-N′-phenyl viologen monomer 12+ and N,N-dimethylacrylamide (DMAAm) only occurs at high initiator loadings (>0.5 mol%, Fig. 1a), leading to low molecular weights and high polydispersity. Using our synthetic approach, 12+ is efficiently copolymerised with DMAAm in the presence of CB[n] (n = 7, 8) macrocycles resulting in control of the polymer molar mass across a broad range, 4–500 kDa (Fig. 1b). Finally, CB[n] are successfully removed from the polymer via competitive host–guest binding and dialysis. Spectroscopic and electrochemical studies revealed that solubilisation/stabilisation of the reduced species and/or shielding of the redox-active monomers from electron transfer processes was responsible for this enhancement.Open in a separate windowFig. 1Schematic representation of the investigated polymerisation. (a) Conventional free radical polymerisation either completely fails to copolymerise redox-active monomers (low initiator loading) or delivers copolymers with limited molar masses and high dispersities (high initiator loading). (b) CB[n]-mediated protection suppresses interference of viologen monomers with radicals formed through the initiation process facilitating copolymerisation. The molar mass of the resulting copolymers is readily tunable via the amount of present CB[n] macrocycles and the CB[n] is post-synthetically removed via competitive binding to yield the final copolymer with desired molar mass. Cl counter-ions are omitted for clarity.Recent studies on symmetric aryl viologens demonstrated 2 : 2 binding modes with CB[8] and high binding constants (up to Ka ∼ 1011 M−2).40,41 Incorporation of polymerisable vinyl moieties, in combination with the relatively static structure of their CB[n] host–guest complexes, was postulated to allow polymerisation without unfavorable side reactions. The asymmetric N-styryl-N′-phenyl viologen monomer 12+ prepared for this study (Fig. S1a and S2–S13) displays a linear geometry and was predicted to bind CB[n] (n = 7, 8) in a 2 : 1 and 2 : 2 binding fashion (Fig. S1b).40,42 Binding modes between CB[n] (n = 7, 8) and 12+ were investigated through titration experiments (1H NMR and ITC) which confirmed the formation of 1·(CB[7])2 and (1)2·(CB[8])2 (see Fig. S25 and S26). 1H NMR titration of CB[7] with 12+ demonstrates encapsulation of both aryl moieties (including the vinyl group) through upfield chemical shifts of the respective signals (Fig. 2a). Similar upfield shifts were observed for CB[8] (Fig. 2c). Different para-aryl substituents (vinyl vs. hydrogen) resulted in either head-to-tail or head-to-head (1)2·(CB[8])2 dimers (Fig. S1b and S26), a previously reported phenomenon.43 Nonetheless, the reversible nature of the complex renders the vinyl group temporarily available for copolymerisation. In the presence of CB[8], 12+ yields polymer molar masses of up to 500 kDa as its complexation is more robust. ITC data confirmed binding stoichiometry, with binding constants of Ka = 2.64 × 106 M−1 for 1·(CB[7])2 and Ka = 9.02 × 1010 M−2 for (1)2·(CB[8])2 (Table S2, Fig. S29a and b).Open in a separate windowFig. 2Supramolecular complexation of 12+ and CB[n]. 1H NMR spectra of 12+ at (a) χCB[7] = 2, (b) χCB[n] = 0 and (c) χCB[8] = 1 in D2O. Cl counter-ions are omitted for clarity.The free radical copolymerisation of 12+ and DMAAm ([M] = 2 M), in the absence of CB[n], was based on optimised DMAAm homopolymerisations (Fig. S14 and S15) and full conversion was confirmed by 1H NMR spectroscopy (Table S1 and Fig. S16). 12+ was maintained at 1 mol% relative to DMAAm and by varying the radical initiator concentration molar masses of up to 30 kDa with broad dispersities (Đ = 11.4) were obtained (Fig. S17). Lower initiator concentrations (<0.25 mol%) limited polymerisation (Mn = 3.7 kDa) and size exclusion chromatography elution peaks exhibited extensive tailing, suggesting that 12+ engages in radical transfer processes.To verify our hypothesis that CB[n] macrocycles can modulate the redox behavior of 12+, FRP of 12+ and DMAAm was conducted with varying amounts of CB[n] (n = 7, 8) (Fig. 3, S18 and S20). Full conversion of all monomers including their successful incorporation into the polymer was verified via1H NMR spectroscopy and SEC (Fig. S18 and S21–S23). Using CB[7], the molar mass of the copolymers was tunable between Mn = 3.7–160 kDa (Fig. 3b and S21a). Importantly, in the presence of CB[8], a broad range of molar masses Mn = 3.7–500 kDa were accessible for 0 < χCB[8] < 1.2 (Fig. S20 and S21b). Increasing the CB[n] (n = 7, 8) concentration caused dispersity values to converge to Đ = 2.2 (χCB[8] = 1.2, χ is the ratio of CB[n] to the redox-active monomer, Fig. S20). The copolymers were purified by addition of adamantylamine (competitive binder) prior to dialysis to deliver CB[n]-free redox-active copolymers (Fig. S23).Open in a separate windowFig. 3(a) In situ copolymerisation of DMAAm with 12+ and CB[7]. (b) Molar mass and dispersity vs. amount of CB[7] in the system. Fitted curve is drawn to guide the eye. Cl counter-ions are omitted for clarity.The range of molar masses obtainable through addition of CB[n] (n = 7, 8) correlated with the measured Ka (Fig. 3b and S20). Binding of 12+ to CB[8] was stronger and therefore lower concentrations of CB[8] were required to shift the binding equilibrium and mitigate disruption of the polymerisation. Dispersity values reached a maximum at χCB[7] = 0.6 or χCB[8] = 0.3, suggesting 1+˙ is only partially encapsulated. Consequently, higher CB[n] concentrations can enable FRP with lower initiator concentrations (0.10 mol%, Fig. S19), which demonstrates the major role of complexation to modulate electron accepting properties of 12+.The redox-active monomer 12+ can engage with propagating primary radicals (P) to either be incorporated into the growing polymer chain (Pm–12+˙) or to abstract an electron deactivating it (Pm). This deactivation likely occurs through oxidative termination producing 1+˙ (energetic sink), inactive oligo- and/or polymer chains (Pm) and a proton H+, causing retardation of the overall polymerisation. Oxidative terminations have been previously observed in aqueous polymerisations of methyl methacrylate, styrenes and acrylonitriles that make use of redox initiator systems.44–47 Another example by Das et al. investigated the use of methylene blue as a retarder, with the primary radical being transferred to a methylene blue electron acceptor via oxidative termination, altogether supporting the outlined mechanism of our system (extended discussion see ESI, Section 1.4).48The process of retardation can, however, be successfully suppressed, when monomer 12+ is encapsulated within CB[n] macrocycles. Herein the formation of 1·(CB[7])2 or (1)2·(CB[8])2 results in shielding of the redox-active component of 12+ from other radicals within the system, hampering other electron transfer reactions. This inhibits termination and results in extended polymerisation processes leading to higher molar mass polymers through mitigation of radical transfer reactions. Moreover, suppressing the formation of 1+˙ through supramolecular encapsulation minimises both π and σ dimerisation of the emerging viologen radical species,39 preventing any further reactions that could impact the molar mass or polydispersity of the resulting polymers.Cyclic voltammetry (CV) and UV-Vis titration experiments were conducted to provide insight into the impact of CB[n] on the redox behavior and control over FRP of 12+. Excess of CB[n] (n = 7, 8) towards 12+ resulted in a complete suppression of electron transfer processes (Fig. S31 and S32). Initially, 12+ shows a quasi-reversible reduction wave at −0.44 V forming 1+˙ (Fig. 4a). Increasing χCB[7], this reduction peak decreases and shifts towards more negative potentials (−0.51 V, χCB[7] = 1) accompanied by the formation of 12+·(CB[7])1. A second cathodic peak emerges at −0.75 V due to the increased formation of 12+·(CB[7])2. At χCB[7] = 2, this peak shifts to −0.80 V, where it reaches maximum intensity, once 12+·(CB[7])2 is the dominating species in solution. When 2 < χCB[7] < 4, the intensity of the reduction peak decreases and the complexation equilibrium is shifted towards the bound state, complete suppression of the reduction peak occurs at χCB[7] = 4. Similarly, the oxidation wave intensity is reduced by 95% at χCB[7] = 4 causing suppression of potential oxidative radical transfer processes (Fig. 4c).Open in a separate windowFig. 4Mechanism of the CB[n]-mediated (n = 7, 8) strategy for the controlled copolymerisation of redox-active monomer 12+. (a) Cyclic voltammogram with varying amounts of CB[7]. (b) UV-Vis titration of 12+ with varying amounts of CB[7]. (c) Intensity decay of the oxidation peak at −0.27 V and change in absorption maximum of 1+˙ at 590 nm vs. χCB[7]. (d) Electron transfer processes of 12+ to generate 1+˙ and 10. (e) Reduction of 12+ resulting in precipitation of 10. (f) Stabilisation of 1+˙ through encapsulation with CB[7]. (g) Protection of 12+ from redox processes through CB[7]-mediated encapsulation.The concentration of 1+˙ can be monitored using UV-Vis (Fig. 4b and S34).49 Absorbance at 590 nm (λmax) vs. χCB[7] was plotted and the concentration of 1+˙ increases, reaching a maximum at χCB[7] = 4 (Fig. 4c). When χCB[7] > 4, a decrease in concentration of 1+˙ was observed. We postulate the following mechanism: at χCB[7] = 0, 12+ is reduced to produce high concentrations of 1+˙ that partially disproportionates to form 10, which precipitates (Fig. 4e and S34). When 0 < χCB[7] < 4, increasing amounts of green 1+˙ are stabilised through encapsulation within CB[7] suppressing disproportionation (Fig. 4c (cuvette pictures), Fig. 4f). For χCB[7] > 4, 12+ is protected from reduction through encapsulation (Fig. 4g).To further demonstrate applicability of this strategy, we chose another viologen-based monomer 22+ for copolymerisation (Fig. 5a). As opposed to 12+, CB binds predominantly to the styryl moiety of 22+ (Fig. S27 and S28).50 ITC data showed that 22+ binds CB[7] in a 1 : 1 fashion with a binding affinity of Ka = 2.32 × 106 M−1 (Fig. S30 and Table S2). Monomer 22+ was also analysed via CV and showed three reversible reduction waves at −0.91 V, −0.61 V (viologen) and 0.40 V (styrene). Similar to 12+, excess CB[7] selectively protects the molecule from redox processes, while the vinyl moiety remains accessible (Fig. 5a, S33c and d). For CB[8], only partial suppression of electron transfer processes was observed (Fig. S33e and f). We therefore chose CB[7] as an additive to increase control over FRP of 22+ (Fig. 5b). Copolymerisation of 22+ (1 mol%) and DMAAm ([M] = 2 M) at χCB[7] = 0 resulted in Mn = 28 kDa. When χCB[7] = 0.1, 0.2 or 0.3, Mn increased gradually from 124 to 230 and 313 kDa, respectively, demonstrating the potential of this strategy for FRP of redox-active monomers. Higher percentages of CB[7] led to copolymers with presumably higher molar masses causing a drastic decrease in solubility that prevented further analysis. Investigations on a broader spectrum of such copolymers, including those with higher contents of 22+ are currently ongoing.Open in a separate windowFig. 5(a) Cyclic voltammogram of viologen-containing monomer 22+ and its complexation with CB[n] (n = 7, 8) at a concentration of 1 mM using a scan rate of 10 mV s−1 in 0.1 mM NaCl solution. (b) Molar mass and dispersity of 22+-containing copolymers vs. equivalents of CB[7]. Cl counter-ions are omitted for clarity.In conclusion, we report a supramolecular strategy to induce control over the free radical polymerisation of redox-active building blocks, unlocking high molar masses and reducing polydispersity of the resulting polymers. Through the use of CB[n] macrocycles (n = 7, 8) for the copolymerisation of styrenic viologen 12+, a broad range of molar masses between 3.7–500 kDa becomes accessible. Our mechanistic investigations elucidated that the redox behavior of monomer 12+ is dominated by either CB[n]-mediated stabilisation of monoradical cationic species or protection of the encapsulated pyridinium species from reduction. In the stabilisation regime (χCB[7] < 4), 12+ is reduced to form the radical cation 1+˙, which is subsequently stabilised through CB[7] encapsulation. Upon reaching a critical concentration of CB[7] (χCB[7] > 4), the system enters a protection-dominated regime, where reduction of 12+ is suppressed and the concentration of 1+˙ diminishes. The resulting copolymers can be purified by use of a competitive binder to remove CB[n] macrocycles from the product. This strategy was successfully translated to a structurally different redox-active monomer that suffered similar limitations. We believe that the reported strategy of copolymerisation of redox-active monomers will open new avenues in the synthesis of functional materials for energy conversion and storage as well as for applications in electrochromic devices and (nano)electronics.  相似文献   
148.
Herein, we present a facile and efficient allylation method via Ni-catalyzed cross-electrophile coupling of readily available allylic acetates with a variety of substituted alkenyl bromides using zinc as the terminal reductant. This Ni-catalyzed modular approach displays excellent functional group tolerance and a broad substrate scope, which the creation of a series of 1,4-dienes including several structurally complex natural products and pharmaceutical motifs. Moreover, the coupling strategy has the potential to realize enantiomeric control. The practicality of this transformation is demonstrated through the potent modification of the naturally antitumor active molecule β-elemene.

Herein, we present a facile and efficient allylation method via Ni-catalyzed cross-electrophile coupling of readily available allylic acetates with a variety of substituted alkenyl bromides using zinc as the terminal reductant.  相似文献   
149.
以N,N-二甲基甲酰胺(DMF)为溶剂,通过改变铜源和表面活性剂,调控反应参数,溶剂热条件下制备了三维十字形、空心及实心的Cu2O球晶。利用XRD、SEM等表征手段,分析探讨了工艺条件变化对Cu2O球晶形貌的影响。研究表明,随着DMF浓度的增大,体系的还原能力增强,Cu+增多,溶液的过饱和度增大,Cu2O晶体集合体形态由晶体结构控制的各向异性与对称性的球晶逐渐向各向同性球晶演变。十二烷基硫酸钠(SDS)、十六烷基三甲基溴化铵(CTAB)、聚乙烯吡咯烷酮(PVP)等表面活性剂有助于降低溶液的过饱和度,增加结晶质的表面扩散能力,有利于规则形态Cu2O晶粒的形成。反应体系中,Cu(Ac)2·H2O水解生成的羧基与DMF中的甲酰基在高温下发生脱羧反应产生CO2气体以及SDS发泡作用产生的气体是形成空心Cu2O球晶的重要原因。  相似文献   
150.
以Zn(NO3)2· 6H2O和C6H12N4为原材料,采用二步水热法在碳纤维布上合成了形貌尺寸均匀的ZnO超细纳米线阵列。用 X 射线衍射(XRD)和扫描电镜(SEM)对其晶体结构和形貌进行了表征,利用恒流充放电测试等手段对其进行电化学性能测试。测试结果表明,材料表现出优异的电化学性能。在200 mA/g的电流密度下循环150次后,ZnO超细纳米线阵列仍然约有730 mAh/g的充放电比容量,库伦效率保持在95%以上。在1 200 mA/g的大倍率条件下,材料的充放电比容量依旧可达481 mAh/g左右,表现出十分良好的循环稳定性和可逆性能,是一种较为理想的锂离子电池负极复合材料。  相似文献   
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