Multicolor biomass based carbon nanodots for bacterial imaging

Biomass-based carbon nanodots(CNDs) are becoming promising fluorescent materials due to their superior optical properties and excellent biocompatibility. However, most fluorescent CNDs are prepared under high temperatures with artificial chemicals as precursors. In this work, multicolor biomass-based CNDs have been prepared by employing natural biomass as precursors through an ultrasonic-assisted method at room temperature. The multicolor biomass-based CNDs can be prepared within 10 min, and cav...     

电化学方法调控荧光碳点的研究

作为零维碳基发光纳米材料,碳点是对现有发光纳米材料的重要补充. 精准控制粒径及表面结构对实现碳点的性质调控及其应用至关重要. 本文介绍了本课题组在利用电化学方法研究荧光碳点方面的进展. 重点展示了利用电化学方法实现对碳点粒径的控制,对表面氧化程度的调节以及对其发光机理的研究. 电化学方法可对只有几纳米厚度的材料表面进行有效的控制,可操作性强且经济环保. 通过对碳点的粒径及表面的调控,作者也进一步揭示了碳点的发光与表面结构的相关性. 这些工作为碳点的合成及其性质调控提供了可循的规律,有利于推动碳点在生物医生成像、传感检测、催化及能源转化等领域的应用.     

Synthetization and Functionalization of Natural,Polymer, and Quantum-Based Carbon Nanodots and Their Application in Biomedicine

Carbon nanodots (CNDs) are a developing branch of nanomaterials and nanoscience. This has generated much more interest in the field and class of biomedicine science by way of unique particular properties, such as high stability, great photoluminescence, easy green synthesis, and simple surface modification. Numerous applications, such as bioimaging, biosensing, and treatment, have made use of CNDs. This review describes the most recent developments in CND research and talks about major changes in the understanding of CNDs and their prospects as biomedical tools. The importance of this work lies in the ability of CNDs to overcome many of the limitations associated with traditional materials used in biomedicine, such as toxicity, poor biocompatibility, and limited functionality. Furthermore, the use of CNDs as drug carriers, imaging agents, and sensors has shown great potential in improving the diagnosis and treatment of various diseases. The novelty of this work lies in the diversity of approaches used in the synthesis and functionalization of CNDs, and the unique properties of CNDs that make them versatile tools for biomedicine. In particular, the ability to tune the size, shape, and surface chemistry of CNDs allows for the creation of tailored materials with specific biomedical applications. The review also discusses the challenges and future prospects of CNDs in biomedicine, including the need for standardization and optimization of CND synthesis, functionalization, and characterization protocols.     

Upconverting Carbon Nanodots from Ethylenediaminetetraacetic Acid (EDTA) as Near-Infrared Activated Phototheranostic Agents

This work describes the synthesis of nitrogen-doped carbon nanodots (CNDs) synthesized from ethylenediaminetetraacetic acid (EDTA) as a precursor and their application as luminescent agents with a dual-mode theranostic role as near-infrared (NIR) triggered imaging and photodynamic therapy agents. Interestingly, these fluorescent CNDs are more rapidly and selectively internalized by tumor cells and exhibit very limited cytotoxicity until remotely activated with a NIR illumination source. These CNDs are excellent candidates for phototheranostic purposes, for example, simultaneous imaging and therapy can be carried out on cancer cells by using their luminescent properties and the in situ generation of reactive oxidative species (ROS) upon excitation in the NIR range. In the presence of CNDs, NIR remote activation induces the in vitro killing of U251MG cells. Through the use of flow imaging cytometry, we have been able to successfully map and quantify the different types of cell deaths induced by the presence of intracellular superoxide anions ( ^. O₂⁻) and hydrogen peroxide (H₂O₂) ROS generated in situ upon NIR irradiation.     

Ultrasmall green-emitting carbon nanodots with 80% photoluminescence quantum yield for lysosome imaging

Carbon-based fluorescent nanomaterials have gained much attention in recent years. In this work, green-photoluminescent carbon nanodots (CNDs; also termed carbon dots, CDs) with amine termination were synthesized via the hydrothermal treatment of amine-containing spermine and rose bengal (RB) molecules. The CNDs have an ultrasmall size of ∼2.2 nm and present bright photoluminescence with a high quantum yield of ∼80% which is possibly attributed to the loss of halogen atoms (Cl and I) during the hydrothermal reaction. Different from most CNDs which have multicolor fluorescence emission, the as-prepared CNDs possess excitation-independent emission property, which can avoid fluorescence overlap with other fluorescent dyes. Moreover, the weakly basic amine-terminated surface endows the CNDs with the acidotropic effect. As a result, the CNDs can accumulate in the acidic lysosomes after cellular internalization and can serve as a favorable agent for lysosome imaging. Besides, the CNDs have a negligible impact on the lysosomal morphology even after 48 h incubation and exhibit excellent biocompatibility in the used cell models.     

Synthetic Strategies for the Selective Functionalization of Carbon Nanodots Allow Optically Communicating Suprastructures

The surface of Carbon Nanodots (CNDs) stands as a rich chemical platform, able to regulate the interactions between particles and external species. Performing selective functionalization of these nanoscale entities is of practical importance, however, it still represents a considerable challenge. In this work, we exploited the organic chemistry toolbox to install target functionalities on the CND surface, while monitoring the chemical changes on the material's outer shell through nuclear magnetic resonance spectroscopy. Following this, we investigated the use of click chemistry to covalently connect CNDs of different nature en-route towards covalent suprastructures with unprecedent molecular control. The different photophysical properties of the connected particles allowed their optical communication in the excited state. This work paves the way for the development of selective and addressable CND building blocks which can act as modular nanoscale synthons that mirror the long-established reactivity of molecular organic synthesis.     

Customizing the Electrochemical Properties of Carbon Nanodots by Using Quinones in Bottom‐Up Synthesis

We show how the redox potentials of carbon nanodots (CNDs) can be modulated by employing quinones as electroactive precursors during a microwave‐assisted synthesis. We prepared and characterized a redox library of CNDs, demonstrating that this approach can promote the use of carbon nanodots for ad hoc applications, including photocatalysis.     

Turning waste into wealth: facile and green synthesis of carbon nanodots from pollutants and applications to bioimaging

In an effort to turn waste into wealth, Reactive Red 2 (RR2), a common and refractory organic pollutant in industrial wastewater, has been employed for the first time as a precursor to synthesize carbon nanodots (CNDs) by a facile, green and low-cost route, without utilization of any strong acids or other oxidizers. The detailed characterizations have confirmed that the synthesized CNDs exhibit good water dispersibility, with a mean particle size of 2.43 nm and thickness of 1–3 layers. Importantly, the excellent fluorescence properties and much reduced biotoxicity of the CNDs confer its potential applications in further biological imaging, which has been successfully verified in both in vitro (cell culture) and in vivo (zebrafish) model systems. Thus, it is demonstrated that the synthesized CNDs exhibit nice biocompatibility and fluorescence properties for bioimaging. This work not only provides a novel economical and environmentally friendly approach in recycling a chemical pollutant, but also greatly promotes the potential application of CNDs in biological imaging.

The pollutant reactive red 2 was employed to synthesize fluorescent carbon nanodots allowing biological imaging in vitro and in vivo.     

Intramolecular Hydrogen Bonds Quench Photoluminescence and Enhance Photocatalytic Activity of Carbon Nanodots

Understanding the photoluminescence (PL) and photocatalytic properties of carbon nanodots (CNDs) induced by environmental factors such as pH through surface groups is significantly important to rationally tune the emission and photodriven catalysis of CNDs. Through adjusting the pH of an aqueous solution of CNDs, it was found that the PL of CNDs prepared by ultrasonic treatment of glucose is strongly quenched at pH 1 because of the formation of intramolecular hydrogen bonds among the oxygen‐containing surface groups. The position of the strongest PL peak and its corresponding excitation wavelength strongly depend on the surface groups. The origins of the blue and green emissions of CNDs are closely related to the carboxyl and hydroxyl groups, respectively. The deprotonated COO^? and CO^? groups weaken the PL peak of the CNDs and shift it to the red. CNDs alone exhibit photocatalytic activity towards degradation of Rhodamine B at different pH values under UV irradiation. The photocatalytic activity of the CNDs is the highest at pH 1 because of the strong intramolecular hydrogen bonds formed among the oxygen‐containing groups.     

Synthesis,Separation, and Characterization of Small and Highly Fluorescent Nitrogen‐Doped Carbon NanoDots

A facile bottom‐up approach to carbon nanodots (CNDs) is reported, using a microwave‐assisted procedure under controlled conditions. The as‐prepared nitrogen‐doped CNDs (NCNDs) show narrow size‐distribution, abundant surface traps and functional groups, resulting in tunable fluorescent emission and excellent solubility in water. Moreover, we present a general method for the separation of NCNDs by low‐pressure size‐exclusion chromatography, leading to an even narrower size distribution, different surface composition, and optical properties. They display among the smallest size and the highest FLQYs reported so far. ¹³C‐enriched starting materials produced N¹³CNDs suitable for thorough NMR studies, which gave useful information on their molecular structure. Moreover, they can be easily functionalized and can be used as water‐soluble carriers. This work provides an avenue to size‐ and surface‐controllable and structurally defined NCNDs for applications in areas such as optoelectronics, biomedicine, and bioimaging.     

A carbon–carbon hybrid – immobilizing carbon nanodots onto carbon nanotubes

The thrust of this work is to integrate small and uniformly sized carbon nanodots (CNDs) with single-walled carbon nanotubes (SWCNT) of different diameters as electron donors and electron acceptors, respectively, and to test their synergetic interactions in terms of optoelectronic devices. CNDs (denoted pCNDs, where p indicates pressure) were prepared by pressure-controlled microwave decomposition of citric acid and urea. pCNDs were immobilized on single-walled carbon nanotubes by wrapping the latter with poly(4-vinylbenzyl trimethylamine) (PVBTA), which features positively charged ammonium groups in the backbone. Negatively charged surface groups on the CNDs lead to attractive electrostatic interactions. Ground state interactions between the CNDs and SWCNTs were confirmed by a full-fledged photophysical investigation based on steady-state and time-resolved techniques. As a complement, charge injection into the SWCNTs upon photoexcitation was investigated by ultra-short time-resolved spectroscopy.     

Aptamer‐Based Turn‐On Detection of Thrombin in Biological Fluids Based on Efficient Phosphorescence Energy Transfer from Mn‐Doped ZnS Quantum Dots to Carbon Nanodots

This paper presents the first example of a sensitive, selective, and stable phosphorescent sensor based on phosphorescence energy transfer (PET) for thrombin that functions through thrombin–aptamer recognition events. In this work, an efficient PET donor–acceptor pair using Mn‐doped ZnS quantum dots labeled with thrombin‐binding aptamers (TBA QDs) as donors, and carbon nanodots (CNDs) as acceptors has been constructed. Due to the π–π stacking interaction between aptamer and CNDs, the energy donor and acceptor are taken into close proximity, leading to the phosphorescence quenching of donors, TBA QDs. A maximum phosphorescence quenching efficiency as high as 95.9 % is acquired. With the introduction of thrombin to the “off state” of the TBA‐QDs‐CNDs system, the phosphorescence is “turned on” due to the formation of quadruplex‐thrombin complexes, which releases the energy acceptor CNDs from the energy donors. Based on the restored phosphorescence, an aptamer‐based turn‐on thrombin biosensor has been demonstrated by using the phosphorescence as a signal transduction method. The sensor displays a linear range of 0–40 nM for thrombin, with a detection limit as low as 0.013 nM in pure buffers. The proposed aptasensor has also been used to monitor thrombin in complex biological fluids, including serum and plasma, with satisfactory recovery ranging from 96.8 to 104.3 %. This is the first time that Mn‐doped ZnS quantum dots and CNDs have been employed as a donor–acceptor pair to construct PET‐based biosensors, which combines both the photophysical merits of phosphorescence QDs and the superquenching ability of CNDs and thus affords excellent analytical performance. We believe this proposed method could pave the way to a new design of biosensors using PET systems.     

Synthesis,Separation, and Characterization of Small and Highly Fluorescent Nitrogen‐Doped Carbon NanoDots

A facile bottom‐up approach to carbon nanodots (CNDs) is reported, using a microwave‐assisted procedure under controlled conditions. The as‐prepared nitrogen‐doped CNDs (NCNDs) show narrow size‐distribution, abundant surface traps and functional groups, resulting in tunable fluorescent emission and excellent solubility in water. Moreover, we present a general method for the separation of NCNDs by low‐pressure size‐exclusion chromatography, leading to an even narrower size distribution, different surface composition, and optical properties. They display among the smallest size and the highest FLQYs reported so far. ¹³C‐enriched starting materials produced N¹³CNDs suitable for thorough NMR studies, which gave useful information on their molecular structure. Moreover, they can be easily functionalized and can be used as water‐soluble carriers. This work provides an avenue to size‐ and surface‐controllable and structurally defined NCNDs for applications in areas such as optoelectronics, biomedicine, and bioimaging.     

有机小分子催化的烯酮的不对称环加成反应

重点从立体选择性和催化机理方面,总结了不同的有机小分子催化剂在烯酮的[2+2]和[4+2]不对称环加成反应中的应用.     

Organocatalytic asymmetric direct vinylogous Michael addition of α,β-unsaturated γ-butyrolactam to nitroolefins

The first organocatalytic enantioselective direct vinylogous Michael reaction of α,β-unsaturated γ-butyrolactam to nitroolefins is developed using cinchona alkaloids as the catalysts. Both product enantiomers are accessible with moderate to good enantioselectivity.     

Scalable and Recyclable All‐Organic Colloidal Cascade Catalysts

We report on the synthesis of core–shell microparticles (CSMs) with an acid catalyst in the core and a base catalyst in the shell by surfactant‐free emulsion polymerization (SFEP). The organocatalytic monomers were separately copolymerized in three synthetic steps allowing the spatial separation of incompatible acid and base catalysts within the CSMs. Importantly, a protected and thermo‐decomposable sulfonate monomer was used as acid source to circumvent the neutralization of the base catalyst during shell formation, which was key to obtain stable, catalytically active CSMs. The catalysts showed excellent performance in an established one‐pot model cascade reaction in various solvents (including water), which involved an acid‐catalyzed deacetalization followed by a base‐catalyzed Knoevenagel condensation. The CSMs are easily recycled, modified, and their synthesis is scalable, making them promising candidates for organocatalytic applications.     

Organocatalytic enantioselective transformations involving quinone derivatives as reaction partners

This digest summarizes the recent progress made in the organocatalytic asymmetric reactions involving 1,4-quinone derivatives. The roles of quinones as Michael donors, Michael acceptors, dienophiles, 1,3-dipolarophiles and cascade reaction partners have been extensively investigated to access complex structural frameworks in the presence of chiral amine catalysts, phosphoric acid catalysts, bifunctional catalysts (Cinchona alkaloids- and thiourea-based), carboxylic acid catalysts, boronic acid catalysts and cationic oxazaborolidinium ions.     

Synthesis and application of novel imidazole and 1H-tetrazolic acid containing catalysts in enantioselective organocatalyzed Diels–Alder reactions

Herein we report studies on the organocatalytic Diels–Alder reaction using a variety of catalysts capable of activating α,β-unsaturated carbonyl compounds for reactions with dienes. The structurally attractive catalysts 4 and 14 were utilized in the enantioselective organocatalytic Diels–Alder reactions. Catalyst 4 provided the products in fair yields and more importantly in good enantioselectivities of up to 83% ee. Catalyst 14 was synthesized in high yield and was assessed in the enantioselective organocatalytic Diels–Alder reaction. Catalyst 14 proved to be a highly active and selective catalyst providing the products in high yield and high enantioselectivities up to 95% ee.     

Dihydroxyacetone variants in the organocatalytic construction of carbohydrates: mimicking tagatose and fuculose aldolases

Dihydroxyacetone variants have been explored as donors in organocatalytic aldol reactions with various aldehyde and ketone acceptors. The protected form of dihydroxyacetone that was chosen for in-depth study was 2,2-dimethyl-1,3-dioxan-5-one, 1. Among the catalysts surveyed here, proline proved to be superior in terms of yield and stereoselectivities in the construction of various carbohydrate scaffolds. In a fashion analogous to aldolase enzymes, the de novo preparation of L-ribulose, L-lyxose, D-ribose, D-tagatose, 1-amino-1-deoxy-D-lyxitol, and other carbohydrates was accomplished via the use of 1 and proline. In reactions using 2,2-dimethyl-1,3-dioxan-5-one 1 as a donor, (S)-proline can be used as a functional mimic of tagatose aldolase, whereas (R)-proline can be regarded as an organocatalytic mimic of fuculose aldolase.     

Bioinspired organocatalytic asymmetric reactions

Several small organic molecule catalysts are reminiscent of natural enzymes in their mode of action and substrate interaction/activation. This striking similarity has been a great source of inspiration for the development of new organocatalytic asymmetric processes. A few representative examples, mostly dealing with catalysts interacting through multiple hydrogen-bonds (synthetic oxyanion holes), are highlighted in this perspective.