Kelei Zhuo

Chloroacetate‐Promoted Selective Oxidation of Heterobenzylic Methylenes under Copper Catalysis

The efficient selective oxidation and functionalization of C-H bonds with molecular oxygen and a copper catalyst to prepare the corresponding ketones was achieved with ethyl chloroacetate as a promoter. In this transformation, various substituted N-heterocyclic compounds were well tolerated. Preliminary mechanistic investigations indicated that organic radical species were involved in the overall process. The N-heterocyclic compounds and ethyl chloroacetate work synergistically to activate C-H bonds in the methylene group, which results in the easy generation of free radical intermediates, thus leading to the corresponding ketones in good yields.

Simple and green synthesis of nitrogen-, sulfur-, and phosphorus-co-doped carbon dots with tunable luminescence properties and sensing application

A simple and green approach to prepare water-soluble, nitrogen-, sulfur-, and phosphorus-co-doped carbon dots (N/S/P-CDs) by one step hydrothermal treatment of cucumber juice is reported. The resultant N/S/P-CDs possess a uniform morphology, a size of less than 10 nm, plentiful O and N functional groups as well as a limited amount of P and S functional groups, and exhibit good luminescence stability, high resistance to photobleaching, high solubility, and excitation-dependent emission behavior. It was also found that a higher reaction temperature favors the formation of N/S/P-CDs with smaller size and longer wavelength of photoluminescence emissions. Moreover, the N/S/P-CDs can be applied as a fluorescent probe for the detection of Hg2+ ions.

Hydrolysis of cellulose catalyzed by novel acidic ionic liquids.

The conversion of cellulosic biomass directly into valuable chemicals becomes a hot subject. Six novel acidic ionic liquids (ILs) based on 2-phenyl-2-imidazoline were synthesized and characterized by UV-VIS, TGA, and NMR. The novel acidic ionic liquids were investigated as catalysts for the hydrolysis of cellulose in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). The acidic ionic liquids with anions HSO4(-) and Cl(-) showed better catalytic performance for the hydrolysis of cellulose than those with H2PO4(-). The temperature and dosage of water affect significantly the yield of total reducing sugar (TRS). When the hydrolysis of cellulose was catalyzed by 1-propyl sulfonic acid-2-phenyl imidazoline hydrogensulfate (IL-1) and the dosage of water was 0.2g, the TRS yield was up to 85.1% within 60 min at 100°C. These new acidic ionic liquids catalysts are expected to have a wide application in the conversion of cellulose into valuable chemicals.

Synthesis of cellulose-derived carbon dots using acidic ionic liquid as a catalyst and its application for detection of Hg2+

Carbon dots (CDs) as versatile carbon-based nanomaterials have attracted increasing attention because of their non-toxicity, good water solubility and photostability, and easy surface functionalization. For their wide application, it is still needed to explore moderate and facile methods for synthesizing CDs from green and inexpensive precursors. In this paper, a moderate method was developed to synthesize water-soluble CDs by ionothermal treatment of cellulose with SO3H-functionalized acidic ionic liquid as a catalyst in 1-butyl-3-methylimidazolium chloride ([Bmim]Cl). The preparation process was carried out at relatively low temperature in non-pressurized vessel. The synthesized CDs exhibit near-spherical morphology with an average diameter of 8.0xa0nm, and the surface is carbon and oxygen rich. The CDs have powder-blue fluorescence with excitation-dependent emission behavior and excellent stability. Moreover, the as-prepared CDs were demonstrated as an effective “turn-off” fluorescent probe for the selective detection of Hg2+ with a good linear relationship over the concentration range from 6 to 80xa0μM. The application of acidic ionic liquid should provide a new path for the synthesis of CDs under mild condition.

Synthesis and interaction studies of benzimidazole derivative with human serum albumin.

A benzimidazole derivative, 1-(2-picolyl)-3-(2-picolyl) benzimidazole iodide (PPB), was synthesized. Fourier transform infrared spectroscopy (FT-IR), UV-visible, three-dimensional (3D) fluorescence, synchronous fluorescence (SF) and fluorescence spectroscopic methods were used to determine the PPB binding mode and the effects of PPB on protein stability and secondary structure. Fluorescence results revealed the presence of static type of quenching mechanism in the binding of PPB to human serum albumin (HSA). The binding constants between PPB and HSA were obtained according to Scatchard equation. The number of binding sites, the binding constants and the thermodynamic parameters were measured. The results showed a spontaneous binding of PPB to HSA through hydrogen bonds and van der Waals forces. In addition, the distance between PPB and the Trp 214 was estimated via employing the Försters non-radiative energy transfer theory, and was found to be 3.49 nm, which indicated that PPB can bind to HSA with high probability. Site marker competitive experiments indicated that the binding of PPB to HSA primarily took place in subdomain IIA.

Facile and shape-controlled electrochemical synthesis of gold nanocrystals by changing water contents in deep eutectic solvents and their electrocatalytic activity

A green, facile and shape-controlled method was developed to synthesize Au nanocrystals (NCs) with different morphologies in deep eutectic solvents (DESs) with different contents of water. The shape and structure of Au NCs were tuned by using different DESs, and/or by controlling the applied potential and the content of water. The resulting Au NCs exhibited a high electrocatalytic activity and poisoning-resistance for ethanol electrooxidation in alkaline media.

A hydrothermal route for synthesizing highly luminescent sulfur- and nitrogen-co-doped carbon dots as nanosensors for Hg2+

Carbon dots have attracted tremendous attention due to their excellent properties, such as outstanding photoluminescence, low cytotoxicity, and superior biocompatibility. In this work, a simple and low cost method was developed to synthesize sulfur- and nitrogen-co-doped carbon dots (S/N-CDs) via hydrothermal treatment of pyritinol hydrochloride in the presence of graphene oxide (GO). The S/N-CDs displayed good water solubility, high luminescence stability, excitation-dependent emission, up-conversion photoluminescence, and strong photoluminescence with a quantum yield of ca. 32.2% without complicated surface modifications. In addition, the prepared S/N-CDs were used as a sensitive probe to detect Hg2+ ions, showing an excellent selectivity and wide linear range. Particularly, the detection limit could reach as low as 1.0 nM.

Ionic Liquid as a Precursor to Synthesize Nitrogen-and Sulfur-co-doped Carbon Dots for Detection of Copper(II) Ions

A facile approach was reported for the synthesis of nitrogen- and sulfur-co-doped carbon dots(N/S-CDs) by the sulfuric acid carbonization of 1-butyl-3-methylimidazolium 2-amino-3-mercaptopropionic acid(L-cysteine) salt([C4mim][Cys]) ionic liquid. The as-prepared N/S-CDs exhibited a good solubility, excitation-dependent emission behavior, and high resistance to photobleaching. Furthermore, the N/S-CDs were employed as a fluorescent probe for detecting Cu2+ in real water samples with satisfactory recovery.

Practical Synthesis of Chromeno[2,3‐b]indole Skeleton via an Aldehyde Group Insertion/Aromatization Strategy

The synthesis of chromeno[2,3-b]indole from simple starting materials remains a demanding process. Herein, 2-bromoindole undergoes nucleophilic attack from salicylaldehyde, followed by intramolecular insertion of an aldehyde group and aromatization to generate the desired chromeno[2,3-b]indoles. Moreover, various functional groups were tolerated and a gram-scale synthesis of the product could be achieved under the optimized condition.

A simple and efficient approach to 2-alkynylbenzofurans under mild copper(I)-catalyzed conditions

The copper(I)-catalyzed synthetic method for the preparation of 2-alkynylbenzofurans from gem-dihaloolefins has been established using DABCO and TBAF·3H2O as a cocatalyst. This methodology relies on a simple reaction system and inexpensive Cu salts as catalysts. It is generally applicable to gem-dihaloolefins and phenylacetylenes.