Asymmetric Synthesis of Enantioenriched (+)-Elaeokanine A

The key transformation in the total synthesis of (+)-elaeokanine A was accomplished by asymmetric deprotonation of N-Boc pyrrolidine, followed by the reaction of the in situ generated enantioenriched stereogenic cuprate reagent with (E)-4-bromo-1-iodo-1-trimethylsilyl-1-butene with retention of configuration. N-Boc deprotection, followed by a one-pot olefin isomerization and intramolecular amine alkylation afforded a bicyclic vinyl bromide that was converted into (+)-elaeokanine A by sequential halogen metal exchange and reaction of the organolithium reagent with N-butanoylmorpholine

Halogen- and <i>N</i>-Haloimide-Promoted Homo- and Heterocoupling of α-(<i>N</i>-Carbamoyl)alkylcuprates and α-(Alkoxy)alkylcuprates

Both homo- and mixed lithium di-α-(heteroatom)alkylcuprates readily dimerize upon addition of halogens (e.g., I2, Br2) or N-halosuccinimides to afford the coupled products in excellent yields. Higher yields result when the requisite α-(heteroatom)alkyllithium reagents are generated via deprotonation rather than by transmetalation of the corresponding stannanes. Mixed lithium dialkyl- or alkyl(aryl)cuprate reagents containing one α-(heteroatom)alkyl ligand and one simple alkyl or aryl ligand give significantly lower yields of coupled product. Low enantioselectivity has been achieved in the oxidative coupling of lithium (n-Bu)(2-pyrrolidinyl)cuprate

Regio- and Enantioselective Control in the Reactions of α-(<i>N</i>-Carbamoyl)alkylcuprates with Allylic Phosphates

α-(N-Carbamoyl)alkylcuprates (RCuCNLi or R2CuLi) react with allylic phosphates to afford homoallylic amines in good chemical yields. Regioselectivity is governed by steric factors in both the cuprate reagent and phosphate substrate and systems can be designed to give either the SN2‘ or SN2 substitution product cleanly. Excellent enantioselectivities can be achieved with either a scalemic α-di[(N-carbamoyl)alkyl]cuprate and an achiral phosphate or with a scalemic allylic phosphate and an achiral cuprate reagent

Reaction of α-(<i>N</i>-Carbamoyl)alkylcuprates with Enantioenriched Propargyl Electrophiles: Synthesis of Enantioenriched 3-Pyrrolines

Enantioenriched propargyl mesylates or perfluorobenzoates react with α-(N-carbamoyl)alkylcuprates to afford scalemic α-(N-carbamoyl) allenes which undergo N-Boc deprotection and AgNO3-promoted cyclization to afford N-alkyl-3-pyrrolines. The synthetic sequence proceeds under optimal conditions with no loss of enantiopurity relative to the starting propargyl alcohols prepared by asymmetric addition of terminal alkynes to aldehydes

Cationic Surfactant-Mediated Coagulation for Enhanced Removal of Toxic Metal–Organic Complexes: Performance, Mechanism, and Validation

Toxic metal ions tend to complex with coexisting organic ligands in contaminated waters, challenging their efficient removal via traditional processes such as adsorption, coagulation, or precipitation. In this study, we demonstrate a proof-of-concept strategy for the removal of metal–organic complexes using cationic surfactants as the coagulant. Using cetyltrimethylammonium bromide (CTAB) as the model one, such a simple strategy is applicable for efficient water decontamination from various metals [Cr­(III), Ni­(II), Cu­(II), Zn­(II), and Cd­(II)] complexed with different ligands (citrate, malate, tartrate, and oxalate), outperforming direct alkaline precipitation and Al­(III) coagulation remarkably. In the case of the Cr­(III)-citrate complex, the CTAB coagulation could result in the Cr­(III) reduction from 10.4 to only 0.2 mg/L. A negligible effect of nine ubiquitous cations or anions was observed on the process, while the carbon chain of surfactants larger than C16 is required to achieve a satisfactory removal of the target complexes. The strong electrostatic interaction between the negatively charged Cr­(III)-citrate species and the positively charged CTA+ results in the dehydration of the head group of CTAB and the formation of unstable aggregates that precipitate from the solution. Furthermore, the CTAB coagulation is demonstrated for effective removal of Cr­(III) complexes in real tannery wastewater, resulting in the residual Cr­(III) below the discharge standard of China. This study may present a new option for water decontamination from metal–organic complexes

Cationic Surfactant-Mediated Coagulation for Enhanced Removal of Toxic Metal–Organic Complexes: Performance, Mechanism, and Validation

Toxic metal ions tend to complex with coexisting organic ligands in contaminated waters, challenging their efficient removal via traditional processes such as adsorption, coagulation, or precipitation. In this study, we demonstrate a proof-of-concept strategy for the removal of metal–organic complexes using cationic surfactants as the coagulant. Using cetyltrimethylammonium bromide (CTAB) as the model one, such a simple strategy is applicable for efficient water decontamination from various metals [Cr­(III), Ni­(II), Cu­(II), Zn­(II), and Cd­(II)] complexed with different ligands (citrate, malate, tartrate, and oxalate), outperforming direct alkaline precipitation and Al­(III) coagulation remarkably. In the case of the Cr­(III)-citrate complex, the CTAB coagulation could result in the Cr­(III) reduction from 10.4 to only 0.2 mg/L. A negligible effect of nine ubiquitous cations or anions was observed on the process, while the carbon chain of surfactants larger than C16 is required to achieve a satisfactory removal of the target complexes. The strong electrostatic interaction between the negatively charged Cr­(III)-citrate species and the positively charged CTA+ results in the dehydration of the head group of CTAB and the formation of unstable aggregates that precipitate from the solution. Furthermore, the CTAB coagulation is demonstrated for effective removal of Cr­(III) complexes in real tannery wastewater, resulting in the residual Cr­(III) below the discharge standard of China. This study may present a new option for water decontamination from metal–organic complexes

Simultaneously Sequestrating and Reducing Bichromate by the Built-in Ethylenediamine Group inside Polystyrene Adsorbent

Simultaneous sequestration and reduction of bichromate [Cr(VI)] poses an attractive and practical fashion for treating Cr(VI)-contaminated wastewater, for it not only immobilizes the pollutant but also reduces its toxicity. To this end, an EDA-functionalized adsorbent (EDA@CMPS) was developed with a simple one-step method by integrating ethylenediamine (EDA, a reversible redox unit) onto the skeleton of chloromethylated polystyrene adsorbent (CMPS), and it can sequestrate Cr(VI) and in situ reduce Cr(VI) to Cr(III), which was then immediately locked inside the adsorbent phase. Batch experiments confirmed that EDA@CMPS had a high removal capacity toward Cr(VI) (419 mg/g, at 25 °C), a large proportion of which was reduced to Cr(III) without leaking into the aqueous phase at pH ≥ 2. Ubiquitous anions (Cl–, NO3–, SO42–, and H2PO4–) and cations (Mg2+ and Ca2+) have a certain effect on the removal efficiencies, but EDA@CMPS still demonstrated satisfied Cr(VI) removal even with the competing ions at 100-times higher concentration. FT-IR and XPS analyses revealed that the amine group of EDA was responsible for sequestrating and reducing Cr(VI), where the amine group was oxidized into an imine group, which then played a key role in immobilizing the generated Cr(III) via chelation. Attractively, even under neutral conditions, EDA@CMPS also demonstrated decent removal and reduction performance toward Cr(VI). Furthermore, the yielded imine group can be perfectly restored to an amine group by simple alkali-acid treatment. Repeated removal–regeneration cycles verified the reusability of EDA@CMPS in treating Cr(VI) solution. Fixed-bed column experiments and treatment of a real electroplating wastewater further validated the potential of EDA@CMPS in treating Cr(VI) wastewater for practical application

Engineering Nano-Au-Based Sensor Arrays for Identification of Multiple Ni(II) Complexes in Water Samples

Advanced techniques for nickel (Ni­(II)) removal from polluted waters have long been desired but challenged by the diversity of Ni­(II) species (most in the form of complexes) which could not be readily discriminated by the traditional analytical protocols. Herein, a colorimetric sensor array is developed to address the above issue based on the shift of the UV–vis spectra of gold nanoparticles (Au NPs) after interaction with Ni­(II) species. The sensor array is composed of three Au NP receptors modified by N-acetyl-l-cysteine (NAC), tributylhexadecylphosphonium bromide (THPB), and the mixture of 3-mercapto-1-propanesulfonic acid and adenosine monophosphate (MPS/AMP), to exhibit possible coordination, electrostatic attraction, and hydrophobic interaction toward different Ni­(II) species. Twelve classical Ni­(II) species were selected as targets to systematically demonstrate the applicability of the sensor array under various conditions. Multiple interactions with Ni­(II) species were evidenced to trigger the diverse Au NP aggregation behaviors and subsequently produce a distinct colorimetric response toward each Ni­(II) species. With the assistance of multivariate analysis, the Ni­(II) species, either as the sole compound or as mixtures, can be unambiguously discriminated with high selectivity in simulated and real water samples. Moreover, the sensor array is very sensitive with the detection limit in the range of 4.2 to 10.5 μM for the target Ni­(II) species. Principal component analysis signifies that coordination dominates the response of the sensor array toward different Ni­(II) species. The accurate Ni­(II) speciation provided by the sensor array is believed to assist the rational design of specific protocols for water decontamination and to shed new light on the development of convenient discrimination methods for other toxic metals of concern

Reaction of α-(<i>N</i>-Carbamoyl)alkylcuprates with Propargyl Substrates: Synthetic Route to α-Amino Allenes and Δ³-Pyrrolines

Carbamate deprotonation followed by treatment with CuCN·2LiCl affords α-(N-carbamoyl)alkylcuprates which react with propargyl halides, mesylates, tosylates, phosphates, acetates, and epoxides to give α-(N-carbamoyl) allenes via an anti-SN2‘ substitution process. Propargyl halides, sulfonates, and phosphates give good yields of carbamoyl allenes, while the acetates afford low yields. Propargyl substrates undergo regiospecific SN2‘ substitution in the absence of severe steric hindrance. The α-(N-carbamoyl) allenes can be cyclized to 2-oxazolidinones or deprotected to afford the free amines which can be cyclized to Δ3-pyrrolines with either AgNO3 or Ru3(CO)12

A Supersensitive Probe for Rapid Colorimetric Detection of Nickel Ion Based on a Sensing Mechanism of Anti-etching

Redundant nickel is harmful to human health and can result in skin diseases, allergies, or cancer. Although many probes based on noble metal nanoparticles have been established for rapid heavy metal ion detection by the naked eye or ultraviolet–visible (UV–vis) spectroscopy, few noble metal nanomaterials have been developed for Ni²⁺ detection. In this study, we propose novel triangular silver nanoprisms (AgNPRs) stabilized with glutathione (GSH) for rapid colorimetric detection of Ni²⁺ based on a sensing mechanism of anti-etching, which has been affirmed by Raman spectra, UV–vis spectra, transmission electron microscopy, and dynamic light scattering. At the optimal experimental parameters, our GSH-AgNPR-based Ni²⁺ probe has an excellent selectivity compared with those of 26 other ions because Ni²⁺ can inhibit the AgNPR etching by iodide ion (I^–) (i.e., anti-etching) while other ions cannot. The limit of detection (LOD) of our Ni²⁺ probe is 50 nM via the naked eye and 5 nM via UV–vis spectroscopy. They are both negligible compared with the permissible limit of Ni²⁺ in drinking water (0.34 μM) prescribed by the World Health Organization. In particular, the latter is far lower than the LOD values of other reported Ni²⁺ probes based on noble metal nanomaterials. A satisfying linear relationship reinforces that our probe can be utilized for the quantitative analysis of Ni²⁺. The detection of real water samples indicates that our probe could be used for rapid Ni²⁺ colorimetric detection with supersensitivity and excellent selectivity in real environmental water samples