Design Strategy and Application of Deep Eutectic Solvents for Green Synthesis of Nanomaterials

The first report of deep eutectic solvents (DESs) was released in 2003 and was identified as a new member of ionic liquid (IL), involving innovative chemical and physical characteristics. Using green solvent technology concerning economical, practical, and environmental aspects, DESs open the window for sustainable development of nanomaterial fabrication. The DESs assist in different fabrication processes and design nanostructures with specific morphology and properties by tunable reaction conditions. Using DESs in synthesis reactions can reduce the required high temperature and pressure conditions for decreasing energy consumption and the risk of environmental contamination. This review paper provides the recent applications and advances in the design strategy of DESs for the green synthesis of nanomaterials. The strategy and application of DESs in wet-chemical processes, nanosize reticular material fabrication, electrodeposition/electrochemical synthesis of nanostructures, electroless deposition, DESs based nano-catalytic and nanofluidic systems are discussed and highlighted in this review.

All-pH-Tolerant In-Plane Heterostructures for Efficient Hydrogen Evolution Reaction

Generally, electrocatalytic hydrogen evolution reaction (HER) by water splitting is a pH-dependent reaction, which limits the widespread harvesting of hydrogen energy. Herein, we present a simple way for chemical bonding of MoS₂ (002) planes and α-MoC {111} planes to form in-plane heterostructures capable of efficient pH-universal HER. Due to the lattice strain from mismatched lattice parameters between α-MoC and MoS₂, this catalyst changes the electronic configuration of the MoS₂ and thus acquires the favorable proton adsorption and desorption activity, suggested by the platinum (Pt)-like free Gibbs energy. Consequently, only a low 78 mV overpotential is needed to achieve the current density of 10 mA cm^-2 in acidic solution along with a favorable Tafel kinetic process with a Tafel slope of 38.7 mV dec^-1. Owing to the synergistic interaction between MoS₂ (002) planes and α-MoC {111} planes with strong water dissociation activities, this catalyst also exhibits high HER performances beyond that of Pt in neutral and alkaline. This work proves the advances of in-plane heterostructures and illustrates the production of low-cost but highly efficient pH-universal HER catalytic materials, promising for future sustainable hydrogen energy.

How and Why to Investigate Multicomponent Reactions Mechanisms? A Critical Review

We review the most innovative efforts and greatest challenges faced when elucidating multicomponent reactions (MCRs) mechanisms. When compared to traditional reactions, the often two or more concurrent reactions pathways and the greater number of possible intermediates in MCRs turn their mechanistic investigation both a harder and trickier task. The common approaches used to investigate reaction mechanisms are often unable to clarify MCRs mechanisms; hence few but clever approaches are currently used to determine these mechanisms and to depict their key transformations. Their complexity has required most innovative approaches and the use of a number of unique techniques that have shed light over the favored pathway selected from the myriad of alternatives theoretically available for MCRs. This review focuses on the most successful efforts applied by a few leading groups to perform these puzzlingly investigations.

Rapid characterization of nonpolar or low-polarity solvent extracts from herbal medicines by solvent-assisted electrospray ionization mass spectrometry

RATIONALE

The direct detection of nonpolar and low-polarity solvent extracts of herbal medicine is difficult by conventional electrospray ionization mass spectrometry (ESI-MS). This problem can be solved by solvent-assisted electrospray ionization mass spectrometry (SAESI-MS). With the help of assisted solvents (ESI-friendly solvents) at the tip of the spray needle, compounds (especially the low-polarity compounds) in nonpolar and low-polarity solvent extracts can be ionized directly.

METHODS

Herbal medicines were ultrasonically extracted with nonpolar or low-polarity solvents, such as petroleum ether. Thereafter, the extracts were analyzed by conventional ESI-MS, atmospheric pressure chemical ionization mass spectrometry (APCI-MS) and SAESI-MS. The mass spectra obtained from these three methods were compared and analyzed.

RESULTS

Unstable ion signals, and even no ion signals, were observed when the nonpolar and low-polarity solvent extracts were detected directly by conventional ESI-MS. Better specificity, higher sensitivity or cleaner spectra were acquired from SAESI-MS by comparing with the performance of conventional ESI-MS. The ion signals generated by SAESI-MS and APCI-MS were observed in clearly different m/z ranges. A variety of potential compounds were detected in the petroleum ether extracts of Pogostemon cablin and Ligusticum chuanxiong. The relative abundances and signal intensities of the same ion signals from the stems, leaves and decoction pieces of Pogostemon cablin were significantly different by SAESI-MS.

CONCLUSIONS

As a convenient and efficient method, SAESI-MS can be used to directly detect compounds (especially the low-polarity compounds) in nonpolar or low-polarity solvent extracts of herbal medicines, providing abundant chemical information for pharmacological studies. SAESI-MS allows the simultaneous qualitative analysis of multiple compounds in the same complex samples and is thus particularly suitable for the preliminary screening of compounds in complex samples. SAESI-MS can be used to differentiate the different parts of herbal medicines.

Study of short-lived and early reaction intermediates in organocatalytic asymmetric amination reactions by ion-mobility mass spectrometry

A study of the reactive intermediates in organocatalytic asymmetric amination reactions by reactive SAESI coupled to ion-mobility mass spectrometry.

Online post-column solvent assisted and direct solvent-assisted electrospray ionization for chiral analysis of propranolol enantiomers in plasma samples

An Online post-column solvent-assisted ionization (OPSAI) method was developed for enhancing the ionization of the beta-blocker propranolol utilizing normal phase LC-MS/MS. Solvent-assisted electrospray ionization (SAESI) was studied by the introduction of the assistant solvents A: 0.5% Formic acid in Isopropanolol, B: 0.5% Formic acid in Isopropanolol-Water (1:1), and C: 0.5% Formic acid in water into the electrospray ionization chamber using a spray needle. Analyte molecules can be directly ionized by the aid of the assistant solvent spray. Both methods were applied to the chiral separation of propranolol enantiomers using normal phase analysis on cellulose-based chiral column. Interestingly, both methods are easy to handle and offer a wide range of assistant solvents that can be used in order to gain the optimum ionization of the analyte molecules. The both methods considerably improved the analyte signal and the peak area greatly increased. The propranolol average signal-to-noise (S/N) ratio was enhanced from 26±1 and 42±1 to 2341±61 and 1725±29 for R-propranolol and S-propranolol, respectively, when the post-column solvent method (OPSAI) was used with isopropanol-assistant solvent (A). While in case of solvent-assisted electrospray ionization method (SAESI) signal was enhanced from 26±1 and 42±1 to 2223±72 and 2155±58 for R-propranolol and S-propranolol, respectively, with water as an assistant solvent. The limit of detection was 10ng/mL and the method was linear in the range 50-2000ng/mL. The NPLC-MS method was applied for the determination of propranolol enantiomers in human plasma after microextraction by packed C18 sorbent.