Combination of capillary electrophoresis and molecular modeling to study the enantiomer affinity pattern between β‐blockers and anionic cyclodextrin derivatives in a methanolic and water background electrolyte

In order to have deep insights into the mechanisms of enantiomer affinity pattern in both aqueous and non‐aqueous systems, an approach combining capillary electrophoresis and molecular modeling was undertaken. A chiral β‐blocker; acebutolol, was enantioseparated in aqueous capillary electrophoresis and non‐aqueous capillary electrophoresis using two anionic β‐cyclodextrin derivatives. The enantiomer affinity pattern of acebutolol was found to be opposite when an aqueous background electrolyte was replaced with non‐aqueous background electrolyte in the presence of heptakis(2,3‐di‐O‐acetyl‐6‐sulfo)‐β‐cyclodextrin but remained the same in the presence of heptakis(2,3‐di‐O‐methyl‐6‐sulfo)‐β‐cyclodextrin. Molecular docking of acebutolol into two β‐cyclodextrin derivatives indicated two distinct binding modes called ‘up’ and ‘down’ conformations. After structure optimization by molecular dynamics and energy minimization, both enantiomers of acebutolol were preferred to the ‘up’ conformation with heptakis(2,3‐di‐O‐methyl‐6‐sulfo)‐β‐cyclodextrin while ‘down’ conformation with heptakis(2,3‐di‐O‐acetyl‐6‐sulfo)‐β‐cyclodextrin. The further calculation of the complex energy with solvent effect indicated that heptakis(2,3‐di‐O‐acetyl‐6‐sulfo)‐β‐cyclodextrin had higher affinity to S‐acebutolol than R‐acebutolol in non‐aqueous capillary electrophoresis while it showed better binding to R‐acebutolol in aqueous capillary electrophoresis. However, the heptakis(2,3‐di‐O‐methyl‐6‐sulfo)‐β‐cyclodextrin bound better to R‐acebutolol in both aqueous and non‐aqueous capillary electrophoresis, implying that the binding mode played more important role in chiral separation of heptakis(2,3‐di‐O‐methyl‐6‐sulfo)‐β‐cyclodextrin while the solvent effect had prevailing impact on heptakis(2,3‐di‐O‐acetyl‐6‐sulfo)‐β‐cyclodextrin.     

A Green Method for Recycling 2‐Propanol from Water during Purification Process of Aqueous Nanocrystals

During traditional 2‐propanol‐based purification of aqueous nanocrystals (NCs), it is very difficult to recycle 2‐propanol from the aqueous solution, which brings great consumption of 2‐propanol during the purification process. A major contribution of this work is to provide a simple way to reduce the consumption via recycling of 2‐propanol during the purification process. The recycled 2‐propanol is available for precipitating NCs from aqueous solution in a new round of NC purification process. Due to the recycling of 2‐propanol, the great consumption of 2‐propanol can be avoided, which makes the purification process of aqueous NCs much greener and at a much lower cost.     

Emulsion and miniemulsion polymerizations with an oil‐soluble initiator in the presence and absence of an aqueous‐phase radical scavenger

Butyl acrylate conventional emulsion (macroemulsion) and miniemulsion polymerizations were carried out with an oil‐soluble initiator (azobisisobutyronitrile) in the presence or absence of an aqueous‐phase radical scavenger. For macroemulsion polymerization, in the presence of an aqueous‐phase radical scavenger, no particle nucleation occurred, whereas in the absence of an aqueous‐phase radical scavenger, particle nucleation proceeded as expected. For miniemulsion polymerization, the rate of polymerization was much higher in the absence of an aqueous‐phase radical scavenger than in its presence. Furthermore, in the absence of an aqueous‐phase radical scavenger, the miniemulsion polymerization rate increased with reduced droplet size, whereas in the presence of an aqueous‐phase radical scavenger, the trend was reversed. It is concluded that (1) for macroemulsion polymerization, the contribution from free radicals originating in the aqueous‐phase is predominant in the micellar nucleation of particles; (2) free radicals originating in the particle phase contribute to the rate of polymerization and the contribution increases with an increase in the particle size; and (3) for polymer particles with diameters of up to approximately 100 nm, polymerization is initiated from free radicals originating in the aqueous phase. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3200–3211, 2002     

Salt Effects on Aqueous Cationic/Anionic Surfactant Two‐Phase Regions

The influence of added salts (KCl, NaF, NaCl, NaBr, Na₂SO₄, Na₃PO₄) on aqueous cetyltrimethylammonium bromide (CTAB)/sodium dodecyl sulfonate (AS) two‐phase regions were studied. For KCl, the concentration dependence of salt effect on aqueous two‐phase regions was investigated. When brine substitutes pure water as a solvent, the positions of aqueous two‐phase regions in the phase diagram change. The results indicate that for aqueous two‐phase systems with excess anionic surfactant (ATPS‐A), the salt effect was mainly dependent on the cationic inorganic counterions, whereas for aqueous two‐phase systems with excess cationic surfactant (ATPS‐C), the salt effect was mainly dependent on the anionic inorganic counterions. The shift of aqueous two‐phase region is strengthened following the Hofmeister series. All the experiments were performed at 318.15 K.     

Role of the Surfactant Structure in the Behavior of Hydrophobic Ionic Liquids within Aqueous Micellar Solutions

The behavior of an ionic liquid (IL) within aqueous micellar solutions is governed by its unique property to act as both an electrolyte and a cosolvent. The influence of the surfactant structure on the properties of aqueous micellar solutions of zwitterionic SB‐12, nonionic Brij‐35 and TX‐100, and anionic sodium dodecyl sulfate (SDS) in the presence of the “hydrophobic” IL 1‐butyl‐3‐methylimidazolium hexafluorophosphate ([bmim][PF₆]) is assessed along with the possibility of forming oil‐in‐water microemulsions in which the IL acts as the “oil” phase. The solubility of [bmim][PF₆] within aqueous micellar solutions increases with increasing surfactant concentration. In contrast to anionic SDS, the zwitterionic and nonionic surfactant solutions solubilize more [bmim][PF₆] at higher concentrations and the average aggregate size remains almost unchanged. The formation of IL‐in‐water microemulsions when the concentration of [bmim][PF₆] is above its aqueous solubility is suggested for nonionic Brij‐35 and TX‐100 aqueous surfactant solutions.     

Graft polymerization of vinyl monomers inside macroporous polyacrylamide gel,cryogel, in aqueous and aqueous‐organic media initiated by diperiodatocuprate(III) complexes

Graft polymerization initiated by diperiodatocuprate(III) complex (Cu(III)) initiator was found to be an effective and convenient method for graft polymerization of vinyl monomers onto macroporous polyacrylamide gels, the so‐called cryogels (pAAm‐cryogels). The effect of time, temperature, monomer and initiator concentration during the graft polymerization in aqueous and aqueous‐organic media was studied. The graft polymerization of water‐soluble monomers as [2‐(methacryloyloxy)ethyl]‐trimethylammonium chloride, 2‐hydroxyethyl methacrylate, N‐isopropylacrylamide, and N,N‐dimethylacrylamide proceeds with higher grafting yield in aqueous medium, as compared with that in aqueous‐organic media. Graft polymerization in aqueous‐organic media such as water–DMSO solutions allows grafting of water‐insoluble monomers such as glycidyl methacrylate and N‐tert‐butylacrylamide with high grafting degrees of 100 and 410%, respectively. It was found that the deposition of initiator on the pore surface of cryogels promoted graft polymerization by facilitating the formation of the redox couple Cu(III)‐acrylamide group. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1952–1963, 2006     

Preparation of carboxyl‐functionalized polyhedral oligomeric silsesquioxane by a structural transformation reaction from soluble rod‐like polysilsesquioxane

Carboxyl‐functionalized polyhedral oligomeric silsesquioxane (SQ; POSS‐COOH ) was successfully prepared by a structural transformation reaction, that is, a process of heating and concentrating soluble carboxyl‐functionalized rod‐like polySQ (PolySQ ‐COOH ) using the aqueous superacid trifluoromethanesulfonic acid (HOTf) as the catalyst and solvent. The obtained POSS‐COOH was a mixture of a cage‐like decamer (T₁₀‐POSS), which was the main product, and an octamer (T₈‐POSS) and a dodecamer (T₁₂‐POSS), which were the minor products. The product obtained by heating and concentrating PolySQ‐COOH using aqueous hydrochloric acid (HCl) as the catalyst and solvent was soluble polySQ rather than POSS. For comparison, heating and concentrating POSS‐COOH in aqueous HOTf and HCl were performed, which yielded POSS‐COOH and PolySQ‐COOH , respectively. Based on these results, the process of heating and concentrating each starting material ( PolySQ‐COOH and POSS‐COOH ) in aqueous HOTf afforded POSS‐COOH , and a similar process in aqueous HCl yielded PolySQ‐COOH . © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2511–2518     

Aqueous two‐phase systems based on deep eutectic solvents and their application in green separation processes

As a new environmentally friendly separation technology, deep eutectic solvent based aqueous two‐phase systems are extensively applied in various fields. Herein, we review recent advances in this field and highlight the possible directions of future developments. This article focuses on the effects of deep eutectic solvent and inorganic salts on the phase equilibrium, the microstructure of deep eutectic solvent based aqueous two‐phase systems, the applications of deep eutectic solvent based aqueous two‐phase systems in separation (proteins, biopolymers, saponins, and organic acids), and removal and recovery technologies for deep eutectic solvent from aqueous two‐phase systems.     

Advanced High‐Voltage Aqueous Lithium‐Ion Battery Enabled by “Water‐in‐Bisalt” Electrolyte

A new super‐concentrated aqueous electrolyte is proposed by introducing a second lithium salt. The resultant ultra‐high concentration of 28 m led to more effective formation of a protective interphase on the anode along with further suppression of water activities at both anode and cathode surfaces. The improved electrochemical stability allows the use of TiO₂ as the anode material, and a 2.5 V aqueous Li‐ion cell based on LiMn₂O₄ and carbon‐coated TiO₂ delivered the unprecedented energy density of 100 Wh kg^?1 for rechargeable aqueous Li‐ion cells, along with excellent cycling stability and high coulombic efficiency. It has been demonstrated that the introduction of a second salts into the “water‐in‐salt” electrolyte further pushed the energy densities of aqueous Li‐ion cells closer to those of the state‐of‐the‐art Li‐ion batteries.     

Aqueous RAFT polymerization of N‐isopropylacrylamide‐mediated with hydrophilic macro‐RAFT agent: Homogeneous or heterogeneous polymerization?

Aqueous RAFT polymerization of N‐isopropylacrylamide (NIPAM) mediated with hydrophilic macro‐RAFT agent is generally used to prepare poly(N‐isopropylacrylamide) (PNIPAM)‐based block copolymer. Because of the phase transition temperature of the block copolymer in water being dependent on the chain length of the PNIPAM block, the aqueous RAFT polymerization is much more complex than expected. Herein, the aqueous RAFT polymerization of NIPAM in the presence of the hydrophilic macro‐RAFT agent of poly(dimethylacrylamide) trithiocarbonate is studied and compared with the homogeneous solution RAFT polymerization. This aqueous RAFT polymerization leads to the well‐defined poly(dimethylacrylamide)‐b‐poly(N‐isopropylacrylamide)‐b‐poly(dimethylacrylamide) (PDMA‐b‐PNIPAM‐b‐PDMA) triblock copolymer. It is found, when the triblock copolymer contains a short PNIPAM block, the aqueous RAFT polymerization undergoes just like the homogeneous one; whereas when the triblock copolymer contains a long PNIPAM block, both the initial homogeneous polymerization and the subsequent dispersion polymerization are involved and the two‐stage ln([M]_o/[M])‐time plots are indicated. The reason that the PNIPAM chain length greatly affects the aqueous RAFT polymerization is discussed. The present study is anticipated to be helpful to understand the chain extension of thermoresponsive block copolymer during aqueous RAFT polymerization. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Ca2+‐complex stability of GAPAGPLIVPY peptide in gas and aqueous phase,investigated by affinity capillary electrophoresis and molecular dynamics simulations and compared to mass spectrometric results

Strong, sequence‐specific gas‐phase bindings between proline‐rich peptides and alkaline earth metal ions in nanoESI‐MS experiments were reported by Lehmann et al. (Rapid Commun. Mass Spectrom. 2006, 20, 2404–2410), however its relevance for physiological‐like aqueous phase is uncertain. Therefore, the complexes should also be studied in aqueous solution and the relevance of the MS method for binding studies be evaluated. A mobility shift ACE method was used for determining the binding between the small peptide GAPAGPLIVPY and various metal ions in aqueous solution. The findings were compared to the MS results and further explained using computational methods. While the MS data showed a strong alkaline earth ion binding, the ACE results showed nonsignificant binding. The proposed vacuum state complex also decomposed during a molecular dynamic simulation in aqueous solution. This study shows that the formed stable peptide–metal ion adducts in the gas phase by ESI‐MS does not imply the existence of analogous adducts in the aqueous phase. Comparing peptide–metal ion interaction under the gaseous MS and aqueous ACE conditions showed huge difference in binding behavior.     

Facile acidic hydrolysis and displacement reactions of 2‐chloro‐and 2,9‐dichloro‐1,10‐phenanthroline

Treatment of 2‐chloro‐ or 2,9‐dichloro‐1,10‐phenanthroline with aqueous HBr or aqueous H₂SO₄ at 120°C yielded 1,10‐phenanthroline‐2(1H)‐one or 1,10‐dihydro‐1,10‐phenanthroline‐2,9‐dione, respectively. The hydrolysis of 2,9‐dichloro‐1,10‐phenanthroline with 37% aqueous HC1 led to the half hydrolyzed amide and the bis‐amide. Under comparable reactions conditions, using aqueous HBr, H₂SO₄ or HC1, 2‐chloropyridine was found to be hydrolytically stable. On the other hand, 2‐chloro‐ or 2,9‐dichloro‐1,10‐phenanthroline on heating with 57% aqueous HI afforded the HI salts of 2‐iodo‐ or 2,9‐diiodo‐1,10‐phenanthroline, which could be isolated. These salts on treatment with aqueous ammonium hydroxide led to good yields of 2‐iodo‐ and 2, 9‐diiodo‐1,10‐phenanthroline, respectively. Treatment of 2‐chloropyridine with 57% aqueous HI under similar reaction conditions led to 2‐iodopyridine in a 10% conversion.     

Protecting‐Group‐Free One‐Pot Synthesis of Glycoconjugates Directly from Reducing Sugars

The conversion of sugars into glycomimetics typically involves multiple protecting‐group manipulations. The development of methodology allowing the direct aqueous conversion of free sugars into glycosides, and mimics of oligosaccharides and glycoconjugates in a high‐yielding and stereoselective process is highly desirable. The combined use of 2‐azido‐1,3‐dimethylimidazolinium hexafluorophosphate and the Cu‐catalyzed Huisgen cycloaddition allowed the synthesis of a range of glycoconjugates in a one‐step reaction directly from reducing sugars under aqueous conditions. The reaction, which is completely stereoselective, may be applied to the convergent synthesis of triazole‐linked glycosides, oligosaccharides, and glycopeptides. The procedure provides a method for the one‐pot aqueous ligation of oligosaccharides and peptides bearing alkyne side chains.     

Compartmentalizing Supramolecular Hydrogels Using Aqueous Multi‐phase Systems

A generic method is used for compartmentalization of supramolecular hydrogels by using water‐in‐water emulsions based on aqueous multi‐phase systems (AMPS). By forming the low‐molecular‐weight hydrogel throughout all phases of all‐aqueous emulsions, distinct, micro‐compartmentalized materials were created. This structuring approach offers control over the composition of each type of the compartments by directing the partitioning of objects to be encapsulated. Moreover, this method allows for barrier‐less, dynamic exchange of even large hydrophilic solutes (MW≈60 kDa) between separate aqueous compartments. These features are expected to find use in the fields of, for instance, micro‐structured catalysts, templating, and tissue engineering.     

Nitroxide‐mediated radical polymerization in miniemulsion: Bimolecular termination in monomer‐free model systems

Bimolecular termination in nitroxide‐mediated radical polymerization in miniemulsion has been investigated through the heating of a polystyrene–2,2,6,6‐tetramethylpiperidinyl‐1‐oxy macroinitiator and its 4‐hydroxy‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy analogue in an aqueous toluene dispersion with sodium dodecyl benzenesulfonate as a surfactant at 125 °C. The level of bimolecular termination by combination, evaluated from the high‐molecular‐weight shoulder, was higher in miniemulsion than in solution and increased with decreasing particle size. Quantitative analysis revealed that these results cannot be rationalized solely by nitroxide partitioning to the aqueous phase. The results are explained by an interface effect, by which nitroxide is adsorbed or located at the aqueous–organic interface. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4995–5004, 2007     

Unravelling the Reaction Mechanism for the Fast Photocyclisation of 2‐Benzoylpyridine in Aqueous Solvent by Time‐Resolved Spectroscopy and Density Functional Theory Calculations

A combined femtosecond transient absorption (fs‐TA) and nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopic investigation of the photoreaction of 2‐benzoylpyridine (2‐BPy) in acetonitrile and neutral, basic and acidic aqueous solvents is reported. fs‐TA results showed that the nπ* triplet 2‐BPy is the precursor of the photocyclisation reaction in neutral and basic aqueous solvents. The cis triplet biradical and the cis singlet zwitterionic species produced during the photocyclisation reaction were initially characterised by ns‐TR³ spectroscopy. In addition, a new species was uniquely observed in basic aqueous solvent after the decay of the cis singlet zwitterionic species and this new species was tentatively assigned to the photocyclised radical anion. The ground‐state conformation of 2‐BPy in acidic aqueous solvent is the pyridine nitrogen‐protonated 2‐BPy cation (2‐BPy‐NH⁺) rather than the neutral form of 2‐BPy. After laser photolysis, the singlet excited state (S₁) of 2‐BPy‐NH⁺ is generated and evolves through excited‐state proton transfer (ESPT) and efficient intersystem crossing (ISC) processes to the triplet exited state (T₁) of the carbonyl oxygen‐protonated 2‐BPy cation (2‐BPy‐OH⁺) and then photocyclises with the lone pair of the nitrogen atom in the heterocyclic ring. Cyclisation reactions take place both in neutral/basic and acidic aqueous solvents, but the photocyclisation mechanisms in these different aqueous solvents are very different. This is likely due to the different conformation of the precursor and the influence of hydrogen‐bonding of the solvent on the reactions.     

Effect of analyte lipophilicity on the resolution of α‐ and β‐amino acids on liquid chromatographic ligand exchange chiral stationary phases

Separation of the two enantiomers of racemic α‐ and β‐amino acids on two ligand exchange chiral stationary phases (CSPs) prepared previously by covalently bonding sodium N‐((S)‐1‐hydroxymethy‐3‐methylbutyl)‐N‐undecylaminoacetate or sodium N‐((R)‐2‐hydroxy‐1‐phenylethyl)‐N‐undecylaminoacetate on silica gel was studied with variation of the organic modifier (methanol) concentration in the aqueous mobile phase. In particular, the variation of retention factors with changing organic modifier concentration in the aqueous mobile phase was found to be strongly dependent on both the analyte lipophilicity and the stationary phase lipophilicity. In general, the retention factors of relatively lipophilic analytes on relatively lipophilic CSPs tend to increase with increasing organic modifier concentration in the aqueous mobile phases while those of less lipophilic or hydrophilic analytes tend to increase. However, only highly lipophilic analytes show decreasing retention factors with increasing organic modifier concentration in the aqueous mobile phase on less lipophilic CSPs. The contrasting retention behaviors on the two CSPs were rationalized by the balance of the two competing interactions, viz. hydrophilic interaction of analytes with polar aqueous mobile phase and the lipophilic interaction of analytes with the stationary phase.     

Fabrication of Tubular Structure Agglomerates of Calcium Carbonate by Using Collodion Film

A novel and simple method for preparing tubular structure agglomerates of calcium carbonate (CC-tube) is described. Calcium chloride and sodium carbonate aqueous solutions were used as reactants separated by a collodion film (a nitrocellulose material) in aqueous solution. The effects of the concentrations of calcium chloride and sodium carbonate aqueous solutions on the morphology and phase structure of the as-obtained samples were investigated. The CC-tube growth was prevented with the increase of reactant concentration from 0.5 to 1.0 mol•L－1. Compared with Na2CO3 aqueous solution, it is favourable to grow calcite crystals in CaCl2 aqueous solution. The products were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron- microscopy.     

Histidine‐modified organic‐silica hybrid monolithic column for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography

A novel organic‐silica hybrid monolith was prepared through the binding of histidine onto the surface of monolithic matrix for mixed‐mode per aqueous and ion‐exchange capillary electrochromatography. The imidazolium and amino groups on the surface of the monolithic stationary phase were used to generate an anodic electro‐osmotic flow as well as to provide electrostatic interaction sites for the charged compounds at low pH. Typical per aqueous chromatographic behavior was observed in water‐rich mobile phases. Various polar and hydrophilic analytes were selected to evaluate the characteristics and chromatographic performance of the obtained monolith. Under per aqueous conditions, the mixed‐mode mechanism of hydrophobic and ion‐exchange interactions was observed and the resultant monolithic column proved to be very versatile for the efficient separations of these polar and hydrophilic compounds (including amides, nucleosides and nucleotide bases, benzoic acid derivatives, and amino acids) in highly aqueous mobile phases. The successful applications suggested that the histidine‐modified organic‐silica hybrid monolithic column could offer a wide range of retention behaviors and flexible selectivities toward polar and hydrophilic compounds.     

Chiral and water‐soluble poly(2‐oxazoline)s

We describe the synthesis and characterization of the first water‐soluble and chiral poly(2,4‐disubstituted‐2‐oxazoline)s. While poly(2,4‐dimethyl‐2‐oxazoline)s are water soluble up to 100 °C, aqueous solutions of poly(2‐ethyl‐4‐methly‐2‐oxazoline) exhibit a lower critical solution temperature. This is discussed in context with its constitutional isomers poly(2‐oxazoline)s and poly(2‐oxazine)s. Circular dichroism spectroscopy revealed strong Cotton effects, which are also responsive to temperature in aqueous solution. It is therefore hypothesized that structures, comparable to polyproline helices, are formed in aqueous solution. In contrast to polyproline, poly(2,4‐disubstituted‐2‐oxazoline)s are highly water soluble and therefore represent very interesting pseudo‐polypeptides that may be useful to develop responsive biomimetic biomaterials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013