The Surface Activity of the Hydrated Proton Is Substantially Higher than That of the Hydroxide Ion

The behavior of hydroxide and hydrated protons, the auto‐ionization products of water, at surfaces is important for a wide range of applications and disciplines. However, it is unknown at which bulk concentration these ions start to become surface active at the water–air interface. Here, we report changes in the D₂O–air interface in the presence of excess D⁺_hyd/OD^?_hyd determined using surface‐sensitive vibrational sum‐frequency generation (SFG) spectroscopy. The onset of the perturbation of the D₂O surface occurs at a bulk concentration as low as 2.7±0.2 mm D⁺_hyd. In contrast, a concentration of several hundred mm OD^?_hyd is required to change the D₂O surface. The hydrated proton is thus orders of magnitude more surface‐active than hydroxide at the water–air interface.     

Tautomerism and isotopic multiplets in the 13C NMR spectra of partially deuterated 3‐arylpyrimido[4,5‐c]pyridazine‐5,7(6H,8H)‐diones and their sulfur analogs—evidence for elucidation of the structure backbone and tautomeric forms

The tautomerism of the synthesized 3‐arylpyrimido[4,5‐c]pyridazine‐5,7(6H,8H)‐diones ( 1a–d ) and 3‐aryl‐7‐thioxo‐7,8‐dihydro‐6H‐pyrimido[4,5‐c]pyridazine‐5‐ones ( 2a–d ) was studied in dimethyl sulfoxide (DMSO)‐d₆. ¹H NMR spectra of 1a–d showed a clustered water molecule in the structure backbone that is attached by strong intermolecular H bonding. The relation between the temperature and H bonding of the clustered water molecule with 1a was also studied as representative. The relation between the electronegativity (χ) of the substituent on phenyl ring and the chemical shifts of clustered water protons in 1a–d was also studied. All of 1a–d and also 2d compounds existed in lactam ( I ) form, whereas 2a–c compounds have two distinguished tautomers in DMSO‐d₆ [lactam ( I ) and lactim ( II ) forms]. The solvent‐substrate proton exchange was examined in compounds 1a–d and 2a–d by adding one drop of D₂O. All compounds (except 1d ) showed proton/deuterium exchange of the clustered water protons in DMSO by adding one drop of D₂O. Some compounds (but not all of them) that are easily soluble in DMSO‐d₆ containing D₂O showed isotopic splitting (β‐isotope effect) in their ¹³C NMR spectra. Among them, compound 1a was the best evidence to help the spectral assignments and structure determination of predominant tautomer by carbon‐13 splitting (β‐isotope effect). Copyright © 2010 John Wiley & Sons, Ltd.     

Phase Behavior of Commercial AES/Ethanol/H2O Ternary System

Phase behavior containing alkyl ethoxysulfates (AES), ethanol, and H₂O over the whole concentration range was explored at 25°C. The system exhibited an isotropic solution phase (L), two different liquid crystalline phases: hexagonal phase (H), lamellar phase (Lα), and a biphasic region appearing with the ethanol concentration increasing. Polarized optical microscopy and small angle x-ray scattering were applied to characterize liquid crystalline phases. Direct two-phase titration and liquid chromatography–mass spectrometry (LC–MS) were employed to analyze the AES activity and homologues composition of the particles appearing in two-phase region.     

Measurement of Residual Dipolar Couplings of Organic Molecules in Multiple Solvent Systems Using a Liquid‐Crystalline‐Based Medium

Residual dipolar coupling (RDC), a robust anisotropic NMR parameter for structural elucidation of organic molecules, is only accessible in an anisotropic environment. Herein, we introduce a novel alignment medium based on the molecular self‐assembly of oligopeptide amphiphile (OPA). This medium is compatible with different intermediate and polar solvent systems, such as CD₃OD, [D₆]DMSO, and D₂O. The preparation of the OPA‐based medium is simple and rapid, while only very weak background signals were observed from OPAs. Furthermore, we show that the purity of OPA has only a minor influence on the quality of the RDC data. These advantages allow RDC measurements of organic molecules with different polarities and solubilities with high efficiency and accuracy.     

Hydrogen‐Bonding Catalyzed Ring‐Closing C−O/C−O Metathesis of Aliphatic Ethers over Ionic Liquid under Metal‐Free Conditions

O‐heterocycles have wide applications, and their efficient and green synthesis is very interesting. Herein, we report hydrogen‐bonding catalyzed ring‐closing metathesis of aliphatic ethers to O‐heterocycles over ionic liquid (IL) catalyst under metal‐ and solvent‐free conditions. The IL 1‐butylsulfonate‐3‐methylimidazolium trifluoromethanesulfonate ([SO₃H‐BMIm][OTf]) is discovered to show outstanding performance, better than the reported catalysts. An interface effect plays an important role in mediating the reaction rate due to the immiscibility between the products and the IL catalyst, and the products can be spontaneously separated. NMR analysis and DFT calculation suggest that a pair of cation and anion of [SO₃H‐BMIm][OTf] could form three strong H‐bonds with an ether molecule, which catalyze the ether transformation via a cyclic oxonium intermediate. A series of O‐heterocycles including tetrahydrofurans, tetrahydropyrans, morpholines and dioxane can be obtained from their corresponding ethers in excellent yields (e.g., >99 %). This work opens an efficient and metal‐free way to produce O‐heterocycles from aliphatic ethers.     

Design,synthesis, and characterization of a combined main‐chain/side‐chain liquid crystalline polymer based on mesogen‐jacketed liquid crystal polymer via atom transfer radical polymerization

A novel combined main‐chain/side‐chain liquid crystalline polymer based on mesogen‐jacketed liquid crystal polymers (MJLCPs) containing two biphenyls per mesogenic core of MJLCPs main chain, poly(2,5‐bis{[6‐(4‐butoxy‐4′‐oxy‐biphenyl)hexyl]oxycarbonyl}styrene) (P1–P8) was successfully synthesized via atom transfer radical polymerization (ATRP). The chemical structure of the monomer was confirmed by elemental analysis, ¹H NMR, and ¹³C NMR. The molecular characterizations of the polymer with different molecular weights (P1–P8) were performed with ¹H NMR, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). Their phase transitions and liquid‐crystalline behaviors of the polymers were investigated by differential scanning calorimetry (DSC) and polarized optical microscope (POM). We found that the polymers P1–P8 exhibited similar behavior with three different liquid crystalline phases upon heating to or cooling in addition to isotropic state, which should be related to the complex liquid crystal property of the side‐chain and the main‐chain. Moreover, the transition temperatures of liquid crystalline phases of P1–P8 are found to be dependent on the molecular weight. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7310–7320, 2008     

Novel Bipyridinium Ionic Liquids as Liquid Electrochromic Devices

Novel mono and dialkylbipyridinium (viologens) cations combined with iodide, bromide, or bis(trifluoromethanesulfonyl)imide [NTf₂] as anions were developed. Selective alkylation synthetic methodologies were optimized in order to obtain the desired salts in moderate to high yields and higher purities. All prepared mono‐ and dialkylbipyridinium salts were completely characterized by ¹H, ¹³C, and ¹⁹F NMR spectroscopy, Fourier‐transform IR spectroscopy, and elemental analysis (in the case of NTf₂ salts). Melting points, glass transition temperatures by differential scanning calorimetry (DSC) studies, and decomposition temperatures were also checked for different prepared organic salts. Viscosities at specific temperatures and activation energies were determined by rheological studies (including viscosity dependence with temperature in heating and cooling processes). Electrochemical studies based on cyclic voltammetry (CV), differential pulsed voltammetry (DPV), and square‐wave voltammetry (SWV) were performed in order to determine the redox potential as well as evaluate reversibility behavior of the novel bipyridinium salts. As proof of concept, we developed a reversible liquid electrochromic device in the form of a U‐tube system, the most promising dialkylbipyridinium‐NTf₂ ionic liquid being used as the electrochromic material and the room‐temperature ionic liquid (RTIL), 1‐ethyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)‐imide [EMIM][NTf₂], as a stable and efficient electrolyte.     

1H and 13C NMR spectroscopic study of oxidation of D,L‐cystine and 3,3′‐dithiobis(propionic acid) with hydrogen peroxide in aqueous solution

The oxidation of symmetrical disulfides [D ,L ‐cystine ( 1 ) and 3,3′‐dithiobis(propionic acid) ( 2 )] with hydrogen peroxide in D₂O–NaOH solution (pH 10–11) was studied by NMR spectroscopy. Assignments of the proton and carbon NMR signals of starting materials ( 1 and 2 ) and products of oxidation are based on conventional 1D NMR methods (DEPT, selective spin decoupling). Formation of C—S bond cleavage products or, in case of 2 , partially oxidized intermediates was not detected. The accelerating effect of Cu²⁺ cations, but not Fe³⁺ cations, on the oxidation rate of 1 in basic medium was demonstrated. Copyright © 2002 John Wiley & Sons, Ltd.     

Isotopic effect on tautomeric behavior of 5‐(2,6‐disubstituted‐aryloxy)‐tetrazoles

Isotopic effect on tautomeric behaviors of the synthesized 5‐phenoxy‐ (1a), 5‐(2,6‐dimethylphenoxy)‐ (1b), 5‐(2,6‐diisopropylphenoxy)‐ (1c), 5‐(2,6‐dimethoxyphenoxy)‐ (1d) and 5‐(4‐methylphenoxy)‐tetrazole (1e) were investigated in DMSO‐d₆ by adding one drop of D₂O. Among 1a–e, 1a, 1d and 1e show small rotational barrier around C5? O1 and O1? C6 while in 1b and 1c there are distinguishable rotational barrier about that bonds. The ¹H NMR spectra of 1b and 1c show slightly different chemical shifts for two methyl and isopropyl groups on those phenyl ring, respectively, while the chemical shifts difference (Δδ) between two methyl and two isopropyl groups were enhanced by adding D₂O. The ¹³C NMR spectra of 1b show two overlapped singlets for methyl groups after adding D₂O. Representatively, the calculations of compound 1c were performed with GAUSSIAN‐03and the rotational barrier about C5? O1 and between isopropyl group and phenyl ring in 1c was calculated with B3LYP/6‐31G(d) basis set. Copyright © 2011 John Wiley & Sons, Ltd.     

Magnetic solid‐phase extraction method for extraction of some pesticides in vegetable and fruit juices

A new version of magnetic solid‐phase extraction performed in a narrow‐bore tube has been proposed for the extraction and preconcentration of different pesticides from various vegetable and fruit juices followed by gas chromatography. A few milligrams of C₈@SiO₂@Fe₃O₄ nanoparticles are added into an aqueous sample solution placed in a narrow‐bore tube. The sorbent particles move down through the tube under gravity and are collected at the end of the tube by applying an external magnetic field. The end of the tube is narrower and it is connected to a stopcock. After a predetermined time, the stopcock is opened and the solution is passed through the bed of the sorbent maintained by the magnet. Then the adsorbed analytes are desorbed using an elution solvent. To achieve high enrichment factors, a dispersive liquid–liquid microextraction method is carried out. The nanoparticles were characterized by scanning electron microscopy, X‐ray diffraction, and FTIR spectroscopy. Under the optimum extraction conditions, limits of detection and quantification were in the ranges of 0.1–0.3 and 0.3–0.9 μg/L, respectively. High enrichment factors (1166–1605) and good extraction recoveries (58–80%) were obtained.     

Nmr Spectroscopic Determination of Water In Deuterium Oxide/Water Mixtures

Abstract

Deuterium oxide was determined in synthetic mixtures of 70–100 % D₂O and 90–100 % D₂O by NMR spectroscopy with a Varian A-60 NMR spectrometer using peak heights and areas. The standard deviation for the best results was 0.4 % D₂O.     

LCST‐type liquid–liquid and liquid–solid phase transition behaviors of hyperbranched polyglycerol bearing imidazolium salt

A hyperbranched polyglycerol bearing imidazolium tosylate units ( ITHB ) was synthesized through the imidazolium salt‐modification of hyperbranched polyglycerol ( HB ). ITHB was found to possess novel reversible lower critical solution temperature (LCST)‐type liquid–liquid and liquid–solid phase transition behaviors in a methanol/chloroform mixed solution. The phase transition temperatures of the liquid–liquid phase transition (PTT_1to2) and liquid–solid phase transition (PTT_2toSus) increased with increasing the ratio of methanol in the mixed solution and decreasing the concentration of ITHB . Additionally, increasing the molecular weight of ITHB decreased the PTT values. The liquid–liquid phase transition was caused by the aggregation of ITHB , which was proved by dynamic light scattering measurement. In contrast, the liquid–solid phase transition was caused by the solvation cleavage between the imidazolium rings and solvents, which was proved by ¹H NMR measurement. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2009     

Ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction for the separation and determination of estrogens in water samples by high‐performance liquid chromatography with fluorescence detection

An ionic liquid foam floatation coupled with ionic liquid dispersive liquid–liquid microextraction method was proposed for the extraction and concentration of 17‐α‐estradiol, 17‐β‐estradiol‐benzoate, and quinestrol in environmental water samples by high‐performance liquid chromatography with fluorescence detection. 1‐Hexyl‐3‐methylimidazolium tetrafluoroborate was applied as foaming agent in the foam flotation process and dispersive solvent in microextraction. The introduction of the ion‐pairing and salting‐out agent NH₄PF₆ was beneficial to the improvement of recoveries for the hydrophobic ionic liquid phase and analytes. Parameters of the proposed method including concentration of 1‐hexyl‐3‐methylimidazolium tetrafluoroborate, flow rate of carrier gas, floatation time, types and concentration of ionic liquids, salt concentration in samples, extraction time, and centrifugation time were evaluated. The recoveries were between 98 and 105% with relative standard deviations lower than 7% for lake water and well water samples. The isolation of the target compounds from the water was found to be efficient, and the enrichment factors ranged from 4445 to 4632. This developing method is free of volatile organic solvents compared with regular extraction. Based on the unique properties of ionic liquids, the application of foam floatation, and dispersive liquid–liquid microextraction was widened.     

Thermotropic liquid crystals based on ferrocenylbiphenyl and ferrocenylterphenyl

4′‐Ferrocenyl‐1,1′‐biphenyl‐4‐yl 4‐alkoxybenzoates Fc–(C₆H₄)₂–OC(O)–C₆H₄–O–C _n H_2n+1 (n = 8, 10, 12) (3a–c), representing a new class of ferrocene‐containing thermotropic mesogens with nematogenic properties, were prepared. Two approaches were used for the construction of these mesogens: (i) reaction of 4′‐ferrocenyl‐1,1′‐biphenyl‐4‐ol with 4‐alkoxybenzoylchlorides, and (ii) crosscoupling of tris(4‐ferrocenylphenyl)boroxine with the corresponding halobenzenes. Crosscoupling was also applied for the synthesis of terphenyl‐containing mesogens Fc–(C₆H₄)₃–OC(O)–C₆H₄–O–C _n H_2n+1 (n = 10, 12) (6a,b) and (RC₅H₄)Fe‐[C₅H₄–(C₆H₄)₃–OC(O)–C₆H₄–O–C₁₀H₂₁] (11a, R = Et; 11b, R = n?Bu). The latter compounds also form nematic phases. Mesogens 6a,b form mesophases with wider temperature ranges than their biphenyl‐containing counterparts 3b,c. The most pronounced mesomorphism was displayed by compounds 11a and 11b, which have mesophases in the ranges 141–253°C and 120–238°C, respectively. The purity of compounds was established by ¹H NMR spectra and elemental analysis. Mesophases were identified by polarizing optical microscopy and differential scanning calorimetry.     

Preparation of monodisperse nanoparticles containing poly(propylene imine)(NH2)32‐polystyrene

Polypropylenimine dendrimer (DAB‐Am‐32, generation 4.0) was converted into a macroinitiator DAB‐Am‐32‐Cl via reaction with 2‐chloropropionyl chloride. Monodisperse nanoparticles containing poly(propylene imine)(NH₂)₃₂‐polystyrene were prepared by emulsion atom transfer radical polymerization (ATRP) of styrene (St), using the DAB‐Am‐32‐Cl/CuCl/bpy as initiating system. The structure of macroinitiator was characterized by FTIR spectrum, ¹H NMR, and ¹³C NMR. The structure of poly(propylene imine)(NH₂)₃₂‐polystyrene was characterized by FT‐IR spectrum and ¹H NMR; the molecular weight and molecular weight distribution of poly(propylene imine)(NH₂)₃₂‐polystyrene were characterized by gel permeation chromatograph (GPC). The morphology, size and size distribution of the nanoparticles were characterized by photon correlation spectroscopy (PCS), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The effects of monomer/macroinitiator ratio and surfactant concentration on the size and size distribution of the nanoparticles were investigated. It was found that the diameters of the nanoparticles were smaller than 100 nm (30–80 nm) and monodisperse; moreover, the particle size could be controlled by monomer/macroinitiator ratios and surfactant concentration. With the increasing of the ratio of St/DAB‐Am‐32‐Cl, the number‐average diameter (D_n), weight‐average diameter (D_w) were both increased gradually. With enhancing the surfactant concentration, the measured D_h of the nanoparticles decreased, while the polydispersity increased. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2892–2904, 2009     

Phase‐vanishing methods based on fluorous phase screen: A simple way for efficient execution of organic synthesis

The phase‐vanishing (PV) method is based on spontaneous reaction controlled by diffusion of reagents into fluorous media, such as perfluorohexanes (FC‐72) and polyperfluoroethers. Thus, the original PV reaction utilizes a triphasic test tube method composed of a bottom reagent phase, a middle fluorous phase, and a top substrate phase. In such a triphasic system, the fluorous phase acts as a liquid membrane to transport the bottom reagents to the top organic phase containing substrates. In the end, the bottom layer disappears and two phases remain. Since the first demonstration of the PV method by bromination of alkenes with molecular bromine, a number of applications have been developed thus far. These include halogenation of alcohols with SOBr₂ and PBr₃, demethylation of methoxyarenes with BBr₃, cyclopropanation of alkenes by CH₂I₂‐AlEt₃, and Friedel–Crafts acylation of aromatic compounds with SnCl₄. A fluorous triphasic U‐tube method is effective for chlorination of alcohols based on lighter (less dense) reagents such as SOCl₂ and PCl₃. A system using a solution containing reagents as a bottom phase is useful for oxidation with m‐CPBA, which may be defined as a new category for the “extractive PV” method. Recent advances include a “quadraphasic” PV method, in which an aqueous “scavenger” phase is added to the original triphasic PV method to remove acidic by‐products. © 2008 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 8: 351–363; 2008: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20161     

Cyclodextrins in Polymer Synthesis: Enantiodiscrimination in Free‐Radical Polymerization of Cyclodextrin‐Complexed Racemic N‐Methacryloyl‐D,L‐phenylalanine Methyl Ester

The enantiodiscriminating polymerization of racemic cyclodextrin‐complexed N‐methacryloyl‐phenylalanine methyl ester is investigated. ¹H NMR spectra of the complexes with methylated β‐cyclodextrin in D₂O manifest splittings due to chiral recognition. The different stabilities of the diastereomeric complexes influence the kinetics of the homopolymerization, particularly at 0 °C. An enrichment of the residual N‐methacryloyl‐L ‐phenylalanine methyl ester of 14 % was achieved after 21 h of polymerization.     

An NMR study of sequential intermediates and collateral products in the conversion of 1,3,6,8-tetraazatricyclo[4.4.1.1]dodecane (TATD) to 1,3,6,8-tetraazatricyclo[4.3.1.1]undecane (TATU)

In situ ¹H nuclear magnetic resonance spectroscopy was used to investigate the processes that occur during the synthesis of 1,3,6,8-tetraazatricyclo[4.3.1.1^3,8]undecane (TATU). NMR analysis showed a reaction mixture containing more than one compound. The production of these intermediates and collateral products was rationally supported by a careful ¹H NMR monitoring study. We characterized 1,3,5-triazabicyclo[3.2.1]octane (TABO, 4) and 3-(2-aminoethyl)-1,3,5-triazabicyclo[3.2.1]octane (AETABO, 7) by ¹H and ¹³C NMR in D₂O solution inside the NMR sample tube, as an intermediate and collateral product of the reaction, respectively. Further, a reaction of 1,3,6,8-tetraazatricyclo[4.4.1.1^3,8]dodecane (TATD) with ¹⁵N-labeled ammonium chloride was carried out. The ¹⁵N NMR and GC-MS experiments indicated that ¹⁵N was incorporated into TATU, TABO, and urotropine.     

Atmospheric pressure laser desorption/ionization using a 6–7 µm‐band mid‐infrared tunable laser and liquid water matrix

Due to the characteristic absorption peaks in the IR region, various molecules can be used as a matrix for infrared matrix‐assisted laser desorption/ionization (IR‐MALDI). Especially in the 6–7 µm‐band IR region, solvents used as the mobile phase for liquid chromatography have absorption peaks that correspond to their functional groups, such as O–H, CO, and CH₃. Additionally, atmospheric pressure (AP) IR‐MALDI, which is applicable to liquid‐state samples, is a promising technique to directly analyze untreated samples. Herein we perform AP‐IR‐MALDI mass spectrometry of a peptide, angiotensin II, using a mid‐IR tunable laser with a tunable wavelength range of 5.50–10.00 µm and several different matrices. The wavelength dependences of the ion signal intensity of [M + H]⁺ of the peptide are measured using a conventional solid matrix, α‐cyano‐4‐hydroxycinnamic acid (CHCA) and a liquid matrix composed of CHCA and 3‐aminoquinoline. Other than the O–H stretching and bending vibration modes, the characteristic absorption peaks are useful for AP‐IR‐MALDI. Peptide ions are also observed from an aqueous solution of the peptide without an additional matrix, and the highest peak intensity of [M + H]⁺ is at 6.00 µm, which is somewhat shorter than the absorption peak wavelength of liquid water corresponding to the O–H bending vibration mode. Moreover, long‐lasting and stable ion signals are obtained from the aqueous solution. AP‐IR‐MALDI using a 6–7 µm‐band IR tunable laser and solvents as the matrix may provide a novel on‐line interface between liquid chromatography and mass spectrometry. Copyright © 2015 John Wiley & Sons, Ltd.     

Main‐chain viologen polymers with organic counterions exhibiting thermotropic liquid‐crystalline and fluorescent properties*

A series of viologen polymers with bromide, tosylate, and triflimide as counterions were prepared by either the Menshutkin reaction or metathesis reaction in a common organic solvent. Their polyelectrolyte behavior in methanol was determined by solution viscosity measurements, and their chemical structures were determined by Fourier transform infrared and Fourier transform NMR spectroscopy. They were characterized for their thermotropic liquid‐crystalline properties with a number of experimental techniques. Each of the viologen polymers with organic counterions had a low melting transition or fusion temperature above which it formed either a high‐order smectic phase or a low‐order smectic phase. Each of them also exhibited a smectic‐to‐isotropic transition. The ranges of the liquid‐crystalline phase were 80–88 °C for viologen polymers with tosylate as a counterion and 120–146 °C for viologen polymers with triflimide as a counterion. They had excellent thermal stability. The ranges of thermal stability were 288–329 °C for viologen polymers with tosylate as a counterion and 343–350 °C for viologen polymers with triflimide as a counterion. The fluorescence property for all of the viologen polymers in either aqueous or methanol solution was also included in this study. For example, the viologen polymer containing the 4,4′‐bipyridinium and p‐xylyl units along the backbone of the polymer chain with triflimide as a counterion had an absorption spectrum (λ_max = 265 nm), an excitation spectrum (λ_ex values = 357, 443, and 454 with monitoring at 533 nm), and an emission spectrum (λ_em = 536 nm with excitation at 430 and 450 nm) in methanol. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 659–674, 2002; DOI 10.1002/pola.10134