Infrared Spectroscopic Study of the Solvation of Tetramethylurea in Protic + Aprotic Mixed Solvents

The infrared spectra of tetramethylurea have been measured in mixtures of dimethylsulfoxide or acetonitrile with D₂O or deuterated methanol (CH₃OD). Marked solvatochroism is observed for bands associated with the C=O and C–N stretches of tetramethylurea, with the former moving to lower wavenumber, and the latter to higher, as the concentration of the protic component is increased. The C=O band shows four distinct absorbances, which are attributed to non-, mono, di-, and trihydrogen bonded tetramethylurea. The relative populations of the different hydrogen bonded species were determined from analyses of the C=O band shapes. It is found that the variations in the populations of the different hydrogen bonded species can be accounted for by a simple mass action treatment.     

Universal Trends between Acid Dissociation Constants in Protic and Aprotic Solvents

pKa values in non-aqueous solvents are of critical importance in many areas of chemistry. Our knowledge is, despite their relevance, still limited to the most fundamental properties and few pKa values in the most common solvents. Taking advantage of a recently introduced computationally efficient procedure we computed the pKa values of 182 compounds in 21 solvents. This data set is used to establish for the first time universal trends between all solvents. Our computations indicate, that the total charge of the molecule and the charge of the acidic group combined with the Kamlet-Taft solvatochromic parameters are sufficient to predict pKa values with at least semi- quantitative accuracy. We find, that neutral acids such as alcohols are strongly affected by the solvent properties. This is contrasted by cationic acids like ammonium ions whose pKa is often almost completely independent from the choice of solvent.     

Comparative Investigation of the Ionicity of Aprotic and Protic Ionic Liquids in Molecular Solvents by using Conductometry and NMR Spectroscopy

Electrical conductivity (σ), viscosity (η), and self‐diffusion coefficient (D) measurements of binary mixtures of aprotic and protic imidazolium‐based ionic liquids with water, dimethyl sulfoxide, and ethylene glycol were measured from 293.15 to 323.15 K. The temperature dependence study reveals typical Arrhenius behavior. The ionicities of aprotic ionic liquids were observed to be higher than those of protic ionic liquids in these solvents. The aprotic ionic liquid, 1‐butyl‐3‐methylimidazolium tetrafluoroborate, [bmIm][BF₄], displays 100 % ionicity in both water and ethylene glycol. The protic ionic liquids in both water and ethylene glycol are classed as good ionic candidates, whereas in DMSO they are classed as having a poor ionic nature. The solvation dynamics of the ionic species of the ionic liquids are illustrated on the basis of the ¹H NMR chemical shifts of the ionic liquids. The self‐diffusion coefficients D of the cation and anion of [HmIm][CH₃COO] in D₂O and in [D₆]DMSO are determined by using ¹H nuclei with pulsed field gradient spin‐echo NMR spectroscopy.     

用2D NMR确定金色酰胺醇酯的结构

从中国南海红藻鹧鸪菜（Caloglossa leprieurii）中首次分离得到二肽金色酰胺醇酯(aurantiamide acetate)。利用^1H－^1H COSY、^13C－^1H COSY、HMBC等二维谱手段鉴定了该化合物的结构,对其^1H和^13C NMR的信号进行了归属,并且确定了其绝对构型。     

Effect of Cation Size on Solvation and Association with Superoxide Anion in Aprotic Solvents

Influence of cation size on solvation strength, diffusion, and kinetics of the association reaction with anions O₂⁻ in aprotic solvents, such as acetonitrile and dimethyl sulfoxide, has been investigated by means of molecular dynamics simulations. The work is motivated by the need to understand the molecular nature of the solvent-induced changes in capacity of Li-air batteries. We have shown that the dependence of the solvation shell stability on the cation size has a maximum at a particular ion radius that corresponds to a solvent coordination number of 4. The shell stability maximum coincides with the diffusion coefficient minimum. The variation of the cation shell stability has a crucial impact on the kinetics of the cation-O₂⁻ association. We have demonstrated that profound inhibition of the association reaction for Li⁺ in dimethyl sulfoxide is a result of the lock-and-key effect that cannot be described in the framework of Hard Soft Acid Base theory.     

The Solubility and Solvation of Salts in Mixed Nonaqueous Solvents. 2. Potassium Halides in Mixed Protic Solvents

The solubilities of potassium fluoride, chloride, and bromide in ethanol, formamide, and N-methylformamide and in binary mixtures of these solvents were determined at 25°C. The standard molar Gibbs energies of solution, Δ_soln G ^o, in the neat solvents were related to their hydrogen bonding abilities. The values of Δ_soln G ^o in the mixtures were fitted with expressions of the quasilattice quasichemical theory, and the preferential solvation of the ions was thereby established.     

Photophysical Properties of Coumarin‐30 Dye in Aprotic and Protic Solvents of Varying Polarities¶

Experimental results on various photophysical properties of coumarin‐30 (C30) dye, namely, Stokes' shift (Δv), fluorescence quantum yield (τ_f), fluorescence lifetime (τ_f), radiative rate constant (k_f) and nonradiative rate constant (k_nr), as obtained using absorption and fluorescence measurements have been reported. Though in most of the solvents the properties of C30 show more or less linear correlation with the solvent polarity function, Δf= [(ε ‐ 1)/(2ε+ 1) ‐ (n² ‐ 1)/ (2n²+ l)], they show unusual deviations in nonpolar solvents at one end and in high‐polarity protic solvents at the other end. From the solvent polarity and temperature effect on the photophysical properties of the dye, following inferences have been drawn: ( 1 ) in nonpolar solvents, the dye exists in a nonpolar structure, where its 7‐NEt₂ substituent adopts a pyramidal configuration and the amino lone pair is out of resonance with the benzopyrone π cloud; ( 2 ) in medium to higher polarity solvents, the dye exists in a polar intra‐molecular charge transfer structure, where the 7‐NEt₂ group and the 1,2‐benzopyrone moiety are in the same plane and the amino lone pair is in resonance with the benzopyrone π cloud; ( 3 ) in protic solvents, the dye‐solvent intermolecular hydrogen bonding influences the photophysical properties of the dye; and ( 4 ) in high‐polarity protic solvents, the excited C30 undergoes a new activation‐controlled nonradiative deexcitation process because of the involvement of a twisted intra‐molecular charge transfer (TICT) state. Contrary to most other TICT molecules, the activation barrier for this deexcitation process in C30 is observed to increase with solvent polarity. A rational for this unusual behavior has been given on the basis of the solvent polarity‐dependent stabilization and crossing of relevant electronic states and the relative propensity of interconversion among these states.     

Li＋在PC＋DMF混合溶剂中优先溶剂化的13C NMR研究

利用¹³C NMR光谱技术研究了Li^＋在碳酸丙烯酯(PC)＋N,N-二甲基甲酰胺(DMF)混合溶剂中的优先溶剂化现象. 根据溶剂分子中碳原子的化学位移随锂盐浓度的变化关系, 确定了与Li^＋发生配位的原子. 碳原子的配位位移值随混合溶剂组成的变化关系表明, 在LiClO₄＋PC＋DMF混合物中, DMF分子对Li^＋的溶剂化作用较PC分子强. 定量计算得到, 在n(PC)∶n(DMF)＝1∶1(摩尔比)的混合溶剂中, PC与DMF分子数在Li^＋第一溶剂化层中的比率为0.12, 说明Li^＋优先被DMF分子溶剂化.     

Multi-Site Conformational Exchange in the Synthetic Neomycin-Sensing Riboswitch Studied by 19F NMR

The synthetic neomycin-sensing riboswitch interacts with its cognate ligand neomycin as well as with the related antibiotics ribostamycin and paromomycin. Binding of these aminoglycosides induces a very similar ground state structure in the RNA, however, only neomycin can efficiently repress translation initiation. The molecular origin of these differences has been traced back to differences in the dynamics of the ligand:riboswitch complexes. Here, we combine five complementary fluorine based NMR methods to accurately quantify seconds to microseconds dynamics in the three riboswitch complexes. Our data reveal complex exchange processes with up to four structurally different states. We interpret our findings in a model that shows an interplay between different chemical groups in the antibiotics and specific bases in the riboswitch. More generally, our data underscore the potential of ¹⁹F NMR methods to characterize complex exchange processes with multiple excited states.     

Inverting the Triiodide Formation Reaction by the Synergy between Strong Electrolyte Solvation and Cathode Adsorption for Lithium–Oxygen Batteries

An exceptionally strong solvation effect of dimethyl sulfoxide (DMSO) on I₂ is identified by the largest shift observed so far of the I₂ Raman peak with respect to I₂ vapor and by elongated I?I bond lengths in first‐principles molecular‐dynamics simulations. This effect together with strong binding by an RuO₂ surface to I₂ is found to invert the direction of the reaction I^?+I₂?I₃^? to the left‐hand side. Inspired by this finding, we prepared a Li–O₂ battery with the Li/DMSO+LiI/RuO₂ structure. The synergic action of DMSO and RuO₂ on I₂ is found to suppress the shuttle effect of the redox mediator (RM) by anchoring I₂ molecules, the oxidation product of the RM. Significantly enhanced stability is demonstrated over 100 cycles at charging voltage below 3.65 V.     

Phase Structures of Nascent Polyethylene Powder Studied by Wideline Proton NMR

The wideline proton NMR spectra of polyethylene powder samples were analyzed in terms of contributions from three components： （1） a rigid part with immobile chains, （2） a soft region with liquid-like character which produces a Lorentzian contribution to the spectrum, and （3） an intermediate region in which the rotation of methylene groups about C-C bonds is partially hindered. The relative mass fractions as well as chain mobilities varied greatly among samples produced by different polymerization techniques. The NMR crystallinity agreed well with that estimated by WAXD and was much higher than DSC crystallinity, indicating an inclusion of the contribution from a crystalline-amorphous interphase. The crystalline defects in the rigid part could be significantly affected by processing parameters when employing the same type of polymerization technique. The intermediate region in the NMR spectra was analyzed according to the comparison between bimodal high density polyethylene and corresponding linear unimodal one. It was found that the mass fraction of the NMR interphase could be an indication of the percentage of tie molecules between crystalline lamellae and thus may significantly affect the mechanical properties of polymeric material.     

Autooxidation Mechanism of Pyrogallol and Its Free Radical Effects Studied by Means of ESR, UV and NMR*

ＩｎｔｒｏｄｕｃｔｉｏｎＰｙｒｏｇａｌｏｌ（ｐｙｒｏｇａｌｉｃａｃｉｄ）ｉｓｅａｓｉｌｙａｕｔｏ－ｏｘｉｄｉｚｅｄ,ｆｏｒｍｉｎｇｆｒｅｅｒａｄｉｃａｌｓｕｎｄｅｒａｌｋａｌｉｎｅｃｏｎｄｉｔｉｏｎｓ［１］．Ｗｈｅｎｔｈｅｂｏｄｙｉｓｓｉｃｋ,ｔｈｅ...     

钠硼硅酸盐玻璃分相及浸析的NMR研究

用多种ＮＭＲ方法，包括＾２９Ｓｉ、＾２３Ｎａ，＾１１Ｂ ＭａＳ及＾２９Ｓｉ ＣＰ／ＭＡＳ ＮＭＲ，研究了一定组成的ａ２Ｏ－Ｂ２Ｏ３－ＳｉＯ２三元体系玻璃在不同温度下分相处理２４小时及用酸浸析处理后的结构变化。结果表明，在低于分相上界临界温度的范围内，存在着一个温度转折点，低于这一温度时，受动力学因素影响，分相未达平衡态，温度愈低，距平衡态愈过，分相愈下完全。超过这一温度，分相可达平衡态，受热力学控     

Methyltrimethoxysilane Sol-Gel Polymerization in Acidic Ethanol Solutions Studied by 29Si NMR Spectroscopy

²⁹Si solution NMR has been used to study the acid-catalyzed polymerization of methyltrimethoxysilane (MTMS) in ethanol. The complex reaction pathways have been analyzed, and the general trends described. New interpretations are given to the rate constants of condensation reactions. The steric effects and inductive effects are found to work in coordination to reduce the reactivity of the silicon sites with the increasing connectivity. The extensive cyclization is attributed to the low steric effects of a tetramer ring closure compared to other end/end species condensations.     

核磁共振法研究三苯甲烷类酸性染料与非离子表面活性剂的相互作用

研究显色螯合剂和表面活性剂之间的相互作用,对于探讨胶束增溶分光光度法的反应机理是很重要的。等曾用核磁共振和分光光度两种方法研究了非离子表面活性剂OS-20与铬天青S(记作CAS)和磺酸铬青的相互作用,并对作用机理提出了他们的看法。本文用NMR研究了非离子表面活性剂TX-100和乳化剂OP与CAS和漂蓝6B(记作ECAB)的相互     

Coordination Structure of Aluminum in Magnesium Aluminum Hydroxide Studied by ^27Al NMR

The coordination structure of aluminum in magnesium aluminum hydroxide was studied by ^27Al NMR.The result showed that tetrahedral aluminum (Al^IV) existed in magnesium aluminum hydroxide,and the contents of Al^TV increased with the increase of the ratio of Al/Mg and with the peptizing temperature.Al^IV originated from the so-called Al13 polymer with the structure of one Al tetrahedron surrounded by twelve Al octahedrons.     

Autooxidation Mechanism of Pyrogallol,Its Free Radical Effects Studied by Means of ESR,UV, NMR

Pyrogallol(pyrogallic acid) is easy to be auto-oxidized, forming a free radical under alkaline condition, but the mechanism has not been clear. The mechanism of the auto-oxidation of pyrogallol was studied with ESR, UV, NMR techniques, it was found that pyrogallol was autooxidized to a quinone radical under alkaline condition. And at the same time oxygen recieved an electron from the reaction to form superoxide anions, the hydroxyl free radical was then produced by Haber-Weiss reaction. The oxygen free radicals generated from this process promoted the auto-oxidation of pyrogallol.     

Polymer-Solvent Interactions in Solutions of Thermoresponsive Polymers Studied by NMR and IR Spectroscopy

Summary: NMR relaxation and diffusion coefficient measurements revealed that a portion of water molecules is bound in mesoglobules formed in poly(N-isopropylmethacrylamide) (PIPMAm) and poly(vinyl methyl ether) (PVME) aqueous solutions above the LCST, with fast exchange between bound and free states (residence time ∼1 ms). Two types of bound water molecules were assigned to water bound inside mesoglobules and on their surface. For highly concentrated PVME/D₂O solutions (c ≥ 20 wt%) a slow exchange was detected by NMR for bound water (residence time = 2.1 s). For PIPMAm aqueous solution IR spectra indicate a two-steps character of the phase transition. For PIPMAm in D₂O/ethanol (EtOH) mixtures the globular structures were observed by NMR at 298 K for certain compositions of the mixed solvent (cononsolvency effect). Virtually no EtOH is bound in these globular structures, in contrast to the temperature-induced globular structures.     

Kinetics of Alkaline Hydrolysis of Quaternary Phosphonium Salts. The Influence of Protic and Aprotic Solvents on the Hydrolysis of Alkyl Phenylphosphonium Salts

Abstract

Third order rate constants have been determined for the alkaline hydrolysis of four series of alkylphenylphosphonium salts and alkylphenylbenzylphosphonium salts at various temperatures in 50%–70% ^v/_v aqueous tetrahydrofuran and 70% ^v/_v aqueous methanol. Thermodynamic activation parameters have been calculated for the reactions of each substrate and the effects of varying the ratio of alkyl to phenyl groups have been compared, as well as the effects of changes in the nature of the alkyl group. Solvation, as revealed by trends in entropy of activation, plays a largely counter-balancing role with respect to enthalpy and energy of activation. The role of the isokinetic effect is discussed. In aqueous tetrahydrofuran, solvation effects on the hydrolyses of phosphonium salts change as the mole fraction of water changes, and for aqueous methanol the trends in the thermodynamic activation parameters actually reverse.     

离子色谱法结合红外光谱法检验氯化琥珀胆碱

建立了离子色谱法结合红外光谱法检验案件中氯化琥珀胆碱的分析方法。用离子色谱法使离子分离后,采用电导检测器检测,同时结合红外光谱法将检材样品挥干后与溴化钾压片用红外光谱仪检测。结果表明,该方法能从案件检材中检出氯化琥珀胆碱成分,相似度达到96%。所建立的方法操作简单,检测灵敏,结果准确,可用于刑事案件中检材的快速检验。