Characterization of metal ions in coordinating solvent mixtures by means of Raman spectroscopy.

Titration Raman spectroscopy has been developed for studying the solvation structure of metal ions in solution. The method affords us the solvation number, and the value thus obtained in neat solvents is in good agreement with that determined by EXAFS. The method is then applied to solvent mixtures, and the individual solvation number for each solvent is extracted. In a solvent mixture of N,N-dimethylformamide (DMF) and N,N,N',N'-tetramethylurea (TMU), the metal ion prefers DMF to TMU, which is ascribed to the solvation steric effect. The same applies also for the solvent mixture of N,N-dimethylpropionamide (DMPA) and DMF. However, unlike TMU, DMPA changes its conformation from the planar cis to non-planar staggered upon solvation to the metal ion. The enthalpy for the conformational change of DMPA is positive in the bulk, while it is significantly negative in the coordination sphere of the manganese(II) ion. Here, we briefly describe the procedure of measurements and analyses for the titration Raman spectroscopy, and review the solvation structure of the alkaline earth, first transition metal(II) and lanthanide(III) ions in some solvent mixtures in view of solvation steric effect.     

系统研究溶剂和温度对形成三种钴簇基金属-有机框架化合物的影响：结构和气体吸附性质

通过调控DMSO/DMF/H2O混合溶剂中溶剂成分的物质的量比和反应温度,合成出3种基于1,3,5-三(4′-羧甲基苯基)苯(H3BTB)和氯化钴的钴簇基金属-有机框架化合物(NH2Me2)2[Co3O(BTB)2(H2O)].2H2O.4.5DMF.7.5DMSO(1),(NH2Me2)2[Co4O(BTB)8/3].6H2O.13DMSO(2)和(NH2Me2)2[Co6O3(BTB)8/3(H2O)4].5H2O.5DMF.13DMSO(3),它们分别含有三核Co3O簇、四核Co4O簇和六核Co6O3簇。这种六核簇为我们首次发现。研究表明,相对中等的温度105℃和较多DMF的使用有利于三核簇的形成;125℃高温和溶剂DMSO有利于四核簇的构建;与形成1的条件相比,较低的温度95℃和更多水的存在则有利于六核簇的生成。2和3虽然由不同的金属簇构成,但具有相同的框架结构,Schlfli符号为(43)8(48.64.812.104)3。此外,还研究了2和3抽出溶剂后产物的气体吸附性质,它们均具有较高的氢气吸附焓。     

Thermodynamic origin of the increased rate of hydrolysis of phosphate and phosphorothioate esters in DMSO/water mixtures

The hydrolysis rates of the dianions of phosphate and phosphorothioate esters are substantially accelerated by the addition of polar aprotic solvents such as DMSO and acetonitrile. The activation barrier DeltaG is smaller due to a lower enthalpy of activation. The enthalpy of transfer of p-nitrophenyl phosphate (pNPP) and p-nitrophenyl phosphorothioate (pNPPT), from water to 0.6 (mol) aq DMSO (60 mol % water in DMSO) were measured calorimetrically. The enthalpies of activation for the hydrolysis reactions in the two solvents permitted the calculation of the enthalpy of transfer of the transition states. This transfer is thermodynamically favorable for both the reactants and the transition states but is more favorable for the transition states. In the case of pNPP, the enthalpy of transfer of the reactant is -23.9 kcal/mol, compared to -28.3 for the transition state. The difference is greater for pNPPT, where the enthalpy of transfer of the reactant is -23.2 kcal/mol and that for the transition state is -35.3. The results show that the reduced enthalpies of activation in both hydrolysis reactions arise not from a destabilization of the reactants in the mixed solvent, but from the fact that the enthalpy of transfer of the transition states to the mixed solvent is significantly more negative than the enthalpy of transfer of the reactants.     

Insight into the effect of methylated urea on the phase transition of aqueous solutions of poly(N‐isopropylacrylamide) by microcalorimetry: Hydrogen bonding and van der Waals interactions

The effect of different functional groups of methylated urea on the phase transition of poly(N‐isopropylacrylamide) (PNIPAM) aqueous solutions has been studied by a high‐sensitivity differential scanning calorimetry. The results reveal that with the addition of osmolytes with N? H groups, the enthalpy change increases with the number of DSC cycles, presumably due to the gradual formation of hydrogen bonds with dehydrated C?O groups of PNIPAM at high temperature. Moreover, with the addition of tetramethylurea (TMU) without hydrogen bond donor groups, the enthalpy change of PNIPAM solution remains unchanged with the number of DSC cycles and decreases with the TMU concentration, suggesting that the van der Waals interactions between TMU and isopropyl groups of PNIPAM and the weakening of hydrophobic interactions between isopropyl groups play a dominant role in the effect of TMU on the phase transition of PNIPAM. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1145–1151     

Proton-transfer reaction of 4-methyl 2,6-diformyl phenol in cyclodextrin nanocage

We report here on the steady-state and time-resolved fluorescence studies on proton-transfer (PT) reaction of 4-methyl 2,6-diformyl phenol (MFOH) in confined nanocavities in three solvents, dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), and water. Though DMSO and DMF individually interact with MFOH in a similar fashion, their modes of interaction get significantly modified in the presence of cyclodextrin (CD) nanocages. In DMSO, in the ground state, the solvated molecular anion of MFOH forms 1:1 inclusion complex with beta- or gamma-CD and attains greater stability compared to the normal form. In DMF, the solvated molecular anion gets converted to the H-bonded complex within the CD cavity resulting in a 50-nm blue shift in the absorption spectra. In the excited state, the anionic species gets more stabilized in DMSO while in DMF it is significantly destabilized in the presence of CDs. However, in case of water, MFOH gets trapped inside the water cages so that the CDs fail to complex with it effectively. There are also no changes in the excited-state lifetimes in water in the presence of CDs, but in case of DMSO and DMF, because of restricted rotation of the formyl group within the CD cavity, the contribution of the shorter lifetime components reduce significantly increasing the larger components. Some theoretical calculations at the AM1 level of approximation have also been carried out to demonstrate how the dipolar nature of the solvent influences excited-state PT in confined media.     

Features of the solvation of meso-triphenylcorrole in organic solvents according to calorimetry

Enthalpies of dissolution of meso-triphenylcorrole are measured according to calorimetry in solvents with various polarities and electron donor abilities, the values of which are more exothermic than those for porphyrins of similar structure. The most negative values Δ_sol H ^○ are found in a medium of polar electron donor solvents, due to the formation of H-associates of the H₃(ms-Ph)₃Cor · Solv type with chemically active NH-bonds of macrocycles; the concentration dependences of the enthalpy of dissolution of tetrapyrrols in DMF and DMSO are determined for the first time. It is shown that the value of the enthalpy of moving from standard solvent to DMF agrees with the heat of vaporization of solvent from H-associate H₃(ms-Ph)₃Cor · DMF obtained earlier, which characterizes the energy of specific corrole-solvent interaction.     

Understanding solvent effects in the selective conversion of fructose to 5-hydroxymethyl-furfural: a molecular dynamics investigation

Selective conversion of fructose to 5-hydroxymethyl-furfural (HMF) involves the participation of high-boiling solvents like dimethyl sulfoxide (DMSO). In order to replace DMSO with low-boiling solvents, it is imperative that we understand the effect of DMSO solvation in protecting (i) HMF from rehydration and humins formation reactions and (ii) fructose from side reactions, other than its dehydration to HMF. In the present work, molecular dynamics simulations of HMF and fructose in water and in water-DMSO mixtures are carried out using the OPLS-AA force field. Radial pair distribution functions, coordination numbers and the hydrogen-bond network between the HMF/fructose molecule and the solvent molecules are analysed. The local 3-dimensional picture of the arrangement of solvent molecules around the solute, which cannot be accessed from pair distribution functions, is also computed. We show preferential coordination of DMSO around HMF and explain how this could provide a shielding effect to the HMF molecule, thus protecting it from further rehydration to levulinic acid and formic acid and from humins formation. In the case of fructose, the presence of DMSO also reduces the number of water molecules in the immediate vicinity of fructose. Though fewer water molecules coordinate around fructose, they are bound strongly to it. Analysis of the local 3-dimensional arrangement of DMSO molecules suggests that it protects the fructose molecule from side reactions that would lead to condensation or reversion products. However, the presence of DMSO molecules does not hamper the water molecules coming into contact with the oxygen atom of the hydroxyl groups of fructose, which is required for a proton transfer from water to fructose, to initiate the dehydration reaction to HMF.     

Solute-solvent complex switching dynamics of chloroform between acetone and dimethylsulfoxide-two-dimensional IR chemical exchange spectroscopy

Hydrogen bonds formed between C-H and various hydrogen bond acceptors play important roles in the structure of proteins and organic crystals, and the mechanisms of C-H bond cleavage reactions. Chloroform, a C-H hydrogen bond donor, can form weak hydrogen-bonded complexes with acetone and with dimethylsulfoxide (DMSO). When chloroform is dissolved in a mixed solvent consisting of acetone and DMSO, both types of hydrogen-bonded complexes exist. The two complexes, chloroform-acetone and chloroform-DMSO, are in equilibrium, and they rapidly interconvert by chloroform exchanging hydrogen bond acceptors. This fast hydrogen bond acceptor substitution reaction is probed using ultrafast two-dimensional infrared (2D-IR) vibrational echo chemical exchange spectroscopy. Deuterated chloroform is used in the experiments, and the 2D-IR spectrum of the C-D stretching mode is measured. The chemical exchange of the chloroform hydrogen bonding partners is tracked by observing the time-dependent growth of off-diagonal peaks in the 2D-IR spectra. The measured substitution rate is 1/30 ps for an acetone molecule to replace a DMSO molecule in a chloroform-DMSO complex and 1/45 ps for a DMSO molecule to replace an acetone molecule in a chloroform-acetone complex. Free chloroform exists in the mixed solvent, and it acts as a reactive intermediate in the substitution reaction, analogous to a SN1 type reaction. From the measured rates and the equilibrium concentrations of acetone and DMSO, the dissociation rates for the chloroform-DMSO and chloroform-acetone complexes are found to be 1/24 ps and 1/5.5 ps, respectively. The difference between the measured rate for the complete substitution reaction and the rate for complex dissociation corresponds to the diffusion limited rate. The estimated diffusion limited rate agrees well with the result from a Smoluchowski treatment of diffusive reactions.     

Heat Effect of the Protonation of Glycine and the Enthalpies of Resolvation of Participating Chemical Species in Water–Dimethylsulfoxide Solvent Mixtures

Enthalpies of the protonation of glycine in water?dimethylsulfoxide (DMSO) mixed solvents are determined calorimetrically in the range of DMSO mole fractions of 0.0 to 0.9, at T = 298.15 K and an ionic strength μ = 0.3 (NaClO₄). It is established that the protonation of glycine becomes more exothermic with an increasing mole fraction of DMSO, and the enthalpies of resolvation of glycine and glycinium ions in water?DMSO solvent mixtures are calculated. It is shown that the small changes in the enthalpy of protonation observed at low mole fractions of DMSO are caused by the contributions from the solvation of proton and protonated glycine cancelling each other out. The enthalpy term of the Gibbs energy of the reaction leading to the formation of glycinium ion is estimated along with the enthalpy of resolvation of the reacting species in the water?DMSO mixed solvent.     

Enthalpies of solvation of alkylated uracils in water,nonaqueous and mixed solvents

The enthalpies of solution of uracil and its alkylated derivatives in water, methanol, N,N-dimethylformamide (DMF) and water+DMF mixtures were measured at 25°C. The enthalpies of solvation were determined. The enthalpies of cavity formation, corresponding to the enthalpies of solvent-solvent interactions were calculated and the enthalpies of solute-solvent interactions were obtained. The presence of the alkyl groups was found to have different effects on the enthalpy of interaction depending on the position and size of the substitution. The effect of alkylation at the nonpolar side of the uracil ring was found to arise mostly from the enhancement of the van der Waals interactions. The alkyl substitutions at the polar side resulted also in the removal of the solvent molecules interacting specifically with the polar groups of uracil. The enthalpy of those specific interactions was determined and found to be stronger in methanol and DMF than in water. Enthalpies of solvation in the binary water+DMF solvent were found to depend in a nonlinear way on the solvent composition. The nonlinearities in the water-rich region were found to arise from the decay of the hydrophobic hydration of the solutes with the increasing DMF content. The substitution of two methyl groups caused the uracil molecule to bahave as a predominantly hydrophobic solute. The nonlinearities in the DMF-rich region were found only for those solutes which can form hydrogen bonds with DMF.     

The effect of carbonyl carbon atom replacement in acetone molecule (ACN) by sulfur atom (DMSO)

The enthalpies of solution of cyclic ethers: 1,4-dioxane, 12-crown-4 (12C4), and 18-crown-6 (18C6) in water–acetone mixtures have been measured within the whole mole fraction range at 298.15 K. Based on the obtained data, the effect of base–acid properties of water–acetone mixtures on the solution enthalpy of cyclic ethers in this mixed solvent has been analyzed. The strong dependence of the enthalpy of solution (solvation) of cyclic ethers on basic properties of mixed solvent has been observed. The effects of carbonyl atom replacement in acetone (ACN) molecule by sulfur atom (DMSO molecule) and base–acid properties of mixed solvent on the solvation process of cyclic ethers have been analyzed.     

Influence of acido ligands on the structure of copper dihalide solvates with dimethyl sulfoxide and <Emphasis Type="Italic">N,N</Emphasis>-dimethylformamide

Structures of copper dihalide solvates with dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) were determined by XRD single crystal analysis. The existence of two DMSO solvates with CuBr₂, but only one with CuCl₂, was attributed to a lower Cu-Br bond strength in comparison with Cu-Cl, and, as a consequence, by its easier breaking to form a bond with a solvent molecule. Fundamentally different structures of CuX₂·2DMF (X = Br, Cl) solvates are caused by different donor power of the acido ligands.     

Optical absorption and NMR spectroscopic studies on paramagnetic trivalent lanthanide complexes with 2,2'-bipyridine.; The solvent effect on 4f-4f hypersensitive transitions

The optical absorption and NMR studies of trivalent lanthanide chloride complexes with 2,2'-bipyridine (bpy) are presented and discussed. The NMR spectra of paramagnetic complexes exhibit lower as well as higher field shifts of bpy resonances that reflect change in geometry and reveals importance of the factor (3 cos2 theta - 1 ) in changing sign of the shift. The paramagnetic shifts recorded have been analyzed and the intramolecular shift ratios suggest that the paramagnetic shift is predominantly dipolar in origin. Electronic spectral studies of the Pr, Nd, Ho, Er and Dy complexes in different solvents (viz. methanol, pyridine, DMSO and DMF), which differ with respect to donor atoms, reveal that the chemical environment around the lanthanide ion has great impact on f-f transitions and any change in the environment results in modifications of the spectra. The oscillator strength for the hypersensitive and non-hypersensitive transitions have been determined and changes in the oscillator strength and band shape with respect to solvent type is rationalized in terms of ligand (solvent) structure and coordination properties.     

Thermochemistry of the silver(I) complexation with 18-crown-6 ether in a binary solvent methanol-dimethylformamide

The effect of methanol-dimethylformamide solvent on the reaction enthalpy of the silver(I) complexation with the 18-crown-6 ether was studied using a calorimetric method. Increase in the DMF concentration was found to cause a decrease in the reaction exothermicity. The determining factor in the change of the reaction enthalpy is shown to be the increased solvation of the central ion.     

Kinetic control of the transmetalation of labile metalloporphyrins in individual and mixed solvents

Transmetalation reactions of cadmium complexes of tetraphenylporphine (CdTPP, I) and tetrabenzoporphine (CdTBP, II) in individual and mixed solvents have been investigated. For individual solvents, provided that the reaction proceeds via the same mechanism, its rate generally increases as the donor number increases in the order DMSO < DMF < PrOH-1 < MeCN (CdTPP-Zn(OAc)₂-Solv system). On passing to the CdTPP-Cu(OAc)₂-Solv system, the reaction rate order changes to DMSO < PrOH-1 < MeCN < DMF because the transmetalation mechanism changes from mixed to associative, as follows from the reaction order with respect to the salt being zero. The effect of the DMSO-DMF mixed solvent on the transmetalation reaction is limited to changing the reaction rate through alteration of the stability of the [CuX₂(Solv¹) _{n ? m ? 2}(Solv²) _m ] solvated salts. The trans effect of the ligands in the solvated salts does not increase the transmetalation rate.     

The charge-transfer polymerization of nitroethylene in electron-donating solvents

The anionic polymerization of nitroethylene was studied in N,N-dimethylformamide (DMF) and in dimethyl sulfoxide (DMSO) at 0–40°C. The polymerization proceeds spontaneously when monomer is mixed with solvent in the absence of light. From the observed results of the rate of polymerization, the molecular weight of polymer, the effects of additives and solvents, the copolymerization with acrylonitrile, and the optical absorption spectra it is concluded that the polymerization is initiated by the nitroethylene radical anion generated by the slow dissociation of the electron donor–acceptor (EDA) complexes between the solvent molecule and the monomer. The activation energy for the rate of polymerization was 50 and 29 kJ/mole in DMF and DMSO, respectively, which seems to be determined primarily by the dissociation of the EDA complexes. The significant features of this polymerization are that the initiation proceeds slowly and there is essentially no termination.     

Stability constants of zinc halide complexes in DMSO—water and DMF—water mixtures

The overall stability constants of zinc bromide and iodide complexes in DMSO—water and those of zinc chloride, bromide and iodide in DMF—water mixtures have been determined potentiometrically at mole ratios about 0.2–1 for the organic solvents at 25°C and in a 0.5 M ammonium perchlorate ionic medium. The complex formation is much stronger in DMF and its mixtures than in DMSO and the log βs are generally higher in solvent mixtures than those expected from the values measured in the pure components.     

Quantification of residual solvents in antibody drug conjugates using gas chromatography

The detection and quantification of residual solvents present in clinical and commercial pharmaceutical products is necessary from both patient safety and regulatory perspectives. Head-space gas chromatography is routinely used for quantitation of residual solvents for small molecule APIs produced through synthetic processes; however residual solvent analysis is generally not needed for protein based pharmaceuticals produced through cultured cell lines where solvents are not introduced. In contrast, antibody drug conjugates and other protein conjugates where a drug or other molecule is covalently bound to a protein typically use solvents such as N,N-dimethylacetamide (DMA), N,N?dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or propylene glycol (PG) to dissolve the hydrophobic small molecule drug for conjugation to the protein. The levels of the solvent remaining following the conjugation step are therefore important to patient safety as these parental drug products are introduced directly into the patients bloodstream. We have developed a rapid sample preparation followed by a gas chromatography separation for the detection and quantification of several solvents typically used in these conjugation reactions. This generic method has been validated and can be easily implemented for use in quality control testing for clinical or commercial bioconjugated products.     

四甲基脲与水二元混合体系的拉曼光谱研究

密度泛函B3LYP方法在6-311G*基组水平对四甲基脲(TMU)气态的几何构型进行全面优化,计算了最优构型的拉曼光谱,并与实验得到的拉曼光谱进行比较,对TMU的各拉曼谱带进行归属。实验测得了TMU与水不同体积比二元混合体系的拉曼光谱,得到了TMU分子的特征拉曼谱线在不同浓度下的频移情况,受氢键和缔合水分子空间位阻的共同作用,在H2O/TMU体积比小于2时,TMU羧基伸缩振动频率向低波数的变化与体积比成线性关系,当体积比大于2时,其振动频率为定值1585cm-1,其它拉曼带的频率受到溶剂的非专一化作用而随溶液中水的增加变化不大。     

Kinetics of the grignard reaction with silanes in diethyl ether and ether-toluene mixtures

Kinetics of the reactions of butylmagnesium chloride and phenylmagnesium bromide with tetraethoxysilane and methyltrichlorosilane was investigated in diethyl ether and diethyl ether-toluene mixtures. Replacement of ether by toluene significantly accelerates the reaction with alkoxysilanes, while no effect was found for the reaction with chlorosilanes. We established that the reaction with alkoxysilanes consists of replacement of a donor molecule at the magnesium center by the silane followed by subsequent rearrangement of the complex to products through a four-center transition state. Chlorosilanes react differently without solvent molecule replacement but also via a four-center transition state. Large negative activation entropies are consistent with formation of cyclic transition states. Small activation enthalpy values together with remarkable exothermicity point to early transition states of the reactions.