Coordination of 1,10-phenanthroline and 2,2'-bipyridine to Li+ in different ionic liquids. How innocent are ionic liquids?

On the basis of (7)Li NMR measurements, we have made detailed studies on the influence of the ionic liquids [emim][NTf(2)], [emim][ClO(4)], and [emim][EtSO(4)] on the complexation of Li(+) by the bidentate N-donor ligands 2,2'-bipyridine (bipy) and 1,10-phenanthroline (phen). For each of the employed ionic liquids the NMR data implicate the formation of [Li(bipy)(2)](+) and [Li(phen)(2)](+), respectively. X-ray diffraction studies were performed to determine the coordination pattern in the solid state. In the case of [emim][ClO(4)] and [emim][EtSO(4)], crystal structures confirmed the NMR data, resulting in the complexes [Li(bipy)(2)ClO(4)] and [Li(phen)(2)EtSO(4)], respectively. On the contrary, the ionic liquid [emim][NTf(2)] generated the C(i) symmetric, dinuclear, supramolecular cluster [Li(bipy)(NTf(2))](2), where the individual Li(+) centers were found to be bridged by two [NTf(2)] anions. Density functional theory (DFT)-calculations lead to further information on the effect of stacking on the coordination geometry of the Li(+) centers.     

Distribution of N-glycosylation sequons in proteins: how apart are they?

N-glycosylation is a common protein modification process, which affects a number of properties of proteins. Little is known about the distribution of N-glycosylation sequons, for example, the distance between glycosylated sites and their position in the protein primary sequence. Using a large set of experimentally confirmed eukaryotic N-glycoproteins we analyzed the relative position and distribution of sequons. N-Glycosylation probability was found to be lower in the termini of protein sequences compared to the mid region. N-glycosylated sequons were found much farther from C terminus compared to the N-terminus of the protein sequence and this effect was more pronounced for NXS sequons. The distribution of sequons, modeled based on balls-in-boxes classical occupancy, showed a near-maximum probability. Considerable proportion of sequons was found within a distance of ten amino acids, indicating that the steric hindrance was not a key factor in protein N-glycosylation. Interestingly, the distribution of all sequons present in N-glycoproteins showed a pattern very similar to that of glycosylated sequons. The results indicate that protein N-glycosylation chiefly follows a random design.     

Protein and solvent dynamics: how strongly are they coupled?

Analysis of Raman and neutron scattering spectra of lysozyme demonstrates that the protein dynamics follow the dynamics of the solvents glycerol and trehalose over the entire temperature range measured 100-350 K. The protein's fast conformational fluctuations and low-frequency vibrations and their temperature variations are very sensitive to behavior of the solvents. Our results give insight into previous counterintuitive observations that protein relaxation is stronger in solid trehalose than in liquid glycerol. They also provide insight into the effectiveness of glycerol as a biological cryopreservant.     

Criticality of metal based functional materials – How multi-functional trans-technical metal based materials are mobilized and how they get lost by dissipation

The enormous diversity of chemical compounds now available is problematic for waste disposal and recovery of essential resources such as rare earth metals. Non-renewable resources are being depleted and need to be managed more effectively. To validate the potential of strategic metals, which often are multi-functional and thus find (competitive) applications in different technologies, a criticality concept is applied. This is based on qualitative and quantitative criteria characterizing the different transformations along supply chains: ranging from the resource deposit to the product and from there into the so-called re-phases or disposal and end-of-life. The trajectories of the resources in real space and time have to be transparent in order to optimize the resource efficiency and its long-ranging compatibility but also to minimize dissipation. This approach allows developing transparent narratives (“Stoffgeschichten”, “Stories of Stuff”) for a responsible and benign use of resources. Only then can re-integration of functional materials be achieved.     

How polar are ionic liquids? Determination of the static dielectric constant of an imidazolium-based ionic liquid by microwave dielectric spectroscopy

In a pilot study of the dielectric constant of room-temperature ionic liquids, we use dielectric spectroscopy in the megahertz/gigahertz regime to determine the complex dielectric function of five 1-alkyl-3-methylimidazolium salts, from which the static dielectric constant epsilon is obtained by zero-frequency extrapolation. The results classify the salts as moderately polar solvents. The observed epsilon-values at 298.15 K fall between 15.2 and 8.8, and epsilon decreases with increasing chain length of the alkyl residue of the cation. The anion sequence is trifluoromethylsulfonate > tetrafluoroborate approximately tetrafluorophosphate. The results indicate markedly lower polarities than found by spectroscopy with polarity-sensitive solvatochromic dyes.     

Activity and stability of α-chymotrypsin in biocompatible ionic liquids: enzyme refolding by triethyl ammonium acetate

In view the of wide scope of structural information of biomolecules in biocompatible ionic liquids (ILs) in various applications including chemical and biochemical, it is essential to study the productive preferential interactions between biological macromolecules and biocompatible ILs. We have therefore explored the stability and activity of α-chymotrypsin (CT) in the presence of five ILs from different families, such as triethyl ammonium acetate (TEAA), triethyl ammonium phosphate (TEAP) from ammonium salts, 1-benzyl-3-methylimidazolium chloride ([Bzmim][Cl]), 1-benzyl-3-methylimidazolium tetrafluoroborate ([Bzmim][BF(4)]) from imidazolium salts and tetra-butyl phosphonium bromide (TBPBr) from phosphonium families. Circular dichroism (CD) and UV-vis spectrophotometer experiments were used to study CT stabilization by ILs, related to the associated structural changes and enzyme activity studies, respectively. We observed that all ILs have a dominant contribution to the stabilization of CT. The stability and activity of CT depends on the structural arrangement of the ions of ILs. Our experimental results explicitly elucidate that more hydrophobic imidazolium and phosphonium cations carrying longer alkyl chains of ILs ([Bzmim][Cl], [Bzmim][BF(4)] and TBPBr) were weak stabilizers for CT, while small alkyl chain molecules of triethyl ammonium salts (TEAA and TEAP) are strong stabilizers and therefore more biocompatible for CT stability. Our CD and NMR measurements reveal that TEAA is a refolding additive for CT from a quenched thermal unfolded enzyme structure.     

Preparation of novel cross-linked fluoroalkyl end-capped cooligomeric nanoparticles–encapsulated cytochrome c in water and ionic liquids

Cross-linked fluoroalkyl end-capped acrylic acid cooligomer containing poly(oxyethylene) units can form the nanometer size-controlled fine particles in aqueous solutions, and these cross-linked nanoparticles interact with cytochrome c (Cyto-c) to afford the corresponding cooligomeric nanoparticles–encapsulated Cyto-c effectively. Interestingly, we can easily isolate the fluorinated nanoparticles–encapsulated Cyto-c powder by the simple centrifugal separation of the corresponding aqueous solutions. The cross-linked fluorinated cooligomer also enables an effective transfer of Cyto-c from aqueous solution to ionic liquids such as 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide to afford the immobilized Cyto-c with the corresponding fluorinated cooligomer in quantitatively immobilized ratio (～100%). The immobilized Cyto-c exhibited a good dispersibility in the parent ionic liquid to afford the nanometer size-controlled fluorinated particles–encapsulated Cyto-c. Similarly, the cross-linked fluorinated cooligomer in ionic liquids such as 3-methylpyrazolium tetrafluoroborate (3MP-BF4) interacted with Cyto-c to afford the corresponding nanoparticles–encapsulated Cyto-c in quantitatively encapsulated ratio (～100%). These cross-linked fluorinated nanoparticles–encapsulated Cyto-c in water and ionic liquids were applied to the oxidation of guaiacol with hydrogen peroxide, and an extremely higher catalytic activity for this oxidation was observed in the ionic liquid (3MP-BF4).     

Study of aromatic nucleophilic substitution with amines on nitrothiophenes in room-temperature ionic liquids: are the different effects on the behavior of para-like and ortho-like isomers on going from conventional solvents to room-temperature ionic liquids related to solvation effects?

The kinetics of the nucleophilic aromatic substitution of some 2-L-5-nitrothiophenes (para-like isomers) with three different amines (pyrrolidine, piperidine, and morpholine) were studied in three room-temperature ionic liquids ([bmim][BF4], [bmim][PF6], and [bm(2)im][BF4], where bmim = 1-butyl-3-methylimidazolium and bm(2)im = 1-butyl-2,3-dimethylimidazolium). To calculate thermodynamic parameters, a useful instrument to gain information concerning reagent-solvent interactions, the reaction was carried out over the temperature range 293-313 K. The reaction occurs faster in ionic liquids than in conventional solvents (methanol, benzene), a dependence of rate constants on amine concentration similar to that observed in methanol, suggesting a parallel behavior. The above reaction also was studied with 2-bromo-3-nitrothiophene, an ortho-like derivative able to give peculiar intramolecular interactions in the transition state, which are strongly affected by the reaction medium.     

Anion-π aromatic neutral tweezers complexes: are they stable in polar solvents?

The impact of the solvent environment on the stabilization of the complexes formed by fluorine (T-F) and cyanide (T-CN) substituted tweezers with halide anions has been investigated theoretically. The study was carried out using computational methodologies based on density functional theory (DFT) and symmetry adapted perturbation theory (SAPT). Interaction energies were obtained at the M05-2X/6-31+G* level. The obtained results show a large stability of the complexes in solvents with large dielectric constant and prove the suitability of these molecular tweezers as potential hosts for anion recognition in solution. A detailed analysis of the effects of the solvent on the electron withdrawing ability of the substituents and its influence on the complex stability has been performed. In particular, the interaction energy in solution was split up into intermonomer and solvent-complex terms. In turn, the intermonomer interaction energy was partitioned into electrostatic, exchange, and polarization terms. Polar resonance structures in T-CN complexes are favored by polar solvents, giving rise to a stabilization of the intermonomer interaction, the opposite is found for T-F complexes. The solvent-complex energy increases with the polarity of the solvent in T-CN complexes, nonetheless the energy reaches a maximum and then decreases slowly in T-F complexes. An electron density analysis was also performed before and after complexation, providing an explanation to the trends followed by the interaction energies and their different components in solution.     

Can marcus theory be applied to redox processes in ionic liquids? A comparative simulation study of dimethylimidazolium liquids and acetonitrile

Simulations of a model system of charged spherical ions in the ionic liquids dimethylimidazolium chloride, [dmim][Cl], dimethylimidazolium hexafluorophosphate, [dmim][PF6], and the polar liquid acetonitrile, MeCN, are used to investigate the applicability of Marcus theory to electrochemical half-cell redox processes in these liquids. The free energy curves for solvent fluctuations are found to be approximately parabolic and the Marcus solvent reorganization free energies and activation free energies are determined for six possible redox processes in each solvent. The similarities between the different types of solvent are striking and are attributed to the essentially long-range nature of the relevant interactions and the effectiveness of the screening of the ion potential. Nevertheless, molecular effects are seen in the variation of solvent screening potential with distances up to 2 nm.     

Studies on the phase behavior and solubilization of the microemulsion formed by surfactant-like ionic liquids with ɛ–β-fish-like phase diagram

The phase behavior and the solubilization of the microemulsion systems surfactant-like ionic liquids 1-hexadecyl-3-methylimidazolium bromide (C₁₆mimBr), 1-tetradecyl-3-methylimidazolium bromide (C₁₄mimBr), or 1-dodecyl-3-methylimidazolium bromide (C₁₂mimBr)/alcohol/alkane/brine have been studied with ɛ–β-fish-like phase diagram method at 40 °C and an oil-to-water mass ratio of 1:1. From the ɛ–β-fish-like phase diagram, the physicochemical parameters, such as the mass fraction of alcohol in the hydrophile–lipophile-balanced interfacial layer (A ^S), and the solubilities of ionic liquid (S ^O) and alcohol (A ^O) in alkane phase, were calculated. The solubilization of the microemulsion system has been discussed based on the ɛ–β-fish-like phase diagram. The smaller the oil molecule, the longer the alcohol chain length, and the larger the NaCl concentration in water, the larger the solubilization of the microemulsion system. In this paper, the solubilization of the microemulsion stabilized by both C₁₂mimBr and sodium dodecyl sulfonate (sodium dodecyl sulfate) was also investigated with the ɛ–β-fish-like phase diagram. The unequimolar composite of anionic and cationic surfactants can avoid the sedimentation aroused by the strong electrostatic attraction, and an obvious synergism effect in solubilization was obtained.     

Solutions of ionic liquids with diverse aliphatic and aromatic solutes – Phase behavior and potentials for applications: A review article

This article principally reviews our research related to liquid–liquid and solid–liquid phase behavior of imidazolium- and phosphonium-based ionic liquids, mainly having bistriflamide ([NTf₂]⁻) or triflate ([OTf]⁻) anions, with several aliphatic and aromatic solutes (target molecules). The latter include: (i) diols and triols: 1,2-propanediol, 1,3-propanediol and glycerol; (ii) polymer poly(ethylene glycol) (PEG): average molecular mass 200, 400 and 2050 – PEG200 (liquid), PEG400 (liquid) and PEG2050 (solid), respectively; (iii) polar aromatic compounds: nicotine, aniline, phenolic acids (vanillic, ferulic and caffeic acid,), thymol and caffeine and (iv) non-polar aromatic compounds (benzene, toluene, p-xylene). In these studies, the effects of the cation and anion, cation alkyl chain and PEG chain lengths on the observed phase behaviors were scrutinized. Thus, one of the major observations is that the anion – bistriflamide/triflate – selection usually had strong, sometimes really remarkable effects on the solvent abilities of the studied ionic liquids. Namely, in the case of the hydrogen-bonding solutes, the ionic liquids with the triflate anion generally exhibited substantially higher solubility than those having the bistriflamide anion. Nevertheless, with the aromatic compounds the situation was the opposite – in most of the cases it was the bistriflamide anion that favoured solubility. Moreover, our other studies confirmed the ability of PEG to dissolve both polar and non-polar aromatic compounds. Therefore, two general possibilities of application of alternative, environmentally acceptable, solvents of tuneable solvent properties appeared. One is to use homogeneous mixtures of two ionic liquids having [NTf₂]⁻ and [OTf]⁻ anions as mixed solvents. The other, however, envisages the application of homogeneous and heterogeneous (PEG + ionic liquid) solutions as tuneable solvents for aromatic solutes.Such mixed solvents have potential applications in separation of the aforesaid target molecules from their aqueous solutions or in extraction from original matrices. From the fundamental point of view the phase equilibrium studies reviewed herein and the diversity of the pure compounds – ionic liquids and target molecules – represent a good base for the discussion of interactions between the molecules that exist in the studied solutions.     

High water solubility and sol–gel transition behavior of titania nanoparticles obtained by an in situ functionalization sol–gel process

Herein, addition reaction occurred between glycidol and partially hydrolyzed Ti⁴⁺ complexes provides a opportunity to obtain dry anatase nanopowder with high redispersity in water. This property is considered to be originated from the two OH groups located in the two ends of glycidol resulted chlorinated propandiol molecules. In aqueous solution, the two OH groups are respectively connected with particle surface and external free water by the formation of hydrogen bonds, resulting in high water redispersity of nanoparticles. Due to the much less amount of chlorinated propandiol molecules than adsorbed molecule water on particle, the wide space between organic molecules facilitates the mutual physical surface touch of individual particles to form hydrogen bond between them. A novel property is then obtained for surface modified titania nanoparticles, which is the gelation of redispered nanoparticles in aqueous solution.     

Synthesis and characterization of carbon-supported transition metal oxide nanoparticles — Cobalt porphyrin as catalysts for electroreduction of oxygen in acids

Unpyrolyzed, non noble metal catalysts for Oxygen Reduction Reaction (ORR), denoted MeOx–CoP/C, were obtained using a two-step procedure. The procedure consisted of a synthesis of carbon-supported transition metal (Me═Co, or Ni, or Fe) nanoparticles, followed by adsorption of cobalt porphyrin (CoP). TEM and XPS analyses confirm the formation of nanoparticles and the presence of transition metal oxides. Rotating disk electrode measurements showed that the as-synthesized materials exhibit catalytic ORR activity in acidic medium toward oxygen reduction, which is higher than that of cobalt porphyrin on carbon. This reveals that the metal oxide nanoparticles enhance the activity of the metalloporphyrin without being electroactive themselves. The catalytic activity follows the sequence: CoOx–CoP/C > NiOx–CoP/C > FeOx–CoP/C, showing the influence of nature of the transition metal on the enhancing effect. The presence of a cobalt center incorporated in the macrocycle was found to be essential to the oxygen reduction reaction, appearing thus to be the catalytic active site of the reaction. Our data suggest the ORR occurs at a single active site.     

Insertion of noble-gas atom (Kr and Xe) into noble-metal molecules (AuF and AuOH): are they stable?

The structure and the stability of a new class of insertion compounds of noble-gas atoms of the type AuNgX (Ng=Kr, Xe and X=F, OH) have been investigated theoretically through ab initio molecular-orbital calculations. All the species are found to have a linear structure with a noble-gas-noble-metal bond, the distance of which is comparable to covalent bond length except the AuKrOH system, for which it lies in between the covalent and van der Waals limits. The dissociation energies corresponding to the lowest-energy fragmentation products, AuX+Ng have been computed to be -166.2, -276.0, -194.4, and -257.6 kJ/mol for AuXeF, AuKrF, AuXeOH, and AuKrOH, respectively, at the MP2 level of theory. The respective barrier heights corresponding to the bent transition states (Au-Ng-X bending mode) have been calculated to be 119.1, 74.9, 160.7, and 141.6 kJ/mol. However, three of these species are found to be metastable in their respective potential-energy surface, and the dissociation energies corresponding to the Au+Ng+X fragments have been calculated to be 112.9, 3.0, and 18.7 kJ/mol for AuXeF, AuKrF, and AuXeOH, respectively, at the same level of theory. An analysis of the nature of interactions involved in the Au-Ng-X systems has been performed using Bader's topological theory of atoms-in-molecules (AIM). Geometric as well as energetic considerations along with AIM results suggest a partial covalent nature of Au-Ng bonds in these systems. This work might have important implications in the preparation of a new class of insertion compounds of noble-gas atoms containing noble-gas-noble-metal bond.     

Interaction of metal ions with biomolecular ligands: how accurate are calculated free energies associated with metal ion complexation?

To address fundamental questions in bioinorganic chemistry, such as metal ion selectivity, accurate computational protocols for both the gas-phase association of metal-ligand complexes and solvation/desolvation energies of the species involved are needed. In this work, we attempt to critically evaluate the performance of the ab initio and DFT electronic structure methods available and recent solvation models in calculations of the energetics associated with metal ion complexation. On the example of five model complexes ([M(II)(CH(3)S)(H(2)O)](+), [M(II)(H(2)O)(2)(H(2)S)(NH(3))](2+), [M(II)(CH(3)S)(NH(3))(H(2)O)(CH(3)COO)], [M(II)(H(2)O)(3)(SH)(CH(3)COO)(Im)], [M(II)(H(2)S)(H(2)O)(CH(3)COO)(PhOH)(Im)](+) in typical coordination geometries) and four metal ions (Fe(2+), Cu(2+), Zn(2+), and Cd(2+); representing open- and closed-shell and the first- and second-row transition metal elements), we provide reference values for the gas-phase complexation energies, as presumably obtained using the CCSD(T)/aug-cc-pVTZ method, and compare them with cheaper methods, such as DFT and RI-MP2, that can be used for large-scale calculations. We also discuss two possible definitions of interaction energies underlying the theoretically predicted metal-ion selectivity and the effect of geometry optimization on these values. Finally, popular solvation models, such as COSMO-RS and SMD, are used to demonstrate whether quantum chemical calculations can provide the overall free enthalpy (ΔG) changes in the range of the expected experimental values for the model complexes or match the experimental stability constants in the case of three complexes for which the experimental data exist. The data presented highlight several intricacies in the theoretical predictions of the experimental stability constants: the covalent character of some metal-ligand bonds (e.g., Cu(II)-thiolate) causing larger errors in the gas-phase complexation energies, inaccuracies in the treatment of solvation of the charged species, and difficulties in the definition of the reference state for Jahn-Teller unstable systems (e.g., [Cu(H(2)O)(6)](2+)). Although the agreement between the experimental (as derived from the stability constants) and calculated values is often within 5 kcal·mol(-1), in more complicated cases, it may exceed 15 kcal·mol(-1). Therefore, extreme caution must be exercised in assessing the subtle issues of metal ion selectivity quantitatively.