The electrochemical reduction of 1-bromo-4-nitrobenzene at zinc electrodes in a room-temperature ionic liquid: a facile route for the formation of arylzinc compounds

The electrochemical reduction of 1-bromo-4-nitrobenzene (p-BrC₆H₄NO₂) at zinc microelectrodes in the [C(₄)mPyrr][NTf₂] ionic liquid was investigated via cyclic voltammetry. The reduction was found to occur via an EC type mechanism, where p-BrC₆H₄NO₂ is first reduced by one electron, quasi-reversibly, to yield the corresponding radical anion. The radical anions then react with the Zn electrode to form arylzinc products. Introduction of carbon dioxide into the system led to reaction with the arylzinc species, fingerprinting the formation of the latter. This method thus demonstrates a proof-of-concept of the formation of functionalised arylzinc species.

Polarisabilities of alkylimidazolium ionic liquids

The molar polarisability and molar volume for 71 ionic liquids were extracted from 157 measurements of their refractive index and density, which were then further deconstructed into atomic contributions by means of a Designed Regression analysis. Using this approach, the density and refractive index for any chosen ionic liquid with alkyl-substituted imidazolium cations can be predicted in good agreement with experimental data.

Atmospheric pressure chemical vapour deposition of boron doped titanium dioxide for photocatalytic water reduction and oxidation

Boron-doped titanium dioxide (B-TiO) films were deposited by atmospheric pressure chemical vapour deposition of titanium(iv) chloride, ethyl acetate and tri-isopropyl borate on steel and fluorine-doped-tin oxide substrates at 500, 550 and 600 °C, respectively. The films were characterised using powder X-ray diffraction (PXRD), which showed anatase phase TiO at lower deposition temperatures (500 and 550 °C) and rutile at higher deposition temperatures (600 °C). X-ray photoelectron spectroscopy (XPS) showed a dopant level of 0.9 at% B in an O-substitutional position. The ability of the films to reduce water was tested in a sacrificial system using 365 nm UV light with an irradiance of 2 mW cm. Hydrogen production rates of B-TiO at 24 μL cm h far exceeded undoped TiO at 2.6 μL cm h. The B-TiO samples were also shown to be active for water oxidation in a sacrificial solution. Photocurrent density tests also revealed that B-doped samples performed better, with an earlier onset of photocurrent. © 2013 The Owner Societies.

Designing and understanding permanent microporosity in liquids

Standard microporous materials are typically crystalline solids that exhibit a regular array of cavities of uniform size and shape. Packing and directional bonding between molecular building blocks give rise to interstitial pores that confer size and shape-specific sorption properties to the material. In the liquid state interstitial cavities are transient. However, permanent and intrinsic "pores'' can potentially be built into the structure of the molecules that constitute the liquid. With the aid of computer simulations we have designed, synthesised and characterised a series of liquids composed of hollow cage-like molecules, which are functionalised with hydrocarbon chains to make them liquid at accessible temperatures. Experiments and simulations demonstrate that chain length and size of terminal chain substituents can be used to tune, within certain margins, the permanence of intramolecular cavities in such neat liquids. Simulations identify a candidate "porous liquid'' in which 30% of the cages remain empty in the liquid state. Absorbed methane molecules selectively occupy these empty cavities.

Brønsted acids in ionic liquids: How acidity depends on the liquid structure

Gutmann Acceptor Number (AN) values have been determined for Brønsted acid–ionic liquid mixtures, over a wide compositional range. Four systems of general formula [C2mim][A]–HA (A− = bistriflamide, [NTf2]−; triflate, [OTf]−; mesylate, [OMs]−; or acetate, [OAc]−, [C2mim]+ = 1-ethyl-3-methylimidazolium cation) were studied. A library of Brønsted acidic systems of varying acidity was constructed and the AN parameter was found to be a convenient approach for quantifying their acidity. HOAc, HOMs and HOTf, when dissolved in ionic liquids, were found to associate with the respective anions to form hydrogen-bonded anionic clusters, [A(HA)x]−. In contrast, HNTf2 was solubilised as a discrete, undissociated molecule. AN values were sensitive to the presence of anionic clusters; acidity could be buffered to a particular AN by binding the solubilised acid in the anionic cluster form. Overall, a simple way to manipulate and quantify the Brønsted acidity of acid–ionic liquid mixtures was demonstrated, and measured AN values were related to liquid speciation.

Protection of DNA against low-energy electrons by amino acids: A first-principles molecular dynamics study

Using first-principles molecular dynamics simulations, we have investigated the notion that amino acids can play a protective role when DNA is exposed to excess electrons produced by ionizing radiation. In this study we focus on the interaction of glycine with the DNA nucleobase thymine. We studied thymine-glycine dimers and a condensed phase model consisting of one thymine molecule solvated in amorphous glycine. Our results show that the amino acid acts as a protective agent for the nucleobase in two ways. If the excess electron is initially captured by the thymine, then a proton is transferred in a barrier-less way from a neighboring hydrogen-bonded glycine. This stabilizes the excess electron by reducing the net partial charge on the thymine. In the second mechanism the excess electron is captured by a glycine, which acts as a electron scavenger that prevents electron localization in DNA. Both these mechanisms introduce obstacles to further reactions of the excess electron within a DNA strand, e.g. by raising the free energy barrier associated with strand breaks.

Structure and thermal properties of salicylate-based-protic ionic liquids as new heat storage media. COSMO-RS structure characterization and modeling of heat capacities

During this research, we present a study on the thermal properties, such as the melting, cold crystallization, and glass transition temperatures as well as heat capacities from 293.15 K to 323.15 K of nine in-house synthesized protic ionic liquids based on the 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate ([H-Im-C₁OC_n][Sal]) with n = 3–11. The 3D structures, surface charge distributions and COSMO volumes of all investigated ions are obtained by combining DFT calculations and the COSMO-RS methodology. The heat capacity data sets as a function of temperature of the 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate are then predicted using the methodology originally proposed in the case of ionic liquids by Ge et al. 3-(Alkoxymethyl)-1H-imidazol-3-ium salicylate based ionic liquids present specific heat capacities higher in many cases than other ionic liquids that make them suitable as heat storage media and in heat transfer processes. It was found experimentally that the heat capacity increases linearly with increasing alkyl chain length of the alkoxymethyl group of 3-(alkoxymethyl)-1H-imidazol-3-ium salicylate as was expected and predicted using the Ge et al. method with an overall relative absolute deviation close to 3.2% for temperatures up to 323.15 K.

On the scaling behavior of electric conductivity in [C(4)mim][NTf2]

In this work we examine, for the first time, the molar conductivity behavior of the deeply supercooled room temperature ionic liquid [C₄mim][NTf₂] in the temperature, pressure and volume thermodynamic space in terms of density scaling (TV^γ)⁻¹ combined with the equation of state (EOS). The exponent γ_σ determined from the Avramov model analysis is compared with the coefficient obtained from the viscosity studies carried out at moderate temperatures. Therefore, the experimental results presented herein provide the answer to the long-standing question regarding the validity of thermodynamic scaling of ionic liquids over a wide temperature range, i.e. from the normal liquid state to the glass transition point. Finally, we investigate the relationship between the dynamic and thermodynamic properties of [C₄mim][NTf₂] represented by scaling exponent γ and Grüneisen constant γ_G, respectively.

Water structure and chaotropicity: their uses, abuses and biological implications

The concept of "water structure" has been invoked to explain all manner of aqueous phenomena. Here we look at the origins of this tendency to understand solute hydration in terms of structural changes in bulk water, and consider the validity of one particular example: the classification of small solutes as chaotropic or kosmotropic, and the putative relation of this terminology to notions of structure-making and structure-breaking in the solvent. We doubt whether complex phenomena such as Hofmeister and osmolyte effects on macromolecules can be understood simply on the basis of a change in solvent structure. Rather, we argue that chaotropicity, if understood in the original sense, arises from the activities that solutes exert on macromolecular systems, as well as from deviations of solvation water from bulk-like behaviour. If applied judiciously, chaotropicity remains a potent, biologically pertinent parameter useful for classifying and understanding solution phenomena in all types of living system.

Association and liquid structure of pyridine-acetic acid mixtures determined from neutron scattering using a ‘free proton’ EPSR simulation model

The liquid structure of pyridine-acetic acid mixtures have been investigated using neutron scattering at various mole fractions of acetic acid, χHOAc = 0.33, 0.50, and 0.67, and compared to the structures of neat pyridine and acetic acid. Data has been modelled using Empirical Potential Structure Refinement (EPSR) with a ‘free proton’ reference model, which has no prejudicial weighting towards either the existence of molecular or ionised species. Analysis of the neutron scattering results shows the existence of hydrogen-bonded acetic acid chains with pyridine inclusions, rather than the formation of an ionic liquid by proton transfer.

3-Methylpiperidinium ionic liquids

A wide range of room temperature ionic liquids based on the 3-methylpiperdinium cation core were produced from 3-methylpiperidine, which is a derivative of DYTEK® A amine. First, reaction with 1-bromoalkanes or 1-bromoalkoxyalkanes generated the corresponding tertiary amines (Rmβpip, R = alkyl or alkoxyalkyl); further quaternisation reactions with the appropriate methylating agents yielded the quaternary [Rmmβpip]X salts (X(-) = I(-), [CF3CO2](-) or [OTf](-); Tf = -SO2CF3), and [Rmmβpip][NTf2] were prepared by anion metathesis from the corresponding iodides. All [NTf2](-) salts are liquids at room temperature. [Rmmβpip]X (X(-) = I(-), [CF3CO2](-) or [OTf](-)) are low-melting solids when R = alkyl, but room temperature liquids upon introduction of ether functionalities on R. Neither of the 3-methylpiperdinium ionic liquids showed any signs of crystallisation, even well below 0 °C. Some related non-C-substituted piperidinium and pyrrolidinium analogues were prepared and studied for comparison. Crystal structures of 1-hexyl-1,3-dimethylpiperidinium tetraphenylborate, 1-butyl-3-methylpiperidinium bromide, 1-(2-methoxyethyl)-1-methylpiperidinium chloride and 1-(2-methoxyethyl)-1-methylpyrrolidinium bromide are reported. Extensive structural and physical data are collected and compared to literature data, with special emphasis on the systematic study of the cation ring size and/or asymmetry effects on density, viscosity and ionic conductivity, allowing general trends to be outlined. Cyclic voltammetry shows that 3-methylpiperidinium ionic liquids, similarly to azepanium, piperidinium or pyrrolidinium counterparts, are extremely electrochemically stable; the portfolio of useful alternatives for safe and high-performing electrolytes is thus greatly extended.

Proton irradiation of DNA nucleosides in the gas phase

The four DNA nucleosides guanosine, adenosine, cytidine and thymidine have been produced in the gas phase by a laser thermal desorption source, and irradiated by a beam of protons with 5 keV kinetic energy. The molecular ions as well as energetic neutrals formed have been analyzed by mass spectrometry in order to shed light on the ionization and fragmentation processes triggered by proton collision. A range of 8-20 eV has been estimated for the binding energy of the electron captured by the proton. Glycosidic bond cleavage between the base and sugar has been observed with a high probability for all nucleosides, resulting in predominantly intact base ions for guanosine, adenosine, and cytidine but not for thymidine where intact sugar ions are dominant. This behavior is influenced by the ionization energies of the nucleobases (G < A < C < T), which seems to determine the localization of the charge following the initial ionization. This charge transfer process can also be inferred from the production of protonated base ions, which have a similar dependence on the base ionization potential. Other dissociation pathways have also been identified, including further fragmentation of the base and sugar moieties for thymidine and guanosine, respectively, and partial breakup of the sugar ring without glycosidic bond cleavage mainly for adenosine and cytidine. These results show that charge localization following ionization by proton irradiation is important in determining dissociation pathways of isolated nucleosides, which could in turn influence direct radiation damage in DNA.

Identifying the distinct features of geometric structures for hole trapping to generate radicals on rutile TiO2(110) in photooxidation using density functional theory calculations with hybrid functional

Using density functional theory calculations with HSE 06 functional, we obtained the structures of spin-polarized radicals on rutile TiO2(110), which is crucial to understand the photooxidation at the atomic level, and further calculate the thermodynamic stabilities of these radicals. By analyzing the results, we identify the structural features for hole trapping in the system, and reveal the mutual effects among the geometric structures, the energy levels of trapped hole states and their hole trapping capacities. Furthermore, the results from HSE 06 functional are compared to those from DFT + U and the stability trend of radicals against the number of slabs is tested. The effect of trapped holes on two important steps of the oxygen evolution reaction, i.e. water dissociation and the oxygen removal, is investigated and discussed.

Density functional theory study on the activation of molecular oxygen on a stepped gold surface in an aqueous environment: a new approach for simulating reactions in solution

The activation of oxygen molecules is an important issue in the gold-catalyzed partial oxidation of alcohols in aqueous solution. The complexity of the solution arising from a large number of solvent molecules makes it difficult to study the reaction in the system. In this work, O-2 activation on an Au catalyst is investigated using an effective approach to estimate the reaction barriers in the presence of solvent. Our calculations show that O-2 can be activated, undergoing OOH* in the presence of water molecules. The OOH* can readily be formed on Au(211) via four possible pathways with almost equivalent free energy barriers at the aqueous-solid interface: the direct or indirect activation of O-2 by surface hydrogen or the hydrolysis of O-2 following a Langmuir-Hinshelwood mechanism or an Eley-Rideal mechanism. Among them, the Eley-Rideal mechanism may be slightly more favorable due to the restriction of the low coverage of surface H on Au(211) in the other mechanisms. The results shed light on the importance of water molecules on the activation of oxygen in gold-catalyzed systems. Solvent is found to facilitate the oxygen activation process mainly by offering extra electrons and stabilizing the transition states. A correlation between the energy barrier and the negative charge of the reaction center is found. The activation barrier is substantially reduced by the aqueous environment, in which the first solvation shell plays the most important role in the barrier reduction. Our approach may be useful for estimating the reaction barriers in aqueous systems.

Identifying the trend of reactivity for sp2 materials: an electron delocalization model from first principles calculations

The reactivity of sp² carbon materials is studied using the adsorption and dissociation of O₂ on graphene and graphene oxide as model systems. The reactions on the basal plane, zigzag and armchair edges of graphene and graphene oxide with different oxygen-containing groups are calculated using first principles calculations. Two Brønsted-Evans- Polanyi relationships are identified and an electron delocalization model is suggested to understand the general trend of reactivity for sp² carbon materials.