Synthesis of Carbon Nanomaterials from Biomass Utilizing Ionic Liquids for Potential Application in Solar Energy Conversion and Storage.

Considering its availability, renewable character and abundance in nature, this review assesses the opportunity of the application of biomass as a precursor for the production of carbon-based nanostructured materials (CNMs). CNMs are exceptionally shaped nanomaterials that possess distinctive properties, with far-reaching applicability in a number of areas, including the fabrication of sustainable and efficient energy harnessing, conversion and storage devices. This review describes CNM synthesis, properties and modification, focusing on reports using biomass as starting material. Since biomass comprises 60-90% cellulose, the current review takes into account the properties of cellulose. Noting that highly crystalline cellulose poses a difficulty in dissolution, ionic liquids (ILs) are proposed as the solvent system to dissolve the cellulose-containing biomass in generating precursors for the synthesis of CNMs. Preliminary results with cellulose and sugarcane bagasse indicate that ILs can not only be used to make the biomass available in a liquefied form as required for the floating catalyst CVD technique but also to control the heteroatom content and composition in situ for the heteroatom doping of the materials.

LC-MS/MS determination of antiretroviral drugs in influents and effluents from wastewater treatment plants in KwaZulu-Natal, South Africa.

South Africa has the largest occurrence of the human immune deficiency virus (HIV) in the world but has also implemented the largest antiretroviral (ARV) treatment programme. It was therefore of interest to determine the presence and concentrations of commonly used antiretroviral drugs (ARVDs) and, also, to determine the capabilities of wastewater treatment plants (WWTPs) for removing ARVDs. To this end, a surrogate standard based LC-MS/MS method was optimized and applied for the detection of thirteen ARVDs used in the treatment and management of HIV/acquired immune deficiency syndrome (HIV/AIDS) in two major and one modular WWTP in the eThekwini Municipality in KwaZulu-Natal, South Africa. The method was validated and the detection limits fell within the range of 2-20 ng L-1. The analytical recoveries for the ARVDs were mainly greater than 50% with acceptable relative standard deviations. The concentration values ranged from

Reactions of Sulfur-Containing Organic Compounds and Peptides in 1-Ethyl-3-methyl-imidazolium Acetate.

The neat ionic liquid (IL) [C2mim][OAc] is not just capable of dissolving thiol- and disulfide-containing compounds, but is able to chemically react with them without addition of any catalytic reagent. Through the analysis of four small organic molecules and a cysteine-containing peptide we could postulate a general reaction mechanism. Here, the imidazolium-carbenes preferentially react with the disulfide bond, but not thiol group. Moreover, the imidazole moiety was found to abstract the sulfur atom from the cysteine residue, providing an alternative way to transform Cys residues, which were artificially inserted into a peptide sequence in order to perform native chemical ligation (NCL) of two peptide fragments. Finally, the chemical reaction of [C2mim][OAc] with a cysteine-containing biomolecules can be tuned or even suppressed through the addition of at least 30% of water to the reaction mixture.

Efficient synthesis of triarylamine-based dyes for p-type dye-sensitized solar cells.

The class of triarylamine-based dyes has proven great potential as efficient light absorbers in inverse (p-type) dye sensitized solar cells (DSSCs). However, detailed investigation and further improvement of p-type DSSCs is strongly hindered by the fact that available synthesis routes of triarylamine-based dyes are inefficient and particularly demanding with regard to time and costs. Here, we report on an efficient synthesis strategy for triarylamine-based dyes for p-type DSSCs. A protocol for the synthesis of the dye-precursor (4-(bis(4-bromophenyl)amino)benzoic acid) is presented along with its X-ray crystal structure. The dye precursor is obtained from the commercially available 4(diphenylamino)benzaldehyde in a yield of 87% and serves as a starting point for the synthesis of various triarylamine-based dyes. Starting from the precursor we further describe a synthesis protocol for the dye 4-{bis[4'-(2,2-dicyanovinyl)-[1,1'-biphenyl]-4-yl]amino}benzoic acid (also known as dye P4) in a yield of 74%. All synthesis steps are characterized by high yields and high purities without the need for laborious purification steps and thus fulfill essential requirements for scale-up.

Triphilic Ionic-Liquid Mixtures: Fluorinated and Non-fluorinated Aprotic Ionic-Liquid Mixtures.

We present here the possibility of forming triphilic mixtures from alkyl- and fluoroalkylimidazolium ionic liquids, thus, macroscopically homogeneous mixtures for which instead of the often observed two domains-polar and nonpolar-three stable microphases are present: polar, lipophilic, and fluorous ones. The fluorinated side chains of the cations indeed self-associate and form domains that are segregated from those of the polar and alkyl domains. To enable miscibility, despite the generally preferred macroscopic separation between fluorous and alkyl moieties, the importance of strong hydrogen bonding is shown. As the long-range structure in the alkyl and fluoroalkyl domains is dependent on the composition of the liquid, we propose that the heterogeneous, triphilic structure can be easily tuned by the molar ratio of the components. We believe that further development may allow the design of switchable, smart liquids that change their properties in a predictable way according to their composition or even their environment.

Design of a Heterogeneous Catalyst Based on Cellulose Nanocrystals for Cyclopropanation: Synthesis and Solid-State NMR Characterization.

Heterogeneous dirhodium(II) catalysts based on environmentally benign and biocompatible cellulose nanocrystals (CNC-Rh2) as support material were obtained by ligand exchange between carboxyl groups on the CNC surface and Rh2(OOCCF3)4, as was confirmed by solid-state (19)F and (13)C NMR spectroscopy. On average, two CF3COO(-) groups are replaced during ligand exchange, which is consistent with quantitative analysis by a combination of (19)F NMR spectroscopy and thermogravimetry. CNC-Rh2 catalysts performed well in a model cyclopropanation reaction, in spite of the low dirhodium(II) content on the CNC surface (0.23 mmol g(-1)). The immobilization through covalent bonding combined with the separate locations of binding positions and active sites of CNC-Rh2 guarantees a high stability against leaching and allows the recovery and reuse of the catalyst during the cyclopropanation reaction.

Order in the chaos: the secret of the large negative entropy of dissolving 1-alkyl-3-methylimidazolium chloride in trihexyltetradecylphosphonium chloride.

The dissolution of 1-alkyl-3-methylimidazolium chloride ILs with short alkyl chains in trihexyltetradecylphosphonium chloride does not only exhibit a large negative entropy. Also, in the resulting mixtures, the phosphonium cation diffuses faster than the much smaller imidazolium cation. Both unexpected features originate from the formation of a large symmetric ion cluster cage in which the imidazolium cation is caught by three chloride anions and four phosphonium cations.

Application of room-temperature aprotic and protic ionic liquids for oxidative folding of cysteine-rich peptides.

The oxidation of the conotoxin µ-SIIIA in different ionic liquids was investigated, and the results were compared with those obtained in [C2 mim][OAc]. Conversion of the reduced precursor into the oxidized product was observed in the protic ILs methyl- and ethylammonium formate (MAF and EAf, respectively), whereas choline dihydrogenphosphate and Ammoeng 110 failed to yield folded peptide. However, the quality and yield of the peptide obtained in MAF and EAF were lower than in the case of the product from [C2 mim][OAc]. Reaction conditions (temperature, water content) also had an impact on peptide conversion. A closer look at the activities of µ-SIIIA versions derived from an up-scaled synthesis in [C2 mim][OAc] revealed a significant loss of the effect on ion channel NaV 1.4 relative to the buffer-oxidized peptide, whereas digestion of either µ-SIIIA product by trypsin was unaffected. This was attributed to adherence of ions from the IL to the peptide, because the disulfide connectivity is basically the same for the differentially oxidized µ-SIIIA versions.

A theoretical and experimental chemist's joint view on hydrogen bonding in ionic liquids and their binary mixtures.

A combined experimental and theoretical approach including quantum chemistry tools and computational simulation techniques can provide a holistic description of the nature of the interactions present in ionic liquid media. The nature of hydrogen bonding in ionic liquids is an especially intriguing aspect, and it is affected by all types of interactions occurring in this media. Overall, these interactions represent a delicate balance of forces that influence the structure and dynamics, and hence the properties of ionic liquids. An understanding of the fundamental principles can be achieved only by a combination of computations and experimental work. In this contribution we show recent results shedding light on the nature of hydrogen bonding, for certain cases the formation of a three-dimensional network of hydrogen bonding, and its dynamics by comparing 1-ethyl-3-methylimidazolium based acetate, chloride and thiocyanate ionic liquids.A particularly interesting case to study hydrogen bonding and other interactions is the investigation of binary mixtures of ionic liquids of the type [cation1][anion1]/[cation1][anion2]. In these mixtures, competing interactions are to be expected. We present both a thorough property meta-analysis of the literature and new data covering a wide range of anions, i.e., mixtures of 1-ethyl-3-methylimidazolium acetate with either trifluoroacetate, tetrafluoroborate, methanesulfonate, or bis(trifluoromethanesulfonyl)imide. In most cases, ideal mixing behavior is found, a surprising result considering the multitude of interactions present. However, ideal mixing behavior allows for the prediction of properties such as density, refractive index, surface tension, and, in most cases, viscosity as function of molar composition. Furthermore, we show that the prediction of properties such as the density of binary ionic liquid mixtures is possible by making use of group contribution methods which were originally developed for less complex non-ionic molecules. Notwithstanding this ideal mixing behavior, several exciting applications are discussed where preferential solvation via hydrogen bonding gives rise to non-additive effects leading to performance improvements. The assessment of the excess properties and (1)H NMR spectroscopic studies provide information on these structural changes and preferential interactions occurring in binary mixtures of ionic liquid, that clearly support the conclusions drawn from the computational studies.

On the nature of interactions between ionic liquids and small amino-acid-based biomolecules.

During the last decade, ionic liquids (ILs) have revealed promising properties and applications in many research fields, including biotechnology and biological sciences. The focus of this contribution is to give a critical review of the phenomena observed and current knowledge of the interactions occurring on a molecular basis. As opposed to the huge advances made in understanding the properties of proteins in ILs, complementary investigations dealing with interactions between ILs and peptides or oligopeptides are underrepresented and are mostly only of phenomenological nature. However, the field has received more attention in the last few years. This Review features a meta-analysis of the available data and findings and should, therefore, provide a basis for a scientifically profound understanding of the nature and mechanisms of interactions between ILs and structured or nonstructured peptides. Fundamental aspects of the interactions between different peptides/oligopeptides and ILs are complemented by sections on the experimental (spectroscopy, structural biology) and theoretical (computational chemistry) possibilities to explain the phenomena reported so far in the literature. In effect, this should lead to the development of novel applications and support the understanding of IL-solute interactions in general.

Agile green process design for the intensified Kolbe-Schmitt synthesis by accompanying (simplified) life cycle assessment.

In order to investigate the potential for process intensification, various reaction conditions were applied to the Kolbe-Schmitt synthesis starting from resorcinol. Different CO2 precursors such as aqueous potassium hydrogencarbonate, hydrogencarbonate-based ionic liquids, DIMCARB, or sc-CO2, the application of microwave irradiation for fast volumetric heating of the reaction mixture, and the effect of harsh reaction conditions were investigated. The experiments, carried out in conventional batch-wise as well as in continuously operated microstructured reactors, aimed at the development of an environmentally benign process for the preparation of 2,4-dihydroxybenzoic acid. To provide decision support toward a green process design, a research-accompanying simplified life cycle assessment (SLCA) was performed throughout the whole investigation. Following this approach, it was found that convective heating methods such as oil bath or electrical heating were more beneficial than the application of microwave irradiation. Furthermore, the consideration of workup procedures was crucial for a holistic view on the environmental burdens.

Carbene formation in ionic liquids: spontaneous, induced, or prohibited?

We present a theoretical study of carbene formation from the 1-ethyl-3-methylimidazolium acetate ionic liquid in the absence and presence of CO2 in gas and liquid phase. Although CO2 physisorption constitutes a precursory step of chemisorption (the CO2's reaction with carbenes, which forms from cations via proton abstraction by anions), it also enables a very stable CO2-anion associate. However, this counteracts the chemical absorption by reducing the basicity of the anion and the electrophilicity of the CO2, which is reflected by charge transfer. Accordingly, the observable carbene formation in the gas phase is hindered in the presence of CO2. In the neat liquid, the carbene formation is also suppressed by the charge screening compared to the case of the gas phase; nevertheless, indications for carbene incidents appear. Interestingly, in the CO2-containing liquid we detect more carbene-like incidents than in the neat one, which is caused by the way CO2 is solvated. Despite the weakness of the CO2-cation interaction, the CO2-anion associate is distorted by cations, which can be seen in longer associate distances and reduced "binding" energies. While the single solvating anion is shifted away from CO2, many more solvating cations approach it compared to the case of the gas phase. This leads to the conclusion that while the ionic liquid effect stabilizes charged species, introducing neutral species such as CO2 provides an opposite trend, leading to an inverse ionic liquid effect with the facilitation of carbene formation and thus of chemical absorption.

Significant cation effects in carbon dioxide-ionic liquid systems.

Carbon dioxide-ionic liquid systems are of great current interest, and significant efforts have been made lately to understand the intermolecular interactions in these systems. In general, all the experimental and theoretical studies have concluded so far that the main solute-solvent interaction takes effect through the anion, and the cation has no, or only a secondary role in solvation. In this theoretical approach it is shown that this view is unfounded, and evidence is provided that, similarly to the benzene-CO(2) system, dispersion interactions are present between the solute and the cation. Therefore, this defines a novel site for tailoring solvents to tune CO(2) solubility.

Ion pairing and dynamics of the ionic liquid 1-hexyl-3-methylimidazolium bis(irifluoromethylsulfonyl)amide ([C6mim][NTf2]) in the low dielectric solvent chloroform.

The structural and dynamic behavior of the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([C(6)mim][NTf(2)]) in chloroform has been studied by experimental measurements of (1)H and (19)F self-diffusion coefficients, viscosity, and excess molar volume in the concentration range of 0.001-1.0 mol·kg(-1) and temperatures ranging from 15 to 45 °C. Within measurement uncertainty, the (1)H and (19)F self-diffusion coefficients are identical at the same experimental conditions of concentration and temperature, indicating that even to the lowest measured concentrations the cation and anion are not completely dissociated. The combined experimental data indicates a progression from ion pairing to aggregate formation as concentration increases where at concentrations near 0.1 mol·kg(-1) aggregate formation becomes dominant. Concurrently with the formation of the IL aggregates at higher concentrations, we also observe an apparent breakdown of the validity of the Stokes-Einstein equation, which we explain by translational motion to become dominated by individual ion pairs moving rapidly between IL aggregates.

On the ideality of binary mixtures of ionic liquids.

In this work, structural and dynamical properties of the binary mixture of 1-ethyl-3-methyl-imidazolium chloride and 1-ethyl-3-methyl-imidazolium thiocyanate are investigated from ab initio molecular dynamics simulations and compared to the pure ionic liquids. Furthermore, the binary mixture is simulated with two different densities to gain insight into how the selected density affects the different properties. In addition, a simple NMR experiment is carried out to investigate the changes of the chemical shifts of the hydrogen atoms due to the composition of the mixture.

Ionic liquid applications in peptide chemistry: synthesis, purification and analytical characterization processes.

This review aims to provide a comprehensive overview of the recent advances made in the field of ionic liquids in peptide chemistry and peptide analytics.

Structural studies on ionic liquid/water/peptide systems by HR-MAS NMR spectroscopy.

The present work reports on an assessment of high-resolution magic angle spinning (HR-MAS) NMR spectroscopy for structural investigations of peptides dissolved in aqueous ionic liquids. Highly resolved one- and two-dimensional NMR spectra are obtained that allow for complete proton resonance assignments of both the peptides as solutes and the ionic liquids as solvents. Successful application of the HR-MAS method facilitates for the first time high-resolution NMR analysis of complex ionic liquid/peptide systems at the molecular level, mainly on the basis of chemical-shift changes.

Proton transfer and polarity changes in ionic liquid-water mixtures: a perspective on hydrogen bonds from ab initio molecular dynamics at the example of 1-ethyl-3-methylimidazolium acetate-water mixtures--part 1.

The ionic liquid 1-ethyl-3-methylimidazolium acetate [C(2)C(1)Im][OAc] shows a great potential to dissolve strongly hydrogen bonded materials, related with the presence of a strong hydrogen bond network in the pure liquid. A first step towards understanding the solvation process is characterising the hydrogen bonding ability of the ionic liquid. The description of hydrogen bonds in ionic liquids is a question under debate, given the complex nature of this media. The purpose of the present article is to rationalise not only the existence of hydrogen bonds in ionic liquids, but also to analyse their influence on the structure of the pure liquid and how the presence of water, an impurity inherent to ionic liquids, affects this type of interaction. We perform an extensive study using ab initio molecular dynamics on the structure of mixtures of the ionic liquid 1-ethyl-3-methylimidazolium acetate with water, at different water contents. Hydrogen bonds are present in the pure liquid, and the presence of water modifies and largely disturbs the hydrogen bond network of the ionic liquid, and also affects the formation of other impurities (carbenes) and the dipole moment of the ions. The use of ab initio molecular dynamics is the recommended tool to explore hydrogen bonding in ionic liquids, as an explicit electronic structure calculation is combined with the study of the condensed phase.

Ionic liquid structure-induced effects on organic reactions.

Understanding the ways in which the constituents of ionic liquids, i.e. the type of cation, its substitution, and the type of anion chosen, interact with reactants is prerequisite to deliberately designing an ionic liquid solvent with optimum performance. Several approaches, including physico-chemical and spectroscopic measurements and computational studies of binary ionic liquid-substrate mixtures have been presented that investigate the strength of interactions.The qualitative order of the basicity (hydrogen bond acceptor potential) of anions as most prominent force is already reasonably well understood, and reliably determined using, e.g. selective solvatochromic dyes. In certain reactions, the relative order of basicity correlates well with the reactivity of substrates. However, the determination of a relative order for the cations is still in its infancy. Owing to the fact that potential cation-derived interactions may not solely be due to hydrogen bond interactions, but also to ion pair interactions (electron pair donor/acceptor properties), the relative magnitudes of interactions between the anion and cation vary considerably - even in the absence of solutes - depending on the experimental method. In addition, it appears that the basicity of the anion superimposes in many instances on the effects exhibited by the cation and/or the cation's substituent. Hence, understanding the effect of the cation on the activation of substrates is still a challenge.This chapter aims at summarising the trends observed for binary model systems in experimental and computational investigations, and drawing conclusions about ionic liquid structure-induced effects relevant to organic reactions, in particular nucleophilic substitution reactions.

(2)H and (19)F solid-state NMR studies of the ionic liquid [C(2)Py][BTA]-d(10) confined in mesoporous silica materials.

Ionic liquids confined in porous materials are important solvents which allow a simple heterogenization of homogenous liquids. The perdeuterated ionic liquid N-ethylpyridinium-bis(trifluoromethanesulfonyl)amide ([C(2)Py][BTA]-d(10)) was prepared and its bulk phase behavior was studied by differential scanning calorimetry (DSC) and temperature-resolved (2)H and (19)F solid-state NMR spectroscopy. Its bulk properties were compared to [C(2)Py][BTA]-d(10) confined in a mesoporous silica support material as model material usable in SILP catalysts. The line shape analysis of the temperature-dependent NMR spectra of the bulk material reveals two phase transitions, one at 287-289 K (solid II/solid I) and one extending over a temperature range of 298-306 K (solid I/liquid). While the first phase transition is caused by the onset of an intramolecular rotation of the ethyl group of the cation, the second is due to the melting of the ionic liquid. In the bulk material, a hysteresis between the transition temperatures in heating and cooling scans occurs. In confinement, the dynamics of the ionic liquid changes considerably: no hysteresis is observed for [C(2)Py][BTA]-d(10) confined in the mesopores. Instead, only a broad transition from solid II to the liquid state, which spans the temperature range of 215-245 K, is observed. This transition is identified as the result of a broad distribution of molecular environments of the confined ionic liquid, which thus forms an amorphous phase inside the pores. Hence, the behavior of the ionic liquid in confinement is similar to the behavior of non-ionic guest molecules in the mesoporous silica. Finally, it was found that the anion and cation of the ionic liquid exhibit the same dynamic behavior in confinement.