Alkali Can Accelerate The Cellulose Dissolution In Aqueous 1-Ethyl-3-Methylimidazole Acetate (EmimAc/10% Water)

Ionic liquids are potential and successful cellulose solvent but still suffer technical and economic issues in the cellulose commercialization. In this work, a relative low-viscosity aqueous 1-ethyl-3-methylimidazole acetate (EmimAc with 10% water) was used instead of EmimAc to dissolve cellulose; the results showed that adding NaOH to water can significantly accelerate cellulose dissolution and the cellulose solubility increased with the NaOH concentration in the EmimAc/10% water solution. NaOH can weaken the strong interaction between water and EmimAc because it can bond preferentially with water by hydrogen bonding and therefore release Ac - from Ac - -water cluster; which can enhance the reaction between Emim + and Ac - and therefore improve the cellulose dissolution. Unfortunately, the NaOH introduction inevitably cause a cellulose degradation via peeling reaction.

A Density Functional Theory Study on the Water Aggregation Behaviour of Fatty-Acid Based Anionic Surface Active Ionic Liquids

The hydrogen bond interactions between methyl-imidazolium cation (MIM+) and fatty-acid anions (CmHnCOO–, where m=1–6; n-3–13) of ionic liquids are studied in both gas phase and water phase using density functional theory. The structural properties show that the presence of N–H···O and C–H···O hydrogen bonds between [MIM]+ and [CmHnCOO]– (m=1–6;n-3–13) ionic liquids. From the vibrational frequency analysis it was found that the hydrogen bond interaction between [MIM]+ and [CmHnCOO]– (m=1–6;n-3–13) ionic liquids are red-shifted in frequency. The natural bond orbital analysis show that the N–H···O hydrogen bond associated with the large charge transfer which has the higher stabilization energy (i.e. E(2) ~ 38 kcal/mol). Further, the cation/anion–water cluster (H2O)1-3 interactions show that the water molecules are preferred to interact with anions. In the case of ionic liquids–water cluster interaction, the water molecules occupies the interstitial space between cation and anion of ionic liquids which results in weakening the cation-anion interaction.

Water cluster in hydrophobic crystalline porous covalent organic frameworks

Progress over the past decades in water confinement has generated a variety of polymers and porous materials. However, most studies are based on a preconception that small hydrophobic pores eventually repulse water molecules, which precludes the exploration of hydrophobic microporous materials for water confinement. Here, we demonstrate water confinement across hydrophobic microporous channels in crystalline covalent organic frameworks. The frameworks are designed to constitute dense, aligned and one-dimensional polygonal channels that are open and accessible to water molecules. The hydrophobic microporous frameworks achieve full occupation of pores by water via synergistic nucleation and capillary condensation and deliver quick water exchange at low pressures. Water confinement experiments with large-pore frameworks pinpoint thresholds of pore size where confinement becomes dominated by high uptake pressure and large exchange hysteresis. Our results reveal a platform based on microporous hydrophobic covalent organic frameworks for water confinement.

Stabilization of Near Identical Hydrogen Bonded Octameric Water Clusters in Crystal Structures of Three Distinct Non-Charged Polyamide Macrocyclic Host Molecules

In this paper, we present a comparative analysis of the solid state structures of three well-resolved hydrates of macrocyclic host molecules 1a, 1b, and 2 containing an intrannular amide-aryl substituent (lariat arm) connected to a fixed 26-membered ring in a normal (-NHCOAr, hosts 1a and 1b) or reverse manner (-CONHAr, host 2). Despite different chemical structures, these hosts crystallize as isostructural tetrahydrates in the same P-1 space group. Moreover, their crystals exhibit identical hydrogen bond motifs resulting in a stabilization of an almost identical unusual octameric water cluster built from the cyclic tetramer core and four water molecules, attached sequentially in an “up-and-down” manner. Further analysis reveals that, among the series, the structure of host 2 provides the most suitable environment for the accommodation of this type of water cluster.

Interaction of HCO+ Cations With Interstellar Negative Grains. Quantum Chemical Investigation and Astrophysical Implications

In cold galactic molecular clouds, dust grains are coated by icy mantles and are prevalently charged negatively, because of the capture of the electrons in the gas. The interaction of the charged grains with gaseous cations is known to neutralize them. In this work, we focus on the chemical consequences of the neutralization process of HCO+, often the most abundant cation in molecular clouds. More specifically, by means of electronic structure calculations, we have characterized the energy and the structure of all possible product species once the HCO+ ion adsorbs on water clusters holding an extra electron. Two processes are possible: (i) electron transfer from the negative water cluster to the HCO+ ion or (ii) a proton transfer from HCO+ to the negative water cluster. Energetic considerations favor electron transfer. Assuming this scenario, two limiting cases have been considered in astrochemical models: (a) all the neutralized HCO+ is retained as neutral HCO adsorbed on the ice and (b) all the neutralized HCO+ gets desorbed to the gas phase as HCO. None of the two limiting cases appreciably contribute to the HCO abundance on the grain surfaces or in the gas.