Conformational States of Ionic Liquid 1‑Ethyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide in Bulk and Confined Silica Nanopores Probed by Crystallization Kinetics Study

The nonaqueous sol–gel process has been used to synthesize the “ionogels” by confining ionic liquid (1-ethyl-3-methyl­imidazolium bis­(trifluoro­methyl­sulfonyl)­imide; [EMIM]­[TFSI]) into silica gel matrices. The present study is concerned mainly with probing the conformational states of the IL ([EMIM]­[TFSI]) through crystallization kinetics study of the bulk and confined ionic liquid (IL) in nanopores of silica matrix. The crystallization kinetics has been studied by the isothermal method using differential scanning calorimetry (DSC). For bulk IL, DSC result shows three crystallization peaks due to different conformations of IL molecules. DSC results show that one of these crystallization peaks disappears upon confinement due to interaction of IL molecules with the silica pore wall surfaces. The crystallization kinetics of bulk and confined IL is quantified using the Avarami analysis. Confinement of IL results in a decrease of the Avarami exponent, indicating one-dimensional crystal growth. To support the results obtained from crystallization kinetics study, investigate the properties of confined IL, and to study the morphological properties of silica gel matrices, some other characterization techniques, viz. TGA, XPS, FTIR, BET, SEM, and TEM, have been used. The XPS and FTIR results show the change in the binding energy of constituents of IL molecule and vibrational bands related to IL, respectively. BET, SEM, and TEM analyses display the uniform pore structures in IL confined silica matrices

Viscoelastic, Surface, and Volumetric Properties of Ionic Liquids [BMIM][OcSO₄], [BMIM][PF₆], and [EMIM][MeSO₃]

Thermophysical properties viz. surface tension, viscosity, density, and ultrasonic velocity of three ionic liquids 1-butyl-3-methyl imadazolium octyl sulfate [BMIM]­[OcSO₄], 1-butyl-3-methyl imadazolium hexafluorophosphate [BMIM]­[PF₆], and 1-ethyl-3-methyl imadazolium methanesulfonate [EMIM]­[MeSO₃] have been measured in a wide temperature range. Experimental data so obtained have been used to calculate isentropic compressibility, isothermal expansion coefficient, surface entropy, surface enthalpy, and critical temperature (temperature where the distinction between liquid and gas phase vanishes and the surface tension tends to zero). Structure–property correlation for different ILs is also discussed

Direct interaction between the MHC-I CD-Nef and μ1: partially purified recombinant proteins were used in GST pulldown assays and analyzed on SDS-PAGE gels by staining with Coomassie blue.

<p>(A) From left to right: protein ladder, recombinant μ121 and μ158 proteins as markers, then six lanes of negative controls as indicated. (B) Specific binding between μ1 and MHC-I CD-Nef. Recombinant proteins (“Input”) were run as markers. Right four lanes show binding of μ121 or μ158 with either MHC-I CD-Nef or MHC-I CD-Nef LL/AA. Nef LL/AA indicates alanine substitution of Nef residues L164 and L165.</p

Purified recombinant truncated μ1 and μ1 mutants (F172A/D174S and V392A/L395A) were subjected to GST pulldown assays using MHC-I CD-Nef and MHC-I CD-Nef LL/AA chimeras:

<p>(A) Ponceau red staining of PVDF membrane. (B) A western blot of the pulldown was probed with anti-His6 antibody to detect the wild-type μ1 and μ1 mutants. Band quantitation using Image J and setting the pulldown of wild-type μ1 by GST-CD-Nef to 100% yielded the following efficiencies for the μ1 mutants: μ1_FD/AS: 57%; μ1_VL/AA: 24%. The results shown are representative of three independent experiments. (C) The amounts of GST-proteins used for binding setup are shown by Coomassie blue staining.</p

Surface expression in CEM T cells of CD8 chimeras containing the MHC-I CD, Nef, or the MHC-I CD-Nef chimeric sequence as cytoplasmic domains was measured by flow cytometry.

<p>Cells were transfected to express GFP as well as the CD8-chimeras, and the cells were gated for low and mid-intensity GFP expression. (A) Relative cell number vs. relative fluorescence intensity of CD8 [phycoerythrin (PE)]. Mean fluorescence intensities for CD8 (PE) are shown. The chimeric MHC-I CD-NefLL/AA sequence directs decreased expression at the cell surface relative to the MHC-I CD alone or NefLL/AA alone. This activity of the MHC-I CD when fused to Nef depends on Y320. (B) The total cellular expression of the chimeric molecules containing Nef was evaluated by western blot. Equal volumes of the transfected cell suspensions were collected before the FACS staining and lysed for western blot analysis using anti-Nef antibody. All chimeric molecules were expressed at a similar level. Actin was probed as a loading control.</p

Schematic representation of the GST-MHC-I CD-Nef fusion protein.

<p>Key residues in MHC-I CD (Y320) and HIV1-Nef (M20, E62-65, P78) used in mutational and binding studies are shown.</p

GST pulldown of recombinant μ1 <i>in vitro</i> using chimeric proteins in which the MHC-I CD is fused to the N-terminus of Nef and by MHC-I CD-Nef chimera mutants.

<p>Various residues within the CD of MHC-I and Nef were mutated to alanine as shown. (A) A western blot of the pulldown was probed with anti-His antibody to detect the recombinant μ1 (μ121). Band quantitation using Image J and setting the pulldown of μ1 by GST-CD-Nef to 100% yielded the following efficiencies for the constructs: GST-CD-NefLL/AA: 77%; GST-CD(Y320A)-NefLL/AA: 16%; GST-CD-Nef M20A,LL/AA: 53%; GST-CD-Nef E62-65A,LL/AA: 30%; GST-CD-Nef P78A,LL/AA: 19%. The results shown are representative of three independent experiments. (B) The amounts of GST-proteins used for binding setup are shown by Coomassie blue staining.</p