Synthesis and characterization of double –SO3H functionalized Brönsted acidic hydrogensulfate ionic liquid confined with silica through sol-gel method

Imidazolium-based metal and halogen-free Brönsted acidic ionic liquid (BAIL) (3,3′-(hexane-1,6-diyl)bis(2-methyl-1-(3-sulfopropyl)-1H-benzimidazolium) hydrogensulfate [HbMBIM-PS][HSO₄] was synthesized. The physicochemical properties of this BAIL were investigated using a variety of different analytical and spectroscopic techniques such as ¹H and¹³C-NMR, FT-IR, mass, UV–vis and TGA spectra. A porous silica matrix has been synthesized using BAIL and tetraethoxysilane (TEOS) as silica source by nonhydrolytic sol–gel method. The properties of IL confined silica gel matrix have been studied using FTIR, TGA, SEM, N₂-sorption measurement (BET characterization for determining pore parameters), and NH₃-TPD techniques. From the N₂-sorption measurement, it has been found that BET surface area decreased while pore volume, average pore size and porosity decreased. The thermal stability of the IL has been found to increase upon confinement in silica gel matrix. The results suggested that IL had been successfully confined on silica gel. This IL confined silica gel catalyst is environment friendly and useful for alkane isomerization and esterification reactions.     

Cerebral blood flow estimation from perfusion-weighted MRI using FT-based MMSE filtering method

INTRODUCTION: Perfusion-weighted MRI can be used for estimating blood flow parameters using bolus tracking technique based on dynamic susceptibility contrast MRI. In order to extract flow parameters, several deconvolution techniques have been proposed, of which the singular value decomposition (SVD) and Fourier transform (FT)-based techniques are more popular and widely used. In this work, an FT-based method has been proposed that involves derivation of an optimal shaped filter (defined as a filter function) estimated using minimum mean-squared error (MMSE) technique in the frequency domain. The proposed technique has been compared with the well-established SVD technique using simulation experiments. SIMULATION METHODS: Simulation was performed in multiple steps. An arterial input function (AIF) was first defined based on a certain blood flow value. The T2* signal change was then derived from this AIF, and noise was added to the signal. Then, a unique and optimal shaped filter function Phi(f) was derived in order to obtain the best estimate of scaled residue function. One way is by minimizing the mean-squared error between the noiseless and noisy scaled residue function, i.e., using an MMSE method. The effect of low and moderate noise and distorted AIF on cerebral blood flow (CBF) estimates was obtained by using FT-based MMSE method. Results were compared with the SVD technique. In this work, SVD technique was assumed to be the standard reference deconvolution technique. RESULTS AND DISCUSSION: For low-noise condition, the FT-based technique was more stable than the SVD technique, while for moderate noise, both techniques consistently underestimated CBF. SVD technique was found to be more stable in presence of AIF distortions. However, SVD technique was found to be unstable due to AIF delay compared to the FT-based MMSE method. The shaped filter function was found to be sensitive to effect of AIF distortions.     

Efficient “on water” green route heterocyclization of thiosemicarbazones with DMAD

A simple, efficient, and eco-friendly procedure for the synthesis of thiazolidin-4-one derivatives in water from cyclocondensation reaction of thiosemicarbazone derivatives and dimethylacetylene dicarboxylate (DMAD) in good yield is reported. The regiochemistry of the cyclized products is established by elemental analysis, IR, NMR, and mass spectral data. A single crystal X-ray diffraction study of a representative compound, 3f, is reported.     

Catalyst-free,ethylene glycol promoted one-pot three component synthesis of 3-amino alkylated indoles via Mannich-type reaction

A highly efficient and sustainable approach for the multi-component synthesis of biologically important 3-amino alkylated indoles has been investigated via Mannich-type reaction under catalyst-free, ethylene glycol as a recyclable promoting medium. The wide applicability of the present method was examined with various substrates viz substituted aldehydes, indoles and secondary amines. This method will be useful for a large scale synthesis of 3-amino alkylated indoles without the use of column chromatography. The present method provides higher environmental compatibility and sustainability factors such as smaller E-factor (0.433) and higher atom-economy (AE = 93.3%).     

Structural trends in the dehydrogenation selectivity of palladium alloys

Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior. To provide molecular-level insights into these effects, a series of Pd intermetallic alloy catalysts with Zn, Ga, In, Fe and Mn promoter elements was synthesized, and the structures were determined using in situ X-ray absorption spectroscopy (XAS) and synchrotron X-ray diffraction (XRD). The alloys all showed propane dehydrogenation turnover rates 5–8 times higher than monometallic Pd and selectivity to propylene of over 90%. Moreover, among the synthesized alloys, Pd₃M alloy structures were less olefin selective than PdM alloys which were, in turn, almost 100% selective to propylene. This selectivity improvement was interpreted by changes in the DFT-calculated binding energies and activation energies for C–C and C–H bond activation, which are ultimately influenced by perturbation of the most stable adsorption site and changes to the d-band density of states. Furthermore, transition state analysis showed that the C–C bond breaking reactions require 4-fold ensemble sites, which are suggested to be required for non-selective, alkane hydrogenolysis reactions. These sites, which are not present on alloys with PdM structures, could be formed in the Pd₃M alloy through substitution of one M atom with Pd, and this effect is suggested to be partially responsible for their slightly lower selectivity.

Alloying is well-known to improve the dehydrogenation selectivity of pure metals, but there remains considerable debate about the structural and electronic features of alloy surfaces that give rise to this behavior.     

NMR studies of mixed cationic surfactants with similar tails and dissimilar bulky head groups

The mixed micelle formation by benzyldimethylhexadecylammonium chloride (BHDACl) with hexadecyltrimethylammonium bromide (HTAB), hexadecylpyridinium bromide (HPyBr), and hexadecylpyridinium choride (HPyCl) has been studied with the help of ¹H and ¹³C NMR studies influenced by both the head-group modifications as well as mutual hydrophobicity. The results showed that the mixed micelles of BHDACl+HPyBr and BHDACl+HPyCl mixtures are significantly affected by the steric factors originating from the bulkiness of the pyridinium head group of both cosurfactants in the stern layer. The result is that BHDACl+HPyBr and BHDACl+HPyCl mixed micelles are in the state of loose micellar arrangements rather than the mixed micelles of the BHDACl+HTAB mixture. A relative comparison between Br ^- and Cl ^- counterion effect suggests that the stronger binding ability of Br ^- than Cl ^-produces relatively compact mixed micelles.