Accelerated microdroplet synthesis of benzimidazoles by nucleophilic addition to protonated carboxylic acids

We report a metal-free novel route for the accelerated synthesis of benzimidazole and its derivatives in the ambient atmosphere. The synthetic procedure involves 1,2-aromatic diamines and alkyl or aryl carboxylic acids reacting in electrostatically charged microdroplets generated using a nano-electrospray (nESI) ion source. The reactions are accelerated by orders of magnitude in comparison to the bulk. No other acid, base or catalyst is used. Online analysis of the microdroplet accelerated reaction products is performed by mass spectrometry. We provide evidence for an acid catalyzed reaction mechanism based on identification of the intermediate arylamides. Their dehydration to give benzimidazoles occurs in a subsequent thermally enhanced step. It is suggested that the extraordinary acidity at the droplet surface allows the carboxylic acid to function as a C-centered electrophile. Comparisons of this methodology with data from thin film and bulk synthesis lead to the proposal of three key steps in the reaction: (i) formation of an unusual reagent (protonated carboxylic acid) because of the extraordinary conditions at the droplet interface, (ii) accelerated bimolecular reaction because of limited solvation at the interface and (iii) thermally assisted elimination of water. Eleven examples are shown as evidence of the scope of this chemistry. The accelerated synthesis has been scaled-up to establish the substituent-dependence and to isolate products for NMR characterization.

We report a metal-free novel route for the accelerated synthesis of benzimidazole and its derivatives in the ambient atmosphere.     

Preparation and characterization of manganese ferrite-based magnetic liposomes for hyperthermia treatment of cancer

Comparative evaluation of two different methods of magnetic liposomes preparation, namely thin film hydration (TFH) and double emulsion (DE) with different molar ratios of egg-phosphatidyl choline (egg-PC) and cholesterol using lauric acid coated manganese ferrite-based aqueous magnetic fluid, is reported. TFH was found to be a better method of encapsulation and TFH 2:1 (egg-PC: cholesterol) magnetic liposomes showed the highest encapsulation efficiency and comparable heating ability to that of magnetic fluids. Stealth TFH 2:1 magnetic liposomes containing DSPE-PEG₂₀₀₀ were three-fold more cytocompatible as compared to the magnetic fluid. Stealth TFH 2:1 manganese ferrite-based magnetic liposomes might be useful for hyperthermia treatment of cancer.     

Wavelength selective detection using excitonic resonances in GaAs/AlGaAs P-I-(MQW)-N structures

The quantum confined Stark effect causes a strong wavelength and voltage dependence of photocurrent near excitonic resonances which is used to study the wavelength selectivity of p-i(MQW)-n photodiode. For a parallel input of optical bits each coming at a different wavelength, the selectivity is considered good if the state of a λ_i wavelength bit can be detected regardless of the λ_j (j ≠ i) state of the bits. Photocurrent is found to have very good selectivity if λ_j bits are all zero, i.e. the optical information is serial. However, we find that differential photocurrent (Δ I_ph/ΔV) provides a good selectivity for random states of λ_j bits (i.e. parallel input). Four channel selectivity is demonstrated at 200K. Specially designed quantum well structures can greatly improve this selectivity.     

Luminescence in ZnSe with Na and Al doping

Photoluminescence of ZnSe doped with Na and Al has been studied. A broad band in the blue region of the spectrum has been observed at temperatures below 150 °K. This band is apparently due to donor-acceptor pair transitions involving Al donors and Na acceptors. Temperature dependence of the luminescence indicates that the Na-acceptor level is relatively shallow.     

In vivo magnetic resonance spectroscopy measurement of gray-matter and white-matter gamma-aminobutyric acid concentration in sensorimotor cortex using a motion-controlled MEGA point-resolved spectroscopy sequence

Gamma-aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the brain. Understanding the GABA concentration, in vivo, is important to understand normal brain function. Using MEGA point-resolved spectroscopy sequence with interleaved water scans to detect subject motion, GABA level of sensorimotor cortex was measured using a voxel identified from a functional magnetic resonance imaging scan. The GABA level in a 20×20×20-mm³ voxel consisting of 37%±7% gray matter, 52%±12% white matter and 11%±8% cerebrospinal fluid in the sensorimotor region was measured to be 1.43±0.48 mM. In addition, using linear regression analysis, GABA concentrations within gray and white matter were calculated to be 2.87±0.61 and 0.33±0.11 mM, respectively.     

Green fluorescent protein for in situ synthesis of highly uniform Au nanoparticles and monitoring protein denaturation

Purified recombinant green fluorescent protein (GFP) expressed in E. coli was used for single-step synthesis of gold nanoparticles (Au NPs) with extraordinary size specificity in aqueous medium. The fluorescence of GFP offered a probe for concomitant changes in the protein during the course of synthesis, in addition to the monitoring of the time-dependent formation of Au NPs by the surface plasmon resonance. Reaction of AuCl⁻₄ with the protein produced spherical Au NPs having diameters ranging from 5–70 nm. Remarkably, addition of 1.0×10⁻⁵ M AgNO₃ in the medium produced uniform spherical Au NPs with particle diameter of 2.2±0.5 nm. Fluorescence spectroscopic measurements suggest that during synthesis of Au NPs in absence of AgNO₃, partial denaturation of the protein occurred resulting in the lowering of fluorescence intensity. On the other hand, when the NPs were synthesized in the presence of AgNO₃ complete denaturation of the protein with complete loss of fluorescence could be observed, which was further confirmed by native and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE). However, use of AgNO₃ only resulted neither in the formation of NPs nor had any significant effect on the fluorescence of GFP.     

Synthesis,structure and magnetic properties of mono- and di-nuclear nickel(II) thiocyanate complexes with tridentate N3 donor Schiff bases

The 1:1 condensation of N-methyl-1,3-diaminopropane and N,N-diethyl-1,2-diminoethane with 2-acetylpyridine, respectively at high dilution gives the tridentate mono-condensed Schiff bases N-methyl-N′-(1-pyridin-2-yl-ethylidene)-propane-1,3-diamine (L¹) and N,N-diethyl-N′-(1-pyridin-2-yl-ethylidene)-ethane-1,2-diamine (L²). The tridentate ligands were allowed to react with methanol solutions of nickel(II) thiocyanate to prepare the complexes [Ni(L¹)(SCN)₂(OH₂) (1) and [{Ni(L²)(SCN)}₂] (2). Single crystal X-ray diffraction was used to confirm the structures of the complexes. The nickel(II) in complex 1 is bonded to three nitrogen donor atoms of the ligand L¹ in a mer orientation, together with two thiocyanates bonded through nitrogen and a water molecule, and it is the first Schiff base complex of nickel(II) containing both thiocyanate and coordinated water. The coordinated water initiates a hydrogen bonded 2D network. In complex 2, the nickel ion occupies a slightly distorted octahedral coordination sphere, being bonded to three nitrogen atoms from the ligand L², also in a mer orientation, and two thiocyanate anions through nitrogen. In contrast to 1, the sixth coordination site is occupied by a sulfur atom from a thiocyanate anion in an adjacent molecule, thus creating a centrosymmetric dimer. A variable temperature magnetic study of complex 2 indicates the simultaneous presence of zero-field splitting, weak intramolecular ferromagnetic coupling and intermolecular antiferromagnetic interactions between the nickel(II) centers.     

Influence of the cavity size of cyclodextrins on the photochromism of azoimidazoles

1-Alkyl-2-(arylazo)imidazole (RaaiR^/) exists in trans configuration about the –NN- bond. Upon optical excitation in UV region the trans-configuration isomerises to cis-RaaiR^/. The photochromism is very susceptible to internal substituents and external environment like solvent polarity, viscosity and presence of innocent foreign species. In this work, the trans-to-cis photoisomerisation of RaaiR^/has been studied in DMF solution of cyclodextrin (α/β/γ-CD). The rate of trans-to-cis isomerisation is decreased in presence of CD compared to native form of RaaiR^/. The quantum yield of the photoisomerisation is decreased by 35–55% in inclusion phase, [email protected]^/, than free photochrome and follows the rate sequence: free state > γ-cyclodextrin > β-cyclodextrin > α-cyclodextrin. The cis-to-trans isomerisation proceeds slowly in visible light irradiation while it is appreciably fast with increasing temperature. The activation energy (E_a) of cis → trans thermal isomerisation is also diminished compared to free state of photochrome. The absorption spectral studies have been used in case of Pai-C₁₈H₃₇ with β-CD and inclusion constant is K_b ?= ?0. 121 M^?1. The ¹H NMR spectral measurement also suggests interaction of aryl protons with cavity protons of β-CD. DFT computation is also attempted to examine the inclusion of RaaiR^/with CD and the negative values of binding energy show that the process of inclusion is spontaneous and complexes formed are stable.