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61.
Catia de Bonis Cataldo Simari Vasiliki Kosma Barbara Mecheri Alessandra D’Epifanio Valentina Allodi Gino Mariotto Sergio Brutti Sophia Suarez Kartik Pilar Steve Greenbaum Silvia Licoccia Isabella Nicotera 《Journal of Solid State Electrochemistry》2016,20(6):1585-1598
An organically functionalized titania, TiO2-RSO3H, was evaluated as filler in sulfonated polyetheretherketone (sPEEK)-based composite membranes for application in high temperature direct methanol fuel cells. The presence of propylsulfonic acid groups covalently bound onto the TiO2 surface and the nanometric nature of the additive were analyzed by Raman spectroscopy and transmission electron microscopy, respectively. The properties of the sPEEK/TiO2-RSO3H composite membranes were compared with those of the pure sPEEK membranes and those of the sPEEK/TiO2 composite membranes containing pristine titania nanoparticles at same filler content. Water and methanol transport properties were investigated by NMR methods, including relaxation times and self-diffusion coefficients as function of temperature (up to 130 °C), and pressure (from 0 up to 2 kbar). The incorporation of the nanoadditivies in the sPEEK polymer demonstrates considerable effects on the morphology and stiffness of the membranes, as well as on the transport properties and barrier effect to the methanol crossover. In particular, the functionalization by propylsulfonic acid groups promotes a higher reticulation between the polymeric chains, increasing the tortuosity of the methanol diffusional paths, so reducing the molecular diffusion, while the proton mobility increases being favored by the Grotthus-type mechanism. Conductivity measurements point out that the filler surface functionalization avoids the reduction of the overall proton conduction of the electrolyte due to the embedding of the low-conducting TiO2. Finally, remarkable improvements were found when using the sPEEK/TiO2-RSO3H composite membrane as electrolyte in a DMFC, in terms of reduced methanol crossover and higher current and power density delivered. 相似文献
62.
E.V. Sampathkumaran Niharika Mohapatra Kartik K. Iyer C.D. Cao W. Löser G. Behr 《Journal of magnetism and magnetic materials》2008
Considering certain interesting features in the previously reported 166Er Mössbauer effect, and neutron diffraction data on the polycrystalline form of ErPd2Si2 crystallizing in the ThCr2Si2-type tetragonal structure, we have carried out magnetic measurements (1.8–300 K) on the single crystalline form of this compound. We observe significant anisotropy in the absolute values of magnetization (indicating that the easy axis is c-axis) as well as in features due to magnetic ordering in the plot of magnetic susceptibility χ versus temperature T at low temperatures. The χ(T) data reveal that there is a pseudo-low-dimensional magnetic order setting in at 4.8 K, with a three-dimensional antiferromagnetic order setting in at a lower temperature (3.8 K). A new finding in the χ(T) data is that, for H∥〈1 1 0〉 but not for H∥〈0 0 1〉, there is a broad shoulder in the range 8–20 K, indicative of the existence of magnetic correlations above 5 K as well, which could be related to the previously reported slow-relaxation-dominated Mössbauer spectra. Interestingly, the temperature coefficient of electrical resistivity is found to be isotropic; no feature due to magnetic ordering could be detected in the electrical resistivity data at low temperatures, which is attributed to magnetic Brillioun-zone boundary gap effects. The results reveal the complex nature of magnetism of this compound. 相似文献
63.
Ekta Nag Sridhar Battuluri Dr. Kartik Chandra Mondal Dr. Sudipta Roy 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(64):e202202324
Silver clusters are attractive candidates for their promising optical properties, and biomedical activities. Herein, we report on the first syntheses and isolation of three homo-/mixed-valence silver nanoclusters (NCs) with Ag12Cl3, Ag29, and Ag8 cores [((cAAC)P)6Ag12Cl3](OTf)3 ( 1 ), [((cAAC)P)6Ag29] ( 2 ), and [((cAAC)P)4Ag8] ( 3 ) having three-/twofold symmetry, employing cyclic alkyl(amino) carbene (cAAC)-supported phosphinidenide (cAACP−) as the π-accepting stabilizing ligand. The average diameters of Ag NCs 1 , and 2 are approximately 1.6 to 2 nm. The redox non-innocent mono-atomic phosphorus anions (P−) anchored with cAAC ligands are generated in situ by the reaction of AgOTf with a boryl-phosphaalkene (cAAC)P−B(NiPr2)2 through cleavage of the P−B bond with the help of a triflate anion (OTf−) as a weak nucleophile. Equivalent number of the (cAAC)P− anions generated in situ are oxidized to produce the corresponding bis-phosphinidene (cAAC)2P2 leading to the generation of Ag0 ions in solution for the formation of the unprecedented mixed-valence Ag NC 2 . Complex 3 is achieved by treating potassium phosphinidenide cAACPK with AgNTf2. The ligand field and the steric hindrance of the (cAAC)P units play crucial roles in stabilizing complexes 1 – 3 , further providing a three- ( 1 , 2 )/two- ( 3 ) fold stand. The Ag12Cl3 NC ( 1 ) with a tricationic core [AgI12Cl3] was found to be diamagnetic, and fluorescent, emitting green light at 563 nm when excited at 400 nm. In contrast, the neutral Ag29 ( 2 ) and Ag8 ( 3 ) clusters were found to be paramagnetic, and NMR silent showing characteristic EPR signals for Ag0 at room temperature. 相似文献
64.
Subhajit Saha Pritam Kumar Roy Kartik Maity Prof. Mahitosh Mandal Prof. Kumar Biradha 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(9):e202103830
Selective detection of H2S in the cellular systems using fluorescent CPs/MOFs is of great scientific interest due to their outstanding aqueous stability, biocompatibility and real-time detection ability. Fabrication of such materials using complete biologically essential elements and applying them as an efficient biosensor is still quite challenging. In this context, two newly synthesized CPs containing biologically essential metal ion (Zn) and nitro/azido functional groups into the framework to sense extracellular and intracellular H2S by reducing into respective amines are presented. The CP- 1 containing the azide group acted as an efficient fluorescent turn-on probe with the lowest detection limit (7.2 μM) and shortest response time (30 s) among the Zn-based probes reported till date. Moreover, CP- 1 exhibited green luminescence in live cells after imaging a very low concentration of H2S, whereas the nitro analogue CP- 2 could not detect the target analyte due to its framework disruption. 相似文献
65.
Formulations of traditional medicines are usually made up of a complex mixture of herbs. However, effective quality control methods in order to select materials of the right quality are lacking. 'Amukkara choornam' is a polyherbal Siddha formulation used for gastritis, spleen enlargement, leucorrhoea, hiccups, anaemia, tuberculosis and kappa diseases. Trans-caryophyllene is an important constituent present in the ingredients of this formulation. In a literature survey, it was found that there is no such method for the quantification of trans-caryophyllene except gas chromatography or gas chromatography-mass spectroscopy (GC-MS). So, a high performance thin layer chromatography (HPTLC) method was developed and validated for the quantification of trans-caryophyllene in amukkara choornam. Pre-coated silica gel 60F-254 plates (10 × 10 cm2) were used for the analysis. The solvent system consisted of toluene-ethyl acetatate (9 : 3, v/v), and trans-caryophyllene was detected at 260 nm. The developed method was validated for linearity (R2 = 0.9996 ± 0.0034), limit of detection (LOD) (0.101 ng), limit of quantification (LOQ) (0.639 ng), accuracy (% recovery = 97.19 ± 1.204), and precision (CV < 5%, for both intra-day and inter-day precisions). The levels of trans-caryophyllene were found to be 3.5-4.10 μg per gram of herbal products. 相似文献
66.
67.
Synthesis,Characterization, and Theoretical Investigation of Two‐Coordinate Palladium(0) and Platinum(0) Complexes Utilizing π‐Accepting Carbenes
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Dr. Sudipta Roy Dr. Kartik Chandra Mondal Dipl.‐Chem. Jann Meyer Dipl.‐Chem. Benedikt Niepötter Christian Köhler Dr. Regine Herbst‐Irmer Prof. Dr. Dietmar Stalke Dr. Birger Dittrich Dr. Diego M. Andrada Prof. Dr. Gernot Frenking Prof. Dr. Herbert W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(26):9312-9318
An elegant general synthesis route for the preparation of two coordinate palladium(0) and platinum(0) complexes was developed by reacting commercially available tetrakis(triphenylphosphine)palladium/platinum with π‐accepting cyclic alkyl(amino) carbenes (cAACs). The complexes are characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. The palladium complexes exhibit sharp color changes (crystallochromism) from dark maroon to bright green if the C‐Pd‐C bond angle is sharpened by approximately 6°, which is chemically feasible by elimination of one lattice THF solvent molecule. The analogous dark orange‐colored platinum complexes are more rigid and thus do not show this phenomenon. Additionally, [(cAAC)2Pd/Pt] complexes can be quasi‐reversibly oxidized to their corresponding [(cAAC)2Pd/Pt]+ cations, as evidenced by cyclic voltammetry measurements. The bonding and stability are studied by theoretical calculations. 相似文献
68.
A Strongly Spin‐Frustrated FeIII7 Complex with a Canted Intermediate Spin Ground State of S=7/2 or 9/2
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Dr. Kartik Chandra Mondal Dr. Valeriu Mereacre Dr. George E. Kostakis Dr. Yanhua Lan Dr. Christopher E. Anson Dr. Ion Prisecaru Prof. Dr. Oliver Waldmann Prof. Dr. Annie K. Powell 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(30):10835-10842
A disk‐shaped [FeIII7(Cl)(MeOH)6(μ3‐O)3(μ‐OMe)6 (PhCO2)6]Cl2 complex with C3 symmetry has been synthesised and characterised. The central tetrahedral FeIII is 0.733 Å above the almost co‐planar FeIII6 wheel, to which it is connected through three μ3‐oxide bridges. For this iron‐oxo core, the magnetic susceptibility analysis proposed a Heisenberg–Dirac–van Vleck (HDvV) mechanism that leads to an intermediate spin ground state of S=7/2 or 9/2. Within either of these ground state manifolds it is reasonable to expect spin frustration effects. The 57Fe Mössbauer (MS) analysis verifies that the central FeIII ion easily aligns its magnetic moment antiparallel to the externally applied field direction, whereas the other six peripheral FeIII ions keep their moments almost perpendicular to the field at stronger fields. This unusual canted spin structure reflects spin frustration. The small linewidths in the magnetic Mössbauer spectra of polycrystalline samples clearly suggest an isotropic exchange mechanism for realisation of this peculiar spin topology. 相似文献
69.
Inside Cover: Synthesis,Characterization, and Theoretical Investigation of Two‐Coordinate Palladium(0) and Platinum(0) Complexes Utilizing π‐Accepting Carbenes (Chem. Eur. J. 26/2015)
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Dr. Sudipta Roy Dr. Kartik Chandra Mondal Dipl.‐Chem. Jann Meyer Dipl.‐Chem. Benedikt Niepötter Christian Köhler Dr. Regine Herbst‐Irmer Prof. Dr. Dietmar Stalke Dr. Birger Dittrich Dr. Diego M. Andrada Prof. Dr. Gernot Frenking Prof. Dr. Herbert W. Roesky 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(26):9266-9266
70.
Kartik Arora Radhakrishna Sureshkumar Matthew P. Scheiner Justin L. Piper 《Rheologica Acta》2002,41(1-2):25-34
We employ digital particle imaging velocimetry (DPIV) to investigate the influence of a drag reducing cationic surfactant
additive, cetyltrimethyl-ammonium chloride (CTAC), on turbulent swirling flows generated in a cylindrical vessel either by
a rotating disk or a rotating disk fitted with vertical flat blades. The largest concentration of CTAC used in this study
(0.05 ≤ C ≤ 0.5 mmol/l) is an order of magnitude smaller than those used in experimental investigations of surfactant induced
drag reduction in turbulent pipe/channel flows. Even for such dilute systems, a number of dramatic and intriguing effects
are observed. In the case of disk-driven flow, it is shown that the surfactant has a non-monotonic influence on turbulence
intensity: both radial and axial root mean square velocity fluctuations first increase with increasing surfactant concentration
C, reach a maximum and decrease upon further increase in C. Moreover, the maximum intensity is attained at a concentration
that is practically independent of the angular frequency Ω of the disk. For the flow driven by bladed impeller, the introduction
of the surfactant leads to flow reversal at the impeller plane for low concentrations. Enhancement in the radial and azimuthal
mean velocities is also observed. For relatively larger concentrations (=0.5 mmol/l), a mean flow field that consists of multiple
transient mixing pockets emerges as Ω exceeds a critical value. Plausible mechanisms are proposed to explain these observations.
Received: 11 September 2000 Accepted: 10 April 2001 相似文献