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AbstractNatural convection inside a cylindrical enclosure is important in many industrial applications. Laminar natural convective heat transfer in the annular space between heated semi-circular cylinder in a horizontal concentric cylindrical enclosure, which has relevance to cooling of electronic components, is studied in this work. Constant wall temperature (CWT) and constant wall heat flux (CWHF) boundary conditions are considered on the inner cylinder, whereas the outer cylindrical enclosure is maintained at a fixed lower temperature. The Finite Volume Method (FVM) is used for the computations. The effect of the Rayleigh number (Ra=102 to 105) and the angular orientation of the semi-circular cylinder on the convective heat transfer is investigated. The fluid flow, temperature profile, and heat flow are visualized via streamlines, isotherms, and heatlines. Further, the overall heat transfer is explained based on the local and average Nusselt number on the inner cylinder wall. The effect of the angular orientation of the inner cylinder is noticeable for Ra≥103. The angular orientation ϕ = 90° greatly enhances the heat transfer as compared to all other orientations for all Ra≥103 for both CWT and CWHF boundary conditions. The correlation between the average Nusselt and Rayleigh numbers for a particular orientation is proposed. [ABSTRACT FROM AUTHOR]

Type-1 and type-2 diabetes mellitus are metabolic disorders governed by the functional efficiency of pancreatic β-cells. The activities of the cells toward insulin production, storage, and secretion are accompanied by Zn(II) ions. Thus, for non-invasive pathology of the cell, developing Zn(II) ion-responsive MRI-contrast agents has earned considerable interest. In this report, we have synthesized a seven-coordinate, mono(aquated) Mn(II) complex (1), which is impregnated within a porous silica nanosphere of size 13.2 nm to engender the Mn(II)-based MRI contrast agent, complex 1@SiO2NP. The surface functionalization of the nanosphere by the Py2Pic organic moiety for the selective binding of Zn(II)-ions yields complex 1@SiO2-Py2PicNP, which exhibits r1 = 13.19 mM−1 s−1. The relaxivity value elevates to 20.38 mM−1 s−1 in the presence of 0.6 mM BSA protein at pH 7.4. Gratifyingly, r1 increases linearly with the increase of Zn(II) ion concentration and reaches 39.01 mM−1 s−1 in the presence of a 40 fold excess of the ions. Thus, Zn(II)-responsive contrast enhancement in vivo is envisaged by employing the nanoparticle. Indeed, a contrast enhancement in the pancreas is observed when complex 1@SiO2-Py2PicNP and a glucose stimulus are administered in fasted healthy C57BL/6 mice at 7 T. [ABSTRACT FROM AUTHOR]

Contrast-agent enhanced magnetic resonance imaging (MRI) has been under continuous investigation for the conspicuous imaging of lesions and the early-stage detection of tumors. To achieve the development of a T1-weighted contrast agent with a high relaxivity value, herein, porous silica nanoparticles that had internalized about 20 aquated cationic Gd(III) complexes (1) of the hexadentate hydroxyethyl-appended picolinate-based ligand H2hbda were demonstrated. Complex 1 exhibited a longitudinal relaxivity value per mM Gd(III) ions, r1, of 9.05 mM−1 s−1 (pH 7.4, 37 °C, 1.41 T), which increased to 86.41 mM−1 s−1 because of the grafting of complex 1 in the inner core of porous silica nanospheres through electrostatic interactions between the anionic silica surface and the cationic complex 1 molecules. A further augmentation in the relaxivity value to 118.32 mM−1 s−1 was realized because of the interaction of the complex 1@SiO2NPs with serum albumin protein. The synthesized nanosystem was impervious to physiologically available anions (HPO42− and HCO31−) and also kinetically inert, as evidenced via a transmetallation experiment in the presence of Zn(II) ions. The developed complex-incorporated nanomaterial was bio- and hemo-compatible. Cellular uptake measurements employing HeLa cells and the concentration-dependent enhancement in the brightness of in vitro phantom images, recorded under a clinical scanner at 1.5 T, demonstrated that the developed biocompatible 1@SiO2NP complex has promising diagnostic applications as a T1-weighted MRI contrast agent. [ABSTRACT FROM AUTHOR]

An elusive aminyl radical and an iminosemiquinone radical-coordinated square pyramidal Cu(II) complex (1) have been isolated by the reaction between the noninnocent ligand H4LPy(AP) and Cu(ClO4)2·6H2O in the presence of Et3N and air as the sole oxidant. The geometry and electronic structure of the complex were concluded by X-ray crystallography, magnetic and EPR measurements, and density functional theory (DFT) calculations. This work reports the first crystallographic example of the two different types of radicals co-existing in a stable complex. [ABSTRACT FROM AUTHOR]

Long-range antiferromagnetic coupling impeded electron flow through the hexaradical-containing tetranuclear CoIII4 complex (1), while the nonradical-containing tetranuclear CoIII4 complex (2), with no paramagnetic centres, was a semiconductor and sensed NH3 efficiently at room temperature (25 °C). [ABSTRACT FROM AUTHOR]

This work synthesizes a four‐coordinate Cu(II) complex {[CuII(LNH2)]; 1} of the tetradentate H2LNH2 ligand. The synthesized complex acted as an electrocatalyst for the CO2 conversion towards C1 and C2 products by activating the stable C−O bond. The catalyst ink (complex 1+DMF+Nafion; catalyst concentration ∼2 mg cm−2) was surface‐coated over the graphite plate to carry out the reduction reaction in a three‐electrode electrochemical system. An H‐type electrolyzer was employed in 0.5 M KHCO3 electrolyte solution at neutral pH in the carbonated system. A maximum amount of 36 % FE was achieved at −1.80 V vs. Ag/AgCl for 60 min of reaction. The total TON and TOF of the catalyst were calculated to be 9230 and 2.6 s−1, respectively. The CO2‐reduced products were obtained as HCOOH>CH3COOH>CH3OH>C2H5OH, which were formed through multiple–electrons transfer (2 e− to 12 e−) proton‐insertion reactions. The catalytic activity of the Cu(II) complex was enhanced by the presence of the terminal ‐NH2 anchoring‐group in the ligand backbone. The fact was confirmed by electrocatalytic CO2 conversion experiments in the presence of complex 2 {[CuII(L)]; 2} as the electrocatalyst, which did not contain the anchoring group in the salen ligand structure. [ABSTRACT FROM AUTHOR]