Unravelling the formation of carbyne nanocrystals from graphene nanoconstrictions through the hydrothermal treatment of agro-industrial waste molasses.

The delicate synthesis of one-dimensional (1D) carbon nanostructures from two-dimensional (2D) graphene moiré layers holds tremendous interest in materials science owing to its unique physiochemical properties exhibited during the formation of hybrid configurations with sp-sp2 hybridization. However, the controlled synthesis of such hybrid sp-sp2 configurations remains highly challenging. Therefore, we employed a simple hydrothermal technique using agro-industrial waste as the carbon source to synthesize 1D carbyne nanocrystals from the nanoconstricted zones of 2D graphene moiré layers. By employing suite of characterization techniques, we delineated the mechanism of carbyne nanocrystal formation, wherein the origin of carbyne nanochains was deciphered from graphene intermediates due to the presence of a hydrothermally cut nanoconstriction regime engendered over well-oriented graphene moiré patterns. The autogenous hydrothermal pressurization of agro-industrial waste under controlled conditions led to the generation of epoxy-rich graphene intermediates, which concomitantly gave rise to carbyne nanocrystal formation in oriented moiré layers with nanogaps. The unique growth of carbyne nanocrystals over a few layers of holey graphene exhibits excellent paramagnetic properties, the predominant localization of electrons and interfacial polarization effects. Further, we extended the application of the as-synthesized carbyne product (Cp) for real-time electrochemical-based toxic metal (As3+) sensing in groundwater samples (from riverbanks), which depicted superior sensitivity (0.22 mA µM-1) even at extremely lower concentrations (0.0001 µM), corroborating the impedance spectroscopy analysis.

A Computational Exploration of Exohedrally Transition Metal Doped Si94- Superatom Based Magnetic MSi9M' Clusters (M, M' = Sc(II) to Cu(II)).

Nanosized clusters are drawing immense attention of the scientific community due to their size and composition dependent tunability of physical and chemical properties. Silicon nanoclusters are especially important because of their abundance and ample utility in the domains of electronics and semiconductor industry. Zintl phases of Si offer an excellent opportunity in the domain of nanocluster research owing to their superior stability and multifarious possibilities of tunability of electronic properties through doping with other elements. Doping silicon clusters with transition elements is a prevalent strategy to induce magnetic properties in such clusters. Although doping silicon clusters with single transition metal atoms can induce significant magnetism in nanoclusters, the dominant covalent interaction between silicon and the transition metal causes the magnetic moment to quench. The rational strategy of inducing a sustainable magnetic moment can be to introduce ferromagnetic interaction between two sites carrying nonvanishing magnetic moments. In the present work, such a possibility is explored in terms of the stability of the clusters and corresponding magnetic exchange coupling in them. The Si94-superatomic cluster is doped with two transition metal atoms exohedrally and the neutral clusters designed thereby are investigated computationally if they reduce or reinforce the high stability of the superatom and substantiate the possibility of obtaining nanosized magnetic units as building blocks of tunable materials for various applications.

SARS-CoV-2 Spike Protein Destabilizes Microvascular Homeostasis.

SARS-CoV-2 infection can cause compromised respiratory function and thrombotic events. SARS-CoV-2 binds to and mediates downregulation of angiotensin converting enzyme 2 (ACE2) on cells that it infects. Theoretically, diminished enzymatic activity of ACE2 may result in increased concentrations of pro-inflammatory molecules, angiotensin II, and Bradykinin, contributing to SARS-CoV-2 pathology. Using immunofluorescence microscopy of lung tissues from uninfected, and SARS-CoV-2 infected individuals, we find evidence that ACE2 is highly expressed in human pulmonary alveolar epithelial cells and significantly reduced along the alveolar lining of SARS-CoV-2 infected lungs. Ex vivo analyses of primary human cells, indicated that ACE2 is readily detected in pulmonary alveolar epithelial and aortic endothelial cells. Exposure of these cells to spike protein of SARS-CoV-2 was sufficient to reduce ACE2 expression. Moreover, exposure of endothelial cells to spike protein-induced dysfunction, caspase activation, and apoptosis. Exposure of endothelial cells to bradykinin caused calcium signaling and endothelial dysfunction (increased expression of von Willibrand Factor and decreased expression of Krüppel-like Factor 2) but did not adversely affect viability in primary human aortic endothelial cells. Computer-assisted analyses of molecules with potential to bind bradykinin receptor B2 (BKRB2), suggested a potential role for aspirin as a BK antagonist. When tested in our in vitro model, we found evidence that aspirin can blunt cell signaling and endothelial dysfunction caused by bradykinin in these cells. Interference with interactions of spike protein or bradykinin with endothelial cells may serve as an important strategy to stabilize microvascular homeostasis in COVID-19 disease. IMPORTANCE SARS-CoV-2 causes complex effects on microvascular homeostasis that potentially contribute to organ dysfunction and coagulopathies. SARS-CoV-2 binds to, and causes downregulation of angiotensin converting enzyme 2 (ACE2) on cells that it infects. It is thought that reduced ACE2 enzymatic activity can contribute to inflammation and pathology in the lung. Our studies add to this understanding by providing evidence that spike protein alone can mediate adverse effects on vascular cells. Understanding these mechanisms of pathogenesis may provide rationale for interventions that could limit microvascular events associated with SARS-CoV-2 infection.

Probing the Effects of Ligand Field and Coordination Geometry on Magnetic Anisotropy of Pentacoordinate Cobalt(II) Single-Ion Magnets.

In this work, the effects of ligand field strength as well as the metal coordination geometry on magnetic anisotropy of pentacoordinated CoII complexes have been investigated using a combined experimental and theoretical approach. For that, a strategic design and synthesis of three pentacoordinate CoII complexes [Co(bbp)Cl2]·(MeOH) (1), [Co(bbp)Br2]·(MeOH) (2), and [Co(bbp)(NCS)2] (3) has been achieved by using the tridentate coordination environment of the ligand in conjunction with the accommodating terminal ligands (i.e., chloride, bromide, and thiocyanate). Detailed magnetic studies disclose the occurrence of slow magnetic relaxation behavior of CoII centers with an easy-plane magnetic anisotropy. A quantitative estimation of ZFS parameters has been successfully performed by density functional theory (DFT) calculations. Both the sign and magnitude of ZFS parameters are prophesied well by this DFT method. The theoretical results also reveal that the α → ß (SOMO-SOMO) excitation contributes almost entirely to the total ZFS values for all complexes. It is worth noting that the excitation pertaining to the most positive contribution to the ZFS parameter is the dxy → dx2-y2 excitation for complexes 1 and 2, whereas for complex 3 it is the dz2 → dx2-y2 excitation.

On exo-cyclic aromaticity.

The domain of aromaticity spans a wide range of molecules, from polycyclic aromatic hydrocarbons, heterocycles to all-metal systems. Here, in silico we demonstrate the aromaticity in C2B2F4, extending beyond the limit of conventional aromatic molecules. This molecule gains the magic number of six π-electrons through an unusual electronic contribution from exo-cyclic atoms. The stability of the molecule is established through density functional theory, ab initio calculations as well as molecular dynamics simulation.

On the control of magnetic anisotropy through an external electric field.

The effect of an external electric field on the magnetic anisotropy of a single-molecule magnet has been investigated, for the first time, with the help of DFT. The application of an electric field can alter the magnetic anisotropy from "easy-plane" to "easy-axis" type. Excitation analysis performed through time-dependent DFT predicts that the external electric field facilitates metal to π-acceptor ligand charge transfer, leading to uniaxial magnetic anisotropy and concomitant spin Hall effect in a single molecule.

Ligand effects toward the modulation of magnetic anisotropy and design of magnetic systems with desired anisotropy characteristics.

Magnetic anisotropy of a set of octahedral Cr(III) complexes is studied theoretically. The magnetic anisotropy is quantified in terms of zero-field splitting (ZFS) parameter D, which appeared sensitive toward ligand substitution. The increased π-donation capacity of the ligand enhances the magnetic anisotropy of the complexes. The axial π-donor ligand of a complex is found to produce an easy-plane type (D > 0) magnetic anisotropy, while the replacement of the axial ligands with π-acceptors entails the inversion of magnetic anisotropy into the easy-axis type (D < 0). This observation enables one to fabricate a single molecule magnet for which easy-axis type magnetic anisotropy is an indispensable criterion. The equatorial ligands are also found to play a role in tuning the magnetic anisotropy. The magnetic anisotropy property is also correlated with the nonlinear optical (NLO) response. The value of the first hyperpolarizability varies proportionately with the magnitude of the ZFS parameter. Finally, it has also been shown that a rational design of simple octahedral complexes with desired anisotropy characteristics is possible through the proper ligand selection.

A theoretical study on photomagnetic fluorescent protein chromophore coupled diradicals and their possible applications.

We have designed and theoretically studied three different pairs of green fluorescent protein chromophores and their different homologue-based diradicals coupled with imino nitroxides. To begin with, the geometries of all these diradicals have been optimized at high spin (HS) state in the gas phase, in a water medium and in a blood plasma medium. The process of calculations is straightforward and well-established in the case of the gas phase. However, for calculations in water, we have adopted our own N-layer integrated molecular orbital and molecular mechanics (ONIOM) method. Similarly for the blood phase calculations, the polarized continuum model (PCM) method has been adopted. With these optimized geometries the magnetic exchange coupling constant (J) values are estimated for these diradicals in different media using the broken symmetry (BS) approach in an unrestricted DFT framework. In order to obtain the BS solutions in the ONIOM method, we have carried out ONIOM-BS, where the BS calculations are done for the inner high-level layer (diradical system) keeping the outer water layer at low level. In a similar fashion, a PCM-BS technique has also been adopted for the BS calculations in the PCM method. We have found that these diradicals have an ability to change their magnetic nature from antiferromagnetic in the trans form to ferromagnetic in the cis form upon irradiation of light with the appropriate wavelength. Using a time-dependent DFT (TDDFT) technique, the required wavelengths of light by which non-fluorescent dark trans diradicals turn into their corresponding bright fluorescent cis isomers are determined for each pair of diradicals for the gas and water media. This color change is indeed a signature of the change in magnetic state of the diradicals concerned. Here, we have also calculated the zero field splitting (ZFS) parameter (D), rhombic ZFS parameter (E) and ZFS magnitude (a2). From our calculations we ambitiously expect that if these diradicals are synthesized then they might be used as a successful, non-hazardous magnetic resonance imaging contrast agent (MRICA) in place of other metal-based contrast agents.