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Shiv Nadar University

(SoNS) School of Natural Sciences

Cytochrome P45051(CYP51) catalyzes C-C bond cleavage during the biosynthesis of the sterol, using a mechanism which is still under debate. Moreover, the mechanistic conundrum is aggravated by the experimental results, which show that the C-C bond cleavage reaction step may start either from the gem-diol or aldehyde intermediates. The present study uses hybrid QM/MM calculations (exploration of potential energy surface) supplemented by long-scale MD simulations to elucidate the mechanism of C-C bond cleavage in 14α-demethylation of lanosterol using both gem-diol and aldehyde as starting substrates for the reaction. For gem-diol, the reaction proceeds via a proton-coupled electron transfer (PCET) type pathway. However, in the aldehyde form, demethylation follows a surprising mechanism assisted by a water molecule. In both mechanisms, the active catalyst is the classical Compound I species, [(Por+•)(Scys)FeIVO]. Since the C-C cleavage plays a crucial role in the natural biosynthesis of many complex organic molecules in the biological kingdom, the present study provides a testable mechanism of this enigmatic reaction. © 2022 American Chemical Society. All rights reserved.

World University root node

Chemistry

ACS Catalysis

Mechanistic Conundrum of C–C Bond Cleavage by CYP51

Cytochrome P450GcoAis an enzyme that catalyzes the guaiacol unit of lignin during the lignin breakdown via an aryl-O-demethylation reaction. This reaction is intriguing and is of commercial importance for its potential applications in the production of biofuel and plastic from biomass feedstock. Recently, the F169A mutation in P450GcoAelicits a promiscuous activity for syringol while maintaining the native activity for guaiacol. Using comprehensive MD simulations and hybrid QM/MM calculations, we address, herein, the origin of promiscuity in P450GcoAand its relevance to the specific activity toward lignin-derived substrates. Our study shows a crucial role of an aromatic dyad of F169 and F395 by regulating the water access to the catalytic center. The F169A mutation opens a water aqueduct and hence increases the native activity for G-lignin. We show that syringol binds very tightly to the WT enzyme, which blocks the conformational rearrangement needed for the second step of O-demethylation. The F169A creates an extra room favoring the conformational rearrangement in the 3-methoxycatechol (3MC) and second dose of the dioxygen insertion. Therefore, using MD simulations and complemented by thorough QM/MM calculations, our study shows how a single-site mutation rearchitects active site engineering for promiscuous syringol activity. © 2022 American Chemical Society. All rights reserved.

ACS Omega

Single-Site Mutation Induces Water-Mediated Promiscuity in Lignin Breaking Cytochrome P450GcoA

Five new mononuclear lanthanide complexes, [LnL2][Et3NH]·THF/H2O (Ln = Nd, Tb, Dy) (H2LCl= 2-bis(2-hydroxy-3,5-dichloro benzyl)aminomethyl]pyridine), Ln = Nd (1), Tb (2), and Dy (3), and (H2LBr= 2-bis(2-hydroxy-3,5-dibromo benzyl)aminomethyl]pyridine), Ln = Nd (4, H2O) and Tb (5), were synthesized and structurally characterized by single-crystal X-ray diffraction analyses. Being isostructural in all the five cases, the metal center is octa-coordinated with a triangular dodecahedron (D2dsymmetry) geometry, and it is independent of the halogen substitution (Cl/Br). This close similarity is due to the composite interplay of hydrogen/halogen bond interactions that control the overall crystal packing, yet notable differences in association patterns among the individual ones arise from the subtle stereo-electronic requirement of individual molecules in the three-dimensional (3D) architecture. Hirshfeld surface and density functional theory (DFT) calculations clearly vouch for the importance of the hydrogen bond and halogen bond interactions observed in the structure. Detailed magnetic measurements using direct-current and alternating-current susceptibility measurements show slow magnetic relaxation in 3, a characteristic feature of the single-molecule magnets (SMMs), which is not shown by 1 and 2. Steady-state and time-resolved photoluminescence of Tb(III) complexes shows a strong ligand-to-metal energy transfer that can be modulated by changing the substitution on phenolic ligands. The results from these analyses indicate that it may be advantageous to consider the subtle role of hydrogen bond (HB)/halogen bond (XB) intermolecular interactions judiciously for the design of SMMs and luminescent materials based on halogen-substituted ligands. © 2022 American Chemical Society. All rights reserved.

Inorganic Chemistry

Halogen Bond Mediated Self-Assembly of Mononuclear Lanthanide Complexes: Perception of Supramolecular Interactions, Slow Magnetic Relaxation, and Photoluminescence Properties

Targeted imaging and therapy for triple-negative breast cancer (TNBC) in the perioperative period are imperative for better disease management and improved life expectancy. Still, they are not available in clinical settings, and only a few nanoparticle-based theranostic agents potentially offer these capabilities. Herein, we develop an innovative class of biocompatible triple-modality nanoprobes (TMNPs) that offer optical imaging using optoacoustic, fluorescence, and surface-enhanced Raman scattering (SERS), as well as photothermal therapy (PTT) with near-infrared (NIR) light. The TMNPs are fabricated by immobilizing positively charged NIR fluorophores on negatively charged DNA-coated gold nanorods (AuNRs), followed by silica encapsulation. The DNA-based design allows the screening of commercially available positively charged NIR fluorophores for the optimum fluorescence emission and SERS. After design optimization, we functionalize TMNPs with folate groups to target folate receptor1 (FOLR1)-overexpressing TNBC in vitro and in vivo. Our results reveal that TMNPs preferentially accumulate in FOLR1 positive tumors in TNBC patient-derived xenograft mouse models and show excellent imaging capabilities with all three imaging modalities. Selective exposure of the tumor to a NIR laser shows efficient thermal tissue ablation without causing systemic toxicity. Collectively, TMNPs hold great promise for real-time multiplexed imaging of cancer biomarkers and therapeutic capability. © 2022 American Chemical Society. All rights reserved.

ACS Applied Nano Materials

DNA-Functionalized Gold Nanorods for Perioperative Optical Imaging and Photothermal Therapy of Triple-Negative Breast Cancer

Inspired by many biological systems such as lotus leaves, insect wings and rose petals, great attention has been devoted to the study and fabrication of artificial superhydrophobic surfaces with multiple functionalities. In the present study, a simple and ecological synthesis route has been employed for large scale fabrication of self-assembled, sustainable nanostructures on unprocessed and micro imprinted aluminum surfaces named ‘Nano’ and ‘Hierarchy’. The processed samples show extreme wettability ranging from superhydrophilicity to superhydrophobicity depending on post-processing conditions. The densely packed ellipsoidal nanostructures exhibited superhydrophobicity with excellent water, bacterial and dust repellency when modified by low surface energy material 1H,1H,2H,2H-perfluorooctyltriethoxysilane (FOTES), characterized by a static contact angle of 163 ± 1° and contact angle hysteresis (CAH) ~3°. These coated surfaces show significant corrosion resistance with current density of 6 nA/cm2 which is 40 times lower than unprocessed counterpart and retain chemical stability after prolonged immersion in corrosive media. These surfaces show excellent self-cleaning ability with significantly low water consumption (&lt; 0.1 µl/mm2-mg) and prevent biofouling which ensures its applicability in biological environment and marine components. The nanostructured superhydrophilic aluminum shows maximum antibacterial activity due to disruption of cell membrane. This work can offer a simple strategy to large scale fabrication of multifunctional biomimetic metallic surfaces. © 2021

Physics

Mechanical Engineering

(SoE) School of Engineering

Colloids and Surfaces B: Biointerfaces

Bioinspired micro/nano structured aluminum with multifaceted applications

Herein we have discussed projects related to blue LED mediated C-H and N-H insertion reaction in indoles and related heterocycles with aryl diazoesters and iodonium ylides as sources of carbenes. Blue LED effectively facilitates these conversions and was optimized from the option of numerous other LED lights. No metal catalysts were required. The reactions provide formation of differently alkylated indoles, pyrroles and furans. Control experiments and DFT calculation were used to understand the mechanism of reactions. As an application compounds bearing azepino[4, 5-b]indole and spiropiperidino indole building blocks were synthesized from the alkylated products. © 2022 Swiss Chemical Society.

Fulltext

Chimia

Blue LED Mediated C-H and N-H Insertion of Indoles into Aryldiazoesters and Iodonium Ylides

We re-examine Hawking radiation for a nonrotating (2 + 1)-dimensional Bañados–Teitelboim–Zanelli (BTZ) black hole and evaluate the transmission probability of tunneling through the barrier of the event horizon employing the standard method of WKB approximation. Our results are presented for both uncharged and charged cases. We also explore the associated thermodynamics in terms of Hawking temperature and provide estimates of black hole parameters like the surface gravity and entropy. © 2022 World Scientific Publishing Company

International Journal of Modern Physics A

Tunneling of hawking radiation for BTZ black hole revisited

For phase change materials (PCMs) to become a viable universal memory candidate and obsolete von-Neumann architecture, materials with very high crystallization speed are needed. Moreover, introducing prestructural ordering inside the material is also being touted as one of the promising techniques to reach the speed of SRAM or further down. In this aspect, GaSb alloys are showing much promise for not only having very low crystallization times by themselves, but also showing an enormous drop in the programming time while crystallizing the reamorphized material. Here, we demonstrate how the threshold switching behavior changes for the fully amorphous film in contrast with the disordered film with nucleation sites using conductive-atomic force microscopy. It is found that the required power and programming current for memory switching with nominally stoichiometric GaSb (44:56) are 23 nW and 6.2 nA, respectively. As expected for a nucleation-oriented PCM, the deposited thin film has two voltage thresholds during the local programming process, one for conduction and another for memory switching. However, when the nucleation sites are introduced inside the disordered film, the conduction and memory switching become simultaneous. This is also found to reduce the threshold power and SET current by 93% (1.5 nW) and 91% (550 pA), respectively. Furthermore, we also reveal the origin behind this behavioral change observed between these two thin films by using high-resolution transmission electron microscopy and synchrotron radiation photoelectron spectroscopy. © 2022 American Chemical Society.

Journal of Physical Chemistry C

Revealing the Impact of Prestructural Ordering in GaSb Thin Films

Antimicrobial coatings on metallic surfaces are rapidly emerging to combat bacterial pathogens. The excess use of conventional antibiotics increases the number of resistant strains at an alarming rate, which in turn leads to detrimental implications in the healthcare sector. Hence, it is of great importance in developing a new class of material with inherent bactericidal activity and good biocompatibility. In the present study, we have modified the aluminium surfaces by a coating of graphene oxide (GO) due to its excellent physicochemical properties, water dispersity and low cytotoxicity. Coatings were developed through facile and enviornment-friendly transfer method. The antimicrobial properties of GO coated aluminium are investigated against Gram-negative strain E. coli through agar plate counting and ‘Live/Dead’ fluorescence staining. Further, to shed light into the mechanism of antibacterial activity of GO at the molecular level, we have performed X-ray reflectivity (XRR) study considering a phospholipid multilayer as a model system to mimic bacteria cell membrane. Results show a significant bactericidal activity of the GO coatings compared to uncoated aluminium with lower concentration showing slightly better antibacterial property due to higher roughness. The obtained results may pave the way for engineering graphene-based antimicrobial coatings on a material surface using an easy, environment-friendly, cost-effective and straight forward processing route. © 2022 The Author(s)

Environmental Technology and Innovation

Graphene oxide coated aluminium as an efficient antibacterial surface

When a connected component of the set of singular points of the maxface X consists of only generalized cone-like singular point, we construct a sequence of maxfaces Xn, with an increasing number of swallowtails, converging to the maxface X. We include the general discussion toward this. © 2022, Indian Academy of Sciences.