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Shiv Nadar University

(SoNS) School of Natural Sciences

The study uses MD simulations and QM/MM calculations to address the preparatory half of the catalytic cycle for two cytochrome P450 (CYP450) enzymes, CYP450CAM and CYP450BM3. We focus on two unexplored/"gray"events: (a) the O2 entrance and binding to form the oxyferrous species as a function of the O2 concentration/pressure and (b) the protonation steps that eventually lead to the formation of the ultimate active species, compound I (cf. 7). Two fundamental and paradigm-shifting findings emerge: (a) the O2 concentration/pressure required for O2 binding must be neither high nor low. The binding is ushered by substrate choreography, which is guided by the moderate O2 pressure and strategic protein residues (Arg112 and Phe87) that block the substrate approach to the heme, thus enabling O2 accumulation near iron. (b) The formation of water channels, which elicit that the protonation steps are different for 5 → 6 and 6 → 7. The process 5 → 6, generating the ferric hydroperoxide, occurs via the channels that are formed by breakage of the salt bridges holding the propionate side chains of the porphyrin, while the formation of compound I, 6 → 7, transpires via the traditional acid-alcohol pairs (Asp251/Thr252 in CAM; Glu267/Thr268 in BM3). The location of acidic ammonium groups (Lys69 in CYP450BM3 and Arg299 in CYP450CAM) near the propionate side chains is generally conserved in the CYP450 family. Therefore, our study highlights the evolutionary need for at least two alternative water channels to tune the P450 nanomachine, so it can complete the two steps of the protonation and form ultimately compound I. Copyright © 2020 American Chemical Society.

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Chemistry

ACS Catalysis

A Paradigm Shift in the Catalytic Cycle of P450: The Preparatory Choreography during O2Binding and Origins of the Necessity for Two Protonation Pathways

Flexible and low-power consuming integrated circuits are some of the basic requirements for smart wearable devices. High mobility solution-processed organic field-effect transistors (OFETs) have the potential to make a big impact in printed electronic circuits, but their overall performance is currently limited by unusually high threshold voltages (Vth). Herein, systematic optimization of donor–acceptor conjugated polymer, based on dithienothiophene (DTT) and thiophene-flanked diketopyrrolopyrrole (DPP), namely, PDPPT–DTT, OFETs by application of self-assembled monolayers (SAMs) at the semiconductor–dielectric, and semiconductor–metal interfaces is reported. The results clearly exhibit that simultaneous application of octyltrichlorosilane (OTS) as semiconductor–dielectric interface modifying layer and pentafluorobenzene thiol (PFBT) as semiconductor–metal interface modifying layer results in significantly lower Vth and subthreshold slope values from −14.07 V and 13.26 (V Dec−1) to +1.06 V and 7.11 (V Dec−1), respectively. This tailored approach is also beneficial in enhancing hole mobility values by an order of magnitude from 0.01 to 0.5 cm2 V−1 s−1 along with the possibility of switching from hole accumulation mode (Vth = −3.75 V) to depletion mode (Vth = +1.06 V) through device engineering. Simultaneous interface engineering reveals OFET electronic properties can be fine-tuned for robust circuits and low power electronic applications. © 2020 Wiley-VCH GmbH

Physics

Physica Status Solidi (A) Applications and Materials Science

Reduced Threshold Voltages and Enhanced Mobilities in Diketopyrrolopyrrole–Dithienothiophene Polymer-Based Organic Transistor by Interface Engineering

Lithium-sulfur (Li–S) batteries are among the most promising candidates for the next-generation rechargeable batteries due to their high energy density, cost-effectiveness, environmental friendliness and being on the verge of commercialization. However, considering the cathode part, low conductivity of sulfur, large volume expansion, dissolution of polysulfides in the electrolyte and their unfavorable shuttle behavior lead to low cell capacity and poor cycle life. More importantly, the high flammability of sulfur causes safety concerns that might hinder the large-scale application of lithium-sulfur batteries in electric vehicles, especially in tropical countries. Herein, we report a covalently linked sulfur (~83\% w/w) flame retarding sustainable copolymer as a suitable and safe cathode material for the practical application of Li–S batteries in tropical region. A remarkable intrinsic flame-retardant property with appreciable specific capacity and excellent capacity retention provide an alternative strategy for designing cathode materials for safe and sustainable Li–S batteries. © 2020

Energy Storage Materials

Halogen-free flame-retardant sulfur copolymers with stable Li–S battery performance

Graphene quantum dots (GQDs) possess excellent optical and electrical properties that can be used in a wide variety of application. Synthesis of hybrid nanoparticles with GQDs have been known to improve the properties further. Therefore, in this method, graphene quantum dots –gold (GQD-Au) hybrid nanoparticles were synthesized using GQDs which reduces HAuCl4.3H2O to Au nanoparticles on its surface at room temperature. The GQDs with self-passivated layers were synthesized by microwave assisted hydrothermal method using glucose as a single precursor. The synthesis process does not involve the use of harmful chemicals. The whole synthesis process of GQD and GQD-Au hybrid nanoparticles takes only five minutes. The synthesized GQDs have been extracted using citrate in order to increase the stability of the hybrid nanoparticles for up to four weeks. The size of the synthesized GQD-Au hybrid nanoparticles is in the range of 5–100 nm and were found to be luminescent under UV-A illumination. The merit of the following method over other synthesis techniques include its rapidity, ease of preparation, and no requirement of elaborate synthesis procedures and/or harmful chemicals. The GQD-Au hybrid nanoparticles can be used in several applications such as luminescent coatings for glass and windowpanes for automobiles, etc. The reducing property of GQDs can further be utilized for the reduction of various metal salts (AgNO3) and organic dyes (methylene blue and methyl orange). It presents a method/protocol-development of the luminescent GQD-Au hybrid particles of size ~ 5–100 nm. The GQD-Au hybrid particles find potential applications in luminescent coating applications. © 2020

Fulltext

MethodsX

Engineering of luminescent graphene quantum dot-gold (GQD-Au) hybrid nanoparticles for functional applications

A mild strategy for consecutive diazenylation and amination of indole moieties has been demonstrated. The functionalization occurs at C3 and C2 carbon atoms, respectively, at the indole scaffold in the presence of catalytic iodine and air at 40 °C in the 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) solvent. It is noteworthy that the aromatic amines are generated in situ by the reaction of aryl hydrazine with iodine. In general, bright red products are obtained in moderate to good yield. Control reactions are conducted to establish the reaction mechanism. Copyright © 2020 American Chemical Society.

Journal of Organic Chemistry

Iodine-Catalyzed Aerobic Diazenylation-Amination of Indole Derivatives

Arylated building blocks or heterocycles are key to myriad applications, including pharmaceutical drug discovery, materials sciences, and many more. Herein, we have reported a mild and efficient strategy for generation of aryl radicals by reacting appropriate aryl hydrazines with catalytic iodine in open air. The aryl radicals were quenched by diversely substituted 1,4-napthoquinones present in the reaction mixture to afford diversely substituted 2,3-napthoquinones in moderate to excellent yield. Control experiments provided insights into the putative reaction mechanism. Copyright © 2020 American Chemical Society.

ACS Omega

Generation of Aryl Radicals from Aryl Hydrazines via Catalytic Iodine in Air: Arylation of Substituted 1,4-Naphthoquinones

New families of non-parity-time-symmetric complex potentials with all-real spectra are derived by the supersymmetry method and the pseudo-Hermiticity method. With the supersymmetry method, we find families of non-parity-time-symmetric complex partner potentials, which share the same spectrum as base potentials with known real spectra, such as the (complex) Wadati potentials. Different from previous supersymmetry derivations of potentials with real spectra, our derivation does not utilize discrete eigenmodes of base potentials. As a result, our partner potentials feature explicit analytical expressions, which contain free functions. With the pseudo-Hermiticity method, we derive a new class of non-parity-time-symmetric complex potentials with free functions and constants, whose eigenvalues appear as conjugate pairs. This eigenvalue symmetry forces the spectrum to be all-real for a wide range of choices of these functions and constants in the potential. Tuning these free functions and constants, phase transition can also be induced, where conjugate pairs of complex eigenvalues emerge in the spectrum. © 2020 Author(s).

Journal of Mathematical Physics

New families of non-parity-time-symmetric complex potentials with all-real spectra

Quadratic programming problems involving distance matrix (D) that arises in trees are considered in the literature by Dankelmann (Discrete Math 312:12–20, 2012), Bapat and Neogy (Ann Oper Res 243:365–373, 2016). In this paper, we consider the question of solving the quadratic programming problem of finding maximum of xTRx subject to x being a nonnegative vector with sum 1 and show that for the class of simple graphs with resistance distance matrix (R) which are not necessarily a tree, this problem can be reformulated as a strictly convex quadratic programming problem. An application to symmetric bimatrix game is also presented. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.

Mathematics

Annals of Operations Research

On solving a non-convex quadratic programming problem involving resistance distances in graphs

Antibiotic drug resistance is a global crisis today. The deleterious impact of this crisis is acting relatively in higher degrees in poor nations compared to developed countries in the world. Low economy and irrational perspective on medical practice are accelerating the development of drug resistance, leading the population in more economically challenged situations. This article discusses current situations, expresses opinions and views on the self-reinforcement process in the emergence and development of drug resistance. © Indian Academy of Sciences.

Current Science

Emergence and burden of antibiotic drug resistance: An endogenous cycle

Public perceptions and sentiments play a crucial role in the success of vaccine uptake in the community. While vaccines have proven to be the best preventive method to combat the flu, the attitude and knowledge about vaccines are a major hindrance to higher uptake in most of the countries. The yearly coverage, especially in the vulnerable groups in the population, often remains below the herd immunity level despite the Flu Awareness Campaign organized by WHO every year worldwide. This brings immense challenges to the nation’s public health protection agency for strategic decision-making in controlling the flu outbreak every year. To understand the impact of public perceptions and vaccination decisions while designing optimal immunization policy, we model the individual decision-making as a two-strategy pairwise contest game, where pay-off is considered as a function of public health effort for the campaign. We use Pontryagin’s maximum principle to identify the best possible strategy for public health to implement vaccination and reduce infection at a minimum cost. Our optimal analysis shows that the cost of public health initiatives is qualitatively and quantitatively different under different public perceptions and attitudes towards vaccinations. When individual risk perception evolves with vaccine uptake or disease induced death, our model demonstrates a feed-forward mechanism in the dynamics of vaccination and exhibits an increase in vaccine uptake. Using numerical simulation, we also observe that the optimal cost can be minimized by putting the effort in the beginning and later part of the outbreak rather than during the peak. It confers that public health efforts towards disseminating disease severity or actual vaccination risk might accelerate the vaccination coverage and mitigate the infection faster. © 2020, Society for Mathematical Biology.