Microwave-assisted rapid and efficient synthesis of chromene-fused pyrrole derivatives through multicomponent reaction and evaluation of antibacterial activity with molecular docking investigation

The current study aimed to identify a new strategy of FeCl₃ catalyzed multicomponent synthesis of substituted 2H-chromene–fused pyrrole derivatives. A series of chromene-based pyrrole prepared by employing an array of 3-nitro-2H-chromenes, aniline, and acetylacetone in toluene under microwave irradiation. Using FeCl₃ as a prompt catalyst and microwave irradiation to synthesize 2H-chromene–fused pyrrole motifs significantly reduces the reaction time and facilitates to high yields (83%-95%). Structure of all synthesized compounds analyzed by spectroscopic analysis. One-pot reaction, short reaction period, and simple experimental procedure are the fascinating properties associated with this protocol. The in vitro antibacterial activity of the entire series was assessed against Staphylococcus aureus and Escherichia coli. Out of all the compounds, 15b and 15h revealed most excellent potency against both the bacterial strains relative to the reference gentamicin. Docking study was employed to determine the possible binding orientation of DNA gyrase with the active sites of chromene-fused pyrrole analog. The docking results show that compounds 15b and 15h have higher binding affinity with energy −8.00 and −8.80 kcal/mol. These results illuminate the mode of binding progression and provide an esteemed pathway for the design and the structural modification of chromene-fused pyrroles as a newly advanced class of antibacterial agent.     

Catalytic Approaches for the Direct Heterofunctionalization of Aliphatic Carboxylic Acids and Their Equivalents with Group 16 Elements

In contrast to traditional multistep synthesis, modern organic synthesis extensively depends on the direct functionalization of unactivated C?H bonds for the construction of various C?C and C‐heteroatom bonds in atom‐ and step‐economic manner. Common aliphatic substrates, e. g. carboxylic acids and their synthetic equivalents, are regiospecifically functionalized based on either a directed approach, in which the polar directing group assists to functionalize a specific C?H bond positioned at β‐ and γ‐carbon centers, or a non‐directed approach typically leading to α‐functionalization. While numerous reviews on catalytic C?H functionalization have appeared, a concise review on the direct C(sp³)?H heterofunctionalization of carboxylic acid synthons with Group 16 elements has been awaited. The recent advances on the direct oxy‐functionalization and chalcogenation of aliphatic carboxylic acid synthons enabled by transition metal, organo‐ and photocatalysts are described herein.     

A Tale of Biphenyl and Terphenyl Substituents for Structurally Diverse Ketiminato Magnesium,Calcium and Germanium Complexes

In this paper, we have used two N,O‐ketiminato ligands ( L1 and L2 ) with biphenyl and terphenyl substituent on the nitrogen atom. Deprotonation of L1 with KN(SiMe₃)₂ and subsequent reaction with MgI₂ led to a homoleptic dinuclear magnesium complex ( 1 ) with a Mg₂O₂ four‐membered ring. Deprotonation with nBuLi and subsequent reaction with MgI₂ afforded a unusual dinuclear magnesium complex ( 2 ) with a Mg₂O₂ ring. Extension of the ligand for calcium resulted in a trinuclear calcium complex ( 3 ) with six four‐membered Ca₂O₂ rings. We could not isolate any chelating complex when L2 was used as a ligand, and only oxygen bound magnesium ( 4 ) and calcium ( 5 ) adducts were isolated. DFT studies were performed to understand this dissimilar behavior. More diverse results were obtained when lithiated L1 and L2 were treated with germanium dichloride. We were able to stabilize a monomeric germylene monochloride ( 7 ) with L1 . However, with L2 , an unusual ligand scrambling, and a C?C coupling take place, leading to the formation of a secondary carbocation with GeCl₃‐ as a counter‐anion ( 8 ). Besides, a germanium dichloride adduct ( 9 ) bound to the oxygen center of the ligand was obtained as the minor product.     

A water-soluble polythiophene-Au nanoparticle composite for pH sensing

In this paper, we report the development of a reversible pH sensor in aqueous medium based on the fluorescence properties of a polythiophene-gold nanoparticle (Au NP) composite. The composite was synthesized in water by simultaneous reduction of HAuCl(4) to Au NPs and polymerization of thiophene in the presence of no additional reagents. It was stable for weeks and had characteristic emissions, which changed in the pH range of 3.0 to 6.0, thus providing a mean for probing the pH of an aqueous solution. Measurement of the pH could be performed over several cycles of titrations, pointing to the robustness of the materials for such sensing applications. The mass spectra of the composite at two extreme pH values were identical, indicating that the primary structure of the polymer was not affected due to changes in pH of the medium. Transmission electron microscopic (TEM) measurements indicated the presence of small sized Au NPs with the polymer in the milieu. The composite could be titrated by acid (or base) and considering the acid-base equilibria at different pHs, we have been able to calculate the pK(eq) of the composite, which was further used in calculating the pH of an aqueous solution from the emission spectrum of the composite. Our approach took advantage of redox chemistry in synthesizing the water-soluble composite and the optical behavior of a conjugated polymer in developing an important pH sensor, which may form the basis of further development of versatile pH or other sensors by suitably modifying the backbone of the monomer.     

Polymer-mediated chain-like self-assembly of functionalized gold nanoparticles

We report an easy solution phase template-based method to assemble mercaptoundecanoic acid-functionalized gold nanoparticles (MUA-GNPs) along poly(ethylene oxide) (PEO) chains. Transmission electron microscopy (TEM) images show one-dimensional and two-dimensional chain-like sequences of GNPs resembling PEO chains. The progress of the assembly was monitored by the evaluation of surface plasmon resonance band of MUA-GNPs with time by UV-vis spectroscopy. The assembly process is a result of hydrogen bonding interaction between the ethereal oxygen of PEO and carboxylic acid group of MUA attached to GNPs surface, which was confirmed through FTIR spectroscopy. The interaction between PEO and MUA-GNPs was further confirmed by thermal analysis using differential scanning calorimetry.     

New [LNiII2]+ complexes incorporating 2-formyl or 2,6-diformyl-4-methyl phenol as inhibitors of the hydrolysis of the ligand L3-: Ni...Ni ferromagnetic coupling and S=2 ground states

Reaction of the dinucleating ligand H3L (2-(2'-hydroxyphenyl)-1,3-bis[4-(2-hydroxyphenyl)-3-azabut-3-enyl]-1,3-imidazolidine) with Ni(NO3)(2).6H2O produces the dimer of monomers [Ni(HL1)]2(NO3)(2).4H2O (1.4H2O) following the hydrolysis of H3L. If the reaction occurs in the presence of 2-formylphenol (Hfp) or 2,6-diformyl-4-methylphenol (Hdfp), this hydrolysis is prevented by incorporation of these co-ligands into the structure and stabilization of the new complexes [Ni2L(fp)(H2O)].3H2O (2.3H2O) and [Ni2L(dfp)].4.5H2O (3.4.5H2O), respectively. Complexes 2 and 3 may be considered to be structural models of the active site of urease, where coordination of the carbonyl ligand mimics binding of urea. In complex 2, coordination of terminal water reproduces the binding of this substrate of the enzyme to the active site. In both dinuclear complexes, the NiII ions are coupled ferromagnetically to yield S=2 ground states, whereas complex 1 exhibits weak intradimer antiferromagnetic exchange through hydrogen bonds. The magnetic data can be modeled by using the Van Vleck equation, incorporating intermolecular interactions, or by diagonalization of a spin Hamiltonian that includes single-ion anisotropy.     

Half-metallic behavior of Co2YZ (Y = V,Cr; Z = Al,Ga) under pressure: a DFT study

The structural, electronic and magnetic properties of Co-based Heusler compounds Co₂YZ (Y = V, Cr; Z = Al, Ga) under pressure are studied using first principles density functional theory. The calculations are performed within generalized gradient approximation. The total magnetic moment decreases slightly on compression. Under application of external pressure, the valence band and conduction band are shifted downward which leads to the modification of electronic structure. There exists an indirect band gap along Г–X for all the alloys studied. Co₂CrAl shows half-metallic nature up to 85 GPa. After this pressure transition from true half-metallic behavior to nearly half-metallic behavior is observed and at 90 GPa it shows metallic behavior. Co₂CrGa shows nearly half-metallic behavior at ambient pressure, but true half-metallic behavior is observed as pressure is increased to 100 GPa. For Co₂VGa, true half-metallic to nearly half-metallic transition is observed at 40 GPa and around 100 GPa, Co₂VGa shows metallic behavior. For Co₂VAl, true half-metallic behavior is not observed at ambient as well as higher pressures. The half metal-to-metal transition in Co₂VAl and Co₂CrAl is accompanied by quenching of magnetic moment.     

Primordial Black Holes Evolution in f(T) Gravity

We consider the effect of accretion of radiation, matter and dark energy in the early universe on primordial black holes (PBH) in f(T) gravity. Due to the Hawking radiation, mass of the primordial black hole decreases. We show that for the phantom accretion inclusion with the Hawking evaporation, the mass of the PBH decreases faster whereas for the accretion of radiation, matter and quintessence together with Hawking evaporation, the mass increases in f(T) gravity.     

Constraining the Parameters of New Variable Modified Chaplygin Gas Model

Assuming the flat FRW universe in Einstein’s gravity filled with New Variable Modified Chaplygin gas (NVMCG) dark energy and dark matter having negligible pressure. In this research work we analyze the viability on the basis of recent observation. Hubble parameter H is expressed in terms of the observable parameters H ₀, $\varOmega_{m}^{0}$ and the model parameters A ₀, B ₀, C ₀, m, n, α and the red shift parameter z. Here we find a best fitted parameter range of A ₀, B ₀ keeping 0≤α≤1 and using Stern data set (12 points) by minimizing the χ ² test at 66 %, 90 % and 99 % confidence levels. Next we do the joint analysis with BAO and CMB observations. Again evaluating the distance modulus μ(z) vs redshift (z) curve obtained in the model NVMCG with dark matter with the best fitted value of the parameters and comparing with that derived from the Union2 compilation data.     

A synthesis technique of single square loop frequency selective surface at terahertz frequency

In this paper, we have explored and extended the use of frequency selective surface towards the terahertz regime of the electromagnetic spectrum where interesting applications such as imaging, sensing and communication exist. We have discussed a synthesis technique to design the single square loop frequency selective surface (SSLFSS) at 150 and 300 GHz which have found suitable application in the fast analysis and fabrication of the frequency selective surface. Moreover, the analytical results have been supported by the CST Microwave Studio and Ansoft HFSS commercial simulators. We have discussed the angular insensitivity of the SSLFSS at 150 GHz as well as 300 GHz. However, the specific problems arise at terahertz frequencies as compared to the radio and microwave frequencies are the ohmic losses. The proposed analysis has been extended from 100 GHz to 350 GHz to discuss the ohmic and dielectric losses. We have also discussed the other important issues which are very much significant in the terahertz regime of the spectrum such as skin depth and surface roughness.