Green Synthesis and Characterization of Hybrid Collagen–Cellulose–Albumin Biofibers from Skin Waste

Collagen (C) and cellulose are prominent biopolymers from the animal and plant kingdom and widely used in bioengineering. Albumin, on the other hand, is the most abundant plasma protein present in mammalian blood. In this work, collagen extracted from animal skin waste was blended with hydroxyethyl cellulose (HEC) and bovine serum albumin (A) and wet-spun to form hybrid biodegradable C/HEC/A fibers. They were further cross-linked with glutaraldehyde vapors and analyzed. X-ray diffraction and infra-red spectroscopic studies of the hybrid fibers display peaks corresponding to collagen, cellulose, and albumin. Incorporation of cellulose into the biopolymeric matrix leads to a reasonable improvement in mechanical, swelling, and thermal properties of hybrid fibers. Addition of albumin improves the regularity of fiber surface without altering the porosity as observed under a microscope. Hence, the formed hybrid biofibers can be potentially used as a suture material as well as for different biomedical applications due to their improved properties.     

An Yb(OTf)3‐catalyzed,convergent synthesis of new pyranyl‐ and chromenyl‐substituted quinolines through an eco‐friendly approach

A one‐pot, multicomponent, convergent microwave synthesis of some new pyranyl‐ and chromenyl‐substituted quinolines has been reported. Twenty compounds were prepared by the reaction of 2‐methoxy‐3‐formyl quinoline ( 1a‐d ), malononitrile ( 2 ), and kojic acid ( 4a‐d )/1,3‐cyclohexadione or dimedone ( 6a ‐ h )/α‐ or β‐naphthol ( 8a ‐ d , 8e ‐ h ). The structures were confirmed by infrared (IR), ¹H nuclear magnetic resonance (NMR), ¹³C NMR, mass, and single‐crystal X‐ray analyses. On comparison with the use of conventional Lewis acid catalysts and various metal triflates under microwave conditions, the latter contributed to good yields, in specific use of the recyclable Yb(OTf)₃ catalyst attributed to high yields of the desired product. The protocol reported herein is solvent free, cost effective, and eco‐friendly.     

Synthesis,Structure, and Highly Efficient Copper‐Catalyzed Aziridination with a Tetraaza‐Bispidine Ligand

The distorted trigonal‐bipyramidal Cu^II complex [Cu(L¹)(NCCH₃)]²⁺ of the novel tetradentate bispidine‐derived ligand L¹ with four tertiary amine donors (L¹=1,5‐diphenyl‐3‐methyl‐7‐(1,4,6‐trimethyl‐1,4‐diazacycloheptane‐6‐yl)diazabicyclo[3.3.1]nonane‐9‐one) is a very efficient catalyst for the aziridination of olefins in the presence of a nitrene source. In agreement with the experimental data (in situ spectroscopy, product distribution, and its dependence on the geometry of the substrate and of the nitrene source), a theoretical analysis based on DFT calculations indicates that the active catalyst has the Cu center in its +II oxidation state, that electron transfer is not involved, and that the conversion of the olefin to an aziridine is a stepwise process involving a radical intermediate. The striking change of efficiency and reaction mechanism between classical copper–bispidine complexes and the novel L¹‐based catalyst is primarily attributed to the structural variation, enforced by the ligand architecture.     

The mechanism of the (bispidine)copper(II)-catalyzed aziridination of styrene: a combined experimental and theoretical study

Experimental and DFT-based computational results on the aziridination mechanism and the catalytic activity of (bispidine)copper(I) and -copper(II) complexes are reported and discussed (bispidine=tetra- or pentadentate 3,7-diazabicyclo[3.1.1]nonane derivative with two or three aromatic N donors in addition to the two tertiary amines). There is a correlation between the redox potential of the copper(II/I) couple and the activity of the catalyst. The most active catalyst studied, which has the most positive redox potential among all (bispidine)copper(II) complexes, performs 180 turnovers in 30 min. A detailed hybrid density functional theory (DFT) study provides insight into the structure, spin state, and stability of reactive intermediates and transition states, the oxidation state of the copper center, and the denticity of the nitrene source. Among the possible pathways for the formation of the aziridine product, the stepwise formation of the two N-C bonds is shown to be preferred, which also follows from experimental results. Although the triplet state of the catalytically active copper nitrene is lowest in energy, the two possible spin states of the radical intermediate are practically degenerate, and there is a spin crossover at this stage because the triplet energy barrier to the singlet product is exceedingly high.     

Ruthenium(II)–arene complexes of diimines: Effect of diimine intercalation and hydrophobicity on DNA and protein binding and cytotoxicity

A series of half‐sandwich Ru(II)–arene complexes [Ru(η⁶‐benzene)(diimine)Cl](PF₆) ( 1 – 4 ), where diimine is 1,10‐phenanthroline ( 1 ), 5,6‐dimethyl‐1,10‐phenanthroline ( 2 ), dipyrido[3,2‐a:2′,3′‐c]phenazine ( 3 ) or 11,12‐dimethyldipyrido[3,2‐a:2′,3′‐c]phenazine ( 4 ), have been isolated and characterized using analytical and spectral methods. Complex 2 possesses a familiar pseudo‐octahedral ‘piano‐stool’ structure. The intrinsic DNA binding affinity of the complexes depends upon the diimine ligand: 3 (dppz) > 4 (11,12‐dmdppz) > 2 (5,6‐dmp) > 1 (phen). The π‐stacking interaction of extended planar ring of coordinated dppz ( 3 ) in between the DNA base pairs is more intimate than that of phen ( 1 ), and the incorporation of methyl groups on the dppz ring ( 4 ) discourages the stacking interaction leading to a lower DNA binding affinity for 4 than 3 . Docking studies show that all the complexes bind in the major groove of DNA. Interestingly, 3 shows an ability to convert supercoiled DNA into nicked circular DNA even at 20 μM concentration beyond which complete oxidative DNA degradation is observed. The protein binding affinity of the complexes decreases in the order 4 > 3 > 2 > 1 , and the higher protein binding affinity of 4 illustrates the strong involvement of methyl groups on dppz ring in hydrophobic interaction with protein. Also, 4 cleaves protein more efficiently than the other complexes in the presence of H₂O₂. It is notable that 2 , 3 and 4 display cytotoxicity against human cervical cancer cell lines (SiHa) with potency higher than the currently used drug cisplatin. Acridine orange/ethidium bromide staining studies reveal that 3 induces apoptosis in cancer cells much more efficiently than 4 .     

Structure, bonding, and catecholase mechanism of copper bispidine complexes

Oxygen activation by copper(I) complexes with tetra- or pentadentate mono- or dinucleating bispidine ligands is known to lead to unusually stable end-on-[{(bispidine)Cu}(2)(O(2))](2+) complexes (bispidines are methyl-2,4-bis(2-pyridin-yl)-3,7-diazabicyclo-[3.3.1]-nonane-9-diol-1,5-dicarboxylates); catecholase activity of these dinuclear Cu(II/I) systems has been demonstrated experimentally, and the mechanism has been thoroughly analyzed. The present density functional theory (DFT) based study provides an analysis of the electronic structure and catalytic activity of [{(bispidine)Cu}(2)(O(2))](2+). As a result of the unique square pyramidal coordination geometry, the d(x(2)-y(2)) ground state leads to an unusual σ/π bonding pattern, responsible for the stability of the peroxo complex and the observed catecholase activity with a unique mechanistic pathway. The oxidation of catechol to ortho-quinone (one molecule per catalytic cycle and concomitant formation of one equivalent of H(2)O(2)) is shown to occur via an associative, stepwise pathway. The unusual stability of the end-on-peroxo-dicopper(II) complex and isomerization to copper(II) complexes with chelating catecholate ligands, which inhibit the catalytic cycle, are shown to be responsible for an only moderate catalytic activity.     

Coordination diversity in palladium(II)-picolinamide ligand complexes: structural and quantum chemical studies

The separation of different metal ions can be successfully accomplished by using picolinamide-based ligands. We herein report the first X-ray structure of picolinamide-based ligands of the type C₅H₄NCONR₂ (where R=ⁱC₃H₇ (L1) and ⁱC₄H₉ (L2)) and C₅H₄NCONHR (R=^tC₄H₉ (L3)) with palladium(II) ion. We have synthesized and characterized the structures of two palladium complexes, [PdCl₂(L1)₂] (1) and [PdCl₂L3] (3). In 1, ligand L1 forms a 2?:?1 complex with palladium(II) chloride, whereas in 3, the ligand L3 forms a 1?:?1 complex. Further, in 1, the ligand L1 acts as a monodentate ligand and is bound only through pyridyl-N atom, whereas in 3, the ligand L3 acts as a bidentate chelating ligand and is bound through both the pyridyl-N and amido-O atoms to the Pd(II) center. Electronic structure calculations are carried out to understand the experimental coordination diversity in the Pd complexes. Our calculations clearly suggest that a combination of steric hindrance of the ligand and the electronic effect of metal ions may modulate the coordination preferences.