Pyridine Complexes Research Articles

Antiviral effect of oversulfated kappa-carrageenan derivatives against COVID-19 for spray coating application on facemasks

The COVID-19 pandemic caused by SARS-CoV-2 has spurred the urgent need for effective antiviral strategies. In this work, we explored the potential of oversulfated kappa-carrageenan (OSKC) in spray-coated facemasks for SARS-CoV-2 inhibition pathway. The sulfated derivative was synthesized with sulfur trioxide pyridine complex in dimethylformamide solution. The antiviral efficacy of OSKC at different concentrations and spray-coated facemasks was evaluated using betacoronavirus Murine Hepatitis Virus strain 3, revealing a significant reduction in viral load compared to commercial kappa-carrageenan. Furthermore, the characterization techniques assessed the effect of the position of the introduced sulfate groups on the antiviral activity and on the physicochemical characteristics. OSKC is able to bind specific proteins of enveloped viruses, preventing viral attachment into target cells. Overall, this study demonstrates the feasibility and effectiveness of OSKC spray coating for breathable facemasks with antimicrobial properties, offering a promising approach to enhancing personal protective equipment against viral transmission in healthcare and community settings.

Enhanced DNA damage and anti-proliferative activity of a novel ruthenium complex with a chlorambucil-decorated ligand

Triphenylphosphine substitution reactions of [RuCl(PPh3)2(tpm)]Cl, 1, featuring tris(pyrazolyl)methane (tpm) as ligand, with the chlorambucil-decorated pyridine ligand PyCA, 3-aminopyridine (PyNH2) and 4-pyridinemethanol (PyOH) afforded the corresponding pyridine complexes 2–4 in high yields. PyCA was preliminarily obtained via esterification of 4-pyridinemethanol with chlorambucil. The new compounds PyCA and 2–3 were characterized by IR and multinuclear NMR spectroscopy. Additionally, the structure of 3 was ascertained by single crystal X-ray diffraction. The in vitro anti-proliferative activity of 2–4 and PyCA was determined against a panel of cancer cell lines, outlining 2 as the most performing compound. Targeted studies were subsequently undertaken using 2 to elucidate mechanistic aspects, including the assessment of ruthenium cellular uptake, cell cycle arrest, production of reactive oxygen species (ROS), western blotting and DNA damage (comet test). Overall, data highlight that the anticancer activity provided by 2 primarily affects the mitochondria pathway with a potential additional contribution from DNA damage.

Tribological properties and synergistic effects of ionic liquids and silver complexes

PurposeThe purpose of this paper is to solve the abrupt deterioration of lubricant performance in high-temperature conditions.Design/methodology/approachThree silver pyrazolyl methyl pyridine complexes with different morphologies were synthesized. A four-ball tribometer was used to assess the tribological characteristics as an additive for pentaerythritol oleate both independently and compound with 1-hexyl-3-methylimidazolium bis(trifluoromethane sulfonyl)imide.FindingsThe results showed that when silver complexes and ionic liquids (IL) act independently, sheet silver complex 1 and rod silver complex 2 exhibit good lubricating performance; the optimal antifriction concentration of the ILs is 0.25 Wt.%. The tribological results of the compounds additive of ILs and silver complexes indicate that the wear scar diameter of compound 1 decreased by 16.914%, the wear volume reduced by 7.44% and the lubrication effect surpassed that of the two substances individually; rod compound 2 exhibited an antagonistic effect, intensifying wear; compound 3’s lubrication effect fell between that of the two individual components.Originality/valueThe compound of sheet silver complexes and ILs effectively solves the agglomeration problem of micro/nano lubricant additives. When the interface fails, self-repair is completed, improving the stability and antiwear performance of the lubricating oil.Peer reviewThe peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2024-0128

A Tetracarbene Iron(II) Complex with a Long‐lived Triplet Metal‐to‐ligand Charge Transfer State due to a Triplet‐Triplet Barrier

Mixed N‐heterocyclic carbene (NHC) / pyridyl iron(II) complexes have attracted a great deal of attention recently because of their potential as photocatalysts and light sensitizers made from Earth‐abundant elements. The most decisive challenge for their successful implementation is the lifetime of the lowest triplet metal‐to‐ligand charge transfer state (3MLCT), which typically decays via a triplet metal‐centered (3MC) state back to the ground state. We reveal by variable‐temperature ultrafast transient absorption spectroscopy that the tripodal iron(II) bis(pyridine) complex isomers trans‐ and cis‐[Fe(pdmi)2]2+with four NHC donors show 3MLCT→3MC population transfers with very different barriers and rationalize this by computational means. While trans‐[Fe(pdmi)2]2+possesses an unobservable activation barrier, the cis isomer exhibits a barrier of 492 cm–1, which leads to a nanosecond 3MLCT lifetime at 77 K. The kinetic and quantum chemical data were analyzed in the context of semi‐classical Marcus theory revealing a high reorganization energy and small electronic coupling between the two triplet states. This highlights the importance of detailed structural control and kinetic knowledge for the rational design of photosensitizers from first row transition metals such as iron.

A Tetracarbene Iron(II) Complex with a Long-lived Triplet Metal-to-Ligand Charge Transfer State due to a Triplet-Triplet Barrier.

Mixed N-heterocyclic carbene (NHC) / pyridyl iron(II) complexes have attracted a great deal of attention recently because of their potential as photocatalysts and light sensitizers made from Earth-abundant elements. The most decisive challenge for their successful implementation is the lifetime of the lowest triplet metal-to-ligand charge transfer state (3MLCT), which typically decays via a triplet metal-centered (3MC) state back to the ground state. We reveal by variable-temperature ultrafast transient absorption spectroscopy that the tripodal iron(II) bis(pyridine) complex isomers trans- and cis-[Fe(pdmi)2]2+ with four NHC donors show 3MLCT→3MC population transfers with very different barriers and rationalize this by computational means. While trans-[Fe(pdmi)2]2+ possesses an unobservable activation barrier, the cis isomer exhibits a barrier of 492 cm-1, which leads to a nanosecond 3MLCT lifetime at 77 K. The kinetic and quantum chemical data were analyzed in the context of semi-classical Marcus theory revealing a high reorganization energy and small electronic coupling between the two triplet states. This highlights the importance of detailed structural control and kinetic knowledge for the rational design of photosensitizers from first row transition metals such as iron.

Local charge redistribution enables single ionic conductor for fast charge solid Li battery

Solid polymer electrolytes (SPEs) have been regarded as hopeful candidate electrolyte for solid-state lithium battery. However, the low Li+ transference number and poor interface stability pose great challenges for the high rate capability of SPE. Herein, inspired from the density functional theory (DFT) calculations that local positive charge distribution can be regulated by introducing strong electron-withdrawing groups, which can selectively anchor TFSI−, largely enhance the Li+ transference number. As predicted, the obtained CPE-NO2 deliver a remarkable Li+ transference number of 0.91, equal to a single-ion conductor for Li+, largely high than that of the SPE (0.31), according well with the molecular dynamics (MD) simulations and pyridine complexation experiments. Furthermore, the PEO||Li interfacial stability, flame retardant ability, and mass transfer of Li+ in interface can also be largely enhanced by interfacial by-product, which are fast Li+ conductors according to TOF-SIMS results. Impressively, the Li|CPE-NO2|Li cell exhibit superior cyclability for 2200 h at 0.1 mA cm−2, and the solid LFP|CPE-NO2|Li battery delivers prominent capacity of 127.4 mAh g−1 at a high rate 5 C (12 mins). This work breaks the fast charge limitation of solid lithium battery, and provides a feasible approach for the construction of advanced solid electrolyte.

Coinage Metal Complexes of a Sterically Encumbered Anionic Pyridylborate.

Sterically loaded, anionic pyridine has been synthesized and utilized successfully in the stabilization of a isoleptic series of coinage metal complexes. The treatment of [4-(Ph3B)-2,6-Trip2Py]K (Trip=2,4,6-iPr3C6H2) with CuBr(PPh3), AgCl(PPh3) or AuCl(PPh3) (Py=pyridine) afforded the corresponding [4-(Ph3B)-2,6-Trip2Py]M(PPh3) (M=Au, Ag, Cu) complexes, via salt metathesis, as isolable, crystalline solids. Notably, these reactions avoid the facile single electron transfer chemistry reported with the less bulky ligand systems. The X-ray structures revealed that they are two-coordinate metal adducts. The M-N and M-P bond distances are longest in the silver and shortest in the copper adduct among the three group 11 family members. Computational analysis revealed an interesting stability dependence on steric bulk of the anionic pyridine (i. e., pyridyl borate) ligand. A comparison of structures and bonding of [4-(Ph3B)-2,6-Trip2Py]Au(PPh3) to pyridine and m-terphenyl complexes, {[2,6-Trip2Py]Au(PPh3)}[SbF6] and [2,6-Trip2Ph]Au(PPh3) are also provided. The Au(I) isocyanide complex, [4-(Ph3B)-2,6-Trip2Py]Au(CNBut) has been stabilized using the same anionic pyridylborate illustrating that it can support other gold-ligand moieties as well.

Probing the Antiaromaticity and Coordination Chemistry of Bowl-Shaped Zinc(II) Norcorrole.

Zinc norcorrole was prepared as its pyridine complex (ZnNc·pyridine) by metalation of freebase norcorrole. The ZnNc·pyridine complex is distinctly bowl-shaped, as demonstrated by both X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy. NMR spectroscopy showed characteristic ring current deshielding effects, with different magnitudes on either face of the bowl-shaped complex. Exchanging the pyridine ligand with the bidentate ligand DABCO results in the formation of a stable (ZnNc)2·DABCO sandwich complex, which was also characterized by crystallography and NMR spectroscopy. The NMR resonances of the axial ligands in all of the complexes demonstrate that the paratropic ring current in zinc norcorrole is approximately 40 nA/T, which is comparable in magnitude to the diatropic ring current in porphyrin. Analysis of the ligand-exchange processes on addition of DABCO to ZnNc·pyridine showed that ZnNc coordinates to axial nitrogen-containing ligands with approximately 1000-fold higher binding constants than analogous zinc porphyrins.

4-[(E)-2-(1-Pyrenyl)Vinyl]Pyridine Complexes: How to Modulate the Toxicity of Heavy Metal Ions to Target Microbial Infections.

Pyrene derivatives are regularly proposed for use in biochemistry as dyes due to their photochemical characteristics. Their antibacterial properties are, however, much less well understood. New complexes based on 4-[(E)-2-(1-pyrenyl)vinyl]pyridine (PyPe) have been synthesized with metal ions that are known to possess antimicrobial properties, such as zinc(II), cadmium(II), and mercury(II). The metal ion salts, free ligand, combinations thereof, and the coordination compounds themselves were tested for their antibacterial properties through microdilution assays. We found that the ligand is able to modulate the antibacterial properties of transition metal ions, depending on the complex stability, the distance between the ligand and the metal ions, and the metal ions themselves. The coordination by the ligand weakened the antibacterial properties of heavy metal ions (Cd(II), Hg(II), Bi(III)), allowing the bacteria to survive higher concentrations thereof. Mixing the ligand and the metal ion salts without forming the complex beforehand enhanced the antibacterial properties of the cations. Being non-cytotoxic itself, the ligand therefore balances the biological consequences of heavy metal ions between toxicity and therapeutic weapons, depending on its use as a coordinating ligand or simple adjuvant.

σ-Hole Site-Based Interactions within Hypervalent Pnicogen, Halogen, and Aerogen-Bearing Molecules with Lewis Bases: A Comparative Study.

σ-Hole site-based interactions in the trigonal bipyramidal geometrical structure of hypervalent pnicogen, halogen, and aerogen-bearing molecules with pyridine and NCH Lewis bases (LBs) were comparatively examined. In this respect, the ZF5···, XF3O2···, and AeF2O3···LB complexes (where Z = As, Sb; X = Br, I; Ae = Kr, Xe; and LB = pyridine and NCH) were investigated. The electrostatic potential (EP) analysis affirmations outlined the occurrence of σ-holes on the systems under consideration with disparate magnitudes that increased according to the following order: AeF2O3 < XF3O2 < ZF5. In line with EP outcomes, the proficiency of σ-hole site-based interactions increased as the atomic size of the central atom increased with a higher favorability for the pyridine-based complexes over NCH-based ones. The interaction energy showed the most favorable negative values of -35.97, -44.53, and -56.06 kcal/mol for the XeF2O3···, IF3O2···, and SbF5···pyridine complexes, respectively. The preferentiality pattern of the studied interactions could be explained as a consequence of (i) the dramatic rearrangement of ZF5 molecules from the trigonal bipyramid geometry to the square pyramidal one, (ii) the significant and tiny deformation energy in the case of the interaction of XF3O2 molecules with pyridine and NCH, respectively, and (iii) the absence of geometrical deformation within the AeF2O3···pyridine and ···NCH complexes other than the XeF2O3···pyridine one. Quantum theory of atoms in molecules and noncovalent interaction index findings reveal the partially covalent nature of most of the investigated interactions. Symmetry-adapted perturbation theory affirmations declared that the electrostatic component was the driving force beyond the occurrence of the considered interactions. The obtained findings will help in improving our understanding of the effect of geometrical deformation on intermolecular interactions.

Pyridine and bipyridine complexes of tri- and tetranuclear ruthenium clusters revisited. Substitution, orthometallation and bridges between cluster units

The reactions of pyridine and 2-, 3- and 4-picoline with [H4Ru4(CO)12] were carried out under several experimental conditions and produced mono- and disubstituted products as well as complexes where Ru-Ru cleavage occurred, and orthometalation of the heterocycle took place. The disubstituted compound [(μ-H)4Ru4(CO)10(py)2] shows that both pyridine rings are coordinated to the same ruthenium atom; the 4-picoline also forms a similar complex. The reaction of [Ru3(CO)12] with 4,4´-bipyridine was also carried out. The product formed shows a bridged structure with both pyridine rings coordinated to a ruthenium triangle in an ortho-metalated mode. Spectroscopic characterization of all new compounds is described and the X-ray crystal structures of [(μ-H)4Ru4(CO)11py], [(μ-H)4Ru4(CO)10(py)2], [(μ-H)2Ru3(CO)8((μ-η2-NC5H4)2] and [{Ru3(CO)10}2(μ-η2–4,4´-(NC5H3)2] are described.

Differences in Photophysical Properties and Photochemistry of Ru(II)-Terpyridine Complexes of CH3CN and Pyridine.

A series of 22 Ru(II) complexes of the type [Ru(tpy)(L)(L')]n+, where tpy is the tridentate ligand 2,2';6,2″-terpyridine, L represents bidentate ligands with varying electron-donating ability, and L' is acetonitrile (1a-11a) or pyridine (1b-11b), were investigated. The dissociation of acetonitrile occurs from the 3MLCT state in 1a-11a, such that it does not require the population of a 3LF state. Electrochemistry and spectroscopic data demonstrate that the ground states of these series do not differ significantly. Franck-Condon line-shape analysis of the 77 K emission data shows no significant differences between the emitting 3MLCT states in both series. Arrhenius analysis of the temperature dependence of 3MLCT lifetimes shows that the energy barrier (Ea) to thermally populating a 3LF state from a lower energy 3MLCT state is significantly higher in the pyridine than in the CH3CN series, consistent with the photostability of complexes 1b-11b, which do not undergo pyridine photodissociation under our experimental conditions. Importantly, these results demonstrate that ligand photodissociation of pyridine in 1b-11b does not take place directly from the 3MLCT state, as is the case for 1a-11a. These findings have potential impact on the rational design of complexes for a number of applications, including photochemotherapy, dye-sensitized solar cells, and photocatalysis.

The Impact of ortho-substituents on Bonding in Silver(I) and Halogen(I) Complexes of 2-Mono- and 2,6-Disubstituted Pyridines: An In-Depth Experimental and Theoretical Study.

The coordination nature of 2-mono- and 2,6-disubstituted pyridines with electron-withdrawing halogen and electron-donating methyl groups for [N-X-N]+ (X=I, Br) complexations have been studied using 15 N NMR, X-ray crystallography, and Density Functional Theory (DFT) calculations. The 15 N NMR chemical shifts reveal iodine(I) and bromine(I) prefer to form complexes with 2-substituted pyridines and only 2,6-dimethylpyridine. The crystalline halogen(I) complexes of 2-substituted pyridines were characterized by using X-ray diffraction analysis, but 2,6-dihalopyridines were unable to form stable crystalline halogen(I) complexes due to the lower nucleophilicity of the pyridinic nitrogen. In contrast, the halogen(I) complexes of 2,6-dimethylpyridine, which has a more basic nitrogen, are characterized by X-crystallography, which complements the 15 N NMR studies. DFT calculations reveal that the bond energies for iodine(I) complexes vary between -291 and -351 kJ mol-1 and for bromine between -370 and -427 kJ mol-1 . The bond energies of halogen(I) complexes of 2-halopyridines with more nucleophilic nitrogen are 66-76 kJ mol-1 larger than those of analogous 2,6-dihalopyridines with less nucleophilic nitrogen. The experimental and DFT results show that the electronic influence of ortho-halogen substituents on pyridinic nitrogen leads to a completely different preference for the coordination bonding of halogen(I) ions, providing new insights into bonding in halogen(I) chemistry.

Zinc‐bis(imino)pyridine Complexes as Catalysts for Intermolecular Amidation of Benzylic C(sp3)−HBond

AbstractEfficient NNN‐pincer type bis(imino)pyridine ligand based zinc(II) catalyzed intermolecular amidation of benzylic hydrocarbons with sulfonamides has been developed. The zinc complexes were synthesized by the reaction of bis(imino)pyridine ligand with zinc(II) precursors such as Zn(OAc)2 ⋅ 2H2Oand ZnBr2. The structure of the bis(imino)pyridine‐Zn(OAc)2 complex was characterized by single crystal X‐ray diffraction. The zinc(II)‐bis(imino)pyridine complexes were utilized as catalysts for the intermolecular amidation of benzylic C(sp3)−H bond in the presence of N‐bromosuccinimide (NBS) as an oxidant. A broad range of substrates delivered the products in moderate to good yields. This protocol provides the synthesis of various amides viaC−H activation.

Structures and stability of I2 and ICl complexes with pyridine: Ab initio and DFT study.

Theoretical investigation of thermodynamic stability and bonding features of possible isomers of the molecular and ionic complexes of pyridine with molecular iodine and iodine monochloride IX (X = I,Cl) is presented. M06-2X DFT functional is found to provide bond distances and dissociation energies which are close to those obtained at high-level ab initio CCSD(T)/aug-cc-pvtz//CCSD/aug-cc-pvtz benchmark computations for the most stable isomers, formed via donation of a lone pair of nitrogen atom of pyridine to the iodine atom. These isomers are by 23-33 kJ mol-1 (in case of I2) and by 39-56 kJ mol-1 (in case of ICl) more stable than other molecular complexes. T-shaped π-σ* bonded isomers turn out to be energetically comparable with van der Waals bound compounds. Among the ionic isomers, structures featuring [IPy2]+ cation with I3 - or ICl2 - counterions are more stable. Oligomerization favors ionic isomers starting from the tetrameric clusters of the composition (IX)4Py4.

Investigation of protein/DNA binding, and in vitro cytotoxicity of novel Cu(ii) and Zn(ii)-dipyrazinyl pyridine complexes

Novel Cu(ii) and Zn(ii) complexes of a dipyrazinyl pyridine (dppy) ligand L, {[CuL2]Cl2 (1) and [ZnL2]Cl2 (2)}, have been prepared and their binding affinity with protein/DNA and in vitro cytotoxicity have been studied.

Structural and electrochemical properties of mononuclear copper(II) complexes with pentadentate ethylenediamine-based ligands with pyridine/quinoline/isoquinoline/quinoxaline binding sites.

N-Monosubstituted ethylenediamine derivatives with three methylene-tethered aromatic groups ((ArCH2)2NCH2CH2N(R)CH2Ar (R-ArArAr), where Ar = 2-pyridyl, 2-quinolyl, 1- and 3-isoquinolyl and 2-quinoxalyl; R = methyl, benzyl and phenyl) were utilized as pentadentate ligands for copper(II) complexation. Fifteen mononuclear copper(II) complexes were synthesized and exhibit differences in cyclic voltammetry, absorption spectroscopy and solid state geometries, depending on the aromatic group (Ar) and the substituent on the aliphatic nitrogen atom (R) of the ligand. Compared with the pyridine and isoquinoline complexes, the quinoline and quinoxaline derivatives exhibit distinct Cu(II)/Cu(I) redox potentials and d-d transition absorption wavelengths. Similarly, the phenyl derivatives are different from their methyl and benzyl counterparts. These characteristic trends are discussed in relation to the square-pyramidal/trigonal-bipyramidal structure of the complexes which is perturbed by the location of quinoline moieties in the penta- or hexacoordinate complexes with Jahn-Teller distortion. In addition, the results are compared to the copper(II) complexes with pyridine/quinoline mixed ligands, Ph-Ar1Ar2Ar3 ((Ar1CH2)(Ar2CH2)NCH2CH2N(Ph)CH2Ar3).

The nature of π-hole spodium bonds in the HgLCl2(L = pyrrole, pyrazole, imidazole, pyridine, pyridazine, and pyrimidine) complexes: from noncovalent to covalent interactions

Computational investigations reveal the electrophilicity of the π-hole and the nature of spodium bonds in the HgLCl2⋯ZH3/CH2Y complexes.

Halogen bonding and mechanochemistry combined: synthesis, characterization, and application of N-iodosaccharin pyridine complexes

Triturating N-iodosaccharin with electron-donating 4-substituted pyridines leads to either charge-neutral XB or cationic iodine(i) complexes, offering promising alternatives to the ubiquitous Barluenga's reagent as electrophilic iodination reagents.

Ortho-Substituent Effects on Halogen Bond Geometry for N-Haloimide⋯2-Substituted Pyridine Complexes.

The nature of (imide)N-X⋯N(pyridine) halogen-bonded complexes formed by six N-haloimides and sixteen 2-substituted pyridines are studied using X-ray crystallography (68 crystal structures), Density Functional Theory (DFT)(86 complexation energies), and NMR spectroscopy (90 association constants). Strong halogen bond (XB) donors such as N-iodosuccinimide form only 1:1 haloimide:pyridine crystalline complexes, but even stronger N-iodosaccharin forms 1:1 haloimide:pyridine and three other distinct complexes. In 1:1 haloimide:pyridine crystalline complexes, the haloimide's N─X bond exhibits an unusual bond bending feature that is larger for stronger N-haloimides. DFT complexation energies (ΔEXB ) for iodoimide-pyridine complexes range from -44 to -99kJmol-1 , while for N-bromoimide-pyridine, they are between -31 and -77kJmol-1 . The ΔEXB of I⋯N XBs in 1:1 iodosaccharin:pyridine complexes are the largest of their kind, but they are substantially smaller than those in [bis(saccharinato)iodine(I)]pyridinium salts (-576kJmol-1 ), formed by N-iodosaccharin and pyridines. The NMR association constants and ΔEXB energies of 1:1 haloimide:pyridine complexes do not correlate as these complexes in solution are heavily influenced by secondary interactions, which DFT studies do not account for. Association constants follow the σ-hole strengths of N-haloimides, which agree with DFT and crystallography data. The haloimide:2-(N,N-dimethylamino)pyridine complex undergoes a halogenation reaction resulting in 5-iodo-2-dimethylaminopyridine.