Self-assembled Dimers Research Articles

Cyclometalated luminescent platinum(II) complexes of dissymmetrical 2,2':4',2''-terpyridine and its self-assembled dimer presenting Pt-Ag dative bonds.

A series of cyclometalated (N^C^N) Pt(II)-platinum complexes featuring a terpyridine ligand with a non-coordinating nitrogen atom and a Pt-C bond was synthesized. In the presence of Ag+, the bis(isonitrile)Pt(II) complex formed a remarkable self-assembled helicoidal dimer stabilized by coordination of Ag(I) and metallophilic Pt-Ag interactions. Its assembly was observed in the solid state and maintained in solution. All complexes show strong luminescence and multiple emitting states, which could be rationalized based on solid state X-ray structures and coordinating environment.

Crystallographic, theoretical and conductivity studies of two new complexes [Ni(II) and Cu(II)] based on mixed ligands approach

Two new complexes [Ni(C7H3NO5) (C15H11N3)]. 4(H2O) (1) and [Cu(C7H3NO5) (C15H11N3)]. 4(H2O) (2) have been synthesized using mixed chelating ligands [4-hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid) (C7H5NO5) and 2,2′:6′,2′′-terpyridine (C15H11N3)] in aqueous medium. The two complexes were characterized by UV–visible, IR spectroscopy as well as by single-crystal X-ray diffraction analysis. The geometries of both the complexes are distorted octahedral with N4O2 chromophore. The non-covalent interactions found in the solid state architectures of complexes 1 and 2 have been described focusing on π•••π stacking and hydrogen bonding interactions. These non-covalent interactions played an imperative role in building of multi-dimensional supramolecular architectures. These interactions have been explored theoretically by density functional theory (DFT) focusing on the antiparallel π-π stacking in self-assembled dimers and the hydrogen bonding networks mediated by the lattice water molecules. MEP surface calculations combined with QTAIM and NCI plot analysis were used to rationalize and characterize the non covalent interactions involved in the assemblies. The low optical band gaps of the two complexes exhibit semiconducting property leading to potentially fabricate Schottky Barrier Diode.

Self-assembly, crystal structure, computational studies, optical investigation, magnetic and biological properties of novel compounds based on methoxyphenyl piperazinium ligand

Two novel methoxyphenyl-based piperazine compounds have been investigated. The crystal structures of [C11H18N2O][Co(SCN)4] (1) and [(C11H18N2O)4]Cl8.7H2O (2) have been determined using single crystal X-ray crystallography. However, (1) crystallizes in an orthorhombic system with the non-centrosymmetric space group P 212121 with the following lattice parameters: a=8.4637(2) Å, b=14.5848 (5) Å, c= 17.1847 (5) Å with V =2121.3 (1) Å3 and Z = 4, otherwise (2) crystallizes in monoclinic system with P 21/c space group and the following lattice parameters: a=7.2551 (2) Å, b=9.0523 (4) Å, c= 22.3575 (8) Å, β = 95.998 (3)° with V =1460.30 (9) Å3 and Z = 1 . Different interactions packed the system through N-H…S hydrogen bonds for (1). The organic entities are grouped into dimers for (2) through weak interactions and N-H∙∙∙Cl, N-H∙∙∙O, and O-H∙∙∙Cl. The robustness of the crystals is also enhanced by C–H…π of the piperazine ring. Infrared spectrums were recorded to reveal the vibrational modes of the compounds, and to highlight the optical behavior, UV–visible analysis has been carried out. Thermal analysis was carried out to highlight the thermal stability of complexes. In addition, the antibacterial assets were investigated against different bacteria. The 13C Nuclear Magnetic Resonance was carried out to highlight the presence of primary reagents in the final product. Intermolecular interaction and stabilization of dimer complexes in the crystal packing are explored using Hirshfeld surface analysis to highlight the role of molecular interaction in the crystal packing. The more detailed quantum computation from crystallographic reported self-assembled dimer complexes occurred for comprehensive structure elucidation and showed good findings. The nature of dimer complexes has been assessed by strong and weak intermolecular interactions which were examined by NCI plots and analyzed by QTAIM calculation. Then, the thermal analysis was used to confirm the crystal thermal stability, Furthermore, biological behavior was performed for the compounds against different antibacterial targets to identify to which target the compounds show the best affinity. and finally, the magnetic properties were studied to show the spin coupling for the metal complex. Magnetic measurements of the novel cobalt compound show χT values that are typical for Co(II) cations with S = 3/2.

Enhanced Liposomal Drug Delivery Via Membrane Fusion Triggered by Dimeric Coiled-Coil Peptides.

An ideal nanomedicine system improves the therapeutic efficacy of drugs. However, most nanomedicines enter cells via endosomal/lysosomal pathways and only a small fraction of the cargo enters the cytosol inducing therapeutic effects. To circumvent this inefficiency, alternative approaches are desired. Inspired by fusion machinery found in nature, synthetic lipidated peptide pair E4/K4 is used to induce membrane fusion previously. Peptide K4 interacts specifically with E4, and it has a lipid membrane affinity and resulting in membrane remodeling. To design efficient fusogens with multiple interactions, dimeric K4 variants are synthesized to improve fusion with E4-modified liposomes and cells. The secondary structure and self-assembly of dimers are studied; the parallel PK4 dimer forms temperature-dependent higher-order assemblies, while linear K4 dimers form tetramer-like homodimers. The structures and membrane interactions of PK4 are supported by molecular dynamics simulations. Upon addition of E4, PK4 induced the strongest coiled-coil interaction resulting in a higher liposomal delivery compared to linear dimers and monomer. Using a wide spectrum of endocytosis inhibitors, membrane fusion is found to be the main cellular uptake pathway. Doxorubicin delivery results in efficient cellular uptake and concomitant antitumor efficacy. These findings aid the development of efficient delivery systems of drugs into cells using liposome-cell fusion strategies.

Influence of non-uniform magnetic field on spatial orientation of Heisenberg dimers with spin [formula omitted

The paper presents exact results for the Heisenberg dimer with spin S=1 placed in a non-uniform magnetic field. It was assumed that the dimer has a degree of freedom of movement enabling the spatial arrangement of the dimer axis parallel or perpendicular to the field gradient. Based on the calculations of the Gibbs magnetic energy, the occurrence of magneto-spatial phase transitions of the 1st kind was found, in which the dimer changing its magnetization state simultaneously changes the spatial orientation relative to the field gradient. Ground state phase diagrams and temperature diagrams are presented, as well as calculations of the Gibbs energy, magnetization, entropy and dimer quadrupolar moment. These calculations form an internally consistent thermodynamic description and are presented in figures. The discussed model illustrates the possibility of a magnetic contribution to the self-assembly of dimers on the surface.

Experimental and Theoretical Study of Tetrel Bonding and Noncovalent Interactions in Hemidirected Lead(II) Phosphorodithioates: An Implication on Crystal Engineering

The importance of tetrel bonds (TtBs) in spontaneous self-assembly has been highlighted in two new lead(II) complexes: i.e. Pb[S2P{OC6H4(4-C(CH3)3)}2]2 (1) and Pb[S2P{OC6H4(4-C2H5)}2]2 (2), which were successfully isolated and characterized by FT-IR, UV–vis and multinuclear NMR (31P, 1H and 13C) spectroscopy. The structures of both complexes have been confirmed by single-crystal X-ray diffraction analyses. Interestingly, lead is coordinated by three sulfur atoms in 1 but by four sulfur atoms in 2, due to stereochemically active lone pair electrons, thus leading to trigonal-pyramidal and tetragonal-pyramidal geometries, respectively. Complex 1 is the first example of a lead(II) dithiophosphate wherein the lead(II) center is coordinated to three S atoms. These complexes are stabilized at a lower coordination number and display hemidirected structures that allow forming σ-hole bonds. The lead(II) center establishes short contacts with sulfur atoms to form Pb···S TtBs that contribute to the construction of a self-assembled dimer in 1 but to a supramolecular polymer in 2. The supramolecular assemblies are further stabilized by Pb···π TtB interactions. The attractive nature of TtBs has been studied by DFT calculations and characterized using a combination of Bader’s quantum theory of atoms-in-molecules (QTAIM) and noncovalent interaction plot (NCI plot) index based on a reduced density gradient (NCI-RDG) analysis. A systematic Hirshfeld surface analysis facilitates a comparison of intermolecular interactions such as C–H···π, π···π, Pb···S, and Pb···π in both complexes, which play a crucial role in the crystal engineering.

A Tetranuclear Ni(II)-Cubane Cluster Molecule Build by Four µ3-O-Methanolate (MeO) Ligands, Externally Cohesive by Four Unprecedented Bridging µ2-N7,O6-Acyclovirate (acv-H) Anions

Metal ion interactions with nuclei acids and their constituents represent a multi-faceted and growing research field. This contribution deals with molecular recognition between synthetic purine 17 nucleosides and first-row transition metal complexes, with O- and/or N-amino chelators which are able to 18 engage in intra-molecular N-H···(N or O) and O-H···(N or O) interligand interactions. Crystals of these complexes can also display inter-molecular aromatic π-stacking and/or other non-conventional interactions. In this manuscript, we used 2-(2-aminoethoxy)ethanol (2aee) as a potential N,O(e),O(ol)-chelator for nickel(II). However, unexpectedly, the reaction between NiCl2, acyclovir (acv), and 2aee in methanol afforded parallelepiped apple-green crystals of [Ni(acv-H)(MeO)(H2O)]4·8H2O, (1) a tetranuclear molecule with an equimolar Ni(II):µ3-methanolate(1-):µ2-N7,O6-acyclovirate(1-) (acv-H) ratio. The µ2-N7,O6-(acv-H) metal-binding pattern (MBP) is unprecedented in terms of both its anionic and bridging roles. The single-crystal X-ray diffraction structure as well as thermogravimetric analysis and the (FT-IR +Vis-UV) spectra of 1 are reported. Theoretical density functional theory (DFT) calculations are used to analyse the antiparallel π-stacking interactions that govern the formation of self-assembled dimers in the solid state.

Synthesis and characterization of new Co(II), Rh(III), and Pt(II) guanidine and thiourea complexes

Guanidine- and thiourea-based complexes have been the subject of extensive study due to their wide range of potential applications, including but not limited to anti-cancer drugs, ion transporters, and sensors. Building upon previous work done in this group, we aimed to demonstrate a new series of organometallic complexes based on functionally diverse guanidine and thiourea ligands. Herein, the synthesis and characterization of new platinum, rhodium, and cobalt complexes is presented. While most of these complexes conformed to properties and behaviours in line with previous work, one complex based on a Pt(II) and guanidine derivative exhibited unusual supramolecular properties, demonstrating a larger self-assembled dimer consisting of six Pt(II) cations.

An account of noncovalent interactions in homoleptic palladium(II) and platinum(II) complexes within the DFT framework: A correlation between geometries, energy components of symmetry-adapted perturbation theory and NCI descriptors

The present work addresses the underlying nature of weak noncovalent interactions (NCIs) in the self-assembled dimers of two square planar palladium(II) and platinum(II) complexes trans-[Pd(Hida)2] (1) and trans-[Pt(Hida)2] (2) (Hida = monoprotonated iminodiacetate) within the framework of density functional theory (DFT) in gas phase. Initial geometries of the dimers in different spatial orientations were extracted from the X-ray crystal structures, reported earlier, and optimized with three dispersion-corrected functionals that are frequently used to explore NCIs. The BP86-D3, M062X-D3 and ωB97X-D3 functionals have been used to test their performances over the present systems. The SARC-ZORA-TZVP and ZORA-def2-TZVP basis sets were applied for the metals and the remaining elements, respectively. The optimizations resulted in equilibrium geometries where the monomers are self-assembled through NCIs to form dimers in a cyclic fashion. This type of structural pattern is absent in the crystal structures of both 1 and 2. Physical components of interaction energies were investigated by symmetry-adapted perturbation theory (SAPT). The UV-Vis absorption spectra of the dimers are described by time-dependent density functional theory (TD-DFT). Global reactivity parameters for the dimers have been computed within the framework of conceptual density functional theory (CDFT). Detailed investigations on NCIs were performed for all dimer geometries. Simulated IR and 1H NMR spectra, charge transfer, QTAIM, NCI-RGD, IGM, ETS-NOCV and ELF studies confirmed the presence of intermolecular hydrogen bonds (HBs) and weak van der Waals interactions. Energies of the hydrogen bonds and associated orbital interaction energies were computed by QTAIM and ETS-NOCV methods, respectively.

Scissor-like Face to Face π-π Stacking: A Surprising Preference Induced by the Isocyano Group in the Self-Assembled Dimer of Phenyl Isocyanide.

Phenyl isocyanide has been chosen as a prototype to probe the π-π interaction modulated by the -NC group, which has a chameleonic nature with two main resonance forms showing a triple bond and being carbenoid. The rotational spectroscopic investigation complemented with theoretical analyses indicates that the phenyl isocyanide dimer has a scissor-like configuration controlled by dispersive forces along with the formation of π-π stacking. This is the first rotational spectroscopic evidence, to the best of our knowledge, that the mono-substitution by an -NC group on benzene can activate the meta position in forming noncovalent interactions. This work also provides experimental evidence on the importance of substituent effects in modulating π-π stacked structures, as well as practical proof of a biased interaction behavior of isocyanide-substituted aromatic molecules.

Supramolecular assemblies involving unconventional non-covalent contacts in pyrazole-based coordination compounds of Co(II) and Cu(II) pyridinedicarboxylates: Antiproliferative evaluation and theoretical studies

Two coordination compounds of Co(II) and Cu(II) viz. [Co(2,6-PDC)(Hdmpz)3]·H2O (1) and [Cu(2,6-PDC)(Hdmpz)2] (2) (2,6-PDC = 2,6-pyridinedicarboxylate, Hdmpz = 3,5-dimethylpyrazole) have been synthesized and characterized using single crystal XRD, elemental analysis, TGA, electronic, FT-IR and 1H NMR spectroscopy. Crystal structure analysis of 1 and 2 reveals the presence of supramolecular assemblies involving various non-covalent interactions. The crystal structure of 1 is stabilized by a structure guiding hydrogen bonded synthon involving the lattice water molecules and unusual double anion–π interactions involving the carboxylate moieties of 2,6-PDC. Unconventional CH⋯π(carbonyl) and CH⋯π(chelate) contacts involving carbonyl moiety and the chelate ring of 2,6-PDC observed in the crystal structure of 2 also provide rigidity to the layered assemblies. Such unconventional CH⋯π contacts involving carbonyl moiety and chelate ring of 2,6-PDC are scarcely explored. DFT calculations in combination with QTAIM and NCI Plot analyses have been performed on supramolecular dimers of the compounds to explore the energetic features of the self-assembled dimers. The large dimerization energies of the dimers indicate the significance of these non-covalent interactions in governing solid state stabilities of the compounds. Antiproliferative evaluation of the compounds considering cell cytotoxicity and apoptosis assays revealed that the compounds induced significant concentration dependent cytotoxicity in Dalton’s lymphoma (DL) cancer cells with nominal effects on normal PBMC cells. Molecular docking and pharmacophore modelling studies of the compounds have been further carried out to establish the structure activity relationship (SAR).

Importance of R-CH3⋯O tetrel bonding and vinyl⋯aryl stacking interactions in stabilizing the crystal packing of 2’,4’-dihydroxy-3’-methoxychalcone: Exploration of antileishmanial activity and molecular docking studies

A detailed experimental and theoretical investigation of a chalcone derivative 2’,4’-dihydroxy-3’-methoxychalcone (DHMC) isolated from Argentinean type-Zuccagnia propolis has been performed. The isolated compound was characterized by 1H and 13C Nuclear Magnetic Resonance (NMR), infrared (IR) and Raman spectroscopies and its crystal structure was solved by single-crystal X-ray diffraction (XRD). The molecular geometry of the title compound was investigated theoretically and a very good agreement between experimental and computed geometrical parameters and vibrational frequencies have been observed. The substance crystallized in the orthorhombic Pbcn crystal system, with Z= 8 molecules per unit cell. The molecular geometry of the molecule is mainly stabilized by intramolecular O-H⋯O(keto) hydrogen bonds. The structure reveals that the crystal packing is mainly governed by O-H⋯O and C-H⋯O hydrogen bonds. The supramolecular assembly of the compound in solid state is also stabilized by σ-hole tetrel bonding interactions (O⋯C) involving the O-atom of the hydroxyl and the carbon atom of the methoxy group. Other interactions such as C-H⋯π and vinyl⋯π stacking interactions are also relevant in the stabilization of the solid structure of DHMC. The interaction energies of the different self-assembled dimers have been estimated using DFT calculations and various computational tools including MEP surfaces, QTAIM, NBO and NCI plot analysis. The antileishmanial activity of DHMC indicates that the compound was active against the main specie that cause tegumentary leishmaniosis in Argentina. The computational molecular docking simulation was used to predict the binding potential of the title chalcone derivative against six different leishmanial protein targets.

Resonance mode analysis of DNA self-assembled metamolecules with an effective refractive index model.

We investigated the feasibility of a simple effective refractive index model based on the finite-difference time-domain method for DNA self-assembled metamolecules. Metamolecules were fabricated with Au nanoparticles (AuNPs) and a two-layer rectangular DNA template. Simulated scattering spectra for AuNPs placed on the template (neff = 1.3), self-assembled DNA dimers (neff = 1.34), and quadrumers (neff = 1.5) matched well with experimental results. Dipolar and Fano-like resonances were predicted from the calculated field distribution. These results indicate that we can easily estimate the resonance mode of fabricated metamolecules on a glass substrate, even when they are surrounded by complex materials such as DNA, by using a simple refractive index model.

Experimental and theoretical insights into the formation of weak hydrogen bonds and H⋯H bonding interactions in the solid-state structure of two eucalyptol derivatives

We report the synthesis and X-ray solid-state structure of two eucalyptol derivatives. Both compounds form self-assembled dimers establishing C–H⋯O hydrogen bonds and H⋯H bonding interactions.

Spodium bonds and metal–halogen···halogen–metal interactions in propagation of monomeric units to dimeric or polymeric architectures

In this work we report on crystal structures of a heteroleptic coordination polymer [Hg2(HL)Cl4]n (1) where the nitrogen atom of the peripheral pyridine fragment is linked to another HgCl2 molecule and two discrete mononuclear heteroleptic complexes [Hg(HL)I2] (2) and [Mn(HL)Cl2]·MeOH (3·MeOH), which were obtained through self-assembling of N'-(1-(pyridin-2-yl)ethylidene)isonicotinohydrazide (HL) with HgCl2, HgI2 or MnCl2, respectively. HL coordinates the HgII salts in its keto-form, while MnCl2 is chelated by a zwitterionic form of HL confirmed by the solid state IR spectroscopy. The studied here ligand molecule has a tendency to involve the 4-pyridyl nitrogen atom in coordination bonding which is correlated with the ability to transfer the electric charge and production of a zwitterionic form. The crystal structure and Hirshfeld surface data analysis show a great importance of spodium bonds and metal–halogen⋯halogen–metal interactions. A prominent consequence of lack of σ- or π-hole interactions in case of MnII ion is the isolation of metal center from the external contacts. Apart form this in 3·MeOH the halogen⋯halogen interactions are absent. It seems that the σ- or π-hole regions formed at the HgII cation in 1 and 2 favor the participation of coordinated Cl or I atoms in the M–Hal⋯Hal'–M' halogen⋯halogen interactions, whereas in complex 3·MeOH there are no metal or halogen centered σ-hole interactions. Thus, the 1D coordination polymer in 1 is stabilized by the Hg⋯Cl spodium bonding. Additionally, the observed intermolecular halogen⋯halogen interactions in 1 provide cross-linking of the 1D coordination polymers, yielding a 2D supramolecular double-layered sheet. In 2 an additional contact between halogen and mercury atoms results in a dimeric unit. These dimers are linked into a 1D polymer by halogen⋯halogen interactions between metal bounded iodine atoms. The DFT theoretical studies were applied to analyze the Hg⋯X non-covalent spodium interactions that govern the formation of the 1D polymeric structure in 1 and self-assembled dimers in 2.

Correlative microscopy of single self-assembled nanorod dimers for refractometric sensing.

Single metallic particles and dimers of nanospheres have been used extensively for sensing, but dimers of particles provide attractive advantages because they exhibit multiple modes that can be tuned by the dimer geometry. Here, we employ correlative microscopy of single self-assembled dimers of gold nanorods to study their performance as refractometric sensors. The correlation between atomic force microscopy and single-particle white-light spectroscopy allows us to relate the measured sensitivity to numerical simulations taking into account the exact geometry of the construct. The sensitivity of the antibonding mode is in good agreement with simulations, whereas the bonding mode exhibits a reduced sensitivity related to the accessibility of the gap region between the particles. We find that the figure of merit is a trade-off between the resonance linewidth and its refractive index sensitivity, which depend in opposite ways on the interparticle angle. The presence of two narrow plasmon resonances in the visible to near-infrared wavelength regime makes nanorod dimers exciting candidates for multicolor and multiplexed sensing.

Exploitation of the electron deficient outer O4 compartment of a compartmental Schiff base to act as H-bond acceptors in forming a self-assembled dimer of a manganese(III) complex: A joint experimental and theoretical venture

A mononuclear manganese(III) complex, [MnL1(DMSO)(OH2)]ClO4, where H2L1 = (2,2-dimethyl-(1,3-propylene))-bis(3-ethoxysalicylideneimine) is a tetradentate Schiff base ligand, has been synthesized and characterized by elemental and spectral analysis and single crystal X-ray diffraction. The most electron rich part of the cationic manganese(III) complex corresponds to the region where the four oxygen atoms (two from the ethoxy arms and two from the phenol groups) are located (−47 kcal/mol) and the most electron deficient part is located at the hydrogen atoms of the coordinated water molecule (+65 kcal/mol). This large value is due to the effect of the coordination of the oxygen atom to the manganese(III) center that increases the acidity of the water protons, thereby facilitating the formation of a H-bond mediated dimer. It is further stabilized by π⋯π stacking interactions involving the aromatic rings. The dimerization energy is very large confirming the relevance of this combination of interactions. The contribution of the H-bonds is also estimated, which confirms that the formation of the dimer is basically governed by the H-bonds.

Synthesis of bio-functional nanoparticles from sono-responsive amino acids using high frequency ultrasound.

A simple, one-pot high frequency ultrasonication (490kHz) methodology to convert hydrophobic and amphipathic amino acids into nanostructures was investigated. The approach involved the oxidative coupling of aromatic amino acids (phenylalanine and tryptophan) in aqueous solutions to form high molecular weight dimers and oligomers. The role of cavitation bubble surface and ultrasonic power to trigger the out-of-equilibrium self-assembly of dimers and trimers to spherical and uniform nanostructures with controlled size has been discussed. The synthesized particles exhibited fluorescence in blue, green and red spectral regions and a strong antioxidant activity.

Relevant π-hole tetrel bonding interactions in ethyl 2-triazolyl-2-oxoacetate derivatives: Hirshfeld surface analysis and DFT calculations

We report the synthesis and X-ray characterization of four triazole derivatives that include an α-ketoester functionality and two phenyl substituents. The compounds form self-assembled dimers in the solid state establishing two symmetrically equivalent O⋯π-hole interactions.

Complexes featuring N-heterocyclic carbenes with bowl-shaped wingtips

Abstract Three imidazolium salts having their two N-substituents equipped with remote calix[4]arenyl termini have been synthesised and converted into N-heterocyclic carbene (NHC) complexes of the type [PdCl2(NHC)(pyridine)]. An X-ray diffraction study carried out for one of the complexes, namely, trans-[1,3-bis(4-{25,26,27,28-tetrapropyloxycalix[4]aren-5-yl}phenyl)imidazol-2-ylidene](pyridine)palladium(II) dichloride, revealed that in the solid state the complex crystallises as a self-assembled dimer, its components being held together by dispersion forces involving the polyphenoxy units, the pyridine ligands and phenylene rings. This structure provides a new example of the diversity of interactions that may occur in NHC complexes of catalytic relevance, which are thus not limited to intramolecular ones. There was no spectroscopic indication that such interactions also occur in solution.