Self-assembled Supramolecular Structures Research Articles

Effect of Mixing Ratio of Oppositely Charged Block Copolymers on Polyion Complex Micelles for In Vivo Application.

Self-assembled supramolecular structures based on polyion complex (PIC) formation between oppositely charged polymers are attracting much attention for developing drug delivery systems able to endure harsh in vivo environments. As controlling polymer complexation provides an opportunity for engineering the assemblies, an improved understanding of the PIC formation will allow constructing assemblies with enhanced structural and functional capabilities. Here, we focused on the influence of the mixing charge ratio between block aniomers and catiomers on the physicochemical characteristics and in vivo biological performance of the resulting PIC micelles (PIC/m). Our results showed that by changing the mixing charge ratio, the structural state of the core was altered despite the sizes of PIC/m remaining almost the same. These structural variations greatly affected the stability of the PIC/m in the bloodstream after intravenous injection and determined their biodistribution.

AFM Research in Catalysis and Medicine

Background: In this study, we show that the AFM method not only allows monitoring the morphological changes in biological structures fixed on the surface due to H-bonds, but also makes it possible to study the self-organization of metal complexes by simulating the active center of enzymes due to intermolecular H-bonds into stable nanostructures; the sizes of which are much smaller than the studied biological objects. The possible role of intermolecular hydrogen bonds in the formation of stable supramolecular metal complexes, which are effective catalysts for the oxidation of alkyl arenes to hydroperoxides by molecular oxygen and mimic the selective active sites of enzymes, was first studied by AFM. Methods and Results: The formation of supramolecular structures due to intermolecular hydrogen bonds and, possibly, other non-covalent interactions, based on homogenous catalysts and models of active centers enzymes, heteroligand nickel and iron complexes, was proven by AFM-technique. AFM studies of supramolecular structures were carried out using NSG30 cantilever with a radius of curvature of 2 nm, in the tapping mode. To form nanostructures on the surface of a hydrophobic, chemically modified silicon surface as a substrate, the sample was prepared using a spin-coating process from solutions of the nickel and iron complexes. The composition and the structure of the complex Ni2(acac)(OAc)3·NMP·2H2O were determined in earlier works using various methods: mass spectrometry, UV- and IR-spectroscopy, elemental analysis, and polarography. Self-assembly of supramolecular structures is due to intermolecular interactions with a certain coordination of these interactions, which may be a consequence of the properties of the components themselves, the participation of hydrogen bonds and other non-covalent interactions, as well as the balance of the interaction of these components with the surface. Using AFM, approaches have been developed for fixing on the surface and quantifying parameters of cells. Conclusion: This study summarizes the authors' achievements in using the atomic force microscopy (AFM) method to study the role of intermolecular hydrogen bonds (and other non-covalent interactions) and supramolecular structures in the mechanisms of catalysis. The data obtained from AFM based on nickel and iron complexes, which are effective catalysts and models of active sites of enzymes, indicate a high probability of the formation of supramolecular structures in real conditions of catalytic oxidation, and can bring us closer to understanding enzymes activity. With a sensitive AFM method, it is possible to observe the self-organization of model systems into stable nanostructures due to H-bonds and possibly other non-covalent interactions, which can be considered as a step towards modeling the active sites of enzymes. Methodical approaches of atomic force microscopy for the study of morphological changes of cells have been developed.

Multi-responsive poly(amidoamine)-initiated dendritic-star supramolecular structures containing UV cross-linkable coumarin groups for smart drug delivery

Dendritic-star supramolecular structure of poly(amidoamine)-g-[polystyrene-b-(2-(dimethylamino)ethyl methacrylate-co-11-((4-methyl-2-oxo-2H-chromen-7-yl)oxy)undecyl acrylate)] (PAMAM-g-P(St-b-(DMAEMA-co-CuA))) was synthesized via grafting-from atom transfer radical polymerization (ATRP) by using PAMAM-initiator as smart drug carrier. This structure consisted of multi-responsive unites of hydrophilic PDMAEMA regarding to pH change, temperature, and CO2 gas and the coumarin molecule as photocrosslinking agent. Photocrosslinking agent is efficient for controlling DOX release after dimerization under UV light. The chemical structure of samples was confirmed by proton nuclear magnetic resonance (1H NMR) and their molecular weight was studied by gel permeation chromatography (GPC). The change of hydrophilic length of PDMAEMA and pH media resulted in various morphologies including hollow sphere, snowman- and dumbbell-like particles. The morphology of supramolecular assemblies was not changed after photocrosslinking, which confirmed the structure stabilization under UV light irradiation of 365 nm. Fluorescence microscopy was confirmed the presence of fluoresce segments in self-assembled supramolecular structures. Dynamic light scattering (DLS) indicated that the size of supramolecular assemblies was changed through the response to external stimuli such as pH, temperature, and CO2 gas. The DOX release behavior was investigated in different conditions such as pH, temperature, and after photocrosslinking under UV light of 365 nm.

Interplay of Self-Assembling Aromatic Amino Acids and Functionalized Gold Nanoparticles Generating Supramolecular Structures.

In the recent years, protein metabolite-based self-assembled supramolecular structures have been linked to various pathological disorders. The self-assembly of protein over nanoparticle surfaces can lead to the formation of corona aggregates that have gained much attention owing to biomedical healthcare relevance. However, limited studies are available at the interface of amyloid formation and nanoparticle surfaces. In this context, the present study demonstrated the effect of specifically functionalized gold nanoparticles on the potential amyloid formation by self-assembled aromatic amino acids. The coassembly of aromatic amino acids and gold nanoparticles was utilized to gain mechanistic insight into altered intermolecular interactions between amino acid monomers. The polymorphism, thermal stability, and morphological pattern of coassembled aromatic amino acids and gold nanoparticle (Co-AA:AuNP) structures were analyzed using X-ray diffraction, thermogravimetric analysis, and field emission scanning electron microscopy, respectively. Finally, amyloid like aggregation of Co-AA:AuNP structures were evaluated using thioflavin T fluorescence assay in solution as well as the deposited phase. The present work is crucial for the design and usage of nanoparticles in biomedical applications, which may trigger amyloid-like metabolite aggregation leading to pathological disorders.

Spectroscopic and structural studies, thermal characterization, optical proprieties and theoretical investigation of 2-aminobenzimidazolium tetrachlorocobaltate(II).

In this study we present the crystal structure, spectroscopic and thermal behavior, Hirshfeld surface analysis, and DFT calculations of a new organic-inorganic hybrid compound (C7H8N3)2[CoCl4]. This compound crystallizes in the centrosymmetric space group P1¯. Single-crystal X-ray diffraction analysis indicates that structure consists of a succession of mixed layers formed by organic cations and inorganic anions parallel to the (001) plane and propagate according to the c-axis. Layers further are assembled into a 3D supramolecular architecture through N-H…Cl hydrogen bonds and π…π interactions. The peak positions of the experimental PXRD pattern are in agreement with the simulated ones from the crystal structure, indicating phase purity of the title compound. The presence of the different functional groups and the nature of their vibrations were identified by ATR-FTIR and FT-Raman spectroscopies. The tetrahedral environment of Co2+ was confirmed by UV-visible spectroscopy, where the spectrum shows three weak absorption bands in the visible range due to d-d electronic transitions 4A2(F) → 4T2(F), 4A2(F) → 4T1(F) and 4A2(F) → 4T1(P) typical of Co(II) coordination compounds. The direct and indirect optical band gap values were determined by Tauc method. The optimized structure and calculated vibrational frequencies were obtained by density functional theory (DFT) using B3LYP functional. TGA and DSC coupled to mass spectrometry (MS) experiments under argon atmosphere in the temperature range (25-950 °C) were carried out in order to determine the thermal stability of the title compound.

Cryo-Electron microscopy for the study of self-assembled poly(ionic liquid) nanoparticles and protein supramolecular structures

Cryo-electron microscopy (cryo-EM) is a powerful structure determination technique that is well-suited to the study of protein and polymer self-assembly in solution. In contrast to conventional transmission electron microscopy (TEM) sample preparation, which often times involves drying and staining, the frozen-hydrated sample preparation allows the specimens to be kept and imaged in a state closest to their native one. Here, we give a short overview of the basic principles of Cryo-EM and review our results on applying it to the study of different protein and polymer self-assembled nanostructures. More specifically, we show how we have applied cryo-electron tomography (cryo-ET) to visualize the internal morphology of self-assembled poly(ionic liquid) nanoparticles and cryo-EM single particle analysis (SPA) to determine the three-dimensional (3D) structures of artificial protein microtubules.Grapical abstract

Polymerization of Self-Assembled Tetraazaporphyrins

Polymerization of self-assembled supramolecular structures considerably increases their often limiting thermal and chemical stability, which widens their potential application in commercial products. Particularly interesting for self-assembled materials is the topochemical polymerization of diacetylenes to polydiacetylenes because it can be initiated photochemically and thermally without the need for additives, it proceeds with minimal structural changes, and it generates new functionality since polydiacetylene is a 1-dimensional organic semiconductor and absorbs visible light. Polydiacetylenes have been generated in single crystals, gel phases, thin films, and membranes but their formation in mesophases, such as liquid crystals, has been surprisingly little studied although higher ordered mesophases should support the topochemical polymerization of diacetylenes (1,3-butadiyne groups) and may give access to large domains of uniformly aligned materials. Presented here are tetraazaporphyrins that contain eight alkyl chains with diacetylene groups to probe their mesomorphism and conversion into multifunctional polydiacetylene materials. While incorporation of diacetylene groups supports columnar mesomorphism, successful photopolymerization required the presence of directing amide groups that suppressed columnar in favour of nematic mesomorphism. Still, polymerization of the nematic mesophase generated a soluble nematic polydiacetylene of significantly higher molecular weight (Mn = 77 kDa or 25 monomer units by GPC) than what has been obtained in gel phases of related compounds. Formation of polydiacetylene was confirmed by Raman spectroscopy and its nematic structure was verified by UV-vis spectroscopy, polarized optical microscopy, and X-ray diffraction. Both, its nematic structure and the incorporation of eight side-chains per discotic unit provide the polydiacetylene with sufficient solubility for casting thin films on substrates. AFM studies of films casted onto silicon wafers revealed a grid-like structure of connected nanofibers.

UV-stabilized self-assembled amphiphilic triblock terpolymers supramolecular structures with low cytotoxicity as doxorubicin carriers.

Amphiphilic polystyrene-b-poly[(7-(Allyloxy)-2H-chromen-2-one)-co-(2-hydroxyethyl methacrylate)]-b-poly(2-(dimethylamino)ethyl methacrylate) (PS-b-P(AC-co-HEMA)-b-P(DMAEMA)) triblock terpolymers were synthesized by atom transfer radical polymerization (ATRP). PS-b-P(AC-co-HEMA)-b-PDMAEMA triblock terpolymers were characterized using proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC). The effect of various pH values on solution self-assembly behavior of PS-b-P(AC-co-HEMA)-b-P(DMAEMA) triblock terpolymers was investigated. Field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), fluorescence microscopy, and dynamic light scattering (DLS) were used to observe the size and morphology of the assembled triblock terpolymers. With altering pH value, different morphologies were obtained including spherical micelles, Janus snowman, and spherical Janus as well as cubic-hexagonal structures. UV light was used to stabilize the self-assembled morphologies and FE-SEM results showed that morphology remained unchanged after photo-dimerization. The self-assembled triblock terpolymers before and after photo-crosslinking were loaded with doxorubicin (DOX) and drug release behavior was examined at different conditions. Due to photo-crosslinking of self-assembled terpolymers, cumulative release was decreased. Thus, they might be more controllable drug carriers in drug delivery systems.

Three supramolecular trinuclear nickel(II) complexes based on Salamo-type chelating ligand: syntheses, crystal structures, solvent effect, Hirshfeld surface analysis and DFT calculation

Three Ni(II) complexes {[NiL(μ-OAc)(CH3CH2OH)]2Ni} (1), {[NiL(μ-OAc)(CH3OH)]2Ni]·2CH2Cl2·2CH3OH (2) and {[NiL(μ-OAc)(CH3OH)]2Ni}·1.5CH3OH (3) based on a Salamo-type bis-oxime ligand (H2L = 2,2′-[ethylenedioxybis(nitrilo-methylidyne)]dinaphthol) have been synthesized and characterized by physicochemical and spectroscopic methods. The complexes 1, 2 and 3 are all trinuclear structures, and the center Ni(II) ions are six-coordinated and show the slightly distorted octahedral coordination. They all consist of three Ni(II) ions, two deprotonated L2- units, two μ-acetato ligands and two coordinated solvent molecules, as well as the crystallizing solvent molecules. Although the molecular structures of the Ni(II) complexes 1, 2 and 3 are similar to each other, obtained in different solvents, the supramolecular structures are entirely different. The complexes 1, 2 and 3 possess the self-assembled infinite 1D, 3D and 2D supramolecular structures via different intermolecular interactions (hydrogen bonds, C–H···π and π···π stacking interaction), respectively. But complex 2 formed a 3D structures by intramolecular hydrogen bonds. It is significant that the solvent molecules have obvious effects on the optical properties and molecular configuration. The Hirshfeld surface analysis showed that the short-range forces of the hydrogen bonds in complexes 1, 2 and 3 accounted for 67.8%, 44.6% and 52.7%, respectively. The molecular orbital energies for ligand H2L and complex 1 were obtained by DFT calculation, and the electron distribution, energy level and energy gap of HOMO and LUMO were given.

Synthesis of ribonucleotides from the corresponding ribonucleosides under plausible prebiotic conditions within self-assembled supramolecular structures

Abiotic synthesis of ribonucleotides, mainly at the 5′ position, from the corresponding ribonucleosides within guanosine:borate hydrogels in the temperature range of 70–90 °C, using urea and a phosphate source (K2HPO4 or hydroxyapatite).

Retraction: Tri-s-triazine (s-heptazine), a novel electron-deficient core for soft self-assembled supramolecular structures.

Retraction of 'Tri-s-triazine (s-heptazine), a novel electron-deficient core for soft self-assembled supramolecular structures' by Irla Siva Kumar et al., Chem. Commun., 2017, 53, 11445-11448.

Formation of supramolecular hydrogen-bonding chains and networks from copper (II) halogenobenzoates with N-methylnicotinamide: Supramolecular isomerism

The self-assembly of supramolecular structures from copper (II) halogenobenzoate complexes containing N-methylnicotinamide ligand have been explored. The following compound and polymorph structures were determined by single-crystal X-ray structural analysis-the compounds [Cu(4-Fbz)2(mna)2(H2O)], [Cu(4-Clbz)2(mna)2(H2O)], [Cu(4-Brbz)2(mna)2(H2O)], two polymorphs of [Cu(2,6-Cl2bz)2(mna)2(H2O)2]·2H2O, [Cu(3,5-Cl2bz)2(mna)2(H2O)2]·2H2O, [Cu(3-Fbz)2(mna)2(H2O)2]·2H2O, and [Cu(3-Clbz)2(mna)2(H2O)2]·2H2O, two polymorphs of [Cu(3-Brbz)2(mna)2(H2O)2]·2H2O, [Cu(3-Ibz)2(mna)2(H2O)2]·2H2O, [Cu(2,5-Cl2bz)2(mna)2(H2O)2]·2H2O, [Cu(2,3-Cl2bz)2(mna)2(H2O)2]·H2O, [Cu(2,6-Cl2bz)2(mna)2(H2O)]·2H2O, [Cu(3,4-Cl2bz)2(mna)2(H2O)]·2H2O, [Cu(3-Brbz)2(mna)2(H2O)] and [Cu(2-Fbz)2(mna)2(μ-H2O)]n, (mna = N-methylnicotinamide, 4-Fbz = 4-fluorobenzoate, 4-Clbz = 4-chlorobenzoate, 4-Brbz = 4-bromobenzoate, 3-Fbz = 3-fluorobenzoate, 3-Clbz = 3-chlorobenzoate, 3-Brbz = 3-bromobenzoate, 3-Ibz = 3-iodobenzoate, 2-Ibz = 2-iodobenzoate, 2,3-Cl2bz = 2,3-dichlorobenzoate, 2,5-Cl2bz = 2,5-dichlorobenzoate, 2,6-Cl2bz = 2,6-dichlorobenzoate, 3,4-Cl2bz = 3,4-dichlorobenzoate and 3,5-Cl2bz = 3,5-dichlorobenzoate). The compounds are monomeric complexes with a distorted octahedral or square-pyramidal coordination sphere around Cu2+ ion. The two polymorph sets of [Cu(2,6-Cl2bz)2(mna)2(H2O)2]·2H2O and [Cu(3-Brbz)2(mna)2(H2O)2]·2H2O are two examples of coordination compounds which are conformation and supramolecular isomers. The crystal structure of complex [Cu(4-Fbz)2(mna)2(H2O)] shows the phase transition in two temperatures. The compound [Cu(2-Fbz)2(mna)2(μ-H2O)]n is a coordination polymer with bridging aqua ligand. The molecules of all compounds are connected by N–H…O and O–H…O hydrogen bonds from NHCH3 groups of N-methylnicotinamide and water molecules which create supramolecular hydrogen-bonding-coordination chains and networks. The intermolecular interactions were studied by Hirshfeld surface analysis.

Topochemical Polymerization of a Nematic Tetraazaporphyrin Derivative To Generate Soluble Polydiacetylene Nanowires.

Polydiacetylenes are well-established one-dimensional organic semiconductors that have been generated by photochemical and thermal polymerizations of diacetylenes in single crystals, gel phases, thin films, and membranes. Their formation in mesophases, such as liquid crystals, has been surprisingly little studied although higher-ordered mesophases should support the topochemical polymerization of diacetylenes (1,3-butadiyne groups) and may give access to large domains of uniformly aligned materials. The polymerization of diacetylenes in a mesophase may also increase the stability of the self-assembled supramolecular structure. Here, the dye and discotic mesogen tetraazaporphyrin was decorated with eight diacetylene-containing alkyl chains to probe its mesomorphism and conversion into multifunctional polydiacetylene materials. While the incorporation of diacetylene groups supports columnar mesomorphism, successful photopolymerization required the presence of directing amide groups that suppressed columnar in favor of nematic mesomorphism. Still, the polymerization of the nematic mesophase generated a soluble nematic polydiacetylene of significantly higher molecular weight (Mn = 77 kDa or 25 monomer units by gel permeation chromatography) than what has been obtained in gel phases of related compounds. The formation of polydiacetylene was confirmed by Raman spectroscopy, and its nematic structure was verified by UV-vis spectroscopy, polarized optical microscopy, and X-ray diffraction. Both its nematic structure and the incorporation of eight side chains per discotic unit provide the polydiacetylene with sufficient solubility for casting thin films on substrates. Atomic force microscopy studies of films on silicon wafers revealed a grid-like structure of connected nanofibers. This study demonstrates the requirements for the formation of multifunctional mesomorphic polydiacetylene materials from mesomorphic precursors and their advantages. Optimization of the presented molecular design should give access to other mesophases and, consequently, functional polydiacetylene materials with tunable structures and optoelectronic properties.

Self-Assembly Toolbox of Tailored Supramolecular Architectures Based on an Amphiphilic Protein Library.

The molecular structuring of complex architectures and the enclosure of space are essential requirements for technical and living systems. Self-assembly of supramolecular structures with desired shape, size, and stability remains challenging since it requires precise regulation of physicochemical and conformational properties of the components. Here a general platform for controlled self-assembly of tailored amphiphilic elastin-like proteins into desired supramolecular protein assemblies ranging from spherical coacervates over molecularly defined twisted fibers to stable unilamellar vesicles is introduced. The described assembly protocols efficiently yield protein membrane-based compartments (PMBC) with adjustable size, stability, and net surface charge. PMBCs demonstrate membrane fusion and phase separation behavior and are able to encapsulate structurally and chemically diverse cargo molecules ranging from small molecules to naturally folded proteins. The ability to engineer tailored supramolecular architectures with defined fusion behavior, tunable properties, and encapsulated cargo paves the road for novel drug delivery systems, the design of artificial cells, and confined catalytic nanofactories.

Size-dependent nonlinear forced oscillation of self-assembled nanotubules based on the nonlocal strain gradient beam model

Self-assembled protein micro/nanotubule has been aroused considerable interest as a self-assembled supramolecular structure with bioactive properties. The prime aim of this study is to predict size dependency in the nonlinear forced oscillation of the self-assembled nanotubules embedded in an elastic biomedium. To accomplish this end, the nonlocal strain gradient elasticity theory including both softening and stiffening features of size effect is applied to the refined hyperbolic shear deformable beam model. By using the principle of Hamilton, unconventional governing differential equations of motion have been extracted. Subsequently, generalized differential quadrature method in conjunction with the Galerkin technique is employed to solve the nonclassical problem numerically. The nonlocal strain gradient frequency response and amplitude response relevant to the primary resonance of the self-assembled nanotubules are obtained corresponding to different types of boundary conditions. It is anticipated that the nonlocal size effect causes to decrease the excitation amplitudes associated with both bifurcation points, but its effect on the first one is more considerable. However, the strain gradient size dependency has an opposite influence and leads to increase them. Furthermore, it is found that by changing the end supports from simply supported to clamped one, the influence of the nonlocality on the excitation amplitude associated with the bifurcation points increases, but the influence of the strain gradient size dependency decreases.

Self-Assembled Supramolecular Ribbon-Like Structures Complexed to Single Walled Carbon Nanotubes as Possible Anticancer Drug Delivery Systems.

Designing an effective targeted anticancer drug delivery method is still a big challenge, since chemotherapeutics often cause a variety of undesirable side effects affecting normal tissues. This work presents the research on a novel system consisting of single walled carbon nanotubes (SWNT), dispersed with Congo Red (CR), a compound that forms self-assembled ribbon-like structures (SRLS) and anticancer drug doxorubicin (DOX). SWNT provide a large surface for binding of planar aromatic compounds, including drugs, while CR supramolecular ribbon-like assemblies can be intercalated by drugs, like anthracycline rings containing DOX. The mechanism of interactions in SWNT–CR–DOX triple system was proposed based on electrophoretic, spectral, Dynamic Light Scattering and scanning electron microscopy analyzes. The profile of drug release from the investigated system was evaluated using dialysis and Differential Scanning Calorimetry. The results indicate that ribbon-like supramolecular structures of CR bind to SWNT surface forming SWNT–CR complexes which finally bind DOX. The high amount of nanotube-bound CR greatly increases the capacity of the carrier for the drug. The high capacity for drug binding and possible control of its release (through pH changes) in the analyzed system may result in prolonged and localized drug action. The proposed SWNT–CR–DOX triple system meets the basic criteria that justifies its further research as a potential drug carrier.

Surfactant-Induced Self-Assembly of CdTe Quantum Dots into Multicolor Luminescent Hybrid Vesicles.

Here, we report the interaction of mercaptosuccinic acid (MSA)-capped CdTe quantum dots (QDs) with hexadecyltrimethylammonium bromide (CTAB) surfactant and subsequent formation of self-assembled multicolor luminescent vesicles in aqueous medium. A continuous phase sequence from clear (C1) to turbid (T1), precipitate (P), turbid (T2), and clear (C2) has been observed for QD solution upon increasing the concentration of positively charged CTAB, indicating dynamic equilibrium between various self-assembled supramolecular structures. In contrast, no such changes have been observed in the presence of negatively charged sodium dodecyl sulfate and neutral Triton X-100 surfactants, indicating specific electrostatic interactions behind the observed phase separation behavior. Epi-fluorescence imaging in the C1 and C2 regions reveals the presence of surfactant-induced aggregates of QD. The morphologies and photoluminescence properties of self-assembled supramolecular structures in the T1 and T2 region have been explored by using scanning electron microscopy (SEM), atomic force microscopy (AFM), and confocal laser scanning microscopy (CLSM). SEM and AFM images reveal distinct spherical vesicles in the T1 and T2 regions of the binary mixture. Moreover, CLSM results show that these spherical vesicles are inherently luminescent due to the presence of self-assembled QDs. Fabrication of multicolor luminescent vesicles has been demonstrated by tuning the size of CdTe QD. Using CLSM, we have further demonstrated efficient encapsulation of Rhodamine 6G dye into these self-assembled vesicles without any structural disruption. While these luminescent vesicles are quite stable in neutral and basic pH (pH = 6.5-11), they are unstable in acidic pH (pH = 4.5-5.5). Moreover, it has been observed that this pH-responsive structural change is totally reversible. The present findings of self-assembled luminescent vesicles from QD-CTAB binary mixture may open up new opportunities in various applications such as bioimaging, drug delivery, and sensing.

Synthesis, crystallographic structure, Hirshfeld surface analysis and DFT calculations of two salen-type halogenated Schiff-base Ni(II) complexes

A detailed description of the crystal structure, Hirshfeld surface analysis and DFT calculations of two new salen-type halogenated Schiff-base Ni(II) complexes are reported. The crystallographic analysis indicates that halogen-atom play a key role in the formation and adjusting of self-assembled supramolecular dimer structures. Hirshfeld surface analysis also show that CH…X interactions are predominated the overall crystal packing. In order to gain a deep insight into the electronic features of the complex, density functional theory (DFT) was used for calculate HOMO and LUMO energies and molecular electrostatic potential of the title compounds. In addition, the variable temperature magnetic susceptibility measurements indicate that, probability due to a closer Ni…Ni distance, title compound exhibit weak ferromagnetic interactions at lower temperature.

Bottom-Up Self-Assembled Supramolecular Structures Built by STM at the Solid/Liquid Interface.

One of the lines of research on organic devices is focused on their miniaturization to obtain denser and faster electronic circuits. The challenge is to build devices adding atom by atom or molecule by molecule until the desired structures are achieved. To do this job, techniques able to see and manipulate matter at this scale are needed. Scanning tunneling microscopy (STM) has been the selected technique by scientists to develop smart and functional unimolecular devices. This review article compiles the latest developments in this field giving examples of supramolecular systems monitored and fabricated at the molecular scale by bottom-up approaches using STM at the solid/liquid interface.

Recent Developments of Supramolecular Metal-based Structures for Applications in Cancer Therapy and Imaging.

The biomedical application of discrete supramolecular metal-based structures, including supramolecular coordination complexes (SCCs), is still an emergent field of study. However, pioneering studies over the last 10 years demonstrated the potential of these supramolecular compounds as novel anticancer drugs, endowed with different mechanisms of action compared to classical small-molecules, often related to their peculiar molecular recognition properties. In addition, the robustness and modular composition of supramolecular metal-based structures allows for an incorporation of different functionalities in the same system to enable imaging in cells via different modalities, but also active tumor targeting and stimuli-responsiveness. Although most of the studies reported so far exploit these systems for therapy, supramolecular metal-based structures may also constitute ideal scaffolds to develop multimodal theranostic agents. Of note, the host-guest chemistry of 3D self-assembled supramolecular structures - within the metallacages family - can also be exploited to design novel drug delivery systems for anticancer chemotherapeutics. In this review, we aim at summarizing the pivotal concepts in this fascinating research area, starting with the main design principles and illustrating representative examples while providing a critical discussion of the state-of-the-art. A section is also included on supramolecular organometallic complexes (SOCs) whereby the (organic) linker is forming the organometallic bond to the metal node, whose biological applications are still to be explored. Certainly, the myriad of possible supramolecular metal-based structures and their almost limitless modularity and tunability suggests that the biomedical applications of such complex chemical entities will continue along this already promising path.