Cyclometalated and NNN Terpyridine Ruthenium Photocatalysts and Their Cytotoxic Activity

The cyclometalated terpyridine complexes [Ru(η2-OAc)(NC-tpy)(PP)] (PP = dppb 1, (R,R)-Skewphos 4, (S,S)-Skewphos 5) are easily obtained from the acetate derivatives [Ru(η2-OAc)2(PP)] (PP = dppb, (R,R)-Skewphos 2, (S,S)-Skewphos 3) and tpy in methanol by elimination of AcOH. The precursors 2, 3 are prepared from [Ru(η2-OAc)2(PPh3)2] and Skewphos in cyclohexane. Conversely, the NNN complexes [Ru(η1-OAc)(NNN-tpy)(PP)]OAc (PP = (R,R)-Skewphos 6, (S,S)-Skewphos 7) are synthesized in a one pot reaction from [Ru(η2-OAc)2(PPh3)2], PP and tpy in methanol. The neutral NC-tpy 1, 4, 5 and cationic NNN-tpy 6, 7 complexes catalyze the transfer hydrogenation of acetophenone (S/C = 1000) in 2-propanol with NaOiPr under light irradiation at 30 °C. Formation of (S)-1-phenylethanol has been observed with 4, 6 in a MeOH/iPrOH mixture, whereas the R-enantiomer is obtained with 5, 7 (50-52% ee). The tpy complexes show cytotoxic activity against the anaplastic thyroid cancer 8505C and SW1736 cell lines (ED50 = 0.31-8.53 µM), with the cationic 7 displaying an ED50 of 0.31 µM, four times lower compared to the enantiomer 6.

Terpyridine Functionalized Cyclodextrin Nanoparticles as Carriers for Doxorubicin: Analysis of In Vitro Antiproliferative Activity

BACKGROUND/AIM

We have recently described the development of cyclodextrin-based nanoparticles (NPs) functionalized with terpyridine and decorated with biotin-terpyridine ligands via Cu(II) and Fe(II) coordination. In the present study, we report the performance of these novel NPs as a delivery system for anticancer drugs. In particular, we analyzed the feasibility of loading these new NPs with the topoisomerase II inhibitor Doxorubicin (Doxo), still administered to patients to treat different forms of cancers. We developed Doxo-encapsulated polymeric NPS to generate nanoformulations with higher efficacy than free Doxo.

MATERIALS AND METHODS

We investigated the inhibition of cell proliferation in A2780, A549, SKHep1, and MDA-MB-453 cancer cell lines using the MTT assay.

RESULTS

NPs loaded with Doxo displayed higher antiproliferative activity than free Doxo.

CONCLUSION

The NPs generated in this study inhibited the proliferation of cancer cells and were able to entrap the classic anticancer drug Doxo. The Doxo-loaded NP showed increased cytotoxicity in comparison to free Doxo.

Urea-catalyzed N-Glycosylation of Amides/Azacycles with Glycosyl Halides

The efficient synthesis of N-glycosides via direct N-glycosylation of amides/azacycles has been reported. The glycosylation of amides/azacycles with glycosyl halides in the presence of a catalytic amount of urea proceeded smoothly to provide the corresponding N-glycosylated amides or nucleosides in good to excellent yields with 1,2-trans-stereoselectivity. Moreover, by the addition of terpyridine, the 1,2-cis-stereoselectivity was achieved.

Spin Crossover and Fluorine-Specific Interactions in Metal Complexes of Terpyridines with Polyfluorocarbon Tails

In coordination chemistry and materials science, terpyridine ligands are of great interest, due to their ability to form stable complexes with a broad range of transition metal ions. We report three terpyridine ligands containing different perfluorocarbon (PFC) tails on the backbone and the corresponding FeII and CoII complexes. The CoII complexes display spin crossover close to ambient temperature, and the nature of this spin transition is influenced by the length of the PFC tail on the ligand backbone. The electrochemical properties of the metal complexes were investigated with cyclic voltammetry revealing one oxidation and several reduction processes. The fluorine-specific interactions were investigated by EPR measurements. Analysis of the EPR spectra of the complexes as microcrystalline powders and in solution reveals exchange-narrowed spectra without resolved hyperfine splittings arising from the 59 Co nucleus; this suggests complex aggregation in solution mediated by interactions of the PFC tails. Interestingly, addition of perfluoro-octanol in different ratios to the acetonitrile solution of the sample resulted in the disruption of the F ⋯ ${\cdots }$ F interactions of the tails. To the best of our knowledge, this is the first investigation of fluorine-specific interactions in metal complexes through EPR spectroscopy, as exemplified by exchange narrowing.

Hourglass-Shaped Nanocages with Concaved Structures Based on Selective Self-Complementary Coordination Ligands and Tunable Hierarchical Self-Assembly

Three-dimensional (3D) structures constructed via coordination-driven self-assemblies have recently garnered increasing attention due to the challenges in structural design and potential applications. In particular, developing new strategy for the convenient and precise self-assemblies of 3D supramolecular structures is of utmost interest. Introducing the concept of self-coordination ligands, herein the design and synthesis of two meta-modified terpyridyl ligands with selective self-complementary coordination moiety are reported and their capability to assemble into two hourglass-shaped nanocages SA and SB is demonstrated. Within these 3D structures, the meta-modified terpyridyl unit preferably coordinates with itself to serve as concave part. By changing the arm length of the ligands, hexamer (SA) and tetramer (SB) are obtained respectively. In-depth studies on the assembly mechanism of SA and SB indicate that the dimers could be formed first via self-complementary coordination and play crucial roles in controlling the final structures. Moreover, both SA and SB can go through hierarchical self-assemblies in solution as well as on solid-liquid interface, which are characterized by transmission electron microscope (TEM) and scanning tunneling microscopy (STM). It is further demonstrated that various higher-order assembly structures can be achieved by tuning the environmental conditions.

Silver-based Terpyridine Complexes as Antitumor Agents

Silver complexes bearing substituted terpyridine or tetra-2-pyridinylpyrazine ligands have been prepared and structurally characterised. The study of the anticancer properties of silver complexes with this type of ligands is scarce, despite the possibilities of combining the properties of the metal and the ability of the ligands for DNA binding. Here, the antiproliferative activity, stability, CT-DNA binding and mechanism of cell death of these types of derivatives are studied. High cytotoxicity against different tumour cells was observed, and, more important, a great selectivity index has been detected between tumour cells and healthy Lymphocytes T for some of these compounds. The CT-DNA interaction study has shown that these derivatives are be able to interact with CT-DNA via moderate intercalation. Furthermore, cell death studies indicate that these derivatives promote the apoptosis via mitochondrial pathway.

A New Concept of Enhancing the Anticancer Activity of Manganese Terpyridine Complex by Oxygen-Containing Substituent Modification

Eleven manganese 4'-substituted-2,2':6',2″-terpyridine complexes (1a-1c and 2a-2h) with three non-oxygen-containing substituents (L^1a-L^1c: phenyl, naphthalen-2-yl and naphthalen-1-yl, L^1a-L^1c) and eight oxygen-containing substituents (L^2a-L^2h: 4-hydroxyl-phenyl, 3-hydroxyl-phenyl, 2-hydroxyl-phenyl, 4-methoxyl-phenyl, 4-carboxyl-phenyl, 4-(methylsulfonyl)phenyl, 4-nitrophenyl and furan-2-yl) were prepared and characterized by IR, elemental analysis or single crystal X-ray diffraction. In vitro data demonstrate that all of these show higher antiproliferative activities than cisplatin against five human carcinoma cell lines: A549, Bel-7402, Eca-109, HeLa and MCF-7. Compound 2d presents the strongest antiproliferative effect against A549 and HeLa cells, with IC₅₀ values being 0.281 μM and 0.356 μM, respectively. The lowest IC₅₀ values against Bel-7402 (0.523 μM) Eca-109 (0.514 μM) and MCF-7 (0.356 μM) were obtained for compounds 2h, 2g and 2c, respectively. Compound 2g with a nitro group showed the best results on the whole, with relevantly low IC₅₀ values against all the tested tumor cells. The DNA interactions with these compounds were studied by circular dichroism spectroscopic and molecular modeling methods. Spectrophotometric results revealed that the compounds have strong affinities in binding with DNA as intercalators, and the binding induces DNA conformational transition. Molecular docking studies indicate that the binding is contributed by the π-π stacking and hydrogen bonds. The anticancer activities of the compounds are correlated with their DNA binding ability, and the modification of oxygen-containing substituents significantly enhanced the anticancer activity, which could provide a new rationale for the future design of terpyridine-based metal complexes with antitumor potential.

Identification of Cadmium Compounds in a Solution Using Graphene-Based Sensor Array

Rapid detection of heavy metals in solution is necessary to ensure human health and environmental protection. Some heavy-metal compounds are present in solution as compounds instead of as ions owing to their low ionization. Therefore, the development of sensor devices for the detection of heavy-metal compounds is important. In this study, as a proof of concept, we propose a sensor device using graphene and a chelating agent, which were used to develop an identification technique for three types of cadmium compounds. Pristine-graphene and two types of chelator-modified graphene-based sensors were successfully used to detect cadmium compounds at concentrations ranging from 50 to 1000 μM. The detection time was less than 5 min. The three type of graphene-based sensors responded differently to each cadmium compound, which indicates that they detected cadmium as a cadmium compound instead of as cadmium ions. Furthermore, we successfully identified cadmium compounds by operating these three types of sensors as a sensor array on the same substrate. The results indicate that sensors that focus on heavy-metal compounds instead of heavy-metal ions can be used for the detection of heavy metals in solution.

Design of A3B-Porphyrin Conjugates with Terpyridine as Potential Theranostic Agents: Synthesis, Complexation with Fe(III), Gd(III), and Photodynamic Activity

This paper reports on the design and synthesis of new multifunctional porphyrin-based therapeutic agents for potential therapeutic and diagnostic applications. Zinc complexes of A3B-type meso-arylporphyrins containing OH- and COOH- groups were modified with chelating ligands based on 4'-(4-methylphenyl)-2,2':6',2″-terpyridine derivatives in high yields. Novel complexes with Gd(III), Fe(III) were obtained for these conjugates. Aggregation behaviour in solutions of different solubilisers was studied to inform the selection of the optimal solubilising platform for the porphyrins obtained; their photophysical and photochemical properties were also characterised. Micellar Pluronic F127 formulation was found to be the most effective solubiliser for stabilising the fluorescence-active monomolecular form of the photosensitisers (PS). In vitro cytotoxicity of the compounds was studied on the HEP-2 cell line with and without irradiation for 1.5 and 24 h. As a result, the IC50 of compounds 12 and 14 at an irradiation dose of 8.073 J/cm2 was shown to be 1.87 ± 0.333 and 1.4 ± 0.152 μM, respectively; without irradiation, the compound had no toxic effect within the studied concentration range (1.5 h). A test for the inhibition of metabolic cooperation or promoter activity was also performed for the abovementioned compounds, showing the efficacy and safety of the conjugates obtained. Preliminary data have indicated the high potential of the new type of PS to be promising molecular theranostic agents.

Shape-Dependent Complementary Ditopic Terpyridine Pair with Two Levels of Self-Recognition for Coordination-Driven Self-Assembly

Molecular recognition in biological systems plays a vital role in the precise construction of biomacromolecules and the corresponding biological activities. Such recognition mainly relies on the highly specific binding of complementary molecular pairs with complementary sizes, shapes, and intermolecular forces. It still remains challenging to develop artificial complementary motif pairs for coordination-driven self-assembly. Herein, a series of shape-dependent complementary motif pairs, based on ditopic 2,2':6',2″-terpyridine (TPY) backbone, are designed and synthesized. The fidelity degrees of self-assemblies from these motifs are carefully evaluated by multi-dimensional mass spectrometry, nuclear magnetic resonance spectroscopy, and molecular modeling. In addition, two levels of self-recognition in both homoleptic and heteroleptic assembly are discovered in the assembled system. Through finely tuning the shape and size of the ligands, a complementary pair is developed with error-free narcissistically self-sorting at two levels of self-recognition, and the intrinsic principle is carefully investigated.

Novel Metallo-Supramolecular Polymers with 1-Thioxophosphole Main-Chain Units and Remarkable Photoinduced Changes in Their Resonance Raman Spectra

New low-bandgap unimers, with the central thiophene-(1-thioxophosphole)-thiophene (TPT) ring sequence and 2,2':6',2″-terpyridin-4'-yl (tpy) end groups connected to the central unit via conjugated linkers of different size, are prepared and assembled with Zn(II) and Fe(II) ions to metallo-supramolecular polymers (MSPs) that are studied regarding their properties. The most interesting feature of Zn-MSPs is the luminescence extended deep into the NIR region. Fe-MSPs not only show the metal-to-ligand charge transfer (MLCT) manifested by the MLCT band (an expected feature) but also an as-yet-undescribed remarkable phenomenon: specific damping of the bands of the TPT sequence in the resonance Raman spectra taken from solid Fe-MSPs using the excitation to the MLCT band (532 nm). The damping is highly reversible at the low laser power of 0.1 mW but gradually becomes irreversible as the power reaches ca. 5 mW. The revealed phenomenon is not shown by the same Fe-MSPs in solutions, nor by Fe-MSPs containing no phosphole units. A hypothesis is proposed that explains this phenomenon and its dependence on the irradiation intensity as a result of the interplay of three factors: (i) enhancement of the MLCT process by excitation radiation, (ii) the electron-acceptor character of the 1-thioxophosphole ring, and (iii) morphological changes of the lattice and their dependence on the population of new structures in the lattice.

Terpyridine Diphosphine Ruthenium Complexes as Efficient Photocatalysts for the Transfer Hydrogenation of Carbonyl Compounds

The cationic achiral and chiral terpyridine diphosphine ruthenium complexes [RuCl(PP)(tpy)]Cl (PP=dppp (1), (R,R)-Skewphos (2) and (S,S)-Skewphos (3)) are easily obtained in 85-88 % yield through a one-pot synthesis from [RuCl₂ (PPh₃ )₃ ], the diphosphine and 2,2':6',2''-terpyridine (tpy) in 1-butanol. Treatment of 1-3 with NaPF₆ in methanol at RT affords quantitatively the corresponding derivatives [RuCl(PP)(tpy)]PF₆ (PP=dppp (1 a), (R,R)-Skewphos (2 a) and (S,S)-Skewphos (3 a)). Reaction of [RuCl₂ (PPh₃ )₃ ] with (S,R)-Josiphos or (R)-BINAP in toluene, followed by treatment with tpy in 1-butanol and finally with NaPF₆ in MeOH gives [RuCl(PP)(tpy)]PF₆ (PP=(S,R)-Josiphos (4 a), (R)-BINAP (5 a)) isolated in 78 % and 86 % yield, respectively. The chiral derivatives have been isolated as single stereoisomers and 3 a, 4 a have been characterized by single crystal X-ray diffraction studies. The tpy complexes with NaOiPr display high photocatalytic activity in the transfer hydrogenation (TH) of carbonyl compounds using 2-propanol as the only hydrogen donor and visible light at 30 °C, at remarkably high S/C (up to 5000) and TOF values up to 264 h^-1 . The chiral enantiomers 2, 2 a and 3, 3 a induce the asymmetric photocatalytic TH of acetophenone, affording (S)- and (R)-1-phenylethanol with 51 and 52 % ee, respectively, in a MeOH/2-propanol mixture.

Multi-Decker Emissive Supramolecular Architectures Based on Shape-Complementary Ligands Pair

Dye aggregates have attracted a great deal of attention due to their widespread applications in organic light-emitting devices, light-harvesting systems, etc. However, the strategies to precisely control chromophores with specific spatial arrangements still remain a great challenge. In this work, a series of double- and triple-decker supramolecular complexes are successfully constructed by coordination-driven self-assembly of carefully designed shape-complementary ligands, one claw-like tetraphenylethylene (TPE)-based host ligand and three tetratopic or ditopic guest ligands. The spatial configurations of these assemblies (one double-decker and three "S-shaped" or "X-shaped" triple-decker structures) depend on the angles of these TPE-derived ligands. Notably, the three triple-decker structures are geometric isomers. Furthermore, photophysical studies show that these complexes exhibit different ratios of radiative (k_r ) and non-radiative (k_nr ) rate constant due to the different spatial arrangements of TPE moieties. This study provides not only a unique strategy for the construction of multi-stacks with specific spatial arrangement, but also a promising platform for investigating the aggregation behavior of fluorescent chromophores.

Fuzzy Logic, Artificial Neural Network, and Adaptive Neuro-Fuzzy Inference Methodology for Soft Computation and Modeling of Ion Sensing Data of a Terpyridyl-Imidazole Based Bifunctional Receptor

Anion and cation sensing aspects of a terpyridyl-imidazole based receptor have been utilized in this work for the fabrication of multiply configurable Boolean and fuzzy logic systems. The terpyridine moiety of the receptor is used for cation sensing through coordination, whereas the imidazole motif is utilized for anion sensing via hydrogen bonding interaction and/or anion-induced deprotonation, and the recognition event was monitored through absorption and emission spectroscopy. The receptor functions as a selective sensor for F^- and Fe²⁺ among the studied anions and cations, respectively. Interestingly, the complexation of the receptor by Fe²⁺ and its decomplexation by F^- and deprotonation of the receptor by F^- and restoration to its initial form by acid are reversible and can be recycled. The receptor can mimic various logic operations such as combinatorial logic gate and keypad lock using its spectral responses through the sequential use of ionic inputs. Conducting very detailed sensing studies by varying the concentration of the analytes within a wide domain is often very time-consuming, laborious, and expensive. To decrease the time and expenses of the investigations, soft computing approaches such as artificial neural networks (ANNs), fuzzy logic, or adaptive neuro-fuzzy inference system (ANFIS) can be recommended to predict the experimental spectral data. Soft computing approaches to artificial intelligence (AI) include neural networks, fuzzy systems, evolutionary computation, and other tools based on statistical and mathematical optimizations. This study compares fuzzy, ANN, and ANFIS outputs to model the protonation-deprotonation and complexation-decomplexation behaviors of the receptor. Triangular membership functions (trimf) are used to model the ANFIS methodology. A good correlation is observed between experimental and model output data. The testing root mean square error (RMSE) for the ANFIS model is 0.0023 for protonation-deprotonation and 0.0036 for complexation-decomplexation data.

Terpyridine-Based 3D Discrete Metallosupramolecular Architectures

Terpyridine (tpy)-based 3D discrete metallosupramolecular architectures, which are often inspired by polyhedral geometry and the biological structures found in nature, have drawn significant attention from the community of metallosupramolecular chemistry. Because of the linear tpy-M(II)-tpy connectivity, the creation of sophisticated 3D metallosupramolecules based on tpy remains a formidable synthetic challenge. Nevertheless, with recent advancement in ligand design and self-assembly, diverse 3D metallosupramolecular polyhedrons, such as Platonic solids, Archimedean solids, prims as well as Johnson solids, have been constructed and their potential applications have been explored. This review summarizes the progress on tpy-based discrete 3D metallosupramolecules, aiming to shed more light on the design and construction of novel discrete architectures with molecular-level precision through coordination-driven self-assembly.

Self-Assembly Methods for Recently Reported Discrete Supramolecular Structures Based on Terpyridine

In this Review, self-assembly methods of discrete metallo-supramolecules based on 2,2' : 6',2''-terpyridine (tpy) are comprehensively summarized. With the development of self-assembly, strategies for discrete 2D and 3D supramolecular architectures have boomed, including the geometry-directed method, template-driven method, and stepwise method. Ligand geometry-directed method mainly depends on the geometry of ligands (i. e., angle, geometric strain, and rigidity), and it is suitable for dual-component systems, while the template-driven method can guide the self-assembly of predesigned supramolecules by the introduction of specific templates. Meanwhile, stepwise method, breaking the inherent self-sorting of ligands and reducing the probability of mismatch, is suitable for multicomponent systems to yield predesigned supramolecules. This review focuses on self-assembly methods and aims to provide a guideline for constructing supramolecular architectures using a suitable approach.

Rhodium-terpyridine Catalyzed Transfer Hydrogenation of Aromatic Nitro Compounds in Water

A rhodium terpyridine complex catalyzed transfer hydrogenation of nitroarenes to anilines with i-PrOH as hydrogen source and water as solvent has been developed. The catalytic system can work at a substrate/catalyst (S/C) ratio of 2000, with a turnover frequency (TOF) up to 3360 h^-1 , which represents one of the most active catalytic transfer hydrogenation systems for nitroarene reduction. The catalytic system is operationally simple and the protocol could be scaled up to 20 gram scale. The water-soluble catalyst bearing a carboxyl group could be recycled 15 times without significant loss of activity.

Synthesis and Characterization of Metallo-Supramolecular Polymers Based on Benzodipyrrolidone

A simple route to the preparation of benzodipyrrolidone (BDP) based monomeric building blocks containing 2,2':6',2″-terpyridines is reported from a common precursor 4'-(4-pinacolatoboronphenyl)-2,2':6',2″-terpyridine via Suzuki coupling reaction. Self-assembly polymerization with ruthenium (II) ions under mild conditions yielded a series of novel metallo-supramolecular polymers with weak donor-acceptor (D-A) structures based on benzodipyrrolidone. The structure of the bridge connected BDP with terpyridine have a significant impact on the wavelength and intensity of the intramolecular charge transfer (ICT) absorption peak. The resulting metallo-polymers exhibited strong double absorption bands around 315 nm and 510 nm involved in π-π* transitions and ICT or metal to ligand charge transfer (MLCT) absorption bands. The forming of D-A structure and coordination with ruthenium (II) ions is favorable to narrow the energy gap and the energy gaps of the resulting metallo-supramolecular polymers are 2.01 and 1.62 eV, respectively.

Synthesis of Bis-Terpyridine-Based Metallopolymers and the Thermoelectric Properties of Their Single Walled Carbon Nanotube Composites

Although the organic and the conventional inorganic thermoelectric (TE) materials have been extensively developed in recent years, the number of cases involving conducting metallopolymers is still quite limited. In view of the versatile coordination capability of the terpyridine fraction and the electron-rich nature of the 3,4-ethylenedioxythiophene moiety, a bis-terpyridine-featured ligand was designed, and a series of metallopolymers were then synthesized. Upon the addition of single-walled carbon nanotube (SWCNT), the TE properties of the resulting metallopolymer-SWCNT composite films were investigated. It was found that metal centres played an important role in affecting the morphology of the thin films, which was a key factor that determined the TE performances of the composites. Additionally, the energy levels of the metallopolymers were feasibly tuned by selecting different metal centres. With the combined effects of a uniform and condensed surface and an optimized band structure, the highest power factor was achieved by the Cu(II)-containing metallopolymer-SWCNT composite at the doping ratio of 75%, which reached 38.3 μW·m-1·K-2.

Iron (II) Metallo-Supramolecular Polymers Based on Thieno[3,2-b]thiophene for Electrochromic Applications

Four new bis(tpy) unimers with different linkers between the thieno[3,2-b]thiophene-2,5-diyl central unit and terpyridine-4′-yl (tpy) end-groups: no linker (Tt), ethynediyl (TtE), 1,4-phenylene (TtPh) and 2,2′-bithophene-5,5′-diyl (TtB) are prepared, characterized, and assembled with Fe²⁺ ions to metallo-supramolecular polymers (Fe-MSPs). The Fe-MSP films prepared by spin-casting on Indium Tin Oxide (ITO) glass are characterized by atomic force microscope (AFM) microscopy, cyclic voltammetry, and UV/vis spectroscopy and studied for their electrochromism and effect of the unimer structure on their electrochromic performance. Of the studied MSPs, Fe-Tt shows the highest optical contrast as well as coloration efficiency (CE = 641 cm² C⁻¹) and the fastest optical response. This makes it an excellent candidate for possible use in electrochromic devices.

Synthesis of Terpyridine End-Modified Polystyrenes through ATRP for Facile Construction of Metallo-Supramolecular P3HT-b-PS Diblock Copolymers

Complementary complexation between 2,2':6',2″-terpyridine (tpy) and 6,6″-dianthracenyl-substituted tpy in the presence of Zn(II) ions provided an efficient strategy for construction of metallo-supramolecular diblock copolymers. To synthesize well-defined tpy-modified polystyrenes (PSs), an Fe(II) bis(tpy) complex bearing α-bromoester as a metallo-initiator was applied to atom transfer radical polymerization (ATRP) to avoid poisoning the Cu(I) catalyst. Subsequently, a series of tpy-functionalized PSs was obtained after the decomplexation of junction by tetrakis(triethylammonium) ethylenediaminetetraacetate (TEA-EDTA) under mild conditions. The metallo-supramolecular poly(3-hexylthiophene) (P3HT)-block-PS diblock copolymers were prepared by simply mixing the corresponding terminally tpy-modified homopolymers with Zn(II) ions, and further characterized by 1H NMR and diffusion ordered spectroscopy (DOSY) experiments. The approach using metallo-initiators for ATRP offers an opportunity to construct tpy-functionalized polymers with controllable molecular weights and low polydispersities. Through the spontaneous heteroleptic complexation, a variety of metallo-supramolecular diblock copolymers with tunable block ratios can be easily constructed.

Metallo-Helicoid with Double Rims: Polymerization Followed by Folding by Intramolecular Coordination

In this study, we established a feasible strategy to construct a new type of metallo-polymer with helicoidal structure through the combination of covalent polymerization and intramolecular coordination-driven self-assembly. In the design, a tetratopic monomer (M) was prepared with two terminal alkynes in the outer rim for polymerization, and two terpyridines (TPYs) in the inner rim for subsequent folding by selective intramolecular coordination. Then, the linear covalent polymer (P) was synthesized by polymerization of M via Glaser-Hay homocoupling reaction. Finally, intramolecular coordination interactions between TPYs and Zn(II) folded the backbone of P into a right- or left-handed metallo-helicoid (H) with double rims. Owing to multiple positive charges on the inner rim of helicoid, double-stranded DNA molecules (dsDNA) could interact with H through electrostatic interactions. Remarkably, dsDNA allowed exclusive formation of H with right handedness by means of chiral induction.

Synthesis of an Alternated Heterobimetallic Supramolecular Polymer Based on Ru(II) and Fe(II)

A heterobimetallic supramolecular polymer (polyRuFe) with alternately complexed Ru(II) and Fe(II) is prepared following a stepwise synthetic route through harnessing first the strongly binding metal ion Ru(II) and then the weakly binding metal ion Fe(II). A high yield of product is achieved in each step. The heterometal ions are incorporated into the polymer chain in identical coordination environments formed by two 2,2′:6′,2″-terpyridine moieties. Characterization is accomplished by NMR spectroscopy, MALDI–TOF mass spectrometry, UV–Vis spectroscopy, and cyclic voltammetry. PolyRuFe shows a wide optical window (λ = 311–577 nm) and a broad distinct reversible redox nature of two types, originated from the coupling of the two heterometallic segments into the polymer chain. Such characteristics of polyRuFe suggest its potential for various electrochemical and electro-optical applications.

Terpyridine-metal complexes: effects of different substituents on their physico-chemical properties and density functional theory studies

A series of different substituted terpyridine (tpy)-based ligands have been synthesized by Kröhnke method. Their binding behaviour was evaluated by complexing them with Co(II), Fe(II) and Zn(II) ions, which resulted in interesting coordination compounds with formulae, [Zn(tpy)₂]PF₆, [Co(tpy)₂](PF₆)₂, [Fe(tpy)₂](PF₆)₂ and interesting spectroscopic properties. Their absorption and emission behaviours in dilute solutions were investigated in order to explain structure-property associations and demonstrate the impact of different aryl substituents on the terpyridine scaffold as well as the role of the metal on the complexes. Photo-luminescence analysis of the complexes in acetonitrile solution revealed a transition from hypsochromic to bathochromic shift. All the compounds displayed remarkable photo-luminescent properties and various maximum emission peaks owing to the different nature of the functional groups. Furthermore, the anti-microbial potential of ligands and complexes was evaluated with docking analyses carried out to investigate the binding affinity of terpyridine-based ligands along with corresponding proteins (shikimate dehydrogenase and penicillin-binding protein) binding sites. To obtain further insight into molecular orbital distributions and spectroscopic properties, density functional theory calculations were performed for representative complexes. The photophysical activity and interactions between chromophore structure and properties were both investigated experimentally as well as theoretically.

Terpyridine-Containing π-Conjugated Polymers for Light-Emitting and Photovoltaic Materials

2,2':6',2″-Terpyridine (tpy) is a versatile moiety used in the construction of small novel molecules or polymers. Extending or coupling tpy with π-conjugation structures can result in interesting optoelectronic properties. This mini-review summarizes the significant progress made over the past decades in the study of tpy-containing π-conjugated polymers and their application in light-emitting and photovoltaic materials. When coordinated with metal ions, tpy exhibits immense potential for the synthesis of metallo-supramolecular or metallo-polymer materials. Therefore, tpy-based metallo-polymers are the primary focus of this study. Selected examples will be reviewed with a special emphasis on the properties of these functional systems, which can consequently help further their application in light-to-electricity or electricity-to-light conversion fields.

Multichromic Monolayer Terpyridine-Based Electrochromic Materials

The article describes novel electrochromic materials (ECMs) that are based on a monolayer consisting of two or three isostructural metal complexes of 4'-(pyridin-4-yl)-2,2':6',2''-terpyridine simultaneously deposited on surface-enhanced support. The support was made by screen printing of indium tin oxide (ITO) nanoparticles on ITO-glass and has a surface area sufficient for a monolayer to give color visible to the naked eye. The ability to separately electrochemically address the oxidation state of the metal centers on the surface (i.e., Co²⁺/Co³⁺, Os²⁺/Os³⁺, and Fe²⁺/Fe³⁺) provides an opportunity to achieve several distinct color-to-color transitions, thus opening the door for constructing monolayer-based multicolor ECMs.

From Dimeric to Octameric Metallo-Supramolecular Macrocycles Based on Sterically Congested Ligand-assisted Self-Assembly with Zn(II), Cd(II), and Fe(II)

Two sterically congested 2,2':6',2″-terpyridine-based ligands LA and LB, composed of asymmetrically contiguous terpyridine units, are designed and synthesized for metallo-supramolecular architectures. The significant advantage of this design is that the terpyridines in these ligands have different chemical environments and show a selective coordination ability with each other. For ditopic ligand LA, the self-assembly with Zn(II), Cd(II), and Fe(II) gave the rhombic dimers, which have the same sets of terpyridine signals as ligand LA. The self-assembly behavior of tritopic ligand LB with Cd(II) and Zn(II) are observed for discrete tetramers under thermodynamic control, whereas ligand LB and Fe(II) are assembled to generate a mixture of tetramer, hexamer, and octamer, which are successfully isolated using regular chromatographic separation. Moreover, the sterically congested ligands and metal ions formed stable intermediates to drive the formation of discrete structures, which is also proved by mixing LB and Cd(II) with a precise stoichiometric ratio of 1:1. These supramolecular complexes are thoroughly characterized by NMR spectroscopy, electrospray ionization-mass spectrometry, and 2D traveling-wave ion mobility-mass spectrometry. This conceptually new design of sterically congested ligands provides a novel strategy for precisely controlled supramolecular complexes with diverse architectures.

A Tetrakis(terpyridine) Ligand-Based Cobalt(II) Complex Nanosheet as a Stable Dual-Ion Battery Cathode Material

Inspired by the flexibility of the bottom-up approach in terms of selecting molecular components and thus tailoring functionalities, a terpyridine derivative (1,2,4,5-tetrakis(4-(2,2':6',2″-terpyridyl)phenyl)benzene) (Tetra-tpy) is synthesized and coordinated with Co(II) ion to self-assemble into a nanosheet Co-sheet by a facile interface-assisted synthesis. The bis(terpyridine)-Co(II) complex nanosheet formed not only shows good stability, but also features the layered structure and rich electrochemical activity inherited from the embedded Co(terpyridine)₂ motif. Thus, Co-sheet can serve as a cathode material for a dual-ion battery prototype, which exhibits a high utilization of redox-active sites, good cycling stability, and rate capability, thus expanding the potential application of this kind of easily prepared metal-complex nanosheets in the field of energy storage.

Constructing Alternated Heterobimetallic [Fe(II)/Os(II)] Supramolecular Polymers with Diverse Solubility for Facile Fabrication of Voltage-Tunable Multicolor Electrochromic Devices

Metallo-supramolecular polymer (MSP)-based electrochromic devices (ECDs) have drawn much attention because of their variable colors and attractive electrochromic (EC) properties. However, fabrication of voltage-tunable multicolor ECDs using single MSP is yet hard to realize. We anticipated alternate introduction of two different redox-active metal ions in an MSP combined with the adjustment of counteranions could be a solution to fabricate multicolor ECDs. The heterometals will induce color variability upon voltage alteration, and counteranions will help to tune the solubility of MSP in different solvents. In an attempt to fulfill this target, we have synthesized four heterobimetallic supramolecular polymers (HBPs) having different counteranions (BF₄^-, Cl^-, PF₆^-, and OAc^-), in which Fe(II) and Os(II) are alternately complexed by two terpyridine units. To apply as EC material, the HBPs should be soluble in methanol and insoluble in acetonitrile for the preparation of EC film as well as ECDs. However, among the HBPs, only HBP-OAc is found to meet this requirement. The EC behaviors of the spray-coating film of HBP-OAc on an indium tin oxide (ITO)-coated glass substrate are investigated in terms of maximum transmittance contrast, coloration voltage, response time, coloration efficiency, and operational stability, which exhibits reversible multicolor electrochromism (the initial purple color of the film is changed to violet followed by greenish-yellow) upon alteration of the voltage from 0.0 to 0.7 V [required to oxidize the Os(II) ion] and to 1.0 V [required to oxidize the Fe(II) ion]. The film is also integrated into a laminated ECD by using lithium-based gel electrolyte. Finally, as a proof-of-concept, a prototype voltage-tunable multicolor EC display (6 cm × 2.5 cm) is fabricated by using a designed image containing a flower, leaves, and a flower pot, which exhibits six different types of multicolor image upon application of tunable voltages.

Cobalt Catalyzed C-P Bond Formation by Cross-Coupling of Boronic Acids with P(O)H Compounds in Presence of Zinc

In our current work, we have reported the first cobalt-catalyzed cross-coupling of arylboronic acid with alkyl/aryl phosphites under mild conditions. The reaction was carried out in the presence of zinc powder as an additive and ter-pyridine as a ligand. The use of non-precious cobalt salt makes the protocol advantageous, as it is inexpensive and more abundant than the previously used methods where precious metal salts (Pd and Pt) were used. The reaction has a wide substrate scope and the products were obtained in good yields.

A turn-off fluorescence probe based on terpyridine for pH monitoring

A new pH-dependent fluorescence probe 2,8-bis((E)-4-([2,2':6',2″-terpyridin]-4'-yl)styryl)-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine (TBPTP) based on Tröger's base (TB) bound to terpyridine was designed and synthesized. Photophysical properties and titration experiments of TBPTP were investigated by absorption and fluorescence spectroscopy. TBPTP exhibited high sensitivity in an acidic environment with the working pH range 7.2-2.5, especially having a good liner response to pH changes in the range 2.5-4.3, which suggested that TBPTP is a good candidate for pH monitoring.

Self-assembly of emissive metallocycles with tetraphenylethylene, BODIPY and terpyridine in one system

Tetraphenylethylene (TPE) related (supra)molecules have been intensively investigated due to their aggregation-induced emission (AIE) effect based on the restriction of intramolecular rotation (RIR). Meanwhile, boron-dipyrromethene (BODIPY) tends to emit intense fluorescence with high quantum yields. Herein, we combined TPE, BODIPY and terpyridine (TPY) into one system to study the emissive behaviour of organic building block as well as a self-assembled metallo-supramolecule. The TPY and BODIPY substituents with bulky sizes provide strong hindrance to restrict the rotation of the phenyl groups on TPE, leading to enhancement of emissive properties in both solution and aggregation states. Furthermore, the BODIPY-TPE-TPY ligand (L) was assembled with Zn (II) through coordination-driven self-assembly to form a cyclic dimer (D) with typical AIE characteristics.

Metallo-Supramolecular Hydrogels from the Copolymers of Acrylic Acid and 4-(2,2':6',2″-terpyridin-4'-yl)styrene

Hydrophilic copolymers containing 2,2′:6′,2″-terpyridine moieties and acrylic acid (AA) units poly (acrylic acid-co-4-(2,2′:6′,2″-terpyridin-4′-yl)styrene) (P(AA-co-TPY)) were synthesized and characterized. Coordinated with different transition metal ions, the dilute aqueous solution of the copolymers exhibited red-shifted UV-vis absorption peaks of π-π* transition from 317 to 340 nm. Further, interacting with iron ions, the copolymer showed new absorption peaks at a longer wavelength region (570 nm) and the absorption intensity enhanced with increase of the ion concentration. When enough ions were added to coordinate with the 2,2′:6′,2″-terpyridine moieties, novel metallo-supramolecular hydrogels were obtained due to the formation of metal coordination bonds between polymer back bones and transition metal ions (Ni²⁺, Zn²⁺, Cd²⁺, Fe²⁺ and Cu²⁺), which acted as self-assembly crosslinking structures. The mechanical strength and morphology of the resulting metallo-supramolecular hydrogels have been investigated.

Synthesis of Terpyridine-Terminated Amphiphilic Block Copolymers and Their Self-Assembly into Metallo-Polymer Nanovesicles

Polystyrene-b-polyethylene glycol (PS-b-PEG) amphiphilic block copolymers featuring a terminal tridentate N,N,N-ligand (terpyridine) were synthesized for the first time through an efficient route. In this approach, telechelic chain-end modified polystyrenes were produced via reversible addition-fragmentation chain-transfer (RAFT) polymerization by using terpyridine trithiocarbonate as the chain-transfer agent, after which the hydrophilic polyethylene glycol (PEG) block was incorporated into the hydrophobic polystyrene (PS) block in high yields via a thiol-ene process. Following metal-coordination with Mn2+, Fe2+, Ni2+, and Zn2+, the resulting metallo-polymers were self-assembled into spherical, vesicular nanostructures, as characterized by dynamic light scattering and transmission electron microscopy (TEM) imaging.

The enrichment ratio of atomic contacts in the crystal structure of isomeric, triply protonated, 4'-functionalized terpyridine cations with [ZnCl4]2- as counter-ion

We report herein the synthesis, crystallographic analysis and a study of the non-covalent inter-actions observed in the new 4'-substituted terpyridine-based derivative bis-[4'-(isoquinolin-2-ium-4-yl)-4,2':6',4''-terpyridine-1,1''-diium] tris-[tetra-chlorido-zincate(II)], (C24H19N4)2[ZnCl4]3 or (44TPH3)2[ZnCl4]3, where (44TPH3)3+ is the triply protonated cation 4'-(isoquinolinium-4-yl)-4,2':6',4'' terpyridinium. The compound is similar in its formulation to the recently reported 2,2':6',2'' terpyridinium analogue {bis-[4'-(isoquinolin-2-ium-4-yl)-2,2':6',2''-terpyridine-1,1''-diium] tris-[tetra-chlorido-zincate(II)] monohydrate; Granifo et al. (2017 ▸). Acta Cryst. C73, 1121-1130}, although rather different and much simpler in its structural features, mainly in the number and type of non-covalent inter-actions present, as well as in the supra-molecular structure they define.

Stepwise Self-Assembly and Dynamic Exchange of Supramolecular Nanocages Based on Terpridine Building Blocks

Coordination-driven self-assembly as a powerful bottom-up approach has been extensively used to construct multifarious supramolecular architectures with increasing complexity and functionality. Due to the unique cavity structures and precisely controllable dimensions, 3D supramolecules display unprecedented properties and functions in catalysis, sensing, gas storage, and smart materials. Herein, we have built two 3D nanocages with different sizes by changing the length of the organic ligand arms. The structures were characterized by 1D and 2D NMR spectroscopy, electrospray ionization-mass spectrometry (ESI-MS), traveling wave ion mobility-mass spectrometry (TWIM-MS), gradient tandem-mass spectrometry (gMS2 ), and transmission electron microscopy (TEM). Furthermore, the intermolecular dynamic exchange of two 3D nanocages was conducted to construct a series of hybrid 3D structures as evidenced by mass spectrometry.

Reversible Assembly of Terpyridine Incorporated Norbornene-Based Polymer via a Ring-Opening Metathesis Polymerization and Its Self-Healing Property

We induced a terpyridine moiety into a norbornene-based polymer to demonstrate its self-healing property, without an external stimulus, such as light, heat, or healing agent, using metal⁻ligand interactions. We synthesized terpyridine incorporated norbornene-based polymers using a ring-opening metathesis polymerization. The sol state of diluted polymer solutions was converted into supramolecular assembled gels, through the addition of transition metal ions (Ni2+, Co2+, Fe2+, and Zn2+). In particular, a supramolecular complex gel with Zn2+, which is a metal with a lower binding affinity, demonstrated fast self-healing properties, without any additional external stimuli, and its mechanical properties were completely recovered.

Vertical Assembly of Giant Double- and Triple-Decker Spoked Wheel Supramolecular Structures

The double- or triple-decker 3D metallo-hexagons were obtained by self-assembly of multitopic tris-terpyridines with Cd2+ ions in near-quantitative yield. Comprising up to 72 ionic pairs, the multiple spoked wheels display characteristic reversible gelation properties under thermodynamic conditions. The supramolecular metallo-nanoarchitectures were characterized by 1 H NMR, 2D NMR (COSY and NOESY), and diffusion-ordered spectroscopy (DOSY) and HR-ESI-MS, traveling-wave ion mobility mass spectrometry (TWIM-MS), TEM, and AFM. For the first time, the self-assembly of 45 units at once was demonstrated to yield exceptional giant triple-decker hexagons of up to circa 42 000 Da.

Synthesis and Guest Recognition of Switchable Pt-Salphen Based Molecular Tweezers

Molecular tweezers are artificial receptors that have an open cavity generated by two recognition units pre-organized by a spacer. Switchable molecular tweezers, using a stimuli-responsive spacer, are particularly appealing as prototypes of the molecular machines that combine mechanical motion and allosteric recognition properties. In this present study, the synthesis of switchable molecular tweezers composed of a central terpyridine unit substituted in 4,4″ positions by two Pt(II)-salphen complexes is reported. The terpyridine ligand can be reversibly converted upon Zn(II) coordination from a free ‘U’-shaped closed form to a coordinated ‘W’ open form. This new substitution pattern enables a reverse control of the mechanical motion compared to the previously reported 6,6″ substituted terpyridine-based tweezers. Guest binding studies with aromatic guests showed an intercalation of coronene in the cavity created by the Pt-salphen moieties in the closed conformation. The formation of 1:1 host-guest complex was investigated by a combination of NMR studies and DFT calculations.

An infinite two-dimensional hybrid water-chloride network in a 4'-(furan-2-yl)-2,2':6',2''-terpyridine nickel(II) matrix

An unprecedented two-dimensional water–chloride anionic {[(H₂O)₁₀Cl₂]²⁻}_n network has been structurally identified in a hydro­phobic matrix of the nickel(II) complex [Ni(ftpy)₂]Cl₂·10H₂O [ftpy = 4′-(furan-2-yl)-2,2′:6′,2′′-terpyridine].

A new complex, namely bis­[4′-(furan-2-yl)-2,2′:6′,2′′-terpyridine]­nickel(II) dichloride deca­hydrate, [Ni(C₁₉H₁₃N₃O)₂]Cl₂·10H₂O, has been crystallized by solvent evaporation and characterized by single-crystal X-ray diffraction. The coordination environment of the Ni^II cation is distorted octa­hedral with slight deviations from an idealized geometry. The most intriguing structural feature is an infinite two-dimensional hybrid water–chloride network parallel to (011) constructed by O—H⋯O and O—H⋯Cl hydrogen bonds involving two independent chloride ions and ten independent solvent water mol­ecules with an l-shaped pattern. One of the furyl rings is disordered with a refined occupancy ratio of 0.786 (13):0.214 (13)

Remote Terpyridine Integrated NHC-IrIII Luminophores as Potential Dual-Emissive Ratiometric O2 Probes

A new class of bi-luminophoric dyad has been designed, consisting of an oxygen-sensitive phosphorescent NHC-Ir^III center with a remotely integrated oxygen-insensitive fluorescent terpyridine unit. The new terpyridine flurophore-integrated NHC-Ir^III molecule was demonstrated as a potential ratiometric O₂ probe with built-in internal reference, exhibiting tunable dual-emissive features, as well as highly linear and reversible O₂ -response behavior.

Transition-Metal-Free Oxidative C(sp2 )-H Hydroxylation of Terpyridines: A HOMO-Raising Strategy for the Construction of a New Super-Stable Terpyridine Chromophores

Direct functionalization of terpyridines is an increasingly important topic in the field of dyes and catalysis as well as supramolecular chemistry, but its synthesis and transformation is usually challenging. Herein, a HOMO-raising strategy is reported for the construction of a super-stable novel terpyridine chromophores, in which the selective oxidation of terpyridines at its 3-position was determined successfully to the synthesis of phenol-functionalization of terpyridines (TPyOHs) bearing a hydrogen bonding group. The corresponding TPyOHs displayed strong aggregation-induced emission and exhibited highly selective and visual detection of Zn^II cation with a record green terpyridine-based luminophore with nanomolar sensitivity (125 nm).

Synthesis and properties of fluorescent 4'-azulenyl-functionalized 2,2':6',2″-terpyridines

4′-Azulenyl-substituted terpyridines were efficiently synthesized following the Kröhnke methodology via azulenylchalcone intermediates. These azulenyl-containing terpyridines showed fluorescent emission with a fluorescence quantum yield varying from 0.14, in the case of parent terpyridine, to 0.64 when methyl groups are grafted on the azulenyl seven-membered ring. According to the crystal structures and TDDFT calculations, different twisting of the aromatic constituents is responsible for the observed fluorescent behavior. The electrochemical profile contains one-electron oxidation/reduction steps, which can only be explained on the basis of the redox behavior of the azulene unit. The ability of the 4′-azulenyl 2,2′:6′,2″-terpyridine to bind poisoning metal cations was studied by UV–vis titrations using aqueous solutions of Hg(II) and Cd(II) chlorides as illustrative examples.

Mesomorphism and Photophysics of Some Metallomesogens Based on Hexasubstituted 2,2':6', 2''-Terpyridines

The luminescent and mesomorphic properties of a series of metal complexes based on hexacatenar 2,2':6',2''-terpyridines are investigated using experimental methods and density functional theory (DFT). Two types of ligand are examined, namely 5,5''-di(3,4,5-trialkoxyphenyl)terpyridine with or without a fused cyclopentene ring on each pyridine and their complexes were prepared with the following transition metals: Zn(II) , Co(III) , Rh(III) , Ir(III) , Eu(III) and Dy(III) . The exact geometry of some of these complexes was determined by single X-ray diffraction. All complexes with long alkyl chains were found to be liquid crystalline, which property was induced on complexation. The liquid-crystalline behaviour of the complexes was studied by polarising optical microscopy and small-angle X-ray diffraction. Some of the transition metal complexes (for example, those with Zn(II) and Ir(III) ) are luminescent in solution, the solid state and the mesophase; their photophysical properties were studied both experimentally and using DFT methods (M06-2X and B3LYP).

Color Bricks: Building Highly Organized and Strongly Absorbing Multicomponent Arrays of Terpyridyl Perylenes on Metal Oxide Surfaces

Terpyridine-substituted perylenes containing cyclic anhydrides in the peri position were synthesized. The anhydride group served as an anchor for assembly of the terpyridyl-crowned chromophores as monomolecular layers on metal oxide surfaces. Further coordination with Zn(2+) ions allowed for layer-by-layer formation of supramolecular assemblies of perylene imides on the solid substrates. With properly selected anchor and linker molecules it was possible to build high quality structures of greater than ten successive layers by a simple and straightforward procedure. The prepared films were stable and had a broad spectral coverage and high absorbance. To demonstrate their potential use, the synthesized dyes were employed in solid-state dye-sensitized solar cells, and electron injection from the perylene antennas to titanium dioxide was observed.

Precise Control over the Rheological Behavior of Associating Stimuli-Responsive Block Copolymer Gels

"Smart" materials have considerably evolved over the last few years for specific applications. They rely on intelligent macromolecules or (supra-)molecular motifs to adapt their structure and properties in response to external triggers. Here, a supramolecular stimuli-responsive polymer gel is constructed from heterotelechelic double hydrophilic block copolymers that incorporate thermo-responsive sequences. These macromolecular building units are synthesized via a three-step controlled radical copolymerization and then hierarchically assembled to yield coordination micellar hydrogels. The dynamic mechanical properties of this particular class of materials are studied in shear flow and finely tuned via temperature changes. Notably, rheological experiments show that structurally reinforcing the micellar network nodes leads to precise tuning of the viscoelastic response and yield behavior of the material. Hence, they constitute promising candidates for specific applications, such as mechano-sensors.

Chelating Surfaces for Native State Proteins Patterning: The Human Serum Albumin Case

The paper reports a new "soft" surface functionalization strategy, based on a highly selective ion metal chelation process. The proposed stepwise methodology implies at first the construction of a monolayer of terpyridine-based thiol (Tpy), whose highly packed structuring has been followed in situ by using quartz crystal microbalance (QCM-D) measurements, showing that the monolayers consist of about 2.7 × 10(14) Tpy/cm(2). Then, the tridentate sites of the each Tpy moiety are employed to partially chelate divalent metal ions, providing an effective platform to anchoring proteins by completing the metal ion coordination with an available site on the protein of interest. We report the case study of the application of the process to the HSA immobilization onto various surfaces, including Tpy-Fe(II) and Tpy-Cu(II) complexes, as well as hydrophilic bare gold substrates and hydrophobic self-assembled Tpy-based monolayers. It is shown that the chelation interaction between Tpy-Cu(II) complexes and HSA produces the highest and most robust HSA immobilization, with an adsorbed mass at the steady state of ∼800 ng/cm(2), with respect to an average adsorption of ∼350 ng/cm(2) for the other surfaces. Furthermore, Cu(II)-chelated surfaces seem to promote a sort of protein "soft" landing, preventing the ubiquitous surface-induced major unfolding and transmitting an orientation information to the protein, owing to the highly specific symmetry coordination of the Tpy-Cu(II)-protein complex. Indeed, the interaction with a specific monoclonal antiboby (anti-HSA) indicated the lack of a significant protein denaturation, while a massive reorientation/denaturation process was found for all the remaining surfaces, including the Tpy-Fe(II) complex. Finally, the metal-ion-dependent HSA immobilization selectivity has been exploited to obtain micropatterned surfaces, based on the strikingly different strength of interaction and stability observed for Fe(II) and Cu(II) complexes.

Crystal structure of 4'-{[4-(2,2':6',2''-terpyrid-yl-4'-yl)phen-yl]ethyn-yl}biphenyl-4-yl (2,2,5,5-tetra-methyl-1-oxyl-3-pyrrolin-3-yl)formate benzene 2.5-solvate

The title compound, C44H35N4O3·2.5C6H6 (1), consists of a terpyridine and a N-oxylpyrroline-3-formate group separated by an aromatic spacer, viz. 4-(phenyl-ethyn-yl)-1,1'-biphenyl. It crystallized in the triclinic space group P-1 with two and a half benzene solvate mol-ecules (one benzene mol-ecule is located about an inversion center), while the di-chloro-methane solvate (2) of the same mol-ecule [Ackermann et al. (2015 ▸). Chem. Commun. 51, 5257-5260] crystallized in the tetra-gonal space group P42/n, with considerable disorder in the mol-ecule. In (1), the terpyridine (terpy) group assumes an all-trans conformation typical for terpyridines. It is essentially planar with the two outer pyridine rings (B and C) inclined to the central pyridine ring (A) by 8.70 (15) and 14.55 (14)°, respectively. The planes of the aromatic spacer (D, E and F) are nearly coplanar with dihedral angles D/E, D/F and E/F being 3.42 (15), 5.80 (15) and 4.00 (16)°, respectively. It is twisted with respect to the terpy group with, for example, dihedral angle A/D being 24.48 (14)°. The mean plane of the N-oxylpyrroline is almost normal to the biphenyl ring F, making a dihedral angle of 86.57 (16)°, and it is inclined to pyridine ring A by 72.61 (15)°. The intra-molecular separation between the O atom of the nitroxyl group and the N atom of the central pyridine ring of the terpyridine group is 25.044 (3) Å. In the crystal, mol-ecules are linked by pairs of C-H⋯O hydrogen bonds, forming inversion dimers. The dimers stack along the c axis forming columns. Within and between the columns, the spaces are occupied by benzene mol-ecules. The shortest oxygen-oxygen separation between nitroxyl groups is 4.004 (4) Å. The details of the title compound are compared with those of the di-chloro-methane solvate (2) and with the structure of a related mol-ecule, 4'-{4-[(2,2,5,5-tetra-methyl-N-oxyl-3-pyrrolin-3-yl)ethyn-yl]phen-yl}-2,2':6',2''-terpyridine (3), which has an ethynylphenyl spacer [Meyer et al. (2015). Acta Cryst. E71, 870-874].

Crystal structure of a mononuclear Ru(II) complex with a back-to-back terpyridine ligand: [RuCl(bpy)(tpy-tpy)](.)

In this first crystal structure of an Ru complex with 6′,6"-bis­(pyridin-2-yl)-2,2′:4′,4":2",2"’-quaterpyridine, a ‘half’ of the ligand (one of the two terpyridyl units) is N^N^N mer-coordinated, whereas the other is free and adopts a trans,trans conformation about the inter­annular C—C bonds. The crystal packing features π–π stacking inter­actions between tpy–tpy ligands.

We report the structural characterization of [6′,6′′-bis­(pyridin-2-yl)-2,2′:4′,4′′:2′′,2′′′-quaterpyridine](2,2′-bi­pyridine)­chlorido­ruthenium(II) hexa­fluorido­phosphate, [RuCl(C₁₀H₈N₂)(C₃₀H₂₀N₆)]PF₆, which contains the bidentate ligand 2,2′-bi­pyridine (bpy) and the tridendate ligand 6′,6′′-bis­(pyridin-2-yl)-2,2′:4′,4′′:2′′,2′′′-quaterpyridine (tpy–tpy). The [RuCl(bpy)(tpy–tpy)]⁺ monocation has a distorted octa­hedral geometry at the central Ru^II ion due to the restricted bite angle [159.32 (16)°] of the tridendate ligand. The Ru-bound tpy and bpy moieties are nearly planar and essentially perpendicular to each other with a dihedral angle of 89.78 (11)° between the least-squares planes. The lengths of the two Ru—N bonds for bpy are 2.028 (4) and 2.075 (4) Å, with the shorter bond being opposite to Ru—Cl. For tpy–tpy, the mean Ru—N distance involving the outer N atoms trans to each other is 2.053 (8) Å, whereas the length of the much shorter bond involving the central N atom is 1.936 (4) Å. The Ru—Cl distance is 2.3982 (16) Å. The free uncoordinated moiety of tpy–tpy adopts a trans,trans conformation about the inter­annular C—C bonds, with adjacent pyridyl rings being only approximately coplanar. The crystal packing shows significant π–π stacking inter­actions based on tpy–tpy. The crystal structure reported here is the first for a tpy–tpy complex of ruthenium.

Ruthenium sensitizers with a hexylthiophene-modified terpyridine ligand for dye-sensitized solar cells: synthesis, photo- and electrochemical properties, and adsorption behavior to the TiO2 surface

Two novel ruthenium sensitizers with a hexylthiophene-modified terpyridine ligand (TUS-35 and TUS-36) were synthesized to improve the molar absorptivity of the previously reported ruthenium sensitizer (TBA)[Ru{4'-(3,4-dicarboxyphenyl)-4,4″-dicarboxyterpyridine}(NCS)3], TBA = tetrabutylammonium (TUS-21). A relatively strong absorption appeared at ∼380 nm, and the molar absorption coefficient at the metal-to-ligand charge transfer (MLCT) band decreased in TUS-35 by introducing a 2-hexylthiophene unit to the 5-position of the terpyridine-derived ligand. For comparison, a relatively strong absorption was observed at ∼350 nm without decreasing the molar absorption coefficient at the MLCT band in TUS-36 by introducing a 2-hexylthiophene unit to the 4-position of the terpyridine-derived ligand. On the other hand, the energy levels of the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals of these two sensitizers were found to be almost equal to those of TUS-21. The adsorption behavior of TUS-35 and TUS-36 was similar to that of (TBA)[Ru{4'-(3,4-dicarboxyphenyl)terpyridine}(NCS)3] (TUS-20), which binds to the TiO2 surface by using the 3,4-dicarboxyphenly unit, rather than that of TUS-21, which adsorbs to the TiO2 photoelectrode using one of the carboxyl groups at the terminal pyridines of the terpyridine-derived ligand. Therefore, TUS-35 and TUS-36 are considered to bind to the TiO2 surface by using the 3,4-dicarboxyphenly unit just like TUS-20. The dye-sensitized solar cells (DSCs) with TUS-35 and TUS-36 showed a relatively lower conversion efficiency (6.4% and 5.7%, respectively) compared to the DSC with TUS-21 (10.2%). Open-circuit photovoltage decay and electrochemical impedance spectroscopy measurements revealed that the promoted charge recombination and/or charge transfer of the injected electrons in the TiO2 photoelectrode is a main reason for the inferior performances of TUS-35 and TUS-36.