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

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

Size-dependent compression of threaded alkyldiphosphate in head to head cyclodextrin [3]pseudorotaxanes.

The encapsulation of guests in a confined space enables unusual conformations and reactivities. In particular, the compression of akyl chains has been obtained by self-assembled molecular capsules but such an effect has not been reported in solution for pseudorotaxane architectures. By exploiting the tendency of cyclodextrin (CD) to form head to head [3]pseudorotaxanes and the hydrogen bonding abilities of phosphate groups, we have studied the effect of the CD dimer cavity on the conformation of threaded α,ω-alkyl-diphosphate axles. The formation of [2]pseudorotaxanes and [3]pseudorotaxanes was investigated by a combination of NMR, ITC and X-ray diffraction techniques. In the solid state, the [3]pseudorotaxane with a C8 axle presents a fully extended conformation with both terminal phosphate groups interacting with hydroxyl groups of the primary rim of CDs. Such hydrogen bonding interactions are also present with the C9 and C10 axles resulting in a compression of the alkyl chain with gauche conformations in the solid state. NMR studies have shown that this effect is maintained in solution resulting in a size-dependent progressive compression of the alkyl chain by the CD [3]pseudorotaxane architecture for C9, C10 and C11 axles.

Precise Rate Control of Pseudorotaxane Dethreading by pH-Responsive Selectively Functionalized Cyclodextrins.

A family of cyclodextrins functionalized with zero, one, two, or six amines was shown to control the rate of their threading and dethreading on a molecular axle depending on the pH and their substitution pattern. The originality of this system lies in the rate control of the switch by operating the stimulus directly on the macrocycle.

Dual switchable molecular tweezers incorporating anisotropic MnIII-salphen complexes.

An alternative strategy for the synthesis of terpyridine based switchable molecular tweezers has been developed to incorporate anisotropic Mn(iii)-salphen complexes. The free ligand was synthesized using a building block strategy based on Sonogashira coupling reactions and was then selectively metalated with manganese in a last step. The conformation of the tweezers was switched from an open 'W' shaped form to a closed 'U' form by Zn(ii) coordination to the terpyridine unit bringing the two Mn-salphen moieties in close spatial proximity as confirmed by X-ray crystallography. An alternate switching mechanism was observed by the intercalation of a bridging cyanide ligand between the two Mn-salphen moieties that resulted in the closing of the tweezers. These dual stimuli are attractive for achieving multiple controls of the mechanical motion of the tweezers. A crystallographic structure of unexpected partially oxidized closed tweezers was also obtained. One of the two Mn-salphen moieties underwent a ligand-centered oxidation of an imino to an amido group allowing an intramolecular Mn-Oamide-Mn linkage. The magnetic properties of the manganese(iii) dimers were investigated to evaluate the magnetic exchange interaction and analyze the single molecule magnet behavior.

Electrochemical primer extension based on polyoxometalate electroactive labels for multiplexed detection of single nucleotide polymorphisms.

Polyoxymetalates (POMs) ([SiW11O39{Sn(CH2)2CO)}]4- and [P2W17O61{Sn(CH2)2CO)}]6-) were used to modify dideoxynucleotides (ddNTPs) through amide bond formation, and applied to the multiplexed detection of single nucleotide polymorphisms (SNPs) in an electrochemical primer extension reaction. Each gold electrode of an array was functionalised with a short single stranded thiolated DNA probe, specifically designed to extend with the POM-ddNTP at the SNP site to be interrogated. The system was applied to the simultaneous detection of 4 SNPs within a single stranded 103-mer model target generated using asymmetric PCR, highlighting the potential of POM-ddNTPs for targeted, multiplexed SNP detection. The four DNA bases were successfully labelled with both ([SiW11O39{Sn(CH2)2CO)}]4- and [P2W17O61{Sn(CH2)2CO)}]6-), and [SiW11O39{Sn(CH2)2CO)}]4- demonstrated to be the more suitable due to its single oxidation peak, which provides an unequivocal signal. The POM-ddNTP enzymatically incorporated to the DNA anchored to the surface was visualised by AFM using gold coated mica. The developed assay has been demonstrated to be highly reproducible, simple to carry out and with very low non-specific background signals. Future work will focus on applying the developed platform to the detection of SNPs associated with rifampicin resistance in real samples from patients suffering from tuberculosis.

Stable Carboxylate-Terminated Gold Surfaces Produced by Spontaneous Grafting of an Alkyltin Compound.

Self-assembled monolayers formed by chemisorption of thiolated molecules on gold surfaces are widely applied for biosensing. Moreover, and due to the low stability of thiol-gold chemistry, contributions to the functionalisation of gold substrates with linkers that provide a more stable platform for the immobilisation of electroactive or biological molecules are highly appreciated. Herein, it is demonstrated that a carboxylated organotin compound can be successfully grafted onto gold substrates to form a highly stable organic layer with reactivity for subsequent binding to an aminated molecule. A battery of techniques were used to characterise the surface chemistry. The grafted layer was used to anchor aminoferrocene and subjected to both thermostability tests and long-term stability studies over a period of one year, demonstrating thermostability up to 90 °C and storage stability for at least 12 months at 4 °C protected from light. The stable surface tethering of molecules on gold substrates can be exploited in a plethora of applications, including molecular techniques, such as solid-phase amplification and solid-phase melting curve analysis, that require elevated temperature stability, as well as biosensors, which require long-term storage stability.

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.

Covalent hybrids based on Re(i) tricarbonyl complexes and polypyridine-functionalized polyoxometalate: synthesis, characterization and electronic properties.

A series of [Re(CO)3Br(N^N)] (N^N = substituted 2,2'-bipyridine ligand) complexes based on polypyridine-functionalized Dawson polyoxometalate (1-3) has been synthesized. The new hybrids (4-6) were characterized by various analytical techniques, including absorption, vibrational and luminescence spectroscopies as well as electrochemistry. Both units, the polyoxometalate and the transition metal complex, retain their intrinsic properties. Their combination in the newly prepared hybrids results in improved photosensitization in the high-energy visible region. However, a complete quenching of the emission for the [Re(CO)3Br(N^N)] complexes is observed due to formation of a charge separated state, Re(ii) - POM-, as shown by quenching experiments as well as theoretical modelling via DFT.

Six States Switching of Redox-Active Molecular Tweezers by Three Orthogonal Stimuli.

A six level molecular switch based on terpyridine(Ni-salphen)2 tweezers and addressable by three orthogonal stimuli (metal coordination, redox reaction, and guest binding) is reported. By a metal coordination stimulus, the tweezers can be mechanically switched from an open "W"-shaped conformation to a closed "U"-shaped form. Theses two states can each be reversibly oxidized by the redox stimulus and bind to a pyrazine guest resulting in four additional states. All six states are stable and accessible by the right combination of stimuli and were studied by NMR, XRD, EPR spectroscopy, and DFT calculations. The combination of the supramolecular concepts of mechanical motion and guest binding with the redox noninnocent and valence tautomerism properties of Ni-salphen complexes added two new dimensions to a mechanical switch.

PCR Incorporation of Polyoxometalate Modified Deoxynucleotide Triphosphates and Their Application in Molecular Electrochemical Sensing of Yersinia pestis.

Redox-labeled nucleotides are of increasing interest for the fabrication of next generation molecular tools and should meet requirements of being thermally stable, sensitive, and compatible with polymerase-mediated incorporation while also being electrochemically discriminable. The synthesis and characterization of Keggin and Dawson polyoxometalate-deoxynucleotide (POM-dNTP) bioconjugates linked through 7-deaza-modified purines is described. The modified POM-dNTPs were used for polymerase-based amplification of a DNA sequence specific for Yersinia pestis and the amplified DNA detected using an electrochemical DNA sensor. This highlights the potential of polyoxometalates as thermally stable, sensitive and polymerase-compatible redox labels for exploitation in bioanalytical applications.

Mechanostereoselective One-Pot Synthesis of Functionalized Head-to-Head Cyclodextrin [3]Rotaxanes and Their Application as Magnetic Resonance Imaging Contrast Agents.

A versatile, five-component, one-pot synthesis of cyclodextrin (CD) [3]rotaxanes using copper-catalyzed azide-alkyne cycloaddition has been developed. Head-to-head [3]rotaxanes of α-CD selectively functionalized by one or two gadolinium 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid monoamide complexes were obtained mechanostereoselectively. The magnetic resonance imaging efficiency, expressed by the longitudinal proton relaxivity of the rotaxanes, was significantly improved as compared to the functionalized CD. In vitro and in vivo preclinical studies showed a higher contrast and retention in the kidney than gadolinium 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid complex, demonstrating the potential of these rotaxanes as MRI contrast agent.

Heteroleptic ruthenium(ii) chromophores based on tunable polytopic 4'-(benzamidinato)-2,2':6',2''-terpyridines.

A modulable and simple approach towards heteroleptic ruthenium(ii) complexes of amidine-based polypyridine ligands is presented. New complexes 1 and 2 ([(terpyridine)Ru(terpyridine-C6H4-C(NR)(NHR))]2+ with R = propyl and R = phenyl derivatives, respectively) were characterized by NMR spectroscopy in solution and by X-ray diffraction, which confirmed the obtention of the (E) stereoisomer alone. Depending on the bulkiness of the R-substituents introduced on the amidine moiety, rotational isomerism around the C-N bond could be observed at r.t. Spectroscopic and electrochemical studies showed that the nature of the R-substituents introduced on the amidine moiety can significantly influence the redox and ground-state acido-basic properties of the complexes, while maintaining their electronic features. This particular tunability of polytopic 4'-(amidinato)-terpyridines offers an interesting perspective for photoactive units in larger multi-functional arrays.

Biofunctionalization of Polyoxometalates with DNA Primers, Their Use in the Polymerase Chain Reaction (PCR) and Electrochemical Detection of PCR Products.

The bioconjugation of polyoxometalates (POMs), which are inorganic metal oxido clusters, to DNA strands to obtain functional labeled DNA primers and their potential use in electrochemical detection have been investigated. Activated monooxoacylated polyoxotungstates [SiW11 O39 {Sn(CH2 )2 CO}](8-) and [P2 W17 O61 {Sn(CH2 )2 CO}](6-) have been used to link to a 5'-NH2 terminated 21-mer DNA forward primer through amide coupling. The functionalized primer was characterized by using a battery of techniques, including electrophoresis, mass spectrometry, as well as IR and Raman spectroscopy. The functionality of the POM-labeled primers was demonstrated through hybridization with a surface-immobilized probe. Finally, the labeled primers were successfully used in the polymerase chain reaction (PCR) and the PCR products were characterized by using electrophoresis.

Chiral Dawson-Type Hybrid Polyoxometalate Catalyzes Enantioselective Diels-Alder Reactions.

Can achiral organocatalysts linked to chiral polyanionic metal oxide clusters provide good selectivity in enantioselective C-C bond formations? The answer to this question is investigated by developing a new active hybrid polyoxometalate-based catalyst for asymmetric Diels-Alder reaction. Chirality transfer from the chiral anionic polyoxometalate to the covalently linked achiral imidazolidinone allows Diels-Alder cycloaddition products to be obtained with good yields and high enantioselectivities when using cyclopentadiene and acrylaldehydes as partners.

Mechanical switching of magnetic interaction by tweezers-type complex.

A control of the interaction between two spin centers was achieved by using a mechanical motion in a terpy(Cu-salphen)2 complex. Upon coordination a conformation change and switching from a paramagnetic to an antiferromagnetically coupled system was observed by EPR and SQUID measurements.

Generation of photocurrent by visible-light irradiation of conjugated dawson polyoxophosphovanadotungstate-porphyrin copolymers.

Four hybrid polyoxometalate-porphyrin copolymer films were obtained by the electrooxidation of zinc octaethylporphyrin in the presence of four different Dawson-type polyoxometalates bearing two pyridyl groups (POM(py)2) with various spacers. The POM monomers were designed around 1,3,5-trisubstituted benzene rings. Two of the substituents of the benzene ring are linked to the pyridyl groups, and the third is connected to the POM subunit. The four monomers vary in the relative positions of the nitrogen atoms of the pyridine rings or in the distance from the carbonyl group. The monomers were fully characterized by (1)H, (31)P, and (13)C NMR spectroscopy, electrospray mass spectrometry, IR and UV/Vis spectroscopy, and electrochemistry. The copolymers were characterized by UV/Vis spectroscopy, X-ray photoelectron spectroscopy, electrochemistry, and AFM. Their photovoltaic performance under visible light irradiation was investigated by photocurrent transient measurements under visible illumination.

Switchable platinum-based tweezers with Pt-Pt bonding and selective luminescence quenching.

Molecular tweezers incorporating peripheral platinum salphen complexes and a central chelating terpyridine group have been synthesized. The terpyridine can be switched upon metal binding between a free 'W' shaped form and a coordinated 'U' form. The crystallographic structure of the zinc-closed molecular tweezers was obtained and presented a strong π-stacking between the Pt-salphen units associated with a Pt-Pt bond. The luminescence properties, notably in response to selected guest ions (Zn(2+), Pb(2+), Hg(2+)) and the resulting mechanical motion, have been investigated by UV-Vis and emission spectroscopy. While ion coordination to the terpy resulted in no significant changes in the luminescence, a selective intercalation of a second Hg(2+) associated with a large differential quenching was observed.

Amphiphilic polyoxometalates for the controlled synthesis of hybrid polystyrene particles with surface reactivity.

Amphiphilic organo-polyoxometalates (POMs) used in the radical emulsion polymerization of styrene allowed the preparation in aqueous medium of stable 50-100 nm polystyrene-POM composite latexes. Thanks to the presence of a trithiocarbonate group in the POM amphiphile, POMs could be covalently linked to the polymer particle surface. The chemical and catalytic integrity of the POMs was confirmed, and the POM-mediated surface photoactivity of the latexes was demonstrated by the spatially controlled nucleation of silver nanoparticles at the periphery of the composites.

Intramolecular anion effect in polyoxometalate-based organocatalysts: reactivity enhancement and chirality transfer by a metal oxide-organic cation interaction.

An α1 -Dawson polyanion bearing a lateral side chain with a 4-aminopyridine end group was synthesized. This organopolyoxometalate catalyzes the addition of indenyl allyl silanes to cinnamoyl fluorides. The polyanionic framework influences the organocatalyst activity and selectivity. A moderate but nonzero chirality transfer from the chiral inorganic framework to the organic substrate was observed.

Terpy(Pt-salphen)2 switchable luminescent molecular tweezers.

The design and synthesis of switchable molecular tweezers based on a luminescent terpy(Pt-salphen)2 (1; terpy=terpyridine) complex is reported. Upon metal coordination, the tweezers can switch from an open "W"-shaped conformation to a closed "U"-shaped form that is adapted for selective recognition of cations. Closing of the tweezers by metal coordination (M=Zn(2+), Cu(2+), Pb(2+), Fe(2+), Hg(2+)) was monitored by (1)H NMR and/or UV/Vis titrations. During the titration, exclusive formation of the 1:1 complex [M(1)] was observed, without appearance of an intermediate 1:2 complex [M(1)2]. The crystallographic structure of the 1:1 complex was obtained with Pb(2+) and showed a distorted helical structure. Selective intercalation of Hg(2+) cations by the closed "U" form was observed. The tweezers were reopened by selective metal decoordination of the terpyridine ligand by using tris(2-aminoethyl)amine (tren) as a competitive ligand without modification of the Pt-salphen complex. Detailed photophysical studies were performed on the open and closed tweezers. Structured emission was observed in the open form from the Pt-salphen moieties, with a high quantum yield and a long lifetime. The emission is slightly modified upon closing with 1 equivalent of Zn(2+) or Hg(2+), whereas a dramatic quenching was obtained upon intercalation of additional Hg(2+).