Formation of Enantiomerically Pure Luminescent Triple-Stranded Dimetallic Europium Helicates and Their Corresponding Hierarchical Self-Assembly Formation in Protic Polar Solutions.

Ditopic helicate ligands 1 and 2 were synthesized for the formation of dinuclear EuIII luminescent chiral helical assemblies (Eu2·L3) in competitive organic and protic solvent media. Spectroscopic analysis revealed formation of the 2:3 (Eu2·L3) and 2:2 (Eu2·L2) species in methanolic solutions. Circular dichroism and circularly polarized luminescence (CPL) spectroscopy confirmed the chiral purity of the helical systems, while scanning electron microscopy imaging demonstrated the formation of hierarchical self-assemblies with spherical morphologies.

Synthesis, Characterization, and Biological Profiling of Ruthenium(II)-Based 4-Nitro- and 4-Amino-1,8-naphthalimide Conjugates.

We report the synthesis, photophysical characterization, and biological evaluation of four DNA-binding ruthenium(II) polypyridyl 4-nitro- and 4-amino-1,8-naphthalimide conjugates. A meta arrangement around the ring connecting the 1,8-naphthalimide to a bipyridine ligand creates a cleft, the result of which renders the shape of the complex complementary to that of DNA. We have demonstrated that each complex exhibits water solubility and a distinctive set of photophysical properties that has allowed the nature of their interaction with DNA to be probed by various ground- and excited-state titrations. Furthermore, by varying the ancillary ligands, we also demonstrate their ability to act as DNA photocleavers, where all compounds have been found to cleave supercoiled DNA with high efficiency. Detailed cellular uptake experiments revealed that the conjugates accumulate in the cytoplasm and nucleus of HeLa cells, showing characteristic red metal-to-ligand charge-transfer emission, and also exhibit photoactivated cytotoxicity within the cells upon irradiation at 450 nm. A comparison between the meta and para arrangements of the 1,8-naphthalimide moiety relative to the Ru(II) center suggests increased DNA binding in the case of the meta arrangement; however, bipyridine-4-amino-1,8-naphthalimide conjugates appear to show superior phototoxicity in comparison to their 4-nitro derivatives.

Rotaxane-Based Transition Metal Complexes: Effect of the Mechanical Bond on Structure and Electronic Properties.

Early work by Sauvage revealed that mechanical bonding alters the stability and redox properties of their original catenane metal complexes. However, despite the importance of controlling metal ion properties for a range of applications, these effects have received relatively little attention since. Here we present a series of tri-, tetra-, and pentadentate rotaxane-based ligands and a detailed study of their metal binding behavior and, where possible, compare their redox and electronic properties with their noninterlocked counterparts. The rotaxane ligands form complexes with most of the metal ions investigated, and X-ray diffraction revealed that in some cases the mechanical bond enforces unusual coordination numbers and distorted arrangements as a result of the exclusion of exogenous ligands driven by the sterically crowded binding sites. In contrast, only the noninterlocked equivalent of the pentadentate rotaxane CuII complex could be formed selectively, and this exhibited compromised redox stability compared to its interlocked counterpart. Frozen-solution EPR data demonstrate the formation of an interesting biomimetic state for the tetradentate CuII rotaxane, as well as the formation of stable NiI species and the unusual coexistence of high- and low-spin CoII in the pentadentate framework. Our results demonstrate that readily available mechanically chelating rotaxanes give rise to complexes the noninterlocked equivalent of which are inaccessible, and that the mechanical bond augments the redox behavior of the bound metal ion in a manner analogous to the carefully tuned amino acid framework in metalloproteins.

A Lanthanide Luminescent Cation Exchange Material Derived from a Flexible Tricarboxylic Acid 2,6-Bis(1,2,3-triazol-4-yl)pyridine (btp) Tecton.

The synthesis of the three-dimensional metal-organic framework material, [Zn7L6]·(H2NMe2)4·(H2O)45 (1), derived from a flexible tricarboxylic acid 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) ligand, is presented. The btp ligand, H3L, adopts a three-dimensional hydrogen bonding network in the crystalline state through a combination of carboxylic acid dimer and syn-anti-btp/carboxylic acid hydrogen bonding synthons. The Zn(II) species 1 exhibits a three-dimensional framework structure with the rare crs topology and contains linear and undulated solvent channels extending in three dimensions. The guest exchange and gas adsorption properties of 1 were investigated; herein we demonstrate the exchange of dimethylammonium cations from the as-synthesized material with cationic guest molecules in the form of dyes and luminescent Ln(III) ions. Sensitization of Eu(III) and Tb(III) inside the porous network of 1 was achieved upon cation exchange, with a view toward developing functional luminescent materials.

One-pot facile synthesis of 4-amino-1,8-naphthalimide derived Tröger's bases via a nucleophilic displacement approach.

We report here a novel one-pot synthetic strategy for the synthesis of a family of N-alkyl-1,8-naphthalimide based Tröger's bases via a nucleophilic substitution reaction of a common 'precursor' (or a 'synthon') N-aryl-1,8-naphthalimide Tröger's base heated at 80 °C in neat aliphatic primary amine, in overall yield of 65-96%. This methodology provides an efficient and one-step facile route to design 1,8-naphthalimide derived Tröger's base structures in analytically pure form without the use of column chromatography purification, that can be used in medicinal chemistry and as supramolecular scaffolds. We also report the formation of the corresponding anhydride, and the crystallographic analysis of two of the resulting products, that of the N-phenyl-4-amino-1,8-naphthalimide and the anhydride derived Tröger's bases.

pH-Regulated Nonelectrogenic Anion Transport by Phenylthiosemicarbazones.

Gated ion transport across biological membranes is an intrinsic process regulated by protein channels. Synthetic anion carriers (anionophores) have potential applications in biological research; however, previously reported examples are mostly nonspecific, capable of mediating both electrogenic and electroneutral (nonelectrogenic) transport processes. Here we show the transmembrane Cl(-) transport studies of synthetic phenylthiosemicarbazones mimicking the function of acid-sensing (proton-gated) ion channels. These anionophores have remarkable pH-switchable transport properties with up to 640-fold increase in transport efficacy on going from pH 7.2 to 4.0. This "gated" process is triggered by protonation of the imino nitrogen and concomitant conformational change of the anion-binding thiourea moiety from anti to syn. By using a combination of two cationophore-coupled transport assays, with either monensin or valinomycin, we have elucidated the fundamental transport mechanism of phenylthiosemicarbazones which is shown to be nonelectrogenic, inseparable H(+)/Cl(-) cotransport. This study demonstrates the first examples of pH-switchable nonelectrogenic anion transporters.

Lanthanide directed self-assembly of highly luminescent supramolecular "peptide" bundles from α-amino acid functionalized 2,6-bis(1,2,3-triazol-4-yl)pyridine (btp) ligands.

Ligands containing the [2,6-bis(1,2,3-triazol-4-yl)pyridine] (btp) motif have recently shown promise in coordination chemistry. The motif is synthesized via the Cu(I)-catalyzed "click" reaction and can be conveniently functionalized when compared to other terdentate chelating motifs. Ligand 1 was synthesized and shown to sensitize Eu(III) and Tb(III) excited states effectively. The use of these ions to synthesize self-assembly structures in solution was investigated by carrying out both (1)H NMR and photophysical titrations. The latter were used to determine high binding constants from changes in the absorption, ligand emission (fluorescence), and lanthanide-centered emission. A small library of amino acid derivatives of 1, ligands 3, were prepared upon coupling reactions with Gly, Ala, Phe, and Trp methyl esters, with a view to introducing biologically relevant and chiral moieties into such ligands. All of these derivatives were shown to form stable, emissive Ln(III) self-assemblies, emitting in the millisecond time range, which were studied by means of probing their photophysical properties in organic solutions using lanthanide ion titrations. All the Tb(III) complexes, with the exception of Trp based derivatives, gave rise to highly luminescent and bright complexes, with quantum yields of Tb(III) emission of 46-70% in CH3CN solution. In contrast, the Eu(III) complexes gave rise to more modest quantum yields of 0.3-3%, reflecting better energy match for the Tb(III) complexes, and hence, more efficient sensitization, as demonstrated by using low temperature measurements to determine the triplet state of 1.

The btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] binding motif: a new versatile terdentate ligand for supramolecular and coordination chemistry.

Ligands containing the btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] motif have appeared with increasing regularity over the last decade. This class of ligands, formed in a one pot 'click' reaction, has been studied for various purposes, such as for generating d and f metal coordination complexes and supramolecular self-assemblies, and in the formation of dendritic and polymeric networks, etc. This review article introduces btp as a novel and highly versatile terdentate building block with huge potential in inorganic supramolecular chemistry. We will focus on the coordination chemistry of btp ligands with a wide range of metals, and how it compares with other classical pyridyl and polypyridyl based ligands, and then present a selection of applications including use in catalysis, enzyme inhibition, photochemistry, molecular logic and materials, e.g. polymers, dendrimers and gels. The photovoltaic potential of triazolium derivatives of btp and its interactions with anions will also be discussed.

Unexpected self-sorting self-assembly formation of a [4:4] sulfate:ligand cage from a preorganized tripodal urea ligand.

The design and synthesis of tripodal ligands 1-3 based upon the N-methyl-1,3,5-benzenetricarboxamide platform appended with three aryl urea arms is reported. This ligand platform gives rise to highly preorganized structures and is ideally suited for binding SO4 (2-) and H2 PO4 (-) ions through multiple hydrogen-bonding interactions. The solid-state crystal structures of 1-3 with SO4 (2-) show the encapsulation of a single anion within a cage structure, whereas the crystal structure of 1 with H2 PO4 (-) showed that two anions are encapsulated. We further demonstrate that ligand 4, based on the same platform but consisting of two bis-urea moieties and a single ammonium moiety, also recognizes SO4 (2-) to form a self-assembled capsule with [4:4] SO4 (2-) :4 stoichiometry in which the anions are clustered within a cavity formed by the four ligands. This is the first example of a self-sorting self-assembled capsule where four tetrahedrally arranged SO4 (2-) ions are embedded within a hydrophobic cavity.

Remarkable scan rate dependence for a highly constrained dinuclear iron(II) spin crossover complex with a wide thermal hysteresis loop.

The abrupt [HS-HS] ↔ localized [HS-LS] spin crossovers of a new triazole-based diiron(II) complex result in a record-equaling thermal hysteresis loop width for a dinuclear complex (ΔT = 22 K by SQUID magnetometer in "settle" mode) and show a remarkable scan rate dependence of only the cooling branch, as revealed by detailed magnetic, DSC, and Mössbauer studies.

Synthesis, photophysical and cytotoxicity evaluations of DNA targeting agents based on 3-amino-1,8-naphthalimide derived Tröger's bases.

The synthesis and characterisation of five bis-1,8-naphthalimide containing Tröger's bases 1­5 formed from their corresponding 3-amino-1,8-naphthalimide precursors 6­10 is described. The photophysical investigations of 1­5 and 6­10 were carried out in several organic solvents as well as in water and as a function of pH using UV-Vis absorption and fluorescence spectroscopies. The DNA binding affinities of 1­5 in aqueous solution at pH 7.4 were also investigated using several UV-Vis absorption and fluorescence experiments by using calf thymus DNA (ct-DNA). These molecules exhibited significant DNA binding affinities; where large binding values (Kb) in the range of 10(6) M(−1) were determined, even in competitive media (50 mM and 160 mM NaCl at pH 7.4). Thermal denaturation measurements also showed that 1­5 significantly stabilised the DNA helix. Using linear and circular dichroism we further demonstrated that the DNA binding interaction occurs both by intercalation and by groove binding. The Tröger's bases were further shown to be rapidly taken up into cells using confocal fluorescence spectroscopy; and cytotoxic studies in HeLa and MCF-7 cells showed that most of the Tröger's bases were effective cytotoxic agents with EC50 values of between 1.1­12 µM and that all the active compounds induced programmed cell death by apoptosis, where up to 70% cellular death was observed after 24 h of incubation for 4.

Ligand Chirality Transfer from Solution State to the Crystalline Self-Assemblies in Circularly Polarized Luminescence (CPL) Active Lanthanide Systems.

The synthesis of a family of chiral and enantiomerically pure pyridyl-diamide (pda) ligands that upon complexation with europium [Eu(CF3SO3)3] result in chiral complexes with metal centered luminescence is reported; the sets of enantiomers giving rise to both circular dichroism (CD) and circularly polarized luminescence (CPL) signatures. The solid-state structures of these chiral metallosupramolecular systems are determined using X-ray diffraction showing that the ligand chirality is transferred from solution to the solid state. This optically favorable helical packing arrangement is confirmed by recording the CPL spectra from the crystalline assembly by using steady state and enantioselective differential chiral contrast (EDCC) CPL Laser Scanning Confocal Microscopy (CPL-LSCM) where the two enantiomers can be clearly distinguished.

Probing the effects of ligand isomerism in chiral luminescent lanthanide supramolecular self-assemblies: a europium "Trinity Sliotar" study.

"Trinity Sliotar" family: Chiral ligands containing pyridyl and naphthalene moieties were synthesized and characterized. These ligands were successfully used for the synthesis of Eu(III) bundles where chirality of the ligand is successfully transferred onto the lanthanide centre resulting in circularly polarized red luminescence.

Near infrared (NIR) lanthanide emissive Langmuir-Blodgett monolayers formed using Nd(III) directed self-assembly synthesis of chiral amphiphilic ligands.

The incorporation of chiral amphiphilic lanthanide-directed self-assembled Nd(III) complexes (Nd.13 and Nd.23) into stable Langmuir monolayers, and the subsequent Langmuir-Blodgett film formation of these, is described. The photophysical properties of the enantiomeric pair of ligands 1 and 2 in the presence of Nd(CF3SO3)3 were also investigated in CH3CN solutions using UV-vis, fluorescence, and lanthanide luminescence spectroscopies. Analysis of the resulting self-assembly processes revealed that two main species were formed in solution,1:1 and 1:3 Nd:L self-assembly complexes, with the latter being the dominant species upon the addition of 0.33 equivalents of Nd(III). Excited state lifetime measurements of Nd.13 and Nd.23 in CH3OH and CD3OD and CH3CN were also evaluated. The formation of the self-assembly in solution was also monitored by observing the changes in the circular dichroism (CD) spectra; and large differences were observed between the 1:3 and other stoichiometries in the spectra, allowing for correlation to be made with that seen in the emission studies of these systems. Surface pressure-area and surface pressure-time isotherms evidenced the formation of stable Langmuir monolayers of Nd.13 and Nd.23 at an air-water interface, and the deposition of these monolayers onto a quartz solid substrate (Langmuir-Blodgett films) gave rise to immobilized chiral monomolecular films which exhibited Nd(III) NIR luminescence upon excitation of the ligand chromophore, demonstrating efficient energy transfer to the Nd(III) excided state (sensitized) with concomitant emission centered at 800 and 1334 nm.

Effect of N4-substituent choice on spin crossover in dinuclear iron(II) complexes of bis-terdentate 1,2,4-triazole-based ligands.

Seven new dinuclear iron(II) complexes of the general formula [Fe(II)2(PMRT)2](BF4)4·solvent, where PMRT is a 4-substituted-3,5-bis{[(2-pyridylmethyl)-amino]methyl}-4H-1,2,4-triazole, have been prepared in order to investigate the substituent effect on the spin crossover event. Variable temperature magnetic susceptibility and (57)Fe Mössbauer spectroscopy studies show that two of the complexes, [Fe(II)2(PMPT)2](BF4)4·H2O (N(4) substituent is pyrrolyl) and [Fe(II)2(PM(Ph)AT)2](BF4)4 (N(4) is N,N-diphenylamine), are stabilized in the [HS-HS] state between 300 and 2 K with weak antiferromagnetic interactions between the iron(II) centers. Five of the complexes showed gradual half spin crossover, from [HS-HS] to [HS-LS], with the following T(1/2) (K) values: 234 for [Fe(II)2(PMibT)2](BF4)4·3H2O (N(4) is isobutyl), 147 for [Fe(II)2(PMBzT)2](BF4)4 (N(4) is benzyl), 133 for [Fe(II)2(PM(CF3)PhT)2](BF4)4·DMF·H2O (N(4) is 3,5-bis(trifluoromethyl)phenyl), 187 for [Fe(II)2(PMPhT)2](BF4)4 (N(4) is phenyl), and 224 for [Fe(II)2(PMC16T)2](BF4)4 (N(4) is hexadecyl). Structure determinations carried out for three complexes, [Fe(II)2(PMPT)2](BF4)4·4DMF, [Fe(II)2(PMBzT)2](BF4)4·CH3CN, and [Fe(II)2(PM(Ph)AT)2](BF4)4·solvent, revealed that in all three complexes both iron(II) centers are stabilized in the high spin state at 90 K. A general and reliable 4-step route to PMRT ligands is also detailed.

The effect of the 4-amino functionality on the photophysical and DNA binding properties of alkyl-pyridinium derived 1,8-naphthalimides.

The synthesis and characterisation of two cationic pyridinium based 4-amino-1,8-naphthalimide derivatives (2 and 3) are described and compared to those of compound 1. The photophysical properties of 2 and 3 are shown to vary greatly with the solvent polarity and H-bonding ability. The dimethylamino substitution in 3 results in a weak quantum yield of fluorescence emission due to faster non-radiative deactivation of the excited singlet state than that seen for 2. As with 1, the fluorescence of 2 was found to be enhanced in its 1 : 1 complex with 5'-adenosine-monophosphate (5'-AMP) while it was partially quenched in its complex with 5'-guanosine-monophosphate (5'-GMP). In contrast, the fluorescence of 3 was enhanced ('switched on') in the presence of both adenine and guanine rich sequences. Linear and circular dichroism studies showed that each of 1, 2 and 3 binds to double-stranded DNA by intercalation. However, 2 and 3 do not show the preference for AT-rich DNA observed for 1. Comparative fluorescence studies with double stranded DNA show that the emission of was 16 times enhanced in its DNA bound form, suggesting potential use of this structure as a spectroscopic probe for studying nucleic acid structure.

White light and colour-tunable emission from a single component europium-1,8-naphthalimide thin film.

The synthesis and fabrication of spin coated films of a new Eu3+ complex [Eu(1)3] derived from the 1,8-naphthalimide containing ligand 1H is presented. The complex is multi-emissive displaying blue emission from the 1,8-naphthalimide fluorophore and red emission from the Eu3+ centre in both solution-state and solid-state. This allows the overall emission to be tuned by changing the excitaton wavelength, where varing degrees of red and blue emission intensity alter the overall emission colour from blue, to red and including white-light emission. The complex was spin-coated onto quartz slides giving 134 nm thick coatings that retained the multi-emissive and colour tunable properties. Overall, resulting in a colour-tunable system which in solution, solid, and thin film states can alter the overall colour from deep red to dark blue.

Synthesis and photophysical evaluation of a pyridinium 4-amino-1,8-naphthalimide derivative that upon intercalation displays preference for AT-rich double-stranded DNA.

The synthesis, characterisation and solid state crystal structure of a cationic 4-amino-1,8-naphthalimide derivative (1) are described. The photophysical properties of 1 are shown to vary with the solvent polarity and H-bonding ability. The fluorescence of 1 is enhanced and blue-shifted in its 1:1 complex with 5'-adenosine-monophosphate while it is partially quenched and red-shifted in its complex with 5'-guanosine-monophosphate. Linear and circular dichroism measurements show that 1 binds to double-stranded DNA by intercalation. Comparative UV-visible and fluorescence studies with double stranded synthetic polynucleotides poly(dA-dT)(2) and poly(dG-dC)(2) show that 1 binds much more strongly to the AT polymer; 1 also has a strong preference for A-T rich sequences in natural DNA. Thermal denaturation measurements also reveal a much greater stabilisation of the double-stranded poly(dA-dT)(2) than of natural DNA.

Effect of counteranion X on the spin crossover properties of a family of diiron(II) triazole complexes [Fe(II)2(PMAT)2](X)4.

Seven diiron(II) complexes, [Fe(II)(2)(PMAT)(2)](X)(4), varying only in the anion X, have been prepared, where PMAT is 4-amino-3,5-bis{[(2-pyridylmethyl)-amino]methyl}-4H-1,2,4-triazole and X = BF(4)(-) (1), Cl(-) (2), PF(6)(-) (3), SbF(6)(-) (4), CF(3)SO(3)(-) (5), B(PhF)(4)(-) (6), and C(16)H(33)SO(3)(-) (7). Most were isolated as solvates, and the microcrystalline ([3], [4]·2H(2)O, [5]·H(2)O, and [6]·½MeCN) or powder ([2]·4H(2)O, and [7]·2H(2)O) samples obtained were studied by variable-temperature magnetic susceptibility and Mössbauer methods. A structure determination on a crystal of [2]·2MeOH·H(2)O, revealed it to be a [LS-HS] mixed low spin (LS)-high spin (HS) state dinuclear complex at 90 K, but fully high spin, [HS-HS], at 293 K. In contrast, structures of both [5]·¾IPA·H(2)O and [7]·1.6MeOH·0.4H(2)O showed them to be [HS-HS] at 90 K, whereas magnetic and Mössbauer studies on [5]·H(2)O and [7]·2H(2)O revealed a different spin state, [LS-HS], at 90 K, presumably because of the difference in solvation. None of these complexes undergo thermal spin crossover (SCO) to the fully LS form, [LS-LS]. The PF(6)(-) and SbF(6)(-) complexes, 3 and [4]·2H(2)O, appear to be a mixture of [HS-LS] and [HS-HS] at low temperature, and undergo gradual SCO to [HS-HS] on warming. The CF(3)SO(3)(-) complex [5]·H(2)O undergoes gradual, partial SCO from [HS-LS] to a mixture of [HS-LS] and [HS-HS] at T(1/2) ≈ 180 K. The B(PhF)(4)(-) and C(16)H(33)SO(3)(-) complexes, [6]·(1)/(2)MeCN and [7]·2H(2)O, are approximately [LS-HS] at all temperatures, with an onset of gradual SCO with T(1/2) > 300 K.

Ultra-thin films of amphiphilic lanthanide complexes: multi-colour emission from molecular monolayers.

We report the synthesis and Langmuir-Blodgett deposition of 4 brightly emissive lanthanide amphiphiles that can be co-deposited to give multi-emissive ultra-thin films where two, three and four distinct lanthanide emission profiles are observed. To the best of our knowledge, this is the first report of a four-component emissive Langmuir-Blodgett film.