Spectroscopic Studies on Photoinduced Reactions of the Anticancer Prodrug, trans,trans,trans-[Pt(N3 )2 (OH)2 (py)2 ].

The photodecomposition mechanism of trans,trans,trans-[Pt(N3 )2 (OH)2 (py)2 ] (1, py=pyridine), an anticancer prodrug candidate, was probed using complementary Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR), transient electronic absorption, and UV/Vis spectroscopy. Data fitting using Principal Component Analysis (PCA) and Multi-Curve Resolution Alternating Least Squares, suggests the formation of a trans-[Pt(N3 )(py)2 (OH/H2 O)] intermediate and trans-[Pt(py)2 (OH/H2 O)2 ] as the final product upon 420 nm irradiation of 1 in water. Rapid disappearance of the hydroxido ligand stretching vibration upon irradiation is correlated with a -10 cm-1 shift to the antisymmetric azido vibration, suggesting a possible second intermediate. Experimental proof of subsequent dissociation of azido ligands from platinum is presented, in which at least one hydroxyl radical is formed in the reduction of PtIV to PtII . Additionally, the photoinduced reaction of 1 with the nucleotide 5'-guanosine monophosphate (5'-GMP) was comprehensively studied, and the identity of key photoproducts was assigned with the help of ATR-FTIR spectroscopy, mass spectrometry, and density functional theory calculations. The identification of marker bands for some of these photoproducts (e.g., trans-[Pt(N3 )(py)2 (5'-GMP)] and trans-[Pt(py)2 (5'-GMP)2 ]) will aid elucidation of the chemical and biological mechanism of anticancer action of 1. In general, these studies demonstrate the potential of vibrational spectroscopic techniques as promising tools for studying such metal complexes.

Towards Utilising Photocrosslinking of Polydiacetylenes for the Preparation of "Stealth" Upconverting Nanoparticles.

We demonstrate a novel strategy for preparing hydrophilic upconverting nanoparticles (UCNPs) by harnessing the photocrosslinking ability of diacetylenes. Replacement of the hydrophobic oleate coating on the UCNPs with 10,12-pentacosadiynoic acid, followed by overcoating with diacetylene phospholipid and subsequent photocrosslinking under 254 nm irradiation produces water-dispersible polydiacetylene-coated UCNPs. These UCNPs resist the formation of a biomolecular corona and show great colloidal stability. Furthermore, amine groups on the diacetylene phospholipid allow for functionalisation of the UCNPs with, for example, radiolabels or targeting moieties. These results demonstrate that this new surface-coating method has great potential for use in the preparation of UCNPs with improved biocompatibility.

Real-time examination of aminoglycoside activity towards bacterial mimetic membranes using Quartz Crystal Microbalance with Dissipation monitoring (QCM-D).

The rapid increase in multi-drug resistant bacteria has resulted in previously discontinued treatments being revisited. Aminoglycosides are effective "old" antibacterial agents that fall within this category. Despite extensive usage and understanding of their intracellular targets, there is limited mechanistic knowledge regarding how aminoglycosides penetrate bacterial membranes. Thus, the activity of two well-known aminoglycosides, kanamycin A and neomycin B, towards a bacterial mimetic membrane (DMPC:DMPG (4:1)) was examined using a Quartz Crystal Microbalance with Dissipation monitoring (QCM-D). The macroscopic effect of increasing the aminoglycoside concentration showed that kanamycin A exerts a threshold response, switching from binding to the membrane to disruption of the surface. Neomycin B, however, disrupted the membrane at all concentrations examined. At concentrations above the threshold value observed for kanamycin A, both aminoglycosides revealed similar mechanistic details. That is, they both inserted into the bacterial mimetic lipid bilayer, prior to disruption via loss of materials, presumably aminoglycoside-membrane composites. Depth profile analysis of this membrane interaction was achieved using the overtones of the quartz crystal sensor. The measured data is consistent with a two-stage process in which insertion of the aminoglycoside precedes the 'detergent-like' removal of membranes from the sensor. The results of this study contribute to the insight required for aminoglycosides to be reconsidered as active antimicrobial agents/co-agents by providing details of activity at the bacterial membrane. Kanamycin and neomycin still offer potential as antimicrobial therapeutics for the future and the QCM-D method illustrates great promise for screening new antibacterial or antiviral drug candidates.

Macrocyclic metal complexes for metalloenzyme mimicry and sensor development.

Examples of proteins that incorporate one or more metal ions within their structure are found within a broad range of classes, including oxidases, oxidoreductases, reductases, proteases, proton transport proteins, electron transfer/transport proteins, storage proteins, lyases, rusticyanins, metallochaperones, sporulation proteins, hydrolases, endopeptidases, luminescent proteins, iron transport proteins, oxygen storage/transport proteins, calcium binding proteins, and monooxygenases. The metal coordination environment therein is often generated from residues inherent to the protein, small exogenous molecules (e.g., aqua ligands) and/or macrocyclic porphyrin units found, for example, in hemoglobin, myoglobin, cytochrome C, cytochrome C oxidase, and vitamin B12. Thus, there continues to be considerable interest in employing macrocyclic metal complexes to construct low-molecular weight models for metallobiosites that mirror essential features of the coordination environment of a bound metal ion without inclusion of the surrounding protein framework. Herein, we review and appraise our research exploring the application of the metal complexes formed by two macrocyclic ligands, 1,4,7-triazacyclononane (tacn) and 1,4,7,10-tetraazacyclododecane (cyclen), and their derivatives in biological inorganic chemistry. Taking advantage of the kinetic inertness and thermodynamic stability of their metal complexes, these macrocyclic scaffolds have been employed in the development of models that aid the understanding of metal ion-binding natural systems, and complexes with potential applications in biomolecule sensing, diagnosis, and therapy. In particular, the focus has been on "coordinatively unsaturated" metal complexes that incorporate a kinetically inert and stable metal-ligand moiety, but which also contain one or more weakly bound ligands, allowing for the reversible binding of guest molecules via the formation and dissociation of coordinate bonds. With regards to mimicking metallobiosites, examples are presented from our work on tacn-based complexes developed as simplified structural models for multimetallic enzyme sites. In particular, structural comparisons are made between multinuclear copper(II) complexes formed by such ligands and multicopper enzymes featuring type-2 and type-3 copper centers, such as ascorbate oxidase (AO) and laccase (Lc). Likewise, with the aid of relevant examples, we highlight the importance of cooperativity between either multiple metal centers or a metal center and a proximal auxiliary unit appended to the macrocyclic ligand in achieving efficient phosphate ester cleavage. Finally, the critical importance of the Zn(II)-imido and Zn(II)-phosphate interactions in Zn-cyclen-based systems for delivering highly sensitive electrochemical and fluorescent chemosensors is also showcased. The Account additionally highlights some of the factors that limit the performance of these synthetic nucleases and the practical application of the biosensors, and then identifies some avenues for the development of more effective macrocyclic constructs in the future.

Comprehensive Vibrational Spectroscopic Investigation of trans,trans,trans-[Pt(N3)2(OH)2(py)2], a Pt(IV) Diazido Anticancer Prodrug Candidate.

We report a detailed study of a promising photoactivatable metal-based anticancer prodrug candidate, trans,trans,trans-[Pt(N3)2(OH)2(py)2] (C1; py = pyridine), using vibrational spectroscopic techniques. Attenuated total reflection Fourier transform infrared (ATR-FTIR), Raman, and synchrotron radiation far-IR (SR-FIR) spectroscopies were applied to obtain highly resolved ligand and Pt-ligand vibrations for C1 and its precursors (trans-[Pt(N3)2(py)2] (C2) and trans-[PtCl2(py)2] (C3)). Distinct IR- and Raman-active vibrational modes were assigned with the aid of density functional theory calculations, and trends in the frequency shifts as a function of changing Pt coordination environment were determined and detailed for the first time. The data provide the ligand and Pt-ligand (azide, hydroxide, pyridine) vibrational signatures for C1 in the mid- and far-IR region, which will provide a basis for the better understanding of the interaction of C1 with biomolecules.

EGF receptor-targeting peptide conjugate incorporating a near-IR fluorescent dye and a novel 1,4,7-triazacyclononane-based (64)Cu(II) chelator assembled via click chemistry.

A new Boc-protected 1,4,7-triazacyclononane (TACN)-based pro-chelator compound featuring a "clickable" azidomethylpyridine pendant has been developed as a building block for the construction of multimodal imaging agents. Conjugation to a model alkyne (propargyl alcohol), followed by deprotection, generates a pentadentate ligand, as confirmed by X-ray crystallographic analysis of the corresponding distorted square-pyramidal Cu(II) complex. The ligand exhibits rapid (64)Cu(II)-binding kinetics (>95% radiochemical yield in <5 min) and a high resistance to demetalation. It may thus prove suitable for use in (64)Cu(II)-based in vivo positron emission tomography (PET). The new chelating building block has been applied to the construction of a bimodal (PET/fluorescence) peptide-based imaging probe targeting the epidermal growth factor (EGF) receptor, which is highly overexpressed on the surface of several types of cancer cells. The probe consists of a hexapeptide sequence, Leu-Ala-Arg-Leu-Leu-Thr (designated "D4"), followed by a Cys-ß-Ala-ß-Ala spacer, then a ß-homopropargylglycine residue with the TACN-based chelator "clicked" to its side chain. A sulfonated near-infrared (NIR) fluorescent cyanine dye (sulfo-Cy5) was introduced at the N-terminus to study the EGF receptor-binding ability of the probe by laser-fluorescence spectroscopy. Binding was also confirmed by coimmunoprecipitation methods, and an apparent dissociation constant (Kd) of ca. 10 nM was determined from radioactivity-based measurements of probe binding to two EGF receptor-expressing cell lines (FaDu and A431). The probe is shown to be a biased or partial allosteric agonist of the EGF receptor, inducing phosphorylation of Thr669 and Tyr992, but not the Tyr845, Tyr998, Tyr1045, Tyr1068, or Tyr1148 residues of the receptor, in the absence of the orthosteric EGF ligand. Additionally, the probe was found to suppress the EGF-stimulated autophosphorylation of these latter residues, indicating that it is also a noncompetitive antagonist.

A bis(dipyridophenazine)(2-(2-pyridyl)pyrimidine-4-carboxylic acid)ruthenium(II) complex with anticancer action upon photodeprotection.

Improving the selectivity of anticancer drugs towards cancer cells is one of the main goals of drug optimization; the prodrug strategy has been one of the most promising. A light-triggered prodrug strategy is presented as an efficient approach for controlling cytotoxicity of the substitutionally inert cytotoxic complex [Ru(dppz)2(CppH)](PF6)2(C1; CppH=2-(2-pyridyl)pyrimidine-4-carboxylic acid; dppz=dipyrido[3,2-a:2',3'-c]phenazine). Attachment of a photolabile 3-(4,5-dimethoxy-2-nitrophenyl)-2-butyl (DMNPB) ester ("photocaging") makes the otherwise active complex C1 innocuous to both cancerous (HeLa and U2OS) and non-cancerous (MRC-5) cells. The cytotoxic action can be successfully unleashed in living cells upon light illumination (350 nm), reaching similar level of activity as the parent cytotoxic compound C1. This is the first substitutionally inert cytotoxic metal complex to be used as a light-triggered prodrug candidate.

Synthesis, spectroscopic properties, and photoinduced CO-release studies of functionalized ruthenium(II) polypyridyl complexes: versatile building blocks for development of CORM-peptide nucleic acid bioconjugates.

A series of ruthenium(II) dicarbonyl complexes of formula [RuCl2(L)(CO)2] (L = bpy(CH3,CH3) = 4,4'-dimethyl-2,2'-bipyridine, bpy(CH3,CHO) = 4'-methyl-2,2'-bipyridine-4-carboxyaldehyde, bpy(CH3,COOH) = 4'-methyl-2,2'-bipyridine-4-carboxylic acid, CppH = 2-(pyridin-2-yl)pyrimidine-4-carboxylic acid, dppzcH = dipyrido[3,2-a:2',3'-c]phenazine-11-carboxylic acid), and [RuCl(L)(CO)2](+) (L = tpy(COOH) = 6-(2,2':6',2″-terpyridine-4'-yloxy)hexanoic acid) has been synthesized. In addition, a high-yield synthesis of a peptide nucleic acid (PNA) monomer containing the 2-(pyridin-2-yl)pyrimidine ligand was also developed, and this compound was used to prepare the first Ru(II) dicarbonyl complex, [RuCl2(Cpp-L-PNA)(CO)2],(Cpp-L-PNA = tert-butyl-N-[2-(N-9-fluorenylmethoxycarbonyl)aminoethyl]-N-[6-(2-(pyridin-2-yl)pyrimidine-4-carboxamido)hexanoyl]glycinate) attached to a PNA monomer backbone. Such metal-complex PNA-bioconjugates are attracting profound interest for biosensing and biomedical applications. Characterization of all complexes has been undertaken by IR and NMR spectroscopy, mass spectrometry, elemental analysis, and UV-vis spectroscopy. Investigation of the CO-release properties of the Ru(II) complexes in water/dimethyl sulfoxide (49:1) using the myoglobin assay showed that they are stable under physiological conditions in the dark for at least 60 min and most of them even for up to 15 h. In contrast, photoinduced CO release was observed upon illumination at 365 nm, the low-energy shoulder of the main absorption maximum centered around 300 nm, establishing these compounds as a new class of PhotoCORMs. While the two 2,2'-bipyridine complexes release 1 equiv of CO per mole of complex, the terpyridine, 2-(2'-pyridyl)pyrimidine, and dipyrido[3,2-a:2',3'-c]phenazine complexes are less effective CO releasers. Attachment of the 2-(2'-pyridyl)pyrimidine complex to a PNA backbone as in [RuCl2(Cpp-L-PNA)CO2] did not significantly change the spectroscopic or CO-release properties compared to the parent complex. Thus, a novel class of Ru(II)-based PhotoCORMs has been established which can be coupled to carrier delivery vectors such as PNA to facilitate cellular uptake without loss of the inherent CORM properties of the parent compound.

Molecular and cellular characterization of the biological effects of ruthenium(II) complexes incorporating 2-pyridyl-2-pyrimidine-4-carboxylic acid.

A great majority of the Ru complexes currently studied in anticancer research exert their antiproliferative activity, at least partially, through ligand exchange. In recent years, however, coordinatively saturated and substitutionally inert polypyridyl Ru(II) compounds have emerged as potential anticancer drug candidates. In this work, we present the synthesis and detailed characterization of two novel inert Ru(II) complexes, namely, [Ru(bipy)(2)(Cpp-NH-Hex-COOH)](2+) (2) and [Ru(dppz)(2)(CppH)](2+) (3) (bipy = 2,2'-bipyridine; CppH = 2-(2'-pyridyl)pyrimidine-4-carboxylic acid; Cpp-NH-Hex-COOH = 6-(2-(pyridin-2-yl)pyrimidine-4-carboxamido)hexanoic acid; dppz = dipyrido[3,2-a:2',3'-c]phenazine). 3 is of particular interest as it was found to have IC(50) values comparable to cisplatin, a benchmark standard in the field, on three cancer cell lines and a better activity on one cisplatin-resistant cell line than cisplatin itself. The mechanism of action of 3 was then investigated in detail and it could be demonstrated that, although 3 binds to calf-thymus DNA by intercalation, the biological effects that it induces did not involve a nuclear DNA related mode of action. On the contrary, confocal microscopy colocalization studies in HeLa cells showed that 3 specifically targeted mitochondria. This was further correlated by ruthenium quantification using High-resolution atomic absorption spectrometry. Furthermore, as determined by two independent assays, 3 induced apoptosis at a relatively late stage of treatment. The generation of reactive oxygen species could be excluded as the cause of the observed cytotoxicity. It was demonstrated that the mitochondrial membrane potential in HeLa was impaired by 3 as early as 2 h after its introduction and even more with increasing time.

Phosphodiester cleavage properties of copper(II) complexes of 1,4,7-triazacyclononane ligands bearing single alkyl guanidine pendants.

Three new metal-coordinating ligands, L(1)·4HCl [1-(2-guanidinoethyl)-1,4,7-triazacyclononane tetrahydrochloride], L(2)·4HCl [1-(3-guanidinopropyl)-1,4,7-triazacyclononane tetrahydrochloride], and L(3)·4HCl [1-(4-guanidinobutyl)-1,4,7-triazacyclononane tetrahydrochloride], have been prepared via the selective N-functionalization of 1,4,7-triazacyclononane (tacn) with ethylguanidine, propylguanidine, and butylguanidine pendants, respectively. Reaction of L(1)·4HCl with Cu(ClO(4))(2)·6H(2)O in basic aqueous solution led to the crystallization of a monohydroxo-bridged binuclear copper(II) complex, [Cu(2)L(1)(2)(µ-OH)](ClO(4))(3)·H(2)O (C1), while for L(2) and L(3), mononuclear complexes of composition [Cu(L(2)H)Cl(2)]Cl·(MeOH)(0.5)·(H(2)O)(0.5) (C2) and [Cu(L(3)H)Cl(2)]Cl·(DMF)(0.5)·(H(2)O)(0.5) (C3) were crystallized from methanol and DMF solutions, respectively. X-ray crystallography revealed that in addition to a tacn ring from L(1) ligand, each copper(II) center in C1 is coordinated to a neutral guanidine pendant. In contrast, the guanidinium pendants in C2 and C3 are protonated and extend away from the Cu(II)-tacn units. Complex C1 features a single µ-hydroxo bridge between the two copper(II) centers, which mediates strong antiferromagnetic coupling between the metal centers. Complexes C2 and C3 cleave two model phosphodiesters, bis(p-nitrophenyl)phosphate (BNPP) and 2-hydroxypropyl-p-nitrophenylphosphate (HPNPP), more rapidly than C1, which displays similar reactivity to [Cu(tacn)(OH(2))(2)](2+). All three complexes cleave supercoiled plasmid DNA (pBR 322) at significantly faster rates than the corresponding bis(alkylguanidine) complexes and [Cu(tacn)(OH(2))(2)](2+). The high DNA cleavage rate for C1 {k(obs) = 1.30 (±0.01) × 10(-4) s(-1) vs 1.23 (±0.37) × 10(-5) s(-1) for [Cu(tacn)(OH(2))(2)](2+) and 1.58 (±0.05) × 10(-5) s(-1) for the corresponding bis(ethylguanidine) analogue} indicates that the coordinated guanidine group in C1 may be displaced to allow for substrate binding/activation. Comparison of the phosphate ester cleavage properties of complexes C1-C3 with those of related complexes suggests some degree of cooperativity between the Cu(II) centers and the guanidinium groups.

Electrochemiluminescent monomers for solid support syntheses of Ru(II)-PNA bioconjugates: multimodal biosensing tools with enhanced duplex stability.

The feasibility of devising a solid support mediated approach to multimodal Ru(II)-peptide nucleic acid (PNA) oligomers is explored. Three Ru(II)-PNA-like monomers, [Ru(bpy)(2)(Cpp-L-PNA-OH)](2+) (M1), [Ru(phen)(2)(Cpp-L-PNA-OH)](2+) (M2), and [Ru(dppz)(2)(Cpp-L-PNA-OH)](2+) (M3) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, dppz = dipyrido[3,2-a:2',3'-c]phenazine, Cpp-L-PNA-OH = [2-(N-9-fluorenylmethoxycarbonyl)aminoethyl]-N-[6-(2-(pyridin-2yl)pyrimidine-4-carboxamido)hexanoyl]-glycine), have been synthesized as building blocks for Ru(II)-PNA oligomers and characterized by IR and (1)H NMR spectroscopy, mass spectrometry, electrochemistry and elemental analysis. As a proof of principle, M1 was incorporated on the solid phase within the PNA sequences H-g-c-a-a-t-a-a-a-a-Lys-NH(2) (PNA1) and H-P-K-K-K-R-K-V-g-c-a-a-t-a-a-a-a-lys-NH(2) (PNA4) to give PNA2 (H-g-c-a-a-t-a-a-a-a-M1-lys-NH(2)) and PNA3 (H-P-K-K-K-R-K-V-g-c-a-a-t-a-a-a-a-M1-lys-NH(2)), respectively. The two Ru(II)-PNA oligomers, PNA2 and PNA3, displayed a metal to ligand charge transfer (MLCT) transition band centered around 445 nm and an emission maximum at about 680 nm following 450 nm excitation in aqueous solutions (10 mM PBS, pH 7.4). The absorption and emission response of the duplexes formed with the cDNA strand (DNA: 5'-T-T-T-T-T-T-T-A-T-T-G-C-T-T-T-3') showed no major variations, suggesting that the electronic properties of the Ru(II) complexes are largely unaffected by hybridization. The thermal stability of the PNA·DNA duplexes, as evaluated from UV melting experiments, is enhanced compared to the corresponding nonmetalated duplexes. The melting temperature (T(m)) was almost 8 °C higher for PNA2·DNA duplex, and 4 °C for PNA3·DNA duplex, with the stabilization attributed to the electrostatic interaction between the cationic residues (Ru(II) unit and positively charged lysine/arginine) and the polyanionic DNA backbone. In presence of tripropylamine (TPA) as co-reactant, PNA2, PNA3, PNA2·DNA and PNA3·DNA displayed strong electrochemiluminescence (ECL) signals even at submicromolar concentrations. Importantly, the combination of spectrochemical, thermal and ECL properties possessed by the Ru(II)-PNA sequences offer an elegant approach for the design of highly sensitive multimodal biosensing tools.

Efficient plasmid DNA cleavage by copper(II) complexes of 1,4,7-triazacyclononane ligands featuring xylyl-linked guanidinium groups.

Three new metal-coordinating ligands, L(1), L(2), and L(3), have been prepared by appending o-, m-, and p-xylylguanidine pendants, respectively, to one of the nitrogen atoms of 1,4,7-triazacyclononane (tacn). The copper(II) complexes of these ligands are able to accelerate cleavage of the P-O bonds within the model phosphodiesters bis(p-nitrophenyl)phosphate (BNPP) and [2-(hydroxypropyl)-p-nitrophenyl]phosphate (HPNPP), as well as supercoiled pBR 322 plasmid DNA. Their reactivity toward BNPP and HPNPP is not significantly different from that of the nonguanidinylated analogues, [Cu(tacn)(OH(2))(2)](2+) and [Cu(1-benzyl-tacn)(OH(2))(2)](2+), but they cleave plasmid DNA at considerably faster rates than either of these two complexes. The complex of L(1), [Cu(L(1)H(+))(OH(2))(2)](3+), is the most active of the series, cleaving the supercoiled plasmid DNA (form I) to the relaxed circular form (form II) with a k(obs) value of (2.7 ± 0.3) × 10(-4) s(-1), which corresponds to a rate enhancement of 22- and 12-fold compared to those of [Cu(tacn)(OH(2))(2)](2+) and [Cu(1-benzyl-tacn)(OH(2))(2)](2+), respectively. Because of the relatively fast rate of plasmid DNA cleavage, an observed rate constant of (1.2 ± 0.5) × 10(-5) s(-1) for cleavage of form II DNA to form III was also able to be determined. The X-ray crystal structures of the copper(II) complexes of L(1) and L(3) show that the distorted square-pyramidal copper(II) coordination sphere is occupied by three nitrogen atoms from the tacn ring and two chloride ions. In both complexes, the protonated guanidinium pendants extend away from the metal and form hydrogen bonds with solvent molecules and counterions present in the crystal lattice. In the complex of L(1), the distance between the guanidinium group and the copper(II) center is similar to that separating the adjacent phosphodiester groups in DNA (ca. 6 Å). The overall geometry of the complex is also such that if the guanidinium group were to form charge-assisted hydrogen-bonding interactions with a phosphodiester group, a metal-bound hydroxide would be well-positioned to affect the nucleophilic attack on the neighboring phosphodiester linkage. The enhanced reactivity of the complex of L(1) at neutral pH appears to also be, in part, due to the relatively low pK(a) of 6.4 for one of the coordinated water molecules.

Synthesis, structure, and DNA cleavage properties of copper(II) complexes of 1,4,7-triazacyclononane ligands featuring pairs of guanidine pendants.

Two new ligands, L(1) and L(2), have been prepared via N-functionalization of 1,4,7-triazacyclononane (tacn) with pairs of ethyl- or propyl-guanidine pendants, respectively. The X-ray crystal structure of [CuL(1)](ClO4)2 (C1) isolated from basic solution (pH 9) indicates that a secondary amine nitrogen from each guanidine pendants coordinates to the copper(II) center in addition to the nitrogen atoms in the tacn macrocycle, resulting in a five-coordinate complex with intermediate square-pyramidal/trigonal bipyramidal geometry. The guanidines adopt an unusual coordination mode in that their amine nitrogen nearest to the tacn macrocycle binds to the copper(II) center, forming very stable five-membered chelate rings. A spectrophotometric pH titration established the pK(app) for the deprotonation and coordination of each guanidine group to be 3.98 and 5.72, and revealed that [CuL(1)](2+) is the only detectable species present in solution above pH ∼ 8. The solution speciation of the CuL(2) complex (C2) is more complex, with at least 5 deprotonation steps over the pH range 4-12.5, and mononuclear and binuclear complexes coexisting. Analysis of the spectrophotometric data provided apparent deprotonation constants, and suggests that solutions at pH ∼ 7.5 contain the maximum proportion of polynuclear complexes. Complex C1 exhibits virtually no cleavage activity toward the model phosphate diesters, bis(p-nitrophenyl)phosphate (BNPP) and 2-hydroxypropyl-p-nitrophenyl phosphate (HPNPP), while C2 exhibits moderate activity. For C2, the respective kobs values measured at pH 7.0 (7.24 (± 0.08) × 10(-5) s(-1) (BNPP at 50 °C) and 3.2 (± 0.3) × 10(-5) s(-1) (HPNPP at 25 °C)) are 40- and 10-times faster than [Cu(tacn)(OH2)2](2+) complex. Both complexes cleave supercoiled pBR 322 plasmid DNA, indicating that the guanidine pendants of [CuL(1)](2+) may have been displaced from the copper coordination sphere to allow for DNA binding and subsequent cleavage. The rate of DNA cleavage by C2 is twice that measured for [Cu(tacn)(OH2)2](2+), suggesting some degree of cooperativity between the copper center and guanidinium pendants in the hydrolysis of the phosphate ester linkages of DNA. A predominantly hydrolytic cleavage mechanism was confirmed through experiments performed either in the presence of various radical scavengers or under anaerobic conditions.

Electrochemiluminescent peptide nucleic acid-like monomers containing Ru(II)-dipyridoquinoxaline and Ru(II)-dipyridophenazine complexes.

A series of Ru(II)-peptide nucleic acid (PNA)-like monomers, [Ru(bpy)(2)(dpq-L-PNA-OH)](2+) (M1), [Ru(phen)(2)(dpq-L-PNA-OH)](2+) (M2), [Ru(bpy)(2)(dppz-L-PNA-OH)](2+) (M3), and [Ru(phen)(2)(dppz-L-PNA-OH)](2+) (M4) (bpy = 2,2'-bipyridine, phen = 1,10-phenanthroline, dpq-L-PNA-OH = 2-(N-(2-(((9H-fluoren-9-yl)methoxy)carbonylamino)ethyl)-6-(dipyrido[3,2-a:2',3'-c]phenazine-11-carboxamido)hexanamido)acetic acid, dppz-L-PNA-OH = 2-(N-(2-(((9H-fluoren-9-yl) methoxy)carbonylamino)ethyl)-6-(dipyrido[3,2-f:2',3'-h]quinoxaline-2-carboxamido)acetic acid) have been synthesized and characterized by IR and (1)H NMR spectroscopy, mass spectrometry, and elemental analysis. As is typical for Ru(II)-tris(diimine) complexes, acetonitrile solutions of these complexes (M1-M4) show MLCT transitions in the 443-455 nm region and emission maxima at 618, 613, 658, and 660 nm, respectively, upon photoexcitation at 450 nm. Changes in the ligand environment around the Ru(II) center are reflected in the luminescence and electrochemical response obtained from these monomers. The emission intensity and quantum yield for M1 and M2 were found to be higher than for M3 and M4. Electrochemical studies in acetonitrile show the Ru(II)-PNA monomers to undergo a one-electron redox process associated with Ru(II) to Ru(III) oxidation. A positive shift was observed in the reversible redox potentials for M1-M4 (962, 951, 936, and 938 mV, respectively, vs Fc(0/+) (Fc = ferrocene)) in comparison with [Ru(bpy)(3)](2+) (888 mV vs Fc(0/+)). The ability of the Ru(II)-PNA monomers to generate electrochemiluminescence (ECL) was assessed in acetonitrile solutions containing tripropylamine (TPA) as a coreactant. Intense ECL signals were observed with emission maxima for M1-M4 at 622, 616, 673, and 675 nm, respectively. At an applied potential sufficiently positive to oxidize the ruthenium center, the integrated intensity for ECL from the PNA monomers was found to vary in the order M1 (62%) > M3 (60%) > M4 (46%) > M2 (44%) with respect to [Ru(bpy)(3)](2+) (100%). These findings indicate that such Ru(II)-PNA bioconjugates could be investigated as multimodal labels for biosensing applications.

Contemporary Synthesis of Ultrasmall (sub-10 nm) Upconverting Nanomaterials.

Due to their unique photophysical properties, upconverting nanoparticles (UCNPs), i. e. particles capable of converting near-infrared (NIR) photons into tunable emissions in the range of ultraviolet (UV) to NIR, have great potential for use in various biomedical fields such as bioimaging, photodynamic therapy and bioanalytical applications. As far as biomedical applications are concerned, these materials have a number of advantageous properties such as brilliant luminescence and exceptional photostability. Very small "stealth" particles (sub-10 nm), which can circulate in the body largely undetected by the immune system, are particularly important for in vivo use. The fabrication of such particles, which simultaneously have a defined (ultrasmall) size and the required optical properties, is a great challenge and an area that is in its infancy. This minireview provides a concise overview of recent developments on appropriate synthetic methodologies to produce such UCNPs. Particular attention was given to the influence of both surfactants and dopants used to precisely adjust size, crystalline phase and optical properties of UCNPs.

Synthesis, Structural Characterization and Photodecarbonylation Study of a Dicarbonyl Ruthenium(II)-Bisquinoline Complex.

A photoactivatable ruthenium(II) carbonyl complex mer,cis-[Ru(II)Cl(BisQ)(CO)2]PF6 2 was prepared using a tridentate bisquinoline ligand (BisQ=(2,6-diquinolin-2-yl)pyridin). Compound 2 was thoroughly characterized by standard analytical methods and single crystal X-ray diffraction. The crystal structure of the complex cation reveals a distorted octahedral geometry. The decarbonylation upon exposure to 350 and 420 nm light was monitored by UV/VIS absorbance and Fourier transform infrared spectroscopies in acetonitrile and 1 % (v/v) DMSO in water, respectively. The kinetic of the photodecarbonylation has been elucidated by multivariate curve resolution alternating least-squares analysis. The stepwise decarbonylation follows a serial mechanism. The first decarbonylation occurs very quickly whereas the second decarbonylation step proceeds more slowly. Moreover, the second rate constant is lower in 1 % (v/v) DMSO in water than in acetonitrile. In comparison to 350 nm irradiation, exposure to 420 nm light in acetonitrile results in a lower second rate constant.

Harnessing the Coordination Chemistry of 1,4,7-Triazacyclononane for Biomimicry and Radiopharmaceutical Applications.

1,4,7-Triazacyclononane (TACN)-based mono- and poly-nuclear metal complexes have found extensive use as biological mimics for understanding the structural and operational aspects of complex natural systems. Their coordination flexibility has also provided researchers access to a vast library of radiometal-binding motifs that display excellent thermodynamic stability and kinetic inertness upon metal complexation. Synthetic modification of the TACN backbone has yielded ligands that can form metal complexes with coordination geometries well suited for these applications. In particular, Leone Spiccia's research has played a significant role in accelerating the progress in these two fields. With a focus on his contributions to the topics of biomimicry and radiopharmaceuticals, this Minireview uses relevant examples to put in perspective the utility of macrocyclic coordination chemistry for biological inorganic chemistry applications.

Facile preparation of multifunctionalisable 'stealth' upconverting nanoparticles for biomedical applications.

Pure hexagonal (ß-phase) NaYF4-based hydrophobic upconverting nanoparticles (UCNPs) were surface-modified with O-phospho-l-threonine (OPLT), alendronic acid, and PEG-phosphate ligands to generate water-dispersible UCNPs. Fourier-transform infrared (FTIR) spectroscopy was used to establish the presence of the ligands on the UCNP surface. These UCNPs exhibit great colloidal stability and a near-neutral surface at physiological pH, as confirmed by dynamic light scattering (DLS) and zeta potential (ζ) measurements, respectively. The particles also display excellent long-term stability, with no major adverse effect on the size of UCNPs when kept at pH 7.4. Upon exposure to human serum, PEG-phosphate- and alendronate-coated UCNPs showed no formation of biomolecular corona, as confirmed by SDS-PAGE analysis. The photophysical properties of water-dispersible UCNPs were investigated using steady-state as well as time-resolved luminescence spectroscopy, under excitation at ca. 800 nm. The results clearly show that the UCNPs demonstrate bright upconversion (UC) luminescence. Furthermore, the presence of reactive groups on the NPs, such as free amine groups in alendronate-coated UCNPs, enables further functionalisation of UCNPs with, for example, small molecules, peptides, proteins, and antibodies. Overall these protein corona resistant UCNPs show great biocompatibility and are worthy of further investigation as potential new biomaging probes.

Rapid Synthesis of Sub-10†nm Hexagonal NaYF4-Based Upconverting Nanoparticles using Therminol®â€ 66.

We report a simple one-pot method for the rapid preparation of sub-10 nm pure hexagonal (ß-phase) NaYF4-based upconverting nanoparticles (UCNPs). Using Therminol®â€…66 as a co-solvent, monodisperse UCNPs could be obtained in unusually short reaction times. By varying the reaction time and reaction temperature, it was possible to control precisely the particle size and crystalline phase of the UCNPs. The upconversion (UC) luminescence properties of the nanocrystals were tuned by varying the concentrations of the dopants (Nd3+ and Yb3+ sensitizer ions and Er3+ activator ions). The size and phase-purity of the as-synthesized core and core-shell nanocrystals were assessed by using complementary transmission electron microscopy, dynamic light scattering, X-ray diffraction, and small-angle X-ray scattering studies. In-depth photophysical evaluation of the UCNPs was pursued by using steady-state and time-resolved luminescence spectroscopy. An enhancement in the UC intensity was observed if the nanocrystals, doped with optimized concentrations of lanthanide sensitizer/activator ions, were further coated with an inert/active shell. This was attributed to the suppression of surface-related luminescence quenching effects.