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/H2O)] intermediate and trans [Pt(py)2(OH/H2O)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 anti-symmetric azido vibration, suggesting a possible second intermediate. Experimental proof of subsequent dissociation of azido ligands from platinum is presented, where at least one hydroxyl radical is formed in the reduction of Pt(IV) to Pt(II). Additionally, the photoinduced reaction of 1 with 5'-guanosine monophosphate was studied, and the identity of key photoproducts was assigned with the help of ATR FTIR spectroscopy, mass spectrometry and DFT calculations. The identification of marker bands for 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

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

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Ruthenium(II) complexes and their peptide nucleic acid bioconjugates for therapeutic and biosensing applications

The availability of a wide range of synthetically viable polypyridyl ligands and attractive physicochemical properties for the corresponding Ru(II)-diimine complexes renders them suitable for use as medicinal and imaging probes. The central theme of this thesis is the development of Ru(II)-polypyridyl bioconjugates for biosensing and therapeutic applications. Towards this end, a library of diverse Ru(II) complexes, with polypyridyl ligands judiciously selected to address the essential criteria for the targeted applications, and their model constructs based on peptide nucleic acid (PNA) backbone were prepared and screened for their photophysical, photochemical, electrochemical, and electrochemiluminescent properties. Furthermore, to assist in live cell applications, analytical studies on uptake and interaction of Ru(II)-PNA bioconjugates with lipid membranes were also performed. A family of carboxy functionalized ruthenium(II) dicarbonyl complexes of formula [Ru(L)(CO)2Cl2] (L = Me2bpy = 4,4'-dimethyl-2,2'-bipyridine; Me-bpyCHO = 4'-methyl-2,2'-bipyridine-4-carboxyaldehyde; Me-bpyCOOH = 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 [Ru(L)(CO)2Cl]+ (L = tpyCOOH = 6-(2,2':6',2''-terpyridine-4'-yloxy)hexanoic acid) were prepared which exhibited photoinduced CO release when irradiated around 310 nm, the wavelength for their maximum absorption. The 2,2'-bipyridine and 2,2':6',2''-terpyridine based complexes displayed better CO release properties (one equivalent per complex) than the corresponding dipyrido[3,2-a:2',3'-c]phenazine and pyridyl-pyrimidine counterparts. Investigations carried out on [Ru(Cpp-L- PNA)(CO)2Cl2] (Cpp-L-PNA = tert-butyl-N [2 (N-9-fluorenylmethoxycarbonyl)aminoethyl]-N-[6-(2-(pyridin-2yl)pyrimidine-4-carboxamido)hexanoyl]-glycinate) also demonstrated that CO release was unaffected by further conjugation of the parent ligand to carrier peptides and delivery vectors, such as a monomeric peptide nucleic acid (PNA) backbone in this case. Such Ru(II)-polypyridyl bis(carbonyl) complexes represent a promising class of photoactivatable CO releasing molecules (PhotoCORMs). A series of PNA-like-monomers containing Ru(II)-pyridylpyrimidine /dipyridoquinoxaline/dipyridophenazine complexes were prepared and characterised by IR and 1H NMR spectroscopy, mass spectrometry, electrochemistry and elemental analysis. These new compounds displayed electronic absorption and emission profiles typical of [Ru(tris(diimine))]2+ complexes, viz., a metal to ligand charge transfer (MLCT) band centered around 450 nm and an emission maximum in the 610-665 nm region following photoexcitation at 450 nm. The emission intensity and quantum yields for monomers incorporating dipyridophenazine or dipyridoquinoxaline units were found to be higher than for other Ru(II)-PNA-like monomers. The cyclic voltammetry revealed a reversible one electron RuII to RuIII oxidation process for these Ru(II)-PNA-like monomers. In comparison to the reversible redox potential for the [Ru(bpy)3]2+/[Ru(bpy)3]3+ system (888 mV vs Fc0/+), a positive shift in potential of up to 179 mV was observed for the Ru(II)-PNA monomers (935-1065 mV vs Fc0/+). The Ru(II)-PNA-like monomers displayed reasonably intense electrochemiluminescence (ECL) responses in the presence of a tripropylamine (TPA) co reactant, with the monomers [Ru(bpy)2(Cpp-L-PNA-OH)]2+ and [Ru(phen)2(Cpp-L-PNA-OH)] showing ECL-activity equivalent to [Ru(bpy)3]2+, regarded as the benchmark ECL emitter. Solid phase synthesis of bioconjugate constructs consisting of Ru(II)-tris(diimine) connected to PNA oligomers was achieved using a Ru(II)-PNA monomer, [Ru(bpy)2(Cpp-L-PNA-OH)]2+. Insertion of the Ru(II) fluorophore within a PNA sequence was demonstrated for the first time using this compound. The absorption spectrum for the Ru(II)-PNA conjugates displayed a broad MLCT transition band centered around 445 nm and an emission maximum at ca. 680 nm following 450 nm excitation. The absorption and emission response of the incorporated Ru(II)-polypyridyl unit were unaffected by duplex formation between the Ru(II)-PNA oligomer and the complementary DNA strand. However, the Ru-PNA•DNA duplexes exhibited greater thermal stability when compared to the corresponding non-metalated duplexes. The stronger electrostatic interactions between the Ru-PNA and polyanionic DNA oligomer, attributed to the additional positive charges introduced (Ru(II) unit and positively charged lysine/arginine), account for the enhanced duplex stability. The Ru(II)-PNA bioconjugates and their corresponding PNA•DNA duplexes were ECL active, producing intense ECL in the presence of a co-reactant (TPA) even at submicromolar concentrations. Quartz Crystal Microbalance with Dissipation (QCM-D) monitoring of interactions between PNA/peptide/Ru(II) conjugates and biomimetic membranes showed the unmodified PNA oligomer and its Ru(II) conjugate to traverse freely across the membrane in a trans-membrane manner without causing significant changes in membrane structure, for all lipid compositions. On the contrary, the Nuclear Localised Signal Peptide (NLS) conjugated PNA sequences showed membrane specific activities. In model mammalian membranes, rapid trans-membrane insertion was observed followed by a concentration dependent material removal (mainly from the membrane surface). The PNA sequences were found to cause greater disruption to the bacterial-mimetic membrane system. Strong interactions with the membranes also tend to cause irreversible structural changes, an effect prevailing in all model systems, suggesting similar activity mechanisms. The variations in the magnitude of the structural changes and disruptive tendency of PNAs are ascribed to their cationic charge and hydrophobicity along with the physical state of the model membrane used

Ruthenium(II) complexes and their peptide nucleic acid bioconjugates for therapeutic and biosensing applications

The availability of a wide range of synthetically viable polypyridyl ligands and attractive physicochemical properties for the corresponding Ru(II)-diimine complexes renders them suitable for use as medicinal and imaging probes. The central theme of this thesis is the development of Ru(II)-polypyridyl bioconjugates for biosensing and therapeutic applications. Towards this end, a library of diverse Ru(II) complexes, with polypyridyl ligands judiciously selected to address the essential criteria for the targeted applications, and their model constructs based on peptide nucleic acid (PNA) backbone were prepared and screened for their photophysical, photochemical, electrochemical, and electrochemiluminescent properties. Furthermore, to assist in live cell applications, analytical studies on uptake and interaction of Ru(II)-PNA bioconjugates with lipid membranes were also performed. A family of carboxy functionalized ruthenium(II) dicarbonyl complexes of formula [Ru(L)(CO)2Cl2] (L = Me2bpy = 4,4'-dimethyl-2,2'-bipyridine; Me-bpyCHO = 4'-methyl-2,2'-bipyridine-4-carboxyaldehyde; Me-bpyCOOH = 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 [Ru(L)(CO)2Cl]+ (L = tpyCOOH = 6-(2,2':6',2''-terpyridine-4'-yloxy)hexanoic acid) were prepared which exhibited photoinduced CO release when irradiated around 310 nm, the wavelength for their maximum absorption. The 2,2'-bipyridine and 2,2':6',2''-terpyridine based complexes displayed better CO release properties (one equivalent per complex) than the corresponding dipyrido[3,2-a:2',3'-c]phenazine and pyridyl-pyrimidine counterparts. Investigations carried out on [Ru(Cpp-L- PNA)(CO)2Cl2] (Cpp-L-PNA = tert-butyl-N [2 (N-9-fluorenylmethoxycarbonyl)aminoethyl]-N-[6-(2-(pyridin-2yl)pyrimidine-4-carboxamido)hexanoyl]-glycinate) also demonstrated that CO release was unaffected by further conjugation of the parent ligand to carrier peptides and delivery vectors, such as a monomeric peptide nucleic acid (PNA) backbone in this case. Such Ru(II)-polypyridyl bis(carbonyl) complexes represent a promising class of photoactivatable CO releasing molecules (PhotoCORMs). A series of PNA-like-monomers containing Ru(II)-pyridylpyrimidine /dipyridoquinoxaline/dipyridophenazine complexes were prepared and characterised by IR and 1H NMR spectroscopy, mass spectrometry, electrochemistry and elemental analysis. These new compounds displayed electronic absorption and emission profiles typical of [Ru(tris(diimine))]2+ complexes, viz., a metal to ligand charge transfer (MLCT) band centered around 450 nm and an emission maximum in the 610-665 nm region following photoexcitation at 450 nm. The emission intensity and quantum yields for monomers incorporating dipyridophenazine or dipyridoquinoxaline units were found to be higher than for other Ru(II)-PNA-like monomers. The cyclic voltammetry revealed a reversible one electron RuII to RuIII oxidation process for these Ru(II)-PNA-like monomers. In comparison to the reversible redox potential for the [Ru(bpy)3]2+/[Ru(bpy)3]3+ system (888 mV vs Fc0/+), a positive shift in potential of up to 179 mV was observed for the Ru(II)-PNA monomers (935-1065 mV vs Fc0/+). The Ru(II)-PNA-like monomers displayed reasonably intense electrochemiluminescence (ECL) responses in the presence of a tripropylamine (TPA) co reactant, with the monomers [Ru(bpy)2(Cpp-L-PNA-OH)]2+ and [Ru(phen)2(Cpp-L-PNA-OH)] showing ECL-activity equivalent to [Ru(bpy)3]2+, regarded as the benchmark ECL emitter. Solid phase synthesis of bioconjugate constructs consisting of Ru(II)-tris(diimine) connected to PNA oligomers was achieved using a Ru(II)-PNA monomer, [Ru(bpy)2(Cpp-L-PNA-OH)]2+. Insertion of the Ru(II) fluorophore within a PNA sequence was demonstrated for the first time using this compound. The absorption spectrum for the Ru(II)-PNA conjugates displayed a broad MLCT transition band centered around 445 nm and an emission maximum at ca. 680 nm following 450 nm excitation. The absorption and emission response of the incorporated Ru(II)-polypyridyl unit were unaffected by duplex formation between the Ru(II)-PNA oligomer and the complementary DNA strand. However, the Ru-PNA•DNA duplexes exhibited greater thermal stability when compared to the corresponding non-metalated duplexes. The stronger electrostatic interactions between the Ru-PNA and polyanionic DNA oligomer, attributed to the additional positive charges introduced (Ru(II) unit and positively charged lysine/arginine), account for the enhanced duplex stability. The Ru(II)-PNA bioconjugates and their corresponding PNA•DNA duplexes were ECL active, producing intense ECL in the presence of a co-reactant (TPA) even at submicromolar concentrations. Quartz Crystal Microbalance with Dissipation (QCM-D) monitoring of interactions between PNA/peptide/Ru(II) conjugates and biomimetic membranes showed the unmodified PNA oligomer and its Ru(II) conjugate to traverse freely across the membrane in a trans-membrane manner without causing significant changes in membrane structure, for all lipid compositions. On the contrary, the Nuclear Localised Signal Peptide (NLS) conjugated PNA sequences showed membrane specific activities. In model mammalian membranes, rapid trans-membrane insertion was observed followed by a concentration dependent material removal (mainly from the membrane surface). The PNA sequences were found to cause greater disruption to the bacterial-mimetic membrane system. Strong interactions with the membranes also tend to cause irreversible structural changes, an effect prevailing in all model systems, suggesting similar activity mechanisms. The variations in the magnitude of the structural changes and disruptive tendency of PNAs are ascribed to their cationic charge and hydrophobicity along with the physical state of the model membrane used

Towards Tris(diimine)-Ru(II) and Bis(quinoline) Re(I)(CO)3 Complexes as Photoactivated Anticancer Drug Candidates

The clinical success of cisplatin continues to inspire the development of metal-based anticancer drug candidates. This article is meant to present the current state-of-the-art and science of ruthenium(II)- and rhenium(I)-based anticancer drug candidates born out of our work in this field. Our recent efforts to elicit photoactivation of intact (organo)metallic anticancer drug candidates as a promising way for commanding their activity within cancer cells are also briefly summarized