Stability Of Metal Complexes Research Articles

New heterocyclic Schiff base‐metal complex: Synthesis, characterization, density functional theory study, and antimicrobial evaluation

A new series of heterocyclic Schiff base complexes derived from the condensation of nicotinohydrazide with different heterocyclic aldehyde, followed by metalation with Co (II) and Cu (II) metal ions. The chemical structures of the synthesized compounds have been characterized by elemental analysis, Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, ultraviolet–visible spectroscopy, and magnetic susceptibility. The spectral and magnetic data confirmed their chemical structures, furthermore, the geometry of Cu (II) and Co (II) complexes were square‐planar or distorted tetrahedral. X‐ray diffraction measurements supported the crystalline structures of the metal complexes rather than the amorphous form of the parent Schiff bases. Thermogravimetric analysis revealed the upgrading of the thermal stability of metal complexes compared to their Schiff base ligands. Antimicrobial efficacies of the Schiff base ligands and their corresponded metal complexes were screened against Staphylococcus aureus and Bacillus subtilis as Gram‐positive bacteria, Escherichia coli, and Proteus vulgaris as Gram‐negative bacteria, and fungi Aspergillus flavus, Candida albicans. The antimicrobial inhibitory data revealed higher antimicrobial activities of metal complexes compared to their Schiff base ligands. Density functional theory module by Gaussian 09 W software proved the chemical reactivity of the prepared Schiff base ligands based on the total energy, energy gap, EHOMO, and ELUMO energies.

Electrochemical Study for the Thiazole Derivative's Using Schiff Base Ligand Based Coordination Complexes

Since the synthesis of transition metal complexes are showing Here we are synthesizing the thiazole derivatives Schiff base ligands, L1 and L2 (where, L1 = N,N'E,N,N'E)-N,N'-(1,3-phenylene bis (methanylylidene)) bis (5-nitrobenzo [d]thiazoL2-amine (m-NTA) and L2 = N,N'E,N,N'E)-N,N'-(1,3-phenylene bis (methanylylidene)) bis(5-methyl thiazoL2-amine (m-MTA) ), and coordinated with transition metals (such as; Co, Ni, Cu, Zn and Cd) using lone-pair coordination method developed complexation is high performance complex material and further using different technique and applicability of the calorimetric sensing and electrochemical sensing. Therefore, These complexes were characterized by FT-IR, 1H NMR, UV-Visible and cyclic voltammetry are having characteristic absorption and potential high performance CV show different type of stable transition metal complex and, Fluorescence and Mass spectra, which shows the significant changes in the cyclic voltammetry the redox potential. The electrochemical study was also carried out for these complexes which show the clear redox behavior of complexes. The significant change in CV properties which is clearly exhibited by CV graphs where we can see a prominent reduction peaks M2+ to M are showing at -0.4 V vs. we found that in the case of L2 there is less prominent reduction peaks observed in comparison to L1.

Phosphorescent Zwitterionic Pt(II) N‐Heterocyclic Allenylidene Complexes: Metallophilicity and Ionic Self‐Assembly†

Main observation and conclusionThree zwitterionic and one cationic N‐heterocyclic allenylidene (NHA) platinum(II) complexes were prepared and characterized via NMR, HR‐MS, and FT‐IR, etc. Single crystal structure analyses revealed the various intermolecular packing modes via multiple noncovalent interactions (short Pt···Pt contacts, π‐π interactions). The spectroscopic data demonstrated stability of the allenylidene metal complexes is largely ascribed to the resonance structures of zwitterionic acetylide. The zwitterionic and analogue cationic NHA Pt(II) monomers showed similar steady‐state photoluminescent properties in dilute fluid solution. Highly efficient solid‐state phosphorescent emissions (quantum yield up to 20%) of these NHA Pt(II) complexes are correlated with their dispersive metallophilic Pt···Pt interactions. HR‐MS spectrum indicated zwitterionic monomers can self‐assemble into oligomers, such as dimer, trimer and even hexamer in a mixed H2O/MeOH solvent. Meanwhile, molecular aggregates showed variable red‐shifted phosphorescence by manipulating the concentration, temperature, time and solvent in the self‐assembly of zwitterionic NHA platinum(II) complex.

AAZTA: The rise of mesocyclic chelating agents for metal coordination in medicine

• AAZTA: an easily synthesised mesocyclic chelating agent. • Paramagnetic AAZTA complexes are studied as efficient MRI contrast agents. • Radioactive AAZTA complexes are evaluated for nuclear medicine applications. • Bifunctional AAZTA derivatives are used to prepare conjugates for diagnostics. The application of metal ions for diagnostic and therapeutic purposes is nowadays a well consolidated practice in current medicine. Gd 3+ for magnetic resonance imaging (MRI), Ga 3+ for positron emission tomography (PET), In 3+ for single photon emission computed tomography (SPECT) and the β-emitter Lu 3+ for tumour treatment are the most representative examples. Metal ions employed in medicine must be administered as stable and inert metal complexes, mainly for safety reasons and targeting purposes. In the last years many new chelating agents have been designed, prepared and studied in order to improve properties such as thermodynamic stability, kinetic inertness, target selectivity and many other characteristics of complexes thereof. The structure of these chelating agents is almost invariably based on linear or macrocyclic backbones. The chelating agent AAZTA (6-amino-6-methylperhydro-1,4-diazepinetetraacetic acid), featuring a mesocyclic 7-membered ring has found steadily increasing attention since its inception in the early 2000s and is now an affirmed alternative for the formation of stable complexes with several metal ions. The scope of this review is to provide the reader with a comprehensive survey on the synthesis and the applications of AAZTA and its derivatives developed in the last two decades.

Synthesis, spectral characterization, and antimicrobial evaluation of new imine derived from 3‐methylthiophene‐2‐carboxaldehyde and its Co(II), Ni(II), Cu(II), and Zn(II) metal complexes

Some new 1:1 (ML) and 1:2 (ML2) metal complexes of Co(II), Ni(II), Cu(II), and Zn(II) have been synthesized with novel ligand, that is, 4‐(3‐methylthiophene‐2‐ylmethyleneamino)‐3‐mercapto‐6‐methyl‐5‐oxo‐1,2,4‐triazine. Ligand and its metal complexes were characterized on the basis of various physicochemical techniques like elemental analysis, magnetic moment, molar conductance, cyclic voltammetry, and spectroscopic (1H‐NMR, infrared [IR], electronic, fluorescence, and electron spin resonance [ESR]) data. On the basis of these studies, octahedral and square planar geometries have been proposed for Co(II), Ni(II), Zn(II), and Cu(II) metal complexes, respectively. Thermogravimetric analysis (TGA) was carried out to study the thermal decomposition and stability of metal complexes. Electrochemical behavior of Cu(II) complexes have also been explored by cyclic voltammetry. The complexes have shown promising antimicrobial activity when checked by in vitro method against some bacterial and fungal strains. In addition to these studies, quantum mechanical approach was also performed in order to find some structural information of newly synthesized compounds.

Synthesis, characterization and DFT investigation of new metal complexes of Ni(II), Mn(II) and VO(IV) containing N,O-donor Schiff base ligand

In this work, a bidentate Schiff base ligand (HL) containing N and O as donor heteroatoms has been used to synthesize series of new stable metal complexes of general composition of M(L)2 with M = Mn, Ni and VO. This ligand was obtained from condensation of 2-methoxybenzylamine on 2,3-dihydroxybenzaldehyde in methanolic solutions in which its complexes were obtained by mixing the corresponding metal acetate salt and the ligand in 1:2 molar ratio. The resulting three complexes have been characterized by different analytical techniques like FT-IR, UV-Vis, mass spectroscopy, thermogravimetry and cyclic voltammetry, to identify their molecular structures and redox/electrochemical properties. Moreover, the effect of the metal on the complexes electronic properties with their reactivity has also been studied by Density Functional Theory (DFT). The stable structures were optimized by using the hybrid B3LYP/6–31 G method. The spectroscopic data obtained suggest that the metal is bonded to the ligand through the phenolic-like oxygen and the imine-type nitrogen atoms. Electronic and vibrational absorption spectra of the nickel complex was found to be of square-planar geometry while square-pyramidal and octahedral geometries have been proposed for VO(IV) and Mn(II) complexes, respectively. The thermogravimetric analyses of these complexes confirmed the presence of water molecules in their structures and thermal decomposition led to the formation of metal oxides as the latest residues. The voltammogram of the Ni(II) complex suggests the existence of quasi-reversible redox system in DMSO solution.

Synthesis of a rod-based porous coordination polymer from a nucleotide as a sequential chiral inductor

We report the two-step synthesis of a novel chiral rod-based porous coordination polymer (PCP). The chemical approach consists of the use of a previously prepared bis(ethylenediamine) copper monomer [Cu(en)]2(NO3)2 [where en = ethylenediamine] reacting with the cytidine 5′-monophosphate (CMP) nucleotide. The bis(ethylenediamine) copper compound—stabilized by axial coordination of nitrate counter-anions—reacts in the presence of sodium salt of CMP to yield right-handed copper(II) chains of P helicity with formula [Cu2(en)2(CMP)2]·5H2O (1). The axial coordination of the CMP2- ligands through the N3 and O2 sites (free nitrogen and carbonyl groups) of the cytosine nucleobase and oxygen atoms of phosphate moieties, ensure stabilization of the neutral chiral polymer. The supramolecular organization involves strong hydrogen bonding interactions to build supramolecular chains of the same helicity. The resulting PCP constitutes one of the few examples of CMP compounds exhibiting coordination involving both nucleobase and phosphate moieties, where a highly stable metal complex is used as precursor for the rational construction of rod-based hydrogen metal-organic frameworks (HMOFs). Furthermore, it shows the intrinsic capability of biomolecules to act as chiral transfer systems.

Benchmarking magnetic and spectroscopic properties on highly stable 3d metal complexes with tuneable bis(benzoxazol-2-yl)methanide ligands.

Two series a and b of 3d metal based complexes 1-4 [MII{(4-R-NCOC6H4)2CH}2], (with M = Mn (1), Fe (2), Co (3), Ni (4) and R = H (a) or Me (b)) were synthesised and structurally characterized. The complexes were found to crystallize differently depending on the dication ionic radius and the ligand substitution. All complexes showed remarkable X-ray diffraction resolution that will allow further advanced diffraction experiments. Subsequently, their spectroscopic and magnetic properties were analysed. Complexes 3a and 3b notably show slow magnetic relaxation of their magnetization and represent simple model systems relaxing through a phonon-bottleneck process (3a) or as a field-induced single-molecule magnet (3b, Ueff = 45.0 cm-1). Remarkably, the magnetic anisotropy in the manganese complex 1b results in induced slow magnetic relaxation. The influence of the dual 4-methylation of the ligands was investigated and found to generate important variations in the physical features of the corresponding complexes. Accessible via one-pot synthesis, these are highly robust against oxidation and moisture. Through smart ligand engineering, they represent stable and tuneable compounds for benchmarking purposes through standard and less-standard characterization methods.

ESTIMATING THE STABILITY OF METAL–LIGAND BONDING IN CARBOXYL-CONTAINING POLYMER COMPLEXES BY IR SPECTROSCOPY

The stability of metal–ligand (carboxyl-containing polymer (CCP)) bonding in transition metal complexes is estimated and juxtaposed using Δν(COO) values. The Δν(COO) value is determined from the difference between stretching vibrations of the carboxylate ion in the IR spectra. It is shown that Δν(COO) values for transition metal complexes with ethylenediaminetetraacetic acid (EDTA) increase in the order that directly depends on the order of their stability in the series Fe3+ > Cr3+ > Cu2+ > Ni2+ > Co2+ > Mn2+. The established relationship between the Δν(COO) value and the stability of metal complexes is used to determine the series of metal affinity for carboxyl-containing biopolymers such as citrus pectin (CP) and chitosan succinate (CS). The obtained data indicate that the affinity for metal corresponds to series Cr3+ > Cu2+ > Co2+ > Mn2+ > Ni2+ for citrus pectin (CP) and to series Cu2+ > Cr3+ ≈ Ni2+ ≈ Co2+ > Mn2+ for chitosan succinate (CS).

Transition metal complexes of 6‐mercaptopurine: Characterization, Theoretical calculation, DNA‐Binding, molecular docking, and anticancer activity

6‐mercaptopurine (6‐MP) is used for treating various cancers and autoimmune disorders. A few examples of transition metal complexes of 6‐MP have been shown to enhance its anticancer activity, but many remain untested. We isolated five highly stable and colored metal complexes of 6‐MP and confirmed their structures by elemental analysis, spectral, and thermal techniques. Infrared (IR) spectra revealed that 6‐MP is a bidentate ligand that interacts through sulfur and pyrimidine nitrogen in a 1:2 (M:L) molar ratio. The magnetic susceptibility and electron paramagnetic resonance (EPR) spectra for the Cu(II) complex revealed an octahedral arrangement around the metal ion with strong covalent bonding. The fully optimized geometries of the metal structures obtained using density function theory (DFT)/B3LYP calculations were used to verify the structural and biological features. DNA titration revealed that the octahedral Cu(II) complex has a critical binding constant value ofKb= 8 × 105. Docking studies using three different cancer protein receptors were used to predict the biological applications of the synthesized drug‐metal complexes. Finally, cytotoxicity assays against a myeloma cancer cell line (MM) and a colon cancer cell line (Caco‐2) revealed favorable anticancer activity for the copper complex, exceeding that of the gold‐standard chemotherapeutic cisplatin.

Extraction of various metal ions by open-chain crown ether bridged diphosphates in supercritical carbon dioxide

Abstract Various toxic metal ions were successfully removed from solid matrix into supercritical CO2 (scCO2) by open-chain crown ether bridged diphosphates at 313.15 K and 20 MPa, these diphosphates with different ester side chains and different length of ethylene oxide bridge group are highly soluble in supercritical CO2. The extraction efficiency (E%) of heavy metals is between 55 and 89%. Mulliken charge distribution of ligand’s P=O coordination group was calculated to indicate the stability of metal complex. The ligand structure effects and the rationale for different selectivity were discussed. In addition, binding property of these diphosphates towards the alkaline earth metals was further studied following the same extraction procedures. Alkaline earth metal ions Ca2+, Sr2+ and Ba2+ were extracted with E% at 49–74%, 50–73% and 16–64%, respectively. DFT calculations were performed to investigate the interaction energy of the complexes and the correlation with the E% was discussed.

Review on the Comparison of the Chemical Reactivity of Cyanex 272, Cyanex 301 and Cyanex 302 for Their Application to Metal Separation from Acid Media

Cyanex extractants, such as Cyanex 272, Cyanex 301, and Cyanex 302 have been commercialized and widely used in the extraction and separation of metal ions in hydrometallurgy. Since Cyanex 301 and Cyanex 302 are the derivatives of Cyanex 272, these extractants have similar functional groups. In order to understand the different extraction behaviors of these extractants, an understanding of the relationship between their structure and reactivity is important. We reviewed the physicochemical properties of these extractants, such as their solubility in water, polymerization degree, acidity strength, extraction performance of metal ions, and the interaction with diluent and other extractants on the basis of their chemical structure. Synthetic methods for these extractants were also introduced. This information is of great value in the synthesis of new kinds of extractants for the extraction of metals from a diverse medium. From the literature, the extraction and stripping characteristics of metals by Cyanex 272 and its derivatives from inorganic acids such as HCl, H2SO4, and HNO3 were also reviewed. The replacement of oxygen with sulfur in the functional groups (P = O to P = S group) has two opposing effects. One is to enhance their acidity and extractability due to an increase in the stability of metal complexes, and the other is to make the stripping of metals from the loaded Cyanex 301 difficult.

Recent Advances on the Preparation and Catalytic Applications of Metal Complexes Supported-Mesoporous Silica MCM-41 (Review)

Heterogeneous catalysts were used in several production processes for the synthesis of different products such as chemicals, drugs, energy resources, fuels and other specific products. In recent years, mesoporous silica, in particular MCM-41 was widely used in several fields, including catalysis and catalytic support, due to its remarkable textural properties. This material cannot be used directly in catalysis due to its inner surface containing only silanol groups. Therefore, several attempts were proposed in order to obtain an effective catalyst. The immobilization of metal complexes on the surface of mesoporous silica is one of the most popular methods. The metal complexes immobilized on the mesoporous silica MCM-41 exhibit significant catalytic activities due to the increased dispersion of the active sites and the faster diffusion of large organic molecules. The strong interactions between the metal and the ligand generate significant stability for this kind of catalyst, which allows them to be reused in several cycles without losing their efficiency. This review mainly discusses the immobilization strategies of different metal complexes supported on the mesoporous silica MCM-41. A recent study was presented and well detailed based on the different preparation methods, catalytic applications and the stability of metal complexes supported on mesoporous silica MCM-41.

Metal Coordination: Improving Metal Adsorption on Triethylenetetramine (TETA) Functionalized SBA‐15 Mesoporous Silica Using Potentiometry, EPR and ssNMR (Adv. Mater. Interfaces 15/2020)

Metal ion chelators combined with nanostructure materials proved effective in the treatment and diagnosis of human diseases. Combine potentiometry, EPR and NMR techniques determine ligand content, metal complex stability constants and competition between metallodrugs and endogenous molecules. More details can be found in article number 2000544 by Joanna Izabela Lachowicz, Mariusz Jaremko, and co-workers.

Synthesis of a new tetradentate chelator with 1-Hydoroxy-2(1H)-pyridinone (HOPO) as chelating unit: Interaction with Fe (III), solution thermodynamics and DFT studies

1,2-Hydroxypyridinone (1,2-HOPO) forms very stable transition metal complexes that may be useful in various ways, among these the iron complexes have been long used for the treatment of iron overload diseases like β-Thalassemia. A new tetradentate chelator, 1-hydroxy-N-[3-[2-[2-[3-[(1-hydroxy-6-oxo-pyridine-2carbonyl)amino]propoxy]ethoxy]ethoxy]propyl]-6-oxo-pyridine-2-carboxamide (L) having two 1,2-HOPO units with long chain amine backbone has been synthesized and characterized through various techniques like TLC, solubility, melting point, FT-IR, 1H NMR, 13C NMR, ESI-MS, UV–Vis and emission spectroscopy. The protonation constants of the ligand were determined by both potentiometrically as well as spectrophotometrically in aqueous medium at 25° ±1 °C. The solution thermodynamics of the ligand its Fe(III) complexes in aqueous solution were also studied. The pKa values for ligand are found to be 7.34 and 6.06 and the formation constant of metal complex (M2L3) is found to be logβ230 = 42.45. To support the experimental data, theoretical calculation at DFT level of theory was done using GGA (Gradient Generalized Approximation) with BLYP functional and DZP basis set. The results of calculated thermodynamic properties suggest that, ΔG follows the same trend of protonation as determined by potentiometry and spectrophotometry. Studies of the DFT optimized structures of LH2, LH− shows that, there is π stacking interaction between the hydroxypyridinone rings in the species and the intramolecular π-stacking interaction decreases as the distance between two pyridine ring increases upon deprotonation and was found to be 2.7, 3.2 and 14.6 Å for LH2, LH− and L−2 respectively.

Ultra stable multinuclear metal complexes as homogeneous catalysts for visible-light driven syngas production from pure and diluted CO2

For high reactivity but poor stability of homogeneous metal complexes in CO2 photoreduction, development of durable systems is still a big challenge. Herein, pentanuclear Co(II) complex [Co5(btz)6(NO3)4(H2O)4] (1, btz = benzotriazolate) is explored for converting CO2 to syngas which shows high stability and reactivity in both pure and diluted CO2. Compared with mononuclear structure, multinuclear complex exhibits 212-fold enhancement in reactivity, up to ~2748 TONs, with wide adjustability of H2/CO ratio from 16:1 to 2:1. This reactivity could be maintained over 200 h which is an order of magnitude higher than the durability of mononuclear complex and exceeds most reported homogeneous molecular catalysts. High reactivity is also achieved in extreme low CO2 content (5%). Structural analysis and density functional theory (DFT) calculations support that multinuclear structure and the low energy barrier for photocatalytic intermediate may account for the durable and efficient performance of complex 1. The multinuclear strategy is also adopted to nickel complex. This work probes origin of metal-node-dependent performance for CO2 photoreduction, providing new insights in design of durable and efficient metal complexes for photocatalysis and other applications.

H2CHXhox: Rigid Cyclohexane-Reinforced Nonmacrocyclic Chelating Ligand for [nat/67/68Ga]Ga3.

A rigid chiral acyclic chelator H2CHXhox was synthesized and evaluated for Ga3+-based radiopharmaceutical applications; it was compared to the previously reported hexadentate H2hox to determine the effect of a backbone reinforced from adding a chiral 1S,2S-trans-cyclohexane on metal complex stability, kinetic inertness, and in vivo pharmacokinetics. NMR spectroscopy and theoretical calculation revealed that [Ga(CHXhox)]+ showed a very similar coordination geometry to that of [Ga(hox)]+, and only one isomer in solution was observed by NMR spectroscopy. Solution studies showed that the modification results in a significant improvement in the exceptionally high thermodynamic stability of [Ga(hox)]+ with a 1.56 log unit increase in stability constant (logKML = 35.91(1)). More importantly, H2CHXhox showed very fast Ga3+ complexation at physiological pH 7.4, and acid-assisted Ga3+ complex dissociation kinetic studies (pH 1) in comparison with H2hox revealed a 50-fold increase of the dissociation half-life time from 73 min to 58 h. Fluorescence microscopy imaging study confirmed its cellular uptake and accumulation in endoplasmic reticulum and mitochondria. MTT studies indicated a quite low cytotoxicity of [Ga(CHXhox)]+ over a large concentration range. Dynamic PET imaging studies showed no accumulation in muscle, lungs, bone, and brain, suggesting no release of free Ga3+ ions. [68Ga][Ga(CHXhox)]+ is cleared from the mouse via hepatobiliary and renal pathways. Compared to [68Ga][Ga(hox)]+, the increased lipophilicity of [68Ga][Ga(CHXhox)]+ enhanced heart and liver uptake and decreased kidney clearance. [67Ga][Ga(CHXhox)]+ SPECT/CT imaging and biodistribution study revealed good clearance from liver to gallbladder after 90 min and finally into feces after 5 h. No decomposition or transchelation was observed over the 5 h study. These results confirmed H2CHXhox to be an obvious improvement over H2hox and an excellent candidate in this new "ox" family for the development of radiopharmaceutical compounds.

COMPLEXATION OF APPLE PECTIN, MODIFIED TO PHARMACOPHORE, WITH THE CATIONS MANGANESE (II) IN AQUEOUS SOLUTIONS

Complex formation in systems containing manganese (II), natural pectin and/or pectin modified by organic pharmacophores (nicotine, salicylic, 5-aminosalicylic, anthranilic acids) was studied by spectral (UV-, IR-, NMR 13C spectroscopy), potentiometric and viscometric methods. Method isomolar series and the molar relationship defined by the molar composition and the range of stability of metal complexes: pectin + nicotinic acid > pectin + acid 5-aminosalicylic > pectin + anthranilic acid > pectin + salicylic acid > native pectin. It is shown that the stability constant of metal complexes is significantly influenced by the reaction temperature and the structure of the pharmacophore. The presence of an amino group in the structure of an aromatic molecule increases the stability of metal complexes by 1.5–2 orders of magnitude. The standard thermodynamic characteristics (∆Hº; ∆Gº; ∆Sº) are calculated, which indicate that the processes of complexation in all cases are enthalpy-entropy favorable (∆Hº<0, ∆Sº>0) and proceed spontaneously (∆Gº<0). The influence of the structure of the drug compound in the polymer ligand on a number of physical and chemical properties of metal complexes was revealed. The data of NMR 13C and IR-spectra allow us to conclude that not only carboxyl groups but also hydroxyl functions of polymer matrices participate in the coordination interaction of pectin and/or pharmacophore-containing pectin with manganese (II) cations.

Synthesis and properties of Cu- and Pd-complexes of cyclen conjugates with pheophorbide and bacteriopheophorbide

Objectives. Chlorin and bacteriochlorin photosensitizers are effective agents for cancer photodynamic therapy and fluorescence imaging. They are also excellent chelators forming stable metal complexes. Besides, 64 Cu and 109 Pd isotopes can serve as emitters for nuclear medicine. Chelation of these metals with cyclen conjugates with chlorin and bacteriochlorin photosensitizers can become a simple and universal strategy for the synthesis of diagnostic and therapeutic radiopharmaceuticals for nuclear medicine. This article reports on the synthesis of similar Cu and Pd complexes of cyclen conjugates with pheophorbide and bacteriopheophorbide and the study of their photophysical properties. Methods. Metalation of cyclen conjugates was carried out with palladium and copper acetates. For bacteriochlorins, 6-O-palmitoyl-L-ascorbic acid was additionally used as a reducing agent. MALDI mass spectrometry, which was carried out on a time-of-flight mass spectrometer Bruker Ultraflex TPF/TOF and a Bruker Daltonics Autoflex II confirmed the structure of the compounds obtained Electronic absorption spectra were obtained on a Shimadzu 3101 spectrophotometer. Fluorescence and phosphorescence spectra were obtained on a FluoTime 300 PicoQuant spectrofluorometer. Results. Photophysical studies of metal complexes showed that the introduction of palladium cations quenches fluorescence and increases the quantum yield of singlet oxygen generation to 0.98 for the chlorin conjugate. Besides, it decreases the quantum yield of fluorescence to 0.10 and increases the quantum yield of singlet oxygen generation to 0.72 for the bacteriochlorin conjugate. Introducing a copper cation to cyclen conjugates with pheophorbide and bacteriopheophorbide leads to photophysical characteristics quenching. Conclusions. Due to the stability of the synthesized metal complexes in acidic media, as well as the short metalation time (5, 20, 10, and 15 minutes) it is reasonable to expect the successful development of effective imaging agents for positron emission tomography and radionuclide therapy. In addition, the residual fluorescence of bacteriochlorins makes it possible to use fluorescence diagnostics in combination with these methods.

Composition, stability and fluorescence properties of metal complexes of an aza-flavonol analog 1-methyl-2-phenyl-3-hydroxy-4(1H)-quinolone in aqueous solution

Aza-flavonols are compounds containing the 3-hydroxy-4(1H)-quinolone moiety, a unique scaffold with applications expanding from fluorescent probes and bioimaging to potential metal-related pharmaceutical drugs. Compositions and stability constants of metal complexes of an aza-flavonol 1-methyl-2-phenyl-3-hydroxy-4(1H)-quinolone (LH) in aqueous micellar medium of hexadecyltrimethylammonium bromide were established by fluorescence and spectrophotometric titrations of LH in the presence of metal ions of different type at variable pH. Strong binding with quenching of ligand fluorescence was observed for Cu2+, Fe2+/3+ and Pb2+ cations. The complexation with Zn2+ induced strong fluorescence enhancement in ZnL+ complex and smaller enhancement in ZnL2 complex. Al3+, Ga3+ and Me2Sn2+ cations induced strong fluorescence enhancement in 1:1 ML complexes, but quenching in ML2 complexes. Together with the relevant literature data these results indicate that the quenching effect in 1:2 complexes along with strong fluorescence enhancement in respective 1:1 complexes is a general phenomenon for 3-hydroxypyranone and 3-hydroxypyridinone ligands. The quantum mechanical Natural Transition Orbital analysis of ground and excited states of LH, AlL2+ and AlL2+ species reveals that the fluorescence of AlL2+ complex is quenched by an internal electron transfer process, which is absent in the 1:1 AlL2+ complex. The results emphasize strong dependence of the coordination induced fluorescence changes on the complex composition.