Binding Constants Of Complexes Research Articles

A joint experimental and theoretical investigation of the binding mechanism between zein and folic acid in an ethanol–water solution

ABSTRACT The aim of the present study was to determine the binding mechanisms between zein and folic acid in an ethanol – water solution. Fluorescence spectroscopy demonstrated that folic acid quenched the fluorescence intensity of zein by both dynamic and static fluorescence quenching mechanisms, with static quenching playing a prominent role. The binding constants (Ka) of the zein-folic acid complex at 292, 302, and 312 K were evaluated to be 5.97 × 105, 3.00 × 105 and 1.54 × 105 L/mol, respectively. The process of folic acid binding zein was driven by ∆H0 = –51.24 kJ/mol, ∆S0 = –64.90 J/mol•K. Van der Waals forces and hydrogen bonding primarily governed the formation of the zein-folic acid complex. Confirmation of the complex formation was obtained via UV-visible absorption spectroscopy, Fourier transform infrared spectroscopy, and circular dichroism spectroscopy, which also revealed alterations in the secondary structure of zein upon binding to folic acid. Measurements of particle size and zeta potential demonstrated an enhancement in the stability of the complex system. Scanning electron microscopy and transmission electron microscopy showed the complex to possess a spherical morphology, with significant changes in the zein’s morphology following its binding to folic acid. Additionally, zein increased the photostability of folic acid against UV light radiation. Molecular docking and molecular dynamics simulations were used to investigate the binding mechanisms involved further, and the results effectively elucidated the observed experimental phenomena. This research establishes a significant theoretical foundation for the utilization of zein as a system for delivering and safeguarding folic acid.

Exploration of the Tungsten(VI) complex of hydroxamic acid's RNA binding affinity, histone deacetylase inhibitory activity, and antioxidant activity

Ribonucleic acid (RNA) is a versatile molecule, thus the opportunity to target RNA is abundant. Hence, the current exploration deals with the interaction of a metal complex of hydroxamic acid with t-RNA, along with HDAC8 inhibition activity and antioxidant activity. Binding characteristics of complex 1, Bis(N-phenylbenzohydroxamato)Tungsten(VI), which is represented as [N-PBHA-W(VI)] with Torula yeast RNA (t-RNA) were investigated by using several types of spectroscopic techniques, measurements of viscosity, and computational study through molecular docking. The intrinsic binding constant, Kb was evaluated for complex 1 which shows changes in the shift of absorption spectra, and the intensity of spectra also varies. From fluorescence measurement, the binding constant of complex 1 towards t-RNA is 6.64 ± 0.05 × 105 M−1. Stern-Volmer quenching constant was calculated. Two displacement method sare performed by using the fluorescence spectroscopic technique which discloses a groove mode of binding. The groove mode of binding is also uncovered by viscosity measurement, which was observed by increasing the complex 1 concentration. An electrochemical investigation was carried out by using cyclic voltammetry. A circular dichroism study was also employed, which further suggests a strong binding occurred between the metal complex used and t-RNA. The docked postures of t-RNA with complex 1 expose the strong interactions which suggest a minor groove mode of binding. All the experimental evidence indicates that the interaction of complex 1 with t-RNA is a minor groove mode of binding which complements the molecular docking results. In-silico studies of HDAC8 inhibition activity of complex 1 reveal that the inhibition takes place mainly by hydrophobic interaction. DPPH–radical scavenging method employed for the antioxidant activity.

Monitoring Hierarchical Assembly of Ring-in-Ring and Russian Doll Complexes Based on Carbon Nanoring by Förster Resonance Energy Transfer.

We presented the construction of the ring-in-ring and Russian doll complexes on the basis of triptycene-derived carbon nanoring (TP-[12]CPP), which not only acts as a host for pillar[5]arene (P5A) but also serves as an energy donor for building Förster resonance energy transfer (FRET) systems. We also demonstrated that their hierarchical assembly processes could be efficiently monitored in real time using FRET. NMR, UV-vis and fluorescence, and mass spectroscopy analyses confirmed the successful encapsulation of the guests P5A/P5A-An by TP-[12]CPP, facilitated by C-H···π and ···π interactions, resulting in the formation of a distinct ring-in-ring complex with a binding constant of Ka = 2.23 × 104 M-1. The encapsulated P5A/P5A-An can further reverse its role to be a host for binding energy acceptors to form Russian doll complexes, as evidenced by the occurrence of FRET and mass spectroscopy analyses. The apparent binding constant of the Russian doll complexes was up to 3.6 × 104 M-1, thereby suggesting an enhanced synergistic effect. Importantly, the Russian doll complexes exhibited both intriguing one-step and sequential FRET dependent on the subcomponent P5A/P5A-An during hierarchical assembly, reminiscent of the structure and energy transfer of the light-harvesting system presented in purple bacteria.

Organotin (2-amino-4-fluorobenzoates): Synthesis, characterization, DFT studies, DNA interaction and cleavage studies

Synthesis of organotin(IV) complexes of 2-amino-4-fluorobenzoic acid (AFA), namely C16H16F2N2O4Sn (1), C22H28F2N2O4Sn (2), C10H14FNO2Sn (3), and C25H20FNO2Sn (4), have been accomplished, and all complexes 1–4 have been characterized using various spectroscopic and analytical techniques, viz. FT–IR and NMR spectroscopy (1H, 13C and 119Sn), ESI–mass spectrometry and elemental analysis. DFT calculations revealed that complexes 1 and 2 exhibited bicapped tetrahedral geometry, while 3 and 4 exhibited distorted tetrahedral environments around tin. Intrinsic binding constants (Kb ≈ 105 M−1) for AFA and complexes 1–4 have been determined by performing UV–vis spectral titration with Calf thymus-DNA (CT-DNA). Further, AFA and complexes 1–4 are luminescent with Kb values of the order of 104 M−1. A significant shift is observed in the circular dichroism (CD) spectra of CT-DNA in the presence of AFA and organotin(IV) complexes 1–4. Based on the UV–vis, fluorescence, and CD studies, it is concluded that AFA and it’s all complexes 1–4 may interact with CT-DNA by minor/major groove binding or electrostatic interaction. Interestingly, triorganotin(IV) complexes 3 and 4 more efficiently cleave the supercoiled form (SC, I) into linear form (L, III) along with the nicked form (NC, II) as compared to complexes 1 and 2, and AFA.

Spectroscopic study of drug–drug interactions: influence of two over-the-counter drugs on the albumin binding affinities of carbamazepine and its major metabolite

BackgroundMultidrug regimens can increase the risk of drug–drug interactions at the level of albumin binding especially for drugs with narrow therapeutic windows such as carbamazepine (CBZ). This risk is particularly heightened for CBZ which is mainly metabolized to the active carbamazepine-10,11-epoxide (CBZE) that has been identified as contributory to both the therapeutic efficacy and severity of toxicity in CBZ-treated individuals. The objective of this study was to investigate the binding affinities of albumin with CBZ and CBZE, and to explore the influence of two competing over-the-counter medicines on the binding characteristics. CBZE was synthesized by epoxidation of CBZ and characterized using IR, NMR and mass spectrometry. The influence of paracetamol and ascorbic acid on the albumin complexes of CBZ and CBZE was investigated using absorption and IR spectrophotometry.ResultsProtein–ligand complexation produced progressive hyperchromic changes in 278 nm band of bovine serum albumin (BSA) with formation constants of 10.28–10.44 and 12.66–13.02 M−1 for CBZ and CBZE, respectively. Thermodynamic considerations confirmed both binding processes as endothermic, spontaneous and driven by hydrophobic interactions. The presence of ascorbic acid increased the binding constants of both CBZ-BSA and CBZE-BSA complexes by non-competitive interference mechanism. Similarly, paracetamol increased the affinity of CBZ for albumin but then competitively interfered with the CBZE-BSA complex. The ratio of albumin binding affinities of CBZ–CBZE varied from 0.81 in the absence of competing drug to 1.29 and 1.0 with paracetamol and ascorbic acid, respectively. IR study confirmed that both CBZ and CBZE induced a reduction from the 67.34% α-helical content of free BSA to 42.56 and 56.43%, respectively. Competitive binding in the presence of either paracetamol or ascorbic acid induced further reduction in the α-helical content of BSA in the complexes. The most extensive perturbation in the secondary structure of BSA (22.78% α-helical content) which was observed with CBZE-BSA complex in the presence of paracetamol is probably due to the increased interaction of the protein for the analgesic.ConclusionThe study has revealed potential interference of paracetamol or ascorbic acid with the albumin binding of carbamazepine and its major metabolite.

Synthesis, characterization and anti-tubercular activities of copper(II) complexes of substituted 2,3-isatin bisthiosemicarbazones: An experimental and theoretical approach

Copper(II) acetate reacted with 2,3-isatin bisthiosemicarbazone (2,3 H2bitsc), 2,3-isatin bis-N1-methyl thiosemicarbazone (2,3 H2bitsc-N1-Me) and 2,3-isatin N1-phenyl thiosemicarbazone (2,3 H2bitsc-N1-Ph) in 1:1 (M: L) to form complexes of formula, [Cu(L)] (L = 2,3 bitsc 1, 2,3 bitsc-N1-Me 2, 2,3 bitsc-N1-Ph 3). The formation of bisthiosemicarbazone ligands and their complexes are supported by elemental analysis, FTIR, NMR (1H and 13C), ESR, and Mass. For complexes 1–3, two g values obtained are: g‖ = 2.24 (1), 2.17 (2), 2.26 (3) and g⊥ = 2.09 (1), 2.11 (2), 2.08 (3) which confirm axial symmetry. The square planar geometry is confirmed from higher g‖ values than g⊥ and presence g value of free electron in dx2-y2 ground term. Ligand to metal binding ratio of 1:1 is confirmed using UV–visible spectroscopy. The ligands (2,3 H2bitsc, 2,3 H2bitsc-N1-Me and 2,3 H2bitsc-N1-Ph) and complexes (1–3) were assessed for anti-tubercular (M. tuberculosis H37RV strain ATCC27294) and antibacterial (against E. coli and S. aureus) activities. The anti- tuberculosis activity of ligands (50 µg/mL-2,3 H2bitsc, 100 µg/mL-2,3 H2bitsc-N1-Me and H2bitsc-N1-Ph) gets enhanced on complexation with copper (25 µg /mL-1, 50 µg/mL 2 and 3). The minimal binding energies calculated through molecular modeling with mycobacterium tuberculosis enoyl reductase (PDB ID: 2H7M) is −7.6 (2,3 H2bitsc), −7.3 (2,3 H2bitsc-N1-Me), −9.6 (2,3 H2bitsc-N1-Ph), −8.7 (1), −8.9 (2), and −10.7 (3) Kcal/mol. Higher negative binding energy indicates more stabilized structure in the docked state for 1–3 which supports the experimental data. The drug-protein binding study with human serum albumin (HSA) was used to explore effective transport of molecules to their target sites in 2,3 H2bitsc and its complex 1. A high binding constant of complex 1 (6.09 × 105 M−1) with respect to the ligand 2,3 H2bitsc (4.90 × 105 M−1) indicates its strong binding affinities with HSA.

4-Oxo-7-fluoro-1,10-phenanthroline-2,9-diamides: Synthesis, Structural Features, Lanthanide Complexes, and Am(III)/Ln(III) Solvent Extraction.

A highly efficient synthetic approach was developed for the synthesis of unsymmetrical 1,10-phenanthroline-2,9-diamides with two different substituents in the fourth and seventh positions of the phenanthroline core. The structures of these ligands were confirmed using various spectral methods including 2D-NMR and X-ray analysis. Quantum chemical calculations supported the presence of tautomeric forms of these ligands. Furthermore, it was discovered that these compounds exhibit polydentate ligand behavior toward lanthanide nitrates. The structural characteristics of the complexes formed between these ligands and lanthanide nitrates were investigated both in the solid state and in solution. To further understand the binding properties of these novel unsymmetrical ligands, the binding constants for potential complexes were quantitatively measured by using UV-vis spectrophotometric titration. This allowed for a comprehensive analysis of the binding affinity and stability of these complexes. Extraction experiments of f-elements were performed for symmetrical and unsymmetrical diamides. Overall, this study presents significant advancement in the synthesis and characterization of unsymmetrical 1,10-phenanthroline-2,9-diamides and provides valuable insights into their potential applications as polydentate ligands for lanthanide nitrates.

Interaction of Doxorubicin Embedded into Phospholipid Nanoparticles and Targeted Peptide-Modified Phospholipid Nanoparticles with DNA.

The interactions of dsDNA with new targeted drug delivery derivatives of doxorubicin (DOX), such as DOX embedded into phospholipid nanoparticles (NPhs) and DOX with the NGR targeted peptide-modified NPhs were studied electrochemically by differential pulse voltammetry technique. Screen-printed electrodes (SPEs), modified with stable fine dispersions of carbon nanotubes (CNTs), were used for quantitative electrochemical investigations of direct electrochemical oxidation of guanine, adenine, and thymine heterocyclic bases of dsDNA, and their changes in the presence of DOX nanoderivatives. Analysing the shifts of peak potentials of nucleobases in the presence of drug, we have shown that the doxorubicin with NGR targeted peptide changed the mode of interaction in DNA-drug complexes from intercalative to electrostatic. Binding constants (Kb) of DNA-drug complexes were calculated in accordance with adenine, guanine, and thymine oxidation signals. Based on our experiments, we have proven that the surface modification of a drug delivery system with NGR targeted peptide dramatically changed the mechanism of interaction of drug with genetic material. DNA-mediated drug toxicity was calculated based on the concentration-dependent "response" of heterocyclic nucleobases on drug influence. DOX, DOX-loaded phospholipid nanoparticles (NPhs), and DOX with NGR addressed peptide-modified NPhs were moderately toxic in the concentration range of 0.5-290 µM.

Pd(II) based anticancer drug candidates with 1,2-Aminoethyl piperidine scaffold and sulfur donor ancillary: Their in vitro bio-activity, molecular docking and DFT study

A series of Pd(II) complexes Pd-1 to Pd-6; out of these [Pd(PIEAM)(LC)]+; Pd-3, [Pd(PIEAM)(NALC)]; Pd-4, [Pd(PIEAM)(GSH)]; Pd-5 and [Pd(PIEAM)(DL-meth)]2+; Pd-6 have been synthesized from water soluble stable diaqua complex [Pd(PIEAM)(OH2)2](NO3)2; Pd-2. The Pd-2 complex was obtained from hydrolysis of [Pd(PIEAM)Cl2]; Pd-1 (where, PIEAM = 1,2-Aminoethyl piperidine, a bidentate carrier ligand and with ancillary groups like; LC = L-cysteine, NALC = N-acetyl-L-cysteine, GSH = Glutathione, DL-meth = DL-methionine). All these Pd-1-Pd-6 complexes were characterized by different spectroscopic studies, like; UV–Vis, FT-IR, 1H NMR, and ESI Mass analyses. The bioactivity and drug-likeness properties of the complexes were assessed by PASS and ADME prediction software. The bioactivity of the complexes was experimentally investigated on DNA binding properties by gel electrophoresis, electronic, fluorescence, and viscometric methods. The binding constant values of Pd-3 complex with CT DNA bining in both absorption (Kb = 7.50 × 104M−1)and fluorosence titration (KSV = 35.10 × 103 M−1) was found greater than other Pd-1, Pd-2, Pd-4-Pd-6 complexes (Kb = (4.25–0.64) × 104 M−1; KSV = (13.57–1.11) × 103 M−1). The comparison in BSA bining of Pd(II) complexes also suggested the higher binding constant of Pd-3 complex in both spectroscopic method (Kb = 32 × 103M−1; KSV = 2.32 × 104 M−1) than other Pd(II) complexes (Kb = 16–2.4 × 103M−1; KSV = 1.99–1.53 × 104 M−1). A theoretical investigation of the structural property and TD-DFT of the complexes was executed by DFT calculations. The detailed BSA binding activity of the complexes was performed by fluorescence quenching, synchronous, and 3D-fluorescence spectroscopic methods. Molecular docking of the complexes with DNA and BSA was under study for their binding mode and different weak forces. Their cytotoxic behaviors, like; anticancer activity by MTT assay and ROS (Reactive Oxygen Species) generation by NBT (Nitro Blue Tetrazolium) assay, were investigated. The cytotoxicity of the complexes was under investigation on human lung adenocarcinoma cell A549, colorectal carcinoma cell HCT 116, and normal human embryonic kidney cell HEK 293.

Macrocyclic Compounds Comprising Tris(3-Aminopropyl)Amine Units and Fluorophore Moieties: Synthesis and Spectroscopic Studies in the Presence of Metal Salts

The synthesis of a variety of polyazamacrocyclic compounds comprising structural units of tris(3-aminopropyl)amine (TRPN) and oxadiamines, decorated with one or two fluorophore groups (dansyl or quinoline) at different nitrogen atoms, was carried out using Pd(0)-catalyzed amination. The dependence of the yields of the macrocycles on the synthetic path was observed. The spectrophotometric and fluorescent properties of the target compounds were studied, and their coordination with metal cations using UV–vis, fluorescence spectra as well as NMR titration was investigated. The stoichiometry and binding constants of several complexes with Cu(II), Zn(II), Cd(II), Pb(II) and Hg(II) were established. Three of the six studied macrocycles can be judged as prospective detectors of Zn(II) cations due to the substantial enhancement of fluorescence.

Mononuclear discrete Ag(I) complexes of aryl substituted (E)-N-phenyl-1-(pyridin-3-yl)methanimine: In vitro biological activities and interactions with biomolecules

The synthesis of three pyridinyl imines (L1-L3) with electron-donating and electron-withdrawing functional groups, as well as their silver(I) complexes (1a-3a, 1b-3b and 1c-3c), resulted from our ongoing search for novel metallodrugs with potential pharmacological activity. Various analytical and spectroscopic analyses were used to characterize the Ag(I) complexes. The single crystal X-ray diffraction analysis of complexes 3a and 3b in the solid state confirmed their linear geometry around the Ag(I) center. In vitro antibacterial properties of the complexes evaluated using the minimum inhibitory concentration (MIC) method revealed that complexes containing either a Me- or an F-substituent exhibited greater activity. The ferric-reducing antioxidant power (FRAP) experiment revealed that complexes with hydroxyl substituents have high antioxidant potential. These complexes with IC50 values ranging from 0.86 to 2.47 mg mL-1 outperformed ascorbic acid, with an IC50 of 2.68 mg mL-1. The reported complexes bound to CT-DNA via intercalation mode with significant binding constants for complexes whose ligands bore the OH- substituent. Bovine serum albumin (BSA) binding affinity to the complexes ranges from moderate to high. The studied complexes with methyl substituents are promising anti-cervical cancer candidates.

Analysis of the interaction between chitosan with different molecular weights and casein based on optical interferometry

Chitosan can be used as a stabilizer in dairy products to help suspend and stabilize casein micelles, but the molecular weight (MW) effect of chitosan has not been much explored. This work aimed to construct interaction models with casein using chitosan with MW of 30 kDa, 150 kDa, 250 kDa and 300 kDa to reveal the effect of MW on the structure and stability of chitosan-casein complexes. These models were based on the ordered porous layer interferometry (OPLI) system that can generate time-resolved signals to monitor the chitosan-casein interaction process dynamically in real time. The zeta potential, size distribution, binding mechanism and binding constants of chitosan-casein complexes with different MW were also analyzed. It was found that the chitosan and casein at pH 5.5 with the strongest interaction. The zeta potential and size analysis of chitosan-casein complexes showed opposite trends with MW before and after the saturation concentration, and MW(150 kDa) chitosan produced the largest size change in the bridging flocculation stage. The order of binding constants for chitosan-casein interactions is MW(300 kDa) < MW(250 kDa) < MW(30 kDa) < MW(150 kDa). In addition to the attraction between chitosan and casein by electrostatic driving forces, the dependence of the hydrophobic interaction between chitosan molecules on MW all influenced the interaction with casein. The dynamic monitoring and accuracy of the OPLI technique open up more possibilities to obtain the interactions of chitosan/casein and other biopolymers in different condition variables.

A Novel Ibuprofen Derivative and Its Complexes: Physicochemical Characterization, DFT Modeling, Docking, In Vitro Anti-Inflammatory Studies, and DNA Interaction.

A novel derivative of ibuprofen and salicylaldehyde N'-(4-hydroxybenzylidene)-2-(4-isobutylphenyl) propane hydrazide (HL) was synthesized, followed by its complexation with Cu, Ni, Co, Gd, and Sm. The compounds obtained were characterized by 1HNMR, mass spectrometry, UV-Vis spectroscopy, FT-IR spectroscopy, thermal analysis (DTA and TGA), conductivity measurements, and magnetic susceptibility measurements. The results indicate that the complexes formed were [Cu(L)(H2O)]Cl·2H2O, [Ni(L)2], [Co(L)2]·H2O, [Gd(L)2(H2O)2](NO3)·2H2O and [Sm(L)2(H2O)2](NO3)·2H2O. The surface characteristics of the produced compounds were evaluated by DFT calculations using the MOE environment. The docking was performed against the COX2 targeting protein (PDB code: 5IKT Homo sapiens). The binding energies were -7.52, -9.41, -9.51, -8.09, -10.04, and -8.05 kcal/mol for HL and the Co, Ni, Cu, Sm, and Gd complexes, respectively, which suggests the enhancement of anti-inflammatory behaviors compared with the binding energy of ibuprofen (-5.38 kcal/mol). The anti-inflammatory properties of the new compounds were assessed in vitro using the western blot analysis method and the enzyme-linked immunosorbent assay (ELISA), consistent with the outcomes obtained from docking. The half-maximal inhibitory concentration (IC50) values are 4.9, 1.7, 3.7, 5.6, 2.9, and 2.3 µM for HL and the Co, Ni, Cu, Sm, and Gd complexes, respectively, showing that they are more effective inhibitors of COX2 than ibuprofen (IC50 = 31.4 µM). The brain or intestinal estimated permeation method (BOILED-Egg) showed that HL and its Co complex have high gastrointestinal absorption, while only the free ligand has high brain penetration. The binding constants of Co, Cu, and Gd complexes with DNA were recorded as 2.20 × 104, 2.27 × 106, and 4.46 × 103 M-1, respectively, indicating the intercalator behavior of interaction. The newly synthesized ibuprofen derivative and its metal complexes showed greater anti-inflammatory activity than ibuprofen.

Selective Cytotoxicity of Novel Copper (II) Complex on Colon Cancer Cell Lines

The synthesis of a novel copper (II) complex, namely, [Cu(phen)(NO2-impi)]2+ (where phen is 1,10-phenanthroline; NO2-impi is 2-(2-(4-nitrophenyl)-5-(pyridin-2-yl)-1H-imidazol-4-yl) pyridine, ZU-3, was performed. UV titration and viscosity measurements were used to determine its interaction with ds-DNA. The binding constant of complex to ds-DNA was 1.3x105 M-1. The Stern-Volmer extinction constant (KSV) for ZU-3 was calculated as 1.2 x 105 M-1. The complex was screened against five human cell lines, namely A 549, PC-3, BEAS-2B, HCT-116 and MDZMB-231, and it was found that ZU-3 shows selective cytotoxicity on colon cancer cells. It has been found that ZU-3 reduced HCT-116 cell density and caused pyknotic morphology that are associated with cell death by apoptosis.

Highly Selective Potentiometric Sensing of Biologically Relevant Pyrophosphate and Lysophosphatidic Acid Using N-Alkyl/Aryl Ammonium Resorcinarenes/Extended-Resorcinarenes as Ionophores.

The ionophore properties of four kinds of N-alkyl/aryl ammonium resorcinarenes and extended-resorcinarenes were inspected for the first time to fabricate polymeric membrane electrodes for determination of biologically relevant pyrophosphate (PPi) and lysophosphatidic acid (LPA). The proposed ion selective electrodes (ISEs) showed significant preference for PPi and LPA with significant selectivity pattern differences from the Hofmeister series. To gain further insight into the performances of the developed ISEs, the binding constants of ionophore-anion complexes in the plasticized membrane phase were investigated, along with the optimized geometries and calculated electrostatic potential. Nernstian potential responses with good reversibility to target anions can be observed when shifting the optimized membranes in aqueous solutions in the concentration range from 10-6.5 to 10-2.3/10-2.2 M. Moreover, potentiometric sensings of PPi and LPA in mineral water and artificial serum were achieved in low μM concentration range, demonstrating their promising real-world applications. These results provide a promising avenue for the development of polymeric membrane electrodes for biological relevant anions and will broaden the scope of potentiometric sensing.

Fluorescence "Turn-off" Sensing of Iron (III) Ions Utilizing Pyrazoline Based Sensor: Experimental and Computational Study.

A simple pyrazoline-based ''turn off'' fluorescent sensor 5-(4-methoxyphenyl)-3-(5-methylfuran-2-yl)-1-phenyl-4,5-dihydro-1H-pyrazole (PFM) was synthesized and well characterized by different techniques such as FT-IR, 1H-NMR, 13C-NMR, and mass spectrometry. The synthesized sensor PFM was utilized for the detection of Fe3+ ions. Fluorescence emission selectively quenched by Fe3+ ions compared to other metal ions (Mn2+, Al3+, Fe2+, Hg2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, and Zn2+) via paramagnetic fluorescence quenching and showed good anti-interference ability over the existence of other tested metals. Under optimum conditions, the fluorescence intensity of sensor quenched by Fe3+ in the range of 0 to 3μM with detection limit of 0.12μM. Binding of Fe3+ ions to PFM solution were studied by fluorescent titration, revealed formation of 1:1 PFM-Fe metal complex and binding constant of complex was found to be of 1.3 × 105M-1. Further, the fluorescent sensor has been potentially used for the detection of Fe3+ in environmental samples (river water, tap water, and sewage waste water) with satisfactory recovery values of 99-101%.

A novel heterometallic ruthenium-silver complex as potential antitumor agent: Studies on its synthesis, in vitro assays and interactions with biomolecular targets

Certain ruthenium compounds are found to be potent growth inhibitors for cancer cells. In the current study, a novel ruthenium-triphenylphosphine (PPh3) cation and silver-2-mercapto nicotinate acid (H2mna) anion complex (RSC) was synthesized, and its molecular structure was determined by IR, NMR and X-ray crystallography. Biological assays revealed that RSC strongly inhibited the viability of MCF-7 and MDA-MB-231 cells with IC50 values of 9.6±1.1 and 7.5±0.8 µM, respectively, and significantly blocked their migration rates. Ultraviolet spectroscopy and fluorescence emission experiments demonstrated that RSC interacted with BSA, but not DNA. Further studies on [Ag6(Hmna)2(mna)4]4− binding with BSA and DNA found the anion did not interact with these biomolecules, indicating that RSC exerted its biological functions through its ruthenium-PPh3 complex (RTC) moiety, and molecular docking provided additional evidence supporting this result. Fluorescence resonance energy transfer showed that the number of binding sites (n) and binding constant of RTC-BSA complex were 1 and 8.60 × 104 M−1 at 310K, suggesting a strong interaction between RTC and BSA. The thermodynamic parameters ΔG0, ΔH0 and ΔS0 of the binding were calculated, and it was demonstrated that the binding of RTC with BSA was enthalpy-driven, and the main forces between RTC and BSA were electrostatic force and hydrogen bonding. Molecular docking showed that the binding site of BSA with RSC was located on the interface between the domains IIA and IIB of the protein. The present study sheds light on that a ruthenium mono-coordinated with PPh3 complex could help to design and develop a new class of antitumor drugs.

Evaluation of the effect of background electrolyte composition and independence of parameters in determining binding constants of betulin derivatives to β- and dimethyl-β-cyclodextrins by affinity capillary electrophoresis.

The values of the apparent binding constants for β-cyclodextrin complexes of betulin derivatives determined by mobility shift affinity capillary electrophoresis were found to be independent of the composition of the two background electrolytes used (tetraborate buffer, pH 9.18, and phosphate buffer, pH 8.00, both of them with 20 mM ionic strength). It has been found that if there is not a constant plateau on the binding curve then four independent parameters can be determined: binding constants (also referred to as stability, association, or formation constants) and ionic mobilities of 1:1 and 1:2 complexes. However, at least 10-12 data points in the binding curve should be used to reliably estimate the parameters. For the first time, the apparent binding constants for complexes of ester betulin derivatives with dimethyl-β-cyclodextrin have been determined by mobility shift affinity capillary electrophoresis. The logarithms of the constants for 1:1 and 1:2 complexes at 25°C for betulin 3,28-diphthalate with a 95% confidence interval are 4.98 (4.95-5.01) and 7.52 (7.26-7.68); for betulin 3,28-disulfate, the values are 4.97 (4.89-5.03) and 8.24 (6.82-8.52). It has been found that betulin 3,28-disuccinate forms only a 1:1 complex and the binding constant logarithm is 5.25 ± 0.02.

Exploratory and machine learning analysis of the stability constants of HgII- triazene ligands complexes

Knowing stability constants for the complexes HgII with extracting ligands is very important from environmental and therapeutic standpoints. Since the selectivity of ligands can be stated by the stability constants of cation–ligand complexes, quantitative structure–property relationship (QSPR) investigations on binding constant of HgII complexes were done. Experimental data of the stability constants in ML2 complexation of HgII and synthesized triazene ligands were used to construct and develop QSPR models. Support vector machine (SVM) and multiple linear regression (MLR) have been employed to create the QSPR models. The final model showed squared correlation coefficient of 0.917 and the standard error of calibration (SEC) value of 0.141 log K units. The proposed model presented accurate prediction with the Leave-One-Out cross validation ( Q LOO 2 = 0.756) and validated using Y-randomization and external test set. Statistical results demonstrated that the proposed models had suitable goodness of fit, predictive ability, and robustness. The results revealed the importance of charge effects and topological properties of ligand in HgII - triazene complexation.

Embedding of Functionalized Coordination Cages and a Molecular Knot in a Polymeric Membrane for Potentiometric Sensing of Environmentally Important Oxyanions and Halides.

Three kinds of coordination cages and a molecular knot with inductively activated +P-H, N-H, or C-H hydrogen bond donors anchoring in the functionalized cavities were inspected as ionophores to develop polymeric membrane ISEs for potentiometric sensing of environmentally important oxyanions and halides. The proposed ISEs displayed significant preference for perrhenate, phosphate, or chloride with a selectivity pattern distinctively different from the sequence depending on the Gibbs free energy of hydration owing to the high degree of shape, charge, and size selectivity originating from the rigidity and complementarity of the binding cavities. To gain further insight into the response characters of the proposed ISEs, the binding constants of ionophore-anion complexes in the membrane phase were investigated, and the binding affinity, together with the Hofmeister series, correlates well with the determined selectivity pattern of the proposed ISEs. Optimizing the composition of the membrane such as lipophilic additives and plasticizers produced ISEs displaying Nernstian/near-Nernstian potentiometric responses to primary anions with a wide linear range, improved detection limits, good reversibility, and satisfying lifetime. Potentiometric determination of perrhenate, phosphate, and chloride in river water, mineral water, and artificial serum samples was achieved with good recovery and accuracy using the proposed ISEs, demonstrating their potential for real-life applications. These results will shed new light on how novel ionophores could be designed for potentiometric sensing and broaden the scope of host-guest chemistry of coordination cages and molecular knots.