Synthesis,characterization, molecular modeling,and DNA interaction studies of a Cu(II) complex containing drug of chronic hepatitis B: adefovir dipivoxil

A new copper(II) complex [Cu(adefovir)₂Cl₂], where adefovir = adefovir dipivoxil drug, was synthesized and characterized by using different physicochemical methods. Binding interaction of this complex with calf thymus DNA (ct-DNA) has been investigated by multi-spectroscopic techniques and molecular modeling study. The complex displays significant binding properties of ct-DNA. The results of fluorescence and UV–vis absorption spectroscopy indicated that, this complex interacted with ct-DNA in a groove-binding mode, and the binding constant was 4.3(±0.2) × 10⁴ M^?1. The fluorimeteric studies showed that the reaction between the complex and ct-DNA is exothermic (ΔH = 73.91 kJ M^?1; ΔS = 357.83 J M^?1 K^?1). Furthermore, the complex induces detectable changes in the CD spectrum of ct-DNA and slightly increases its viscosity which verified the groove-binding mode. The molecular modeling results illustrated that the complex strongly binds to the groove of DNA by relative binding energy of the docked structure ?5.74 kcal M^?1. All experimental and molecular modeling results showed that the Cu(II) complex binds to DNA by a groove-binding mode.     

Effect of cucurbit[n]urils on tropicamide and potential application in ocular drug delivery

The supramolecular interactions of the ocular drug tropicamide (TR) with cucurbit[7]uril (CB7) and cucurbit[8]uril (CB8) were investigated in aqueous solutions by using ¹H NMR, ESI-MS and UV–vis spectroscopic techniques. The results indicate a 1:1 binding stoichiometry of TR with CB7 and CB8. The binding constants of TR in its protonated form were higher (e.g. K = 4 × 10⁶ M^? 1 with CB8) than in its neutral form (e.g. K = 1.4 × 10⁴ M^? 1 with CB8), which led to a complexation-induced increase in its pK _a value of ca. 0.5 and 2 units with CB7 and CB8, respectively. In the presence of about 1% (w/v) CB8, the ionisation degree of 0.1% (w/v) TR was increased from 2% to 62% at neutral pH. The increase in the pK _a value and thus stabilisation of the protonated TR species at neutral pH is discussed in the context of supramolecular drug delivery of ophthalmologic drugs.     

Host–guest interaction of hemicucurbiturils with phenazine hydrochloride salt

The host–guest interactions between phenazine hydrochloride salt (PheH⁺) and hemicucurbit[n]uril (n = 6 or 12) (HemiQ[6 or 12]) have been studied by ¹H NMR, UV–vis, IR, mass spectrometry (MS) and quantum chemistry. In ¹H NMR spectra, the broadening of proton resonances of the hosts suggests the interactions of PheH⁺ with HemiQs. The quantitative stabilities of the host–guest systems have been obtained by UV–vis titration experiments, that is, the stoichiometric interactions of PheH⁺ with HemiQ[6] have been observed with an association constant of K_a = (2.5 ± 1.2) × 10⁶ L mol^? 1, while the 2:1 ratio complexes of PheH⁺ with HemiQ[12] are formed with stepwise association constants of K₁ = (9.2 ± 2.8) × 10⁴ L mol^? 1 and K₂ = (6.4 ± 0.9) × 10⁵ L mol^? 1, respectively, which induce a total association constant of K_a = 5.9 × 10¹⁰ L² mol^? 2. Both the 1:1 and 2:1 complexes have been detected by MS. Quantum chemistry calculations have been used to understand the static structures and thermodynamic stabilities of the supramolecular assemblies.     

Isomeric Effect on the anticancer Behavior of two Zinc (II) complexes based on 3,5‐bis(1‐imidazoly) pyridine: Experimental and Theoretical Approach

Two isomeric Zinc (II) complexes constructed by 3,5‐bis(1‐imidazoly) pyridine has been synthesized and characterized by single crystal X‐ray diffraction, elemental analyses and infrared spectroscopy. The binding mode and ability of complex 1–2 with CT‐DNA were studied by UV and fluorescence spectra. The intrinsic binding constant K_b (K_b1 = 2.305 × 10⁴ M^?1, K_b2 = 3.095 × 10⁴ M^?1) and the observed association constant K_obs (K_obs1 = 1.523*10⁶ M^?1, K_obs2 = 2.057*10⁶ M^?1) indicated that the insertion ability of complex 2 with CT‐DNA is stronger than complex 1. Gel electrophoresis showed that complexes have a good ability to hydrolyze cleavage pBR322 plasmid DNA. The cytotoxicity and apoptosis studies showed that complexes exhibited excellent cytotoxic activity against HeLa cells, especially complex 2 had better growth inhibition than Cisplatin. Molecular docking study simulated the binding model of complexes with DNA (PDB:4av1), showing an imidazole plane of complex 2 can be inserted into a DNA base pair in relative parallel. Both complexes can be used as potential anticancer agents.     

A new quinoline-based chemosensor in ratiometric sensing of Hg2+ ions

A new quinoline-based chemosensor 1 has been designed and synthesised. Its metal ion-binding properties have been documented in organic and aqueous organic solvents. While chemosensor 1 recognises Hg²⁺ ions (K _a = 2.15 × 10⁴ M^? 1) by exhibiting ratiometric change in emission in CHCl₃/CH₃OH (1:1, v/v), under similar condition both Zn²⁺ and Cd²⁺ ions are sensed by significant non-ratiometric increase in emission with measurable red shift. In DMSO/H₂O (5:95, v/v), the sensor 1 exhibits a greater selectivity towards Hg²⁺ ions (K _a = 9.20 × 10³ M^? 1) over the other metal ions examined.     

Molecular dynamics and energetic perceptions of substrate recognition by thymidylate kinase

Plasmodium deoxyguanylate pathways are an attractive area of investigation for future metabolic and drug discovery studies due to their unusual substrate specificities. We investigated the energetic contribution to thymidylate kinase substrate binding, and the forces underlying ligand recognition. The binding constant varied from 8 × 10⁴ M^?1 at 290 K to 6 × 10⁴ M^?1 at 310 K for dGMP, and from 16 × 10⁴ M^?1 at 290 K to 4 × 10⁴ M^?1 at 310 K for TMP. ΔC _p was estimated as ?1.75 kJ mol^?1 K^?1 for TMP and +2 kJ mol^?1 K^?1 for dGMP. In comparison with TMP, the binding of dGMP to PfTMK produced less favorable enthalpy change, positive or favorable entropic contribution at lower temperature, positive heat capacity change, negative $ \Updelta S_{\text{HE}}^{^\circ } $ , positive ΔS _other, higher total solvent-exposed surface area and more or less rigid body binding. These changes indicate unfavorable conditions for proper binding and lower conformational changes, and suboptimal structural reordering during dGMP binding.     

KINETICS OF FORMATION AND STABILITY CONSTANTS OF MONO AND BIS l-TYROSINE COMPLEXES OF Cu(II), Co(II), AND Ni(II)

Abstract

The kinetics and stability constants of l-tyrosine complexation with copper(II), cobalt(II) and nickel(II) have been studied in aqueous solution at 25° and ionic strength 0.1 M. The reactions are of the type M(HL)^(3-n)+ _n-1 + HL- ? M(HL)^(2-n)+_n(k_n, forward rate constant; k_-n, reverse rate constant); where M=Cu, Co or Ni, HL^? refers to the anionic form of the ligand in which the hydroxyl group is protonated, and n=1 or 2. The stability constants (K_n=k_n/k_-n) of the mono and bis complexes of Cu²⁺, Co²⁺ and Ni²⁺ with l-tyrosine, determined by potentiometric pH titration are: Cu²⁺, log K₁=7.90 ± 0.02, log K₂=7.27 ± 0.03; Co²⁺, log K₁=4.05 ± 0.02, log K₂=3.78 ± 0.04; Ni²⁺, log K₁=5.14 ± 0.02, log K₂=4.41 ± 0.01. Kinetic measurements were made using the temperature-jump relaxation technique. The rate constants are: Cu²⁺, k₁=(1.1 ± 0.1) × 10⁹ M ^?1 sec^?1, k_-1=(14 ± 3) sec^?1, k₂=(3.1 ± 0.6) × 10⁸ M ^?1 sec^?1, k^?2=(16 ± 4) sec^?1; Co²⁺, k₁=(1.3 ± 0.2) × 10⁶ M ^?1 sec^?1, k_-1=(1.1 ± 0.2) × 10² sec^?1, k₂=(1.5 ± 0.2) × 10⁶ M ^?1 sec^?1, k_-2=(2.5 ± 0.6) × 10² sec^?1; Ni²⁺, k₁=(1.4 ± 0.2) × 10⁴ M ^?1 sec^?1, k_-1=(0.10 ± 0.02) sec^?1, k₂=(2.4 ± 0.3) × 10⁴ M ^?1 sec^?1, k_-2=(0.94 ± 0.17) sec^?1. It is concluded that l-tyrosine substitution reactions are normal. The presence of the phenyl hydroxyl group in l-tyrosine has no primary detectable influence on the forward rate constant, while its influence on the reverse rate constant is partially attributed to substituent effects on the basicity of the amine terminus.     

Synthesis,structure and spectroscopic studies on DNA binding,BSA interaction of a nickel(II) complex containing l–methionine Schiff base and 1,10-phenanthroline

A new nickel(II) complex, [Ni(o-van-L-met)(phen)(CH₃OH)] (o-van-L-met = Schiff base derived from o-vanillin and l-methionine, phen = 1,10–phenanthroline), has been synthesized and characterized by elemental analyses, IR spectra, and single-crystal X-ray diffraction. The crystal structure shows nickel is six-coordinate in a distorted octahedral geometry. In this crystal, molecules form a 2-D plane structure via hydrogen bonds and π–π interactions. The interaction of the complex with calf thymus DNA (CT-DNA) was investigated by absorption, fluorescence, circular dichroism (CD), spectroscopies, and viscosity measurement. The complex binds to CT-DNA in an intercalative mode with a binding constant of (4.7 ± 0.5) × 10⁴ M^?1. The interaction of the complex with bovine serum albumin (BSA) was also studied by the multispectroscopic methods. Results illustrated that the nickel(II) complex can effectively quench the intrinsic fluorescence of BSA via a static quenching mechanism and cause conformational changes. The binding constant K_b was (6.3 ± 1.6) × 10⁴ M^?1 and the binding site number n was 0.96 ± 0.04; its bind site was located within subunit IIA of BSA.     

Synthesis,characterization and DNA interaction studies of a new platinum(II) complex containing caffeine and histidine ligands using instrumental and computational methods

A new Pt(II) complex, [Pt(Caff)(His)(Cl)] (Caff is Caffeine (3,7-dihydro-1,3,7-trimethyl-1H-purine-2,6-dione) and His is l-Histidine), was synthesized and characterized using different physicochemical methods. The interaction of this complex with calf thymus DNA (ct-DNA) was investigated by absorption, emission, circular dichroism (CD), and viscosity measurements and molecular docking techniques. The calculated binding constant, K_b, was 5.3 × 10³ M^?1. In fluorimetric studies, the enthalpy and entropy of the reaction between the complex and ct-DNA showed that the reaction is exothermic (?H = ?184.07 kJ mol^?1, ?S = ?551.97 J mol^?1 K^?1). CD spectra of DNA in the presence of different amounts of the complex showed little changes in both the negative and positive band intensities, which imply a non-intercalative mode between the DNA and the platinum complex. Furthermore, the study of molecular docking also indicated that the complex binds to DNA via a groove binding mode.     

Solubilization of cholesterol in aqueous solution by two β-cyclodextrin dimers and a negatively charged β-cyclodextrin derivative

Two βCD dimers (linked by succinic acid, 2, or ethylenediaminetetraacetic acid, EDTA, 3, bridges) and a negatively charged monomer derivative of βCD, 1, have been synthesized and their ability to solubilize cholesterol in aqueous solution was studied. The three compounds exhibit a great capacity in solubilizing cholesterol as, for instance, concentrations up to 6 mM of cholesterol were measured in the presence of 25 mM of 3. The phase-solubility diagrams of the two dimers exhibit A _L type profiles while the monomer 1 follows an A _P isotherm. The cholesterol/dimer complexes have 1:1 stoicheiometries while monomer 1 forms two complexes with molar ratios of 1:1 and 1:2 (cholesterol/1). The equilibrium constants are K _1:1 = (5.9 ± 0.3) × 10⁴ M^?1 and K _1:1 = (8.8 ± 0.2) × 10⁴ M^?1 for 2 and 3, respectively, and K _1:1 = 73 ± 19 M^?1 and K _1:2 = 204 ± 65 M^?1 for 1. The comparison of K _1:1(3) with the product K _1:1 × K _1:2 (1) reveals that a chelate effect in binding the cholesterol by 3 exists. The structure of the cholesterol/3 complex was studied by ROESY experiments and by molecular dynamics simulations.     

The Host-Guest Chemistry of Proflavine with Cucurbit[6,7,8]urils

The binding of the polyaromatic guest, 3,6-diaminoacridine (Proflavine) to cucurbit[n]uril (CB[n]) where n = 6, 7 and 8 has been studied by fluorescence spectrophotometry and binding constants determined using a least squares fitting method. Titration of CB[8] into a solution of Proflavine results in a 95% decrease in fluorescence up to a CB[8] to Proflavine ratio of 2:1. From the induced fluorescence spectra a binding constant of 1.9 × 10⁷ M^? 1 was determined. When Proflavine is titrated into a solution of CB[8] a similar binding constant is calculated (1.3 × 10⁷ M^? 1). Titration of CB[6] into a solution of Proflavine yields a decrease in fluorescence of 18–20%, but no binding is observed beyond what is seen within experimental error. Finally, titration of CB[7] into a solution of Proflavine results in an increase in fluorescence (32%) and a blue-shift of the emission wavelength from 509 nm to 485 nm. From the induced fluorescence spectra a binding constant of 1.65 × 10⁷ M^? 1 was determined. From ¹H NMR it appears that the decrease in fluorescence for Proflavine with CB[6] and CB[8] is due to collisional quenching, whereas the increase in fluorescence with CB[7] may be due to rotational restriction.     

Flexibility of Na,K-ATPase secondary structure upon drug-protein interaction

The enzyme Na⁺, K⁺-ATPase is an integral membrane protein which transports sodium and potassium cations against an electrochemical gradient. The transport of Na⁺ and K⁺ ions is connected to an oscillation of the enzyme between the two conformational states, the E₁ (Na⁺) and the E₂ (K⁺) conformations. The enzymatic activity of ATPase is largley affected by different ligands complexation. This review reports the effects of several drugs such as AZT (anti-AIDS), cis-Pt (antitumor), aspirin (anti-inflammatory) and vitamin C (antioxidant) on the stability and secondary structure of Na,K-ATPase in vitro. Drug-enzyme binding is mainly through H-bonding to the polypeptide C=O and C-N groups with two binding constants K_1(AZT) = 5.30 × 10⁵ M^?1 and K_2(AZT) = 9.80 × 10³ M^?1 for AZT and one binding constant for K_cis-Pt = 1.93 × 10⁴ M^?1, K_aspirin = 6.45 × 10³ M^?1 and K_ascorbate = 1.04 × 10⁴ M^?1 for cis-Pt, aspirin and ascorbic acid. The enzyme secondary structure was altered from that of α-helix 19.8% (free protein) to almost 22–26% and the β-sheet from 25.6% to 18–22%, upon drug complexation with the order of induced stability AZT > cis-Pt > ascorbate > aspirin.     

Two new heteroleptic ruthenium(II) dithiocarbamates: synthesis,characterization, DFT calculation and DNA binding

Two ruthenium(II) dithiocarbamates, cis-[Ru(DMP)₂L](BF₄), where L = 4-(4-methoxy-phenyl)piperazine-1-carbodithioate (1) and 4-(3-methoxyphenyl)piperazine-1-carbodithioate (2) and DMP = 2,9-dimethyl-1,10-phenanthroline, have been synthesized and characterized. The DNA-binding affinity of these metal complexes was investigated by UV–visible spectrophotometry with DNA-binding constants of 6.2 × 10⁴ M^?1 (1) and 1.2 × 10⁵ M^?1 (2) and electrostatic binding mode was confirmed by viscometric measurements. For insight into the structural differences, both complexes were studied computationally. B3LYP/LANL2DZ level of Density Functional Theory was used for the computational studies in Gaussian 09. The optimized bond lengths are in agreement with the reported values. Comparative computational studies reveal interesting transformations in bond lengths, angles, Natural Bond Orbital charges, molecular orbitals, Molecular Electro Static Potentials, and global chemical reactivity indices. Based on quantum chemical results a structure–activity relationship has been attempted.     

Investigation on the Binding of Terazosin Hydrochloride and Naftopidil to an Immobilized α 1-Adrenoceptor by Zonal Elution

The interaction between drugs and receptors is particularly important in revealing the drug acting mechanism and developing new leads. In this work, α ₁-Adrenoceptor (α ₁-AR) from HEK293 cell line is purified and immobilized on the surface of macro-pore silica gel to prepare an high-performance affinity chromatography stationary phase for the pursuit of drug–receptor interactions by competition zonal elution. Naftopidil is found to have only one type of binding site to α ₁-AR with an association constant of 1.45 × 10⁶ M^?1 and a concentration of binding sites of 1.56 × 10^?6 M, while terazosin hydrochloride proves to present two kinds of binding site on the receptor at which the association constants are determined to be 1.61 × 10⁵ M^?1 and 2.06 × 10³ M^?1, and the corresponding concentrations of the binding sites are 1.56 × 10^?6 M and 1.11 × 10^?3 M, respectively. It is concluded that the stationary phase containing attached α ₁-AR can be used to realize the binding of a drug to the receptor.     

Dimerisation and complexation of 6-(4′-t-butylphenylamino)naphthalene-2-sulphonate by β-cyclodextrin and linked β-cyclodextrin dimers

This study shows that stereochemical factors largely determine the extent to which 6-(4′-t-butylphenylamino)-naphthalene-2-sulphonate, BNS^?  and its dimer, (BNS^? )₂, are complexed by β-cyclodextrin, βCD, and a range of linked βCD dimers. Fluorescence and ¹H NMR studies, respectively, show that BNS^?  and (BNS^? )₂ form host–guest complexes with βCD of the stoichiometry βCD.BNS^?  (10^? 4 K ₁ = 4.67 dm³ mol^? 1) and βCD.BNS₂ ^2 ?  (10^? 2 K ₂′ = 2.31 dm³ mol^? 1), where the complexation constant K ₁ = [βCD.BNS^? ]/([βCD][BNS^? ]) and K ₂′ = [βCD. (BNS^? )₂]/([βCD.BNS^? ][BNS^? ]) in aqueous phosphate buffer at pH 7.0, I = 0.10 mol dm³ at 298.2 K. (The dimerisation of BNS^?  is characterised by 10^? 2 K _d = 2.65 dm³ mol^? 1.) For N,N-bis((2^AS,3^AS)-3^A-deoxy-3^A-β-cyclodextrin)succinamide, 33βCD₂su, N-((2^AS,3^AS)-3^A-deoxy-3^A-β-cyclodextrin)-N′-(6^A-deoxy-6^A-β-cyclodextrin)urea, 36βCD₂su, N,N-bis(6^A-deoxy-6^A-β-cyclodextrin)succinamide, 66βCD₂su, N-((2^AS,3^AS)-3^A-deoxy-3^A-β-cyclodextrin)-N′-(6^A-deoxy-6^A-β-cyclodextrin)urea, 36βCD₂ur, and N,N-bis(6^A-deoxy-6^A-β-cyclodextrin)urea, 66βCD₂ur, the analogous 10^? 4 K ₁ = 11.0, 101, 330, 29.6 and 435 dm³ mol^? 1 and 10^? 2 K ₂′ = 2.56, 2.31, 2.59, 1.82 and 1.72 dm³ mol^? 1, respectively. A similar variation occurs in K ₁ derived by UV–vis methods. The factors causing the variations in K ₁ and K ₂ are discussed in conjunction with ¹H ROESY NMR and molecular modelling studies.     

Synthesis of nickel(II) complexes of isatin thiosemicarbazone derivatives: in vitro anti-cancer,DNA binding,and cleavage activities

Six new nickel(II) complexes of thiosemicarbazone Schiff base with isatin moiety [Ni(L1)₂–Ni(L6)₂] were synthesized through reaction of Ni(II) with (Z)-2-(2-oxoindolin-3-ylidene)-N-phenylhydrazinecarbothioamide (L1H), (Z)-2-(5-methyl-2-oxoindolin-3-ylidene)-N-phenylhydrazinecarbothioamide (L2H), (Z)-2-(5-fluoro-2-oxoindolin-3-ylidene)-N-phenylhydrazinecarbothioamide (L3H), (Z)-N-methyl-2-(5-nitro-2-oxoindolin-3-ylidene)hydrazinecarbothioamide (L4H), (Z)-N-methyl-2-(5-methyl-2-oxoindolin-3-ylidene)hydrazinecarbothioamide (L5H), and (Z)-N-ethyl-2-(5-methyl-2-oxoindolin-3-ylidene)hydrazinecarbothioamide (L6H). The structures of the Ni complexes were characterized through elemental analysis, infrared, and mass spectral data. The structure of the NiL2 complex was further characterized through single-crystal X-ray diffraction. The interaction of these complexes with calf thymus (CT-DNA) exhibited high intrinsic binding constants (K_b = 1.4 × 10⁵–2.4 × 10⁶ M^?1), which reflected their intercalative activity toward CT-DNA. This result was also confirmed by viscosity data. Electrophoresis studies revealed that these complexes could cleave the DNA through the oxidative pathway. The in vitro anti-proliferative study establishes the anticancer potency of these compounds against human colorectal carcinoma cell line.     

Binding of a neutral guest to cucurbiturils: photophysics,thermodynamics and molecular modelling

Steady-state and time-resolved fluorescence techniques were used to study the thermodynamics of binding of a neutral polarity-sensitive guest, the methyl 2-naphthalenecarboxylate (2MN), with three cucurbiturils (CBn; n = 6, 7 and 8) in water. Association constants (K) were obtained from nonlinear regression analysis of the fluorescence intensity against [CB] in the 5–45°C range. 2MN complexed with CB7 exhibited a 1:1 stoichiometry (K ≈ 10³ M^? 1 at 25°C); however, it hardly did with CB6 (K < 10 M^? 1) and it did not with the larger CB8 macrocyclic ring. The (1:1) 2MN:CB7 complexation process was accompanied by a small unfavourable enthalpy change and was, therefore, entropically governed. Molecular mechanics and molecular dynamics calculations in the presence of water were also used to study the geometry of the complexes formed and the driving forces responsible for their formation. The results were compared with those previously obtained for the complexation of the same guest, 2MN, with natural α-, β- and γ-cyclodextrins.     

Mass Spectrometric Determination of Association Constants of Bovine Serum Albumin (BSA) with para-Sulphonato-Calix[n]arene Derivatives

Electrospray Ionization Mass Spectrometry (ESI/MS) has been used to determine the association constants (K_As) and binding stoichiometries for parent para-Sulphonato-calix[n]arenes and their derivatives with bovine serum albumin (BSA). K_A values were determined by titration experiments using a constant concentration of protein. K_A measurements were carried out in a methanol–formic acid solution. 5,11,17,23–tetra-Sulphonato-calix[4]arene (1a) and 25-mono-(2-aminoethoxy)-5,11,17,23-tetra-Sulphonato-calix[4]arene (1d) interact strongly with BSA showing 3 non-equivalent binding sites with K_A1 = 7.69 × 10⁵ M⁻¹, K_A2 = 3.85 × 10⁵ M⁻¹, K_A3 = 0.33 × 10⁵ M⁻¹ and K_A1 = 1.69 × 10⁵ M⁻¹, K_A2 = 2.94 × 10⁵ M⁻¹, K_A3 = 0.60 × 10⁵ M⁻¹, respectively. The strength of the interactions between the calixarene and BSA is inversely proportional to the size of macrocyclic ring: n = 4 > n=6>>n=8.     

Octahedral copper(II) carboxylate complex: synthesis,structural description,DNA-binding and anti-bacterial studies

Self-assembly of CuSO₄, para-methyl-2-phenyl acetate and 1,10-phenanthroline afforded good-quality crystalline complex in quantitative yield. The complex was characterized by FTIR and UV-visible spectroscopy, electrochemistry, and powder and single-crystal XRD studies. Its structure was found to possess axially elongated octahedral symmetry with CuO₄N₂ chromophore. Its purity was assessed by powder XRD spectrum. Absorption study yielded a broad band corresponding to ²E_g→²T_2 g transition. Electrochemical solution study indicated diffusion-controlled irreversible electron transfer process corresponding to Cu(II)/Cu(I) redox couple with diffusion coefficient = 7.89(±0.1)×10^?9 cm²s^?1. Results of spectroscopic techniques support each other. Complex exhibited excellent DNA-binding ability through UV-visible spectroscopy and cyclic voltammetry yielding K_b values 1.399 × 10⁴ M^?1 and 5.81 × 10³ M^?1, respectively. The complex exhibited significant activity against bacterial strains Escherichia coli, Micrococcus luteus and Staphylococcus aureus and good activity against Bacillus subtilis. These preliminary studies impart good biological relevance on the synthesized complex.     

Halide‐Anion Binding by Singly and Doubly N‐Confused Porphyrins

The halide‐binding properties of N‐confused porphyrin (NCP, 1 ) and doubly N‐confused porphyrins (trans‐N₂CP ( 2 ), cis‐N₂CP ( 3 )) were examined in CH₂Cl₂. In the free‐base forms, cis‐N₂CP ( 3 ) showed the highest affinity to each anion (Cl^?, Br^?, I^?) with association constants K_a=7.8×10³, 1.9×10³, and 5.8×10² M ^?1, respectively. As metal complexes, on the other hand, trans‐N₂CP 2–Cu exhibited the highest affinity to Cl^?, Br^?, and I^? with K_a=9.0×10⁴, 2.7×10⁴, and 1.9×10³ M ^?1, respectively. The corresponding K_a values for cis‐N₂CP 3–Cu and NCP 1–Cu were about 1/10 and 1/2, respectively, of those of 2–Cu . With the help of density functional theory (DFT) calculations and complementary affinity measurements of a series of trisubstituted N‐confused porphyrins, the efficient anion binding of NCPs was attributed to strong hydrogen bonding at the highly polarized NH moieties owing to the electron‐deficient C₆F₅ groups at meso positions as well as the ideally oriented dipole moments and large molecular polarizability. The orientation and magnitude of the dipole moments in NCPs were suggested to be important factors in the differentiation of the affinity for anions.