The electronic effect in supramolecular self-assembly of <Emphasis Type="Italic">para-</Emphasis>substituted tetraphenylporphyrinatozinc(II) with imidazolyl-linked porphyrinatomanganese(III) by coordinative bonding

The supramolecular self-assembly of para-substituted tetraphenylporphyrin complexes of zinc(II), Zn(p-X)TPP, with imidazolyl-linked porphyrinatomanganese(III), Mn(p-lmBPTPP)Cl, driven by coordinative bonding has been investigated by fluorescence spectra, electrospray mass spectrometry, ¹H-n.m.r. and u.v.–vis. spectra. The association constants of the supramolecular complexes, K_c, were calculated using fluorescence spectroscopic titration data at suitable dilute concentration ranges in which the fluorescent quenching of Zn(p-X)TPP by Mn(p-ImBPTPP)Cl is a static process. The electronic effect in the supramolecular self-assembly of para-substituted . porphyrinatozinc(II) with imidazolyl-linked porphyrinatomanganese(III) is discussed. The non-linear dependence of log K_c on the Hammett constants was found, which suggested that the electronic effect in para-substituents of tetraphenylporphyrin complexes of zinc(II) is an important, but not a sole factor effecting the association constants of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complexes. The results indicate that the closed conformation of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complex is another important factor effecting the association constants of the Zn(p-X)TPP–Mn(p-ImBPTPP)Cl supramolecular complexes.     

Impact of a Water-Soluble Gallic Acid-Based Dendrimer on the Color-Stabilizing Mechanisms of Anthocyanins

The interaction of two anthocyanins with a water-soluble polyanionic dendrimer was studied through UV/Vis, stopped-flow, and NMR spectroscopy. Cyanidin-3-glucoside (cy3glc) revealed a stronger interaction than malvidin-3-glucoside (mv3glc) at pH 1 according to their apparent association constants. A higher color increased was also obtained for cy3glc at pH 3.5 as a result of this stronger interaction. A high-frequency chemical shift of the cy3glc aromatic protons suggest the formation of ionic pairs. The interaction parameters (K≈700 m ⁻¹, n≈295) indicated the binding of approximately two anthocyanin molecules by each sulfate group. The equilibrium and rate constants of cy3glc in the presence of dendrimer showed an increased stability of the flavylium cation and a higher protection of this species from hydration (pK′_a and pK_h increased almost one pH unit). The tuning and color stabilization of anthocyanins by using this dendrimer allow novel applications as colorimetric sensors for food packaging.     

On The Effect of Dielectric Constant on Formation and Stability Constants of Vanadium(v) with Leucine in Mixed Solvent of Methanol + Water at 298.15 K

Abstract

Equilibria in aqueous solutions in the system leucine + VO₂ ⁺ has been studied by a combination of potentiometric and spectrophotometric methods, in the p^H range 3–4.4 with high ligand-to-metal ratios. An equilibrium model, MY, is assumed, where M and Y represent the metal ion and fully dissociated amino acid anion, respectively. The results showed that formation and stability constants of complex system increased with decrease of dielectric constants. Linear relationships were observed when log K_P was plotted vs. 1/D, where K_P and D represent stability and dielectric constants of the system, respectively.     

Clamshell Opening in the Mixed‐Metal Supramolecular Aggregates Formed by Fourfold Reduced Corannulene for Maximizing Intercalated Metal Content

The first members of a new class of supramolecular organometallic compounds with mixed‐alkali‐metal cluster cores, LiK₅ and Li₃K₃, sandwiched between two four‐fold reduced corannulene decks are prepared and fully characterized. The triple‐decker supramolecular anions, [(C₂₀H₁₀^4?)(LiK₅)⁶⁺(C₂₀H₁₀^4?)]^2? and [(C₂₀H₁₀^4?)(Li₃K₃)⁶⁺(C₂₀H₁₀^4?)]^2?, illustrate a record ability of bowl‐shaped and highly charged corannulene to provide all its sites, five benzene rings fused to a central five‐membered ring, for binding of six alkali‐metal ions. The previously unseen engagement of the hub‐site of C₂₀H₁₀^4? in lithium binding is accompanied by unprecedented shifts up to ?24 ppm in ⁷Li NMR spectra. The discussion of product formation mechanism, augmented by calculations, is provided.     

Mixed-Valence BN-Doped Corannulene Trimer Radical Cations

Mixed-valence (MV) dimers have been extensively investigated, however, the structure and properties of purely organic MV trimers based on open-shell polycyclic aromatic hydrocarbons remain elusive. Herein, unprecedented MV BN-doped corannulene radical cations [ BN-Cor1 ]₃⋅⋅²⁺ ⋅ 2[BAryl^F₄]⁻ and [ BN-Cor2 ]₃⋅⋅²⁺ ⋅ 2[BAryl^F₄]⁻ were synthesized via chemical oxidation, and their structures were unambiguously confirmed by single-crystal X-ray diffraction. These uncommon radical cations consist of three corannulene cores and two [BAryl^F₄]⁻ anions, and three corannulene motifs [ BN-Cor1 ]₃⋅⋅²⁺ and [ BN-Cor2 ]₃⋅⋅²⁺ in the unit cell exhibit a trimer structure with a slipped π-stacking configuration. Detailed structural analyses further revealed that the corannulene cores exhibit an infinite layered self-assembly configuration, allowing their potential applications as building blocks for molecular conductors. The detection of a forbidden transition (Δm_s=±2) by electron paramagnetic resonance (EPR) spectroscopy further confirmed the existence of two unpaired electrons in the π-trimers and the MV characteristic of these two species. Variable-temperature EPR and conductivity measurements suggested that the BN-doped π-trimers exhibited antiferromagnetic coupling and conductivity properties.     

Carboxylic acid to thioamide hydrogen bonding

The lactam groups of dipyrrinones avidly engage in amide-amide hydrogen bonding to form dimeric association complexes in non-polar solvents (in CHCl₃, K_D ∼25,000 M⁻¹ at 22 °C). The corresponding thioamides (dipyrrinthiones), prepared from dipyrrinones by reaction with Lawesson's reagent, also form intermolecularly hydrogen-bonded dimers in non-polar solvents, albeit with much weaker association constants (in CHCl₃, K_D ∼200 M⁻¹ at 22 °C). When a carboxylic acid group is tethered to C(9) of the dipyrrinone, as in the hexanoic acid of [6]-semirubin, tight intramolecular hydrogen bonding between the carboxylic acid group and the lactam moiety (intramolecular K_assoc ?25,000) is found in CHCl₃ with no evidence of dimers. In contrast, the analogous dipyrrinthione, [6]-thiosemirubin, eschews intramolecular hydrogen bonds, as determined using NMR spectroscopy and vapor pressure osmometry, preferring to form intermolecularly hydrogen-bonded dimers of the thioamide-thioamide type.     

Oligonucleotide Analogues with Integrated Bases and Backbone. Part 16

The self‐complementary, ethylene‐linked U*[c_a]A⁽*⁾ dinucleotide analogues 8, 10, 12, 14, 16 , and 18 , and the sequence‐isomeric A*[c_a]U⁽*⁾ analogues 20, 22, 24, 26, 28 , and 30 were obtained by Pd/C‐catalyzed hydrogenation of the corresponding, known ethynylene‐linked dimers. The association of the ethylene‐linked dimers was investigated by NMR and CD spectroscopy. The U*[c_a]A⁽*⁾ dimers form linear duplexes and higher associates (K between 29 and 114M ^?1). The A*[c_a]U⁽*⁾ dimers, while associating more strongly (K between 88 and 345M ^?1), lead mostly to linear duplexes and higher associates; they form only minor amounts of cyclic duplexes. The enthalpy–entropy compensation characterizing the association of the U*[c_x]A⁽*⁾ and A*[c_x]U⁽*⁾ dimers (x=y, e, and a) is discussed.     

Hydroxyoxo(5,10,15,20-tetraphenylporphinato)tungsten(V) as a receptor for foodstuff and drug components. Thermodynamics of supramolecular complexation

The thermodynamics of stepwise reactions of hydroxyoxo(5,10,15,20-tetraphenylporphinato)tungsten(V) (O=W(OH)TPP) with biologically active base molecules was studied. For the reaction of O=W(OH)TPP with benzimidazole, four steps were found and studied; the equilibrium constants K _n were determined to be 2.55 × 10⁴, 1.87 × 10³ L/mol, 1.06 × 10⁶, 4.09 × 10⁴ L²/mol². The reaction of O=W(OH)TPP with pyrazine was a one-step reversible process of Pyz coordination to the eighth coordination site (K = 399 L/mol). The correlation equations relating the stability of supramolecular complexes to pK of the bases were obtained. The thermodynamic data were used to demonstrate the prospects of applying the metal porphyrin as a receptor for N-bases in membranes, sensors, and analytical devices for quality control of foodstuffs, drugs, and gas mixtures for the content of VOCs.     

Face-Fusion of Icosahedral Boron Hydride Increases Affinity to γ-Cyclodextrin: closo,closo-[B21H18]− as an Anion with Very Low Free Energy of Dehydration

The supramolecular recognition of closo,closo-[B₂₁H₁₈]⁻ by cyclodextrins (CDs) has been studied in aqueous solution by isothermal titration calorimetry and nuclear magnetic resonance spectroscopy. These solution studies follow up on previous mass-spectrometric measurements and computations, which indicated the formation and stability of CD ⋅ B₂₁H₁₈⁻ complexes in the gas phase. The thermodynamic signature of solution-phase binding is exceptional, the association constant for the γ-CD complex with B₂₁H₁₈⁻ reaches 1.8×10⁶ M⁻¹, which is on the same order of magnitude as the so far highest observed value for the complex between γ-CD and a metallacarborane. The nature of the intermolecular interaction is also examined by quantum-mechanical computational protocols. These suggest that the desolvation penalty, which is particularly low for the B₂₁H₁₈⁻ anion, is the decisive factor for its high binding strength. The results further suggest that the elliptical macropolyhedral boron hydride is another example of a CD binder, whose extraordinary binding affinity is driven by the chaotropic effect, which describes the intrinsic affinity of large polarizable and weakly solvated chaotropic anions to hydrophobic cavities and surfaces in aqueous solution.     

One‐pot Preparation,Spectroscopic and Structural Characterization of Mercury(II) Complexes of Bulky Diimines with Halides and Pseudohalides

The preparation and characterization of two novel HgCl₂ and Hg(SCN)₂ complexes with bis[N‐(2‐tert‐butylphenyl)imine]acenaphthene is here described. One‐pot reaction techniques were used, leading to high yields of 75 % and 81 %, respectively. The complexes were characterized by microanalysis, i.r. and ¹HNMR spectroscopy, and by single crystal X‐ray diffraction. The structures of the complexes present similar characteristics, the most outstanding being the formation of dimers via intermolecular interaction. Whereas the HgCl₂ complex shows a unidimensional network due to strong π–π interactions, its Hg(SCN)₂ counterpart displays a supramolecular arrangement resulting from non classical hydrogen bond formation.     

Binding of benzene-1,2,3,4,5,6-hexacarboxylate by polyammonium cations

The interaction between mellitate (benzene-1,2,3,4,5,6-hexacarboxylate) and diethylenetriamine and spermidine was studied by potentiometric and calorimetric techniques in aqueous solution at t = 25°C, moreover by diffractometric technique in the solid state. Thermodynamic parameters of several A_pLH_q species with p = 1, q = 2…5, for both systems, were calculated; in addition the following species were found: A₂LH₆, for A = dien; ALH₆, for A = spd. The stabilities of these species are quite high; for example formation constants regarding the ALH₃³⁻ species are: logK⁰ = 5.7 for A = dien and logK⁰ = 10.1 for A = spd. Thermodynamic parameters are generally function of charges involved in the formation reaction and some linear relationships were found. The speciation profiles show that the formation percentages, for the mononuclear species in particular, are high, in a wide pH range. The sequestering ability of mlt towards polyamines was analysed, also considering the already published data regarding ethylenediamine. By considering the formation constants at various ionic strength and the enthalpy values of triamine–mellitate species, it was possible to evaluate the dependence of sequestering ability on ionic strength, temperature and pH. Solid state investigation of two cocrystals, made by mellitate trianion and triammonium cations, provides information on the formation of supramolecular anionic layers. Comparison with the stability of mellitate–alkaline earth metals species was made.     

Current-potential curves for facilitated ion transfer across oil/water interfaces in the presence of successive complex formation

A theoretical analysis of the current-potential curves for facilitated ion transfer across an oil/water interface is presented for the case where two complex species having an ion-to-ligand ratio of 1:1 and 1:2 are allowed to exist in the oil phase. Cyclic voltammograms are calculated numerically by using a finite difference method assuming that the ion transfer is reversible and the complex formation equilibria are maintained throughout the oil phase. When the ligand concentration in the oil phase is much smaller than the ion concentration in the aqueous phase and the former limits the ion-transfer current, two well separated peaks may develop even under the assumption of equilibrium conditions for the complex formation. The shape of the voltammogram is determined primarily by the ratio of the two reduced stability constants: b₁ = K₁^bc_L^O and b₂ = K₁K₂(^bc^O_L)², where K₁ and K₂ are the stability constants for 1:1 and 1:2 complexes in the oil phase and ^bc^O_L the ligand concentration in the bulk of the oil phase. The degree of peak separation thus depends not only on K₂/K₁ but also on ^bc^O_L. A method for estimating the two stability constants from the voltammograms is proposed.     

Steric and Inductive Effects on Ionic Association in Aqueous Solutions Using an ion Selective Electrode Technique. II. Magnesium Salts

The stoichiometric association constants, K, the thermodynamic association constants, K_A, and the thermodynamic parameters ΔS°, ΔH°, ΔG° for the association between Mg(II) ion with o-, m and p-toluates,o-,m, and p-chlorobenzoates, and o-, m- and p-bromobenzoates have been determined at 15°C, 25°C, 35°C and 45°C in aqueous media. Ion selective electrodes were used to measure the Mg^{2 +} activities. The trends in the association behavior of Mg(II) salts of aromatic acids connot be explained on the basis of steric effects but can be explained according to the trend of the pKa of the parent organic acids, and the Hammett function, σ, of the salts themselves relative to the corresponding benzoate salt.     

Physico-chemical studies on the chelation behaviour of acenaphthenequinone monothiosemicarbazone (AQTS) with some bivalent metal ions

Summary The stability constants of the chelates formed from acenaphthenequinone monothiosemicarbazone and magnesium(II), manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) or cadmium(II) have been determined pH-metrically in 75% v/v aqueous dioxan at various ionic strengths of NaClO₄ and at different temperatures. The method of Bjerrum and Calvin^{(1, 2)} as modified by Irving and Rossotti⁽³⁾, has been used to determine the ñ and pL values. The stability constants were calculated on an IBM 360 FORTRAN-IV computer patterned after that of Sullivanet al. ⁽⁴⁾ to give _n values using a weighted least squares method. The S_min, values were also calculated. The thermodynamic stability constant has been determined by extrapolating the log K₁ vs plot at zero ionic strength. The other thermodynamic functions have been calculated from the stability constants obtained for different temperatures at constant ionic strength. The bivalent metal stability sequence of AQTS chelates is in agreement with reported metal orders for other chelating reagents. The order of free energies and enthalpies of chelate formation for AQTS are: Mn²⁺2+2+2+>Zn²⁺.     

NMR spectroscopy in coordination supramolecular chemistry: A unique and powerful methodology

Metal-mediated self-assembly is emerging as a very important strategy for the synthesis of supramolecular species. Still, a major challenge in coordination supramolecular chemistry continues to be the characterization of the self-assembled complexes and the investigation of their dynamic behaviour in solution. In this context, NMR spectroscopy appears as a unique and powerful methodology. This practical-oriented review describes the rich variety of NMR techniques which are applied to the investigation of different aspects of the structure and behaviour of supramolecular complexes. “Classic” 1D NMR spectra reflect characteristic chemical shifts due to metal–ligand interactions or encapsulation phenomena, as well as symmetry and chiral properties of host–guest assemblies. Mainstream ¹H, ¹³C, ¹⁹F and ³¹P spectra are eventually complemented by the use of NMR-active metal nuclides. Homo- and heteronuclear 2D correlation experiments are ubiquitous in the literature, providing through-bond and through-space connectivities. Increasingly, diffusion measurements are also gaining popularity in this field, being used to gain information about molecular size, intermolecular interactions and even association constants of supramolecular complexes. Knowledge about the thermodynamic properties and the dynamic behaviour of coordination supramolecular assemblies is essential for the development of their practical applications. The most frequently used NMR methodologies for the calculation of association constants (simple signal integration, NMR titration and diffusion measurements) and for the investigation of dynamic supramolecular equilibria (lineshape analysis, selective inversion recovery experiments and 2D EXSY spectra) are described, together with the use of variable-temperature investigations for the determination of the thermodynamic and activation parameters of self-assembly and encapsulation processes.     

氨基甲酸酯型脱氧胆酸分子钳对中性分子的识别性能研究

利用差紫外光谱法考察了新型分子钳1～6对苯胺、对硝基苯胺、对甲氧基苯胺等中性分子的识别性能, 测定了25 ℃下, 在CHCl₃中主客体间的结合常数(K_a)和自由能变化(ΔG⁰). 结果表明, 所有分子钳主体对所考察的客体分子显示良好的识别作用, 主客体间形成1∶1型主客体络合物. 识别作用的主要推动力为多重氢键和π-π重叠等的作用. 讨论了主客体间形状、大小匹配和几何互补及识别模式等因素对识别能力的影响, 并利用核磁共振氢谱与计算机模拟作为辅助手段对实验结果进行了解释.     

Effect of 4f-shell excitation of Eu(fod)3 on its complex formation with alicyclic ketones

The complex formation of alicyclic ketones, viz., camphor, cyclohexanone, menthone, and cytisine, with the Eu(fod)₃ chelate (fod is 7,7-dimethyl-1,1,1,2,2,3,3-heptafluorooctane-4,5-dione) in the ground and excited states was studied by chemiluminescence and kinetic luminescence spectroscopy, respectively. The stability constants and thermodynamic parameters of complex formation were determined. An increase in the stability of the electron-excited complexes [Eu(fod)₃*·Ketone] is explained by the enhancement of the acceptor ability of the Eu³⁺ chelate due to an increase in the fraction of the covalent component caused by the involvement of 4f-orbitals. The results obtained give direct evidence for the effect of the 4f-shell excitation of Eu(fod)₃ on complex formation due to the involvement of f-electrons in the chemical bonds.     

Mixed Ligand Complex Formation Reactions and Equilibrium Studies of Cu(II) with Bidentate Heterocyclic Alcohol (N,O) and Some Bio-Relevant Ligands

The formation equilibria of copper(II) complexes and the ternary complexes Cu(HMI)L (HMI=4-Hydroxymethyl-imidazole, L=amino acid, amides or DNA constituents) have been investigated. Ternary complexes are formed by a simultaneous mechanism. The results showed the formation of Cu(HMI)L and Cu(HMI,H₋₁)(L) complexes. The stability of ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameters Δlog ₁₀ K and log ₁₀ X. The effect of the side chains of amino acid ligands (Δ_R) on complex formation was discussed. The concentration distributions of various species formed in solution were also evaluated as a function of pH. The thermodynamic parameters ΔH° and ΔS° calculated from the temperature dependence of the equilibrium constants are investigated. The effects of dioxane as a solvent, on the protonation constant of HMI and the formation constants of Cu^II–HMI complexes, were discussed.     

NMR as a tool for simultaneous study of diasteroisomeric inclusion complexes, part 2: complexes formed by racemic mixture of 4′-hydroxyflavanone and two cyclodextrins

Complexes formed by (±)-4′-hydroxyflavanone (OHFL) and the cyclodextrins β-cyclodextrin and (2-hydroxypropyl)-β-CD were obtained using the racemic mixture of the OHFL. These complexes were able to be studied due to their enantiodifferentiation by ¹H-NMR spectroscopy. Stoichiometry, association constants and thermodynamic parameters were obtained from these NMR data, and inclusion geometries were proposed from ROESY spectra. The results show a 1:1 stoichiometry, K _a values decrease with increasing temperature, a spontaneous and exothermic complexes formation, and that ROESY spectra cannot differentiate between enantiomers, and therefore the estimated inclusion geometries were proposed for the mixture of diasteroisomeric complexes.     

A spectroscopic study of phenylbutazone and aspirin bound to serum albumin in rheumatoid diseases

Interaction of phenylbutazone (PBZ) and aspirin (ASA), two drugs recommended in rheumatoid diseases (RDs), when binding to human (HSA) and bovine (BSA) serum albumins, has been studied by quenching of fluorescence and proton nuclear magnetic resonance (¹HNMR) techniques.On the basis of spectrofluorescence measurements high affinity binding sites of PBZ and ASA on albumin as well as their interaction within the binding sites were described. A low affinity binding site has been studied by proton nuclear magnetic resonance spectroscopy.Using fluorescence spectroscopy the location of binding site in serum albumin (SA) for PBZ and ASA was found. Association constants K_a were determined for binary (i.e. PBZ–SA and ASA–SA) and ternary complexes (i.e. PBZ–[ASA]–SA and ASA–[PBZ]–SA).PBZ and ASA change the affinity of each other to the binding site in serum albumin (SA). The presence of ASA causes the increase of association constants K_aI of PBZ–SA complex. Similarly, PBZ influences K_aI of ASA–SA complex. This phenomenon shows that the strength of binding and the stability of the complexes increase in the presence of the second drug. The decrease of K_aII values suggests that the competition between PBZ and ASA in binding to serum albumin in the second class of binding sites occurs. The analysis of ¹HNMR spectral parameters i.e. changes of chemical shifts and relaxation times of the drug indicate that the presence of ASA weakens the interaction of PBZ with albumin. Similarly PBZ weakens the interaction of ASA with albumin. This conclusion points to the necessity of using a monitoring therapy owning to the possible increase of uncontrolled toxic effects.