Binding Effect of Common Ions to Human Serum Albumin in the Presence of Norfloxacin: Investigation with Spectroscopic and Zeta Potential Approaches

In this work, the toxic influence of metallic ions (Al³⁺, Cu²⁺, Mg²⁺, Pb²⁺) on human serum albumin (HSA) in the absence and presence of norfloxacin (NRF) was studied by spectroscopic approaches [fluorescence quenching, synchronous fluorescence, three-dimensional fluorescence, circular dichroism, resonance light scattering (RLS) and zeta potential techniques] under simulated physiological conditions. Fluorescence spectroscopy revealed that these metallic ions and NRF can quench the HSA fluorescence, and this quenching effect became more significant when both ion and drug are present together. The binding constants and binding sites of metal ions with HSA in the absence and presence of NRF were determined, based on the fluorescence quenching results. Ion aggregation gives rise to an enhancement of the RLS intensity for HSA and the critical induced aggregation concentration (C _CIAC) of the ions, causing HSA aggregation for binary and ternary systems. The zeta potential measurements indicate a combination of electrostatic and hydrophobic interactions between ion, NRF and HSA and the formed micelle-like clusters. These data illustrated that NRF has an effect on the interaction between HSA and metal ions, with relevance for various toxicological and therapeutic processes.     

Characteristics of proflavine solubilized in complexes of anionic polymers with a cationic surfactant

Absorption and emission spectra of 3,6-diaminoacridine (proflavine) are reported in mixed solutions of dodecyltrimethylammonium bromide (DTAB) with various polyelectrolytes including the sodium salts of poly(acrylic acid) (PAA). poly(methacrylic acid) (PMA), poly(styrenesulfonic acid) (PSS), poly(garacturonic acid) (pectate), and the alternating copolymers of maleic acid with ethylene (PMA-E) and styrene (PMA-S). The spectral change indicates the association of the dye (blue-shift) on these polyions except on PSS, the easy dissociation of the aggregated form into the monomeric form and the solubilization into the hydrophobic PMA-S/DTAB complex (red-shift), the little dissociation in the PAA/DTAB, PMA/DTAB and PMA-E/DTAB complexes, and the liberation of the bound dye in the case of pectate/DTAB complexes. In the PSS system, the strong interaction of the dye with the styrene groups induces the completely different spectral behavior. These results are discussed with the cooperative binding of the dye and the surfactant ion.     

A Sulfur Heterocyclic Quinone Cathode and a Multifunctional Binder for a High‐Performance Rechargeable Lithium‐Ion Battery

We report a rational design of a sulfur heterocyclic quinone (dibenzo[b,i]thianthrene‐5,7,12,14‐tetraone=DTT) used as a cathode (uptake of four lithium ions to form Li₄DTT) and a conductive polymer [poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate)=PEDOT:PSS) used as a binder for a high‐performance rechargeable lithium‐ion battery. Because of the reduced energy level of the lowest unoccupied molecular orbital (LUMO) caused by the introduced S atoms, the initial Li‐ion intercalation potential of DTT is 2.89 V, which is 0.3 V higher than that of its carbon analog. Meanwhile, there is a noncovalent interaction between DTT and PEDOT:PSS, which remarkably suppressed the dissolution and enhanced the conductivity of DTT, thus leading to the great improvement of the electrochemical performance. The DTT cathode with the PEDOT:PSS binder displays a long‐term cycling stability (292 mAh g^?1 for the first cycle, 266 mAh g^?1 after 200 cycles at 0.1 C) and a high rate capability (220 mAh g^?1 at 1 C). This design strategy based on a noncovalent interaction is very effective for the application of small organic molecules as the cathode of rechargeable lithium‐ion batteries.     

Complexation and Self-Assembling of Sulfonatomethylated Calix[4]resorcinarene with Both Organic and Lanthanide Ions in Aqueous Media

The stoichiometry and binding constant of the paramagnetic lanthanide ion(Gd³⁺) with sulfonatomethylated calix[4]resorcinarene (H₈Xna₄) were evaluated from the NMR relaxation data. Both ¹H NMR spectroscopy and NMR relaxation data indicate that interaction of tetramethylammonium (TEMA) and N-methylpyridinium (MePy) cations with H₈Xna₄ in the presence of Ln³⁺ (Lu³⁺ or Gd³⁺) results in theformation of ternary complexes [Ln(G)H₈X] with lanthanide ions,coordinated via sulfonate groups and organic cation included intothe cavity of H₈Xna₄. The inclusion of long-chainedN-decyl-(DePy) and N-cetylpyridinium (CPy) ions into H₈Xna₄ cavity leads to self-assembling which can be revealed by NMR relaxation method with Gd³⁺ probe ions. The excess of alkylpyridinium or TEMA cations leads to disassembling of (Gd)_n(H₈X)_m(RPy)_maggregates.     

Ion hydration co-sphere interactions in the double-layer and ionic solutions

Two-dimensional concentrations of adsorbed ions in double-layers at charged interfaces, especially when appreciable specific adsorption obtains, are equivalent to quite substantial (1–4 M) three-dimensional concentrations in regular electrolyte solutions. Under such conditions, ion-specific Gurney co-sphere overlap interactions give an important contribution to the non-ideal free energy of electrolytes in solution. It is proposed that similar interaction effects arise two-dimensionally in double-layers, giving rise to a contribution to the lateral interaction energy in monolayer arrays of ions. Three types of calculations are described by which these interaction effects can be evaluated. One is applied to some recent data on tetrapropylammonium ion adsorption at Hg, where hydrophobic interactions arise.Related problems concerned with solvent dipole orientation in the inner layer, when appreciable surface concentrations of hydrated ions are present, are referred to. The probable role of field-gradient/quadrupole interactions is noted.     

Polyelectrolyte gel transitions: experimental aspects of charge inhomogeneity in the swelling and segmental attractions in the shrinking

This paper aims to provide a systematic discussion based on our experimental results both previously published and unpublished, to promote better understanding of volume-phase transitions in polyelectrolyte gels. Special attention was paid to the distribution of network charges as well as to the attractive interaction among polymer segments. From looking at how these effects appear in the swelling curves, an exploration of the nature of polyelectrolyte gel transitions was attempted. Two sorts of polyelectrolyte gels, temperature-responsive ionic gels based on N-isopropylacrylamide (NIPA) and cationic poly(ethyleneimine) (PEI) gels, were mainly employed with various modifications. The charge inhomogeneity within the gel phase was created by surfactant binding, immobilized enzyme reaction and physical entrapment of polyions. The attractive interactions holding the gel in a collapsed state were studied in comparison with phase separations of the corresponding linear polyelectrolyte. The main conclusions are summarized as follows: (i) The charge inhomogeneity exhibits a large influence on the volume transition in ionic gels. (ii) Hydrogen bonding and hydrophobic association, other than electrostatic attraction, can be considered to play an important role in the segmental association. (iii) Stably associated segments via one or more of these attractive interactions causes a large hysteresis in the swelling process, in which the repulsive interaction among the fixed charges on the network is dominant as shown in the Katchalsky's model. (iv) A distribution of "neutral but hydrophilic" moieties (e.g., ion pair or salt-linkage formed between the opposite charged groups) within the gel shows a marked effect on the temperature-induced volume collapse, the aspect of which is similar to that observed in the gels with a charge inhomogeneity.     

Calix[4]pyrrole‐Based Heteroditopic Ion‐Pair Receptor That Displays Anion‐Modulated,Cation‐Binding Behavior

A new ditopic ion‐pair receptor 1 was designed, synthesized, and characterized. Detailed binding studies served to confirm that this receptor binds fluoride and chloride ions (studied as their tetraalkylammonium salts) and forms stable 1:1 complexes in CDCl₃. Treatment of the halide‐ion complexes of 1 with Group I and II metal ions (Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, and Ca²⁺; studied as their perchlorate salts in CD₃CN) revealed unique interactions that were found to depend on both the choice of the added cation and the precomplexed anion. In the case of the fluoride complex [ 1? F]^? (preformed as the tetrabutylammonium (TBA⁺) complex), little evidence of interaction with the K⁺ ion was seen. In contrast, when this same complex (i.e., [ 1? F]^? as the TBA⁺ salt) was treated with the Li⁺ or Na⁺ ions, complete decomplexation of the receptor‐bound fluoride ion was observed. In sharp contrast to what was seen with Li⁺, Na⁺, and K⁺, treating complex [ 1? F]^? with the Cs⁺ ion gave rise to a stable, receptor‐bound ion‐pair complex [Cs ?1? F] that contains the Cs⁺ ion complexed within the cup‐like cavity of the calix[4]pyrrole, which in turn was stabilized in its cone conformation. Different complexation behavior was observed in the case of the chloride complex [ 1? Cl]^?. In this case, no appreciable interaction was observed with Na⁺ or K⁺. In addition, treating [ 1? Cl]^? with Li⁺ produces a tightly hydrated dimeric ion‐pair complex [ 1? LiCl(H₂O)]₂ in which two Li⁺ ions are bound to the crown moiety of the two receptors. In analogy to what was seen in the case of [ 1? F]^?, exposure of [ 1? Cl]^? to the Cs⁺ ion gives rise to an ion‐pair complex [Cs ?1? Cl] in which the cation is bound within the cup of the calix[4]pyrrole. Different complexation modes were also observed when the binding of the fluoride ion was studied by using the tetramethylammonium and tetraethylammonium salts.     

Unusual complex between 18-Crown-6 and tetramethylammonium cation—detection by electrospray ionization mass spectrometry

Complexes between crown ethers and quaternary ammonium cations have been studied by electrospray ionisation mass spectrometry (ESI-MS). The ESI-MS method has been shown to allow observation of not only stable inclusion complexes between large crown ethers and tetramethylammonium cation (e.g. [DB30C10 + (CH₃)₄N]⁺ ion) but also of unstable inclusion complexes between smaller crown ethers and quaternary ammonium cations which are difficult to observe by other methods, namely [18C6 + (CH₃)₄N]⁺ ion. Stability of the complexes between crown ethers containing aromatic ring and tetramethylammonium cation is enhanced by cation-Π interactions. The molecule of 18C6 does not contain aromatic rings, thus [18C6 + (CH₃)₄N]⁺ ion exists due to the formation of C–H···O hydrogen bonds. Such a complex is quite unusual, since C–H···O hydrogen bonds are very weak and usually coexist with other strong interactions.     

Complexes of iron(II) with cysteine-containing peptides in the gas phase

Gas-phase interactions of peptides that contain cysteine with iron(II) atoms were examined by using fast-atom bombardment and tandem mass spectrometry. Specific and strong interactions of iron and sulfur from the thiol group of the cysteine side chain occur in the gas phase and are the basis for highly specific fragmentation to give abundant [a _n ?⁺ ions. For peptides that contain two cysteines, an internal ion, which results from the interaction of Fe and both thiol groups, is formed upon collisional activation. The mechanism for the formation of [a _n ?2H+Fe]⁺ fragment ions requires the metal to be coordinated at sulfur in close proximity to the site of reaction. Iron-bis(pentapeptide) complexes, which form under the same conditions, decompose predominantly to lose a pentapeptide molecule and, to a lesser extent, to give [a _a ?2H+Fe]⁺ ions.     

Aromatic-aromatic interaction between 2,3,5-triphenyl-2H-tetrazolium chloride and poly(sodium 4-styrenesulfonate)

Aromatic-aromatic interactions are found between the cationic molecule 2,3,5-triphenyl-2H-tetrazolium chloride (TTC) and the molecule poly(sodium 4-styrenesulfonate) (PSS) which makes the overall interaction of TTC with PSS more intense than the interaction with other polyanions containing sulfonate groups and produces a decrease on the redox ability of TTC. Diafiltration was used to compare the binding of TTC to PSS, poly(sodium vinylsulfonate) (PVS), and the more hydrophobic poly(sodium 2-(N-acrylamido)-2-methyl-propanesulfonate) (PAMPS). The UV-vis spectrum of TTC is changed in the presence of the aromatic polyanion. The 1H NMR signals of TTC are broadened and shifted in the presence of PSS, suggesting the occurrence of pi-pi interactions. Moreover, nuclear Overhauser effects (NOE) between the TTC and PSS protons are found. Possible structures for the complex are proposed.     

Analytical determination of the [Ln-aminoxyl radical] exchange interaction taking into account both the ligand-field effect and the spin-orbit coupling of the lanthanide ion (Ln = DyIII and HoIII)

Numerous compounds in which a paramagnetic LnIII ion is in an exchange interaction with a second spin carrier, such as a transition metal ion or an organic radical, have been described. However, except for GdIII, very little has been reported about the magnitude of the interactions. Indeed, for these ions both the ligand-field effects and the exchange interactions between the magnetic centers become relevant in the same temperature range; this makes the analysis of the magnetic behavior of such compounds more difficult. In this study, quantitative analyses of the thermal variations of the static isothermal initial magnetic susceptibility measured on powdered samples of the [Ln(NO3)3-[organic radical]2] (Ln = DyIII and HoIII) compounds were performed. The ligand-field effects on the Ln ions were taken into account, and the exchange interactions within a molecule were treated exactly within an appropriate Racah formalism. Values of the intramolecular [Ln-aminoxyl radical] exchange parameter have thus been rigorously deduced for both the Dy Kramers and Ho non-Kramers ion-based compounds. Ferromagnetic [Ln-radical] interactions are found for both the Dy and Ho derivatives with J = 8 cm(-1) and J = 4.5 cm(-1), respectively.     

Preparation of a new 1,3-alternate-calix[4]arene-bonded HPLC stationary phase for the separation of phenols, aromatic amines and drugs

We have synthesized the 1,3-alternate 25,27-dioctyloxy-26,28-bis-[3-aminopropyloxy]-calix[4]arene and then immobilized onto γ-chloropropylsilica gel (CPS). The high-performance liquid chromatographic behavior of some aromatic hydrocarbons, phenolic compounds, aromatic amines and drug compounds was studied on this 1,3-alternate-calix[4]arene-bonded silica gel stationary phase (CIMS). The effect of organic modifier content and pH of the mobile phase on retention and selectivity of these compounds were investigated. According to chromatographic data, it can be concluded that the selectivity of CIMS for analytes ascribes to various interactions between CIMS and the analytes, such as hydrophobic interaction, hydrogen bonding interaction, π-π interaction and inclusion interaction.     

Modelling of ligand–receptor interactions: ab-initio and DFT calculations of solvent reaction field effects on methylated ammonium–π and –acetate complexes

Interaction energies of increasingly methylated ammonium ions with aromatics (benzene, phenol, indole) and with acetate were calculated in vacuo and under the influence of polar media in order to model the binding of ammonium group containing ligands to receptors that offer either carboxylic or aromatic amino acid side chains as ligand anchoring alternatives. Semiempirical, ab-initio and DFT methods were applied to in vacuo calculations while the latter was used at the B3LYP6-31G(d) level in connection with the SCRF procedure of Miertu et al. [Chem. Phys. 55 (1981) 117] to simulate the free energies of transfer from the aqueous (=78.3) to the proteinaceous medium (=20). The in vacuo absolute interaction energies decrease with increasing methylation but the opposite becomes true under the influence of SCRF; only in the example of the tetramethylammonium ion the free energy stays negative. Concerning the interaction of the latter with acetate, it is only slightly more favourable than the binding of tetramethylammonium to indole. This result indicates that aromatic side chains are thermodynamically comparable to the carboxylic ones in the recognition process of the respective receptors for acetylcholine type ligands.     

Rapid metal ions shuttling through 1,3-alternate Thiacalix[4]crown tubes

Several new thiacalix[4]monocrown and thiacalix[4]biscrown compounds were synthesized. Their metal ion extractabilities are found to be lower than those of conventional calix[4]crowns. By use of X-ray crystal structures and (1)H NMR spectroscopy, this result is explained by weaker electrostatic interactions of the polyether ring oxygen atoms with the metal ions and diminished pi-metal ion interactions between the metal ions and the aromatic rings of the thiacalix[4]crowns. Temperature-dependent (1)H NMR spectroscopic measurements reveal coalescence temperatures T(c)(intra) and T(c)(inter) for metal ion exchange. In one case, this exchange was rationalized as metal ion shuttling through a thiacalix[4]biscrown tube. Since the metal ions are less tightly complexed by the polyether units in thiacalix[4]biscrowns than in conventional calix[4]biscrowns, more facile metal ion exchange between the two polyether units takes place in the former.     

Interaction of angiotensin peptides and zinc metal ions probed by electrospray ionization mass spectrometry

Electrospray ionization-tandem mass spectrometry experiments were used to provide evidence regarding the sites of interactions between zinc metal ions and angiotensin peptides. The electrospray ionization mass spectra of histidine-containing human angiotensin II (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe) and angiotensin I (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu) in the presence of zinc show abundant multiply charged ions for the zinc-attached peptide [M + aZn²⁺ +(c ? 2a)H⁺]^c+, where a = 1, 2 and c is charge. From collisionally activated dissociation experiments, with both low energy (triple quadrupole mass spectrometry) and high energy collisions (linked scan at constant B/E with a double focusing instrument) of the [M + Zn]²⁺ and [M + Zn + H]³⁺ ions for angiotensin II, a [b ₆ + Zn]²⁺ species is produced as the most abundant product ion, suggesting that the zinc interaction site is in the vicinity of the His⁶ residue. Additionally, tandem mass spectra from the zinc-attached ions for angiotensin I show abundant [b ₆ + Zn]²⁺ and [b ₉ + Zn]²⁺ products, providing evidence that both His⁶ and His⁹ are involved in zinc coordination.     

Structure and interaction between the [BMIM][Ala] alanine anion and the 1-butyl-3-methylimidazolium cation in ion pairs

The equilibrium geometries and vibrational frequencies of the ionic liquid 1-butyl-3-methylimidazolium cation and the alanine anion [BMIM][Ala] are studied using density functional theory (DFT) at the B3PW91/6-311+G(d,p) leve1. The most stable structures of the anion, the cation, and the ion pairs are obtained and characterized, and the geometry parameters of the ion pairs confirm the presence of a hydrogen bonding interaction between the anion and the cation. Natural bond orbital (NBO) analysis is also performed to analyze the atomic charge distribution and charge transfer in the [BMIM]⁺ cation and [BMIM][Ala] ionic liquids. The results show that there are the electrostatic interaction and multiple hydrogen bond interactions between the cation and the anion of the ionic liquids, and the stability of the ground state of the ion pairs mostly results from the hydrogen bonding between the lone pairs of O atoms in the anion and H in the imidazole cycle of the cation. There are some changes in microstructures and the charge distribution during the formation of the ion pairs.     

Interaction between the water soluble poly{1,4-phenylene-[9,9-bis(4-phenoxy butylsulfonate)]fluorene-2,7-diyl} copolymer and ionic surfactants followed by spectroscopic and conductivity measurements

The interaction has been studied in aqueous solutions between a negatively charged conjugated polyelectrolyte poly{1,4-phenylene-[9,9-bis(4-phenoxybutylsulfonate)]fluorene-2,7-diyl} copolymer (PBS-PFP) and several cationic tetraalkylammonium surfactants with different structures (alkyl chain length, counterion, or double alkyl chain), with tetramethylammonium cations and with the anionic surfactant sodium dodecyl sulfate (SDS) by electronic absorption and emission spectroscopy and by conductivity measurements. The results are compared with those previously obtained on the interaction of the same polymer with the nonionic surfactant C12E5. The nature of the electrostatic or hydrophobic polymer-surfactant interactions leads to very different behavior. The polymer induces the aggregation with the cationic surfactants at concentrations well below the critical micelle concentration, while this is inhibited with the anionic SDS, as demonstrated from conductivity measurements. The interaction with cationic surfactants only shows a small dependence on alkyl chain length or counterion and is suggested to be dominated by electrostatic interactions. In contrast to previous studies with the nonionic C12E5, both the cationic and the anionic surfactants quench the PBS-PFP emission intensity, leading also to a decrease in the polymer emission lifetime. However, the interaction with these cationic surfactants leads to the appearance of a new emission band (approximately 525 nm), which may be due to energy hopping to defect sites due to the increase of PBS-PFP interchain interaction favored by charge neutralization of the anionic polymer by cationic surfactant and by hydrophobic interactions involving the surfactant alkyl chains, since the same green band is not observed by adding either tetramethylammonium hydroxide or chloride. This effect suggests that the cationic surfactants are changing the nature of PBS-PFP aggregates. The nature of the polymer and surfactant interactions can, thus, be used to control the spectroscopic and conductivity properties of the polymer, which may have implications in its applications.     

Interactions of quaternary ammonium salt-type gemini surfactants with sodium poly(styrene sulfonate)

The interactions of cationic gemini surfactants, 1,2-bis(alkyldimethylammonio)ethane dibromide (m-2-m: m is hydrocarbon chain length, m = 10 and 12), and an anionic polymer, sodium poly(styrene sulfonate) (PSS), have been characterized by several techniques such as tensiometry, fluorescence spectroscopy, and dynamic light scattering. The surface tension of gemini surfactant/PSS mixed systems decreases with surfactant concentration, reaching break points, which are taken as critical aggregation concentrations (cac). The surface tension at the cac of mixtures is higher than that of single surfactants, and it is found that at concentrations above the cac, the surfactant molecules are associated with the polymer in the bulk. The 12-2-12/PSS mixed system shows higher surface activity than both 10-2-10/PSS and the monomeric surfactant of dodecyltrimethylammonium bromide/PSS systems. Fluorescence measurements of these mixed systems suggest the formation of a complex with a highly hydrophobic environment in the bulk of the solution. Additionally, dynamic light scattering measurements show that the hydrodynamic diameter of the 12-2-12/PSS mixed system is smaller than that of PSS only at low concentration, indicating interactions between surfactant and polymer. These result from the electrostatic attraction between ammonium and sulfate headgroups as well as the hydrophobic interaction between their hydrocarbon chains.     

High performance liquid chromatography of aromatic carboxylic acids on p-tert-butyl-calix[8]arene-bonded silica gel stationary phase

A new p-tert-butyl-calix[8]arene-bonded silica gel stationary phase (CABS) was used for the separation of some aromatic carboxylic acids by HPLC. The chromatographic behaviour of the solutes on CABS was studied in comparison with conventional ODS. The results show that the calix[8]arene-bonded phase exhibits a stronger retention and better selectivity than ODS for the aromatic carboxylic acids. The different elution order of the analytes was also observed on both packings, which show the existence of distinct retention mechanisms. According to chromatographic data, it can be concluded that the high selectivity of CABS for aromatic carboxylic acids ascribes to various interactions between CABS and the analytes, such as hydrophobic interaction, hydrogen bonding interaction, π-π interaction and inclusion interaction.     

Electronic and topological properties of interactions between imidazolium-based ionic liquids and thiophenic compounds: a theoretical investigation

To deepen the understanding the interactions of thiophenic compounds in ionic liquids, we have performed a systemic study on the electronic structures, and topological properties of interactions between N-ethyl-N-ethylimidazolium diethyl phosphate ([EEIM][DEP]) ionic liquid and 3-methylthiophene (3-MT), benzothiophene (BT), or dibenzothiophene (DBT) using density functional theory. From NBO atomic charges and electrostatic potential analyses, most of the positive charge is located on C2–H2 in the [EEIM] cation, and the negative charge is focused on oxygen atoms in [DEP] anion, implying oxygen atoms in [DEP] should easily attack C2–H2 in [EEIM]. The electrostatic interaction between anion and cation may be dominant for the formation of the [EEIM]–[DEP] ion pair. The large stabilizing effect is due to the strong orbital interactions between the antibonding orbital of proton donor σ*(C2–H2) in [EEIM] cation and the lone pairs of proton acceptor LP(O) in [DEP] anion. A common feature of [EEIM][DEP], [EEIM][DEP]-3-MT/BT/DBT complexes is the presence of hydrogen bonds between [EEIM] cation and [DEP] anion. This work has also given the interacting mechanism of 3-MT, BT, and DBT adsorption on [EEIM][DEP] ionic liquid. Both [EEIM] cation and [DEP] anion are shown to play important roles in interactions between 3-MT, BT, DBT and [EEIM][DEP], which has been corroborated by NBO and AIM analyses. The π···π, π···C–H and hydrogen bonding interactions occur between [EEIM][DEP] and 3-MT, BT, DBT. The strength of sulfur involved interactions between 3-MT, BT, DBT and [EEIM][DEP] follows the order of 3-MT > BT > DBT. The order of interaction energies between [EEIM][DEP] and 3-MT, BT, DBT is 3-MT < BT < DBT, in agreement with the order of extractive selectivity from fuel oils (DBT > BT > 3-MT) in terms of sulfur partition coefficients.