Naringenin Schiff base: antioxidant activity,acid–base profile,and interactions with DNA

A Schiff base derived from naringenin (NTSC) and its complex with Cu(II) ([Cu(H₃L)(OAc)]·H₂O, Cu(II)–NTSC) have been synthesized and characterized by physicochemical and spectroscopic methods. EPR studies confirmed that nitrogen, oxygen, and sulfur are the donor atoms bound to Cu(II) in the complex. The geometry of the complex has been modelled using DFT methods. Furthermore, naringenin and NTSC were used for the formation of Cu(II) complexes in solution, for comparison of biological activities. Antioxidant studies confirmed better radical scavenging activity of both NTSC and its Cu(II) complex compared to naringenin. The interaction of these compounds with calf thymus DNA was monitored by UV–Vis spectroscopy.     

Second-order dispersion interactions in π-conjugated polymers

We calculate the ground state and excited state second-order dispersion interactions between parallel π-conjugated polymers. The unperturbed eigenstates and energies are calculated from the Pariser-Parr-Pople model using CI-singles theory. Based on large-scale calculations using the molecular structure of trans-polyacetylene as a model system and by exploiting dimensional analysis, we find that: (1) For inter-chain separations, R, greater than a few lattice spacings, the ground-state dispersion interaction, ΔE(GS), satisfies, ΔE(GS)～L(2)/R(6) for L ? R and ΔE(GS)～L/R(5) for R ? L, where L is the chain length. The former is the London fluctuating dipole-dipole interaction while the latter is a fluctuating line dipole-line dipole interaction. (2) The excited state screening interaction exhibits a crossover from fluctuating monopole-line dipole interactions to either fluctuating dipole-dipole or fluctuating line dipole-line dipole interactions when R exceeds a threshold R(c), where R(c) is related to the root-mean-square separation of the electron-hole excitation. Specifically, the excited state screening interaction, ΔE(n), satisfies, ΔE(n) ～ L∕R(6) for R(c) < L ? R and ΔE(n) ～ L(0)∕R(5) for R(c) < R ? L. For R < R(c) < L, ΔE(n) ～ R(-ν), where ν ? 3. We also investigate the relative screening of the primary excited states in conjugated polymers, namely the n = 1, 2, and 3 excitons. We find that a larger value of n corresponds to a larger value of ΔE(n). For example, for poly(para-phenylene), ΔE(n = 1) ? 0.1 eV, ΔE(n = 2) ? 0.6 eV, and ΔE(n = 3) ? 1.2 eV (where n = 1 is the 1(1)B(1) state, n = 2 is the m(1)A state, and n = 3 is the n(1)B(1) state). Finally, we find that the strong dependence of ΔE(n) on inter-chain separation implies a strong dependency of ΔE(n) on density fluctuations. In particular, a 10% density fluctuation implies a fluctuation of 13 meV, 66 meV, and 120 meV for the 1(1)B(1), m(1)A state, and n(1)B(1) states of poly(para-phenylene), respectively. Our results for the ground-state dispersion are applicable to all types of conjugated polymers. However, our excited state results are only applicable to conjugated polymers, such as the phenyl-based class of light emitting polymers, in which the primary excitations are particle-hole (or ionic) states.     

Two new micro-isostructural metal–organic polymers based on mixed-ligand copper(I): Structures and selective sensing of nitro explosives in water

Two new one-dimensional metal–organic polymers (MOPs) {[Cu(L)(PPh₂Py)·I₂]·CH₃Cl}_n ( I ) and {[Cu(L)(PPh₂Py)·Br₂]·CH₃Cl}_n ( II ) (L = (1E,2E)-1,2-bis(pyridine-4-ylmethylene)hydrazine) (4-bpmh)) have been synthesized and elucidated by single crystal X-ray diffraction. The results of X-ray diffraction analysis unambiguously revealed that the two polymers are isostructural with the major intermolecular CH⋯π and π⋯π interactions. Microstructures of these polymers were also synthesized using a sonochemical method in different concentrations and reaction times. Field emission scanning electron microscopy, powder X-ray diffraction, thermogravimetric analysis and IR spectroscopy were applied to fully characterize these compounds. The photoluminescent properties of microrod MOPs were also evaluated to add to our understanding of their potential ability for nitro compound sensing. These experiments showed that MOPs I and II are good luminescence sensors for detection of nitro explosives in aqueous media. The probes maintained their high sensitivity and selectivity for 4-nitrophenol (4-NP). The energy transfer process accompanied by electrostatic interactions of 4-NP with these MOPs can be considered as an influential reason for the selectivity of 4-NP. The competitive study of the quenching process has a6lso shown superior operation with microparticles compared with bulky polymers. These results indicate that this method may be useful to synthesize luminescent materials possessing good sensing properties.     

Lewis acid/base modulation in β-diiminate zinc-catalyzed switchable ring-opening polymerization of rac-lactide

Two β-diiminate zinc complexes were prepared and found to show high activity and well-controlled catalytic behavior in the ring-opening polymerization of rac-lactide. Coordination of the Lewis acid to the zinc complexes completely terminated the polymerization. The coordinated Lewis acid was easily cleaved by using a Lewis base, so that the polymerization could resume.Thus, switchable polymerization could be realized by the subsequent addition of a Lewis acid and a Lewis base. This work provides a new strategy to control the ring-opening polymerization of rac-lactide.     

Acid–base interactions and swelling of cellulose fibers in organic liquids

Drago’s acid–base approach was used to quantify the hydrogen bonding interactions in solvent swelling of cellulose fibers. The fiber swelling was correlated with acid–base, dispersive interactions and solvent molar volume. The acid–base interaction potentials of solvents were expressed in terms of their electron pair donor and acceptor numbers. The acid–base interaction terms of cellulosic materials were determined by using: (1) Flory–Huggins; (2) multiple regression models. We have used the swelling data of Mantanis and coworkers, which were based on the equilibrium liquid holding capacities of various compressed fibers in water and series of organic solvents. According to our interpretations, acid–base interactions and molar volume parameters were the major contributors to the overall solubility parameter. Acid–base interaction terms were balanced in alpha-cellulose sample. However spruce wood and sulfite pulp samples were more acidic than basic and therefore swollen better in organic basic solvents. For a good swelling behavior solvent must have high electron pair donor number/acceptor number ratio and high electron pair donor number–acceptor number difference.     

Plasmon waveguide resonance for sensing glycan–lectin interactions

Carbohydrate-modified interfaces have been shown to be valuable tools for the study of protein–glycan recognition events. Label-free approache such as plasmonic based techniques are particularly attractive. This paper describes a new analytical platform for the sensitive and selective screening of carbohydrate–lectin interactions using plasmon waveguide resonance. Planar optical waveguides (POW), consisting of glass prisms coated with silver (50 nm) and silica (460 nm) layers were derivatized with mannose or lactose moieties. The specific association of the resulting interface with selected lectins was assessed by following the changes in its plasmonic response. The immobilization strategy investigated in this work is based on the formation of a covalent bond between propargyl-functionalized glycans and surface-linked azide groups via a Cu(I) “click” chemistry. Optimization of the surface architecture through the introduction of an oligo(ethylene glycol) spacer between the plasmonic surface and the glycan ligands provided an interface which allowed screening of glycan–lectin interactions in a highly selective manner. The limit of detection (LOD) of this method for this particular application was found to be in the subnanomolar range (0.5 nM), showing it to constitute a promising analytical platform for future development and use in a pharmaceutical or biomedical setting.     

Enantioselective bromocycloetherification by Lewis base/chiral Brønsted acid cooperative catalysis

A binary catalyst system for the enantioselective bromocycloetherification of 5-arylpentenols is described. The combination of an achiral Lewis base and a chiral Br?nsted acid affords good enantioselectivities for the cyclization of Z configured 5-arylpentenols to form bromomethyltetrahydrofurans. The constitutional site selectivity is highly dependent upon the aromatic substituent and the configuration of the double bond.     

Metal–base pairing in DNA

The use of DNA as a molecular wire in nanoscale electronic architectures would greatly benefit from its capability of sequence-specific self-assembly. Although single electrons and positive charges have been shown to be transmitted by natural DNA over a distance of several base pairs, the high ohmic resistance of unmodified oligonucleotides imposes a serious obstacle. Exchanging some or all of the Watson–Crick base pairs in DNA by metal complexes may solve this problem and evolve DNA-like materials with superior conductivity for future nano-electronic applications. The so-called metal–base pairs are formed from suitable transition metal ions and ligand-like nucleosides which are introduced into both of the two pairing strands by automated DNA synthesis. This review illustrates the basic concepts of metal–base pairing and highlights recent developments in the field.     

Thermochemical study of the reactions of acid–base interaction in an aqueous solution of α-aminobutyric acid

The heat effects of the interaction between a solution of α-aminobutyric acid and solutions of HNO₃ and KОН are measured by means of calorimetry in different ranges of рН at 298.15 K and values of ionic strength of 0.25, 0.5, and 0.75 (KNO₃). The heat effects of the stepwise dissociation of the amino acid are determined. Standard thermodynamic characteristics (Δ_r H ⁰, Δ_r G ⁰, and Δ_r S ⁰) of the reactions of acid–base interaction in aqueous solutions of α-aminobutyric acid are calculated. The connection between the thermodynamic characteristics of the dissociation of the amino acid and the structure of this compound is considered.     

Effect of temperature on acid–base equilibria in separation techniques. A review

Studies on the theoretical principles of acid–base equilibria are reviewed and the influence of temperature on secondary chemical equilibria within the context of separation techniques, in water and also in aqueous-organic solvent mixtures, is discussed. In order to define the relationships between the retention in liquid chromatography or the migration velocity in capillary electrophoresis and temperature, the main properties of acid–base equilibria have to be taken into account for both, the analytes and the conjugate pairs chosen to control the solution pH. The focus of this review is based on liquid–liquid extraction (LLE), liquid chromatography (LC) and capillary electrophoresis (CE), with emphasis on the use of temperature as a useful variable to modify selectivity on a predictable basis. Simpli?ed models were evaluated to achieve practical optimizations involving pH and temperature (in LLE and CE) as well as solvent composition in reversed-phase LC.     

New approach in the treatment of data from an acid–base potentiometric titration

Based on precise analysis of the acid-base equilibrium, a new approach in the treatment of experimental data from a potentiometric titration is proposed. A new general formula giving explicitly the relation V=f([H(+)]) is derived, valid for every acid-base titration, which includes mono- and polyfunctional protolytes and their mixtures. The present study is the first practical application of this formula for the simplest case, the analysis of one monofunctional protolyte. The collected mV data during the titration are converted into pH-values by means of an auto pH-calibration procedure, thus avoiding preliminary preparation of the measuring system. The mentioned pH-calibration method is applicable also in water-organic mixtures and allows the quantitative determination of sparingly soluble substances (particularly pharmaceuticals). The treatment of the data is performed by means of ready-to-use software products, which makes the proposed approach accessible for a wide range of applications.     

Determination of microscopic acid–base parameters from NMR–pH titrations

The theory and practice of proton microspeciation based on NMR–pH titrations are surveyed. Principles of bi-, tri-, tetra-, and n-protic microequilibrium systems are discussed. Evaluation methods are exemplified by case studies on bi- and tetraprotic biomolecules. Selection criteria and properties of reporter NMR nuclei are described. Literature data on complete microspeciations of small ligands and site-specific basicity characterizations of peptides and proteins are critically reviewed.     

Thermodynamic characteristics of acid–base equilibria of glycyl-glycyl-glycine in water–ethanol solutions at 298 K

The enthalpies of the acid dissociation of glycyl-glycyl-glycine zwitterions and triglycinium ions are determined calorimetrically in water–ethanol solvents containing 0.0, 0.10, 0.30, and 0.50 molar fractions of ethanol at ionic strengths of 0.1 (maintained by sodium perchlorate) and Т = 298.15 K. It is found that increasing the ethanol content in the solvent enhances the endothermic effect of triglycinium ion dissociation and reduces the endothermic effect of glycyl-glycyl-glycine dissociation. The results are discussed in terms of the solvation thermodynamics.     

Site-specific acid–base properties of pholcodine and related compounds

The acid–base properties of pholcodine, a cough-depressant agent, and related compounds including metabolites were studied by ¹H NMR-pH titrations, and are characterised in terms of macroscopic and microscopic protonation constants. New N-methylated derivatives were also synthesized in order to quantitate site- and nucleus-specific protonation shifts and to unravel microscopic acid–base equilibria. The piperidine nitrogen was found to be 38 and 400 times more basic than its morpholine counterpart in pholcodine and norpholcodine, respectively. The protonation data show that the molecule of pholcodine bears an average of positive charge of 1.07 at physiological pH, preventing it from entering the central nervous system, a plausible reason for its lack of analgesic or addictive properties. The protonation constants of pholcodine and its derivatives are interpreted by comparing with related molecules of pharmaceutical interest. The pH-dependent relative concentrations of the variously protonated forms of pholcodine and morphine are depicted in distribution diagrams.     

Investigation of the kinetics of the chain-radical process in the system iron carbonyl–Lewis base

An ESR spectroscopy investigation of the kinetics of accumulation and consumption of iron carbonyl radical anions, Fe₃(CO)₁₂⁻ and Fe₃(CO)₁₁⁻, arising in the reaction of Fe₃(CO)₁₂ with (Et₄N)SEt in THF at 19.5°C, was carried out using the stopped-flow technique. The solution of the inverse kinetic problem showed a satisfactory agreement between calculated and experimental data. This supports the principal idea that chain radical processes including preliminary complex formation followed by one-electron redox-initiation lie at the heart of the interaction of iron carbonyls with Lewis bases, and that the following transformations are due to electron and ligand changes in the coordination sphere of seventeen-electron coordinatively unsaturated species.     

A method for calculating the acid–base equilibria in aqueous and nonaqueous electrolyte solutions

Russian Journal of Physical Chemistry A - Concentrations of particles in acid–base equilibria in aqueous and nonaqueous solutions of electrolytes are calculated on the basis of logarithmic...     

Characterization of an Algerian diatomite by inverse gas chromatography: Specific and non-specific contribution and Lewis acid–base parameters

The fundamental understanding of the behavior of a solid is intimately related to the understanding of the interactions on the surface of the latter, a major challenge in particular if the material is natural and ecological. The infinite dilution-inverse gas chromatography was used to evaluate the surface thermodynamic properties of several phases (grafted and/or coated) diatomite. A series of non- or polar-solute probes were injected at temperatures of 45?°C and 90?°C. The dispersive surface free energies values of the supports decrease with increasing temperature and their active surface is amphoteric with predominantly acidic character.     

Solid–liquid equilibria in the acetic acid–propanoic acid and propanoic acid–trifluoroacetic acid systems

Solid–liquid equilibria in the binary systems, propanoic acid–acetic acid and propanoic acid–trifluoroacetic acid, were measured by a synthetic method. A solid compound (1:1) was found in the propanoic acid–trifluoroacetic acid system. The obtained activity coefficients were successfully fitted by the Wilson equation.