Molecularly imprinted polystyrene–titania hybrids with both ionic and π–π interactions: a case study with pyrenebutyric acid

We present hybrid films consisting of a composite prepared from polystyrene (PS) and titanium dioxide (titania; TiO₂) and molecularly imprinted with 1-pyrenebutyric acid (PBA). The interaction of PBA with the polymer is shown to occur via binding of the carboxylic group to TiO₂ and hydrophobic interaction of the pyrene moiety with the PS network. We investigated the effects of the PS fraction on morphology, imprinting properties, and guest binding. The template could be completely removed by incubating the films in an acetonitrile solution of pyrene, which is due to the stronger π–π interaction between PBA and pyrene than the interaction between PBA and its binding site. A guest binding study with pyrene, 1-aminopyrene, pyrenemethanol, and anthracene-9-carboxylic acid showed that the hybrid films possessed selectivity and much higher binding capacity for PBA. This study demonstrates the first case of clear PS-assisted imprinting, where the π–π interaction of the template with a linear (non-crosslinked) polymer creates selective binding sites and enhances the binding capacity. This is a driving force for guest binding in addition to the interaction of the template/analyte with TiO₂. All molecularly imprinted films displayed better binding, repeatability and reversibility compared to the respective non-imprinted films.

Drum-shaped mono-organooxotin assembly through solvothermal synthesis with 2,3,4,5-tetrafluorobenzoic acid: crystal structure,hydrogen bonding and π–π stacking interactions

A drum-shaped organooxotin (IV) complex with 2,3,4,5-tetrafluorobenzoic acid of the type {[SnR₂(2,3,4,5-F₄C₆HCO₂)]O}₆ (R?=?m-Cl-PhCH₂) has been solvothermally synthesized and structurally characterized by elemental, IR, ¹H, ¹³C, ¹¹⁹Sn NMR spectra and X-ray crystallography diffraction analysis. This complex exhibits a new structural environment appearing as a “drum” arrangement with hexa-coordinated tin atoms in a four-membered stannoxane ring, (–Sn–O–)₂, as a common structural feature. Each tin(IV) displays a distorted octahedral geometry. Weak, but significant, intramolecular C–H?···?F hydrogen bonds and π–π stacking interactions are shown. These contacts lead to aggregation and supramolecular self-assembly. Cleavage of Sn–C bond occurred in complexes under the influence of strong acid.     

3-D frameworks assembled by lanthanide dimers with 1,4-cyclohexanedicarboxylic acid and 1,10-phenanthroline via hydrogen bonds and π–π stacking interactions

Two complexes [Ln(e,a-cis-1,4-chdc)(e,a-cis-1,4-Hchdc)(phen)(H₂O)]₂?10H₂O (Ln = Eu, 1; Tb, 2, 1,4-H₂chdc = 1,4-cyclohexanedicarboxylic acid; phen = 1,10-phenanthroline) have been synthesized and structurally characterized by single-crystal X-ray diffraction. Both complexes are doubly e,a-cis-1,4-chdc-bridged dimers. The e,a-cis-1,4-Hchdc, phen, and water molecules bond to Ln³⁺, forming nine-coordinate complexes. 3-D supramolecular frameworks are constructed by hydrogen bonds and π–π stacking interactions. Luminescence spectra exhibit the ⁵D₀ → ⁷F _J (J = 0–4) and ⁵D₄ → ⁷F _J (J = 6–3) transitions of Eu³⁺ for 1 and Tb³⁺ ion for 2, respectively.     

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.     

Comparative study of ionic interactions of 1 : 1 and 1 : 2 electrolytes of nitrates salts solutions with water analysed with physicochemical data

Densities (ρ), viscosities (η) and surface tension (γ) as function of the molarity of 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 for LiNO₃, NaNO₃, KNO₃, Sr(NO₃)₂, Ba(NO₃)₂ and Pb(NO₃)₂ electrolytes are reported at 32°C. Data were regressed for limiting values for solute–solvent interactions and effects of shell numbers and electronic configurations. A confidence variance of 95.5% at Gaussian distribution was noted. Densities explained ionic forces and sizes, and viscosities defined frictional forces while the surface tension focused surface energies of hydrated ions. Slopes of densities, viscosities and surface tensions explained the concentration effects on ionic interactions. Limiting densities from Li⁺ to Ba²⁺ increased with increase in sizes. Pb²⁺ smaller in size than the Ba²⁺ had lower limiting densities. The ρ ⁰ are Ba^2+?>?Sr^2+?>?Pb^2+?>?K^+?>?Na^+?>?Li⁺ with 3.24, 2.98, 4.53, 2.109, 2.257 and 2.38?×?10^3?kg?m^?3 densities of nitrate salts, respectively, in the solid state.     

Detailed study of polystyrene solubility using pyrolysis–gas chromatography–mass spectrometry and combination with size-exclusion chromatography

Measuring polymer solubility accurately and precisely is challenging. This is especially true at unfavourable solvent compositions, when only very small amounts of polymer dissolve. In this paper, pyrolysis–gas chromatography–mass spectrometry (Py-GC-MS) is demonstrated to be much more informative and sensitive than conventional methods, such as ultraviolet spectroscopy. By using a programmed-temperature-vapourisation injector as the pyrolysis chamber, we demonstrate that Py-GC-MS can cover up to five orders of magnitude in dissolved polymer concentrations. For polystyrene, a detection limit of 1 ng mL^?1 is attained. Dissolution in poor solvents is demonstrated to be discriminating in terms of the analyte molecular weight. Py-GC-MS additionally can yield information on polymer composition (e.g. in case of copolymers). In combination with size-exclusion chromatography, Py-GC-MS allows us to estimate the molecular weight distributions of minute amounts of a dissolved polymer and variations therein as a function of time.

Investigation of π–π and ion–dipole interactions on 1-allyl-3-butylimidazolium ionic liquid-modified silica stationary phase in reversed-phase liquid chromatography

1-Allyl-3-butylimidazolium bromide ionic liquid [AyBIm]Br was prepared and used for the modification of mercaptopropyl-functionalized silica through surface radical chain-transfer addition. The obtained ionic liquid-modified silica (SiImBr) was characterized by elemental analysis, infrared spectroscopy, NMR spectroscopy, and thermogravimetric analysis. The selective retention behaviours of polycyclic aromatic hydrocarbons (PAHs) including some positional isomers were investigated using SiImBr as a stationary phase in reversed-phase liquid chromatography. The results showed that SiImBr presented multiple interactions including hydrophobic, π–π, and ion–dipole interactions during the separation of PAHs and dipolar compounds. However, it is proposed that π–π and ion–dipole interactions play important roles in the separation of PAHs and dipolar compounds. These results indicate that the ionic liquid-modified silica stationary phase is promising for future applications. A commercially available monomeric octadecylated silica (ODS) column and a custom-made poly(styrene)-grafted silica (Sil-St_n) column were used as references.     

Host–guest complexation of a nitroheterocyclic compound with cyclodextrins: a spectrofluorimetric and molecular modeling study

Nitroheterocyclic compounds (NC) were candidate drugs proposed for Chagas disease chemotherapy. In this study, we investigated the complexation of hydroxymethylnitrofurazone (NFOH), a potential antichagasic compound, with α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), Hydroxypropyl-β-cyclodextrin (HP-β-CD), Dimethyl-β-cyclodextrin (DM-β-CD) and γ-cyclodextrin (γ-CD) by fluorescence spectroscopy and molecular modeling studies. Hildebrand–Benesi equation was used to calculate the formation constants of NFOH with cyclodextrins based on the fluorescence differences in the CDs solution. The complexing capacity of NFOH with different CDs was compared through the results of association constant according to the following order: DM-β-CD > β-CD > α-CD > HP-β-CD > γ-CD. Molecular modeling studies give support for the experimental assignments, in favor of the formation of an inclusion complex between cyclodextrins with NFOH. This is an important study to investigate the effects of different kinds of cyclodextrins on the inclusion complex formation with NFOH and to better characterize a potential formulations to be used as therapeutic options for the oral treatment of Chagas disease.     

Geometric effects in olefinic cation-π interactions with alkali metals: a computational study

Although cation-π interactions commonly involve aromatic or heteroaromatic rings as the source of π-electrons, isolated and nonconjugated olefins are equally effective donors of π-electron density. Previous comparisons of these π-electron sources have indicated that the net energy of the binding interactions is not a simple additive function of the number of π-bonds involved. For instance, the enthalpy of binding (ΔH°) of Li(+), Na(+), or K(+) cations to two ethylene molecules or to one benzene molecule is approximately the same, despite the 4:6 ratio of π-electrons involved. This present density functional theory study indicates that geometric factors can partially account for the proportionally greater interaction energies of olefins, but whether they are symmetrically placed around the cation or grouped on one hemisphere has little effect on the binding energy. Instead, flexible ligands that permit olefinic π-electrons to be oriented more favorably toward the metal than those in rigid aromatic rings can be correlated with greater bonding. For Li(+) complexes, this appears to be an appreciable factor, although it is less significant with Na(+) and K(+) complexes. For all three cations, stronger polarization interactions with olefins compared to arenes contribute to the strength of cation-π interactions involving olefinic π-bonds.     

Effect of an underdamped vibration with both diagonal and off-diagonal exciton–phonon interactions on excitation energy transfer

A numerically exact approach, named as the hierarchical stochastic Schrödinger equation, is employed to investigate the resonant vibration-assisted excitation energy transfer in a dimer system, where an underdamped vibration with both diagonal and off-diagonal exciton–phonon interactions is incorporated. From a large parameter space over the site-energy difference, excitonic coupling, and reorganization energy, it is found that the promotion effect of the underdamped vibration is significant only when the excitonic coupling is smaller than the site-energy difference. Under the circumstance, there is an optimal strength ratio between diagonal and off-diagonal exciton–phonon interactions for the resonant vibration-assisted excitation energy transfer as the site-energy difference is greater than the reorganization energy, whereas in the opposite situation the most efficient energy transfer occurs as the exciton–phonon interaction is totally off-diagonal. © 2018 Wiley Periodicals, Inc.     

Hydrolytic and redox transformations of chromium(III) bis-oxalato complexes with glutaminic acid and glutamine: a kinetic,UV–Vis and EPR,study

The title complexes have been synthesized, chromatographically isolated and characterized by their ligands to metal ratio determinations and spectroscopic analyses. The kinetics of the first aquation stage, i.e., the amino acid chelate ring opening via the Cr–N bond cleavage, has been studied spectrophotometrically in acidic and alkaline media. Hydrogen peroxide oxidizes the complexes in alkaline media to CrO ₄ ^2? anion and a relatively stable Cr(V) complex. Consecutive biphasic kinetics through two first-order steps were observed for the base hydrolysis and the oxidation process, whereas the acid-catalyzed aquation obeys a simple first-order pattern. Based on the kinetic and spectroscopic data, mechanisms of the coordinated amino acid liberation and chromium(III) oxidation are discussed.     

Simultaneous interactions of pyridine with substituted benzene ring and H–F in X-ben⊥pyr···H–F complexes: a cooperative study

The cooperative effects between T-shape stacking and hydrogen bond interactions in X-ben⊥pyr···H–F complexes were investigated in this work. The results indicate that the electron-withdrawing/donating substituents decrease/increase the magnitude of the binding energies compared to the unsubstituted X-ben⊥pyr···H–F (X = H) complex. The cooperative effects have been studied while using the atoms in molecules (AIM) and natural bond orbital (NBO) methods, allowing us to evaluate the interplay between T-shape stacking and hydrogen bond interactions. There are good relationships among binding energies, Hammett constants, geometrical parameters, and the results of AIM and NBO analysis in X-ben⊥pyr···H–F complexes.     

Poly(urethane–urea) based on functionalized polystyrene with HMDI: Synthesis and characterization

The poly(urethane–urea) (PUU) based on α, Ω, hydroxy terminated polystyrene (OH-PSt-OH), 1,6-hexamethylene diisocyanate (HMDI) and three different diamines (1,2-ethylenediamine (EDA), 1,4-butanediamine (BDA), 1,6-hexamethylene diamine (HMDA)) is prepared by a melt polymerization method. The length of the soft segment is varying from 2000 to 8900 g/mol using HMDI as a chain extender. The inherent viscosity of the polymer is found to be in the range of 0.36–2.0 dL/g suggesting that the polymer is of high molecular weight. FT-IR results conclude that the urea groups form both monodendate and bidendate assemblies. Temperature dependent FT-IR and WAXS data confirm that the crystallinity of the copolymer is very high and depends on the spacer length. DSC data show the peaks for Tg of soft and Tm of hard segments. Depending on the concentration and the type of hard segments, melting temperature of the polymers was varied from 142 °C to 266 °C. The solubility of the polymer in chloroform is depending on the concentration of the hard segment. The TGA data reveal that the polymer shows single stage decomposition cantered around 413 °C.     

Poly(oxyethylene)–cation interactions in aqueous solution: a molecular dynamics study

We have performed molecular dynamics simulations of a poly(oxyethylene) (POE) chain with 15 ethylene oxide units in an aqueous solution in the presence of potassium cations for 1 ns. The effect of the potassium ions on the POE aqueous solution characteristics are examined for the energetics, the hydration, the chain conformation and dynamics, and the solvent structure in comparison to those in the absence of cations. The POE's helical conformation is considerably distorted by complex formations with K⁺, and a significant perturbation of the POE hydration by K⁺ is observed. The competition between the K⁺–water and the K⁺–POE associations is found to be heavily shifted toward the latter. Furthermore, the POE–water pair interaction energy drastically decreases upon addition of K⁺. The observations, along with the decreased chain flexibility, point to the salting-out of POE salt aqueous solutions.     

Formation of a porphyrin/fullerene light-harvesting system from self-assembly of porphyrin-end-functionalized polycyclohexane and [6,6]-phenyl-C61-butyric acid methyl ester: Effects of microphase separation and π–π interactions

Thin films composed of zinc tetraphenylporphyrin-end-functionalized polycyclohexane (ZnTPP-PCHE) and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM) blends were prepared to investigate their potential as light-harvesting systems within polymer solar cells (PSCs). Both the microphase separation characteristics and the extent of π–π interactions in these ZnTPP-PCHE/PCBM blends had significant effects on the optical properties of the films. The extent to which the absorption bands of the films overlapped the terrestrial solar spectrum was increased considerably when the blends formed a co-continuous structure, even though films of pure ZnTPP-PCHE or PCBM exhibited only weak absorption over that wavelength region. We conclude that these polymer blend films may be considered as viable candidates for light-harvesting systems within PSCs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Ruthenium hydrazone complexes with 1:1 and 1:2 metal–ligand stoichiometry: a comparison of biomolecular interactions and in vitro cytotoxicities

Transition Metal Chemistry - Two ruthenium(II) complexes [RuIICl(PPh3)2(L)] (1) and [RuII(L)2] (2) were synthesized by reacting [RuCl2(PPh3)3] and thiophene-2-carboxylic acid...