Study of the interaction between cyclodextrins and liposome membranes: effect on the permeability of liposomes

We wanted to compare and understand the effect of the most currently used cyclodextrins on a model membrane. We studied the influence of most currently used cyclodextrins on the release of a fluorescent marker encapsulated in the inner cavity of SUV liposomes. It was shown that the observed effect on calcein release can be directly related to the affinity of cyclodextrins for both lipid components of liposomes, cholesterol and phosphatidylcholine. From this relationship, we were able to determine, for each cyclodextrin, a theoretical concentration giving rise to 50% or 100% calcein release. This theoretical concentration was confirmed experimentally.     

Base-induced decomposition of dioxetanes bearing a 3-hydroxyphenyl moiety substituted with a proton-donating group at the 4-position: effect of intramolecular hydrogen bonding on decomposition rate and chemiluminescence efficiency

Bicyclic dioxetanes bearing a 3-hydroxyphenyl moiety substituted with an amidomethyl group (3a-c) or a hydroxymethyl group (4) were synthesized. On treatment with tetrabutylammonium fluoride in CH₃CN, they decomposed rapidly with accompanying emission of blue light. Their decomposition rates and chemiluminescence efficiencies were found to be affected by the intramolecular hydrogen bonding between the phenoxy anion and the adjacent proton-donating group.     

The crystal structures at 80 K and IR spectra of the complex of 4-methylpyridine with pentachlorophenol and its deuterated analogue

The crystal structures of the complex of 4-methylpyridine with pentachlorophenol (MP-PCP) and its deuterated analogue (MP-PCP-d) were determined at 80 K by X-ray diffraction. The MP-PCP complex crystallizes in the space group P with a = 7.267(7), b = 8.966(9), c = 13.110(14)Å, = 99.70(8), β = 118.16(9), γ = 103.38(8)° and Z = 2 and the MP-PCP-d complex in the monoclinic Cc space group with a = 3.826(2), b = 27.54(2), c = 13.209(12)Å, β = 101.38(9)° and Z = 4. The O… H … N bridge bond distance of 2.515(4) Å is significantly shorter than that determined at room temperature (2.552(4) Å) and the O---D … N bond length of 2.628(6) Å is only slightly shorter than at room temperature (2.638(3) Å). The temperature dependence of the IR spectra confirms the symmetrization of the OHN hydrogen bond.     

The crystal structures at 80 K and IR spectra of the complex of 4-methylpyridine with pentachlorophenol and its deuterated analogue

The crystal structures of the complex of 4-methylpyridine with pentachlorophenol (MP---PCP) and its deuterated analogue (MP---PCP-d) were determined at 80 K by X-ray diffraction. The MP---PCP complex crystallizes in the space group with a = 7.267(7), b = 8.966(9), c = 13.110(14) Å, = 99.70(8), β = 118.16(9), γ = 103.38(8)° and Z = 2 and the MP---PCP-d complex in the monoclinic Cc space group with a = 3.826(2), b = 27.54(2), c = 13.209(12) Å, β = 101.38(9)° and Z = 4. The O…H…N bridge bond distance of 2.515(4) Å is significantly shorter than that determined at room temperature (2.552(4) Å) and the O---D…N bond length of 2.628(6) Å is only slightly shorter than at room temperature (2.638(3) Å). The temperature dependence of the IR spectra confirms the symmetrization of the OHN hydrogen bond.     

Water wafers: structure and melting of a hydrate inclusion compound of a neutral Pt(IV) complex with 1-methylcytosinato ligands

The characterization by X-ray analysis of the trans,trans,trans-[bis(1-methylcytosinate,N4)bis(ammine)bis(hydroxo)platinum(IV)] octahydrate complex (I) reveals an unexpected crystal packing. The neutral complex molecule is hosted by layers, totally built up by water molecules which do not exhibit a direct coordination to metal ions. These corrugated layers are made by puckered eight- and planar four-membered rings of water molecules, held together by hydrogen bonds with an ordered proton arrangement.     

Self-assembly of DMF with chloromethane and their structures: a theoretical study

The stability of hydrogen-bonded complexes, DMF–H _n CCl_4−n (n = 1–3), has been investigated by several theoretical methods including the MP2 level of ab initio theory at various basis sets from 6-31+G* to 6-311++G**. Two stable configurations (respectively a and b) were obtained for each complex with no imaginary frequencies. The minimum energy structure of these complexes has also been analyzed by means of the atoms in molecule theory at MP2/6-311++G** level. It is found that C–H···O hydrogen bonding exists in these systems and that the intensity of HB interaction gradually increases with successive chlorination. Computed results indicate that these complexes automatically assemble into different stable configurations. For the complexes under consideration, their stabilities can be mainly ascribed to the intermolecular HB interaction. The present work is helpful to clearly understand the interaction mechanism of these complexes in theory.     

Synthesis and crystal structure of a new one-dimensional system with end-to-end single dicyanamide bridges between nickel(II) centres

The complex [Ni(tn)₂{N(CN)₂}]ClO₄ (tn=trimethylenediamine) has been synthesized and the structure has been determined. The complex forms a one-dimensional chain structure via the bidentate bridging ligand dicyanamide. A two-dimensional networks is formed via interchain hydrogen bond interactions.     

Direct spectrophotometric measurements of acid-catalyzed complexation of palladium(II) with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol at the heptane/water interface by a centrifugal liquid membrane method.

The centrifugal liquid membrane (CLM) method, designed for the rapid sample injection, was applied to the kinetic study of the complexation of palladium(II) with 2-(5-bromo-2-pyridylazo)-5-diethyaminophenol (5-Br-PADAP) in the heptane/water system. The formation rates of Pd(II)-5-Br-PADAP complex, which existed only at the heptane/water interface, could be directly measured by the CLM method combined with transmission spectrophotometry. We found that the formation rates of Pd(II)-5-Br-PADAP complex were accelerated by the protonation of 5-Br-PADAP at the diethylamino-group that did not coordinate to Pd(II) ion and that the rate constant for the reaction of protonated 5-Br-PADAP at the interface was close to that in the aqueous phase. The present study demonstrated that the CLM method was easily applicable for the measurements of relatively fast interfacial reactions.     

Formation of hydrogen-bonded chains between a strong base with guanidine-like character and phenols with various pKa values - an FT-IR study

The complexes formed by phenols with 1,3,4,6,7,8-hexahydro-1-methyl-2H-pyrimido[1,2-a]pyrimidine (mTBD), an N-base with guanidine-like character, were studied as a function of the pK_a of the phenols by FT-IR spectroscopy. The following phenols were used: 4-cyanophenol (4-CNPh), pentachlorophenol (PCP) and 2,6-dichloro-4-nitrophenol (DNPh). In the case of chloroform solutions of 1:1 mixtures of the phenols with MTBD the corresponding complexes are formed completely. With increasing acidity of the phenols the hydrogen bonds become increasingly asymmetrical. The OH … N ⁻O … H⁺N hydrogen bond in the 4-CNPh-MTBD complex shows large proton polarizability. In the other cases only the polar structure is realized. With increasing phenol MTBD ratio, the formation of chains with two phenol molecules is observed. With decreasing pK_a of the phenols the fluctuation is limited to the phenol-phenolate bond and finally, the phenol-protonated MTBD bond begins to dissociate. In acetonitrile solutions, N⁺H … O⁻ hydrogen bonds are observed in the case of the 1:1 mixture of 4-CNPh with MTBD. A weak continuum indicates the presence of homoconjugated phenol-phenolate bonds with large proton polarizability. In the case of 2:1 mixtures only protonated MTBD and homoconjugated phenol-phenolate bonds are observed, independent of the pK_a of the phenols. The results are discussed with regard to the proton pathway in bacteriorhodopsin.     

Formation of hydrogen-bonded chains between a strong base with guanidine-like character and phenols with various pKa values - an FT-IR study

The complexes formed by phenols with 1,3,4,6,7,8-hexahydro-l-methyl-2H-pyrimido[1,2-a]pyrimidine (mTBD), an N-base with guanidine-like character, were studied as a function of the pK_a of the phenols by FT-IR spectroscopy. The following phenols were used: 4-cyanophenol (4-CNPh), pentachlorophenol (PCP) and 2,6-dichloro-4-nitrophenol (DNPh). In the case of chloroform solutions of 1: 1 mixtures of the phenols with MTBD the corresponding complexes are formed completely. With increasing acidity of the phenols the hydrogen bonds become increasingly asymmetrical. The O … N ⁻O … H⁺N hydrogen bond in the 4-CNPh-MTBD complex shows large proton polarizability. In the other cases only the polar structure is realized. With increasing phenol MTBD ratio, the formation of chains with two phenol molecules is observed. With decreasing pK_a of the phenols the fluctuation is limited to the phenol-phenolate bond and finally, the phenol-protonated MTBD bond begins to dissociate. In acetonitrile solutions, N⁺H …O⁻ hydrogen bonds are observed in the case of the 1:1 mixture of 4-CNPh with MTBD. A weak continuum indicates the presence of homoconjugated phenol-phenolate bonds with large proton polarizability. In the case of 2:1 mixtures only protonated MTBD and homoconjugated phenol-phenolate bonds are observed, independent of the pK_a of the phenols. The results are discussed with regard to the proton pathway in bacteriorhodopsin.     

A novel measurement method of Donnan potential at an interface between a charged membrane and mixed salt solution

We developed a novel measurement method of the Donnan potential difference at a charged membrane/salt solution interface. The method can measure the potential under the condition that the membrane charge density is much lower than the KCl concentration of the salt bridge. This method is very useful for obtaining the effective charge density of each layer of a bipolar membrane. The present experiments in a system of a negatively charged poly(vinyl alcohol) membrane and a single salt solution of KCl, NaCl, LiCl, CaCl₂ and LaC₃ revealed that the membrane effective charged density has the same value for all the ions. The experiments in mixed KCl and CaCl₂ solution revealed that the potential in the system is governed mainly by the concentration of the counterion having the highest valence in the system.     

Recognition of a dicarboxylic acid with dipicolyl urea in solution and in solid phases: intramolecular hydrogen bond inhibiting both pyridine nitrogens from binding carboxyl groups

Recognition of a dicarboxylic acid in solution as well as in the solid phase by the pyridyl urea based pseudoditopic receptor 1 has been studied. The X-ray structures of both the receptor and its complex with 1,4-phenylenediacetic acid are also presented. Intramolecular hydrogen bonding inhibits both the pyridine ring nitrogens from forming hydrogen bonds with the carboxyl group and force the receptor to behave in a monotopic manner, using the syn urea amide moiety to bind carboxyl group of a dicarboxylic acid to form a 2:1 complex. Binding of receptor 1 with a monocarboxylic acid is also compared.     

Medium-ring aminocyclitols: a concise synthesis of nine-membered aminocarbasugar analogs and the solid-state supramolecular architectures of two key precursors

A stereocontrolled synthesis of nine-membered aminocarbasugar analogs (amino-cyclononanoses) from a rigid bicyclo[4.3.1]deca-2,4-dien-10-one platform, harboring a latent functionalized cyclononane ring, is described.     

Recognition of concanavalin A at the interface between a solvent polymeric membrane and an aqueous sample monitored by electric impedance spectroscopy

In a novel biosensing approach, a stearyl-[small beta]-d-glucopyranoside layer is formed by self-organization at the interface between a solvent polymeric membrane and the aqueous sample phase and its interaction with concanavalin A is detected by electric impedance spectroscopy.     

A dihydrogen bond between a bridging hydride and the NH proton of a coordinated dimethylamine: solid state, solution and theoretical characterization

The addition of one equivalent of dimethylamine (DMA) to the 44 valence-electron triangular cluster anion [Re₃(μ₃-H)(μ-H)₃(CO)₉]⁻ (1) affords the novel unsaturated derivative [Re₃(μ-H)₄(CO)₉(DMA)]⁻ (2, 46 valence electrons) which contains a dimethylamine molecule terminally coordinated to a cluster vertex. Theoretical calculations (DFT) reveal that in the more stable conformation the dimethylamine NH proton is directed towards the hydride bridging the opposite cluster edge in syn position, the close proximity of the ligands bound to the cluster surface allowing the formation of an unconventional N-H ? (μ-H)Re₂ hydrogen bond. The presence of this conformation in the solid state has been proven by an X-ray structural analysis of crystalline [PPh₄]2. Spectroscopic evidences (IR and NMR) indicate that the dihydrogen bond is maintained also in solution and, by the evaluation of the proton spin-lattice relaxation rates at variable temperature, a good estimate of the H ? H distance in solution has been determined.     

Fundamental studies on the intermediate layer of a bipolar membrane: Part III. Effect of starburst dendrimer PAMAM on water dissociation at the interface of a bipolar membrane

Starburst dendrimer polyamidoamine (PAMAM) with ellipsoidal or spheroidal shape is structure-regular and has much more amino groups than conventional polymers. This paper investigates the possibility of these amino groups on water dissociation in a bipolar membrane interface. To do this, a bipolar membrane is prepared by casting the solution of sulfonated poly(phenylene oxide) (SPPO) in dimethyl formamide (DMF) on a commercial anion exchange membrane that is immersed in PAMAM aqueous solution in advance. The existence of PAMAM adsorbed on the membrane is proved by X-ray photoelectron spectroscopy (XPS), and the adsorption amount is evaluated by weighting method. The junction thickness of the prepared bipolar membrane is determined by electrochemical impedance spectroscopy (EIS), and the performance is evaluated by current–voltage curves. The experiments show that both the generation and concentration of PAMAM would strongly affect the characteristics of the bipolar membranes. There exists a transitional concentration for various generations PAMAMs to catalyze effectively the water dissociation, and above or below the transitional concentration the performance of bipolar membranes is decreasing. The higher the generation, the lower the concentration. Moreover, at a fixed solution concentration, there is not the simple relation of monotone decreasing or increasing between the performance of bipolar membranes and the generations of PAMAMs. All these can be explained according to the characteristics of PAMAMs combined with available water dissociation theory.     

Macromolecular conformations at the water-air interface: Interactions between alpha and beta conformations of polypeptides

Bidimensional miscibility between alpha and beta conformations of polypeptides was investigated at the water-air interface in the 15°–30°C temperature range. The polypeptides were poly--methyl-L-glutamate (PGMG), poly--benzyl-L-glutamate (PGBG) and poly--benzyl-L-aspartate (PBBA). The polypeptide conformations, alpha or beta, were checked by IR spectroscopy using the MIR technique.The spreading isotherms for mixed monolayers alpha-PGMG/alpha-PGBG and beta-PGMG/beta-PBBA showed bidimensional miscibility both for alpha-alpha and beta-beta mixtures.For the alpha-alpha system, attractive interactions among the polypeptide alphahelices were found (G_mix<0) and the driving factor appeared to be the entropic one (packing). Compressibility moduli and surface potential measurements showed a fluidification effect of alpha-PGBG on mixed monolayers. In the case of beta-beta mixed monolayers, ideal behaviour was observed and no fluidification effect detected.Scanning electron micrographs made on collapsed monolayers showed hexagonal structures for alpha-alpha mixtures and no well-defined or characterized features for the beta-beta system.     

Hydrothermal synthesis and crystal structure of a new molybdenum oxide compound with manganese-o-phen subunit: [Mn(o−phen)(H2O)MoO4]·H2O (o-phen=o-phenanthroline)

A new one-dimensional molybdenum oxide compound with manganese-o-phen subunit: [Mn(o-phen)(H₂O)MoO₄]·H₂O (1) (o-phen=o-phenanthroline) was synthesized by thehydrothermal reaction of Na₂MoO₄·2H₂O, MnSO₄·H₂O, oxalic acid, o-phenanthroline (o-phen) and water. Its structure was determined by elemental analyses, ESR spectrum, TG analysis, IR spectrum and single-crystal X-ray diffraction. Compound 1 crystallizes in triclinic system, space group P-1 with a=7.0401(2) Å, b=10.4498(2) Å, c=10.5720(2) Å, α=73.26(7)°, β=83.34(8)°, γ=77.33(9)°, V=725.5089(0) Å³, Z=2, and R₁=0.0322 for 2337 observed reflections. Compound 1 exhibits one-dimensional chain structure. The chains are linked up via hydrogen bonding to 2D layers, which are further assembled through π-π stacking interactions to a 3D supermolecular structure.