Polar Carboxyl Research Articles

Residues from Transmembrane Helices 3 and 5 Participate in Leukotriene B4 Binding to BLT1

Leukotrienes are inflammatory mediators that bind to seven transmembrane, G-protein-coupled receptors (GPCRs). Here we examine residues from transmembrane helices 3 and 5 of the leukotriene B4 (LTB4) receptor BLT1 to elucidate how these residues are involved in ligand binding. We have selected these residues on the basis of (1) amino acid sequence analysis, (2) receptor binding and activation studies with a variety of leukotriene-like ligands and recombinant BLT1 receptors, (3) previously published recombinant BLT1 mutants, and (4) a computed model of the active structure of the BLT1 receptor. We propose that LTB4 binds with the polar carboxylate group of LTB4 near the extracellular surface of BLT1 and with the hydrophobic LTB4 tail pointing into the transmembrane regions of the receptor protein. The carboxylate group and the two hydroxyls of LTB4 interact with Arg178 and Glu185 in transmembrane helix 5. Residues from transmembrane helix 3, Val105 and Ile108, also line the pocket deeper inside the receptor. LTB4 is becoming increasingly important as an immunomodulator during a number of pathologies, including atherosclerosis. Detailed information about the LTB4 binding mechanism, and the receptor residues involved, will hopefully aid in the design of new immunomodulatory drugs.

Synthesis of New Amphiphilic Dendrons Bearing Aliphatic Hydrocarbon Surface Sectors and a Monocarboxylic or Dicarboxylic Acid Focal Point

[structure: see text]. A new series of amphiphilic G1-G3 dendrons containing purely aliphatic hydrocarbon dendritic surface sectors and one or two carboxylic acid group(s) at the focal point was synthesized in good yields. The key branching steps involve diallylation reactions of diethyl malonate or Meldrum's acid. These dendrons are highly soluble in hexane despite having highly polar carboxylic acid groups at the focal point.

Growth Inhibitors of Lettuce Seedlings From Bacillus cereus EJ-121

The ethyl acetate extract of the Bacillus sp. EJ-121 culture broth exhibited growth inhibitory activity on a lettuce (Lactuca sativa L.) seedlings assay. Bacillus sp. EJ-121 was identified as Bacillus cereus by the morphological characteristic and nucleotide sequence of the 16S rDNA. The bioassay-guided fractionation of the ethyl acetate extract led to the isolation of two compounds. Their structures were deduced by spectroscopic methods and determined as sodium vanillate (1) and 2-aminobenzoic acid (2). Both compounds 1 and 2 inhibited more than 90% of root length at 50 ppm (0.26 and 0.36 mM, respectively) while they had a limited effect on shoot growth at the same concentration level. Roots and shoots of lettuce seedlings showed severe deterioration at 100 ppm. In order to study the fundamental structure–activity relationship, several structurally related benzoic acid derivatives were also assayed. The existence of a polar carboxyl moiety seemed to be responsible for the stronger activity.

Comparison of the aqueous solubilization of practically insoluble niclosamide by polyamidoamine (PAMAM) dendrimers and cyclodextrins

This study is the first report of the solubilization of niclosamide by cyclodextrin complexation or the interaction between the drug and polyamidoamine (PAMAM) dendrimers. Half generation dendrimers with more polar carboxylate surface functional groups did not increase the solubility of niclosamide. From the phase solubility studies, when the fold enhancement in solubility of niclosamide combined with full generation amine terminated PAMAM dendrimers was compared with that obtained when the drug was combined with β- or hydroxypropyl-β-cyclodextrin, the results showed that, except for G-0 dendrimer at pH 7, the solubility of niclosamide was significantly higher in the presence of the dendrimers. In addition, higher equilibrium stability constants and complexation efficiency showed that the dendrimers formed stronger more stable complexes than the CDs. However, the strong interaction between the amine surface functional groups and the niclosamide molecule complexes caused a decrease in dissolution rate compared to the CDs because the interaction retarded the release of the drug from the dendrimers. In addition to increasing the solubility, PAMAM dendrimers therefore also offer the possible for the controlled release of the drug from solid dosage forms.

Characterization of a Novel 1,3-Bis(<I>p</I>-iminobenzoic acid)indane Langmuir-Blodgett Film for Organic Vapor Sensing

In the present paper we report about the Langmuir-Blodgett thin film characterization and organic vapor sensing properties of a novel 1,3-bis(p-iminobenzoic acid)indane (IBI) containing polar carboxylic acid groups. LB film properties of IBI material is characterized by UV-visible spectroscopy, atomic force microscopy, and quartz crystal microbalance. Our results show that high-quality and uniform LB films can be prepared with the transfer ratio of over 0.95. Organic vapor sensing properties are studied using quartz crystal microbalance measurement system. IBI film is found to be significantly more sensitive to benzene and the response of LB sample is fast, large, and reversible. The sensitivity of detection of toluene, ethyl alcohol, and isopropyl alcohol is much smaller than that of benzene. This newly synthesized IBI is a suitable molecule for the fabrication of an LB film and can be regarded as a promising sensing material in the development of a room temperature gas sensor for benzene vapor applications.

Mapping molecular orientation of pentacene on patterned Au surface

With a photoemission electron microscope, we investigated the orientation of pentacene films deposited on Au surface that has been patterned with self-assembled monolayers (SAMs). Organic thiols X(CH 2) nSH with X = COOH or CH 3 and an aromatic thiol; served as alignment layers to control the orientation of pentacene molecules thermally deposited on top of the SAM. According to the PEEM images and near-edge X-ray absorption fine structure spectra, a SAM exposing a non-polar methyl group, a terphenyl group or a polar carboxyl group all induced perpendicular alignment of the pentacene moiety, in contrast with parallel alignment on a bare gold surface.

Supramolecular dendrimers: Unusual mesophases of ionic liquid crystals derived from protonation of DAB dendrimers with facial amphiphilic carboxylic acids

Supramolecular liquid crystalline (LC) dendrimers were prepared by self-assembly of first to fifth generation amino terminated DAB dendrimers with facial amphiphilic carboxylic acids. These carboxylic acids are composed of three distinct incompatible segments, a rigid rod-like terphenyl core, two terminal alkyl chains and a polar lateral carboxylate group. The COOH groups were either directly connected to the terphenyl core or via oligo(oxyethylene) chains of different lengths. Depending upon the length of the polyether chain used, the dendrimer generation, the ratio of dendrimer to carboxylic acid or the temperature, a series of six different LC phases were observed. As well as a smectic phase (SmA), two different square columnar phases (Colsqu), a mesophase combining a layer structure with a hexagonal organisation of columns (channelled layer phase, ChLhex) and two additional mesophases (Colhex and M) with unknown structures were found. The square columnar phases are either composed of square cylinders (plane group p4mm) or a regular arrangement of square and triangular cylinders (plane group p4gm). In these dendrimer–carboxylic acid complexes protons are transferred from the COOH groups to the amino groups of the dendrimer, which gives rise to ionic complexes (dendroelectrolyte–amphiphile complexes). This concept allows the tailoring of the mesomorphic properties in a thermodynamically controlled self assembly process. The T-shaped ternary amphiphilic structure of the acid components and the incompatibility of the ionic species formed during the self assembly process are responsible for the formation of unconventional mesophase structures.

Hydrolytic degradation of blends of polyhydroxyalkanoates and functionalized polyhydroxyalkanoates

The hydrolytic degradation of poly(3-hydroxyalkanoates), PHA, blends with low and high molecular weight additives was examined. The PHA films were characterised by Differential Scanning Calorimetry, DSC, and Atomic Force Microscopy, AFM. The DSC and AFM results revealed that hydrolyzable PLA and hydrophilic PEG, selected as additives which might accelerate hydrolytic degradation, were immiscible with PHAs over the range of compositions studied. PHA blends were incubated in tetraborate buffer (pH=10) at 37 °C for periods ranging from 7 to 160 days. Film degradation was studied by weight loss and Size Exclusion Chromatography (SEC). The results show that the presence of a second component, whatever its chemical nature, is sufficient to perturb the crystallization behavior of highly crystalline poly(3-hydroxybutyrate- co-3-hydroxyvalerate), PHBHV, and increase hydrolytic degradation. In contrast, the degradation of poly(3-hydroxyoctanoate), PHO, was unaffected by blending with PLA or PEG. PHO degradation is a very slow process, requiring several months of incubation. However, the introduction of polar carboxylic groups in side chains led to an increase in the degradation rate. Carboxylic groups promote water penetration into the polymer.

Hydrolytic degradation of blends of polyhydroxyalkanoates and functionalized polyhydroxyalkanoates

The hydrolytic degradation of poly(3-hydroxyalkanoates), PHA, blends with low and high molecular weight additives was examined. The PHA films were characterised by Differential Scanning Calorimetry, DSC, and Atomic Force Microscopy, AFM. The DSC and AFM results revealed that hydrolyzable PLA and hydrophilic PEG, selected as additives which might accelerate hydrolytic degradation, were immiscible with PHAs over the range of compositions studied. PHA blends were incubated in tetraborate buffer (pH=10) at 37 °C for periods ranging from 7 to 160 days. Film degradation was studied by weight loss and Size Exclusion Chromatography (SEC). The results show that the presence of a second component, whatever its chemical nature, is sufficient to perturb the crystallization behavior of highly crystalline poly(3-hydroxybutyrate- co -3-hydroxyvalerate), PHBHV, and increase hydrolytic degradation. In contrast, the degradation of poly(3-hydroxyoctanoate), PHO, was unaffected by blending with PLA or PEG. PHO degradation is a very slow process, requiring several months of incubation. However, the introduction of polar carboxylic groups in side chains led to an increase in the degradation rate. Carboxylic groups promote water penetration into the polymer.

In-service aging and degradation of 345 kV EPDM transmission line insulators in a coastal environment

Aging and degradation of 345 kV ethylene propylene diene monomer (EPDM) transmission line insulators removed from service is presented. These suspension type insulators were installed in a New Hampshire coastal area in 1995 and were removed in 2000 after unexplained outages in that structure. The purpose of this paper is to better understand the aging and degradation mechanisms of EPDM insulators in service. The insulators showed severe chalking and discoloration and partial loss of hydrophobicity on the side facing the sun. The surface structural changes were studied in detail using advanced surface analysis techniques, such as attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). For the first time, the significant differences in surface properties between the chalked/discolored (white) and the other surfaces (dark) were studied quantitatively. The Fourier transform infrared (FTIR) absorption spectra showed a significant decomposition of the CH groups of the white surface, elucidating the effect of photo-oxidation on the EPDM polymer. The SEM micrographs showed the cracking of the surfaces. The XPS spectra showed the formation of various polar carboxyl groups and the presence of high surface energy compounds, such as silica, and silicates. This study provided valuable basic information on the changes in the surface properties of EPDM insulators during service in a coastal environment.

An amphiphilic approach to nanocrystal quantum dot-titania nanocomposites.

The addition of octylamine-modified poly(acrylic acid) to nanocrystal quantum dots (NQDs) results in robust, alcohol-soluble nanoparticles that can be readily incorporated into titania matrices without large changes in photoluminescence quantum yields. This approach relies on the amphiphilic nature of the polymer to create an NQD-polymer complex in which the alkyl chains interact with the hydrophobic part of the NQD, leaving the polar carboxylic acid groups on the periphery. This procedure is applicable to hydrophobically capped NQDs of a variety of shapes and compositions, making it a truly generalized route to nanocrystal-titania nanocomposites.

The formation of amino acid and dipeptide complexes with α-cyclodextrin and cucurbit[6]uril in aqueous solutions studied by titration calorimetry

The complex stabilities and the thermodynamic data for the complexation of α-cyclodextrin and cucurbit[6]uril with some amino acids (glycine, l-alanine, l-valine, l-phenylalanine, 6-amino hexanoic acid, 8-amino octanoic acid, 11-amino undecanoic acid) and dipeptides (glycyl–glycine, glycyl– l-valine, glycyl– l-leucine and glycyl– l-phenylalanine) have been determined in aqueous solution by calorimetric titrations. The complex formation with α-cyclodextrin is mainly favoured by entropic contributions due to the release of water molecules from the cavity of the ligand. The values of the reaction enthalpies are small with the exception of 11-amino undecanoic acid. In case of the ligand cucurbit[6]uril, ion–dipole interactions between the protonated amino groups of the amino acids and the carbonyl groups take place. By steric reasons these interactions are lowered for native amino acids because the polar carboxylic groups are always located outside the hydrophobic cavity of cucurbit[6]uril. The complexes of both ligands with dipeptides in water are characterised by hydrophobic interactions and in case of cucurbit[6]uril by additional ion–dipole interactions.

Use of pyrogenic silicas for petroleum oil polar fraction characterisation. Fourier transform infrared spectroscopy and microelectrophoresis studies

In the power transformer, the presence of polar or charged species in the insulating oil can cause failure and electric discharges. Solid substrates such as silica can be used to extract the polar species and to refine the oil in order to prevent future failure in the power transformer. However, the use of silica for petroleum oil separation and refining will depend on the silica characteristics such as surface charge, surface composition, specific surface area and particle size. Various pyrogenic silicas having various specific surface areas (49–200 m 2 g −1) and particle sizes (207–500 nm) were used to extract the polar fractions from the neat transformer insulating oils (a new, NO, and used, UO2, oils). The oil covered silica samples were investigated by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy in the range 4000–600 cm −1. The bare silica surfaces present two main hydroxyl components, a sharper peak at 3745 cm −1, I 3745, due to isolated silanols and a second broad, which spreads over 3745–3000 cm −1, I 3745–3000, due to H-bonded silanols. The relative intensities of the two components, I 3745/ I 3745–3000, varied for the bare and the oil covered silicas depending on the solid surface characteristics. The adsorption of the NO polar fraction onto silica leads to strong reduction in intensity of the sharper peak in favour of the broad one. However, the adsorption of the UO2 polar fraction onto silica leads in all cases to the decrease in the intensity of the both silica OH components. Further, the UO2 adsorption on the silica leads to the apparition of a broad peak at low frequency in the region 3250–3300 cm −1 which, is due to the associated phenolic groups of UO2 oil polar fraction. The analysis of the DRIFT spectra for various samples indicates that the oil polar fraction resembles to asphaltenes compounds. The microelectrophoresis method used to investigate the surface charge at the water/oil polar fraction covered silica interface, indicates negatively charged particles. Further, the negative charge increased with the pH, as resulting from the increase of the ionisation and/or the amount of the oil polar carboxylic and phenolic groups. The oil polar fraction, i.e. the asphaltene components, in contact with both the silica surface and water at high pH values rearrange, due to their amphiphilic character. Finally, the use of the silica substrates seems to be suited to extract and analyse polar species present in petroleum oil. A correlation is found between the nature of the oil, its functionalities, and the magnitude of its zeta potential value at the water/oil covered silica interface.

Dehydration, hydration behavior, and structural analysis of fenoprofen calcium

Fenoprofen calcium (FC) is a nonsteroidal, anti-inflammatory, analgesic, and antipyretic agent. The dehydration behavior of FC dihydrate and the rehydration of the dried FC were investigated using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and powder X-ray diffractometry (PXRD). The stoichiometry, the crystal packing arrangement, and water environments in FC dihydrate were determined using single-crystal X-ray diffraction (XRD) analysis. The Arrhenius plot (natural logarithm of the dehydration rate constant versus the reciprocal of absolute temperature) for FC dihydrate from isothermal TGA is not linear. The activation energy of dehydration was 309 kJ/mol in the 50–60°C range and 123 kJ/mol in the 60–80°C range. The difference in activation energy can be explained from the crystal structure data where one water molecule is sandwiched between repeating polar carboxylate groups and the other water is in a slightly less polar region of the crystal. Single-crystal XRD analysis also indicated each calcium ion is coordinated to six oxygens. Two coordinating oxygens are provided by two water molecules and the other four oxygens are provided by the carboxylate group of four separate fenoprofen anions. Each fenoprofen anion, which can provide two oxygens for coordination, is associated with two different calcium ions. Hot-stage PXRD suggested that only a loss of 1 mole of water per mole of FC dihydrate (forming a monohydrate) was required to convert the material to a partially crystalline state. The monohydrate is not completely disordered as evidenced by a strong diffraction peak as well as some weaker peaks in the PXRD pattern. The rehydration of the anhydrous form of FC follows a solution-mediated transformation, prior to crystallizing as the dihydrate. © 2001 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 90:845–859, 2001

Association Behavior of Polyurethanes in Polar Solvents Studied by SEC Coupled with Light Scattering

The solution behavior of non-carboxylated and carboxylated polyurethanes (PU) in THF, LiBr/DMF, and DMF was studied by size exclusion chromatography coupled with multiangle light scattering (SEC-MALS). This paper focuses on the association of PU macromolecules in DMF considering the influences of composition, solution concentration, and temperature. The degree of association increases with increasing amounts of polar urethane and carboxyl groups, with decreasing solution concentration, and by increasing the temperature of measurements or heat treatment—all of which demonstrate the role of impurities present in DMF on PU dilute solution behavior.

The suppression of water-diffusion in polycarbonate through Ar- and He-plasma as a new model for the origin of improved adhesion of Al

The diffusion process from water into and out of the bulk of an injection-molded bisphenol-A-polycarbonate sample has been characterized by weighing. In the equilibrium state, the amount of water inside the polycarbonate depends, therefore, on the environmental humidity. Transferring the experiments into UHV showed that the amount of water could be determined by the time-integrated H 2O-signal of a mass-spectrometer as depending on the storage time in vacuum before measurement. After Ar-plasma etching; samples showed a reduced H 2O-signal, which is the consequence of a hydrophobic barrier on the sample’s surface created by the plasma. The thesis of a barrier was supported by XPS-measurements, which showed a decrease of the polar carboxylic group of the polycarbonate.

CD exciton chirality method for determination of the absolute configuration of β‐hydroxy‐α‐amino acid derivatives

The absolute configuration of beta-hydroxy-alpha-amino acids was studied by CD exciton chirality method using 7-diethylaminocoumarin-3-carboxylate as a red-shifted chromophore. The CD spectra of bischromophoric derivatives of (S)-serine and (2S,3R)-threonine methyl esters (2 and 7) were compared with those of acyclic vic-aminoalcohols and diols (3--6 and 8--9). This study indicates that the polar carboxylate group of beta-hydroxy-alpha-amino acids makes them a unique subclass of vic-aminoalcohols. By combining the data of CD and NMR coupling constants, we are able to correlate their preferred conformer B and positive CD to the corresponding absolute configuration.

The effect of high-dose nitrogen plasma immersion ion implantation on siliconesurfaces

The effect of plasma immersion ion implantation (PIII) treatment onsilicone surfaces was investigated by x-ray photoelectron spectroscopy (XPS),Fourier transform infrared spectroscopy (FTIR-ATR), and scanning electronmicroscopy (SEM). Low-energy (at voltages of 4 and 8 kV) and high-fluence (8×1017 cm-2) implantation of nitrogen was performed using an inductivelycoupled plasma source (ICP) at low pressure (~0.03 Pa). The IR absorptionspectra showed a significant decomposition in the CH3, Si-CH3, and C-F groupsof the silicone surface after PIII treatment. The percentage of decompositionwas dependent on the implantation energy. The XPS C 1s spectra of the PIIImodified surfaces showed an increase in the polar carboxyl (O-C=O) groups anda decrease in the CF3 groups. PIII treatment shifted the XPS Si 2p peak ofsilicone to a higher binding energy (around 103.2 eV) and the N 1s peak tolower binding energy (around 398.5 eV). The modified Si 2p, N 1s, and O 1sspectra suggest the formation of SiOx phases, silicon oxynitrides, and siliconnitrides on the silicone surface after PIII treatment.

Synthesis, Surface Properties, and Hydrolysis of Chemodegradable Anionic Surfactants: Diastereomeric Sodium Carboxylates Derived from 1,3-Dioxane

Mixtures of cis- and trans-2-n-alkyl-5-carboxy-5-methyl-1,3-dioxanes, 3a–3e, were obtained in the reaction of aliphatic aldehydes 1a–1e (from n-octanal to n-dodecanal) with 2,2-bis(hydro-xymethyl)propionic acid (DMPA), 2, carried out in boiling n-hexane or in the isomerization reaction of an appropriate cis-3a–3e. Pure trans-3a–3e were isolated from the above mixtures by selective crystallization and then converted into surface-active sodium salts, trans-4a–4e, by neutralization with sodium hydroxide or sodium methoxide. Surface properties of these surfactants, i.e., critical micelle concentration (CMC), surface excess concentration (ΓCMC), surface area demand per molecule (ACMC), effectiveness of surface tension reduction (γCMC), and standard free energy of micellization (ΔG°mic) were determined and compared with the appropriate surface properties of isomeric cis-4a–4e. It was shown that the properties of surfactants under study are dependent both on the length of a hydrophobic n-alkyl substituent at the C2 carbon atom of the 1,3-dioxane ring and on the configuration of a polar sodium carboxylate group at C5. The acids 3 undergo hydrolysis/isomerization reactions in acidic D2/d6-DMSO media. The cis isomers are hydrolyzed faster than trans isomers probably due to the steric hindrance of the axial methyl group at C5 of the latter ones.

Structure of the inclusion complex of beta-cyclodextrin with 1,12-dodecanedioic acid using synchrotron radiation data; a detailed dimeric beta-cyclodextrin structure

A detailed crystal structure study of the dimeric inclusion complex of beta-cyclodextrin (betaCD) with 1,12-dodecanedioic acid is presented [IUPAC name: beta-cyclodextrin-1,12-dodecanedioic acid (2/1)]. The structure was solved with synchrotron high-resolution data (0.65 A) at 100 K [crystal data: P1, Z= 1, a = 18.153 (7), b = 15.456 (8), c = 15.251 (4) A, alpha = 102.81 (2), beta = 113.13 (2), gamma = 99.90 (3)degrees, V = 3,673 (3) A3, R = 0.0474 for 25,134 unique reflections with I > 2sigma(I)]. Moreover, the room-temperature structure is used for comparison [crystal data: P1, Z = 1, a = 18.220 (3), b = 15.488 (3), c = 15.409 (3) A, alpha = 102.903 (6), beta = 113.122 (5), gamma = 99.708 (5)degrees, V = 3735.2 (12) A3, R = 0.0828 for 8,235 unique reflections with I > 2sigma(I)]. Combining the high-resolution data and the low-temperature made possible the location of the disordered guest molecule, 1,12-dodecanedioic acid, inside the wide cavity of the macrocycle formed by two betaCD monomers. Moreover, almost all the H atoms of the betaCD macrocycle and many of the water molecules have been located in the low-temperature structure. Thus, for the first time, it has been possible to show in detail, up to now only given by neutron diffraction data, that two betaCD monomers self-assemble through O3...O3 intermolecular hydrogen bonds to form the betaCD dimer, as well as describe the hydrogen-bonding scheme between the dimer's hydroxyl groups among themselves and with water molecules in the lattice. The long guest threads through two host molecules forming a [3]pseudorotaxane. Its polar carboxyl groups, fully hydrated at the primary faces of the betaCD dimers, influence their packing so that those faces are exposed to the solvent. This is in contrast to the packing of the beta-cyclodextrin complexes of the corresponding aliphatic monoacids, where the dimeric complexes form channels in order to isolate the terminal methyl group from the water environment of the lattice.