Showing papers on "Carboxylic acid published in 2005"

Facile Conversion of Alcohols into Esters and Dihydrogen Catalyzed by New Ruthenium Complexes

Abstract: An efficient, environmentally benign method for the preparation of esters from alcohols under mild, neutral conditions without the need for carboxylic acid derivatives and condensing agents was developed. Catalyst design, based on new Ru(II) hydrido carbonyl complexes incorporating electron-rich PNP and PNN ligands has resulted in the novel complex (I) which is an outstanding catalyst for the dehydrogenation of primary alcohols to esters and H2 under neutral conditions.

pH-responsive carrier system based on carboxylic acid modified mesoporous silica and polyelectrolyte for drug delivery

Abstract: An efficient pH-responsive carrier system has been constructed by oppositely charged ionic interaction between carboxylic acid modified SBA-15 silica rods and polyelectrolyte. Active molecules such as vancomycin can be stored and released from the pore voids of SBA-15 by changing pH values at will. The amount of vancomycin stored in the pores of sample based on carboxylic acid modified SBA-15 rods and poly(dimethyldiallylammonium chloride) is up to 36.4 wt % at pH 6.8. When the pH is at mild acidity, vancomycin is steadily released from the pores of SBA-15. Both nitrogen adsorption−desorption isothems and X-ray diffraction patterns show that this system possesses stable mesostructure, which will be considered an interesting alternative to a polymeric delivery system.

On the Mechanism of the Palladium(II)-Catalyzed Decarboxylative Olefination of Arene Carboxylic Acids. Crystallographic Characterization of Non-Phosphine Palladium(II) Intermediates and Observation of Their Stepwise Transformation in Heck-like Processes

Abstract: Mechanistic studies of a palladium-mediated decarboxylative olefination of arene carboxylic acids are presented, providing spectroscopic and, in two instances, crystallographic evidence for intermediates in a proposed stepwise process. Sequentially, the proposed pathway involves carboxyl exchange between palladium(II) bis(trifluoroacetate) and an arene carboxylic acid substrate, rate-determining decarboxylation to form an arylpalladium(II) trifluoroacetate intermediate (containing two trans-disposed S-bound dimethyl sulfoxide ligands in a crystallographically characterized form), then olefin insertion and β-hydride elimination. Because of the unique mode of generation of the arylpalladium(II) trifluoroacetate intermediate, a species believed to be substantially electron-deficient relative to phosphine-containing arylpalladium(II) complexes previously studied, it has been possible to gain new insights into those steps that are common to the Heck reaction, namely, olefin insertion and β-hydride elimination....

Tape and layer structures in cocrystals of some di- and tricarboxylic acids with 4,4′-bipyridines and isonicotinamide. From binary to ternary cocrystals

Abstract: Linear, zigzag tapes and flat, corrugated sheet structures are described in binary cocrystals 1–9 of some di- and tricarboxylic acids with 4,4′-bipyridine bases and isonicotinamide. Carboxylic acid⋯pyridine O–H⋯N, its proton transfer form N+–H⋯O−, carboxamide dimer N–H⋯O, and extended motifs are present in these crystal structures. Our results show modular expansion of carboxylic acid dimer in neutral cocrystals with pyridine type bases. Even as the structures of these aggregates can be understood from the molecular constituents in a straightforward manner, the nature of acid⋯pyridine synthon, i.e. neutral or ionic, is difficult to anticipate from their ΔpKa values. We modify the ΔpKa (pKa conjugate acid of pyridine base – pKa carboxylic acid) rule in COOH–pyridine cocrystals: ΔpKa 3.75 results in proton migration to the ionic interaction N+–H⋯O−. Proton transfer results in the assembly of a supramolecular 3-connected node of cyclohexane tricarboxylate and these anions form chair cyclohexane or parquet grid sheets in 10 and 11. The length of bipyridinium cation plays a role in the overall structure. A novel approach to three-component adducts is crystallization of 1,3cis,5cis-cyclohexane tricarboxylic acid with 4,4′-bipyridine and 4,4′-bipyridine-N-oxide bases of different strengths, which results in a ternary cocrystal 12 sustained via O–H⋯N and O–H⋯O− hydrogen bonds.

Effect of tip functionalization on transport through vertically oriented carbon nanotube membranes.

Abstract: Ionic flux through a composite membrane structure, containing vertically aligned carbon nanotubes crossing a polystyrene matrix film, was studied as a function of chemical end groups at the entrance to carbon nanotubes' (CNTs) cores. Plasma oxidation during the membrane fabrication process introduced carboxylic acid groups on the CNTs' tips that were modified using carbodiimide mediated coupling between the carboxylic acid and an accessible amine groups of the functional molecule. Functionalization molecules included straight chain alkanes, anionically charged dye molecules, and an aliphatic amine elongated by polypeptide spacers. Functionalization was confirmed by FTIR spectroscopy, and areal functional density was estimated by transmission electron microscopy studies of thiol terminated sites decorated by nanocrystalline gold. The transport through the membrane of two different sized but equally charged molecules (ruthenium bipyridine [Ru-(bipy)32+] and methyl viologen [MV2+]) was quantified in a U-tube...

Improved method for the preparation of carboxylic acid and amine terminated self-assembled monolayers of alkanethiolates.

Abstract: We present an improved method to prepare carboxylic acid (COOH) and amine (NH2) terminated self-assembled monolayers (SAMs) of alkanethiolates. In this method, a small amount of CF3COOH (for COOH−SAM) or N(CH2CH3)3 (for NH2−SAM) is added into the ethanolic solution of alkanethiols during SAM formation. The freshly formed COOH− and NH2−SAMs are then rinsed with an ethanolic solution of NH4OH or CH3COOH, respectively. Both SAMs prepared with the improved method show better quality in terms of surface chemical composition, roughness, and wettability as measured by X-ray photoelectron spectroscopy, atomic force microscopy, and contact angle, respectively. The formation of better SAMs can be attributed to the disruption of interplane hydrogen bonds.

Gold(I)-catalyzed intermolecular addition of phenols and carboxylic acids to olefins.

Abstract: Ph3PAuOTf can catalyze efficient intermolecular addition of phenols and carboxylic acids to olefins under relatively mild conditions.

Synergism between ammonia, lactic acid and carboxylic acids as kairomones in the host-seeking behaviour of the malaria mosquito Anopheles gambiae sensu stricto (Diptera: Culicidae).

Abstract: Host odours play a major role in the orientation and host location of blood-feeding mosquitoes. Anopheles gambiae Giles sensu stricto, which is the most important malaria vector in Africa, is a highly anthropophilic mosquito species, and the host-seeking behaviour of the females of this mosquito is guided by volatiles of human origin. Ammonia, lactic acid and several carboxylic acids are known to be present in the human odour blend. We investigated the effect of these compounds on naive female mosquitoes using a dual-port olfactometer. Ammonia was an attractant on its own, whereas lactic acid was not attractive. Carboxylic acids, offered as a mixture of 12 compounds, were repellent at the concentration tested. The addition of ammonia to the carboxylic acid mixture overruled the repellent effect of the latter. Combining ammonia with either lactic acid or the carboxylic acids did not enhance the attractiveness of ammonia alone. However, a synergistic effect was found when ammonia, lactic acid and the carboxylic acids were applied as a blend. Our findings indicate that An. gambiae s.s. relies on the combination of ammonia, lactic acid and carboxylic acids in its orientation to human hosts. The role of lactic acid in this tripartite synergism differs from that reported for the yellow fever mosquito Aedes aegypti.

Oxidative cyclizations in a nonpolar solvent using molecular oxygen and studies on the stereochemistry of oxypalladation.

Abstract: Oxidative cyclizations of a variety of heteroatom nucleophiles onto unactivated olefins are catalyzed by palladium(II) and pyridine in the presence of molecular oxygen as the sole stoichiometric oxidant in a nonpolar solvent (toluene). Reactivity studies of a number of N-ligated palladium complexes show that chelating ligands slow the reaction. Nearly identical conditions are applicable to five different types of nucleophiles: phenols, primary alcohols, carboxylic acids, a vinylogous acid, and amides. Electron-rich phenols are excellent substrates, and multiple olefin substitution patterns are tolerated. Primary alcohols undergo oxidative cyclization without significant oxidation to the aldehyde, a fact that illustrates the range of reactivity available from various Pd(II) salts under differing conditions. Alcohols can form both fused and spirocyclic ring systems, depending on the position of the olefin relative to the tethered alcohol; the same is true of the acid derivatives. The racemic conditions served as a platform for the development of an enantioselective reaction. Experiments with stereospecifically deuterated primary alcohol substrates rule out a “Wacker-type” mechanism involving anti oxypalladation and suggest that the reaction proceeds by syn oxypalladation for both mono- and bidentate ligands. In contrast, cyclizations of deuterium-labeled carboxylic acid substrates undergo anti oxypalladation.

A Metal−Organic Framework Functionalized with Free Carboxylic Acid Sites and Its Selective Binding of a Cl(H2O)4- Cluster

Abstract: A metal−organic framework with one-dimensional channels decorated with −COOH binding sites was synthesized under aqueous acidic conditions, which inhibited the participation of these groups to metal coordination or self-association by hydrogen bonding. This material selectively includes Cl(H2O)4- clusters in its channels, as revealed by single-crystal X-ray diffraction analysis, which represents the first structural characterization of such a water−chloride cluster.

Purification and characterization of a biodegradable plastic-degrading enzyme from Aspergillus oryzae.

Abstract: We used biodegradable plastics as fermentation substrates for the filamentous fungus Aspergillus oryzae. This fungus could grow under culture conditions that contained emulsified poly-(butylene succinate) (PBS) and emulsified poly-(butylene succinate-co-adipate) (PBSA) as the sole carbon source, and could digest PBS and PBSA, as indicated by clearing of the culture supernatant. We purified the PBS-degrading enzyme from the culture supernatant, and its molecular mass was determined as 21.6 kDa. The enzyme was identified as cutinase based on internal amino acid sequences. Specific activities against PBS, PBSA and poly-(lactic acid) (PLA) were determined as 0.42 U/mg, 11 U/mg and 0.067 U/mg, respectively. To obtain a better understanding of how the enzyme recognizes and hydrolyzes PBS/PBSA, we investigated the environment of the catalytic pocket, which is divided into carboxylic acid and alcohol recognition sites. The affinities for different substrates depended on the carbon chain length of the carboxylic acid in the substrate. Competitive inhibition modes were exhibited by carboxylic acids and alcohols that consisted of C4-C6 and C3-C8 chain lengths, respectively. Determination of the affinities for different chemicals indicated that the most preferred substrate for the enzyme would consist of butyric acid and n-hexanol.

The 2-Aminopyridinium-carboxylate Supramolecular Heterosynthon: A Robust Motif for Generation of Multiple-Component Crystals

Abstract: An analysis of the Cambridge Structural Database reveals that 77% of compounds that contain both 2-aminopyridine and carboxylic acid moieties generate 2-aminopyridine-carboxylic acid supramolecular heterosynthons rather than carboxylic acid or 2-aminopyridine supramolecular homosynthons. In the absence of other competing functionalities, the occurrence of heterosynthons increases to 97%. This observation is supported by the determination of single-crystal structures of 10 new compounds that contain both a 2-aminopyridine and a carboxylic acid moiety: 2-aminopyridinium 4-aminobenzoate, 1; 2-aminopyridinium isophthalate, 2; bis(2-aminopyridinium) terephthalate, 3; 2-amino-5-methylpyridinium benzoate, 4; bis(2-amino-5-methylpyridinium) 5-tertbutylisophthalate, 5; 2-amino-5-methylpyridinium terephthalate, 6; bis(2-amino-5-methylpyridinium) 2,6-naphthalenedicarboxylate, 7; bis(2-amino-5-methylpyridinium) adipate adipic acid, 8; bis(2-amino-5-methylpyridinium) 2,5-thiophenedicarboxylate 2,5-thiophenedicarboxyl...

Synthesis, characterization of dihydrolipoic acid capped gold nanoparticles, and functionalization by the electroluminescent luminol.

Abstract: The use of gold nanoparticles as biological probes requires the improvement of colloidal stability. Dihydrolipoic acid (DHLA), a dithiol obtained by the reduction of thioctic acid, appears therefore very attractive for the stabilization and the further functionalization of gold nanoparticles because DHLA is characterized by a carboxylic acid group and two thiol functions. The ionizable carboxylic acid groups ensure, for pH 8, the water solubility of DHLA-capped gold (Au@DHLA) nanoparticles, prepared by the Brust protocol, and the stability of the resulting colloid by electrostatic repulsions. Moreover almost all DHLA, adsorbed onto gold, adopts a conformation allowing their immobilization by both sulfur ends. It is proved by sulfur K-edge X-ray absorption near edge structure spectroscopy, which appears as an appropriate tool for determining the chemical form of sulfur atoms present in the organic monolayer. Such a grafting renders the DHLA monolayers more resistant to displacement by dithiothreitol than mercaptoundecanoic acid monolayers. The presence of DHLA on gold particles allows their functionalization by the electroluminescent luminol through amine coupling reactions assisted by 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride and N-hydroxysuccinimide. As a luminol-functionalized particle is nine times as bright as a single luminol molecule, the use of the particles as a biological probe with a lower threshold of detection is envisaged.

cis-Dihydroxylation and Epoxidation of Alkenes by [Mn2O(RCO2)2(tmtacn)2]: Tailoring the Selectivity of a Highly H2O2-Efficient Catalyst

Abstract: The carboxylic acid promoted cis-dihydroxylation and epoxidation of alkenes catalyzed by [MnIV2O3(tmtacn)2]2+ 1 employing H2O2 as oxidant is described. The use of carboxylic acids at cocatalytic levels not only is effective in suppressing the inherent catalase activity of 1, but also enables the tuning of the catalyst's selectivity. Spectroscopic studies and X-ray analysis confirm that the control arises from the in situ formation of carboxylate-bridged dinuclear complexes, for example, 2 {[MnIII2O(CCl3CO2)2(tmtacn)2]2+} and 3 {[MnII2(OH)(CCl3CO2)2(tmtacn)2]+}, during catalysis. For the first time, the possibility to tune, through the carboxylate ligands employed, both the selectivity and activity of dinuclear Mn-based catalysts is demonstrated. To our knowledge, the system 1/2,6-dichlorobenzoic acid (up to 2000 turnover numbers for cis-cyclooctanediol) is the most active Os-free cis-dihydroxylation catalyst reported to date.

Ketonization of carboxylic acids over CeO2-based composite oxides

Abstract: The ketonization of propanoic acid to form 3-pentanone over CeO 2 -based composite oxides at temperatures of 300–425 °C was investigated. A CeO 2 -based solid solution, CeO 2 –Mn 2 O 3 , was effective for the ketonization. The citrate process was the most appropriate method for preparing a well-dispersed solid solution. In the ketonization of propanoic acid with another linear carboxylic acid, an asymmetric ketone together with two symmetric ketones was formed, and the ketone composition was approximated by a binomial distribution. The reactivity of the carboxylic acid was slightly decreased as its chain length was increased. In contrast to linear aliphatic acids, branched acids were less reactive. Methyl group substituents at the α- and β-positions of carboxylic acids decreased their reactivities in both homo- and cross-ketonization. The lack of an α-hydrogen or the increase in steric hindrance was surmised to be the cause of the decrease in reactivity.

Dimers of formic acid, acetic acid, formamide and pyrrole-2-carboxylic acid: an ab initio study.

Abstract: The intermolecular hydrogen bonds in dimers of formic acid, acetic acid, and formamide were investigated. Additionally, three configurations of the pyrrole-2-carboxylic acid (PCA) dimer were studied to analyze how the pyrrole π-electron system influences the carboxylic groups connected by double O−H···O hydrogen bonds. The ab initio calculations for the systems investigated were performed at MP2/6-311++G(d,p), MP2/aug-cc-pVDZ, and MP2/aug-cc-pVTZ//MP2/aug-cc-pVDZ levels of theory. The “atoms in molecules” theory of Bader was used and the analysis of the critical points was performed to study the nature of hydrogen bonds. The decomposition of the total interaction energy applied here reveals that the delocalization energy term is a particularly important attractive contribution in these systems, more important in the case of systems forming homonuclear O−H···O double hydrogen bonds than in the case of those connected through heteronuclear N−H···O bonds. Because the systems analyzed may be formally classifi...

Lewis acid-Lewis acid heterobimetallic cooperative catalysis: mechanistic studies and application in enantioselective aza-Michael reaction.

Abstract: The full details of a catalytic asymmetric aza-Michael reaction of methoxylamine promoted by rare earth−alkali metal heterobimetallic complexes are described, demonstrating the effectiveness of Lewis acid−Lewis acid cooperative catalysis. First, enones were used as substrates, and the 1,4-adducts were obtained in good yield (57−98%) and high ee (81−96%). Catalyst loading was successfully reduced to 0.3−3 mol % with enones. To broaden the substrate scope of the reaction to carboxylic acid derivatives, α,β-unsaturated N-acylpyrroles were used as monodentate, carboxylic acid derivatives. With β-alkyl-substituted N-acylpyrroles, the reaction proceeded smoothly and the products were obtained in high yield and good ee. Transformation of the 1,4-adducts from enones and α,β-unsaturated N-acylpyrroles afforded corresponding chiral aziridines and β-amino acids. Detailed mechanistic studies, including kinetics, NMR analysis, nonlinear effects, and rare earth metal effects, are also described. The Lewis acid−Lewis ac...

Three-Component Carboxylic Acid−Bipyridine Lattice Inclusion Host. Supramolecular Synthesis of Ternary Cocrystals

Abstract: Cocrystallization of 1,3,5-cyclohexanetricarboxylic acid with 4,4‘-bipyridine bases of different CH2 chain lengths (n = 0, 2, 4) has afforded the ternary host framework [H3CTA·bipy-eta(gauche)·(bip...