Optimising oxygen-sensitivity of optical sensor using pyrene carboxylic acid by myristic acid co-chemisorption onto anodic oxidized aluminium plate

Optical oxygen-sensitivity using pyrene carboxylic acid with long alkyl chain (1-pyrenedecanoic acid and 1-pyrenedodecanoic acid) and myristic acid co-chemisorption layer was controlled by varying the molar ratio of myristic acid to pyrene carboxylic acid. The ratio I₀/I₁₀₀, where I₀ and I₁₀₀ represent the detected fluorescence intensities from a substrate exposed to 100% argon and 100% oxygen, respectively, is used as an indicator of the sensitivity of the sensing film. At a composition ratio of 1 pyrene carboxylic acid to 10 myristic acids, the I₀/I₁₀₀ attained its maximum value and then the ratio decreased with increase in the molar ratio of myristic acid to pyrene carboxylic acid. The Stern-Volmer constant (K_SV) also attained its maximum value at a composition ratio of one pyrene carboxylic acid to ten myristic acids and then the ratio decreased with increase in the molar ratio of myristic acid to pyrene carboxylic acid. The oxygen-sensitivity of optical sensor using pyrene carboxylic acid is optimized by myristic acid co-chemisorption.     

Novel photopolymerizations initiated by alkyl radicals generated from photocatalyzed decarboxylation of carboxylic acids over oxide semiconductor nanoparticles: Extended photo-Kolbe reactions

Polymerizations of vinyl acetate are photocatalyzed by TiO₂ nanoparticles in presence of carboxylic acids including propionic acid, n-butyric acid and pivalic acid. Nuclear magnetic resonance (NMR) analysis using ¹³C-labeled n-butyric acid as the probing molecule demonstrates that the polymerization of vinyl acetate is initiated by alkyl radicals generated from photocatalytic decarboxylation of the carboxylic acid. A universal mechanism is established with extending the photo-Kolbe reaction from acetic acid to the carboxylic acids with longer chains. Kinetics studies find that n-butyric acid has higher initiation rate than acetic acid, indicating more efficient decarboxylation for butyric acid than acetic acid in their aqueous solutions. It is proved that carboxylates participate in the decarboxylation. Attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectra are obtained with aqueous solutions of the carboxylic acids in contact with a layer of the TiO₂ nanoparticles, and the observations are discussed with respect to the interaction between the TiO₂ and carboxylic acids.     

Directly Bridging Indoles to 3,3′‐Bisindolylmethanes by Using Carboxylic Acids and Hydrosilanes under Mild Conditions

A straightforward Lewis acid‐promoted protocol for 3,3′‐bisindolylmethanes (BIMs) synthesis by reductive alkylation of indoles at the C3 position with carboxylic acids in the presence of hydrosilane was developed for the first time. Instead of aldehydes, more readily available, stable, and easy‐to‐handle carboxylic acids have been employed as alternative alkylating agents. As an efficient organocatalyst, B(C₆F₅)₃ enables the reductive alkylation of various substituted indole derivatives with carboxylic acids with up to 98 % yield at room temperature and under neat conditions. This metal‐free strategy offers an alternative approach for the direct functionalization of indoles to BIMs with carboxylic acids and such protocol allows selective reduction of carboxylic acid to aldehyde in combination with C−C bond formation.     

Identification and determination of carboxylic acids in food samples using 2-(2-(anthracen-10-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)ethyl 4-methylbenzenesulfonate (APIETS) as labeling reagent by HPLC with FLD and APCI/MS

A new labeling reagent for carboxylic acids, 2-(2-(anthracen-10-yl)-1H-phenanthro[9,10-d]imidazol-1-yl)ethyl 4-methylbenzenesulfonate (APIETS) has been designed and synthesized. It was used to label eight fatty acids (lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, oleic acid, linoleic acid and linolenic acid) and four hydroxy pentacyclic triterpene acids (oleanolic acid, ursolic acid, betulinic acid and maslinic acid), successfully. APIETS could easily and quickly label carboxylic acids in the presence of K₂CO₃ catalyst at 85 °C for 35 min in N,N-dimethylformamide solvent. The carboxylic acids derivatives were separated on a C₈ reversed-phase column with gradient elution and fluorescence detection at λ_ex/λ_em = 315/435 nm. Identification of these derivatives was carried out by online mass spectrometry with atmospheric pressure chemical ionization in positive ion mode. The detection limits obtained were 13.37-30.26 fmol (signal-to-noise ratio of 3). The proposed method has been applied to the quantification of carboxylic acids in sultana raisin (Thompson seedless), hawthorn flake (Crataegus pinnatifida Bge.), Lycium barbarum seed oil and Microula sikkimensis seed oil with recoveries over 95.3%. It has been demonstrated that APIETS is a prominent labeling reagent for determining carboxylic acids with high performance liquid chromatography.     

Structural Study of Mesoporous Titania Prepared from Titanium Alkoxide and Carboxylic Acids

Mesoporous titania with regulated pore size as well as high specific surface area was prepared from titanium alkoxide and various carboxylic acids with different alkyl-chain length [CH₃(CH₂) _n COOH : n = 0–20]. Although the pore size and pore volume of titania changed slightly at n < 10, they increased with increasing the alkyl-chain length of carboxylic acid at n 10. Each carboxylic acid forms a complex with titanium alkoxide in an organic-inorganic precursor, while the precursor prepared by using carboxylic acid with n 10 consists of a lamella-type mesophase. The interplanar distance of the lamella structure increases with increasing the alkyl-chain length of carboxylic acid. During calcination, the lamella structure collapses together with the combustion of organic moieties and titania particles crystallized to anatase aggregate to provide pores. Although carboxylic acid does not act as a true template, the formation of the lamella-type mesophase in the precursor plays an important role in controlling the pore size of titania.     

Reduction and N-Alkylation of α-Methylene-indolines with Sodium Cyanoborohydride in Carboxylic Acids

The reaction of α-methylene-indolines with NaCNBH₃ in carboxylic acids at room temperature can yield either 2β,3β-dihydro-indolines or their N-alkyl derivatives as main products with high selectivity, depending mainly on the carboxylic acid and on the reaction time when using a large excess of NaCNBH₃.     

FT-IR study on interactions between solutes and entrainers in supercritical carbon dioxide

Fourier transform infrared (FT-IR) spectroscopy has been used to measure the molarities of hydrogen bonding species between carboxylic acids (acetic acid and palmitic acid) and water in supercritical CO₂. The equilibrium constants of dimerization for the carboxylic acids were determined in supercritical CO₂ with octane. Further, the interactions of propanol-d (1- and 2-propanol-d) or xylenol (2,5-, 2,6- and 3,4-xylenol) isomers with acetone in supercritical CO₂ were studied. Experiments were carried out at 308.2–313.2 K and 7.0–20.0 MPa. The molarities of hydrogen bonding species between the carboxylic acids and water in supercritical CO₂ increase with the increasing molarity of water. The carboxylic acids interact more easily with ethanol than water in supercritical CO₂. For supercritical CO₂+carboxylic acid+octane systems, the equilibrium constants between the carboxylic acid monomer and dimer increase with the increasing molarity of octane. The equilibrium constants of the carboxylic acids seem to approach to those in liquid paraffin according to addition of octane in supercritical CO₂. The amount of the interaction species between 1-propanol-d and acetone is larger than that between 2-propanol-d and acetone. The amount of acetone interacting with OH group for 3,4-xylenol is the largest among those for xylenol isomers. These differences among the isomers may be caused by the screen effects of methyl groups around hydroxyl group for the isomers.     

Decarboxylation with Carbon Monoxide: The Direct Conversion of Carboxylic Acids into Potent Acid Triflate Electrophiles

We report a new strategy for the conversion of carboxylic acids into potent acid triflate electrophiles. The reaction involves oxidative carbonylation of carboxylic acids with I₂ in the presence of AgOTf, and is postulated to proceed via acyl hypoiodites that react with CO to form acid triflates. Coupling this chemistry with subsequent trapping with arenes offers a mild, room temperature approach to generate ketones directly from broadly available carboxylic acids without the use of corrosive and reactive Lewis or Bronsted acid additives, and instead from compounds that are readily available, stable, and functional group compatible.     

Reversible gelation of poly(dimethylsiloxane) with ionic and hydrogen‐bonding substituents

Poly(dimethylsiloxane) copolymers containing a small fraction of carboxylic acid or Zn‐carboxylate groups were prepared and compared regarding reversible gelation by hydrogen‐bonding and ion‐pair interaction. The polymers were synthesized by condensation of a t‐butylcarboxylate functionalized dichlorosilane with an α,ω‐dihydroxy‐poly(dimethylsiloxane), followed by thermal cleavage of the ester bond. Neutralization of the resulting carboxylic acid substituents was achieved by addition of Zn (acac)₂. Reversible crosslinking was investigated by step stress and oscillating shear experiments. The carboxylic acid containing poly(dimethylsiloxane) became rubberlike upon increasing the temperature and liquified again when it was brought back to room temperature. This observation has been explained tentatively by segregation of the carboxylic acid groups into polar domains at high temperatures [i.e., a behavior like it is observed for systems with a lower critical solution temperature (LCST)]. At ambient temperature, the carboxylic acid groups undergo hydrogen bonding to the Si–O–Si backbone. Clustering of the carboxylic acid groups occurs only as these hydrogen bonds break upon raising temperature. Moisture was found to have a strong influence on the reversal of the crosslinking. Addition of zinc acetylacetonate resulted in the formation of an elastic network already at ambient conditions consistent with the concept of ionomers which undergo reversible gelation by formation of ion‐pair multiplets and clusters in the hydrophobic polymer matrix in particularly at low temperatures. At high temperature, both the carboxylic acid and the carboxylate sample exhibited a rather similar viscoelastic behavior consistent with a common structure where transient crosslinks are formed by clusters of the carboxylic acid and the carboxylate groups. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 485–495, 1999     

Peripherally and Axially Carboxylic Acid Substituted Subphthalocyanines for Dye‐Sensitized Solar Cells

A series of subphthalocyanines (SubPcs) bearing a carboxylic acid group either at the peripheral or axial position have been designed and synthesized to investigate the influence of the COOH group positions on the dye‐sensitized solar cell (DSSC) performance. The DSSC devices based on SubPcs with axially substituted carboxylic acid groups showed low photovoltaic performance, whereas peripherally substituted one exhibited higher power conversion efficiency owing to improved injection from LUMO of SubPcs to the TiO₂ conduction band.     

Photosensitization of Nanocrystalline TiO2 Electrode Modified with C60 Carboxylic Acid Derivatives

C₆₀ carboxylic acid derivatives can be readily adsorbed on the surface of nanocrystalline TiO₂ film. The C₆₀ carboxylic acids adsorbed on nanocrystalline TiO₂ films act as charge‐transfer sensitizer. The electron transport from TiO₂ to the C₆₀ derivatives results in the generation of the cathodic photocurrent. The short‐circuit photocurrent of a C₆₀ tetracarboxylic acid is 0.45 μA/cm² under 464 nm light illumination. The photoelectric behaviour of ITO electrodes modified by the same C₆₀ carboxylic acids is different from that of the modified TiO₂ electrodes, and shows anodic photocurrent.     

Selective Esterification of Aliphatic Carboxylic Acids in the Presence of Aromatic Carboxylic Acids Over Monoammonium Salt of 12‐Tungstophosphoric Acid

Monoammonium salt of 12‐tungstophosphoric acid [(NH₄)H₂PW₁₂O₄₀] was found to be a practical and useful heterogeneous catalyst for an efficient and selective esterification of aliphatic carboxylic acids with alcohols in the presence of aromatic carboxylic acids. The heteropoly acid–based heterogeneous catalyst has the advantages of a simple workup procedure, water insolubility, and good activity.     

Solution phase electron transfer versus bridge mediated electron transfer across carboxylic acid terminated thiols

Self-assembled monolayers (SAMs) of thiols with carboxylic acid terminal groups were formed on gold substrates. The electron transfer characteristics of redox species on the above SAM-modified electrodes were studied in acid and neutral media with the help of voltammetry under two different conditions: (1) solution phase electron transfer and (2) bridge mediated electron transfer. Two redox systems, viz., [Fe(CN)₆]^4-/3− and Ru[(NH₃)₆]^2+/3+ were chosen for the solution phase study. Investigations of bridge mediated electron transfer were carried out by functionalising the SAM with redox moieties and then studying their redox behaviour. For this study, ferrocene carboxylic acid and 1,4-diamino anthraquinone were used and they were linked to carboxylic acid terminated thiols by covalent linkage. The voltammetric results with mercaptoundecanoic acid SAM demonstrate the difference in behaviour between solution phase and bridge mediated electron transfer processes.     

Study on surface acid-base property of carboxylic acid-terminated self-assembled monolayers by cyclic voltammetry and electrochemical impedance spectroscopy

Cyclic voltammetry and electrochemical impedance spec-troscopy were used to study the surface acid-base property of carboxylic acid-terminated self-assembled monolayers(SAMs).A carboxylic acid-terminated thiol,such as thioctic acid(1,2-dithiolane-3-pentanoic acid),was self-assembled on gold electrodes.Electron transfer between the bulk solution and the SAM modified electrode was studied at different pH using Fe(CN)63-as a probe.The surface pka of thioctic acid was determined by cyclic voltammetry and electrochemical impedance spectroscopy to be 5.6 ±0.1 and 5.8±0.1,respectively.The method is compared with other methods of monolayer pKa measurement.     

Effect of Concentration of Structurally-Different Carboxylic Acids on Growth and Aggregation of Calcium Oxalate in Gel Systems

The effect of concentration of structurally-different carboxylic acids such as ethylene diamine tetraacetic acid （H4edta）, citric acid （H3cit）, tartaric acid （H2tart）, and acetic acid （HOAc） on growth and aggregation of calcium oxalate （CaOxa） in gel systems was comparatively investigated. H2tart and H3cit could change the morphology of cal- cium oxalate monohydrate （COM） and induce the formation of calcium oxalate dihydrate （COD）. H4edta could induce the formation of COD at a lower concentration of 0.33 mmol/L and have the strongest ability to inhibit aggregation of COM. HOAc inhibited COM aggregation only at a higher concentration than 500 mmol/L. With increasing the number of carboxylic groups in an acid or increasing the concentration of carboxylic acid, the capacity of this acid to induce COD formation and to inhibit growth and aggregation of COM crystals increased. That is, this capacity followed the order： H4edta〉H3cit〉H2tart〉 〉HOAc. The result in this work suggested that the presence of H3cit and H2tart in urine played a role in the natural defense against stone formation.     

Synthesis of 1,2,3‐Triazole Substituted Isoxazoles via Copper (I) Catalyzed Cycloaddition

The synthesis of a series of 3,5‐disubstituted isoxazole‐4‐carboxylic esters containing N‐substituted 1,2,3‐triazoles ( V ) starting from various benzaldehydes ( I ) is reported. Benzaldehydes undergo oximation with hydroxylamine hydrosulfate. Later, chlorination followed by condensation with methylacetoacetate and the hydrolysis of the resulting ester afforded respective carboxylic acid ( II ), which on chlorination with PCl₅ gave the corresponding acid chlorides ( III ). The coraboxylic acid chlorides ( III ) on propargylation gave propargylic esters ( IV ) and these on click reaction gave the title compounds ( V ).     

Selective oxidation of cellulose catalyzed by NHPI/Co(OAc)2 using air as oxidant

With NHPI/Co(OAc)₂ as catalyst and air as oxidant, carboxylic group functionalized cellulose was prepared by oxidation of cellulose in acetic acid. Fourier transform infrared spectroscopy was utilized to detect the generation of carboxylic group and the acid amount was determined by acid–base titration method. The present results revealed that C6 primary hydroxyl groups on glucose units were partly converted to carboxylic groups during the catalytic oxidation process. The degree of polymerization of oxidized cellulose, which was determined by viscosity measurement, decreased slightly as compared with its parent. The structure of cellulose was characterized by X-ray diffraction and scanning electron microscopy, and it was almost unchanged.     

Reversed Phase High Performance Liquid Chromatography Using Carboxylic Acids in the Mobile Phase

Abstract

This report describes the use of different carboxylic acids as mobile phase modifiers. The effect on retention of acid chain length, pH, and eluent composition for a series of phenylalkanols, phenol, and the amines aniline, N-methylaniline, and benzylamine is discussed. The retention of both neutral and positively charged compounds is influenced by the dissociation equilibrium of the carboxylic acid in the mobile phase. By using l-pentanol to coat excess exposed silanol groups on the reversed phase column used, the inflection in the retention of both neutral and charged solutes as pH is changed occurs at the pK_a of the acid in the mobile phase. In addition, by using an acid and amine with the same or similar pK_a values, selective ion-pairing of this pair over others with dissimilar pK_a values can be promoted. Application of this technique to the selective retention of amino acids and peptides was unsuccessful.     

A simple and efficient method of preparing α-bromo carboxylic acids

A new and convenient method for α-bromination of aliphatic carboxylic acids is reported. Heating carboxylic acids for 16 hours at 85 °C in trifluoroacetic acid with 1.5 equivalents of N-bromosuccinimide and a catalytic amount of concentrated H₂SO₄ leads to good yields of the respective α-bromocarboxylic acids.     

Methodology for translocating the carboxy group in gibberellins: the partial synthesis of 7(6→15βH)abeo-GA4

The carboxylic acid group has been excised from phytohormone gibberellin A₄ and relocated on the D-ring, thereby generating a new clas of gibberellin derivatives related structurally to helminthosporic acid.