Trifluoroacetic Acid Solution Research Articles

Novel chromium trinuclear trifluoroacetate complexes Cr3(μ3-O)(CF3COO)6(CH3COOH)2(CF3COO) and Cr3(μ3-O)(CF3COO)6(CH3COOH)2(THF): Synthesis and crystal structure

Novel anhydrous trinuclear μ3-oxo complexes of Cr(III), Cr3(μ3-O)(CF3COO)6(CH3COOH)2(CF3COO) (I) and of Cr(III,III,II), Cr3(μ3-O)(CF3COO)6(CH3COOH)2(THF) (II) (where THF is (CH2)4O) are synthesized by anodic dissolution of metallic chromium in solutions of trifluoroacetic acid in acetonitrile and in tetrahydrofuran and their structures are studied by X-ray diffraction analysis. Complex I forms orthorhombic crystals with space group Pna21, a = 9.778(1) A, b = 16.042(2) A, c = 22.851(4) A, Z = 4, R1 = 0.0332; complex II crystallizes in monoclinic system: space group P21/c, a = 9.866(1) A, b = 17.895(2) A, c = 21.167(4) A, β = 100.75(2)°, Z = 4, R = 0.0422. The average Cr-(μ3-O) distances in compounds I and II are almost equal (1.943(3) and 1.927(3) A). An average length of the Cr-O bond in octahedral surrounding of metal atoms is different in complexes I and II (1.985(4) and 2.003(3) A, respectively), which is specified by different oxidation states of the metal atom. The Cr⋯Cr distances lie in an interval of 3.366(1)−3.337(1) A.

Ionizing properties of complexes with strong symmetrical hydrogen bonds in acid solutions in aprotic solvents

The acidity functions H0 of solutions of trifluoroacetic acid (TFA) in DMF and methanesulfonic acid (MSA) in 2-pyrrolidone over an acid (HA) concentration range of 0–100% and of H2SO4 solutions in 2-pyrrolidone (66.7–100 mol % HA) at 25°C were determined using the indicator method. Data were obtained on the relative ionizing powers of the quasi-ion pairs S⋯H⋯A (S is a solvent molecule) formed by DMF with acids (HCl, MSA, and TFA) and by MSA with DMF and 2-pyrrolidone. The effects of the acid anion (with MSA and H2SO4 solutions in 2-pyrrolidone acting as examples) and the counterion SH+ (with MSA solutions in DMF and 2-pyrrolidone acting as examples) on the ionizing power of (A⋯;H⋯A)− ions with strong symmetrical H-bonds were studied. It was found that, under comparable conditions, the replacement of a 2-pyrrolidone molecule by a DMF molecule in the SH+ cation insignificantly decreased the acidity of solution, whereas the (A⋯;H⋯A)− ions in H2SO4 solutions exhibited a much higher ionizing power than that of structurally similar anions in MSA solutions.

Development of a validated HPLC method for the determination of iodotyrosines and iodothyronines in pharmaceuticals and biological samples using solid phase extraction

Identification, separation and quantitation of iodoaminoacids, is essential for the biological research and the clinical diagnosis of thyroid gland disease. Under this aspect a reversed-phase high-performance liquid chromatographic method was developed for the determination of thyroid gland hormones and some of their primary metabolites, 3,3′,5,5′-tetra-iodo- l-thyronine ( l-thyroxine), 3,3′,5-tri-iodo- l-thyronine, 3,5-di-iodo- l-thyronine, l-thyronine, 3,5-di-iodo- l-tyrosine, 3-iodo- l-tyrosine and l-tyrosine. Analysis was performed on an Inertsil C 18 column with photodiode-array detection, using a 25 min gradient scale program of a binary mobile phase consisted of 0.1% aqueous solution of trifluoroacetic acid at pH 3 as solvent A and acetonitrile as solvent B, at a flow rate of 1 mL/min. Quantitation was performed using were obtained using theophylline as internal standard. The method was applied to commercial pharmaceuticals and biological samples (serum, urine and tissue). Drug-free urine and serum samples were spiked with known concentrations of the analytes standards and pretreated by solid phase extraction to remove matrix interferences. C 18 cartridges were used, yielding recoveries ranging from 87.1% to 107.6% for serum samples and from 92.1% to 98.7% for urine samples. With regard to total-T 4 concentrations in serum samples, results are cross-validated with RIA and found to agree well.

Separation, pre‐concentration, and HPLC analysis of methylxanthines in urine samples

An SPE method, using RP18 phases, for the simultaneous extraction of caffeine, theobromine, theophylline, paraxanthine, 1-methylxanthine, 3-methylxanthine, 7-methylxanthine, 1-methyluric acid, 1,3-dimethyluric acid, 1,7-dimethyluric acid, and 1,3,7-trimethyluric acid from urine has been developed. Besides a gradient HPLC system for the analysis of the compounds of interest on a LiChrosorb RP-18 (7 microm) column with mobile phase containing 0.05% aq. solution of trifluoroacetic acid and acetonitrile has been elaborated. The procedure has been successfully applied to the analysis of methylxanthines and methyluric acids in urine of patients with chronic asthma treated with theophylline and in urine of healthy subjects.

Study of acid-base interactions of mono- and diazaporphyrin indium complexes with acetic and trifluoroacetic acids by 1H NMR and electronic spectroscopy

Indium complex of 13,17-dibutyl-2,3,7,8,12,18-hexamethyl-5-azaporphyrin (Cl)InMAP was synthesized, and acid-base interactions of the meso-nitrogen atoms in (Cl)InMAP and its diaza analog (Cl)InDAP with acetic and trifluoroacetic acids were studied by 1H NMR and electronic spectroscopy. Depending on the medium, the complexes and proton-donor species HA give rise to acid solvates >N⋅⋅⋅(HA)n which are converted to final acid-base interaction products, H-complexes >N⋅⋅⋅H+⋅⋅⋅A−(HA)m or ionic associates >NH+⋅⋅⋅A−(HA)l , as the acidity of the medium rises. In acetic acid solution, the acid solvates derived from more basic (Cl)InMAP exist in equilibrium with the H-associates (pK a1 = 4.45±0.03). From (Cl)InDAP, the corresponding H-associates are formed only in the presence of H2SO4 (pK a1 = 2.10±0.03). In more polar media (solutions of trifluoroacetic acid in methylene chloride), ionic associates are formed, which involve one [(Cl)InMAP, pK 1 = 2.46±0.02] or two meso-nitrogen atoms [(Cl)InDAP, pK 1 = 2.11±0.03, pK 2 = 0.41±0.04).

Efficacy and compatibility with mass spectrometry of methods for elution of proteins from sodium dodecyl sulfate–polyacrylamide gels and polyvinyldifluoride membranes

The resolving power of sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS–PAGE) combined with isoelectric focusing in two-dimensional gel electrophoresis has made it one of the most important techniques for resolving complex mixtures, and it is of great importance for proteome mapping projects. As a result of this, methods for postelectrophoretic protein characterization are of great interest as exemplified by in situ protease digestion combined with mass spectrometry (MS), which is the method of choice for identification of proteins. In this study we have developed and compared methods for recovering intact proteins from polyacrylamide gels and electroblotting membranes to define efficient methods compatible with MS. These methods complement in situ digestion protocols and allow determination of the molecular mass of whole proteins separated by SDS–PAGE. Passive elution of proteins from SDS–PAGE gels was efficient only in the presence of SDS, whereas electroelution was achieved using buffers without SDS. Surface-enhanced laser desorption/ionization MS (SELDI-MS) analysis of proteins eluted in the presence of SDS was possible using ion exchange ProteinChip arrays for concentration of sample and removal of SDS. Comparison of different electroblotting methods verified that the different membranes and buffers were equally efficient for transfer of proteins in the range 20–100 kDa. Elution from polyvinyldifluoride membranes was most efficient using either concentrated solutions of trifluoroacetic acid (TFA) or combinations of 8 M urea and 1% Triton X-100, 1% Tween 20, or 40% isopropanol. The same result was obtained using nitrocellulose membranes, except that these were incompatible with organic solvent and TFA. Elution by TFA was compatible with matrix-assisted laser desorption/ionization MS (MALDI-MS) but was complicated by a high degree of trifluoroacetylation of the proteins. Alternatively, elution by 8 M urea + 1% Triton X-100, 1% Tween 20, or 40% isopropanol was compatible with both SELDI-MS and MALDI-MS. Eluted proteins were identified in MS experiments by intact mass determination, by peptide mapping, and by MS/MS analysis.

Solvent specified conformation in poly(alpha-L-glutamic acid) thin films.

The ability to control conformational properties of polypeptides in their films is of considerable interest for many possible applications of these materials. By rational choice of the solvent system for film fabrication, control over the conformation of the main chain, the intermolecular hydrogen bonding in the side chain is easily achieved in poly(alpha-L-glutamic acid) (PLGA) thin films. The spectral data from circular dichromism (CD), FT-IR, and solid state (13)C NMR spectroscopies suggest that the beta-sheet conformation is dominant in PLGA films cast from trifluoroacetic acid (TFA) solution, whereas the right-handed alpha-helix is dominant in those cast from pyridine or DMF solution. In comparison with films cast from TFA solutions, the films fabricated from pyridine or DMF solutions exhibit strong intermolecular hydrogen bondings between -COOH groups and have a more ordered arrangement of side chains. Moreover, the extent of alpha-helix conformation of the PLGA backbone in films cast from pyridine or DMF solution is several times higher than that observed in the PLGA powder precipitated from aqueous solution at pH 4. All spectroscopic studies indicate clearly that the solvents (used for casting these films) play a crucial role in directing the organization of PLGA in these thin films.

Synthesis of dicarboxylic acylcarnitines

Syntheses of malonyl, methylmalonyl, succinyl, glutaryl, methylglutaryl, dodecanedioyl and hexadecanedioyl carnitines are described. The dicarboxylic acylcarnitines were prepared from eight equivalents of cyclic anhydride or isopropylidene ester of the dicarboxylic acid and carnitine chloride in trifluoroacetic acid solution. Long chain dicarboxylic acylcarnitines were additionally purified by partitioning between water and n-butanol. Stable isotope labeled analogs, containing 3, 6 or 9 deuterium atoms, were also prepared. They are for use as standards in the electrospray ionization tandem mass spectrometric analysis of dicarboxylic acylcarnitines in samples from patients with inherited disorders of fatty acid oxidation.

A study of the conformational stability of poly(β-benzyl l-aspartate), poly(γ-benzyl l-glutamate) and poly(β-benzyl l-aspartate)/poly(γ-benzyl l-glutamate) blend in the solid state by variable-temperature 13C CP/MAS NMR

Abstract 13 C CP/MAS NMR experiments on polypeptides, poly(β-benzyl l -aspartate) (PBLA), poly(γ-benzyl l -glutamate) (PBLG) and PBLA/PBLG blend have been carried out, in order to elucidate the conformational stability of the polypeptides in the solid state over a wide range of temperatures and its blending effect. The PBLA/PBLG blend with a mixture ratio of 1/1 is prepared by adding trifluoroacetic acid (TFA) solution to alkaline water (TFA-alkaline treatment). From these experimental results, it is found that the conformation of PBLA in the PBLA/PBLG blend sample is changed from left-handed helix (α L -helix and/or ω L -helix) form to the α R -helix form, and then the origin of the formation of the α R -helix form in PBLA comes from the existence of PBLG. Further, from the variable-temperature 13 C CP/MAS NMR experiments results, it is shown that the conformational behavior of PBLA in the PBLA/PBLG blend is similar to that of the TFA-alkaline treated PBLA, and also the conformational behavior of PBLG in the PBLA/PBLG blend is similar to that of the TFA-alkaline treated PBLG.

BAL resin for the preparation of secondary amines

Although amino acids anchored through the amino function to BAL resins can not easily be released from the resin by treatment with neat trifluoroacetic acid, we have shown that secondary amines can be obtained from BAL resins using trifluoroacetic acid solutions.

A study of conformational stability of polypeptide blends by solid state two-dimensional 13C– 1H heteronuclear correlation NMR spectroscopy

The intermolecular hydrogen-bond interactions in polyglycine (PG)/poly( l-valine) (PLV) blend with a ratio of 1/1 have been studied through high-speed frequency-switched Lee–Goldburg (FSLG) 13C– 1H heteronuclear correlation (HETCOR) NMR experiments, where the PG/PLV blend sample is prepared by adding trifluoroacetic acid (TFA) solution of their polypeptide mixture containing a 2.0 wt/wt% amount of sulfuric acid (H 2SO 4) to alkaline water. The spectral assignment of the polypeptide blend is made by using multiple proton cross-peaks, which appeared in the HETCOR spectra. Intermolecular correlation peaks between PG(β-sheet) and PLV(β-sheet) appear in the HETCOR spectra with long contact time. From these experimental results, it has been clarified that intermolecular hydrogen-bond interactions ( C O⋯ H– N) between the PG(β-sheet) and PLV(β-sheet) are formed and thus the PG/PLV blend with high miscibility is formed.

Electronic Absorption and Resonance Raman Signatures of Hyperporphyrins and Nonplanar Porphyrins

We have carried out a broad survey of tetraphenylporphyrin derivatives in relation to their possible hyperporphyrin character. The majority of the free-base tetraphenylporphyrins studied, i.e., TArPH2; Ar = p-X−C6H4, where X = CH3, H, F, CF3, and NO2, when dissolved in trifluoroacetic acid (i.e. when centrally diprotonated), exhibit red-shifted “hyperporphyrin” spectra. The “hyper” features are attributable to phenyl-to-porphyrin charge-transfer transitions. However, certain free-base tetraphenylporphyrins with extremely electron-deficient phenyl groups, such as TPFPPH2, do not exhibit hyperporphyrin spectra in trifluoroacetic acid solution. Certain anionic tetraphenylporphyrin derivatives such as T(p-OH−P)PH2 or Ni[T(p-OH−P)P] dissolved in methanolic Bu4NOH also qualify as hyperporphyrins. The hyper transitions in these cases involve charge transfer from anionic phenolate substituents to the neutral porphyrin core. This study also presents a first systematic resonance Raman spectroscopic exploration of h...

Resin-bound aminothiols: synthesis and application

Aminothiols were attached through their thiol group onto the 4,4′-dimethoxytrityl (Dmt)-, 4-methoxytrityl (Mmt)-, 4-methyltrityl (Mtt)-, trityl (Trt)- and 2-chlorotrityl (Clt)-resins. The new resins were used in the solid-phase synthesis of aminothiol containing peptides utilizing N-Fmoc amino acids. The synthesized peptides were cleaved from the resins by treatment with trifluoroacetic acid (TFA) solutions using triethylsilane (TES) or ethanedithiol (EDT) as scavengers.

Processing the Complete Canine Tooth

This paper describes a unique, reproducible method for the processing, sectioning, and staining of sections of the canine tooth intact with the bony matrix and gingiva. A 10% trifluoroacetic acid solution was employed to de-enamelize the tooth; de-enamelization was assessed using X-rays. This method supports sectioning through the complete tooth, a process which frequently requires re-infiltration steps, and generates nearly 2,000 individual sections. An overoxidized hematoxylin was employed which yielded staining that distinguished between the incremental lines in the dentin portion of the tooth. Masson's Trichrome stain demonstrated excellent preservation of structures, including dentin, cementum, dental pulp, periodontal membrane. vessels, nerves, and alveolar bone. (The J Hisrorechnol 25:137, 2002)Submitted May 7, 2002; Accepted with revisions August 8, 2002

Processing the Complete Canine Tooth

This paper describes a unique, reproducible method for the processing, sectioning, and staining of sections of the canine tooth intact with the bony matrix and gingiva. A 10% trifluoroacetic acid solution was employed to de-enamelize the tooth; de-enamelization was assessed using X-rays. This method supports sectioning through the complete tooth, a process which frequently requires re-infiltration steps, and generates nearly 2,000 individual sections. An overoxidized hematoxylin was employed which yielded staining that distinguished between the incremental lines in the dentin portion of the tooth. Masson's Trichrome stain demonstrated excellent preservation of structures, including dentin, cementum, dental pulp, periodontal membrane. vessels, nerves, and alveolar bone. (The J Hisrorechnol 25:137, 2002)Submitted May 7, 2002; Accepted with revisions August 8, 2002

Infrared laser ablation and ionization of water clusters and biomolecules from ice

We demonstrate the direct desorption and ionization of angiotensin II from frozen water ice samples without supplementary matrix, using a pulse train of approximately 340 intense (∼10 9 W/cm 2) picosecond pulses from a tunable, mid-infrared free-electron laser, at a wavelength of 5.9 μm. The pulse train was delivered at equally spaced intervals over a total duration of 120 ns. Ions thus formed were detected using a reflectron time-of-flight mass spectrometer. Single-shot ablation at spatially separated locations on the ice surface produced parent ions as well as Na and K adducts. Multiple pulse impact at a single location on the ice generated the parent ion signal and also protonated water clusters of the form (H 2O) n−1 H 3O +. Investigations of clusters produced by infrared laser ablation of frozen trifluoroacetic acid solution support a mechanism involving electrostatic ejection of pre-formed ions.

A study of conformational stability of poly(L-alanine), poly(L-valine), and poly(L-alanine)/poly(L-valine) blends in the solid state by (13)C cross-polarization/magic angle spinning NMR.

13C cross-polarization/magic angle spinning (CP/MAS) NMR and (1)H T(1rho) experiments of poly(L-alanine) (PLA), poly(L-valine) (PLV), and PLA/PLV blends have been carried out in order to elucidate the conformational stability of the polypeptides in the solid state. These were prepared by adding a trifluoroacetic acid (TFA) solution of the polymer with a 2.0 wt/wt % of sulfuric acid (H(2)SO(4)) to alkaline water. From these experimental results, it is clarified that the conformations of PLA and PLV in their blends are strongly influenced by intermolecular hydrogen-bonding interactions that cause their miscibility at the molecular level.

Resin-bound mercapto acids: synthesis and application

Mercapto acids were attached through their thiol group onto 2-chlorotrityl (Clt)-, trityl (Trt)-, 4-methyltrityl (Mtt)-, 4-methoxytrityl (Mmt)- and 4,4′-dimethoxytrityl (Dmt)-resins. The new resins were used in the solid-phase synthesis of small mercaptoacylamino alcohols. Cleavage from the resins was performed by treatment with trifluoroacetic acid (TFA) solutions in dichloromethane (DCM) using triethylsilane (TES) as scavenger.

A study of the conformational stability of poly( l-alanine), poly( d-alanine), poly( l-isoleucine), polyglycine and poly( l-valine) and their polypeptide blends in the solid-state by 13C CP/MAS NMR

13C CP/MAS NMR and 1H T 1 ρ experiments on homopolypeptides obtained from d- and l-alanines, l-isoleucine, glycine and l-valine, and on their polypeptide blends have been carried out, in order to elucidate the conformational stability of the polypeptides in the solid-state. These polypeptide blends were prepared by adding trifluoroacetic acid (TFA) solutions of the polypeptides containing a 2.0% (w/w) amount of sulfuric acid (H 2SO 4) to alkaline water. From these experimental results, it was clarified that the conformations of the polypeptides in their blends are strongly influenced by intermolecular hydrogen bonding interactions which cause their miscibility at the molecular level.

Homogeneous rhodium-copper-halide catalytic systems for the oxidation and oxidative carbonylation of methane

Homogeneous catalytic systems for the oxidation and oxidative carbonylation of methane in aqueous trifluoroacetic acid solutions were developed. The system included rhodium compounds and copper compounds as cocatalysts. Methanol, methyl trifluoroacetate, formic acid, and acetic acid were the reaction products. The process was accompanied by the intense oxidation of CO to CO2. Regularities of the process were studied, optimum process parameters were determined, and conditions at which methyl trifluoroacetate was formed with ∼90% selectivity were found. Kinetic isotope effects with respect to the solvent were determined. For the formation of organic products, kH/kD was ∼1, whereas it was ∼1.6 for the oxidation of CO. Studies were also performed with the use of compounds containing the 18O isotope. Conceivable mechanistic models of this process are discussed.