Trifluoroacetic Acid Solution Research Articles

Antioxidant Activity of Anthocyanin Extract from Purple Black Rice.

Antioxidant activity was studied for anthocyanins extracted from purple black rice (PBR) by a 3% aqueous trifluoroacetic acid solution (TFA), as well as for anthocyanins extracted from blueberry (Bluetta, high bush type). Capillary zone electrophoresis revealed that the PBR extract contained almost exclusively a single anthocyanin, which was identified as cyanidin 3-O-beta-D-glucoside (Cy 3-Glc) after purification by polyvinylpyrrolidone column chromatography. In contrast, 11 anthocyanins were identified in the blueberry extract. PBR extract showed slightly weaker superoxide scavenging and crocin bleaching activities than blueberry extract did. Both PBR and blueberry extracts, however, showed 10 to 25 times stronger activity than the same concentration of Trolox used as a reference antioxidant. It was further noted that the purified Cy 3-Glc from PBR extract retained approximately 74% of the antioxidant activity (both crocin bleaching and superoxide scavenging) observed in the original TFA extract. The hydroxyl radical scavenging activity of both extracts was several times weaker than that of the same concentration of Trolox, although the PBR extract showed approximately two times stronger activity than blueberry extract did. The hydroxyl radical scavenging activity of the purified Cy 3-Glc from PBR, however, decreased to approximately 20% of that of the original PBR extract. These results indicate that the anthocyanin Cy 3-Glc contributes to the antioxidant activity of PBR through its strong superoxide radical but not hydroxyl radical scavenging activity.

Spectrophotometric flow-injection analysis of the total base number in lubricants by using acid–base buffers

A spectrophotometric FIA method for the determination of the total base number (TBN) in a lubricant was proposed, which involved using an acid–base buffer solution prepared with a nonaqueous solvent. This method is based on measurements of the absorbance change of an indicator contained in the acid–base buffer solution, which is generated due to a neutralization reaction of base in the lubricant with the buffer acid. The sample injected into a stream of a nonaqueous solvent, toluene/H 2O/2-propanol (52/1/47 v/v/v), was merged with a stream of perchloric acid (HClO 4) solution, and then neutralized with HClO 4. An excess of HClO 4 was subsequently merged with a stream of tetrabutylammonium salt of trifluoroacetic acid (TFA·TBA) solution containing an indicator ( m-cresol purple), which p K a value was found to be similar to p K a value of TFA in the present mixed nonaqueous solvent. The reaction of the excess HClO 4 with TFA·TBA gave rise to the composition change of the acid–base buffer solution, TFA/TFA·TBA. Since the indicator, m-cresol purple, behaves similarly to the buffer component, the change in the concentration ratio of TFA/TFA·TBA can be determined by the measurement of the absorbance change of the indicator. The absorbance changes were monitored with a spectrophotometric detector. The sensitivity of the proposed method for several kinds of basic compounds, which were often added to lubricant, was nearly identical irrespective of the basicity of the compounds. The proposed method was successfully applied to the determination of the total base number in lubricant.

Crystal forms of nylon 10 12 crystallized from melt and after solution casting

Nylon 10 12 samples prepared under different conditions, melt-crystallized, meta-cresol and trifluoroacetic acid cast, were studied by Fourier transform-infrared and wide angle X-ray diffraction. It was found that crystal forms are dependent on the approaches of sample preparation: α-form and γ-form crystals grown from melt-crystallized and trifluoroacetic acid solution cast samples, respectively. When meta-cresol cast was used, different crystal forms (including α-form, γ-form and the two forms mixture) can be obtained with different cast temperature.

Poly(ethylene terephthalate) copolymers containing 5‐nitroisophthalic units. II. Crystallization studies

AbstractThe microstructure and crystallization behavior of a set of poly(ethylene terephthalate‐co‐5‐nitroisophthalate) copolymers (PETNI) containing 5‐nitroisophthalic units in the 10–50 mol % range were examined and compared to those of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate‐co‐isophthalate) (PETI) copolymers. A 13C NMR analysis of PETNI copolymers in a trifluoroacetic acid solution indicates that they are random copolymers with average sequence lengths in accordance with ideal polycondensation statistics. Differential scanning calorimetry (DSC) studies show that PETNI containing 5‐nitroisophthalic units up to 20 mol % are able to crystallize and that crystallization takes place in these copolymers at much slower rates than in PET. Wide‐angle X‐ray diffraction from powder and fibers reveals that crystallizable PETNI adopts the same triclinic crystal structure as PET, with the nitroisophthalate units being excluded from crystallites. Fourier transform infrared in combination with cross‐polarization/magic‐angle spinning 13C NMR spectroscopy demonstrates the occurrence of a gauche–trans conversion encompassing the crystallization process. A correlation between DSC and spectroscopic data leads us to conclude that the content of trans conformer in the noncrystallized phase of PETNI is higher than in both PET and PETI copolymers and suggests that secondary crystallization in the homopolymer must proceed by a mechanism different than that in copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1553–1564, 2001

Polyaniline thin films – structural anisotropy study by use of synchrotron radiation surface diffraction

Polyaniline (PANI) protonated with camphorsulfonic acid (CSA) receives high interest but its molecular and crystalline structure is still unclear. We undertook detailed studies of thin films cast from m-cresol, dichlorometane and trifluoroacetic acid (TFAA) solutions. Such samples were subjected to diffraction measurements by use of the grazing incident beam technique, applying the z-axis diffractometer installed at the beamline BW2 at HASYLAB. We obtained very important information concerning an anisotropy of the crystalline reflections for all samples investigated. These results demonstrate the significance of the solvents on the structural ordering, and the observed anisotropy plays an important role in new modelling attempts for the crystalline structure.

Solid phase synthesis of benzothiazolyl compounds

Abstract 2-Aminobenzenethiol, bound through its thiol function to the 2-chlorotrityl (Clt)-, trityl (Trt)-, 4-methyltrityl (Mtt)- and 4-methoxytrityl (Mmt)-resins, was acylated at the amino-function by aliphatic and aromatic acids. The obtained 2-N-acyl-aminobenzenethiols were cleaved from the resin by treatment with trifluoroacetic acid solutions in dichloromethane. The 2-N-acyl-aminobenzenethiols released from the resin were cyclised to the corresponding 2-substituted benzothiazoles, by standing in a solution of dithiothreitol in DMF or methanol for 1–3 h at room temperature.

Solvent effects on 15N NMR chemical shifts of 2,6-di-tert-butylpyridine. Absence of hydrogen bonding with the nitrogen atom

Comparison of the 15N chemical shifts of 2,6-di-tert-butylpyridine (DTBP) and pyridine (Py) in a series of solvents demonstrates the inability of the nitrogen atom in DTBP to participate in hydrogen bonds. Both bases are fully hydronated in trifluoromethanesulfonic acid (TFMSA) and trifluoroacetic acid (TFA) solutions, but the chemical shift values for Py differ in the two media, indicating hydrogen bonding between the N–H group of the pyridinium ion and the trifluoroacetate anion in the ion pair, which is absent in hydronated DTBP.

Separation of 17 [formula omitted]-Amino Acids and Chiral Sequential Analysis of Peptides by Reversed-Phase Liquid Chromatography after Labeling with R(−)-4- (3-Isothiocyanatopyrrolidin-1-yl)-7-(N,N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole

Seventeen dl-amino acids labeled with a fluorescent chiral labeling reagent, R(−)-4-(3-isothiocyanatopyrrolidin-1-yl)-7-(N,N-dimethylaminosulfonyl)-2,1,3-benzoxadiazole (R(−)-DBD-PyNCS), were separated by reversed-phase chromatography and detected fluorometrically at 550 nm (excitation at 460 nm). The reagent reacted with amino functional group in dl-amino acids under basic medium. The thiocarbamoyl derivatives were converted to thiohydantoin via thiazolinone in trifluoroacetic acid (TFA) solution. The epimerization ratios during the reaction of the cyclization were less than 37% in all dl-amino acids tested. The resulting thiohydantoin derivatives of individual dl-amino acids were completely separated with isocratic elutions using acidic mobile phase involving 0.1% TFA. The separations of the thiohydantoins yielded from acidic, basic, neutral, hydroxyl, and aromatic amino acids were good enough for the identification of dl-amino acid. The method using the reagent was adopted to identification of dl-amino acid sequences in eight peptides. The separation and identification of the thiohydantoin derivatives liberated from the peptides labeled were performed by the isocratic elutions. The applicability of the proposed procedure to sequential analysis of peptide was demonstrated with [d-Ala2]-leucine enkephalin, [d-Ala2]-deltorphin II, d-Phe-Met-Arg-Phe-amide, and Phe-d-Met-Arg-Phe-amide. d-Ala, d-Phe, and d-Met in the peptides were positively identified with the proposed procedures. [l-Ala2]-leucine enkephalin, β-lipotropin, Asp-Ser-Asp-Pro-Arg, and Pro-Asp-Val-Asp-His-Val-Phe-Leu-Arg-Phe-amide were also analyzed as the references without d-amino acid.

Evaluation of volatile eluents and electrolytes for high-performance liquid chromatography–electrospray ionization mass spectrometry and capillary electrophoresis–electrospray ionization mass spectrometry of proteins: I. Liquid chromatography

Proteins ranging in molecular mass from 14 000 to 80 000 were analyzed by reversed-phase high-performance liquid chromatography–electrospray mass spectrometry (RP-HPLC–ESI-MS) using 60×1.0 mm I.D. microbore-columns packed with 2.3 μm highly crosslinked, octadecylated poly(styrene–divinylbenzene) particles. Proteins were eluted at temperatures of 80–90°C with gradients of acetonitrile in 0.10–0.50% aqueous solutions of trifluoroacetic acid, formic acid or acetic acid. Substitution of trifluoroacetic acid, the most commonly used mobile phase additive for RP-HPLC, by formic acid resulted in a 35–160-fold improvement in analyte detectability at the cost of an only 32–104% increase in peak width at half height of eluting chromatographic peaks. The lower limits of detection for carbonic anhydrase ( M r 29 022.7) in full scan and selected ion monitoring mode were 37 and 2.3 fmol, respectively. Measurement of protein masses by RP-HPLC–ESI-MS was accurate and highly reproducible with maximum mass deviations of 0.025% and relative standard deviations of less than 0.011%. Calibration plots of peak area versus concentration allowed the reliable quantitation of proteins in a concentration range of 0.010–1.0 mg/ml. Finally, the optimized method was applied to the separation, identification and quantification of proteins in real samples such as commercial protein preparations, monoclonal antibody fragments, allergen extracts and whey drinks.

Synthesis and characterization of the anionic fluorocarboranes 6,7,8,9,10-CB 9H 5F 5 −, 6,7,8,9-CB 9H 5F 4-10-OH −, and 6,7,8,9-CB 9H 5F 4-10-NHCOCH 3 −

The reactions of salts of the 6,7,8,9-CB 9H 6F 4 − and CB 9H 10 − anions with 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (F-TEDA) in acetonitrile in the presence or absence of trifluoroacetic acid were studied. The addition of trifluoroacetic acid to the reaction mixture significantly changed the concentration ratio of the two pentafluoro isomers produced in the reactions, [6,7,8,9,10-CB 9H 5F 5 −]/[2,6,7,8,9-CB 9H 5F 5 −]. The ratio increased from 0.6 to >23 when the solvent was changed from neat acetonitrile to a 20% solution of trifluoroacetic acid in acetonitrile while simultaneously raising the temperature from 25°C to 60°C. The synthesis and 11B and 19F NMR spectroscopic characterization of the 6,7,8,9,10-CB 9H 5F 5 − anion are reported here for the first time. Chromatographic separation of the reaction mixtures led to the isolation of salts of two additional new anions, 6,7,8,9-CB 9H 5F 4-10-NHCOCH 3 − and 6,7,8,9-CB 9H 5F 4-10-OH −. The structure of [PPh 4][6,7,8,9-CB 9H 5F 4-10-NHCOCH 3] was determined by X-ray crystallography: monoclinic, space group P2 1/ n, a=7.5169(3), b=23.2793(10), c=16.6170(7) Å, Z=4, T=−113°C, least-squares refinement on F 2, R 1 ( I>2 σ( I))=0.0805, wR 2 (all data)=0.1922.

Indolopyridines with an angular heteroatom. 11. Synthesis of 12-arylidenindolo-[2,1-a]isoquinolinium salts

The condensation of aromatic aldehydes with indolo[2,1-a]isoquinoline in a solution of trifluoroacetic acid yielded a series of 12-arylidenindolo[2,1-a]isoquinolinium trifluoroacetates. Analogous quaternary salts are formed with trichloroacetic and acetic acids as well as upon the reaction of indoloisoquinolinium hydrochloride with p-nitrobenzaldehyde or with p-nitrophenyldiazonium chloride in ethanol.

Regioselective deprotection of p-methoxybenzyl ethers of furanose derivatives

Reaction of per-p-methoxybenzylated hexofuranoses and pentofuranoses with either a catalytic amount of tin chloride dihydrate (SnCl 2·2H 2O) or 0.5–10% solution of trifluoroacetic acid in dichloromethane afforded regioselectively the corresponding monosaccharide derivatives having a single free hydroxyl group at C(5) in good yields.

An improved extraction procedure for the rapid, quantitative high-performance liquid chromatographic estimation of the main eleutherosides (b and e) inEleutherococcus senticosus (eleuthero)

Eleutherosides were extracted with aqueous methanol and analysed by reversed-phase high performance liquid chromatography on a C-18 column. Recovery was better than 80% for eleutheroside B within the concentration range 500 to 10,000 μg, and similarly for eleutherosides E in the range 500 to 2,500 μg. Lower recovery values were obtained at higher concentrations for eleutheroside E due to its insolubility in alcoholic solutions. The use of trifluoroacetic acid solution in methanol was found to resolve the solubility problem. The concentration ranges over which a linearity of response for both eleutherosides could be validated were improved significantly by this adjustment. Copyright © 1998 John Wiley & Sons, Ltd.

Separation and enzymatic degradation of blend films of poly(L‐lactic acid) and cellulose

Blend films of poly(L-lactic acid) (PLLA) and cellulose with various composition was prepared by casting from trifluoroacetic acid solution. One hydroxyl group per each glucose unit was esterified by trifluoroacetic acid. The trifluoroacetyl group was hydrolyzed completely during the degradation. Weight losses for 90/10 and 75/25 PLLA/cellulose blends by proteinaze K were greatly increased compared with pure PLLA sample due to the large depression of the crystallinity of PLLA component, while cellulase was effective only for the degradation of pure cellulose film. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1861–1864, 1998

Separation and enzymatic degradation of blend films of poly(L-lactic acid) and cellulose

Blend films of poly(L-lactic acid) (PLLA) and cellulose with various composition was prepared by casting from trifluoroacetic acid solution. One hydroxyl group per each glucose unit was esterified by trifluoroacetic acid. The trifluoroacetyl group was hydrolyzed completely during the degradation. Weight losses for 90/10 and 75/25 PLLA/cellulose blends by proteinaze K were greatly increased compared with pure PLLA sample due to the large depression of the crystallinity of PLLA component, while cellulase was effective only for the degradation of pure cellulose film. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1861–1864, 1998

Nanoscale analysis of pharmacologically active catechins in body fluids by HPLC using borate complex extraction pretreatment

A pretreatment method based on borate complex formation is described for the selective and simultaneous quantitation of pharmacologically active catechins in human plasma and saliva. This method is based on the interaction of catechins with diphenylborate (as a complexing agent) and tetra- n-butylammonium (as a counter ion) in alkaline media to give the catechin–diphenylborate complex and ion-pair that are extractable to the organic phase. The complex extracted in an organic solvent is dissociated by shaking with an aqueous trifluoroacetic acid solution to back-extract free catechins to the aqueous phase, followed by high-performance liquid chromatography (HPLC) analysis with fluorometric and diode array detection. Under optimal conditions, all catechins originating from green tea extracts were selectively purified from plasma and saliva samples, and they were stabilized during the extraction procedures by forming the complex. The nano-scale quantitative analysis of eight catechins was achieved with high recovery and analytical reproducibility. The proposed method would be a useful tool for pharmacokinetic studies of catechins in plasma and saliva.

Charged droplet formation in sonic spray

The reasons why sonic spray ionization can readily produce multiply-charged ions when a high voltage is applied to the source housing have been investigated by using aerosol techniques. Charged droplets were produced by sonic spray from a trifluoroacetic acid solution in triethylene glycol/ethanol. These droplets were analyzed with a differential mobility analyzer to obtain their mobilities, and also analyzed with an aerodynamic particle size spectrometer to obtain their diameters. By combining these results, the charge numbers of the droplets have been determined. The results show that some droplets have charge numbers close to the Rayleigh limit and that the abundance of these droplets increases as the voltage applied to the source housing increases. A qualitative explanation is given for the formation of multiply-charged ions.

Evaporation of charged fine droplets

At about the minimum flow rate, mono-disperse charged droplets have been produced by electrospray from an aqueous solution of trifluoroacetic acid. Charged droplets and ions formed from the droplets were passed through a heated copper tube and then analyzed with a differential mobility analyzer. In the mobility spectra it was found that with increasing temperature the current of the charged droplet peak at 3.75 × 10 −5m 2 V −1 s −1 decreases and finally disappears, while that of the ion peak at 7.20 × 10 −5m 2 V −1 s −1 decreases much less. This result shows that ions are formed from heated droplets. The electric field at the droplet surface was determined as (1.32 ± 0.09) × 10 9V m −1.

Effects of Acid on Line Widths in the Proton NMR Spectra of Porphyrins Not Substituted at the meso-Positions

It was shown in earlier work that the proton NMR spectra of some meso-tetraarylporphyrins in deuterochloroform−trifluoroacetic acid solutions show little dependence of signal line widths upon acid concentration, but chemical shifts (particularly of the N-H signal) are strongly acid dependent. In contrast, the corresponding NMR spectra of meso-unsubstituted coproporphyrin I tetramethyl ester in deuterochloroform solution show weak signals assigned to porphyrin N−H and to O−H (water impurity in solvent). Addition of trifluoroacetic acid at mole ratios TFA:COPH2 as low as 0.05 produces simultaneous broadening of these signals, both of which become too broad to observe at normal instrument gain and room temperature when this mole ratio exceeds 0.3. Additional acid causes the N−H signal to narrow again and then reappear as a very broad line when the TFA:COPH2 ratio exceeds 2. It gradually narrows and moves upfield as the TFA concentration increases further. Within the same range of TFA:COPH2 concentration rati...

Adamantylation and Adamantylalkylation of Amides, Nitriles and Ureas in Trifluoroacetic Acid

A new preparative method for N-adamantylation of carboxylic acid amides, ureas and for C5-adamantylation of barbituric acid in trifluoroacetic acid (TFA) is proposed. Tertiary 1-adamantanols and l-(l-adamantyl)alkanols were used as adamantylating agents. The reaction of l-(l-adamantyl)alkanols with nitriles in TFA solution was employed for the first time for the preparation of N-[\-(\adamantyl)alkyl]amides.