Determination of ascorbic acid, dehydroascorbic acid, and isoascorbic acid in blood

Summary High-performance liquid chromatography with UV-detection at 254 nm was used for determining ascorbic acid, dehydroascorbic acid, and isoascorbic acid in plasma and erythrocytes obtained from healthy volunteers and from patients with coronary infarct, acute lymphatic leukemia (ALL), and acute myeloic leukemia (AML). Deproteinisation was done by a simple ultrafiltration technique. Dehydroascorbic acid (DHA) was determined after reduction to ascorbic acid with dithiothreitol. The separation system chosen allows the search for the stereoisomer isoascorbic acid. To exclude interfering substances which could coelute with ascorbic or isoascorbic acid, several other compounds present in plasma were investigated including e.g. the aromatic amino acids, glutathione, cysteine, and uric acid. The results reveal a drastic decrease in total vitamin C concentration in plasma and erythrocytes with a concomitant increase in rel. DHA concentration in patients with AML. In ALL patients, both the total vitamin C and rel. DHA concentrations were increased.

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Bestimmung von Ascorbinsäure, Dehydroascorbinsäure und Isoascorbinsäure in Blut

Zusammenfassung High-performance-liquid-Chromatographie mit UV-Nachweis bei 254 nm wurde zur Bestimmung von Ascorbinsäure, Dehydroascorbinsäure und Isoascorbinsäure in Plasma und Erythrocyten von gesunden Probanden und von Patienten mit Herzinfarkt, akuter lymphatischer Leukämie (ALL) und akuter myeloischer Leukämie (AML) benutzt. Deproteinisierung erfolgte mittels einer einfachen Ultrafiltrationstechnik. Dehydroascorbinsäure wurde nach Reduktion mit Dithiothreitol als Ascorbinsäure bestimmt. Die benutzte Methode erlaubt auch die Bestimmung des Stereoisomers Isoascorbinsäure. Der mögliche Einfluß von im Plasma vorkommenden Substanzen auf die Bestimmung des Vitamin C wurde untersucht. Die Ergebnisse zeigen eine drastische Abnahme der Gesamt-Vitamin C-Konzentration in Plasma und Erythrocyten mit einer parallelen Zunahme der relativen DHA-Konzentration in AML-Patienten. In ALL-Patienten sind sowohl die Gesamt-Vitamin C- als auch die relative DHA-Konzentrationen erhöht.

     

Raman spectra of glycolic acid,l-lactic acid and d,l-lactic acid oligomers

Polymerization of glycolic acid, l- and d,l-lactic acid was followed by Raman spectroscopy in aqueous solution at different concentrations, in viscous and solid states. The Raman spectra of some oligomers obtained by progressive polycondensation of α-hydroxycarboxylic acid aqueous solutions were investigated in the 200–18 cm⁻¹ region. Vibrational analysis revealed the characteristic peaks of ester groups that appeared in the repeat unit of the polymeric chain during the polymerization reaction, and those of the monomers which disappeared. In particular, the ν(CC) stretching vibrations occur in the 800–1000 cm⁻¹ range, which is easily accessible because of the weak diffusion of water. Moreover, spectral monitoring of the semicrystalline sample of poly(glycolic acid) oligomers showed Raman peaks associated with the vibrations of the polymer in the amorphous and semicrystalline states.     

Simultaneous and direct determination of oxalic acid, tartaric acid, malic acid, vitamin C, citric acid, and succinic acid in Fructus mume by reversed-phase high-performance liquid chromatography

A method for the simultaneous separation and direct determination of oxalic acid (OA), tartaric acid (TA), malic acid (MA), vitamin C (VC), citric acid (CA), and succinic acid (SA) in Fructus mume using reversed-phase high-performance liquid chromatography with a UV detector in an acidic medium is presented in this study. In the experiment, the optimization of chromatographic conditions (i.e., the pH and flow rate of the mobile phase, the absorption wavelength, and temperature of column) that affect the separation degree and peak shape of organic acids has been obtained. The linear ranges are found to be 0.05-4.7 microg for OA (r = 0.9999), 0.11-10.5 microg for TA (r = 0.9999), 0.114-11.4 microg for MA (r = 0.9999), 0.033-3.30 microg for VC (r = 0.9999), 0.155-15.5 microg for CA (r = 0.9998), and 0.194-19.4 microg for SA (r = 0.9996). For OA, TA, MA, VC, CA, and SA, the even recovery (n = 3) of six effective components are 100.9%, 99.97%, 101.2%, 102.1%, 101.1%, and 100.7%, respectively, and the largest relative standard deviation (n = 11) for the six components is less than 1.7%. The detection limits are 0.01 microg for OA, TA, and VC; 0.05 microg for MA; 0.03 microg for CA; and 0.1 microg for SA. In a single chromatographic run, OA, TA, MA, VC, CA, and SA can be determined in less than 7 min. The method can be used for the purpose of routine analysis and the quality control of a botanic (Fructus mume) containing these effective components.     

Fragmentation of the deprotonated ions of peptides containing cysteine, cysteine sulfinic acid, cysteine sulfonic acid, aspartic acid, and glutamic acid

We examined the fragmentation of the electrospray-produced [M-H]- and [M-2H]2- ions of a number of peptides containing two acidic amino acid residues, one being aspartic acid (Asp) or glutamic acid (Glu), and the other being cysteine sulfinic acid [C(SO2H)] or cysteine sulfonic acid [C(SO3H)], on an ion-trap mass spectrometer. We observed facile neutral losses of H2S and H2SO2 from the side chains of cysteine and C(SO2H), respectively, whereas the corresponding elimination of H2SO3 from the side chain of C(SO3H) was undetectable for most peptides that we investigated. In addition, the collisional activation of the [M-H]- ions of the C(SO2H)-containing peptides resulted in the cleavage of the amide bond on the C-terminal side of the C(SO2H) residue. Moreover, collisional activation of the [M-2H]2- ions of the above Asp-containing peptides led to the cleavage of the backbone N-Calpha bond of the Asp residue to give cn and/or its complementary [zn-H2O] ions. Similar cleavage also occurred for the singly deprotonated ions of the otherwise identical peptides with a C-terminal amide functionality, but not for the [M-H]- ions of same peptides with a free C-terminal carboxylic acid. Furthermore, ab initio calculation results for model cleavage reactions are consistent with the selective cleavage of the backbone N-Calpha bond in the Asp residue.     

Solubilities of l-glutamic acid, 3-nitrobenzoic acid,p-toluic acid,calcium-l-lactate,calcium gluconate,magnesium-dl-aspartate,and magnesium-l-lactate in water

Solubilities of l -glutamic acid, 3-nitrobenzoic acid, p -toluic acid, calcium-l -lactate, calcium gluconate, magnesium- dl -aspartate, and magnesium- l -lactate in water were determined in the temperature range 278 K to 343 K. The apparent molar enthalpies of solution at T =  298.15 K as derived from these solubilities areΔ_solH_m (l -glutamic acid,m_sat =  0.0565 mol · kg ^− 1)  =  30.2 kJ · mol ^− 1,Δ_solH_m (3-nitrobenzoic acid, m =  0.0188 mol · kg ^− 1)  =  28.1 kJ · mol ^− 1, Δ_solH_m( p - toluic acid, m =  0.00267 mol · kg ^− 1)  =  23.9 kJ · mol ^− 1,Δ_solH_m (calcium- l -lactate tetrahydrate,m =  0.2902 mol · kg ^− 1)  =  25.8 kJ · mol ^− 1,Δ_solH_m (calcium gluconate, m =  0.0806 mol · kg ^− 1)  =  22.1 kJ · mol ^− 1, Δ_solH_m(magnesium-dl -aspartate tetrahydrate, m =  0.1469 mol · kg ^− 1)  =  11.5 kJ · mol ^− 1, andΔ_solH_m (magnesium- l -lactate trihydrate,m =  0.3462 mol · kg ^− 1)  =  3.81 kJ · mol ^− 1.     

Efficient access to 2-isobetulinic acid, 2-isooleanolic acid, and 2-isoursolic acid

An efficient access to 2-isobetulin, 2-isobetulinic acid, 2-isooleanolic acid, and 2-isoursolic acid has been developed. The key step is a novel one-pot conversion of 2,3-dihydroxy triterpenes to 3-deoxy-2-oxo triterpenes. This method provides a new access to 3-deoxy-2-substituted pentacyclic triterpenes as potential therapeutic agents against metabolic diseases, tumors, and HIV infection.     

Simultaneous determination of chlorogenic acid, caffeic acid, ferulic acid, protocatechuic acid and protocatechuic aldehyde in Chinese herbal preparation by RP-HPLC

In the present study, a reversed phase high performance liquid chromatographic (RP-HPLC) method was established for simultaneous determination of chlorogenic acid, caffeic acid, ferulic acid, protocatechuic acid and protocatechuic aldehyde in a Chinese herbal preparation (Fufang-Pugongying-Mixture). The separation was performed on a Hypersil ODS-2 column by isocratic elution with methanol and 0.2 M acetate buffer (pH 3.6) (15 : 85, v/v) as the mobile phase at the flow-rate of 1.0 ml/min with operating temperature of 30 degrees C, and detection wavelength of 300 nm. A good linear regression relationship between peak-areas and concentrations was obtained over the range of 2-200 microg/ml for the five marker compounds mentioned above. The spike recoveries were within 96.72-104.07%. The variation coefficient (CV) values of the precision were in the range of 0.89-4.50%. Moreover the developed method has reference value for quantitative analysis of Taraxacum, Lonicera and Angelica.     

Further studies on the fragmentation of protonated ions of peptides containing aspartic acid, glutamic acid, cysteine sulfinic acid, and cysteine sulfonic acid

Here we examined the fragmentation, on a quadrupole ion-trap mass spectrometer, of the protonated ions of a group of peptides containing one arginine and two different acidic amino acids, one being aspartic acid (Asp) or glutamic acid (Glu) and the other being cysteine sulfinic acid [C(SO2H)] or cysteine sulfonic acid [C(SO3H)]. Our results showed that, upon collisional activation, the cleavage of the peptide bond C-terminal to C(SO2H) is much more facile than that of the peptide bond C-terminal to Asp, Glu, or C(SO3H). There is no significant difference, however, in susceptibility to cleavage of peptide bonds that are C-terminal to Asp, Glu, and C(SO3H). To understand these experimental observations, we carried out B3LYP/6-31G* density functional theory calculations for a model cleavage reaction of GXG --> b2 + Gly, in which X is Asp, Glu, C(SO2H), or C(SO3H). Our calculation results showed that the cleavage reaction is thermodynamically more favorable when X = C(SO2H) than when X = Asp or C(SO3H). We attributed the less facile cleavage of the amide bond after Glu to that the formation of a six-membered ring b ion for Glu-bearing peptides is kinetically not as favorable as the formation of a five-membered ring b ion for peptides containing the other three acidic amino acids. The results from this study may provide useful tools for peptide sequencing.     

Density,viscosity, and surface tension of binary liquid systems: Ethanoic acid,propanoic acid,and butanoic acid with nitrobenzene

Density, viscosity, and surface tension of three binary liquid systems: ethanoic acid+nitrobenzene, propanoic acid+nitrobenzene, and butanoic acid+nitrobenzene have been determined at 25, 35, and 45°C, over the whole composition range. The excess molar volumes, viscosities, Gibbs energies for the activation of flow, and surface tension were evaluated and fitted to a Redlich-Kister type of equation. The Grunberg-Nissan parameter d was also calculated. Binary viscosity data were fitted to the models of McAllister, Heric, Krishnan, and Laddha, Auslander, and Teja and Rice. Surface tension data were fitted to the models of Zihao and Jufu, Rice, and Teja, and an empirical two-constant model.     

Collision-induced dissociation of protonated tetrapeptides containing beta-alanine, gamma-aminobutyric acid, epsilon-aminocaproic acid or 4-aminomethylbenzoic acid residues

The influence of the presence and position of a single beta-alanine, gamma-aminobutyric acid, epsilon-aminocaproic acid or 4-aminomethylbenzoic acid residue on the tendency to form b(n)+ -and y(n)+ -type product ions was determined using a group of protonated tetrapeptides with general sequence XAAG, AXAG and AAXG (where X refers to the position of amino acid substitution). The hypothesis tested was that the 'alternative' amino acids would influence product ion signal intensities by inhibiting or suppressing either the nucleophilic attack or key proton transfer steps by forcing the adoption of large cyclic intermediates or blocking cyclization altogether. We found that specific b ions are diminished or eliminated completely when betaA, gammaAbu, Cap or 4AMBz residues are positioned such that they should interfere with the intramolecular nucleophilic attack step. In addition, differences in the relative proton affinities of the alternative amino acids influence the competition between complementary b(n) and y(n) ions. For both the AXAG and the XAAG series of peptides, collision-induced dissociation (CID) generated prominent b ions despite potential inhibition or suppression of intramolecular proton migration by the betaA, gammaAbu, Cap or 4AMBz residues. The prominent appearance of b ions from the AXAG and XAAG peptide is noteworthy, and suggests either that proton migration occurs through larger, 'whole' peptide cyclic intermediates or that fragmentation proceeds through a population of [M+H]+ isomers that are initially protonated at amide O atoms.     

Surface treatment of LLDPE and LDPE blends by nitric acid,sulfuric acid,and chromic acid etching

Surface treatment of linear low density polyethylene and low density polyethylene blends is investigated herein using nitric acid, sulfuric acid, and chromic acid. These chemical treatments not only make the surface rough but also introduce polar groups. A new method, “sulfonic groups index” (SI) is employed to quantify the newly generated polar groups in the wavenumber of 1,250–840 cm⁻¹ in the Fourier transform infrared spectra. The SI values effectively indicate that the most polar groups are incorporated into the chromic acid-etched samples among the three inorganic acids, which is also confirmed by scanning electron microscopy and roughness tests. Besides, annealing treatment can enhance the crystallinity X _c of all etched samples which plays a predominant role in the increase of roughness within 2 h. As etching time increases, chain scission and destruction of amorphous parts happen and roughness increases a lot for chromic acid-treated samples, but for sulfuric acid- and nitric acid-treated samples, the destruction of amorphous parts may not happen so that the roughness has not many changes.     

Highly renewable,thermoplastic tetrapolyesters based on hydroquinone,p‐hydroxybenzoic acid or its derivatives,phloretic acid,and dodecanedioic acid

A series of tetrapolyesters were obtained by polymerizing phloretic acid, hydroquinone, p‐hydroxybenzoic acid, or its derivatives, that is, vanillic acid or syringic acid, and dodecanedioic acid. Each monomer was polymerized in its acetylated form, except for the diacid to undergo polymerization by acidolysis. Initial polymerizations had shown that the use of phloretic acid resulted in better polymer properties than with p‐coumaric acid. The predominantly renewable polymers were obtained by melt polymerization using a two‐stage condensation process whereby antimony(III) oxide was applied as catalyst. Monomer conversions were typically close to 90%. ¹H and ¹³C NMR, DSC, TGA, solution viscometry, and GPC were applied, as well as polarized microscopy to determine polymer microstructure and composition, transition temperatures, decomposition temperatures, intrinsic viscosities, and other molecular weight properties, and when applicable the liquid crystalline behavior of the polymers. All peaks, including end group peaks in the ¹³C NMR spectra were assigned, the monomer sequence distribution was verified to be random, and a complete dyad analysis involving nine dyads and eight peaks was performed. By using p‐hydroxybenzoic acid and its derivatives without any, one or two methoxy groups and varying the copolymer compositions, melting temperatures could be tuned between 106 and 181 °C. The tetrapolyesters, which included residues of p‐hydroxybenzoic acid, formed nematic liquid crystals. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1498–1507     

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

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 pi-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 classified as the resonance-assisted hydrogen bonds (RAHBs), it seems that the dominant contribution from the delocalization interaction energy term is a distinguished feature of such interactions.