DL-thioctic Acid Research Articles

Ultrahighly Sensitive and Selective Glutathione Sensor Based on Carbon Dot-Functionalized Solution-Gate Graphene Transistor.

A new type of carbon dot (CD)-functionalized solution-gated graphene transistor (SGGT) sensor was designed and fabricated for the highly sensitive and highly selective detection of glutathione (GSH). The CDs were synthesized via a one-step hydrothermal method using DL-thioctic acid and triethylenetetramine (TETA) as sources of S, N, and C. The CDs have abundant amino and carboxyl groups and were used to modify the surface of the gate electrode of SGGT as probes for detecting GSH. Remarkably, the CDs-SGGT sensor exhibited excellent selectivity and ultrahigh sensitivity to GSH, with an ultralow limit of detection (LOD) of up to 10-19 M. To the best of our knowledge, the sensor outperforms previously reported systems. Moreover, the CDs-SGGT sensor shows rapid detection and good stability. More importantly, the detection of GSH in artificial serum samples was successfully demonstrated.

Carbon Dot-Functionalized Solution-Gated Graphene Transistors for Highly Sensitive Detection of Cobalt(II) Ions

A carbon dot-functionalized solution-gated graphene transistor (CD-SGGT) was designed and prepared via the modification of CDs on the gate of SGGT. The above CDs were hydrothermally synthesized using DL-thioctic acid and triethylenetramine as C, N and S sources. The average size of CDs was ~6.2 nm, and there were many amino and carboxyl groups on the CDs’ surfaces. The CDs was then used as a probe for preparation of CD-SGGT sensor for the cobalt(II) (Co2+) ions detection. The CD-SGGT sensor showed excellent sensitivity and high selectivity. Remarkably, the limit of detection (LOD) reached 10−19 M. The linear detection range was obtained from 10−19 to 10−15 M. Additionally, the CD-SGGT also showed fast response and good stability.

N and S doped carbon dots as novel probes with fluorescence enhancement for fast and sensitive detection of Cr(VI)

Cr(VI) is a toxic heavy metal, which is not readily decomposed and ingested by bacteria. Therefore, there is an urgent need for a sensing method with high selectivity and high sensitivity to detect Cr(VI) in other widely distributed metal ions. Here, a fluorescent probe based on carbon dots (CDs) was developed, with the characteristics of low cost, low environmental impact, high stability, and good water solubility. Although many sensors have been reported for the detection of Cr(VI), most of them are based on the quenching fluorescence method, whereas the one reported here is based on fluorescence enhancement, for which o-phenylenediamine and dl-Thioctic acid were used as raw materials. The transmission electron microscopy, Fourier infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and ultraviolet-visible spectroscopy measurements showed that Cr(VI) can significantly enhance the fluorescence of the probe compared to previous sensors, as the obtained CDs have excellent fluorescence properties (quantum yield up to 21.82%) and high light stability. The detection limit of the probe for Cr(VI) is as low as 0.64 μM, indicating that the developed probe can detect Cr(VI) quickly, sensitively, and selectively, and has broad application prospects in environmental analysis applications. To facilitate rapid detection of Cr(VI), the CDs were also incorporated into a fluorescent composite film suitable for visual inspection.

Determining the parameters governing the electrochemical stability of thiols and disulfides self-assembled monolayer on gold electrodes in physiological medium

Herein we study the electrochemical potential-dependent and time-dependent stability of thiols and disulfides as self-assembled monolayers on gold electrodes. The stability of four representative sulfur-containing compounds: 3-mercaptopropionic acid, 2-mercaptoethanol, 1,4-dithiothreitol and dl-thioctic acid, was assessed in simulated physiological conditions (i.e. phosphate buffer saline). The stability of these molecules was evaluated using cyclic voltammetry and step-potential chronoamperometry. Coordination of the thiols and disulfides significantly affects the stability of the self-assembled monolayer. In addition, studies performed using gold single crystal (100) and (111) electrodes show the superior binding strength of the SAM on the Au(100) surface structure.

Controlled co-delivery nanocarriers based on mixed micelles formed from cyclodextrin-conjugated and cross-linked copolymers

The combination of multiple drugs within a single nanocarrier can provide significant advantages for disease therapy and it is desirable to introduce a second drug based on host–guest interaction in these co-delivery systems. In this study, a core-stabilized mixed micellar system consisting of β-cyclodextrin-conjugated poly(lactic acid)-b-poly(ethylene glycol) (β-CD-PLA-mPEG) and DL-Thioctic acid (TA) terminated PLA-mPEG (TA-PLA-mPEG) was developed for the co-delivery of DOX and fluorescein isothiocyanate labeled adamantane (FA). DOX can be loaded within the hydrophobic segment of PLA and FA may form stable complexation with β-CD in the core. The mixed micelles (MM) are based on well-accepted medical materials and can be easily cross-linked by adding 1,4-dithio-d,l-threitol (DTT), which can enhance the stability of the system. Drug-loaded MM system was characterized in terms of particle size, morphology, drug loading and in vitro release profile. Cytotoxicity test showed that blank MM alone showed negligible cytotoxicity whereas the drug-loaded MM remained relatively high cytotoxicity for HeLa cancer cells. Confocal laser scanning microscopy (CLSM) demonstrated that the MM could efficiently deliver and release DOX and FA in the same tumor cells to effectively improve drugs’ bioavailability. These results suggested that the core-stabilized MM are highly promising for intracellular co-delivery of multiple drugs.

Self-assembled monolayers of thiols adsorbed on Au/ZnO-functionalized silica nanosprings: photoelectron spectroscopy-analysis and detection of vaporized explosives.

Self-assembled monolayers (SAMs) of thiols of L-cysteine, 6-mercaptohexanol, 4-mercaptobenzoic acid, DL-thioctic acid and 11-(1-pyrenyl)-1-undecathiol, which have been selected for their propensity to interact with vaporized explosives, have been attached from solution onto gold decorated ZnO-coated nanosprings. X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) have been used to investigate the surface electronic structure of the SAMs coated nanosprings. On the basis of XPS analysis, it has been determined that the packing densities of L-cysteine, 6-mercaptohexanol, 4-mercaptobenzoic acid, DL-thioctic acid and 11-(1-pyrenyl)-1-undecathiol on gold (zinc oxide) are 5.42 × 10(14) (2.83 × 10(14)), 3.26 × 10(14) (2.54 × 10(14)), 9.50 × 10(13), 2.55 × 10(14) (1.12 × 10(14)), and 5.23 × 10(13) molecules/cm(2), respectively. A single S 2p core level doublet is observed for 4-mercaptobenzoic acid and 11-(1-pyrenyl)-1-undecathiol, which is assigned to the S-Au bond. The S 2p core level for L-cysteine, 6-mercaptohexanol, and DL-thioctic acid consist of two doublets, where one is S-Au bond and the other is the S-Zn bond. Analysis of the C/S ratios agrees well with the stoichiometry of the respective thiols. UPS analysis shows that the hybridization of S 3p states and Au d-bands produces antibonding and bonding states, above and below the Au d-bands, which is characteristic of molecular chemisorption on Au nanoparticles. Gas sensors were constructed with thiolated nanosprings and their responsiveness to ammonium nitrate at 100-150 °C was tested. Nanosprings sensors functionalized with 4-mercaptobenzoic acid and 6-mercaptohexanol showed the strongest responses by a factor of 4 to 5 relative to the less responsive thiols. The response to ammonium nitrate can be correlated to the packing density and ordering of the SAMs.

Synthesis and characterization of dl-thioctic acid (DLTA)–Fe 3O 4 nanocomposite

dl-Thioctic acid (DLTA) coated magnetite (Fe 3O 4) NP's have been prepared by the co-precipitation of iron oxide in the presence of DLTA. The product identified as magnetite, which has an average crystallite size of 7 ± 2 nm as estimated from X-ray line profile fitting. Particle size was estimated as 11 ± 1 nm from TEM micrographs. FT-IR analysis showed that the binding of DLTA on the surface of iron oxide is through carboxyl group is bidentate. VSM analysis explained the super-paramagnetic nature of the nanocomposite. TG analysis showed that the 80% of the nanocomposite was DLTA and 10% was Fe 3O 4, respectively. The conductivity measurements displayed the magnetic transition at ∼60 °C for DLTA–Fe 3O 4 NPs. Analysis of the conductivities reveals the fact that the a.c. conductivity shows a frequency-dependent behavior while d.c. electrical conductivity is strongly temperature dependent and is classified into two regions over a limited temperature range of up to 120 °C. Toxicity was tested measured by LDH assay.

Myogenic Satellite Cell Proliferative and Differentiative Responses to Components of Common Oral Ergogenic Supplements

This study evaluated the ability of common ergogenic supplement components to alter satellite cell proliferative activity in vitro. Compounds studied were cinnamic acid, ferulic acid, L-glutathione, β-hydroxybutyric acid, calcium-β-hydroxy-β-methylbutyrate monohydrate, DL-thioctic acid (α-lipoic acid), and ornithine α-ketoglutarate. Satellite cells were exposed to different levels of ergogenic test compound for a specified amount of time and analyzed by counting mononucleated and multinucleated cells. At the levels evaluated, none of these compounds altered satellite cell proliferation over that of control cultures (p > 0.05). Four of the compounds were shown to alter satellite cell differentiation over control cultures (p < 0.05), but due to the small amounts of fusion, the biological relevance is in question (e.g. differences in small numbers). These data suggest that a few of the ergogenic compounds examined by this laboratory do influence satellite cell activity in vitro. However, additional studies are vital in order to define the biological relevance of our observations.

Electrogenerated chemiluminescence of lucigenin enhanced by the modifications of electrodes with self-assembled monolayers and of solutions with surfactants

Electrogenerated chemiluminescence (ECL) of lucigenin (Luc 2+·2NO − 3, N, N′-dimethyl-9,9′-biacridinium dinitrate) in dioxygen-saturated alkaline aqueous solutions of pH 10 has been examined utilizing modifications of electrodes (i.e. self-assembled monolayer (SAM)-modified gold electrodes) and of solutions (i.e. micellar solutions containing a nonionic surfactant, Triton X-100) for the first time. In both cases of the modifications, enhanced ECL was observed, and the ECL was considered to be derived from the decomposition of a dioxetane-type intermediate formed by the radical–radical coupling reaction between an electrogenerated superoxide ion (O 2 − ) and a one-electron reduced form of Luc 2+ (i.e. a radical cation, Luc + ). The surface modification of gold electrodes was achieved with dimercaptosuccinic acid (DMSA) and dl-thioctic acid ( dl-TA) having carboxyl end groups. The amount of ECL at dl-TA-SAM-modified electrodes was about five times as great as that at the bare electrode. The enhancement of ECL at the SAM-modified electrodes would be due to the concentration effect of positively charged Luc 2+ ions, the prevention of adsorption of the electrogenerated chemiluminescent product (i.e. N-methylacridone (NMA)) and the two-electron reduced form of Luc 2+ (Luc 0) on the electrode surfaces, and the effective generation of O 2 − . On the other hand, the amount of ECL in the micellar solution increased by about six times in comparison with that in the solution containing no surfactant. The enhanced ECL in micellar solutions would result mainly from the inhibition of adsorption of NMA and Luc 0 insoluble in water on electrode surfaces.

Inactivation of Lipoamide Dehydrogenase by Cobalt(II) and Iron(II) Fenton Systems: Effect of Metal Chelators, Thiol Compounds and Adenine Nucleotides

Fe(II)- and Co(II)-Fenton systems (FS) inactivated the lipoamide reductase activity but not the diaphorase activity of pig-heart lipoamide dehydrogenase (LADH). The Co(II) system was the more effective as LADH inhibitor. Phosphate ions enhanced the Fe(II)-FS activity. EDTA, DETAPAC, DL-histidine, DL-cysteine, glutathione, DL-dithiothreitol, DL-lipoamide, DL-thioctic acid, bathophenthroline, trypanothione and ATP, but not ADP or AMP, prevented LADH inactivation. Reduced disulfide compounds were more effective protectors than the parent compounds. Mg ions counteracted ATP protective action. Glutathione and DL-dithiothreitol partially restored the lipoamide dehydrogenase activity of the Fe(II)-FS-inhibited LADH. DL-histidine exerted a similar action on the Co(II)-FS-inhibited enzyme. Ethanol, mannitol and benzoate did not prevent LADH inactivation by the assayed Fenton systems and, accordingly, it is postulated that site-specific generated HO. radicals were responsible for LADH inactivation. With the Co(II)-FS, oxygen reactive species other than HO., might contribute to LADH inactivation.

アルミニウム合金の孔食に及ぼす有機系食品添加物の影響

The effects of organic food additives on pitting corrosion of aluminum alloys were studied in a neutral solution of sodium chloride. The advance of corrosion was estimated by time variation of the rest potential, anodic and cathodic polarization curves and polarization resistance. Pit depth was evaluated with an optical microscope and photoacoustic spectroscopy (PAS) was newly applied to evaluate the spatial distribution of corrosion pits.Results obtained were as follows.1) Organic substances that showed an inhibiting effect, decreasing the maximum pit depth, were: for 3003 alloy DL-thioctic acid, caffein anhydride and L-tryptophan; for 5052 alloy casein; and for 6063 alloy pyridoxine hydrochloride and hydantoin.2) In the presence of an organic substance as pitting corrosion inhibitor, obtained corrosion potential at pH7 shifted to the noble side, and these results support the evaluated results for the maximum pit depth.In an acid solution of pH3, obtained corrosion current decreased in the presence of the organic substance. These results suggests the possibility of an inhibitive effect inside the pits as well as outside the pits.

Determination of thioctic acid by adsorptive stripping voltametry.

DL-Thioctic acid (α-lipoic acid) is adsorbed on a mercury electrode in the potential region more positive than ca. -0.4 V vs. SCE and yields a reduction peak at ca. -0.6 V. The adsorption of thioctic acid is employed in the preconcentration step of the stripping voltammetry of thioctic acid (adsorptive stripping voltammetry). From the fundamental studies it was found that in 0.1 M ammonium acetate the stripping peak height for thioctic acid was maximum. The optimal preconcentration potential, preconcentration time, scan rate and temperature are -0.2 V, 5 min, 50 mV/s and 25 °C, respectively. Under the optimum conditions described above, the calibration curve is linear up to 1.6 μM and the detection limit is 0.1 μM. Thioctic acid and riboflavin in milk were determined by this method.

Evidence for Facilitated Transport of Biotin by Hamster Enterocytes

The uptake of biotin by isolated hamster intestinal cells was investigated in the zone of physiological concentrations. Uptake of the vitamin was not a linear function of the external concentrations and kinetics could be saturated [Km = 1.12 µm, Vmax = 33.9 pmol/(mg protein·min)]. Metabolic inhibitors (antimycin A, 2,4-dinitrophenol) had no effect, so uptake is not energy dependent. Ouabain and N-ethylmaleimide, inhibitors of cation gradients, had no effect on biotin uptake, thus showing the absence of cotransport. The inhibition of uptake by analogs of biotin, that is, biocytin and dl-thioctic acid, indicates that the terminal carboxyl group and the thiophane ring play a role in the recognition of biotin. Counterflow experiments showed competitive inhibition of efflux when excess biotin was present in the cells. These findings are consistent with biotin uptake by isolated hamster enterocytes being a process of facilitated diffusion.

Charge Transfer Properties of dl-Thioctic Acid and Other Disulphides

THE ability of organic sulphur compounds to act as donors with electron acceptor molecules is well established. As far as disulphides are concerned, previous studies have been limited to simple aliphatic compounds with iodine as the acceptor1. In these systems, the charge transfer (CT) band appears between the disulphide absorption and the blue-shifted iodine absorption, and its position appears to be little affected by changing the alkyl groups. We wish to report that alkyl aryl and cyclic disulphides form 1 : 1 complexes in solution with tetracyanoethylene (TCNE), which show well-separated CT bands in the visible region. Further, the position of these bands clearly reflects steric and electronic factors in the disulphide molecule.

The toxicity of 2-mercaptoethylamine to Saccharomyces carlsbergensis and its reversal

2-Mercaptoethylamine (cysteamine, 2-aminoethanethiol) inhibited the growth of Saccharomyces carlsbergensis (A.T.C.C. 4228); the toxicity was found to be alleviated by a variety of compounds, such as β-alanine and its related compounds, dl-penicillamine, the intermediates of the tricarboxylic acid cycle and their related compounds, malonic acid, dl-thioctic acid, kojic acid, soybean phospholipides, orthophosphoric acid, organic phosphates, and inorganic salts. The degree of growth inhibition by 2-mercaptoethylamine also decreased as the pH of the assay medium changed from 5.5 to 3.0. The results have been interpreted to mean: ( a) 2-Mercaptoethylamine forms a complex with a metallic ion (especially a bivalent one) which is essential for the growth of S. carlsbergensis, thus causing growth inhibition. ( b) As the pH of the medium decreases, the fraction of a metal ion bound with 2-mercaptoethylamine also diminishes, thus causing poor growth inhibition, ( c) A type of reversing agent competes with 2-mercaptoethyl-amine for a metal, and the complex thus formed with the former is able to donate the metal for the growth of the organism. Results showed that such competition can take place solely in vitro. ( d) Another type of reversing agent saturates the active sites in 2-mercaptoethylamine and thus the mercapto compound can no longer function as an inhibitor.

Failure of Thioctic Acid to Stimulate Chick Growth ,

Stokstad, Broquist and Patterson (1953) reported that they were unable to obtain significant growth increases in chicks by the addition of dl-thioctic acid (lipoic acid) to the diet, either in the absence or the presence of aureomycin or sulfasuxidine. DeBusk and Williams (1955), on the other hand, presented evidence that dl-thioctic acid stimulated the growth or food utilization or both of chicks and rats fed purified diets, and chicks fed a corn-soybean meal diet containing alfalfa meal or a commercial chick starter. Except for slower growth, no symptoms of a thioctic acid deficiency were observed in the animals fed the experimental diets.In an attempt to reconcile the discrepancy in the results of these investigators, this laboratory conducted two experiments, one with crossbred New Hampshire × Barred Plymouth Rock chicks of mixed sex, hatched from the eggs of hens fed a corn-soybean meal diet and depleted of unidentified factors, and …

Failure to obtain growth responses with thioctic acid in chicks from different sources

dl-Thioctic acid was added to two different purified and one practical chick ration and fed to chicks of three different genetic sources and from dams fed different diets without effect as measured by growth and feed efficiency.