Antibacterial drugs as environmentally-friendly corrosion inhibitors for carbon steel in acid medium

The effect of cefazolin (CZ) and cefotaxime (CT) as corrosion inhibitors for carbon steel in 0.5 M H₂SO₄ solution was investigated by use of potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM), and scanning electron microscopy (SEM). CZ and CT acted as mixed-type inhibitors. Inhibition increased with increasing inhibitor concentration and decreased with increasing temperature. Adsorption of the inhibitors obeyed the Langmuir adsorption isotherm. SEM confirmed inhibition by the inhibitors. Inhibition by 5 × 10^?4 M CZ and 7 × 10^?4 M CT approached 99.6 % and 90.9 %, respectively. The EIS and EFM results were in good agreement with the potentiodynamic data.     

Intercalation of Mg–Al layered double hydroxides by l-proline: synthesis and characterization

The intercalations of l-proline into Mg–Al layered double hydroxides (LDH-CO₃) have been prepared by three different methods: calcine-recovering, coprecipitation and anion exchange. The products thus obtained have been characterized by several experimental techniques: XRD, FT-IR and DSC-TG. The results show that the original interlayer carbonate ions can be replaced by the organic anions under the controlled conditions. The interlayer spaces of the materials are expanded to 0.86, 1.12 and 1.07 nm. l-proline entered into the layers as vertical and horizontal, the molecules of l-proline may stay in the layers in a bilayer with the carboxylate groups pointing towards the LDHs layers, and the structure models are shown. The crystal has a good regularity of the layered structure, which increases thermal stability of l-proline, and thermal analysis confirms that the intercalation can make l-proline stable up to 429 °C, which is 200 °C higher than that for pure l-proline.     

Thermodynamic study of metal corrosion and inhibitor adsorption processes in copper/N-1-naphthylethylenediamine dihydrochloride monomethanolate/nitric acid system: part 2

N-1-Naphthylethylenediamine dihydrochloride monomethanolate (N-NEDHME) was tested as a corrosion inhibitor for copper in 2 M HNO₃ solution using the standard gravimetric technique at 303–343 K. N-NEDHME acts as an inhibitor for copper in an acidic medium. Inhibition efficiency increases with increase in concentration of N-NEDHME but decreases with a rise in temperature. Thermodynamic parameters such as adsorption heat ( $ \Updelta H_{\text{ads}}^\circ $ ), adsorption entropy ( $ \Updelta S_{\text{ads}}^\circ $ ) and adsorption free energy ( $ \Updelta G_{\text{ads}}^\circ $ ) were obtained from experimental data of the temperature studies of the inhibition process at five temperatures ranging from 303 to 343 K. Kinetic parameters activation such as $ E_{a} $ , $ \Updelta H_{\text{a}}^\circ $ , $ \Updelta S_{\text{a}}^\circ $ and pre-exponential factors have been calculated and are discussed. Adsorption of N-NEDHME on the copper surface in 2 M HNO₃ follows the Langmuir isotherm model.     

Crystal structure and thermodynamic properties of dipotassium diiron(III) hexatitanium oxide

In the present work, the temperature dependence of heat capacity of dipotassium diiron(III) hexatitanium oxide has been measured for the first time in the range from 10 to 300 K by means of precision adiabatic vacuum calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity $ C_{p}^{ \circ } (T) $ , enthalpy $ H^{ \circ } (T) - H^{ \circ } (0) $ , entropy $ S^{ \circ } (T) - S^{ \circ } (0), $ and Gibbs function $ G^{ \circ } (T) - H^{ \circ } (0) $ for the range from T → 0 to 300 K. The structure of K₂Fe₂Ti₆O₁₆ is refined by the Rietveld method: space group I4/m, Z = 1, a = 10.1344(2) Å, c = 2.97567(4) Å, V = 305.618(7) Å³. The high-temperature X-ray diffraction was used for the determination of coefficients of thermal expansion.     

Thermochemistry of hydroxymethylphenol isomers

The standard (p° = 0.1 MPa) molar enthalpies of formation in the crystalline state of the 2-, 3- and 4-hydroxymethylphenols, $ {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{cr)}} = \, - ( 3 7 7. 7 \pm 1. 4)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ , $ {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{cr) }} = - (383.0 \pm 1.4) \, \,{\text{kJ}}\,{\text{mol}}^{ - 1} $ and $ {{\Updelta}}_{\text{f}} H_{\text{m}}^{\text{o}} ( {\text{cr)}} = - (382.7 \pm 1.4)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ , respectively, were derived from the standard molar energies of combustion, in oxygen, to yield CO₂(g) and H₂O(l), at T = 298.15 K, measured by static bomb combustion calorimetry. The Knudsen mass-loss effusion technique was used to measure the dependence of the vapour pressure of the solid isomers of hydroxymethylphenol with the temperature, from which the standard molar enthalpies of sublimation were derived using the Clausius–Clapeyron equation. The results were as follows: $ \Updelta_{\rm cr}^{\rm g} H_{\rm m}^{\rm o} = (99.5 \pm 1.5)\,{\text{kJ}}\,{\text{mol}}^{ - 1} $ , $ \Updelta_{\rm cr}^{\rm g} H_{\rm m}^{\rm o} = (116.0 \pm 3.7) \,{\text{kJ}}\,{\text{mol}}^{ - 1} $ and $ \Updelta_{\rm cr}^{\rm g} H_{\rm m}^{\rm o} = (129.3 \pm 4.7)\,{\text{ kJ mol}}^{ - 1} $ , for 2-, 3- and 4-hydroxymethylphenol, respectively. From these values, the standard molar enthalpies of formation of the title compounds in their gaseous phases, at T = 298.15 K, were derived and interpreted in terms of molecular structure. Moreover, using estimated values for the heat capacity differences between the gas and the crystal phases, the standard (p° = 0.1 MPa) molar enthalpies, entropies and Gibbs energies of sublimation, at T = 298.15 K, were derived for the three hydroxymethylphenols.     

Experimental study of inhibition of corrosion of mild steel in 1 M HCl solution by two newly synthesized calixarene derivatives

Inhibition of the corrosion of mild steel in molar hydrochloric acid by two calixarenes, including the effect of inhibitor concentration and temperature, has been investigated by use of weight loss and electrochemical measurements (polarisation and impedance). The results obtained showed that the rate of corrosion decreased substantially in the presence of the compounds, with maximum inhibition of 98.2 % by one of the compounds at a concentration of 10^?3 M. The effect of temperature on corrosion behaviour in the presence of different concentrations of the two new calixarenes was studied in the range 45–75 °C. The efficiency of inhibition by the compounds increased with increasing inhibitor concentration and was independent of temperature. Polarisation curves revealed that the calixarenes are mixed-type inhibitors. Adsorption of the inhibitors by the carbon steel surface obeyed the Langmuir adsorption isotherm. Some thermodynamic data for the dissolution and adsorption processes were also determined.     

Comparison of ordered mesoporous materials sorption properties towards amino acids

The adsorption of amino acids such as l-phenylalanine and l-histidine was carried out on a series of mesoporous carbons obtained with the use ordered silicas KIT-6, SBA-16, SBA-15 as templates and furfuryl alcohol as carbon precursor. Small angle XRD analysis confirmed the ordered mesoporous structures of all materials obtained. They were also characterised by well-developed surface areas and high pore volumes. Adsorption behaviour of amino acids on ordered mesoporous carbons was investigated in potassium phosphate buffer solutions with adjustable l-phenylalanine and l-histidine concentration, ion strength, and pH. The highest sorption capacity towards the amino acids were observed at pH close to the isoelectric point of l-phenylalanine (pI = 5.48) and l-histidine (pI = 7.59). Electrostatic, hydrophobic and steric interactions had very strong effect on the adsorption of amino acids on mesoporous carbons. The amount of l-phenylalanine and l-histidine adsorbed decreased in the following sequence: C_KIT-6 > C_SBA-16 > C_SBA-15 that was strongly related to their structure, surface areas and average pore diameters.     

Experimental and DFT study on complexation of Eu3+ with a macrocyclic lactam receptor

From extraction experiments and $ \gamma $ -activity measurements, the extraction constant corresponding to the equilibrium $ {\text{Eu}}^{ 3+ } \left( {\text{aq}} \right) + 3 {\text{A}}^{ - } \left( {\text{aq}} \right) + {\mathbf{1}}\left( {\text{nb}} \right) \Leftrightarrow {\mathbf{1}} \cdot {\text{Eu}}^{ 3+ } \left( {\text{nb}} \right) + 3 {\text{A}}^{ - } \left( {\text{nb}} \right) $ taking place in the two-phase water–nitrobenzene system ( $ {\text{A}}^{ - } = \text {CF}_{3} \text{SO}_{3}^{ - } $ ; 1 = macrocyclic lactam receptor—see Scheme 1; aq = aqueous phase, nb = nitrobenzene phase) was evaluated as $ { \log } K_{{{\text{ex}} }} ({\mathbf{1}} \cdot {\text{Eu}}^{ 3+ } ,{\text{ 3A}}^{ - } )\; = \; - 4. 9 \pm 0. 1 $ . Further, the stability constant of the 1·Eu³⁺ cationic complex in nitrobenzene saturated with water was calculated for a temperature of 25 °C: $ { \log } \beta_{{{\text{nb}} }} ({\mathbf{1}} \cdot {\text{Eu}}^{ 3+ } ) \; = \; 8. 2 \pm 0. 1 $ . Finally, using DFT calculations, the most probable structure of the cationic complex species 1·Eu³⁺ was derived. In the resulting 1·Eu³⁺ complex, the “central” cation Eu³⁺ is bound by five bond interactions to two ethereal oxygen atoms and two carbonyl oxygens, as well as to one carbon atom of the corresponding benzene ring of the parent macrocyclic lactam receptor 1 via cation-π interaction.

Calorimetric study of poly(2-ethylhexyl acrylate) over the range from T → 0 to 350 K

For the first time, the heat capacity $ C_{\text{p}}^{^\circ } $ of poly(2-ethylhexyl acrylate) has been studied in an adiabatic vacuum calorimeter between 7 and 350 K, the standard thermodynamic functions: heat capacity $ C_{\text{p}}^{^\circ } $ (T), enthalpy H°(T) ? H°(0), entropy S°(T) ? S°(0), Gibbs function G°(T) ? H°(0) have been calculated from T → 0 to 350 K. The energy of combustion Δ_c U of the compound under study has been measured in a calorimeter with a stationary bomb and an isothermal shell. The standard enthalpy of combustion Δ_c H° and thermodynamic parameters of formation—enthalpy Δ_f H°, entropy Δ_f S°, Gibbs function Δ_f G°—at T = 298.15 K have been calculated. The results have been used to calculate the thermodynamic characteristics of 2-ethylhexyl acrylate bulk polymerization into poly(2-ethylhexyl acrylate) over the range from T → 0 to 350 K.     

A Validated Chiral LC Method for the Enantiomeric Separation of Nateglinide and the Quantitative Determination of Its l-Enantiomer

A simple and accurate chiral liquid chromatographic method was developed for the enantiomeric purity determination of d-nateglinide and quantitative determination of l-nateglinide in bulk drug samples. Good resolution (R _s  > 6.0) between d-enantiomer and l-enantiomer of nateglinide were achieved with Chiralpak AD-H (250 × 4.6 mm, 5 μm particle size) column using hexane and ethanol (90:10 v/v) as mobile phase at 25 °C temperature. Flow rate was kept as 1.0 mL min^?1 and elution was monitored at 210 nm. The effects of the mobile phase composition, the flow rate and the temperature on the chromatographic separation were investigated. Developed method is capable to detect (LOD) and quantitate (LOQ) l-nateglinide to the levels of 0.3 and 1.0 μg mL^?1 respectively, for 10 μL injection volume. The percentage RSD of the peak area of six replicate injections of l-nateglinide at LOQ concentration was 5.2. The percentage recoveries of l-nateglinide from d-nateglinide ranged from 97.9 to 99.7. The test solution and mobile phase was found to be stable up to 24 h after preparation. The developed method was validated with respect to LOD, LOQ, precision, linearity, accuracy, robustness and ruggedness.     

Quantum chemical study of inhibition of the corrosion of mild steel in 1 M hydrochloric acid solution by newly synthesized benzamide derivatives

The inhibitory effect of some new synthesized benzamide compounds on corrosion of mild steel in 1 M HCl solution has been studied by use of weight loss measurements and the electrochemical techniques potentiodynamic polarization and electrochemical impedance spectroscopy. The inhibiting action is more pronounced with increasing concentration. Inhibition efficiency is maximum (approximately 99 %) at 10^?3 M. Polarization measurements also show that the compounds act as mixed inhibitors. The cathodic curves indicate that reduction of protons at the mild steel surface occurs as a result of a pure activating mechanism. EIS measurements reveal increased transfer resistance with increasing inhibitor concentration. The presence of heteroatoms increases inhibition efficiency without causing a drastic change in adsorption mechanism, which follows the Langmuir isotherm model. Significant correlations were obtained between inhibition efficiency with the chemical indexes calculated, by use of the standard software Gaussian03, on the basis of density functional theory (DFT) at the B3LYP/6-31G** level of theory, indicating that variation of inhibition with inhibitor structure may be explained in terms of electronic properties. The effect of temperature on the corrosion behaviour of steel in 1 M HCl without and with inhibitors at 10^?3 M was studied in the temperature range from 308 to 333 K, and the associated activation energy was determined.     

Characteristics of α-l-Arabinofuranosidase from Streptomyces sp I10-1 for Production of l-Arabinose from Corn Hull Arabinoxylan

Streptomyces sp I10-1 α-l-arabinofuranosidase efficiently produced l-arabinose from high arabinose-content corn hull arabinoxylan (ratio of arabinose to xylose, 0.6). The optimum pH at 40 °C was around 6, and the enzyme was stable from pH 5 to 11. The optimum temperature was 50 °C at pH 5, and the activity was stable at 40 °C. The enzymatic activity against corn hull arabinoxylan was 2.3 times higher than towards p-nitrophenyl-α-l-arabinofuranoside. Approximately 45 % l-arabinose recovery was achieved from corn hull arabinoxylan. It was considered that l-arabinose residues not removed by the enzyme were attributable to those linked with ferulic acid. The open reading frame of the enzyme gene consisted of 1,224 bp, and the predicted peptide was 408 amino acids, which corresponded to a molecular size of 45, 248 Da. It was presumed that the smaller molecular size (31,000 Da) estimated on SDS-PAGE resulted from proteolysis by proteases. I10-1 α-l-arabinofuranosidase belongs to the Alpha-l-AF C superfamily, which is associated with glycoside hydrolase family 51, but the properties were unique.     

Exploiting thermodynamic data to optimize the enantioseparation of underivatized amino acids in ligand exchange capillary electrophoresis

Stereoselective amino acid analysis has increasingly moved into the scope of interest of the scientific community. In this work, we report a study on the chiral separation of underivatized d,l-His by ligand exchange capillary electrophoresis (LECE), utilizing accurate ex ante calculations. This has been obtained by the addition to the background electrolytes (BGE) of NaClO₄ which renders the separations “all in solution processes”, allowing to accurately calculate in advance the concentrations of the species present in solution and to optimize the system performances. To this aim, the formation of ternary complexes of Cu²⁺ ion and l-lysine (l-Lys) or l-ornithine (l-Orn) with l- and d-histidine (His), and histamine (Hm) have been studied by potentiometry and calorimetry at 25 °C and with 0.1 mol dm^?3 (KNO₃) in aqueous solution. The ternary species [Cu(L)(l-His)H]⁺ and [Cu(L)(d-His)H]⁺ (where L?=?l-Lys or l-Orn) show a slight but still detectable stereoselectivity, and the determination of ΔH° and ΔS° values allowed the understanding of the factors which determine this phenomenon. The stereoselectivity showed by the protonated ternary species has been exploited to chirally separate d,l-His in LECE, by using the binary complexes of copper(II) with l-Lys or l-Orn as background electrolytes added with the appropriate amounts of NaClO₄.

Thermodynamic properties of crystalline magnesium zirconium phosphate

Heat capacity $ C_{\text{p}}^{^\circ } $ (T) of crystalline magnesium zirconium phosphate was measured between 6 and 815 K. The experimental data obtained were used to calculate the standard thermodynamic functions $ C_{\text{p}}^{^\circ } $ (T), H°(T) ? H°(0), S°(T), G°(T) ? H°(0) over the temperature ranging from T → 0 to 810 K and standard entropy of formation at 298.15 K. The fractal dimension of Mg_0.5Zr₂(PO₄)₃ was calculated from experimental data on the low-temperature (6 ≤ T/K ≤ 50) heat capacity, and the topology of the phosphate’s structure was estimated. Thermodynamic properties of structurally related phosphates M_0.5Zr₂(PO₄)₃ (M = Mg, Ca, Sr, Ba, Ni) were compared.     

Interactions of some protonated α-amino acid methyl esters with hexaethyl p-tert-butylcalix[6]arene hexaacetate in nitrobenzene saturated with water

The exchange extraction constants corresponding to the general equilibrium C⁺(aq) + 1·Cs⁺(nb) ? 1·C⁺ (nb) + Cs⁺(aq) occurring in the two-phase water–nitrobenzene system (C⁺ = protonated α-amino acid methyl ester, 1 = hexaethyl p-tert-butylcalix[6]arene hexaacetate; aq = aqueous phase, nb = nitrobenzene phase) were evaluated on the basis of extraction experiments and γ-activity measurements. Further, the stability constants of the 1·C⁺ cationic complex species in nitrobenzene saturated with water were calculated; they were found to increase in the following cation order: protonated l-tryptophan methyl ester < protonated l-phenylalanine methyl ester < protonated l-leucine methyl ester < protonated l-methionine methyl ester < protonated l-valine methyl ester.     

Simultaneous Determination of Ten Sugars in Tinospora cordifolia by Ultrasonic Assisted Extraction and LC-ELSD

Sugars present in medicinal plants are known for protecting and stimulating the immune system against various biological disorders. Tinospora cordifolia is a reputed Indian herb used for immunity enhancing which is mainly attributed to saccharides. In the present study, a simple, sensitive, and reliable liquid chromatography method based on ultrasonic assisted extraction and evaporative light scattering detection was developed for simultaneous determination of ten sugars comprising of monosaccharides (l-(+)-rhamnose, d-(+)-xylose, d-(?)-arabinose, β-d-(+)-glucose), disaccharides (sucrose, d-(+)-cellobiose, α-lactose), alditols (xylitol, d-(+)-mannitol) and a polyalcohol (myo-inositol) in T. cordifolia. The separation was achieved on Zorbax-NH₂ column (250 mm × 4.6 mm, 5 µm) in gradient elution of acetonitrile: water as mobile phase with flow rate of 0.5 mL min^?1. The drift tube temperature and nitrogen flow-rate were optimized at 70 °C and 2.0 standard litres per minute, respectively. The method was validated for linearity, accuracy, precision, limits of detection and quantification. The calibration equation revealed a good linear relationship (r ²  = 0.959–0.999). The sufficient recovery was observed in the range of 94.1–99.9%. The method showed good reproducibility with intra- and inter-day precision of <0.99 and 0.97% (RSD), respectively. The detection and quantification limits for the compounds were in the range of 8.32–44.29 and 25.23–134.20 μg mL^?1, respectively.     

The Formation and Stability of the [FePy3Cl3]· Py Clathrate in the Pyridine–Iron(III) Chloride System: Phase Diagram and Solid–Gas Equilibria Study

The phase diagram of the pyridine–iron(III) chloride system has been studied for the 223–423 K temperature and 0–56 mass-% concentration ranges using differential thermal analysis (DTA) and solubility techniques. A solid with the highest pyridine content formed in the system was found to be an already known clathrate compound, [FePy₃Cl₃]·Py. The clathrate melts incongruently at 346.9 ± 0.3 K with the destruction of the host complex: [FePy₃Cl₃]·Py_(solid)=[FePy₂Cl₃]_(solid) + liquor. The thermal dissociation of the clathrate with the release of pyridine into the gaseous phase (TGA) occurs in a similar way: [FePy₃Cl₃]·Py_(solid)=[FePy2Cl₃]_(solid) + 2 Py_(gas). Thermodynamic parameters of the clathrate dissociation have been determined from the dependence of the pyridine vapour pressure over the clathrate samples versus temperature (tensimetric method). The dependence experiences a change at 327 K indicating a polymorphous transformation occurring at this temperature. For the process ${1 \over 2}[\hbox{FePy}_{3}\hbox{Cl}_{3}]\cdot \hbox{Py}_{\rm (solid)} = {1 \over 2}[\hbox{FePy}_{2}\hbox{Cl}_{3}]_{\rm (solid)} + \hbox{Py}_{\rm (gas)}$ in the range 292–327 K, ΔH $^{0}_{298}$ =70.8 ± 0.8 kJ/mol, ΔS $^{0}_{298}$ =197 ± 3 J/(mol K), ΔG $^{0}_{298}$ =12.2 ± 0.1 kJ/mol; in the range 327–368 K, ΔH $^{0}_{298}$ =44.4 ± 1.3 kJ/mol, ΔS $^{0}_{298}$ =116 ± 4 J/(mol K), ΔG $^{0}_{298}$ =9.9 ± 0.3 kJ/mol.     

l-Ribose Production from l-Arabinose by Immobilized Recombinant Escherichia coli Co-expressing the l-Arabinose Isomerase and Mannose-6-Phosphate Isomerase Genes from Geobacillus thermodenitrificans

l-Ribose is an important precursor for antiviral agents, and thus its high-level production is urgently demanded. For this aim, immobilized recombinant Escherichia coli cells expressing the l-arabinose isomerase and variant mannose-6-phosphate isomerase genes from Geobacillus thermodenitrificans were developed. The immobilized cells produced 99 g/l l-ribose from 300 g/l l-arabinose in 3 h at pH 7.5 and 60 °C in the presence of 1 mM Co²⁺, with a conversion yield of 33 % (w/w) and a productivity of 33 g/l/h. The immobilized cells in the packed-bed bioreactor at a dilution rate of 0.2 h^?1 produced an average of 100 g/l l-ribose with a conversion yield of 33 % and a productivity of 5.0 g/l/h for the first 12 days, and the operational half-life in the bioreactor was 28 days. Our study is first verification for l-ribose production by long-term operation and feasible for cost-effective commercialization. The immobilized cells in the present study also showed the highest conversion yield among processes from l-arabinose as the substrate.     

Estimation of the critical rate of temperature rise for thermal explosion of nitrocellulose using non-isothermal DSC

The expressions to calculate the critical rate of temperature rise of thermal explosion $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ for energetic materials (EMs) were derived from the Semenov’s thermal explosion theory and autocatalytic reaction rate equation of nth order, C_nB, B_na, first-order, apparent empiric-order, simple first-order, A_u, apparent empiric-order of m = 0, n = 0, p = 1 and m = 0, n = 1, p = 1, using reasonable hypotheses. A method to determine the kinetic parameters in the autocatalytic-decomposing reaction rate equations and the $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ in EMs when autocatalytic decomposition converts into thermal explosion from data of DSC curves at different heating rate was presented. Results show that (1) under non-isothermal DSC conditions, the autocatalytic-decomposing reaction of NC (12.97 % N) can be described by the first-order autocatalytic reaction rate equation dα/dt = 10^16.00exp(?174520/RT)(1 ? α) + 10^16.00exp(?163510/RT)α(1 ? α); (2) the value of $ ({\text{d}}T / {\text{d}}t)_{{\text{T}_{\text{b}} }} $ for NC (12.97 % N) when autocatalytic decomposition converts into thermal explosion is 0.354 K s^?1.     

The yjjN of E. coli codes for an l-galactonate dehydrogenase and can be used for quantification of l-galactonate and l-gulonate

Escherichia coli is able to utilize l-galactonate as a sole carbon source. A metabolic pathway for l-galactonate catabolism is described in E. coli, and it is known to be interconnected with d-galacturonate metabolism. The corresponding gene encoding the first enzyme in the l-galactonate pathway, l-galactonate-5-dehydrogenase, was suggested to be yjjN. However, l-galactonate dehydrogenase activity was never demonstrated with the yjjN gene product. Here, we show that YjjN is indeed an l-galactonate dehydrogenase having activity also for l-gulonate. The K _m and k _cat for l-galactonate were 19.5?±?0.6 mM and 0.51?±?0.03 s^?1, respectively. In addition, YjjN was applied for a quantitative detection of the both of these substances in a coupled assay. The detection limits for l-galactonate and l-gulonate were 1.65 and 10 μM, respectively.