Determination of enzyme activity inhibition by FTIR spectroscopy on the example of fructose bisphosphatase

A mid-infrared enzymatic assay for label-free monitoring of the enzymatic reaction of fructose-1,6-bisphosphatase with fructose 1,6-bisphosphate has been proposed. The whole procedure was done in an automated way operating in the stopped flow mode by incorporating a temperature-controlled flow cell in a sequential injection manifold. Fourier transform infrared difference spectra were evaluated for kinetic parameters, like the Michaelis–Menten constant (K _M) of the enzyme and V _max of the reaction. The obtained K _M of the reaction was 14 ± 3 g L⁻¹ (41 μM). Furthermore, inhibition by adenosine 5′-monophosphate (AMP) was evaluated, and the K _M^App value was determined to be 12 ± 2 g L⁻¹ (35 μM) for 7.5 and 15 μM AMP, respectively, with V _max decreasing from 0.1 ± 0.03 to 0.05 ± 0.01 g L⁻¹ min⁻¹. Therefore, AMP exerted a non-competitive inhibition.     

Effects of Temperature and Common Ions on Binding of Puerarin to BSA

The effects of temperature and common ions on binding of puerarin to bovine serum albumin (BSA) are investigated. The binding constants (K _a) between puerarin and BSA are 1.13×10⁴ L⋅mol⁻¹ (20 °C) and 1.54×10⁴ L⋅mol⁻¹ (30 °C), and the number of binding sites (n) is (0.95±0.02). However, at a higher temperature (40 °C) the stability of the puerarin–BSA system decreases, which results in a lower binding constant (1.58×10³ L⋅mol⁻¹) and number of binding sites (n=0.73) of the puerarin–BSA system. However, the presence of Cu²⁺ and Fe³⁺ ions increases the binding constants and the number of binding sites in the puerarin–BSA complex.     

Immobilization of Hemoglobin on the Gold Colloid Modified Pretreated Glassy Carbon Electrode for Preparing a Novel Hydrogen Peroxide Biosensor

A novel hydrogen peroxide (H₂O₂) biosensor was developed by immobilizing hemoglobin on the gold colloid modified electrochemical pretreated glassy carbon electrode (PGCE) via the bridging of an ethylenediamine monolayer. This biosensor was characterized by UV-vis reflection spectroscopy (UV-vis), electrochemical impendence spectroscopy (EIS) and cyclic voltammetry (CV). The immobilized Hb exhibited excellent electrocatalytic activity for hydrogen peroxide. The Michaelis–Menten constant (K _m) was 3.6 mM. The currents were proportional to the H₂O₂ concentration from 2.6 × 10⁻⁷ to 7.0 × 10⁻³ M, and the detection limit was as low as 1.0 × 10⁻⁷ M (S/N = 3).     

A new amperometric H<Subscript>2</Subscript>O<Subscript>2</Subscript> biosensor based on nanocomposite films of chitosan–MWNTs,hemoglobin, and silver nanoparticles

A new H₂O₂ biosensor was fabricated on the basis of nanocomposite films of hemoglobin (Hb), silver nanoparticles (AgNPs), and multiwalled carbon nanotubes (MWNTs)–chitosan (Chit) dispersed solution immobilized on glassy carbon electrode (GCE). The immobilized Hb displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ′) of −22.5 mV in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) in the Chit–MWNTs film was evaluated as 2.58 s⁻¹ according to Laviron’s equation. The surface concentration (Γ*) of the electroactive Hb in the Chit–MWNTs film was estimated to be (2.48 ± 0.25) × 10⁻⁹ mol cm⁻². Meanwhile, the Chit–MWNTs/Hb/AgNPs/GCE demonstrated excellently electrocatalytical ability to H₂O₂. Its apparent Michaelis–Menten constant (K _M^app) for H₂O₂ was 0.0032 mM, showing a good affinity. Under optimal conditions, the biosensors could be used for the determination of H₂O₂ ranging from 6.25 × 10⁻⁶ to 9.30 × 10⁻⁵ mol L⁻¹ with a detection limit of 3.47 × 10⁻⁷ mol L⁻¹ (S/N = 3). Furthermore, the biosensor possessed rapid response to H₂O₂ and good stability, selectivity, and reproducibility.     

Direct electrochemistry and biocatalysis of glucose oxidase immobilized on magnetic mesoporous carbon

A magnetic mesoporous carbon material (i.e., mesoporous iron oxide/C, mesoFe/C) is synthesized for protein immobilization, using glucose oxidase (GOx) as model. Transmission electron microscopy images show that mesoFe/C has highly ordered porous structure with uniform pore size, and iron oxide nanoparticles are dispersed along the wall of carbon. After adsorption of GOx, the GOx-mesoFe/C composite is separated with magnet. The immobilized GOx remains its natural structure according to the reflection–absorption infrared spectra. When the GOx-mesoFe/C composite is coated on a Pt electrode surface, the GOx gives a couple of quasireversible voltammetric peaks at −0.5 V (vs. saturated calomel electrode) due to the redox of FAD/FADH₂. The electron-transfer rate constant (k _s) is ca. 0.49 s⁻¹. The modified electrode presents remarkably amperometric response to glucose at 0.6 V. The response time (t _95%) is less than 6 s; the response current is linear to glucose concentration in the range of 0.2–10 mM with a sensitivity of 27 μA mM⁻¹ cm⁻². The detection limit is 0.08 mM (S/N = 3). The apparent Michaelis–Menten constant (K _m^app) of the enzyme reaction is ca. 6.6 mM, indicating that the GOx immobilized with mesoFe/C has high affinity to the substrate.     

Microanalysis of Hydrogen, Boron and Fluorine in Vesuvianite by Means of SIMS, EPMA and FTIR

Vesuvianite, a complex sorosilicate, often contains variable (from trace-to-minor-element) amounts of H, B and F. We describe a microanalytical study of H, B and F in vesuvianite by means of Electron Probe Microanalysis (EPMA), Secondary Ion Mass Spectrometry (SIMS), and single-crystal Fourier-Transform InfraRed (FTIR) spectroscopy. Most crystals investigated are B- (up to 3.67 wt% B₂O₃) and F-rich (up to 2.38 wt%); H₂O ranges from 0.243 to 0.665 wt%. The H data obtained by SIMS allowed us to calibrate the quantitative analysis of H₂O by FTIR spectroscopy. The resulting molar absorption coefficient (ɛ _i = 100 000 ± 2000 L · mol⁻¹ · cm⁻²) is in excellent agreement with working curves available from the literature. Moreover, the SIMS data allowed us to obtain the calibration curve to estimate the B₂O₃ content on the basis on the FTIR absorbance: a _i = 34000 ± 1400 · B₂O₃ (wt%).     

A hydrogen peroxide biosensor based on direct electrochemistry of hemoglobin in palladium nanoparticles/graphene-chitosan nanocomposite film

Thermally two-dimensional lattice graphene (GR) and biocompatibility chitosan (CS) act as a suitable support for the deposition of palladium nanoparticles (PdNPs). A novel hydrogen peroxide (H₂O₂) biosensor based on immobilization of hemoglobin (Hb) in thin film of CS containing GR and PdNPs was developed. The surface morphologies of a set of representative membranes were characterized by means of scanning electron microscopy and showed that the PdNPs are of a sphere shape and an average diameter of 50 nm. Under the optimal conditions, the immobilized Hb showed fast and excellent electrocatalytic activity to H₂O₂ with a small Michaelis–Menten constant of 16 μmol L⁻¹, a linear range from 2.0 × 10⁻⁶ to 1.1 × 10⁻³ mol L⁻¹, and a detection limit of 6.6 × 10⁻⁷ mol L⁻¹. The biosensor also exhibited other advantages, good reproducibility, and long-term stability, and PdNPs/GR–CS nanocomposites film would be a promising material in the preparation of third generation biosensor.     

TiO2 nanotube array film prepared by anodization as anode material for lithium ion batteries

TiO₂ array film fabricated by potentiostatic anodization of titanium is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and charge–discharge measurements. The XRD results indicated that the TiO₂ array is amorphous, and after calcination at 500 °C, it has the anatase form. The pore size and wall thickness of TiO₂ nanotube arrays synthesized at different anodization voltages are highly dependent on the applied voltage. The electrochemical performance of the prepared TiO₂ nanotube array as an electrode material for lithium batteries was evaluated by galvanostatic charge–discharge measurement. The sample prepared at 20 V shows good cyclability but low discharge capacity of 180 mA h cm⁻³, while the sample prepared at 80 V has the highest discharge capacity of 340 mA h cm⁻³.     

Electrochemistry at cobalt(II)tetrasulfophthalocyanine-multi-walled carbon nanotubes modified glassy carbon electrode: a sensing platform for efficient suppression of ascorbic acid in the presence of epinephrine

Electrochemistry of water-soluble cobalt(II) tetrasulfophthalocyanine (CoTSPc) electrodeposited on glassy carbon nanotube pre-modified with acid-functionalized multi-walled carbon nanotubes (MWCNT) is described. Both charge transfer resistances toward [Fe(CN)₆]^3−/4− redox probe and electrocatalytic responses toward epinephrine (EP) detection follow the trend: bare GCE < GCE-MWCNT < GCE-CoTSPc < GCE-MWCNT-CoTSPc. EP analysis was then carried out in details using GCE-MWCNT-CoTSPc. The catalytic rate constant value k _ch = 2.2 × 10⁷ (mol cm⁻³)⁻¹ s⁻¹ was obtained from rotating disk electrode experiment. Interestingly, GCE-MWCNT-CoTSPc efficiently suppressed the detection of ascorbic acid (the natural interference of neurotransmitters in physiological conditions) showing good sensitivity (0.132 ± 0.003 A l mol⁻¹), limit of detection (4.517 × 10⁻⁷ mol l⁻¹), and quantification (15.056 × 10⁻⁷ mol l⁻¹). In addition, GCE-MWCNT-CoTSPc was conveniently used to determine EP in epinephrine hydrochloric acid injection with recovery of 101.1 ± 2.2%.     

Organosilica composite for preconcentration of phenolic compounds from aqueous solutions

A new adsorbent is proposed for the solid-phase extraction of phenol and 1-naphthol from polluted water. The adsorbent (TX-SiO₂) is an organosilica composite made from a bifunctional immobilized layer comprising a major fraction (91%) of hydrophilic diol groups and minor fraction (9%) of the amphiphilic long-chain nonionic surfactant Triton X-100 (polyoxyethylated isooctylphenol) (TX). Under static conditions phenol was quantitatively extracted onto TX-SiO₂ in the form of a 4-nitrophenylazophenolate ion associate with cetyltrimethylammonium bromide. The capacity of TX-SiO₂ for phenol is 2.4 mg g⁻¹ with distribution coefficients up to 3.4 × 10⁴ mL g⁻¹; corresponding data for 1-naphthol are 1.5 mg g⁻¹ and 3 × 10³ mL g⁻¹. The distribution coefficient does not change significantly for solution volumes of 0.025–0.5 L and adsorbent mass less than 0.03 g; 1–90 μg analyte can be easily eluted by 1–3 mL acetonitrile with an overall recovery of 98.2% and 78.3% for phenol and 1-naphthol, respectively. Linear correlation between acetonitrile solution absorbance (A ₅₄₀) and phenol concentration (C) in water was found according to the equation A ₅₄₀ = (6 ± 1) × 10⁻² + (0.9 ± 0.1)C (μmol L⁻¹) with a detection range from 1 × 10⁻⁸ mol L⁻¹ (0.9 μL g⁻¹) to 2 × 10⁻⁷ mol L⁻¹ (19 μL g⁻¹), a limit of quantification of 1 μL g⁻¹ (preconcentration factor 125), correlation coefficient of 0.936, and relative standard deviation of 2.5%. A solid-phase colorimetric method was developed for quantitative determination of 1-naphthol on adsorbent phase using scanner technology and RGB numerical analysis. The detection limit of 1-naphthol with this method is 6 μL g⁻¹ while the quantification limit is 20 μL g⁻¹. A test system was developed for naked eye monitoring of 1-naphthol impurities in water. The proposed test kit allows one to observe changes in the adsorbent color when 1-naphthol concentration in water is 0.08–3.2 mL g⁻¹.     

Studies of the reaction of the hydroxyl radical with the oxalate ion in an acidic aqueous solution by pulse radiolysis

The reaction of the · OH radical with the oxalate ion in an acidic aqueous solution was studied by pulse radiolysis. The rate constant for the reaction of formation of the radical HOOC-COO·(λ_max = 250 nm, ɛ = 1800 L mol⁻¹ cm⁻¹) is (5.0±0.5)·107 L mol⁻¹ s⁻¹. In the reaction with the hydrogen ion (k = 1.1·10⁷ L mol⁻¹ s⁻¹), the radical HOOC-COO· is transformed into a nonidentified radical designated arbitrarily as H⁺(HOOC-COO)· (λ_max = 260 nm, ɛ = 4000 L mol⁻¹ cm⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1167, June, 2008.     

Preparation and characterization of lithium ion conducting ionic liquid-based biodegradable corn starch polymer electrolytes

Thin films of biodegradable corn starch-based biopolymer electrolytes were prepared by solution casting technique. Lithium hexafluorophosphate (LiPF₆) and 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BmImTf) were employed as lithium salt and ionic liquid, respectively. With reference to the temperature dependence study, Arrhenius relationship was observed. The highest ionic conductivity of (6.00 ± 0.01) × 10⁻⁴ S cm⁻¹ was obtained at 80 °C. Based on x-ray diffraction (XRD) result, the peaks became broader with doping of ionic liquid revealing the higher amorphous region of the biopolymer electrolytes. Ionic liquid-based biopolymer electrolytes exhibited lower glass transition temperature (T _g).     

Catalytic Spectrophotometric Determination of Molybdenum

Summary.  A highly selective, sensitive, and simple catalytic method for the determination of molybdenum in natural and waste waters was developed. It is based on the catalytic effect of Mo(VI) on the oxidation of 2-aminophenol with H₂O₂. The reaction is monitored spectrophotometrically by tracing the oxidation product at 430 nm after 10 min of mixing the reagents. Addition of 800 μg · cm⁻³ EDTA conferred high selectivity; however, interfering effects of Au(III), Cr(III), Cr(VI), and Fe(III) had to be eliminated by a reduction and co-precipitation procedure with SnCl₂ and Al(OH)₃. Mo(VI) shows a linear calibration graph up to 11.0 ng · cm⁻³; the detection limit, based on the 3S _b-criterion, is 0.10 ng · cm⁻³. The unique selectivity and sensitivity of the new method allowed its direct application to the determination of Mo(VI) in natural and waste waters. Received April 11, 2001. Accepted (revised) June 18, 2001     

Physicochemical Properties of Plant Protection Substances: I Polymorphism and Binary Systems of Triadimenol

 The fungicide triadimenol consists of a mixture of two diastereoisomers. Diastereoisomer A (1RS,2SR) could be obtained from the mixture by fractionated crystallization from ethanol/water and toluene, successively, whereas diastereoisomer B (1RS,2RS) could be separated by column chromatography on a silica gel column using ethylacetate as eluent. Four different crystal forms of diastereoisomer A could be derived. The modifications were characterized by means of thermal analysis (thermomicroscopy, DSC), FTIR-spectroscopy, FT-Raman-spectroscopy and powder X-ray diffraction, as well as pycnometry. The thermodynamic relationships are illustrated in a semischematic energy/temperature-diagram which provides information about the relative thermodynamic stabilities and physical properties of the four crystal forms. Mod. II (m.p. 132 °C, ΔH_f 33.1±0.2 kJ mol⁻¹, density 1.271±0.001 g cm⁻³) was obtained from toluene after the separation of diastereoisomer A and is enantiotropically related to mod. I (m.p. 138 °C, ΔH_f 32.0 ± 0.2 kJ mol⁻¹, density 1.243±0.001 g cm⁻³). The transition point of mod. II with mod. I was determined between 30 and 40 °C, which means that mod. II is thermodynamically stable at ambient conditions. Mod. III (m.p. 112 °C, ΔH_f 25.1±0.5 kJ mol⁻¹) and mod. IV were obtained from the melt. Furthermore, the phase diagrams of the binary systems of diastereoisomer B and the four modifications of diastereoisomer A were calculated by means of the experimentally obtained thermodynamical data. Received September 30, 1999. Revision July 30, 2000.     

Kinetics and mechanism of the reaction between chromium(III) and picolinic acid in weak acidic aqueous solution

Abstract  

The interaction between chromium(III) and picolinic acid in weak acid aqueous solution was studied, resulting in the formation of a complex upon substitution of water molecules in the chromium(III) coordination sphere. Experimental results show that the reaction takes place in multiple steps. The first step is the formation of an ion pair, the second step (two consecutive steps) is the slow one corresponding to substitution of the first water molecule from the chromium aqueous complex coordination sphere by a picolinic acid molecule via oxygen atom of the carboxylic acid group and substitution of the second water molecule via nitrogen of the pyridine ring forming an 1:1 complex. Both consecutive steps were independent of chromium concentration. The rate constants of the 1st and 2nd consecutive steps were increased by increasing picolinic acid concentration. The corresponding activation parameters are ∆H _1obs ^* = 28.4 ± 4 kJ mol⁻¹, ∆S _1obs ^* = −202 ± 26 J K⁻¹ mol⁻¹, ∆H _2obs ^* = 39.6 ± 5 kJ mol⁻¹, and ∆S _2obs ^* = −175 ± 19 J K⁻¹ mol⁻¹. The third step is fast, corresponding to formation of the final complex [Cr(pic)₃]. The logarithms of the formation constants of 1:1 and 1:3 complexes were found to be 1.724 and 4.274, respectively.     

Concerning the Chiral Discrimination and Helix Inversion Barrier in Hypericinates and Hypericin Derivatives

 It was found that the hypericinate salts of (R)-1-phenylethylamine and (S)-1-(1-naphthyl)-ethylamine display a small chiroptical signal of the same sign only at high concentrations in an apolar solvent. No further indications of a chiral discrimination between the helical conformers of hypericinate could be found in these cases. However, upon esterification of the 3-hydroxyl group of hypericin with (1S)-camphanic chloride, the two diastereomers were found in an 1:1 ratio equilibrating rather fast at temperatures above 30°C with one diastereomer in excess. From the temperature dependence of the equilibrium positions (measured by means of CD and ¹H NMR), a ΔG ⁰ value of 5.8±0.5 kJ·mol⁻¹ was derived. Accordingly, the chiral discrimination of the (M)-configured enantiomer of the helix by the (S)-configured auxiliary occurred at an intermediate level. From the temperature dependence of the equilibration kinetics an activation energy of E _a = 70±0.5 kJ·mol⁻¹ was derived, which thus defines the upper limit of the helix inversion of hypericin and hypericinate. This value is by about 10 kJ·mol⁻¹ lower than the recently estimated limit.     

Kinetic and mechanistic studies on the reaction of thiosemicarbazide with [(H<Subscript>2</Subscript>O)(tap)<Subscript>2</Subscript>RuORu(tap)<Subscript>2</Subscript>(H<Subscript>2</Subscript>O)]<Superscript>2+</Superscript> {tap = 2-(m-tolylazo)pyridine}

The interaction of thiosemicarbazide with the title complex has been studied spectrophotometrically in aqueous medium as a function of [complex], [thiosemicarbazide], pH and temperature at constant ionic strength. At pH 7.4, the reaction shows two distinct paths; both of which are [thiosemicarbazide] dependent. A parallel reaction scheme fits well with the experimental findings. An associative interchange mechanism is proposed for both the paths; the activation parameters calculated from Eyring plots are ΔH₁^≠ = 14.2 ± 0.8 kJ mol⁻¹, ΔS₁^≠ = −241 ± 2 JK⁻¹ mol⁻¹, ΔH₂^≠ = 30.8 ± 1.4 kJ mol⁻¹ and ΔS₂^≠ = −236 ± 4 JK⁻¹ mol⁻¹. From the temperature dependence of the outer sphere association complex equilibrium constants, the thermodynamic parameters calculated are ΔH₁^° = 34.25 ± 1.9 kJ mol⁻¹, ΔS₁^° = 146 ± 6 J K⁻¹ mol⁻¹ and ΔH₂^° = 9.4 ± 1.1 kJ mol⁻¹, ΔS₂^° = 71 ± 3 JK⁻¹ mol⁻¹, which gives a negative ΔG° at all temperatures studied, supporting the spontaneous formation of an outer sphere association complex.     

Kinetic study of crystallization of PHB in presence of hydroxy acids

Poly(3-hydroxybutyrate), PHB, has been structurally modified through reaction with hydroxy acids (HA) such as tartaric acid (TA) and malic acid (MA). The crystallization kinetic of the samples was evaluated by isoconversional method through nonlinear fitting to obtain the estimation for activation energy (E _a ) and pre-exponential (A) values. The thermal behavior of the crystallization temperature, 44.8 and 58.9 °C at 5 °C/min, and results obtained to the average activation energy, 73 ± 9 kJ mol⁻¹ and 63 ± 1 kJ mol⁻¹, to PHB/MA and PHB, respectively, are suggesting that malic acid may be deriving plasticizer units from its own PHB chain. PHB/TA show increase in the medium value of E _a, 119 ± 2 kJ mol⁻¹ and T _c = 48.2 °C (at 5 °C/min), indicating that tartaric acid is probably interacts in different way to the of PHB chain (E _a=73 ± 9 kJ mol⁻¹, T _c = 44.8 °C at 5 °C/min).     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

Summary. The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.     

The Potential Energies of Cohesion of a Crystalline Organic Enantiomer and the Racemate; on the Energy for the Liquid Racemate [1]

The cohesion potential energy of the crystal of one enantiomer of ethyl 3-cyano-3-(3,4-dimethyloxyphenyl)-2,2,4-trimethylpentanoate, −47.7 ± 0.1 kJ mol⁻¹ (0–90°C), was found out from the heat of sublimation (123.2 ± 5.1 kJ mol⁻¹, 78.6°C) and the kinetic energies for the gas phase and the crystal. It was found that the entropy function of Debye’s theory of solids mathematically agreed with the vibrational entropy of the gas (variationally obtained), allowing to disclose the vibrational energy using the Debye energy function (E _vib 835.0 kJ mol⁻¹ (78.6°C), E ⁰ included). E _kin for the crystal (771.1 kJ mol⁻¹ (78.6°C)) was obtained by Debye’s theory with the experimental heat capacity. The cohesion energy represented a moderate part of the sublimation energy. The cohesion energy of the racemic crystal, −44.2 kJ mol⁻¹, was obtained by the heat of formation of the crystal in the solid state (3.0 kJ mol⁻¹, 83.3°C) and E _kin for the crystal (by Debye’s theory). The decrease in cohesion on formation of the crystal accounted for the energy of formation. The change in potential energy on liquefaction of the racemate from the gas state was disclosed obtaining added-up E _{vib + rot} for the liquid in the way as to E _vib for the gas, the Debye entropy function being increasedly suited for the liquid (E _{vib + rot} 763.4 kJ mol⁻¹ (115.4°C)). Positive ΔE _pot, 13.0 kJ mol⁻¹, arised from the increase in electronic energy (Δ _l ν_mean − 154.3 cm⁻¹, by the dielectric nature of the liquid), added to the cohesion energy.