Calorimetric Standards Research Articles

STANDARD FORMATION ENTHALPIES OF L-ARGININE AND PRODUCTS OF ITS DISSOCIATION IN AQUEOUS SOLUTION

Depending on the chemical nature of side radicals, amino acids can be divided into aromatic and aliphatic ones, as well as amino acids that have non-polar or polar functional groups in their side radical. Since specific features of individual amino acids in the protein are determined by the nature (physicochemical properties) of their side radicals that exist in the hydrated state, it also seems extremely important to study the thermodynamic characteristics of hydration of side radicals of amino acids of different chemical nature. In order to obtain empirical correlations that would establish a relationship between the thermodynamic parameters of interaction of a dissolved compound with the solvent and the size of molecules being dissolved (that have different physicochemical nature), one needs to accumulate a sufficient amount of experimental data on heats of dissolution of amino acids and peptides. This would allow one to verify the addictively of contributions of intermolecular interactions for different groups of molecules. Reagent L-arginine was used without additional purification. Prior to weighing, the substance was dried at 110 °C. The heats of dissolution of crystalline L-arginine were measured using an isothermal-jacket calorimeter with automatic recording of the temperature-time curve. The performance of the calorimetric setup was verified in accordance with the conventional calorimetric standards: the heat of dissolution of crystalline potassium chloride in water and the heat of neutralization of a strong acid with a strong base. The agreement between the experimental enthalpies of dissolution of KCl (cr.) in water and the heats of neutralization of nitric acid with a KOH solution with the most reliable published data indicates that there are no evident systematic errors in the performance of the calorimetric setup. The equilibrium compositions of solutions were calculated using RRSU software. The heats of dissolution of crystalline amino acid in water and potassium hydroxide solutions at 298.15 K were measured by direct calorimetry. The standard enthalpies of formation of L-arginine and the products of its dissociation in aqueous solutions were calculated.Forcitation:Lytkin A.I., Chernikov V.V., Krutova O.N., Krutov P.D. Standard formation enthalpies of L-arginine and products of its dissociation in aqueous solution. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 2. P. 40-45

Changes in thermal denaturation properties of the long head of the biceps during lifetime

Long head of the biceps (LHB) is an intra-articular tendon component of the shoulder joint. The function of this tendon is complex. First, it is an origin of flexion in upper limb, and second it plays role in joint stabilisation during shoulder movements. Histological type of tendon tissues is connective tissue. The mechanical behaviour of connective tissue is primarily determined by the composition and organisation of collagens. In tendons, type I collagen is the principal structural element of the extracellular matrix, which acts to transmit force between bones or bone and muscle. Owing to the special localisation of this tendon, the intra-articular mechanical forces affect it to a considerable extent. The LHB is known as a source of pain in pathologic states of the shoulder joint. The goal of this study was to establish the calorimetric standards of the LHB in different ages, and to observe the changes of thermal properties of collagen during lifetime. LHB samples were taken from 38 cadavers (between ages 0 and 90 years) without macroscopic sign of shoulder pathology. DSC analyses were performed with SETARAM Micro DSC-II. The thermal denaturation parameters varied between Tm (°C): 57, ΔH (J/g): 0.26 (age: 0 year) and Tm (°C): 62.92, ΔH (J/g): 1.28 (age: 90 years). The ageing of collagenous tendon tissue can be clearly followed in changes of thermal denaturation properties. The knowledge of the ageing of normal collagen provides a good basis to analyse further the LHB pathology.

Differential sacnning calorimetric examination of the human intervertebral disc: establishment of calorimetric standards of different stages of degeneration

Intervertebral disc (IVD) degeneration is a common orthopaedic disorder with significant social and economic impact. The major pathological changes occur in the structure of anulus fibrosus (AF) and nucleus pulposus (NP). According to previous reports differential sacnning calorimetric (DSC) proved to be a suitable method for the demonstration of thermal consequences of local and global conformational changes in the structure of the human intervertebral discs. According to the present study, the DSC results clearly proved that definitive differences are present between the stages of disc degeneration in calorimetric measures. The structural differences between the stages could be also demonstrated by histology.

Calorimetric standards for photothermal methods at the 248 nm excitation

The time-resolved thermal lensing measurements were carried out on 2-hydroxybenzophenone, pyridazine and benzene in acetonitrile at the 248 nm excitation in order to investigate the feasibility for the calorimetric standards on photothermal methods. The heat conversion efficiency values of 2-hydroxybenzophenone and pyridazine were estimated to be unity compared with that of benzene, revealing that 2-hydroxybenzophenone and pyridazine should show no fluorescence and no photochemical reactions. Therefore, these molecules should be good calorimetric standards at the 248 nm excitation.

NIST and standards for calorimetry

The present article describes briefly some of NISTs more recent work on calorimetric standards. New reference-quality measurements of the enthalpy of solution of aqueous sodium chloride, obtained with an adiabatic solution calorimeter, are presented and compared to a previous equation of state for NaCl(aq). Other calorimetric standards that are discussed are potassium chloride used for solution calorimetry and reference materials used for calibration of enthalpy-increment and heat-capacity calorimeters, namely synthetic sapphire (α-Al 2O 3) and copper.

Thermodynamic Properties of the KCl+H2O System

The thermodynamic properties of the KCl+H2O system were examined in order to provide: (1) an improved equation for the osmotic coefficient as a function of molality and temperature for purposes of isopiestic measurements, (2) a determination of the thermodynamic properties of the standard-state solution process, and (3) a test of the accuracy of the enthalpy of solution values for KCl(cr), a calorimetric standard. New equations that describe the thermodynamic properties of the KCl+H2O system were obtained from previously published measurements for this system. The measured values included in the fitted equations spanned the range of temperature from approximately 260 to 420 K for KCl(aq) and 1.5 K to 1033.7 K for KCl(cr). New equations and/or values for the following properties are given in the present work: (1) thermal properties of KCl(cr) from 0 K to the melting point, 1045 K, (2) the change in chemical potential for both KCl and H2O in KCl(aq) as a function of temperature, and molality, valid from 260 to 420 K, and (3) standard-state properties for the aqueous solution process. The effect of heat treatment on the determination of enthalpy of solution values was also examined. This examination indicated that the NIST recommendation of heating Standard Reference Material 1655, potassium chloride, at 800 K for a minimum of 4 h prior to its use in calorimeter calibration, should probably not be followed. The heat treatment recommended by the NIST certificate appears, at this point, to have a higher probability of corrupting the sample than improving the accuracy of the measurement.

Double Proton Transfer Reaction of 7-Azaindole Dimer and Complexes Studied by Time-Resolved Thermal Lensing Technique

Time-resolved thermal lensing (TRTL) technique was applied to the determination of enthalpy change in double proton transfer reaction of 7-azaindole (AI) dimer and its complexes with acetic acid (AcOH) and methanol in solution. Excited AI dimer/complexes emit violet fluorescence or undergo rapid double proton transfer (DPT) reaction to form excited tautomers, which emit green fluorescence. The emission quantum yields were successfully determined with a calorimetric standard of pyridazine to be 0.006 (AI dimer), 0.16 (AI dimeric tautomer), 0.002 (AI−AcOH complex), 0.11 (AI−AcOH tautomer), and 0.08 (AI−methanol complex). By analyzing the time evolution of TRTL signals of AI dimer, the lifetime of the tautomer in the ground state was determined to be 19 μs, which well agreed with the values obtained with flash photolysis and stepwise two-color laser-induced fluorescence experiments. The enthalpy change of the tautomer to the AI dimer in the ground state was obtained to be surprisingly low, 340 cm-1. The TRTL...

Calorimetric standards for photothermal methods in ultraviolet and visible spectral regions

Utilizing a time-resolved thermal lensing (TRTL) technique coupled with laser flash excitation, we have determined the heat conversion efficiency, a, of photoexcited molecules in solution at room temperature. The efficiencies of pyridazine, dicumarol, and 8-quinolinol are unity in the ultraviolet region. Azulene is demonstrated to be a good calorimetric standard in the visible region. The solvent effect on the thermal lens signal is well explained by thermal properties of solvent molecules, i.e. the cubic expansion coefficient and the specific heat capacity.

Thermodynamic properties of calcium zirconate (CaZrO 3)

Characterized synthetic CaZrO 3 was used by the Bureau of Mines to determine the standard enthalpy of formation (Δ Hf 0 298 = −424.58±0.47 kcal mol −1; −1776.43±1.97 kJ moP −1) and the standard enthalpy of formation from the oxides (Δ H 0 298 (from oxides) = −9.75±0.11 kcal mol −1; −40.78±0.46 kJ mol −1) at 298.15 K. These data compare with the reaction calorimetric values determined by L'vova) (Δ Hf 0 298 = −422.3 kcal mol −1; −1766.90 kJ mol −1) listed in NBSTN 270-6 by Parker. This compound, CaZrO 3, easily prepared and characterized, is potentially useful for a calorimetric standard. The reaction scheme for hydrofluoric acid solution calorimetry does not require a reaction step adding a liquid to the solvent.

A Comparison of the United Kingdom National Standards of Microwave Power in Waveguide and Coaxial Lines

A series of comparisons at 8.2 GHz between bolometric waveguide power standards and 50-Ω coaxial line calorimetric standards resulted in differences, with respect to the waveguide standard, of +0.20 to -0.06 percent during 12 comparisons and combined estimated 95-percent confidence limits of +0.35 percent.

A new calorimetric standard: 4-aminopyridine

The need for a new solution calorimetric standard is discussed. The standard proposed is 4-aminopyridine which is shown to be more satisfactory than the previously accepted standards of sodium hydroxide or trishydroxyaminomethane. The reaction is HClO 4(aq) + 4–AP(aq)→4–APH +ClO − 4(aq) with Δ H° N(298.15 K) =11.164±0.011 kcal mol −1.

Recent developments in calorimetry: Part two. Some associated measurements (cont.)

Examines the measurement of electricity, calorimetric standards, solution calorimetry, and specific types of calorimeters.

Heat Capacity of Copper

In order to establish the suitability of copper as a low temperature calorimetric standard, the heat capacities of four samples were measured between 1.3 and 20°K with a precision of 0.1%. All samples were at least 99.999% copper. One was a single crystal, one polycrystalline and annealed, one chill cast, and one polycrystalline and cold worked. The heat capacities of the annealed and chill cast samples differ by less than 0.1%. The heat capacity of the single crystal is 0.2% higher. The heat capacity of the cold worked sample is 0.7% higher at low temperatures and 0.3% higher above 10°K. It is concluded that high purity cast copper samples are excellent as low temperature calorimetric standards.

Differential thermal analysis of high polymers. III. Polyamides

AbstractDifferential thermal analysis has been used to study melting and glass transitions in various homo‐ and copolyamides, as well as crystallite disorientation in nylon monofilaments. Transition temperatures obtained from the thermograms of the commoner polyamides agree well with literature values, but the less common polyamides gave slightly higher melting points. Heats of fusion of polyamides 66 and 610 were obtained from the thermograms by calibration with a calorimetric standard. These values together with the independently determined degree of crystallinity have been used to calculate the true heats of fusion. The thermograms of two series of copolyamides, the adipamide–sebacamides and adipamide–terephthalamides, showed changes in peak shapes, positions, and areas from those of the parent homopolymers. Decrease in crystallinity led to pronounced glass transitions. Two melting peaks observed for certain copolymers are interpreted as evidence for the production of block copolymers, which are favored by the reaction conditions existing in interfacial polycondensations.

Calorimetric Standards Discussed at Second Conference

Calorimetric Standards Discussed at Second Conference

The heat of combustion of the proposed calorimetric standard: Salicylic acid: (A reply to L. J. P. Keffler)

Recueil des Travaux Chimiques des Pays-BasVolume 49, Issue 9 p. 864-865 Articles The heat of combustion of the proposed calorimetric standard: Salicylic acid: (A reply to L. J. P. Keffler) P. E. Verkade, P. E. Verkade Rotterdam, Laboratory of the Dutch Commercial UniversitySearch for more papers by this authorJ. Coops Jr., J. Coops Jr. Rotterdam, Laboratory of the Dutch Commercial UniversitySearch for more papers by this author P. E. Verkade, P. E. Verkade Rotterdam, Laboratory of the Dutch Commercial UniversitySearch for more papers by this authorJ. Coops Jr., J. Coops Jr. Rotterdam, Laboratory of the Dutch Commercial UniversitySearch for more papers by this author First published: 1930 https://doi.org/10.1002/recl.19300490908AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume49, Issue91930Pages 864-865 RelatedInformation