Isothermal Calorimetry Methods Research Articles

Nano-crystallization behavior of Zr–Cu–Al bulk glass-forming alloy

The glass-forming ability and devitrification behavior of a Zr55Cu35Al10 bulk glass-forming alloy were examined to elucidate the very high nanocrystallization product density (>1023m−3). The crystallization kinetics and structural changes in the glassy alloy were studied using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The observed sequential phase formation during isothermal reaction and the high nanocrystal density are consistent with the influence of residual oxygen even at low levels (<500ppm) to promote nucleation.

Investigation of Hydration Heat of Slag in Portland Cement Environment

The hydration of slag in Portland cement is studied by considering the interaction between the hydrations of slag and Portland cement clinker. The slag hydration heat value that the different dosage of slag is in Portland cement is measured with isothermal calorimetry method as quartz sand sample contrast. The kinetic analysis was used to obtain parameters, which were employed to find out the influence of the slag content on the reaction rate constant value. The reaction stages have been analyzed and explained in accordance with kinetic models. The model predictions show that as the slag proportions in the blended cement changes, water retention in the hydration products changes only slightly if compared to that of Portland cement, The investigations have shown that the addition of silica fume of more than 30 mass% reduces the duration of the phase boundary interaction as a rate-determined process resulting in the fast diffusion rate-determining process. The results of this study have also revealed evidence of the accelerator effect of slag during the first 24 h of hydration when it still exists as chemically inert filler.

Novel inhibitors of glyceraldehyde-3-phosphate dehydrogenase: Covalent modification of NAD-binding site by aromatic thiols

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH, EC 1.2.1.12) is a glycolytic enzyme catalyzing the formation of 1,3-diphosphoglycerate from glyceraldehyde-3-phosphate and inorganic phosphate. In cooperation with E3 ubiquitin-kinase Siah1, GAPDH directly participates in the apoptotic death of neurons in Parkinson's disease. Potential GAPDH inhibitors were screened in silico, and three compounds with high affinity to the NAD-binding site and theoretically capable of forming a disulfide bond with amino acid residue Cys149 were found among cysteine and glutathione derivatives. The inhibitory effect of these compounds was tested on GAPDH from rabbit muscles using isothermal calorimetry and kinetic methods. As a result of experimental screening, we selected two compounds that inhibit GAPDH by forming disulfide bonds with the Cys149 residue in the enzyme active site. Since Cys149 is the key residue not only for the catalyzed reaction, but also for interaction with Siah1, the compounds can be assumed to inhibit the formation of the proapoptotic complex GAPDH-Siah1 and therefore have potential effect against Parkinson's disease.

Thermodynamics of zinc binding to human S100A2

The regulatory protein S100A2 is localized in the cell nucleus and takes part in the regulation of the cell cycle and cancerogenesis. It belongs to a large family of S100 proteins and can simultaneously bind calcium and zinc ions. Using a direct thermodynamical method of isothermal titration calorimetry we have determined that in the absence of calcium ions the S100A2 protein can bind three zinc ions per each monomer. Besides that it was determined that the thermodynamics of zinc binding to different binding sites on the S100A2 are significantly different. Zinc binding to the first two sites on the S100A2 is enthalpically unfavorable and is driven only by entropic factors, while the binding of the third zinc ion is enthalpically favorable. Analysis of the zinc ion adsorption isotherms shows that their binding occurs in a consecutive order.

Study on the interaction of oxymatrine with bovine serum albumin

The binding reaction of oxymatrine (OMT) with bovine serum albumin (BSA) was studied by the methods of isothermal titration calorimetry, fluorescence, and circular dichroism (CD) spectroscopy. The thermodynamic results indicated that there were two classes of binding sites on the BSA molecule for OMT molecule. When the drug molecule binding to the first class of sites, the standard changes of enthalpy (ΔH 1°) and entropy (ΔS 1°) were (−1.07 ± 0.50) kJ/mol and (98.3 ± 0.50) J/mol/K, respectively. The possible largest number of binding site (N 1) was (10.0 ± 0.20). This type of binding was an enthalpy–entropy synergically driven process. On the second class of binding sites, the standard changes of enthalpy (ΔH 2°) and entropy (ΔS 2°) were (1.91 ± 0.03) kJ/mol and (79.8 ± 0.40) J/mol/K, respectively. The possible largest number of binding site (N 2) was (25.0 ± 0.30). This type of binding was entropy driven process. The intrinsic fluorescence of BSA was slightly quenched by the formation of BSA–OMT complex. The CD spectra experiment showed that the α-helix contents of BSA decreased. These revealed that the microenvironment and conformation of BSA were changed in the binding reaction.

Effect of Fe on the glass-forming ability, structure and devitrification behavior of Zr–Cu–Al bulk glass-forming alloys

We report on the glass-forming ability and devitrification behavior of Zr60Cu30Al10, Zr60Cu25Al10Fe5 and Zr62.5Cu22.5Al10Fe5 bulk glass-forming alloys on heating. The effect of Fe addition on the structure of Zr–Al–Cu alloys is also discussed. Crystallization kinetics and structural changes in the glassy alloys were studied using X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The results indicate that good glass-formers, such as Zr62.5Cu22.5Al10Fe5, are located somewhat beyond the equilibrium eutectic point. Possible phase separation in the supercooled liquid on heating and electron beam-induced in situ crystallization are observed and discussed.

Energetics of the binding of Cu(II) ions by thermosensitive copolymers of N-vinylcaprolactam and N-vinylimidazole in different conformational states of macromolecules

Random and protein-like copolymers based on N-vinylcaprolactam and N-vinylimidazole are synthesized by free radical polymerization in an aqueous solution. The above copolymers show a different thermal behavior in aqueous media at pH 7.2. At 45°C, the solution of a random copolymer experiences phase separation, whereas a protein-like copolymer undergoes a transition from the unfolded conformation to the compact conformation without any phase separation. The method of isothermal titration calorimetry is used to study the binding of Cu(II) ions by protein-like and random copolymers of N-vinylcaprolactam and N-vinylimidazole at 25 and 45°C, which correspond to different conformational states of macromolecules. The standard enthalpy and constant of binding are estimated. For both copolymers, the enthalpies of binding are negative and similar. When temperature is increased from 25 to 45°C, the constant of binding of copper ions by a protein-like copolymer increases by more than three orders of magnitude, whereas the corresponding constant of a random copolymer remains almost unchanged. Therefore, the transition of protein-like copolymer from the coiled conformation to the compact conformation noticeably facilitates the formation of an imidazole quasi-receptor, which is characterized by a certain spatial configuration and by a high affinity for the functional ligand. This effect is provided by an entropy gain no less than 50 J/(mol K).

Limitations of amorphous content quantification by isothermal calorimetry using saturated salt solutions to control relative humidity: Alternative methods

Despite the high sensitivity of isothermal calorimetry (IC), reported measurements of amorphous content by this technique show significant variability even for the same compound. An investigation into the reasons behind such variability is presented using amorphous lactose and salbutamol sulfate as model compounds. An analysis was carried out on the heat evolved as a result of the exchange of water vapor between the solid sample during crystallization and the saline solution reservoir. The use of saturated salt solutions as means of control of the vapor pressure of water within sealed ampoules bears inherent limitations that lead in turn to the variability associated with the IC technique. We present an alternative IC method, based on an open cell configuration that effectively addresses the limitations encountered with the sealed ampoule system. The proposed approach yields an integral whose value is proportional to the amorphous content in the sample, thus enabling reliable and consistent quantifications. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99: 2080–2089, 2010

Glass-forming ability and differences in the crystallization behavior of ribbons and rods of Cu36Zr48Al8Ag8 bulk glass-forming alloy

The crystallization behavior of melt-spun ribbons and bulk samples of the Cu36Zr48Al8Ag8 glassy alloy on heating is presented here. The crystallization kinetics and structural changes in the Cu36Zr48Al8Ag8 glassy alloy were studied using x-ray diffraction, transmission electron microscopy, differential scanning, and isothermal calorimetry methods. A clear comparison is made of the differences in the crystallization kinetics of the melt-spun ribbons and the copper-mold-cast bulk rod samples. It was suggested that the kinetics of crystallization in the rod sample, at any given temperature, are somewhat different than in the ribbon samples, probably because of size and free volume effects. Differences in the crystallization behavior of this alloy with other Cu-Zr-Al-Ag alloys have also been discussed.

Effect of isomerization of aspartate-7 on the binding of copper (II) ion by the β-amyloid peptide

It has been shown for the first time by the method of isothermal calorimetry of titration that the N-terminal amino group of the beta-amyloid protein, which plays a key role in the binding of copper ion, ceases to form the proper coordinating bond as a result of the isomerization of aspartate-7.

Photochemically Stable Fluorescent Heteroditopic Ligands for Zinc Ion

Photochemically stable fluorescent heteroditopic ligands (9 and 10) for zinc ion were prepared and studied. Two independent metal coordination-driven photophysical processes, chelation-enhanced fluorescence (CHEF) and internal (or intramolecular) charge transfer (ICT), were designed into our heteroditopic ligand framework. This strategy successfully relates three coordination states of a ligand, non-, mono-, and dicoordinated, to three fluorescence states, fluorescence OFF, ON at one wavelength, and ON at another wavelength. This ligand platform has provided chemical foundation for applications such as the quantification of zinc concentration over broad ranges (Zhang, L.; Clark, R. J.; Zhu, L. Chem.-Eur. J. 2008, 14, 2894-2903) and molecular logic functions (Zhang, L.; Whitfield, W. A.; Zhu, L. Chem. Commun. 2008, 1880-1882). The binding stoichiometries of dipicolylamino and 2,2'-bipyridyl, the two binding sites featured in heteroditopic ligands 7-10, were studied in acetonitrile using both Job's method of continuous variation and isothermal titration calorimetry (ITC). The fluorescence enhancement of 7-10 upon the formation of monozinc complexes (defined as the fluorescence quantum yield ratio of monozinc complex and free ligand) is qualitatively related to the highest occupied molecular orbital (HOMO) energy levels of their fluorophores. This is consistent with our hypothesis on the thermodynamics of the coordination-driven photophysical processes embodied in the designed heteroditopic system, which was supported by cyclic voltammetry studies. In conclusion, compounds 9 and 10 not only possess better photochemical stability but also display a higher degree of fluorescence turn-on upon formation of monozinc complexes than their vinyl counterparts 7 and 8.

Synthesis and free-radical polymerization of water-soluble acrylamide monomers

Water-soluble acrylamide monomers N-(hydroxymethyl)acrylamide, N-(hydroxymethyl)methacrylamide, N,N-diethanolacrylamide, N,N-diethanolmethacrylamide, N,N-methylethanolacrylamide, and N,N-methylethanolmethacrylamide have been synthesized and characterized. The kinetics and thermodynamics of the free-radical polymerization of these monomers and of the model compounds N-isopropylacrylamide and acrylamide have been studied by the methods of isothermal and scanning calorimetry. The structure and the solubility of the said polymers in water and organic solvents have been investigated and their molecular-mass characteristics and temperatures of glass transition (T g) and melting (T m) have been examined by DSC, liquid chromatography, 1H NMR and IR spectroscopy, and chemical analysis of functional groups. Hydrogels and amphiphilic network polymers based on acrylamide monomers have been prepared and characterized.

Highly Effective Binding of Methyl Viologen Dication and Its Radical Cation byp-Sulfonatocalix[4,5]arenes

The binding behaviors and thermodynamic origins of p-sulfonatocalix[4]arene (C4AS) and p-sulfonatocalix[5]arene (C5AS) with methyl viologen (MV2+) have been investigated by the methods of isothermal titration calorimetry, NMR, and cyclic voltammetry, showing that the binding abilities of C4AS and C5AS and their host selectivity are dramatically pH-controlled, which is closely discussed from the viewpoint of thermodynamics. Moreover, the radical form of MV+* can also be effectively included by C4AS and C5AS.

Effects of ytterbium ion on the growth, metabolism and membrane fluidity of Tetrahymena thermophila

Power-time curves and metabolic properties of Tetrahymena thermophila BF5 exposed to different Yb3+ levels were studied by ampoule method of isothermal calorimetry at 28°C. Metabolic rate (r) decreased significantly while peak time (PT) increased with the increase of Yb3+. These results were mainly due to the inhibition of cell growth, which corresponded to the decrease of cell number obtained by cell counting. Compared with cell counting, calorimetry was sensible, easy to use and convenient for monitoring the toxic effects of Yb3+ on cells and freshwater ecosystem. It was also found that cell membrane fluidity decreased significantly under the effects of Yb3+, which indicated that Yb3+ could be membrane active molecules with its effect on cell membranes as fundamental aspect of its toxicity.

Simultaneous Measurement of Water Desorption Isotherm and Heats of Water Desorption of Proteins Using Perfusion Isothermal Microcalorimetry

The purpose of this work was to study protein-water interactions using a perfusion isothermal calorimetry method by simultaneously measuring the water (de)sorption isotherm and heats of desorption (DeltaH(desorption)). Lysozyme, bovine serum albumin (BSA), and a monoclonal immunoglobulin (IgG) were studied. Desorption isotherms and DeltaH(desorption) were calculated using data from two perfusion systems, which measured heat flow resulting from interaction of water vapor with the protein sample and with pure water, respectively. The desorption isotherms calculated from the calorimetry were in good agreement with the gravimetric data. The average DeltaH(desorption) at high hydration was 54.6 kJ/mol and decreased (approaching heat of water evaporation) with desorption and passed through a minimum at protein specific water content, below which it increased again reaching 59.0 kJ/mol at the lowest hydration levels. The difference between the DeltaH(desorption) above the minimum and heat of water evaporation has been attributed to conformational changes in the protein. This conclusion is supported with data for lysozyme in which a dynamic glass like transition has been observed at the water content of the minimum in the calorimetric enthalpy data at 293 K. This work establishes perfusion calorimetry as a rapid and controlled method to study the thermodynamics of protein-water interaction.

Devitrification behavior and glass-forming ability of Cu–Zr–Ag alloys

This paper presents an influence of Ag addition on the glass-forming ability and devitrification behavior of Cu–Zr glassy alloys on heating. The crystallization kinetics and structure changes in Cu 45Zr 45Ag 10 and Cu 35Zr 45Ag 20 glassy alloys on heating were studied by X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. Based on the results obtained one can assume that the improvement of the glass-forming ability of the Cu–Zr alloys by the addition of Ag is connected with a particular crystallization mechanism and a higher reduced glass-transition temperature of the Cu 45Zr 45Ag 10 ternary alloy compared to the binary Cu 55Zr 45 counterpart. As observed in the present work crystallization of the Cu–Zr–Ag alloys is found to cause embitterment of the samples and should be avoided as these alloys are considered to be used as structural materials. The Cu 35Zr 45Ag 20 alloy shows possible submicron-scale phase separation upon annealing.

Influence of Al and Ag on the Devitrification Behavior of a Cu-Zr Glassy Alloy

This paper presents an influence of Al and Ag additions on the thermal stability and devitrification behavior of Cu-Zr glassy alloy on heating. The crystallization kinetics and structure changes in Cu50Zr45Al5 and Cu45Zr45Al5Ag5 glassy alloys on heating were studied by X-ray diffraction, transmission electron microscopy, differential scanning and isothermal calorimetry methods. The addition of Al and Ag to Cu50Zr50 alloy drastically changes its crystallization behavior. It is found that Cu50Zr45Al5 and Cu45Zr45Al5Ag5 glassy alloys show rather eutectic crystallization forming mostly stable phases while Cu50Zr50 glassy alloy exhibits a primary crystallization behavior forming a metastable monoclinic CuZr phase at the initial crystallization stage.

Thermochemistry of potassium morpholinodithiocarbamate

Results of thermochemical studies of a new compound, potassium morpholinodithiocarbamate, are presented. The enthalpies of its solution in water at various dilutions and the specific heat at 173–348 K were examined by the experimental methods of isothermal and dynamic calorimetry.

Calorimetric study of the enthalpies of solution of methyl iodides of dimethylamino grosshemin and diethylamino grosshemin in water and evaluation of the thermodynamic properties of their analogues

The method of isothermal calorimetry at dilutions (moles salt/moles water) of 1:9000, 1:18000, and 1:36000 was applied to study the heats of solution of methyl iodides of dimethyl-and diethylamino grosshemin. The data obtained were used to calculate the standard enthalpies of solution of C18H28O4NI and C20H32O4NI in an infinitely diluted (standard) aqueous solution. The heats of combustion and melting of C18H28O4NI and C20H32O4NI were estimated. The experimental and calculational techniques were combined to calculate the standard heats of formation of methyl iodides of dimethyl-and diethylamino grosshemin and their 66 analogues.

Improved method for measuring absolute O2(a1Δg) concentration by O2(a1Δg→X3Σg−) IR radiation

We describe an improved technique for measuring the absolute O2(a1Δ) concentration via the quantitative determination of IR radiation from O2(a1Δg→X3Σg−) transition. An exact geometrical optical model was first established, in which the influence of reflection and refraction on the radiation characteristics of a luminous volume source was given full consideration, making possible the accurate calculation of the coupling efficiency between the volume source and a receiving area. Then, an IR radiation receiving apparatus (IRRRA) was constructed and its responsivity (mV/W) to the power of IR radiation calibrated by a tungsten standard lamp. An optical detection system was, in turn, built according to the optical model with fine alignment between the IRRRA and an optical cell. We then demonstrate the procedure to obtain the absolute concentration of O2(a1Δ) flowing through the optical cell from a jet singlet oxygen generator from the signal of the IRRRA, the optical cell volume, and the coupling efficiency between the cell and the IRRRA. Moreover, to verify the accuracy of this method, the absolute O2(a1Δ) concentration was compared to that measured by an established isothermal calorimetry method. Based on the comparison of the O2(a1Δ) concentrations determined by the two methods, the Einstein A-coefficient was estimated as (2.70±0.84)×10−4 s−1, which agrees with Badger’s value of 2.58×10−4, Špalek’s of 2.24×10−4, Newman’s of 2.19×10−4, and Miller’s of 2.3×10−4 within the uncertainty of the experimental techniques. The method advanced in this article is worthwhile for the measurement of absolute O2(a1Δ) concentration in a chemical oxygen iodine laser or a singlet oxygen generator. It can also provide a general technique for the measurement of absolute concentrations of long-lifetime luminous species other than O2(a1Δ).