Isothermal Calorimetric Method Research Articles

Hydration kinetics and apparent activation energy of cement pastes containing high silica fume content at lower curing temperature

To promote the application of silica fume (SF) in civil engineering in cold regions, relative influences from SF content and low temperature environment on the early hydration kinetics of composite cement pastes were evaluated based on the isothermal calorimetric method. The effect of high SF content on the apparent activation energy (Ea) of Portland cement and the filler effect (via the index of area multiplier) of SF on the hydration parameters was also analyzed. The results showed that the intensity of the shoulder peak (Al peak) of the hydration kinetic curve (heat flow curve) gradually grew as the SF content increased, and the double-peak phenomenon was gradually clear. The heat flow peak is delayed and lowered with the decreasing curing temperature, while the final time of the induction stage and the duration of the acceleration stage are delayed. Moreover, the duration of the acceleration stage was slightly extended with the increase of SF content. The full-width at half-maximum (FWHM) value of the heat flow curves dropped as the SF content and curing temperature increased. The low temperature environment and the inclusion of SF inhibited the growth in early hydration degree. The higher SF content mitigated the impact of low temperature on the hydration time parameter τ. The apparent Ea results also indicated that the SF reduced the temperature sensitivity of the hydration process of the composite cement pastes, which might contribute to the development of the hydration reaction at low temperatures. The AM (Area Multiplier) factor increased approximately linearly with increasing SF replacement levels. Apparent Ea decreased linearly with increasing AM, which may be attributed to a further reduction in the diffusion-controlled hydration rate of composite cement pastes with larger AM.

Analysis of Maximum Growth Rate and Construction of Predictive Growth Model for Bacillus cereusin Mashed Potato by Calorimetric Method

The maximum growth rate (μmax) of Bacillus cereus was estimated using a non-destructive isothermal calorimetric method, and a growth prediction model was constructed based on the measurement results. SCD medium and mashed potato were inoculated with serial-diluted inoculum of B. cereus. Heat generation curves were determined using an isothermal calorimeter at 35, 25, and 15℃. The μmax was determined from the relationship between the increase in B. cereus cell number and incubation time, which was detected through the heat generation of the B. cereus biological process. Moreover, the growth prediction model was constructed using Ratkowsky's square-root model. The results of the growth prediction model based on the data of the calorimetric and conventional culture methods for SCD were expressed as √μCalmax=0.0354 (T-4.9)[R2=0.99] and √μCCMmax=0.0335 (T-5.0)[R2=0.99]; a similar equation was provided by both methods. Conversely, the results of the growth prediction model based on the calorimetric method data for mashed potato were given as √μCalmax=0.0390 (T-8.5)[R2=0.99]; the maximum growth rates at 30 and 20℃ were predicted as 0.70 and 0.20 (1/hr), respectively. The maximum growth rates obtained using the conventional culture method were 0.63 and 0.29 (1/hr), respectively, similar to the calorimetric method results. The predictive microbiological analysis using the calorimetric method enabled the rapid provision of a growth prediction equation, and the number of samples could be substantially reduced compared with that for the conventional culture method.

Kinetic study on liquid propylene polymerization using a modified heat flow reaction calorimeter

Bulk phase polymerization of propylene with a 4th generation of Ziegler-Natta catalyst was kinetically investigated by means of heat flow calorimetry. The assumptions and modifications on isothermal calorimetric method were demonstrated. Our calibration method showed that heat exchange with the reactor cover plate is not constant over time. Therefore, the dynamic of cover plate temperature was considered in the calorimetric method. The polymerization rate profiles depending on hydrogen and external electron donor concentration have been investigated. Normalized polymerization profiles (Rp /Rpmax) are plotted and expressed as an exponential function of time. Effects of hydrogen and external electron donor (ED) concentration on Rpmax and polymerization rate were investigated as well. The results showed that by increasing hydrogen concentration, initial polymerization rate (Rpmax) increased. Hydrogen increased productivity by increasing the initial polymerization rate, while it had no negative effect on the rates of decay or its effect was small. The ED concentration was optimized so that the catalyst deactivation rate was at its lowest level. Also, changes in the ratio of activation to inactivation with ED concentration were examined, and a proportional change was observed.

Analysis of correlation between hydration heat release and compressive strength for blended cement pastes

This paper investigated the quantitative correlation relationship between hydration heat release and compressive strength in various blended cement pastes. Particularly, binary, ternary, and quaternary blends with three typical substitution materials were analysed (by mass): silica fume (0–5%), fly ash (0–30%), and quartz powder (0–20%). Techniques with the isothermal calorimetric method, strength measurement and scanning electron microscopy (SEM) were used to analyse the initial and hardened stages of blended cementitious pastes. Then, linear relationships were evaluated by using the Pearson statistical method. The results showed that adding substitution materials significantly changes release peak value and cumulative hydration heat, but peak time does not fluctuate evidently. Cumulative hydration heat of binary, ternary and quaternary blended cement pastes reduced to varying degrees compared with reference cement. The compressive strength of quaternary blends substantially decreased at 28 d when the substitution of cement exceeds 45%. Binary, ternary, and quaternary cement mixtures exhibited a strong linear correlation between cumulative hydration heat (hydration exothermic peak) and 28-day compressive strength at some special conditions, and the Pearson correlation coefficient of 0.8–1. Hence, the prediction of 28-day compressive strength from measuring hydration heat with isothermal calorimetric is valid for the particular blended mixture employed in this study.

Using isothermal calorimetry and FT-Raman spectroscopy for step-by-step monitoring of maize seed germination: case study

Thermoanalytical methods are widely used to study seed germination processes. Our research aimed to use them in order to monitor the germination of maize seeds. To this end, we employed—for the first time—the isothermal calorimetric method with full oxygen access. Dry seeds were placed in ampoules with threaded caps, filled with distilled water. Heat flow was recorded in microwatts at 20 °C for 72 h in order to determine changes in thermal power associated with germination. In parallel with these measurements, in the same time regime, we measured FT-Raman spectra, which allowed us to analyze how endosperm and embryo changed their chemical compositions during imbibition and germination. Spectra obtained for endosperm reflected chemical changes resulting from catabolic processes. We also analyzed variations in the secondary structure of proteins in the embryo accompanying germination. Decomposition of amide I bands proved that during germination and protein hydrolysis, the content of helical and β-sheet structures decreased. Furthermore, in the embryos of dry seeds, S-S linkages were in both gauche–gauche-trans and trans-gauche-trans conformations, but after imbibition, only gauche–gauche-trans conformation can be identified.

Critical insight into the interaction of naringenin with human haemoglobin: A combined spectroscopic and computational modeling approaches

The present study demonstrates critical insight into the binding of a bioactive flavanone naringenin with normal human haemoglobin (NHb). Both spectrophotometric and spectrofluorimetric studies reveal that naringenin interacts with NHb. The binding affinity constant and number of binding sites appear to be approximately (1.5 ± 0.2) × 104 M−1 and 1, respectively. Static quenching seems to be an important factor in binding process, as evident from steady-state and time-resolved fluorescence spectroscopic studies. Far UV circular dichroism spectroscopy depicts that binding of naringenin to NHb causes no change in the secondary structure of the protein, which is also evident from Fourier transform infrared spectroscopic study. Free energy change (ΔG0) for naringenin-NHb interaction, determined by spectroscopic and isothermal calorimetric method, appears to be −5.67 kcal/mol and −6.90 kcal/mol, respectively, and is close to the docking energy −6.84 kcal/mol. Molecular docking suggests that naringenin binds near the cavity of the tetrameric heme protein, forming hydrogen bonds with surrounding amino acid residues. The binding site is away from the heme moieties, implicating naringenin binding does not affect the oxygen binding capacity of NHb, which makes the protein a suitable carrier of the flavonoid.

Reversible Nanoparticle-Micelle Transformation of Ionic Liquid-Sulfonatocalix[6]arene Aggregates.

The effect of temperature and NaCl concentration variations on the self-assembly of 1-methyl-3-tetradecylimidazolium (C14mim(+)) and 4-sulfonatocalix[6]arene (SCX6) was studied by dynamic light scattering and isothermal calorimetric methods at pH 7. Inclusion complex formation promoted the self-assembly to spherical nanoparticles (NP), which transformed to supramolecular micelles (SM) in the presence of NaCl. Highly reversible, temperature-responsive behavior was observed, and the conditions of the NP-SM transition could be tuned by the alteration of C14mim(+):SCX6 mixing ratio and NaCl concentration. The association to SM was always exothermic with enthalpy independent of the amount of NaCl. In contrast, NPs were produced in endothermic process at low temperature, and the enthalpy change became less favorable upon increase in NaCl concentration. The NP formation was accompanied by negative molar heat capacity change, which further diminished when NaCl concentration was raised.

Dynamics in Polysaccharide Glasses and Their Impact on the Stability of Encapsulated Flavors

The aim of this work is to examine the correlation between measured instability of model flavor compounds in glassy matrices with the calorimetric relaxation times of the matrices. Spray-dried carbohydrate matrices were chosen as the model compounds for this study. Enthalpy relaxation times were determined for spray-dried carbohydrate matrices using differential and isothermal calorimetric methods. The losses of the volatile methyl acetate, ethyl acetate and limonene, as well as formation of limonene oxidation products, were measured by gas chromatography. Storage conditions were 30 and 40 °C, with samples equilibrated with 11, 23, 33 and 43 % RH at each temperature. A comparison of the relaxation times for temperatures below Tg was made using Modulated DSC (MDSC) and a Thermal Activity Monitor (TAM). TAM yields significantly lower values for relaxation times implying that it is capturing some of the faster dynamics as well as dynamics that are activated near Tg. However, plots of relaxation times as determined by both techniques versus temperature appear to converge at Tg. An increase in the relative humidity results in moderately higher loss of volatiles (methyl acetate, ethyl acetate and limonene) and greater oxidation rates. In general, there is a good correlation between relaxation time and stability, with greater enthalpy relaxation time associated with better stability. Enthalpy relaxation time appears to be a useful predictor of stability for both loss of volatiles and oxidation of limonene.

Effect of torsional isomerization and inclusion complex formation with cucurbit[7]uril on the fluorescence of 6-methoxy-1-methylquinolinium

Inclusion of 6-methoxy-1-methylquinolinium (C1MQ) in the cavity of cucurbit[7]uril (CB7) was studied by absorption, fluorescence, NMR and isothermal calorimetric methods in aqueous solution at 298 K. The free C1MQ exhibited dual-exponential fluorescence decay kinetics due to the two torsional isomers differing in the orientation of the methoxy moiety relative to the heterocyclic ring. The enthalpy-driven encapsulation of the heterocycle in CB7 led to a very stable 1 : 1 complex with a binding constant of (2.0 ± 0.4) × 10(6) M(-1). The rate of C1MQ-CB7 complex dissociation was found to be comparable to the NMR timescale. Because the methoxy moiety is oriented outward from the host, its s-cis-s-trans isomerization is slightly affected by the confinement. Inclusion complex formation significantly slowed down the photoinduced electron transfer from I(-) and N3(-) to the singlet-excited C1MQ, but did not preclude the reaction because long distance electron transfer occurred through the wall of the CB7 macrocycle. Due to the large difference in the quenching rate constant for free and encapsulated forms, C1MQ is an excellent probe for the study of the inclusion of nonfluorescent compounds in CB7 in the presence of Cl(-) or Br(-).

N-Hexane Bromination Using Barium Fluorobromate Ba(BrF4)2

It was observed that Ba(BrF4)2 demonstrates a high reactivity towards n-hexane. It was found that the heating the reaction mass proceed with intensive self-heating up to 40°C and release of elemental bromine. The GC-MS analysis showed that the main product of Ba(BrF4)2 interaction with n-hexane is 3-bromohexane. The optimal interaction parameters were found. The heat effect of the reaction was determined by isothermal calorimetric method, it was –1451kJ/mole. The qualitative composition of solid precipitate was determined by EDXRF and XRD analyses. BaF2 is formed as only solid product of the reaction between Ba(BrF4)2 and n-hexane. It was found that conditions of researched reaction are quite unusual for known free-radical hydrogen substitution processes in case of alkanes. Also we can conclude that Ba(BrF4)2 is much more soft reagent is case of interaction with alkanes in comparison with BrF3 and it can provide more or less selective bromination of alkane unlikely to BrF3.

Low Temperature n-alkanes Bromination without Catalysts

It has been observed that Ba (BrF4)2 demonstrated a high reactivity towards normal alkanes from C6H14 to C16H34. It has been found that the reactions ran with intensive self-heating and release of elemental bromine. The GC-MS analysis showed that the main product of Ba (BrF4)2 interaction with each alkane was its 3-bromoderivative. The optimal interaction parameters have been found. The heat effects of the reaction have been determined by the isothermal calorimetric method, it has been found that the heat effect of the bromination increased with the increase of the length of carbon chain of alkane.

Glycerol and urea can be used to increase skin permeability in reduced hydration conditions

The natural moisturizing factor (NMF) is a group of hygroscopic molecules that is naturally present in skin and protects from severe drying. Glycerol and urea are two examples of NMF components that are also used in skin care applications. In the present study, we investigate the influence of glycerol and urea on the permeability of a model drug (metronidazole, Mz) across excised pig skin membranes at different hydrating conditions. The degree of skin hydration is regulated by the gradient in water activity across the membrane, which in turn depends on the water activity of the formulation in contact with the skin membrane. Here, we determine the water activity of all formulations employed using an isothermal calorimetric method. Thus, the gradient in water activity is controlled by a novel experimental set-up with well-defined boundary conditions on both sides of the skin membrane. The results demonstrate that glycerol and urea can retain high steady state flux of Mz across skin membranes at dehydrating conditions, which otherwise would decrease the permeability due to dehydration. X-ray diffraction measurements are performed to give insight into the effects of glycerol and urea on SC molecular organization. The novel steady state flux results can be related to the observation that water, glycerol, and urea all affect the structural features of the SC molecular components in a similar manner.

Structure and Properties of a Complex of α-Synuclein and a Single-Domain Camelid Antibody

The aggregation of the intrinsically disordered protein α-synuclein to form fibrillar amyloid structures is intimately associated with a variety of neurological disorders, most notably Parkinson's disease. The molecular mechanism of α-synuclein aggregation and toxicity is not yet understood in any detail, not least because of the paucity of structural probes through which to study the behavior of such a disordered system. Here, we describe an investigation involving a single-domain camelid antibody, NbSyn2, selected by phage display techniques to bind to α-synuclein, including the exploration of its effects on the in vitro aggregation of the protein under a variety of conditions. We show using isothermal calorimetric methods that NbSyn2 binds specifically to monomeric α-synuclein with nanomolar affinity and by means of NMR spectroscopy that it interacts with the four C-terminal residues of the protein. This latter finding is confirmed by the determination of a crystal structure of NbSyn2 bound to a peptide encompassing the nine C-terminal residues of α-synuclein. The NbSyn2:α-synuclein interaction is mediated mainly by side-chain interactions while water molecules cross-link the main-chain atoms of α-synuclein to atoms of NbSyn2, a feature we believe could be important in intrinsically disordered protein interactions more generally. The aggregation behavior of α-synuclein at physiological pH, including the morphology of the resulting fibrillar structures, is remarkably unaffected by the presence of NbSyn2 and indeed we show that NbSyn2 binds strongly to the aggregated as well as to the soluble forms of α-synuclein. These results give strong support to the conjecture that the C-terminal region of the protein is not directly involved in the mechanism of aggregation and suggest that binding of NbSyn2 could be a useful probe for the identification of α-synuclein aggregation in vitro and possibly in vivo.

Effect of Cu and P on the Crystallization Behavior of Fe-Rich Hetero-Amorphous FeSiB Alloy

The effect of simultaneously adding P and Cu on the crystallization behavior of hetero-amorphous FeSiB alloy was investigated. Thermal properties and microstructure evolution were studied by means of X-ray diffraction, transmission electron microscopy, differential scanning, and isothermal calorimetric methods. It is found that the addition of P and Cu to the FeSiB alloy changes its crystallization temperature as well as the apparent activation energy for crystallization. The crystallization process is mainly dominated by three-dimensional growth with various nucleation rates for the selected FeSiB(PCu) alloys. The phases formed during crystallization for the different alloys of Fe84Si4B12, Fe83:3Si4B12Cu0:7, and Fe83:3Si4B8P4Cu0:7 are similar. The refinement effect of adding P and Cu to the FeSiB alloys is observed. The mean size of � -Fe phases decreases from 200 nm to about 20 nm. [doi:10.2320/matertrans.M2009206]

An in vitro method for the quantitative determination of the antimicrobial efficacy of silver-containing wound dressings

Treatment with silver-containing wound dressings is becoming an increasingly popular strategy to eliminate growth of opportunistic wound pathogens during the healing process. However, there are concerns over the possible side-effects of silver to the patient; coupled to the cost of silver as an ingredient there is a desire to ensure that wound dressings contain the least quantity of active ingredient to ensure the minimum bactericidal concentration (MBC) of silver is maintained in the wound environment. This requires the ability to determine the efficacy of silver directly within the wound environment; an extremely complicated task that is difficult using classical (plate counting) microbiological assays because these cannot be conducted in situ. Here, we report a quantitative method for determining the efficacy of silver in wound dressings using an isothermal calorimetric method. The growth curves of P. aeruginosa (NCIMB 8628) were recorded in growth medium and in growth medium containing AQUACEL ® Ag Hydrofiber ® dressing. It was found that 10 mg of dressing was sufficient to ensure no detectable growth of organism in 2.5 mL of medium inoculated to 10 6 cfu/mL. This corresponded to a silver load of 1.1 × 10 −6 moles (equivalent to 4.4 × 10 −4 M, in the volume of medium used in the experiment). Experiments conducted with silver nitrate rather than dressing indicated the MBC of silver against P. aeruginosa was 1 × 10 −4 M. The results suggested that not all of the silver in the dressing was bioavailable, at least over the lifetime of the experiment. One advantage of this effect would be the lack of excess availability of the silver, which allays fears of potential toxicity to the patient and may provide an extended period of time over which the dressing is bactericidal.

Photoswitchable multivalent sugar ligands: synthesis, isomerization, and lectin binding studies of azobenzene-glycopyranoside derivatives.

Coating of azobenzene chromophore with multivalent sugar ligands has been accomplished. Such sugar coating allows the study of the isomerization properties of this chromophore in aqueous solutions. The predominantly cis-isomer-containing photostationary state (PS) mixture of these azobenzene derivatives is found to be stable for hours. The rate constants for their isomerization, as well as the Arrhenius activation energies, are determined experimentally. An assessment of the lectin binding properties of the lactoside bearing isomeric azobenzene derivatives, by isothermal calorimetric methods, reveals the existence of an unusual cooperativity in their binding to lectin peanut agglutinin. Thermodynamic parameters evaluated for the trans and the PS mixture are discussed, in detail, for the lactoside bearing bivalent azobenzene derivative.

Absolute Measurements of the Combustion Heat of Natural Gas

A new isothermal calorimetric method for measuring the combustion heat of gas, relying upon the operation principle of the heat pipe, is considered together with the sequence of thermal processes occurring when this method is used. The functional diagram of the calorimeter is analyzed. Two procedures for measuring the heat effects are presented.

AC loss measurements of Nb/sub 3/Sn wire carrying transport current

The AC losses of internal-tin Nb/sub 3/Sn wires have been measured by an isothermal calorimetric method in triangular-wave fields at ramp rates of up to 1.2 T/s and in small-amplitude ripple fields biased with DC fields of up to 9 T. Measurements were made both with and without transport currents, which were both AC and DC. Without transport currents, losses had near-parabolic profiles when plotted against bias field with constant ripple amplitude, against triangular-wave ramp rate, or against triangular-wave ramp amplitude. With transport currents of up to 90% of critical, losses for triangular-wave field were shown to increase up to 17% with increasing DC currents and up to 10% with increasing AC currents. With DC transport currents, the scaling of loss by (1+i/sup 2/), where i is the ratio of transport current to critical current, may be a good approximation.

The calorimetric study in the 13·8–340°K range of δ-valerolactone, its polymer, and of the δ-valerolactone polymerization

Precision adiabatic and isothermal calorimetric methods have been used for the first time to study the thermodynamic properties of δ-valerolactone (VL), its polymer (PVL) and the thermodynamic parameters of the VL bulk polymerization. The heat contents C° p of the monomer and polymer were determined with ∼0·3% precision, also the temperature and enthalpy of the physical transitions; the functions H° ( T)− H° (0), S° ( T) and G° ( T)− H° ()) have been calculated for the 0–350°K range. The S° g (0), S° er, H° g (0)− H° er (0) values of the PVL have been estimated in the glass-like state. The enthalpy of the VL→PVL process has been determined at 298·15°K and p = 101·325 kPa. The found values have been used to calculate the enthalpy, entropy and Gibbs energy of the VL polymerization and also the equilibrium concentration of the monomer in the reaction mass at normal pressure.

Twin isothermal calorimeter method for the determination of specific heat of soil

Abstract The twin isothermal calorimeter method was proposed for determining the specific heat of soil. A high accuracy of measurement (±3%) was gained in comparison with other methods. The twin isothermal calorimeter consisted of two Dewar flasks of the same size in a constant-temperature bath. Each flask was equipped with a thermometer, a heater, and a stirrer. The most advantageous point in this method is to measure directly the temperature changes of the samples by means of the twin structure of the calorimeter. The specific heat of quartz sand and a few kinds of clay was measured. The results were sufficiently good.