Calorimetric Signals Research Articles

Investigation and development of programmable system on chip based differential scanning calorimeter for thermal analysis of materials.

A differential scanning calorimeter was designed to study the thermal analysis of the materials for the nuclear reactor/allied facilities. The hardware and software were developed for measuring the calorimetric signals and had various features for the thermal analysis of the material. The processing of calorimetric signals was carried out by a programmable system-on-chip. Using a programmed temperature profile, the differential scanning calorimeter setup was tested, calibrated, and validated with standard aluminum and indium metal samples. It was found that the obtained results agree with the literature values. The methodology for the experiment was optimized. Various experiments were carried out, and the thermal analysis of different materials for nuclear reactors was investigated and studied. The instrumentation is also compact, accurate, reliable, and cost-effective for the thermal analysis of materials.

Acoustic emissions from spin crossover complexes.

Acoustic emission from the compounds [Fe(HB(tz)3)2] and [Fe(Htrz)(trz)2]BF4 was detected during the thermally induced spin transition and is correlated with simultaneously recorded calorimetric signals. We ascribe this phenomenon to elastic waves produced by microstructural and volume changes accompanying the spin transition. Despite the perfect reversibility of the spin state switching (seen by the calorimeter), the acoustic emission activity decreases for successive thermal cycles, revealing thus irreversible microstructural evolution of the samples. The acoustic emission signal amplitude and energy probability distribution functions followed power-law behavior and the characteristic exponents were found to be similar for the two samples both on heating and cooling, indicating the universal character, which is further substantiated by the well scaled average temporal shapes of the avalanches.

Impact of severe plastic deformation on the relaxation of glassy and supercooled liquid states of amorphous Pd40Ni40P20

The impact of severe plastic deformation by high-pressure torsion on the relaxation of the glassy and supercooled liquid states of Pd40Ni40P20 was investigated using a combination of differential scanning calorimetry, low-temperature heat capacity, and fluctuation electron microscopy. The changes in the calorimetric signals due to deformation and subsequent heat treatments were analyzed and a correlation between deformation (rejuvenation) and annealing (relaxation) was found in relation to medium-range order (MRO). Moreover, a coupling between the occurrence of an exothermic peak in the supercooled liquid state and specific changes in the MRO types were identified. These findings are comprehended in a potential energy landscape scheme offering a new approach for MRO engineering of glasses.

Cement Mortar Porosity by Modified Analysis of Differential Scanning Calorimetry Records.

A modified method of interpreting a heat flux differential scanning calorimetry records in pore structure determination is presented. The method consists of determining the true phase transition energy distribution due to the melting of water during a differential scanning calorimetry (DSC) heating run. A set of original apparatus functions was developed to approximate the recorded calorimetric signals to the actual processes of the water phase transition at a given temperature. The validity of the proposed calorimetric curves-based algorithm was demonstrated through tests on a cement mortar sample. The correct analysis required taking into account both the thermal inertia of the calorimeter and the thermal effects that are associated with water transitions over the fairly narrow temperature ranges close to 0 °C. When evaluating energy distribution without taking the shifts of the proposed modified algorithm into account, the volume of the pores with radii bigger than 20 nm was greatly overestimated, while that of the smaller pores (rp < 20 nm) was underestimated, in some cases by approximately 70%.

Preparation and characterization of a new solid form of praziquantel, an essential anthelmintic drug. Praziquantel racemic monohydrate

Praziquantel (PZQ) is a highly effective low-cost anthelmintic agent used as the first-choice treatment against schistosomiasis. The low solubility of the active is a major drawback for pharmaceutical formulation. A valid approach of the pharmaceutical industry for the improvement of the pharmacotechnical features of the active principles (such as solubility, processability, stability, among others), is the preparation of new solid forms, such as salts, polymorph, and pseudo-polymorph.Herein we report the preparation and characterization of a new solid form PZQ. The PZQ monohydrate (PZQ-MH) was prepared by a solventless procedure from the commercial racemate and the product was characterized at the solid-state employing optical digital microscopy, thermal methods (melting point, differential scanning calorimetry and thermogravimetric analysis), as well as and mid-infrared and near infrared spectroscopies. The chemical structure and content of water were full assessed by 1H nuclear magnetic resonance (NMR) in solution. The amount of water in PZQ-was also determined by different approaches, including thermogravimetric analysis and the loss on drying test. Solid-state 13C NMR (ssNMR) and X-ray powder diffraction (XRPD) completed the structural characterization of the new monohydrate.PZQ-MH showed a crystalline behavior during XRPD experiments and showed relevant differences in spectroscopic, calorimetric, ssNMR and XRPD signals when it was compared with the known crystal (Form A) and amorphous forms of PZQ. The determination of the intrinsic dissolution rate (IDR) of PZQ-MH was carried out as a functional characterization, observing that the new form had slightly higher IDR than Form A.

Heat Compensation Calorimeter as a Process Analytical Tool To Monitor and Control Bioprocess Systems

Biocalorimetry is a process analytical tool extensively employed to measure metabolic heat in order to track cellular activity. To eliminate the inherent demerits in conventional biocalorimeters, an advanced bench-scale heat compensation fermentation biocalorimeter was designed. Improvement in calorimetric signal sensitivity for bioprocess monitoring was achieved by ensuring isothermal condition in the reactor, by operating two independent proportional, integral, and derivative (PID) controls in tandem. Significant reduction in heat loss to the environment was accomplished by incorporating a secondary cascade loop into the cryostat controller. Nonbiological heat measured under different process conditions was calibrated and taken into account as part of the dynamic heat balance. Sensitivity of the system was further improved by incorporating two individual theromostating setups in the reactor housing, viz, a preheated bubble column and a circulating thermal bath fluid in the head plate. Sensitivity and stability of the calorimetric signal were improved to 6.73 mW/L and 0.43 mW/(L h), respectively. The performance of the developed calorimeter was evaluated via real-time monitoring of hyaluronic acid (HA) fermentation by S. zooepidemicus MTCC 3523 and aerobic growth of P. pastoris GSM 115, respectively. The calorimetric signals fingerprinted the changes in cellular metabolism and process behavior with viable precision. Experimentally determined oxy-calorific coefficients, for HA fermentation (684.4 kJ/mol) and P. pastoris growth (471.6 kJ/mol), were in good agreement with theoretical predictions, which validated the reliability and reproducibility of the developed application. Therefore, the developed high-sensitivity calorimeter offered a wide scope for its application as a process analytical technology (PAT) tool for bioprocess monitoring.

Calorimetric study of alkali and alkaline-earth cation adsorption and exchange at the quartz-solution interface

Cations in natural solutions significantly impact interfacial processes, particularly dissolution and surface charge measurements for quartz and silica, which are amongst the most naturally abundant and technologically important solids. Thermodynamic parameters for cation-specific interfacial reactions have heretofore been mostly derived instead of directly measured experimentally. This work investigates the energetics of adsorption and exchange reactions of alkali metal (M+) and alkaline earth (M2+) cations with the quartz surface by flow adsorption microcalorimetry, in tandem with in-situ pH measurements. The magnitudes of the heats of adsorption and exchange were found to increase along the Hofmeister series i.e., Li+<Na+<K+<Rb+<Cs+ and Mg2+<Ca2+<Sr2+<Ba2+, and exhibited strong correlations to bulk cation hydration enthalpies (ΔHhyd). These results suggest inner-sphere adsorption for all studied cations and highlight the role ΔHhyd plays in rationalizing these reactions and controlling their net overall enthalpy. pH measurements demonstrate that quartz surface charge will vary depending on the cation present, as is well known for amorphous forms of silica. Along with calorimetric signals, pH data revealed kinetic differences between the adsorption and desorption reactions of M+ and M2+, and individual cations within each group.

Thermodynamic properties and phase transitions of ternary Co–Cu–Si alloys with equiatomic Co/Cu ratio

Different amounts of Si element were introduced into binary Co50Cu50 alloy to investigate the thermodynamic properties and phase transitions of ternary Co50−x/2Cu50−x/2Six (x = 10, 20, 30, 40 and 50 at%) alloys. Their liquidus and solidus temperatures versus Si content were determined by the differential scanning calorimetry (DSC) method. It was found that the addition of Si element depressed both the liquidus and solidus temperatures as compared with binary Co50Cu50 alloy. In particular, the additions of 10 and 20 at% Si remarkably reduced the critical undercooling for liquid demixing to only 3 and 1 K, whereas no liquid phase separation took place in other Co50−x/2Cu50−x/2Six alloys. The relationship between the enthalpy of fusion and alloy composition was also established by a polynomial function on the basis of the measured data. The solidification microstructures of the DSC samples were investigated corresponding to the calorimetric signals, based on which the solidification pathway for each Co50−x/2Cu50−x/2Six alloy was elucidated. The Si element displays stronger affinity with the Co element than the Cu element. As Si content rises, the pseudobinary eutectic (Co + Co2Si), (Co2Si + CoSi), (CoSi + CoSi2) and (Cu3Si + Si) structures were successively formed, and there were no ternary intermetallic compounds in these alloys. The thermal diffusivity of solid ternary Co50−x/2Cu50−x/2Six alloys was determined by a laser flash method in a wide temperature range from 300 to 1180 K, which showed a decreasing tendency with the increase of Si content.

Engineered and Native Coenzyme B12-dependent Isovaleryl-CoA/Pivalyl-CoA Mutase

Adenosylcobalamin-dependent isomerases catalyze carbon skeleton rearrangements using radical chemistry. We have recently demonstrated that an isobutyryl-CoA mutase variant, IcmF, a member of this enzyme family that catalyzes the interconversion of isobutyryl-CoA and n-butyryl-CoA also catalyzes the interconversion between isovaleryl-CoA and pivalyl-CoA, albeit with low efficiency and high susceptibility to inactivation. Given the biotechnological potential of the isovaleryl-CoA/pivalyl-CoA mutase (PCM) reaction, we initially attempted to engineer IcmF to be a more proficient PCM by targeting two active site residues predicted based on sequence alignments and crystal structures, to be key to substrate selectivity. Of the eight mutants tested, the F598A mutation was the most robust, resulting in an ∼17-fold increase in the catalytic efficiency of the PCM activity and a concomitant ∼240-fold decrease in the isobutyryl-CoA mutase activity compared with wild-type IcmF. Hence, mutation of a single residue in IcmF tuned substrate specificity yielding an ∼4000-fold increase in the specificity for an unnatural substrate. However, the F598A mutant was even more susceptible to inactivation than wild-type IcmF. To circumvent this limitation, we used bioinformatics analysis to identify an authentic PCM in genomic databases. Cloning and expression of the putative AdoCbl-dependent PCM with an α2β2 heterotetrameric organization similar to that of isobutyryl-CoA mutase and a recently characterized archaeal methylmalonyl-CoA mutase, allowed demonstration of its robust PCM activity. To simplify kinetic analysis and handling, a variant PCM-F was generated in which the αβ subunits were fused into a single polypeptide via a short 11-amino acid linker. The fusion protein, PCM-F, retained high PCM activity and like PCM, was resistant to inactivation. Neither PCM nor PCM-F displayed detectable isobutyryl-CoA mutase activity, demonstrating that PCM represents a novel 5'-deoxyadenosylcobalamin-dependent acyl-CoA mutase. The newly discovered PCM and the derivative PCM-F, have potential applications in bioremediation of pivalic acid found in sludge, in stereospecific synthesis of C5 carboxylic acids and alcohols, and in the production of potential commodity and specialty chemicals.

Deconvolution of calorimeter response from electrical signals for extracting kinetic data

Calorimetry is a powerful tool for the study of chemical reactions and of biological systems. Nevertheless, reaction calorimeters and calorimeters may have high time constants. In this study, the correction brought by two types of deconvolution methods using electrical signals has been compared. The distortion of the calorimetric signals has been evaluated and its effect on kinetic parameters determination has been quantified. For this purpose, relative errors on activation energy, pre-exponential factors and kinetic exponents have been computed by reference to measured signals whose thermokinetic parameters were perfectly known. 1st and 2nd order deconvolutions were found to be more suitable for kinetic analyses. Integral methods allow obtaining the most accurate results with model-fitting and model-free kinetic methods, while differential methods are more sensitive to noise and submitted to numerical instability. The correction proposed allows slightly improving the accuracy in the estimation of kinetic parameters and to adapt the correction to the kind of kinetic method used. The deconvolution method has been applied to isothermal data, but the method is easily transposable to nonisothermal measurements.

Chip calorimetry and biomagnetic separation: Fast detection of bacterial contamination at low cell titers

Microcalorimetryisananalyticaltoolthatallowsthedirectmea-surementofheatgeneratedbybiologicalprocessesinlivingcells.Due to its high sensitivity, accuracy, and simplicity, the methodhas been widely employed in biology, microbiology, pharma-cology,biotechnology,andecology[1].Althoughnonspecificityof calorimetric signals can be a limiting factor, it can also beadvantageous since it is more likely to discover unknown phe-nomena[2].Indiagnosticmicrobiology,apromisingapplicationofcalorimetry,molecularmethodssuchaspolymerasechainre-action are increasingly used, but these methods are inherentlyrestricted to the detection of the specified pathogens [3].Despite the recent extensive research in living systems’ mi-crocalorimetry, there are only a few practical applications em-ploying this technology. This is mostly caused by the low sam-ple throughput of conventional microcalorimeters. One way tosolve this problem is to use multichannel instruments such asthe TAM 48-channel isothermal microcalorimeter (TA Instru-ments, New Castle, DE, USA). Using this device, Trampuz [4]and Daniels [5] conducted some extensive and successful clini-cal studies of the detection of bacterial contaminations in bodyfluids and analyzed antibiotic resistance of various pathogens.Furthermore, the Swedish company SymCel has recently an-

Rapid analysis of bacterial contamination of tap water using isothermal calorimetry

Highly sensitive calorimetry was evaluated for its potential for the monitoring of the bacterial contamination of drinking water. For that purpose, water samples were added to different media and bacterial growth was followed microcalorimetrically. Drinking water samples were either tested untreated or after artificial contamination with selected bacterial strains. Two bacteria, two growth media and two growth conditions (i.e. aerobic and anaerobic) were applied. Even minor initial bacterial contamination (1–100 cells mL−1) gave rise to calorimetric signals after 5–17 h growth. Calorimetry was thus faster than detection of bacterial contamination by plating on agar and inspection of colony formation, which was performed for comparison. It was further demonstrated theoretically that calorimetric detection is superior to colony detection. The heat production curves were characteristic for the strain, the medium and the growth conditions. It is hypothesized that a further refinement of the microcalorimetric method via the application of sets of specific media in combination with selective growth conditions should allow delimiting the identity of the contaminant.

Signal processing in cryogenic particle detection

We describe a signal-processing program for a data acquisition system for cryogenic particle detectors. The program is based on an optimal-filtering method for high-resolution measurement of calorimetric signals with a significant amount of noise of unknown origin and non-stationary behavior. The program was applied to improve the energy resolution of the alpha particle spectrum of an 241Am source.

Microcalorimetric qualitative analysis of biofilm development in porous media used in wastewater treatment by constructed wetland

In wastewater treatment by constructed wetland, the biodegradation capability of the biomass developed in the soil is one of the most important factors. For this kind of treatment unit, soil properties are studied to improve its filtration capacity and hydraulic residence time of the wastewater. The impact of soil properties like porosity and soil components on biomass development and biodegradation capacity seem to be less studied certainly due to the complexity of microbial identification techniques currently used. The study presented here is a preliminary work to validate that calorimetric technique could be a tool in the understanding of biodegradation capacity of wastewater treatment processes. Biofilm is preliminary developed in columns filled with different porous materials of well known porosity and constitutive components. These columns are fed with the same continuous flow of synthetic solution (C, N, and P) as a substrate amending during 3 weeks. Then each week, 2 mL samples of porous media from these columns are analyzed in isothermal calorimeter for 48 h. Net heat flow is recorded before and after substrate injection. This work results in the definition of the procedure for batch experiments in calorimeter for wastewater process efficiency. The results of these experiments show that the microbial reaction due to substrate amendment is highly depending on the porous material used for biofilm growth. Indeed calorimetric signals recorded lead to conclude that biofilm grown on plastic beads has a faster and more intensive reaction to glucose amendment than biofilm grown on glass beads. At least, two glass beads samples analyzed in the calorimeter after the same duration of feeding with synthetic solution have very different response to glucose or synthetic solution.

Calorimetric real time monitoring of lambda prophage induction

Calorimetry can be used for a noninvasive monitoring of metabolic and energy changes in bacterial cultures in real time. This potentially includes changes occurring during phage infection cycles. To demonstrate this, the growth of Escherichia coli K124 F − carrying the lambda prophage was monitored in a reaction calorimeter, while inducing the shift from lysogeny to lysis using methotrexate (MTX) as the inducer. Different phases of the phage infection were distinguishable calorimetrically. The calorimetric signals corresponded well to changes in growth stoichiometry and kinetics that were measured non-calorimetrically. The comparison of the calorimetric results with other measurements of activity revealed that the calorimetric method was superior since the calorimetric data mirrored the progress of infection in more detail. Contradictions between the calorimetric data and the appearance of infectious phages could result from inactivation of phage by MTX.

Isothermal measurement of heats of hydration in zeolites by simultaneous thermogravimetry and differential scanning calorimetry

AbstractA calorimetric method for determining isothermal partial and integral heats of hydration reactions (ΔH¯R,T,P${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ and ΔH∼R,T,P${\rm{\Delta }}{\tilde H_{{\rm{R,}}T,\,P}}$, respectively) in zeolites and other mineral hydrates is presented. The method involves immersing a dehydrated sample in a humid gas stream under isothermal conditions within a thermal analysis device that records simultaneous differential scanning calorimetric (DSC) and thermogravimetric analysis (TGA) signals. Monitoring changes in sample mass (corresponding to extent of reaction progress) coincident with a quantitative measurement of heat flow allows for direct detection of ΔH¯R,T,P${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ as a function of the extent of hydration, which can be integrated to determine ΔH∼R,T,P${\rm{\Delta }}{\tilde H_{{\rm{R,}}T,\,P}}$. In addition, it eliminates uncertainties associated with imprecise knowledge of the starting and final states of a sample during hydration. Measurement under isothermal conditions removes uncertainties associated with heat capacity effects that complicate interpretations of DSC measurements of dehydration heats conducted under traditional scanning temperature conditions. Example experiments on the zeolites natrolite, analcime and chabazite are used to illustrate strategies for quantifying ΔH¯R,T,P${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ and ΔH∼R,T,P${\rm{\Delta }}{\tilde H_{{\rm{R,}}T,\,P}}$ and minimizing errors associated with baseline uncertainties. Results from this method agree well with previously published values determined by other calorimetric techniques and regression of phase equilibrium data. In the case of chabazite, the results allowed detailed measurements of the variation in ΔH¯R,T,P${\rm{\Delta }}{\bar H_{{\rm{R,}}T,\,P}}$ for energetically different water types encountered progressively as the sample absorbed water. This technique complements and in many cases improves the quality of thermodynamic data obtained through phase equilibrium observations and other calorimetric techniques.

Synthesis of nitrate sodalite: An in situ scanning calorimetric study

The formation of nitrate sodalite, an important constituent of the resilient heels at DOE nuclear waste storage sites, was closely followed by oven synthesis, in situ calorimetry as a function of heating rate from 0.01 to 0.1 °C/min and X-ray diffraction. A transition sequence of amorphous–zeolite A–sodalite–cancrinite was confirmed. For in situ synthesis calorimetry, the heat flow peaks related to zeolite A formation are shifted to higher temperatures as heating rate increases. Although the end products are mostly nitrate sodalite, no calorimetric signals associated with zeolite A to sodalite conversion are detected. This suggests that the enthalpy of formation of zeolite A and sodalite are very similar and the zeolite A to sodalite conversion enthalpy is small. This conclusion is in accord with previous measurements by oxide melt solution calorimetry.

Combined laser calorimetry and photothermal technique for absorption measurement of optical coatings

To the best of our knowledge, a combined sensitive technique employing both laser calorimetry and a surface thermal lens scheme for measuring absorption values of optical coatings is presented for the first time. Laser calorimetric and pulsed surface thermal lens signals are simultaneously obtained with a highly reflecting UV coating sample irradiated at 193 nm. The advantages and potential applications of the combined technique and the experimental factors limiting the measurement sensitivity are discussed.

Energetics of Interaction between the G-protein Chaperone, MeaB, and B12-dependent Methylmalonyl-CoA Mutase

MeaB is an auxiliary protein that supports the function of the radical B(12)-dependent enzyme, methylmalonyl-CoA mutase, although its precise role is not understood. Mutations in the human homolog of MeaB, MMAA, lead to methylmalonic aciduria, an inborn error of metabolism that can be fatal. To obtain insights into the function of this recently discovered protein, we have characterized the entropic and enthalpic contributions to DeltaGdegree (assoc) for complexation of MeaB (in the presence and absence of nucleotides) with methylmalonyl-CoA mutase (in the presence and absence of cofactor). The dissociation constant for binding of methylmalonyl-CoA mutase and MeaB ranges from 34 +/- 4 to 524 +/- 66 nm, depending on the combination of nucleotide and mutase form. Holomutase binds MeaB 15-fold more tightly when the nonhydrolyzable GTP analog, GMPPNP, is bound versus GDP. In contrast, the apomutase binds MeaB with similar affinity in the presence of either nucleotide. Our studies reveal that a large structural rearrangement accompanies interaction between these proteins and buries between approximately 4000 and 8600A(2) of surface area, depending on the combination of ligands in the active sites of the two proteins. Furthermore, we demonstrate that MeaB binds GTP and GDP with similar affinity (K(d) of 7.3 +/- 1.9 and 6.2 +/- 0.7 microm, respectively at 20 degrees C) and has low intrinsic GTPase activity (approximately 0.04 min(-1) at 37 degrees C), which is stimulated approximately 100-fold by methylmalonyl-CoA mutase. These studies provide insights into the energetics of interaction between the radical enzyme methylmalonyl-CoA mutase and MeaB, which are discussed.

Study of the Hydrogenation of Selected Nitro Compounds by Simultaneous Measurements of Calorimetric, FT-IR, and Gas-Uptake Signals

The hydrogenation of nitrobenzene (NB) and ethyl-4-nitrobenzoate (NEE) over a Pd/carbon (1 wt % Pd) catalyst has been studied using a new small-scale, pressure-resistant reaction calorimeter (CRC.v4) fitted with an integrated infrared−attenuated total reflection (FT-IR−ATR) probe. This new calorimeter exploits the principles of power compensation and heat balance in combination with IR spectroscopy and on-line gas-uptake measurements. Thus, the reactions can be followed by three independent signals based on different properties of the chemical components. It was shown that, in the temperature and pressure range studied, all three simultaneous measurements of the NB hydrogenation can be described by a simple empirical kinetic model. The presence of an electron acceptor substituent like that in NEE leads to a consecutive hydrogenation with the accumulation of the corresponding hydroxylamine as an intermediate. The different information content of the simultaneously measured signals allow a quantitative desc...