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PubMed1983

Extent of polymerization of dental resins by differential scanning calorimetry.

The traditional infrared spectroscopic methods for assessing the degree of polymerization of dental monomers are often hampered by the difficulties of sample preparation and, in the case of composites, by interference from the filler component. These difficulties may be circumvented by the use of another technique, differential scanning calorimetry (DSC). In this preliminary investigation, DSC was used to ascertain the degree of vinyl polymerization of an experimental monomer system consisting of seven parts BIS-GMA and three parts TEGDMA (triethylene glycol dimethacrylate). Thermally-activated polymerizations of this monomer system were studied using benzoyl peroxide (BP) as the initiator. Both the heating rate and the concentration of BP affected the percent of reacted vinyl groups. For a BP concentration of 0.39% and heating rates of 10 degrees/min and 2.5 degrees/min, conversions were 73 and 38%, respectively. Chemically-activated polymerizations using BP and fast-acting amine accelerators (e.g., p-t-butyl-N,N-dimethylaniline) gave approximately the same results (e.g., 50% conversion) as those obtained with slower-acting promoters (e.g., ascorbyl palmitate). Experimental difficulties are encountered in observing an exotherm with the very reactive accelerators unless the other parameters (e.g., BP or inhibitor content) involved in the reaction are adjusted accordingly. As a method for evaluating the performance of various dental monomers, initiator systems, and inhibitors, DSC has great potential utility.

Bisphenol A-Glycidyl Methacrylate↗
PubMedDate not supplied

Achievement of steady state optimizes results when performing indirect calorimetry.

BACKGROUND: The use of steady state as the endpoint for performance of indirect calorimetry (IC) is controversial. We designed this prospective study to evaluate the necessity and significance of achieving steady state. METHODS: Patients with respiratory failure placed on mechanical ventilation in a short- or long-term acute care unit at any 1 of 3 university-based urban hospitals were eligible for the study. The 24-hour total energy expenditure (TEE) was determined by a Nellcor Puritan Bennett 7250 continuous IC monitor. Measured gas exchange parameters were obtained and averaged every 1 minute for the initial hour and then every 15 minutes for the next 23 hours. Over the initial hour, resting energy expenditure (REE) was averaged for intervals over the first 20, 30, 40, and 60 minutes, and for various definitions of steady state where oxygen consumption (VO2) and carbon dioxide production (VCO2) changed by <10%, 15%, and 20%. Coefficient of variation (CV) was calculated for VO2 over the first 30 minutes of study. RESULTS: Twenty-two patients (mean age, 52.8 years, 59% male, mean Acute Physiology and Chronic Health Evaluation (APACHE III) score 42.0) were entered in the study. The best correlation between short-term "snapshot" REE and the 24-hour TEE was achieved by the steady-state period defined by the most stringent criteria (change in VO2 and VCO2 by <10%). The average REE for all steady-state and interval periods correlated significantly to TEE with no significant difference in the absolute values for REE and TEE. Adding 10% for an activity factor to the average REE for each steady-state and interval period again correlated to TEE in a similar fashion with the same R value, but the absolute values for REE + 10% for all steady-state and interval periods were significantly different than the corresponding TEE. In those patients with less variation (CV for VO2 < or = 9.0), the REE obtained for the steady-state period defined by the most stringent criteria still had the best correlation, but similar correlation could be obtained by interval testing of > or = 30-minute duration. In those patients with greater variation (CV for VO2 >9.0), interval testing of at least 60 minutes or more was required to attain levels of correlation similar to that achieved by the steady-state period defined by the most stringent criteria. CONCLUSIONS: These data support the use of steady state, best defined as an interval of 5 consecutive minutes whereby VO2 and VCO2 change by <10%. The mean REE from this period correlates best to the 24-hour TEE regardless of CV. IC testing can be completed after achievement of steady state. Activity factors of 10% to 15% should not be added to the steady-state REE, because this practice significantly decreases the accuracy. In patients who fail to achieve steady state, the CV helps to determine the appropriate duration of IC testing. In those patients with a low CV (< or = 9.0), 30-minute test duration is adequate. In patients with CV >9.0, test duration of at least 60 minutes may be required. These latter patients should be considered for 24-hour IC testing.

Adolescent↗
PubMedDate not supplied

Clinical use of the respiratory quotient obtained from indirect calorimetry.

BACKGROUND: The respiratory quotient (RQ) obtained from indirect calorimetry (IC), defined by the ratio carbon dioxide production (VCO2)/oxygen consumption (VO2), is affected by extremes of substrate use by the body. Underfeeding, which promotes use of endogenous fat stores, should cause decreases in the RQ, whereas overfeeding, which results in lipogenesis, should cause increases in the RQ. Marked increases in VCO2 (with subsequent increases in RQ) in response to overfeeding may cause respiratory compromise in patients with limited pulmonary reserve. Thus, variation in the RQ in response to the feeding regimen may indicate inappropriate feeding and serve as a marker for patient intolerance. This prospective, multicenter study was designed to determine the clinical use of RQ for monitoring adequacy and tolerance of nutrition support. METHODS: Patients in any 1 of 30 long-term acute care Kindred hospitals made nil orally (NPO) and placed on total parenteral or enteral feeding were eligible for this study. Arterial blood gas, serum ketones, 24-hour collection of urine urea nitrogen, and IC measurements were obtained on all. Actual volume of enteral/parenteral feeding infused over the 24 hours before performance of IC was documented. RESULTS: A total of 263 patients (mean age, 70.2 years, 57.4% male) were entered in the study. Of the 263 study patients, 88.6% required mechanical ventilation, and 92.0% received enteral tube feeding only. Overall, 41.5% of patients were overfed, receiving >110% of required calories, whereas 34.2% were underfed, receiving <90% of required calories. The ratio of calories provided/required correlated significantly with overall measured RQ (p < .0001; R2 = .16). Correcting for the metabolism of protein by calculating a nonprotein RQ (NPRQ) from a 24-hour urine urea nitrogen did not improve this correlation (p < .0001, R2 = .32). Using a measured NPRQ >1.0 to identify overfeeding had an acceptable specificity of 85.1% but a low sensitivity of 38.5%. Similarly, use of a NPRQ <0.85 to determine underfeeding had a specificity of 72.2% and a sensitivity of 55.8%. Comparing the measured NPRQ with a predicted reference RQ (based on percent infusion of carbohydrate/fat and the Lusk table) did not improve the overall use of RQ. In the majority of patients (67.7%), comparison of the measured NPRQ to the predicted value failed to differentiate appropriate (meeting 100% +/- 10% of requirements) from inappropriate feeding. Deviation of the measured NPRQ from predicted failed to identify factors unrelated to substrate use purported to affect the RQ (such as acid/base disturbances or hyper/hypoventilation). Increasing measured RQ did correlate significantly with increasing respiratory rate (p = .002, R2 = .04) and decreasing tidal volume (p = .002, R2 = .04), suggesting reduced tolerance with development of shallow rapid respirations and ventilatory compromise. CONCLUSIONS: Although changes in the overall and nonprotein RQ correlate to percent calories provided/required, low sensitivity and specificity limit its efficacy as an indicator of over- or underfeeding. The RQ should not be used to finely adjust the nutrition support regimen. Elevation of overall measured RQ > or = 1.0 may be associated with reduced tolerance and mild respiratory compromise. The clinical use of RQ is limited to a marker of test validity (to confirm measured RQ values are in physiologic range) and a marker for respiratory tolerance of the nutrition support regimen.

Adult↗
PubMedDate not supplied

Metabolic response to injury and illness: estimation of energy and protein needs from indirect calorimetry and nitrogen balance.

The metabolic response to injury and illness as manifested by increases in energy expenditure and nitrogen losses makes it difficult for the clinician to evaluate calorie and protein needs. A method for determining daily calorie needs in hospitalized patients is presented. Average increases in resting metabolic expenditure for a group of patients following elective operation, skeletal trauma, skeletal trauma with head injury, blunt trauma, sepsis and burns were determined by indirect calorimetry and protein need by urinary nitrogen losses over extended time periods. Total daily calorie needs were then calculated, using the Harris-Benedict equation and adjusting this value upward using a previously measured activity and injury factor to arrive at the daily needs. Protein requirements may be determined on periodic 24 hour urine samples analyzed for the urinary urea nitrogen and adjusting this to a total nitrogen or protein equivalent. This approach to estimating the calorie nitrogen needs of the hospitalized patient under various degrees of stress more closely approximates the patient's variable needs at the height of the catabolic response and during convalescence.

Basal Metabolism↗
PubMedDate not supplied

Comparative study of maltitol and sucrose by means of continuous indirect calorimetry.

The metabolism of the hydrogenated disaccharide maltitol was compared to that of sucrose in a group of eight normal subjects. On two separate days, with an interval of at least one week each subject ingested a load of 30 g of either substance. The evolution of the levels of plasma glucose, insulin, and free fatty acids was followed during the 6 hr following the oral load. Carbohydrate and lipid oxidation rates were assessed simultaneously by continuous indirect calorimetry during the 6 hr following the oral load. Plasma glucose and insulin peaks occurred 30 min after ingestion of the load for both sugars. The peak of the delta glucose concentration was significantly smaller after maltitol than after sucrose (21 +/- 4 vs 38 +/- 4 mg/100 ml, p less than 0.02), as was the peak of the delta insulin concentration (9.3 +/- 2.7 microU/ml after maltitol vs 25.5 +/- 5.0 microU/ml after sucrose, p less than 0.001). The peak of the stimulation of glucose oxidation occurred 60 min after the load of sucrose and 90 min after the load of maltitol. The delta glucose oxidation was significantly lower with maltitol than with sucrose during the first 90 min after the ingestion of the load. It was slightly higher (although not significantly) with maltitol than with sucrose starting from the 210th min. Maltitol resulted in a cumulated suprabasal glucose oxidation which amounted to 40% that obtained with sucrose after 180 min.

Adult↗
PubMedDate not supplied

Short-term infusion of azelaic acid vs intralipid in healthy subjects evaluated by indirect calorimetry.

Medium-chain dicarboxylic acids (MCDA) are usually considered byproducts of beta-oxidation when omega-oxidizable medium-chain monocarboxylic acids are accumulated, as in beta-oxidation impairment. However, evidence exists of a mitochondrial and cytoplasmatic peroxisomal carnitine independent beta-oxidation of these diacids. Our purpose was to evaluate whether MCDA could be used as source of calories. The metabolic response to intravenous administration of azelaic acid (AA) vs Intralipid (IL) was evaluated in six healthy overnight fasting male volunteers who received an infusion of 10 g of AA over 80 min and as a control 10 g of IL. AA reached a peak concentration at 80 min, (589 +/- 61 micrograms/ml) and was rapidly cleared from plasma (82 +/- 5 micrograms/ml at 240 min). Respiratory and metabolic parameters were evaluated by indirect calorimetry from the beginning of the infusion for 240 min. In both groups the CO2 production (VCO2) remained unchanged with no significant change from basal values. The O2 consumption (VO2 ml/min/m2) increased over basal values reaching a peak at the end of the infusion in both groups (AA from 119.4 +/- 16.9 to 143.0 +/- 27.6; IL from 124.7 +/- 16.8 to 152.3 +/- 29.5). Respiratory quotient (RQ) consequently decreased significantly (AA from 0.85 +/- 0.06 to 0.76 +/- 0.06; IL from 0.89 +/- 0.06 to 0.78 +/- 0.03) and calories derived from lipids increased. Metabolic rate (MR kcal/hr/m2) showed a slight increase (AA from 34.0 +/- 4.4 to 40.3 +/- 6.8; IL from 35.9 +/- 5.1 to 41.3 +/- 10.5). There was no significant difference between AA and IL treatment in all measurements.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMedDate not supplied

Factors contributing to increased energy expenditure in thermal injury: a review of studies employing indirect calorimetry.

In summary, a remarkably close agreement exists for the mean MEE measured in 28 studies of severe burn trauma. This is especially surprising given the variability in sample sizes, measurement techniques, study designs, and DPBs studied. The mean MEE calculated from the data published in these reports is listed in the final column of Table I. For more than 450 cases, an unweighted MEE is 2750 +/- 85 kcal/day. For those studies prior to 1980, the mean MEE exceeds 3000 kcal/day in eight of 14 reports vs only two of 14 published after 1980. Even so, the mean MEE for the pre-1980 reports differs by only 200 kcal/day (2960 +/- 120, n = 14). The accepted notion that the degree of elevation in MEE is in proportion to the % BSAB up to about 60% BSAB is useful in a general sense but must be applied with caution. The recent studies, which include proportionately more burns exceeding 80% BSAB, suggest an elevation in MEE in these cases. Nevertheless, a physiologic plateau apparently exists at or slightly below 2 x normal RMR at the peak of MEE. The magnitude of the MEE response results from an undefined interaction among several factors of which some have been examined while others such as inflammatory mediators are only beginning to receive study. The contributions to reduction in MEE from interventions to control cardiac output and peripheral cooling, core temperature, evaporative water (heat) loss, and substrate cycling have been reviewed. The importance of indirect calorimetry in patient care is highlighted by the large variability in similarly injured individuals and in the unexplained component of regression analyses.(ABSTRACT TRUNCATED AT 250 WORDS)

Burns↗
PubMedDate not supplied

Accuracy of 30-minute indirect calorimetry studies in predicting 24-hour energy expenditure in mechanically ventilated, critically ill patients.

BACKGROUND: There is no consensus regarding the optimal duration of measurement or time of day to perform indirect calorimetry (IC). Energy expenditure (EE) varies at different times of day and with different activity levels. We sought to assess the variability of EE in mechanically ventilated patients over a 24-hour period and the accuracy of 30-minute IC studies in predicting the 24-hour energy expenditure (EE24). METHODS: The study was a prospective comparison between the resting EE obtained by 30-minute measurement of IC and EE values obtained from 24-hour measurements. Tests were performed in the Medical Intensive Care Unit (MICU) of a tertiary care, university hospital. Oxygen consumption (VO2) and carbon dioxide production (VCO2) were measured for 24 hours in eight ventilated patients. Measurements were made every 3 minutes and used to calculate 30-minute and 24-hour oxygen consumption values. EE24 was calculated using the modified Weir equation. Each 30-minute interval was compared with the value obtained from the 24-hour measurement. RESULTS: Three hundred forty-one of 384 30-minute intervals remained for analysis. Average EE24 measured was 1490 +/- 486 kcal/d. Average EE24 predicted by extrapolation from 30-minute studies was 1501 +/- 503 kcal/d, with a mean difference of 0 +/- 209 kcal/d from the measured 24-hour values (range: -1068 to +585 kcal/d). Thirty-minute studies were within 20% of 24-hour measurements for 89% of intervals. The difference between 24-hour and 30-minute studies correlated with changes in minute ventilation (VE), heart rate, systolic blood pressure, and breath rate from their 24-hour means (p < .001). The mean error of EE estimate was greatest between 3 and 11 PM (p < .001). CONCLUSIONS: We conclude the following: (1) EE in MICU patients is variable; (2) 30-minute IC studies predict measured EE24 acceptably well for clinical purposes; and (3) accuracy is maximized if a 30-minute study is performed between 11 PM and 3 PM, and when Ve, heart rate, systolic blood pressure, and breath rate are near the day's average.

Adult↗
PubMed2005

Determination of thermodynamic parameters of Xerocomus chrysenteron lectin interactions with N-acetylgalactosamine and Thomsen-Friedenreich antigen by isothermal titration calorimetry.

BACKGROUND: Lectins are carbohydrate-binding proteins which potentially bind to cell surface glycoconjugates. They are found in various organisms including fungi. A lectin from the mushroom Xerocomus chrysenteron (XCL) has been isolated recently. It shows insecticidal activity and has antiproliferative properties. RESULTS: As the monosaccharide binding specificity is an important determinant of lectin function, we determined the affinity of XCL for the galactose moiety. Isothermal titration calorimetry studies revealed a dissociation constant Kd of 5.2 microM for the XCL:N-acetylgalactosamine interaction at 27 degrees C. Higher affinities were observed at lower temperatures and higher osmotic pressures. The dissociation constant was five hundred times higher for the disaccharide beta-D-Gal(1-3)-D-GalNAc, Thomsen-Friedenreich (TF) antigen (Kd of 0.94 microM). By using fetuin and asialofetuin in interaction with the XCL, we revealed its ability to recognize the Thomsen-Friedenreich motif on glycoproteins. CONCLUSION: The XCL antiproliferative effect and the TF antigen specificity presented in this work suggest that XCL and ABL may have similar binding mechanisms. The recent structure determination of these two proteins lead us to analyse these interactions in the light of our thermodynamic data. The understanding of this type of interaction may be a useful tool for the regulation of cell proliferation.

Acetylgalactosamine↗
PubMed1997

Comparison of face mask, head hood, and canopy for breath sampling in flow-through indirect calorimetry to measure oxygen consumption and carbon dioxide production of preterm infants < 1500 grams.

Complete sampling of expired air is essential for accurate O2 consumption(CO2 production) [VO2(VCO2)] measurements with flow-through indirect calorimetry. In preterm infants complete sampling is critical, because only low sampling flows can be used. The accuracy of the various breath sampling systems at low flows and their patient compatibility is untested. We therefore measured 1) the accuracy of VO2(VCO2) measurements with a face mask, a head hood, and a canopy in vitro at low sampling flows; 2) the effect of breathing on measurements with the face mask; and 3) the effect of breath sampling systems on activity and body temperature of preterm infants. VO2(VCO2) were measured with a Deltatrac II. In vitro we used a methanol miniburner incorporated into a doll, which could simulate low VO2(VCO2) and tidal breathing. In vivo we studied seven preterm infants < 1500 g. With the face mask VO2(VCO2) measurements were accurate at a flow of 3 L/min (error -1 +/- 0.8%), when tidal volume was < 15 mL/breath and the distance between mask and manikin < 1 cm. With hood and canopy VO2(VCO2) were underestimated at a flow of 3 L/min (error -13 +/- 1% and -14 +/- 5%), and results were markedly influenced by body position. For accurate measurements, the hood needed a flow of 4.5 L/min, the canopy 8.3 L/min. In vivo the face mask did not increase heart rate, respiration, activity, or rectal temperature, but hood and canopy increased rectal temperature by 0.3-0.4 degree C. For VO2(VCO2) measurements in infants < 1500 g, a face mask should be used, which is accurate at low flows and does not change body temperature. Accuracy at low flows and patient compatibility of breath sampling systems should be evaluated and reported for VO2(VCO2) measurements in preterm infants.

Body Temperature↗
PubMed2003

Thermal porosity analysis of croscarmellose sodium and sodium starch glycolate by differential scanning calorimetry.

The aim of the study was to demonstrate the applicability of differential scanning calorimetry (DSC) on porosity analysis for cellulose and starch. Croscarmellose sodium (CCS) and sodium starch glycolate (SSG) were allowed to sorb moisture in 85%, 90%, 95%, and 100% relative humidity (RH) at 40 degrees C for 24 hours. The pretreated samples were then subjected to DSC running temperature ranging from 25 degrees C to -50 degrees C at a cooling rate of 10 degrees C/min. The cooling traces of water crystallization, if present, were transformed to porosity distribution via capillary condensation using Kelvin's equation. The porosity analysis of CCS and SSG was also done using nitrogen adsorption as a reference method. It was found that sorbed water could not be frozen (in cases of 85% and 90% RH) until the moisture content exceeded a cutoff value (in cases of 95% and 100% RH). The nonfreezable moisture content was referred to tightly bound, plasticizing water, whereas the frozen one may be attributed to loosely bound water condensation in pore structure of CCS and SSG surfaces. Not only capillary condensation but also the tightly bound, nonfreezable monolayer water lying along the inner pores of the surface contributed to porosity determination. Good agreement with less than 5% deviation of mean pore size was observed when the results were compared with nitrogen adsorption. The narrower pore size distributions, however, were obtained because of the limitations of the technique. It was concluded that pore analysis by DSC could be successful. Further research needs to be done to account for limitations and to extend the applicability of the technique.

Calorimetry, Differential Scanning↗
PubMed2006

Quantitative measurement of indomethacin crystallinity in indomethacin-silica gel binary system using differential scanning calorimetry and X-ray powder diffractometry.

Differential scanning calorimetry (DSC) and X-ray powder diffractometry (XRPD) methods were developed for the quantitative analysis of the crystallinity of indomethacin (IMC) in IMC and silica gel (SG) binary system. The DSC calibration curve exhibited better linearity than that of XRPD. No phase transformation occurred in the IMC-SG mixtures during DSC measurement. The major sources of error in DSC measurements were inhomogeneous mixing and sampling. Analyzing the amount of IMC in the mixtures using high-performance liquid chromatography (HPLC) could reduce the sampling error. DSC demonstrated greater sensitivity and had less variation in measurement than XRPD in quantifying crystalline IMC in the IMC-SG binary system.

Calibration↗
PubMed1985

Study of glucose and lipid metabolism by continuous indirect calorimetry in Graves' disease: effect of an oral glucose load.

Glucose and lipid metabolism were studied in 12 patients with hyperthyroid Graves' disease for 3 h during an oral glucose tolerance test (100 g) by continuous indirect calorimetry. In the postabsorptive state, glucose oxidation was not different from that in normal subjects, but lipid oxidation was significantly increased. Impaired glucose tolerance was found, but total glucose oxidation increased after the glucose load to 47.1 +/- 2.0 (+/- SEM) vs. 33.4 +/- 1.4 g/3 h in the control group (P less than 0.001). Total glucose oxidation corresponded, in hyperthyroid patients, to the highest rate obtained with progressively increasing insulin and glucose administration in normal man. Glucose storage was clearly lower in hyperthyroid patients. After treatment in 7 patients, glucose tolerance improved significantly, and the metabolic patterns almost normalized. In the 12 hyperthyroid patients and the 7 patients after treatment (n = 19), a correlation was found between total serum T3 concentration and both basal lipid oxidation and suprabasal glucose oxidation. It is concluded that the decrease in glucose tolerance in hyperthyroidism cannot be explained by an alteration in glucose oxidation, but, rather, by a defect in nonoxidative glucose uptake in the periphery.

Adult↗
PubMed2000

An investigation into the low temperature thermal behaviour of vitamin E preparation USP using differential scanning calorimetry and low frequency dielectric analysis.

The thermal and dielectric responses of Vitamin E Preparation USP have been examined to further understand the melting and solidification of this material. A TA Instruments 2920 Differential Scanning Calorimeter was used to examine the thermal response of the sample at a range of scanning speeds. Isothermal dielectric studies were performed using a Novocontrol Dielectric Spectrometer over a range of temperatures down to -70 degrees C and a frequency range of 10(6)-10(-2) Hz. The differential scanning calorimetry (DSC) studies showed an anomalous response whereby at slow heating rates (2 degrees C min(-1)) a small exotherm followed immediately by an endotherm was observed. This response was considerably diminished in magnitude at higher rates (5 degrees C min(-1)) and was not observed at the fastest heating rate of 10 degrees C min(-1). No thermal events were seen on cooling the sample to -60 degrees C. It was suggested that the material formed a glass on cooling, with a predicted transition temperature of approximately -100 degrees C. Further studies using a liquid nitrogen cooling system indicated that the system did indeed exhibit a glass transition, albeit at a higher temperature than predicted (ca -63 degrees C). Low frequency dielectric analysis showed a clear relaxation peak in the loss component, from which the relaxation time could be calculated using the Havriliak-Negami model. The relationship between the relaxation time and the temperature was studied and was found to follow the Vogel-Tammann-Fulcher (VTF) modification of the Arrhenius equation. It is therefore concluded that Vitamin E Preparation USP is a glass-forming material that exhibits kinetically-hindered recrystallisation and melting behaviour. The study has also indicated that DSC and low frequency dielectric analysis may be powerful complementary tools in the study of the low temperature behaviour of pharmaceuticals.

Calorimetry, Differential Scanning↗
PubMed2001

An investigation into the thermal behaviour of an amorphous drug using low frequency dielectric spectroscopy and modulated temperature differential scanning calorimetry.

The objective of the study was to investigate the use of low frequency dielectric spectroscopy as a means of characterizing the thermal transitions of an amorphous drug substance, indometacin, with particular emphasis on modelling the response using the Dissado-Hill function. The low frequency dielectric behaviour of indometacin was measured over a temperature range of 10-160 degrees C and a frequency range of 10(-3)-10(6) Hz. Modulated temperature differential scanning calorimetry (MTDSC) studies were also performed on equivalent samples, showing a glass transition, recrystallization and melting. Isothermal low frequency dielectric spectra of the sample at temperatures below recrystallization showed the dynamic dielectric relaxation associated with the amorphous phase, while changes in the real and imaginary permittivities were observed that were associated with recrystallization and subsequent melting. A small discontinuity was observed immediately above the recrystallization process in the MTDSC and dielectric data, suggested to correspond to a solid state transformation. The use of the Dissado-Hill function as a means of modelling the dielectric behaviour has also been described. The study suggests that low frequency dielectric spectroscopy, used in conjunction with MTDSC and Dissado-Hill modelling, may be a useful tool for the characterization of amorphous and crystalline drugs.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2001

Binding of urate and caffeine to haemocyanin analysed by isothermal titration calorimetry.

Haemocyanin serves as an oxygen carrier in the haemolymph of decapod crustaceans. The oxygen-binding behaviour of the pigment is modulated by the two major anaerobic metabolites, l-lactate and urate. The binding of these two metabolites to haemocyanin has been investigated mainly indirectly by following the effector-induced changes in the oxygen-binding properties of the respiratory pigment. Only a few direct investigations of effector binding, employing ultracentrifugation techniques and equilibrium dialysis, have been carried out. No evidence for cooperative binding for either effector was detected using these methods. However, isothermal titration calorimetry (ITC) offers a useful tool to gain additional insight into the binding of effectors to these highly allosterically regulated macromolecules. By applying the ITC method to the fully oxygenated dodecameric haemocyanin of the lobster Homarus vulgaris, cooperativity in binding has been found for the urate analogue caffeine but not for urate itself: using urate and the urate analogue caffeine as ligands, two conformations of the oxygenated pigment were detected.

Allosteric Regulation↗
PubMed1990

Protein denaturation in dosage forms measured by differential scanning calorimetry.

The stability of beta-galactosidase dosage forms was studied by differential scanning calorimetry (DSC). It was found that the observed enthalpy of thermal denaturation was approximately in proportion to remaining enzyme activity, and denaturation temperature was related to protein stability. These results suggest that DSC can be used to determine native proteins in dosage forms and to clarify the factors affecting protein stability. The DSC method seems to be more convenient than conventional activity assay methods, and useful to follow protein denaturation during the manufacturing process and storage of dosage forms.

Calorimetry, Differential Scanning↗
PubMed1992

A study of the phase transition behaviours of cholesterol and saturated egg lecithin, and their interaction by differential scanning calorimetry.

The thermal behaviours of hydrogenated egg lecithin (PC) and cholesterol (C) in anhydrous form and in aqueous dispersions were studied by differential scanning calorimetry. The role of C in phase transitions of C-PC mixtures prepared by physical mixing or coprecipitating from chloroform has been examined. C underwent a phase transition at 34 degrees C and a second one at 76-78 degrees C which depended on the thermal history of the samples. C lowered the gel to liquid crystalline phase transition temperature (Tt) of the aqueous dispersions prepared from C-PC coprecipitates, broadened the endothermic peak at the Tt, and at 1:1 molar ratio the C-PC system did not undergo the phase transition. The C-PC interaction was observed below the Tt. In aqueous dispersions prepared from C-PC physical mixtures, C did not influence the phase transition and acted like an inert diluent. Pellets prepared from C-PC mixtures formed myelin bodies as a result of their erosion in 0.185 M borate buffer (pH 7.4) at below Tt, but the thermal behaviours of these myelin bodies were different for pellets prepared differently. Addition of bovine serum albumin (BSA) (10%, w/w) to the physical mixtures or coprecipitates of C-PC, or to PC alone did not show any effect on the thermal behaviours of their aqueous dispersions at the Tt.

Buffers↗