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PubMed1991

Differential scanning calorimetry studies of NaCl effect on the inverse temperature transition of some elastin-based polytetra-, polypenta-, and polynonapeptides.

Differential scanning calorimetry studies of the effect of NaCl on protein-based polymer self-assembly has been carried out on six elastin-based synthetic sequential polypeptides--i.e., the polypentapeptide (L-Val1-L-Pro2-Gly3-L-Val4-Gly5)n and its more hydrophobic analogues (L-Leu1-L-Pro2-Gly3-L-Val4-Gly5)n and (L-Val1-L-Pro2-L-Ala3-L-Val4-Gly5)n; the polytetrapeptide (L-Val1-L-Pro2-Gly3-Gly4)n and its more hydrophobic analogue (L-Ile1-L-Pro2-Gly3-Gly4)n; and the polynonapeptide (a pentatetra hybrid), (L-Val1-L-Pro2-Gly3-L-Val4-Gly5-L-Val6-L-Pro7-Gly8-Gly9++ +)n. Previous physical characterizations of the polypentapeptides have demonstrated the occurrence of an inverse temperature transition since increase in order of the polypentapeptide, as the temperature is raised from below to above that of the transition, has been repeatedly observed using different physical characterizations. In the present experiments, it is observed that the transition temperatures of the polypeptides studied are linearly dependent on NaCl concentration. The molar effectiveness of NaCl in shifting the transition temperature delta Tm/[N], is about 14 degrees C/[N], with the dependence on peptide hydrophobicity being fairly small. Interestingly, however, the delta delta Q/[N] does depend on the hydrophobicity of a polypeptide.

Amino Acid Sequence↗
PubMed1992

Hydrophobicity of amino acid residues: differential scanning calorimetry and synthesis of the aromatic analogues of the polypentapeptide of elastin.

Relative hydrophobicities of aromatic amino acid residues are investigated by using differential scanning calorimetry (DSC) on 10 synthetic copolypentapeptides of poly(VPGVG) of elastin. Utilizing the hydrophobic-driven process of the inverse temperature transition exhibited by these polypentapeptides in aqueous solution, the relative hydrophobicities of Phe, Trp, and Tyr residues are determined by the critical temperature and heat of the transition. The DSC data for the aromatic residue containing copolypentapeptide aqueous solution indicate that tryptophan is the most hydrophobic amino acid residue, phenylalanine the third most hydrophobic on basis of transition temperature and the second on basis of transition heat. For tyrosine, significant differences are observed between the phenolic and the phenoxide anionic states. At pH 7, where tyrosine is protonated, it is found to be the second most hydrophobic amino acid residue on the basis of the transition temperature, whereas on the basis of the heat of transition, it is less hydrophobic than both tryptophan and phenylalanine. Changing the pH from pH 7 to pH 12, for example, for poly[0.8(VPGVG), 0.2(VPGYG)] in aqueous solution shifts the transition temperature from 7 to 49 degrees C with a dramatically reduced heat. On the basis of both the transition temperature scale and the heat of transition, the hydroxylated tyrosine appears less hydrophobic than glycine.

Amino Acid Sequence↗
PubMed2006

Capillary electrophoresis versus differential scanning calorimetry for the analysis of free enzyme versus enzyme-ligand complexes: in the search of the ligand-free status of cholinesterases.

Cholinesterases (ChEs) are highly efficient biocatalysts whose active site is buried in a deep, narrow gorge. The talent of CE to discover inhibitors in the gorge of highly purified preparations has fairly altered the meaning of a ChE ligand-free status. To attempt at a description of this one, we investigated the stability of Bungarus fasciatus acetylcholinesterase (AChE), alone or complexed with different inhibitors. Determination of mid-transition temperature for thermal denaturation, using differential scanning calorimetry (DSC) and CE, provided conflicting results. Discrepancies strongly question the reality of a ligand-free AChE state. DSC allowed estimation of the stability of AChE-ligands complexes, and to rank the stabilizing effect of different inhibitors. CE acted as a detector of hidden ligands, provided that they were charged, reversibly bound, and thus dissociable upon action of electric fields. Then, CE allowed quantification of the stability of ligand-free AChE. CE and DSC providing each fractional and nonredundant information, cautious attention must be paid for actual estimation of the conformational stability of ChEs. Because inhibitors used in purification of ChEs by affinity chromatography are charged, CE remains a leading method to estimate enzyme stability and detect the presence of bound hidden ligands.

Acetylcholinesterase↗
PubMed2003

Thermal properties of cowpea flour: a study by differential scanning calorimetry.

The thermal properties of 12 varieties of cowpea flour were studied by differential scanning calorimetry (DSC). Flour samples were prepared to a paste of 60% moisture content and sealed in standard DSC pans. Samples were scanned at a heating rate of 5 degrees C/min over a scan range of 40- 130 degrees C. Samples exhibited single major endotherms, which occurred over varied temperatures. The transition enthalpy (deltaH) ranged between 1.4 J/g and 4.7 J/g. Transition onset (T(o)) and transition peak (T(p)) temperatures ranged between 75-78 degrees C and 78-82 degrees C,respectively. All the DSC parameters measured varied significantly among the varieties. The transition enthalpy (deltaH) was the most discriminating parameter and accounted for 80% of the total variance. The major chemical components of cowpea flour, starch amylose and protein are significant predictors of deltaH. Protein denaturation appears to be a significant modification which occurs during processing of cowpea seeds to flour. The transition enthalpy deltaH could become an important functional index of cowpea flour when related to some quality parameters in products that contain the flour.

Calorimetry, Differential Scanning↗
PubMed1994

Protein adsorption on low-temperature isotropic carbon: I. Protein conformational change probed by differential scanning calorimetry.

This is the first of a set of articles on protein adsorption on low-temperature isotropic carbon (LTIC), a reputed blood compatible material. Surface-induced conformational changes of albumin, fibrinogen, and some small proteins were measured by differential scanning calorimetry (DSC) on LTIC powders and colloidal silica. The LTIC surface significantly alters the DSC response (denaturation?) in proteins studied in different buffer solutions. We use the term "denaturation" to refer to altered protein behavior in the adsorbed state. Hydrophobic interactions between LTIC and the proteins are thought to be the major driving force. The presence of air at the water-carbon interface seems to prevent the surface denaturation of fibrinogen. The silica surface greatly denatures albumin but only slightly denatures fibrinogen. Because LTIC is considered to be a nonthrombogenic material, but silica is considered to be a thrombogenic one, whether a surface denatures adsorbed proteins cannot be the sole criterion for its blood compatibility. The latter largely depends on what protein the surface denatures, and in what sequences.

Adsorption↗
PubMed2006

Real-time monitoring of the setting reaction of brushite-forming cement using isothermal differential scanning calorimetry.

The setting behavior of a brushite-forming cement (beta-tricalcium phosphate/mono calcium monophosphate) was investigated using an indentation technique (the Gillmore needles method) and isothermal differential scanning calorimetry (DSC). The two objectives of the study were to investigate whether DSC could be used to real-time monitor a fast-setting calcium phosphate cement (CPC) and to determine if it is possible to correlate DSC results directly with conventional setting-time measurements. Best-fit linear correlation analysis revealed that both the initial and final setting time (T(i) and T(f)) measured by indentation were strongly correlated to the maximum heat flow measured with DSC. It seems therefore possible to predict the setting times, usually achieved with user dependent indentation methods, of this specific fast setting CPC on the basis of objective DSC measurements. The drawbacks of DSC, however, are its overall complexity and expense and the fact that only exothermal reactions can be investigated in comparison to the Gillmore needles method, furthermore, it is not possible to monitor the complete reaction as the first 2 or 3 min are lost due to sample preparation and apparatus set up.

Bone Cements↗
PubMed1988

Thermal analysis of CHL V79 cells using differential scanning calorimetry: implications for hyperthermic cell killing and the heat shock response.

Differential scanning calorimetry (DSC) was used to assay thermal transitions that might be responsible for cell death and other responses to hyperthermia or heat shock, such as induction of heat shock proteins (HSP), in whole Chinese hamster lung V79 cells. Seven distinct peaks, six of which are irreversible, with transition temperatures from 49.5 degrees C to 98.9 degrees C are detectable. These primarily represent protein denaturation with minor contributions from DNA and RNA melting. The onset temperature of denaturation, 38.7 degrees C, is shifted to higher temperatures by prior heat shock at 43 degrees and 45 degrees C, indicative of irreversible denaturation occurring at these temperatures. Thus, using DSC it is possible to demonstrate significant denaturation in a mammalian cell line at temperatures and times of exposure sufficient to induce hyperthermic damage and HSP synthesis. A model was developed based on the assumption that the rate limiting step of hyperthermic cell killing is the denaturation of a critical target. A transition temperature of 46.3 degrees C is predicted for the critical target in V79 cells. No distinct transition is detectable by DSC at this temperature, implying that the critical target comprises a small fraction of total denaturable material. The short chain alcohols methanol, ethanol, isopropanol, and t-butanol are known hyperthermic sensitizers and ethanol is an inducer of HSP synthesis. These compounds non-specifically lower the denaturation temperature of cellular protein. Glycerol, a hyperthermic protector, non-specifically raises the denaturation temperature for proteins denaturing below 60 degrees C. Thus, there is a correlation between the effect of these compounds on protein denaturation in vivo and their effect on cellular sensitivity to hyperthermia.

Alcohols↗
PubMed1990

Increased thermostability of thermotolerant CHL V79 cells as determined by differential scanning calorimetry.

Heat shock denatures cellular protein and induces both a state of acquired thermotolerance, defined as resistance to a subsequent heat shock, and the synthesis of a category of proteins referred to as heat-shock proteins (HSPs). Thermotolerance may be due to the stabilization of thermolabile proteins that would ordinarily denature during heat shock, either by HSPs or some other factors. We show by differential scanning calorimetry (DSC) that mild heat shock irreversibly denatures a small fraction of Chinese hamster lung V79-WNRE cell protein (i.e., the enthalpy change, which is proportional to denaturation, on scanning to 45 degrees C at 1 degree C/min is approximately 2.3% of the total calorimetric enthalpy). Thermostability, defined by the extent of denaturation during heat shock and determined from DSC scans of whole cells, increases as the V79 cells become thermotolerant. Cellular stabilization appears to be due to an increase in the denaturation temperature of the most thermolabile proteins; there is no increase in the denaturation temperatures of the most thermally resistant proteins, i.e., those denaturing above 65 degrees C. Cellular stabilization is also observed in the presence of glycerol, which is known to increase resistance to heat shock and to stabilize proteins in vitro. A model is presented, based on a direct relationship between the extent of hyperthermic killing and the denaturation or inactivation of a critical target that defines the rate-limiting step in killing, which predicts a transition temperature (Tm) of the critical target for control V79-WNRE cells of 46.0 degrees C and a Tm of 47.3 degrees C for thermotolerant cells. This shift of 1.3 degrees C is consistent with the degree of stabilization detected by DSC.

Animals↗
PubMed2001

Differential scanning calorimetry studies of intraembryonic freezing and cryoprotectant penetration in zebrafish (Danio rerio) embryos.

Nucleation temperatures of intraembryonic water and cryoprotectant penetration in zebrafish embryos were studied using differential scanning calorimetry. The effects of embryo developmental stage, dechorionation, partial removal of yolk, cooling rate, and cryoprotectant treatment on the temperatures of intraembryonic freezing were investigated. Embryo stages were found to have a significant effect on the nucleation temperatures of intact embryos. Freeze onset temperatures of -11.9 +/- 1.5, -15.6 +/- 0.3, and -20.5 +/- 0.1 degrees C were obtained for intact embryos at 6-somite, prim-6, and high-pec stages, respectively. After dechorionation, the freeze onset temperatures of intraembryonic water shifted to significantly lower temperatures, being -23.5 +/- 0.8, -18.7 +/- 0.7, -24.9 +/- 0.8 degrees C for 6-somite, prim-6, and high-pec stages, respectively. Yolk-reduced high-pec stage embryos showed significantly lower nucleation temperatures with an average onset at -27.9 +/- 0.4 degrees C. The effect of cryoprotectant treatment on the nucleation temperatures of intraembryonic water varies among different embryo stages and different cryoprotectants. Thirty-minute treatment with 2 M methanol significantly decreased the nucleation temperatures of dechorionated 6-somite embryos whilst no temperature decrease was observed for prim-6 or yolk-reduced high-pec embryos. Thirty-minute exposure to 1 M propylene glycol did not significantly affect the nucleation temperatures of dechorionated 6-somite, prim-6, or yolk-reduced high-pec embryos. In order to increase the permeability of embryos to cryoprotectants, the yolk sacs of dechorionated embryos at 6-somite or prim-6 embryos were punctured with a sharp micro-needle before exposure to cryoprotectants. The punctured prim-6 embryos showed significantly lower temperatures of intraembryonic freezing after 30 min of exposure to 2 M methanol following the multi-punctures. The nucleation temperatures of punctured 6-somite or prim-6 embryos were also decreased significantly after exposure to 1 M propylene glycol for 30 min. These results suggested that in intact embryos, intraembryonic freezing appeared to be seeded by the external ice in the perivitelline fluid and that in dechorionated embryos (in the absence of external water) intraembryonic freezing was more likely a consequence of heterogeneous nucleation. Methanol was demonstrated to show a limited degree of penetration into prim-6 stage embryos, but it did not penetrate later-stage embryos such as prim-6 and yolk-reduced high-pec. No propylene glycol permeation was observed for embryos at all stages. However, multi-punctures of yolk resulted in the permeation of both cryoprotectants into prim-6 embryos and propylene glycol permeation into 6-somite embryos. These findings may have important implications in overcoming the problem associated with the low membrane permeability of zebrafish embryos to cryoprotectants.

Adaptation, Physiological↗
PubMedDate not supplied

A survey of the year 2002 literature on applications of isothermal titration calorimetry.

Isothermal titration calorimetry (ITC) is becoming widely accepted as a key instrument in any laboratory in which quantification of biomolecular interactions is a requisite. The method has matured with respect to general acceptance and application development over recent years. The number of publications on ITC has grown exponentially over the last 10 years, reflecting the general utility of the method. Here all the published works of the year 2002 in this area have been surveyed. We review the broad range of systems to which ITC is being directed and classify these into general areas highlighting key publications of interest. This provides an overview of what can be achieved using this method and what developments are likely to occur in the near future.

Calorimetry↗
PubMedDate not supplied

A survey of the year 2003 literature on applications of isothermal titration calorimetry.

Over the last decade isothermal titration calorimetry (ITC) has developed from a specialist method which was largely restricted in its use to dedicated experts, to a major, commercially available tool in the arsenal directed at understanding molecular interactions. The number of those proficient in this field has multiplied dramatically, as has the range of experiments to which this method has been applied. This has led to an overwhelming amount of new data and novel applications to be assessed. With the increasing number of publications in this field comes a need to highlight works of interest and impact. In this overview of the literature we have attempted to draw attention to papers and issues for which both the experienced calorimetrist and the interested dilettante hopefully will share our enthusiasm.

Calorimetry↗
PubMedDate not supplied

Survey of the year 2004: literature on applications of isothermal titration calorimetry.

The market for commercially available isothermal titration calorimeters continues to grow as new applications and methodologies are developed. Concomitantly the number of users (and abusers) increases dramatically, resulting in a steady increase in the number of publications in which isothermal titration calorimetry (ITC) plays a role. In the present review, we will focus on areas where ITC is making a significant contribution and will highlight some interesting applications of the technique. This overview of papers published in 2004 also discusses current issues of interest in the development of ITC as a tool of choice in the determination of the thermodynamics of molecular recognition and interaction.

Calorimetry↗
PubMedDate not supplied

Survey of the year 2005: literature on applications of isothermal titration calorimetry.

Isothermal titration calorimetry (ITC) can provide a full thermodynamic characterization of an interaction. Its usage does not suffer from constraints of molecular size, shape or chemical constitution. Neither is there any need for chemical modification or attachment to solid support. This ease of use has made it an invaluable instrumental resource and led to its appearance in many laboratories. Despite this, the value of the thermodynamic parameterization has, only quite recently, become widely appreciated. Although our understanding of the correlation between thermodynamic data and structural details continues to be somewhat naïve, a large number of publications have begun to improve the situation. In this overview of the literature for 2005, we have attempted to highlight works of interest and novelty. Furthermore, we draw attention to those works which we feel have provided a route to better analysis and increased our ability to understand the meaning of thermodynamic change on binding.

Animals↗
PubMed2002

Interactions of cyclosporines with lipid membranes as studied by solid-state nuclear magnetic resonance spectroscopy and high-sensitivity titration calorimetry.

Cyclosporin A (CyA) interacts with lipid membranes. Binding reaction and membrane location of CyA and analogs were examined with 2H-NMR, high-sensitivity isothermal titration calorimetry (ITC), and CD spectroscopy. Effects of CyA and charged analogs on the phosphocholine head group and on the membrane interior were investigated using selectively deuterated phospholipids. Incorporation of cyclosporin generated small disordering of the lipid acyl chains. Binding of CyA and neutral and positively charged analogs to lipid membranes showed endothermic heats of reaction between + 5.9 and + 11.3 kcal/mol, whereas enthalpy of binding was close to zero for the negatively charged derivative. Binding constants of cyclosporines to liposomal membranes were in the range of K(P) = 1650-5560 M(- 1) depending on the cholesterol content. (2)H-NMR provides evidence that CyA is essentially located in the interior of the bilayer membrane. For the charged analogs an additional interaction occurs at the head group level, placing the polar groups of these CyA analogs in the vicinity of the phosphocholine dipoles. The association of CyA and its analogs is accompanied by a positive enthalpy change, which is overcompensated by positive entropy changes. Binding of CyA to lipid membranes thus follows the classical hydrophobic effect, which is in contrast to many other peptide-lipid binding reactions.

Algorithms↗
PubMed2002

Terpenes in propylene glycol as skin-penetration enhancers: permeation and partition of haloperidol, Fourier transform infrared spectroscopy, and differential scanning calorimetry.

The respective alcoholic terpenes carvacrol, linalool, and alpha-terpineol were used at 5% w/v in propylene glycol (PG) to increase the in vitro permeation of haloperidol (HP) through human skin. The possible enhancement mechanism was then elucidated with HP-stratum corneum (SC) binding studies, Fourier transform infrared spectroscopy, and differential scanning calorimetry. The greatest increase in the permeation of HP was achieved with linalool followed by carvacrol and terpineol. HP permeation with linalool was predicted to reach a therapeutic plasma concentration and therapeutic daily-permeated amounts. Carvacrol increased lag time, which was attributed to slow redistribution of the enhancer within SC. Carvacrol increased the partition of the drug to the pulverized SC. Pure PG extracted lipids from SC but less than that achieved by the terpenes in PG. Terpenes extracted lipids to a similar extent. An increase in bilayer cohesion in the remaining lipids present in the SC could be attributed to the alignment of terpenes within the lipid bilayer. The higher permeation with linalool was attributed to its molecular orientation within the lipid bilayer. Terpenes showed different rates of SC dehydration but did not change the percentages of secondary structures of keratin.

Calorimetry, Differential Scanning↗
PubMed2003

An investigation into the subambient behavior of aqueous mannitol solutions using differential scanning calorimetry, cold stage microscopy, and X-ray diffractometry.

The subambient behavior of aqueous mannitol solutions is of considerable relevance to the preparation of freeze dried formulations. In this investigation the properties of 3% w/v mannitol solutions were investigated using differential scanning calorimetry (DSC), cold stage microscopy (CSM), and X-ray diffraction (XRD) to identify the thermal transitions and structural transformations undergone by this system. It was found that on cooling from ambient the system formed ice at circa -20 degrees C while a further exotherm was seen at approximately -30 degrees C. Upon reheating an endotherm was seen at circa -30 degrees C followed immediately by an exotherm at circa -25 degrees C. Temperature cycling indicated that the thermal transitions observed upon reheating were not reversible. Modulated temperature DSC (MTDSC) indicated that the transitions observed upon reheating corresponded to a glass transition immediately followed by recrystallization, XRD data showed that recrystallization was into the beta form. Annealing at -35 degrees C for 40 min prior to cooling and reheating resulted in a maximum enthalpy being observed for the reheating exotherm. It is concluded that on cooling 3% w/v aqueous mannitol solutions an amorphous phase is formed that subsequently recrystallises into the beta form. The study has also shown that DSC, CSM, and XRD are useful complementary techniques for the study of frozen systems.

Calorimetry, Differential Scanning↗
PubMed2001

Characterization of amorphous ketoconazole using modulated temperature differential scanning calorimetry.

The objective of the present study was to characterize the glassy state of ketoconazole and to calculate its molecular mobility below the glass transition, with a view to further developing the use of modulated temperature differential scanning calorimetry (MTDSC) as a means of studying relaxation behavior. Particular emphasis is placed on identifying the influence of the choice of experimental parameters on the measured values of both the glass transition temperature (T(g)) and the relaxation enthalpy magnitude. Amorphous ketoconazole was studied using an amplitude of +/-0.212 K, a period of 40 s, and an underlying heating rate of 2 K/min. The correction required for the calculation of the relaxation endotherm magnitude (the "T(g) shift effect") was demonstrated and is discussed in terms of the mechanism underpinning this phenomenon. Similarly, the influence of the choice of MTDSC experimental parameters on the measured T(g) was studied by varying the amplitude from +/-0.011 to +/-0.424 K and the period from 25 to 50 s. The influence of the cooling rate from the melt on the magnitude of the relaxation endotherm and position of the glass transition was investigated. It was noted that the magnitude of the relaxation endotherm increased with slower cooling rates, this being ascribed to a combination of annealing during the cooling and heating cycle and a further facet of the T(g) shift effect. Annealing experiments were performed at aging temperatures T(g)-12--T(g)-42 K for periods ranging from 10 min up to 16 h. The relaxation behavior was characterized by fitting the calculated extent of relaxation to the Williams-Watts equation. Overall, the study has highlighted theoretical and experimental issues that need to be considered when using both DSC and MTDSC for the calculation of relaxation times.

Antifungal Agents↗
PubMed2004

Water distribution studies within microcrystalline cellulose and chitosan using differential scanning calorimetry and dynamic vapor sorption analysis.

The objective of the study was to assess and compare the interaction and distribution of water within microcrystalline cellulose (MCC) and chitosan by differential scanning calorimetry (DSC) and dynamic vapor sorption analysis. The amounts of nonfreezing and freezing water in hydrated samples were determined from melting endotherms obtained by DSC. After accounting for the percent crystallinity of MCC and chitosan, no statistically significant difference was observed in their ability to bind water molecules per repeating unit at the minimum water content at which freezing water is evident. Exposure of chitosan to water for 30 min was sufficient to achieve equilibration at 61% w/w actual water content. The moisture sorption profiles were analyzed according to the GAB and Young and Nelson equations. The adsorbed monolayer, externally adsorbed moisture, and internally absorbed moisture were not statistically different for MCC and chitosan after accounting for the amorphous content of the polymers. These studies suggest that chitosan can act as a "molecular sponge," and thus aid in the production of beads by extrusion and spheronization.

Adsorption↗