Novel poly(3-hydroxybutyrate) nanocomposites containing WS2 inorganic nanotubes with improved thermal, mechanical and tribological properties

Poly(3-hydroxybutyrate) (PHB) nanocomposites containing environmentally-friendly tungsten disulphide inorganic nanotubes (INTeWS2) have been successfully prepared by a simple solution blending method. The dynamic and isothermal crystallization studies by differential scanning calorimetry (DSC) demonstrated that the INTeWS2 exhibits much more prominent nucleation activity on the crystallization of PHB than specific nucleating agents or other nanoscale fillers. Both crystallization rate and crystallinity significantly increase in the nanocomposites compared to neat PHB. These changes occur without modifying the crystalline structure of PHB in the nanocomposites, as shown by wide-angle X-ray diffraction (WAXS) and infrared/Raman spectroscopy. Other parameters such as the Avrami exponent, the equilibrium melting temperature, global rate constant and the fold surface free energy of PHB chains in the nanocomposites were obtained from the calorimetric data in order to determine the influence of the INTeWS2 filler. The addition of INTeWS2 remarkably influences the energetics and kinetics of nucleation and growth of PHB, reducing the fold surface free energy by up to 20%. Furthermore, these nanocomposites also show an improvement in both tribological and mechanical (hardness and modulus) properties with respect to pure PHB evidenced by friction and nanoindentation tests, which is of important potential interest for industrial and medical applications.

The N-terminal domain of Escherichia coli enzyme I of the phosphoenolpyruvate/glycose phosphotransferase system: molecular cloning and characterization.

The bacterial phosphoenolpyruvate/glycose phosphotransferase system (PTS) comprises a group of proteins that catalyze the transfer of the phosphoryl group from phosphoenolpyruvate (PEP) to sugars concomitant with their translocation. The first two steps of the phosphotransfer sequence are PEP <--> Enzyme I (EI) <--> HPr (the histidine-containing phosphocarrier protein). We have proposed that many functions of the PTS are regulated by EI, which undergoes a monomer/dimer transition. EI monomer (63.5 kDa) comprises two major domains: a flexible C-terminal domain (EI-C) and a protease-resistant, structurally stable N-terminal domain (EI-N) containing the active site His. Trypsin treatment of Salmonella typhimurium EI yielded EI-N, designated EI-N(t). Homogeneous recombinant Escherichia coli EI-N [i.e., EI-N(r)], has now been prepared in quantity, shows the expected thermodynamic unfolding properties and, similarly to EI-N(t), is phosphorylated by phospho-HPr, but not by PEP. In addition, binding of EI-N(r) to HPr was studied by isothermal titration calorimetry: K/a = 1.4 x 10(5) M(-1) and delta H = +8.8 kcal x mol(-1). Both values are comparable to those for HPr binding to intact EI. Fluorescence anisotropy [dansyl-EI-N(r)] and gel filtration of EI-N(r) show that it does not dimerize. These results emphasize the role of EI-C in dimerization and the regulation of intact EI.

Sequence-specific DNA-binding dominated by dehydration.

Fluorescence spectroscopy and isothermal titration calorimetry were used to study the thermodynamics of binding of the glucocorticoid receptor DNA-binding domain to four different, but similar, DNA-binding sites. The binding sites are two naturally occurring sites that differ in the composition of one base pair, i.e., an A-T to G-C mutation, and two sites containing chemical intermediates of these base pairs. The calorimetrically determined heat capacity change (Delta C(p)o(obs)) for glucocorticoid receptor DNA-binding domain binding agrees with that calculated for dehydration of solvent-accessible surface areas. A dominating effect of dehydration or solvent reorganization on the thermodynamics is also consistent with an observed linear relationship between observed enthalpy change (Delta Ho(obs)) and observed entropy change (Delta So(obs)) with a slope close to the experimental temperature. Comparisons with structural data allow us to rationalize individual differences between Delta Ho(obs) (and Delta So(obs)) for the four complexes. For instance, we find that the removal of a methyl group at the DNA-protein interface is enthalpically favorable but entropically unfavorable, which is consistent with a replacement by an ordered water molecule.

Measurement of the binding of tyrosyl phosphopeptides to SH2 domains: a reappraisal.

Src homology 2 (SH2) domain-mediated interactions with phosphotyrosine residues are critical in many intracellular signal transduction pathways. Attempts to understand the determinants of specificity and selectivity of these interactions have prompted many binding studies that have used several techniques. Some discrepancies, in both the absolute and relative values of the dissociation constants for particular interactions, are apparent. To establish the correct dissociation constants and to understand the origin of these differences, we have analyzed three previously determined interactions using the techniques of surface plasmon resonance and isothermal titration calorimetry. We find that the binding of SH2 domains to phosphopeptides is weaker than generally presumed. A phosphopeptide based on the hamster polyoma middle tumor antigen interacts with the SH2 domain from Src with an equilibrium dissociation constant (Kd) of 600 nM; a phosphopeptide based on one binding site from the platelet-derived growth factor receptor binds to the N-terminal SH2 domain of the 1-phosphatidylinositol 3-kinase p85 subunit with a Kd of 300 nM; and a phosphopeptide based on the C terminus of Lck binds to the SH2 domain of Lck with a Kd of 4 microM. In addition, we demonstrate that avidity effects that result from the dimerization of glutathione S-transferase fusion proteins with SH2 domains could be responsible for overestimates of affinities for these interactions previously studied by surface plasmon resonance.

Synergistic action of actinoporin isoforms from the same sea anemone species assembled into functionally active heteropores

Among the toxic polypeptides secreted in the venom of sea anemones, actinoporins are pore forming toxins whose toxic activity relies on the formation of oligomeric pores within biological membranes. Intriguingly, actinoporins appear as multigene families which give rise to many protein isoforms in the same individual displaying high sequence identities but large functional differences. However, the evolutionary advantage of producing such similar isotoxins is not fully understood. Here, using sticholysins I and II (StnI and StnII) from the sea anemone Stichodactyla helianthus, it is shown that actinoporin isoforms can potentiate each other’s activity. Through hemolysis and calcein releasing assays, it is revealed that mixtures of StnI and StnII are more lytic than equivalent preparations of the corresponding isolated isoforms. It is then proposed that this synergy is due to the assembly of heteropores since (i) StnI and StnII can be chemically cross-linked at the membrane and (ii) the affinity of sticholysin mixtures for the membrane is increased with respect to any of them acting in isolation, as revealed by isothermal titration calorimetry experiments. These results help to understand the multigene nature of actinoporins and may be extended to other families of toxins that require oligomerization to exert toxicity.

Synergistic Action of Actinoporin Isoforms from the Same Sea Anemone Species Assembled into Functionally Active Heteropores

Among the toxic polypeptides secreted in the venom of sea anemones, actinoporins are the pore-forming toxins whose toxic activity relies on the formation of oligomeric pores within biological membranes. Intriguingly, actinoporins appear as multigene families that give rise to many protein isoforms in the same individual displaying high sequence identities but large functional differences. However, the evolutionary advantage of producing such similar isotoxins is not fully understood. Here,using sticholysins I and II (StnI and StnII) from the sea anemone Stichodactyla helianthus, it is shown that actinoporin isoforms can potentiate each other’s activity. Through hemolysis and calcein releasing assays, it is revealed that mixtures of StnI and StnII are more lytic than equivalent preparations of the corresponding isolated isoforms. It is then proposed that this synergy is due to the assembly of heteropores because (i) StnI and StnII can be chemically cross-linked at the membrane and (ii) the affinity of sticholysin mixtures for the membrane is increased with respect to any of them acting in isolation, as revealed by isothermal titration calorimetry experiments. These results help us understand the multigene nature of actinoporins and may be extended to other families of toxins that require oligomerization to exert toxicity.

Chemical Reactors. Problem 3: Isothermal plug flow reactor with multiple reactions (2011-2012 Course)

Wording of problem 3: Isothermal plug flow reactor with multiple reactions.

Isothermal (liquid + liquid) equilibrium data at T = 313.15 K and isobaric (vapor + liquid + liquid) equilibrium data at 101.3 kPa for the ternary system (water + 1-butanol + p-xylene)

The (vapor + liquid), (liquid + liquid) and (vapor + liquid + liquid) equilibria of the ternary system (water + 1-butanol + p-xylene) have been determined. (Water + 1-butanol + p-xylene) is a type 2 heterogeneous ternary system with partially miscible (water + 1-butanol) and (water + p-xylene) pairs. By contrast, (1-butanol + p-xylene) is totally miscible under atmospheric conditions. This paper examines the (vapor + liquid) equilibrium in both heterogeneous and homogeneous regions at 101.3 kPa of pressure. (Liquid + liquid) equilibrium data at T = 313.15 K have also been determined, and for comparison, the obtained experimental data have been calculated by means of several thermodynamic models: UNIQUAC, UNIFAC and NRTL. Some discrepancies were found between the (vapor + liquid + liquid) correlations; however, the models reproduced the (liquid + liquid) equilibrium data well. The obtained data reveal a ternary heterogeneous azeotrope with mole fraction composition: 0.686 water, 0.146 1-butanol and 0.168 p-xylene.

Calorimetry in medicine,

"References": p. 84-98.

Methods and standards in bomb calorimetry /

"August 29, 1910."

Reducing the time period of steady state does not affect the accuracy of energy expenditure measurements by indirect calorimetry

Achievement of steady state during indirect calorimetry measurements of resting energy expenditure (REE) is necessary to reduce error and ensure accuracy in the measurement. Steady state is often defined as 5 consecutive min (5-min SS) during which oxygen consumption and carbon dioxide production vary by +/-10%. These criteria, however, are stringent and often difficult to satisfy. This study aimed to assess whether reducing the time period for steady state (4-min SS or 3-min SS) produced measurements of REE that were significantly different from 5-min SS. REE was measured with the use of open-circuit indirect calorimetry in 39 subjects, of whom only 21 (54%) met the 5-min SS criteria. In these 21 subjects, median biases in REE between 5-min SS and 4-min SS and between 5-min SS and 3-min SS were 0.1 and 0.01%, respectively. For individuals, 4-min SS measured REE within a clinically acceptable range of +/-2% of 5-min SS, whereas 3-min SS measured REE within a range of -2-3% of 5-min SS. Harris-Benedict prediction equations estimated REE for individuals within +/-20-30% of 5-min SS. Reducing the time period of steady state to 4 min produced measurements of REE for individuals that were within clinically acceptable, predetermined limits. The limits of agreement for 3-min SS fell outside the predefined limits of +/-2%; however, both 4-min SS and 3-min SS criteria greatly increased the proportion of subjects who satisfied steady state within smaller limits than would be achieved if relying on prediction equations.

Gelatinisation of starch in mixtures of sugars. II. Application of differential scanning calorimetry

Differential scanning calorimetry was used to investigate the effect of mixtures of glucose and fructose, and five types of honeys on starch gelatinisation. At a 1:1 starch:water ratio, glucose generally increased the enthalpy (DeltaH(gel)) and temperatures (T-onset, T-peak and T-end) of gelatinisation more than fructose. Upon mixing, DeltaH(gel) of the low-temperature endotherm decreased in comparison to the sole sugars, but was fairly constant (7.7 +/- 0.33 J/g dry starch). DeltaH(gel) of the high-temperature endotherm increased with the fructose content. For both endotherms, the gelatinisation temperatures were unchanged (CV less than or equal to 3%) for the mixtures. With the honeys (moisture, 14.9-18.0%; fructose, 37.2-44.0%; glucose, 28.3-31.9%) added at 1.1-4.4 g per g dry starch, the enthalpy and temperatures of gelatinisation did not vary significantly (CV less than or equal to 6%). Typical thermograms are presented, and the results are interpreted in the light of the various proposed mechanisms for starch gelatinisation in sugar-water systems, total sugar content and possible sugar-sugar interactions. The thermograms were broader in the presence of the sugars and honeys, and a biphasic character was consistently exhibited. The application of an exponential equation to the gelatinisation temperatures of the starch-honey mixtures revealed an opposing influence of fructose and glucose during gelatinisation. The mechanism of starch gelatinisation may be better understood if techniques could be perfected to quantify breakage and formation of hydrogen bonds in the starch granules, and suggested techniques are discussed. (C) 2004 Elsevier Ltd. All rights reserved.

Investigation of the starch gelatinisation phenomena in water-glycerol systems: application of modulated temperature differential scanning calorimetry

The use of modulated temperature differential scanning calorimetry (MTDSC) has provided further insight into the gelatinisation process since it allows the detection of glass transition during gelatinisation process. It was found in this work that the glass transition overlapped with the gelatinisation peak temperature for all maize starch formulations studied. Systematic investigation on maize starch gelatinisation over a range of water-glycerol concentrations with MTDSC revealed that the addition of glycerol increased the gelatinisation onset temperature with an extent that depended on the water content in the system. Furthermore, the addition of glycerol promoted starch gelatinisation at low water content (0.4 g water/g dry starch) and the enthalpy of gelatinisation varied with glycerol concentration (0.73-19.61 J/g dry starch) depending on the water content and starch type. The validities of published gelatinisation models were explored. These models failed to explain the glass transition phenomena observed during the course of gelatinisation and failed to describe the gelatinisation behaviour observed over the water-glycerol concentrations range investigated. A hypothesis for the mechanisms involved during gelatinisation was proposed based on the side chain liquid crystalline polymer model for starch structure and the concept that the order-disorder transition in starch requires that the hydrogen bonds (the major structural element in the granule packing) to be broken before the collapse of order (helix-coil transition) can take place. (C) 2004 Elsevier Ltd. All rights reserved.

Wheat grain cooking process as investigated by modulated temperature differential scanning calorimetry

The thermal properties of soft and hard wheat grains, cooked in a steam pressure cooker, as a function of cooking temperature and time were investigated by modulated temperature differential scanning calorimetry (MTDSC). Four cooking temperatures (110, 120, 130 and 140 degrees C) and six cooking times (20, 40, 60, 80, 100 and 120 min) for each temperature were studied. It was found that typical non-reversible heat flow thermograms of cooked and uncooked wheat grains consisted of two endothermic baseline shifts localised around 40-50 degrees C and then 60-70 degrees C. The second peaks of non-reversible heat flow thermograms (60-70 degrees C) were associated with starch gelatinisation. The degree of gelatinisation was quantified based on these peaks. In this study, starch was completely gelatinised within 60-80 min for cooking temperatures at 110-120 degrees C and within 20 min for cooking temperatures at 130-140 degrees C. MTDSC detected reversible endothermic baseline shifts in most samples, localised broadly around 48-67 degrees C with changes in heat capacity ranging from 0.02 to 0.06 J/g per degrees C. These reversible endothermic baseline shifts are related to the glass transition, which occurs during starch gelatinisation. Data on the specific heat capacity of the cooked wheat samples are provided. (C) 2005 Elsevier Ltd. All rights reserved.