Differential Enthalpy Research Articles

High resolution N2 adsorption isotherms by graphitized carbon black and nongraphitized carbon black – αs-Curves, adsorption enthalpies and entropies

The high resolution N(2) adsorption isotherms (77.4 K) by graphitized carbon blacks (GCB-I: A(BET)=54.2 m(2) g(-1) and GCB-II: A(BET)=69.4 m(2) g(-1)) and nongraphitized carbon black (NGCB: A(BET)=18.87 m(2) g(-1)) have been measured at p/p°=5×10(-8)-0.99. α(s)-Curve of the N(2) adsorption isotherm by GCB-I is completely overlapped with that by GCB-II in the pressure range of p/p°=5×10(-6)-0.90, but the N(2)α(s)-curve by GCB-I is remarkably different from that by NGCB. The standard N(2)α(s)-data by GCB-I and NGCB have been determined in the range of α(s)=0.002-2.2. On the basis of the N(2) adsorption isotherms at the two temperatures (77.4 K, 87.3 K), the isosteric heat of adsorption (differential adsorption enthalpies), the differential adsorption entropies, and the integral adsorption entropies of N(2) molecules have been evaluated between θ (coverage)=0.05 and θ=1.50. The surface homogeneity/heterogeneity of carbon black samples has been discussed by the N(2) differential adsorption enthalpies. The adsorbed state of N(2) molecules on the carbon black surfaces has been considered by the differential and integral adsorption entropies.

Solvent and Temperature Effects on Diastereodifferentiating Paternó−Büchi Reaction of Chiral Alkyl Cyanobenzoates with Diphenylethene upon Direct versus Charge-Transfer Excitation

In the Paternó-Büchi reaction of chiral p-cyanobenzoates (1) with 1,1-diphenylethene (2), we revealed that the excited charge-transfer (CT) complex formed upon selective excitation at the CT band is distinctly different in structure and reactivity from the conventional exciplex generated through the direct excitation of acceptor 1 which subsequently associates with donor 2. Thus, the favored diastereoface upon photocycloaddition, as well as the temperature- and solvent-dependent behavior of the product's diastereoselectivity, were highly contrasting, often opposite, to each other upon direct versus CT excitation. From the activation parameters obtained by the Eyring analyses of the diastereoselectivity, we are able to infer that the conventional exciplex is relatively flexible and susceptible to the environmental variants, whereas the CT complex is better pi-pi stacked and more rigid in the ground state and also in the excited state, leading to the significantly smaller differential activation enthalpies and entropies. More interestingly, the signs of the differential activation parameters determined for direct and CT excitation are consistently opposite to each other and the isokinetic temperatures calculated therefrom differ significantly, unambiguously revealing the distinctly different nature in structure and reactivity of these two excited-state complex species. Thus, the combined use of irradiation wavelength, temperature, and solvent provides us with a convenient, powerful tool not only for elucidating the mechanistic details of photoreaction but also for critically controlling the stereochemical outcomes of photochirogenic reaction.

A Layered Titanium Phosphate Ti2O3(H2PO4)2·2H2O with Rectangular Morphology: Synthesis, Structure, and Cysteamine Intercalation

Layered titanium phosphate (TiP) composed of rectangular-shaped lamellae was synthesized from titanium isopropoxide and orthophosphoric acid. The as-prepared TiP was refluxed in a 2-propanol/water mixture at ∼363 K for periods up to 144 h. The bulk and surface properties of the lamellar material with novel morphology were studied. The structural investigations and elemental analysis identified TiP as Ti2O3(H2PO4)2·2H2O. The reactions of the TiP samples with cysteamine (CEA) in aqueous suspensions afforded TiP/CEA intercalation complexes. X-ray measurements on these complexes revealed CEA monolayers incorporated between the TiP lamellae, increasing the original basal spacing from 1.00 nm to 1.43 nm. The enthalpy change of the intercalation reaction was measured by isothermal titration calorimetry. The amount of CEA adsorbed was determined, and differential adsorption enthalpy was calculated via the mass balance.

Moisture adsorption isotherms and thermodynamics properties of sucuk (Turkish dry-fermented sausage)

Moisture adsorption isotherms of sucuk were determined using the isopiestic method at 10 °C, 20 °C and 30 °C and within the range of 0.2–0.9 water activity. The isotherms of sucuk exhibited Type II behavior according to BET classification. The adsorption data were analyzed using mathematical equations of Halsey, Caurie, Peleg, Smith, Oswin, Henderson, Modified-BET, GAB, Ferro-Fontan and Harkins–Jura. The best fit of experimental data was obtained with Peleg equation in the range of temperatures and water activities investigated. Thermodynamic properties such as differential enthalpy and entropy, enthalpy–entropy compensation, spreading pressure, net integral enthalpy and entropy were determined from moisture adsorption isotherm data of sucuk. The net isosteric heat of sorption and differential entropy decreased with increasing moisture contents in an exponential function. The spreading pressure increased with increasing water activity, and decreased with increasing temperature. The net integral enthalpy decreased with increased moisture content. The integral entropy increased with moisture content, but it was negative in value. The enthalpy–entropy compensation theory was applied to water adsorption of sucuk.

Dissolution of 3,4,5‐Triamino‐1,2,4‐triazole Dinitramide in N‐Methyl Pyrrolidone

AbstractThe dissolution properties of 3,4,5‐triamino‐1,2,4‐triazole dinitramide in N‐methyl pyrrolidone (NMP) was measured using a RD496‐2000 Calvet microcalorimeter at four different temperatures under atmospheric pressure. Differential enthalpies (ΔdifH) and molar enthalpies (ΔsolH) were determined for 3,4,5‐triamino‐1,2,4‐triazole dinitramide in NMP. The corresponding kinetic equations that describe the four dissolution processes are \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{{\rm d\alpha }}}{{{\rm d}t}} = 1.78 \times 10^{ - 4} \left({1 - {\rm \alpha }} \right)^{1.01} \left({T = 298.15{\rm K}} \right) $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{{\rm d\alpha }}}{{{\rm d}t}} = 1.96 \times 10^{ - 4} \left({1 - {\rm \alpha }} \right)^{1.06} \left({T = 303.15{\rm K}} \right) $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{{\rm d\alpha }}}{{{\rm d}t}} = 2.15 \times 10^{ - 4} \left({1 - {\rm \alpha }} \right)^{0.96} \left({T = 308.15{\rm K}} \right) $\end{document}, \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{{{\rm d\alpha }}}{{{\rm d}t}} = 2.34 \times 10^{ - 4} \left({1 - {\rm \alpha }} \right)^{1.06} \left({T = 313.15{\rm K}} \right) $\end{document} solution of 3,4,5‐triamino‐1,2,4‐triazole dinitramide in NMP, respectively. The values of activation energy E and pre‐exponential factor A for the dissolution process are obtained as 14.13 kJṁmol−1 and 5.34 × 10−2 s−1.

Trends in the Adsorption of Volatile Organic Compounds in a Large-Pore Metal−Organic Framework, IRMOF-1

Metal-organic frameworks have been proposed as useful sorbents for the capture of a variety of compounds. In this work, inverse gas chromatography (IGC) utilizing micropacked capillary columns was used to probe the adsorption of more than 30 volatile organic compounds (VOCs) on IRMOF-1. In an attempt to study the effect of structural degradation upon VOC adsorption, multiple samples of IRMOF-1 with widely ranging properties were investigated. Trends in the differential enthalpies and equilibrium constants for the adsorption of VOCs were determined on the basis of the molecular properties of the adsorbate and the structural properties of the MOF sample. The results indicate that samples of IRMOF-1 that are affected by a moderate amount of structural degradation interact with adsorbed species more strongly than does a sample with fewer defects, resulting in higher heats of adsorption. Samples of IRMOF-1 with specific surface areas of around 1000 m(2)/g show heats of adsorption for alkanes that are higher than those estimated previously via Monte Carlo calculations. Although the data for nonpolar (and weakly polar) species showed many of the anticipated trends for the interactions with IRMOF-1, the equilibrium behavior of polar VOCs did not correlate well with the molecular properties of the adsorbate (i.e., vapor pressure and deformation polarizability), leaving some uncertainty about the nature of the interaction mechanism. The equilibrium data and the heats of adsorption were found to fit well to a small group of molecular descriptors through the application of the Abraham linear free-energy relationship, thus providing insight into the complex interactions between the MOF structure and the VOC compounds. Hydrogen bonding interactions were determined to be the primary contributors to specific interactions between adsorbates and the MOF surface. Size exclusion also seems to play a role in the adsorption of larger species. These results show that the interaction of VOCs with MOFs is more complex than previously assumed and that more work is needed to probe the mechanisms of these processes.

Adsorption isotherms of pinhão ( Araucaria angustifolia seeds) starch and thermodynamic analysis

The seeds of Araucaria angustifolia, commonly known as pinhão, are widely consumed in both Southern and Southeastern Brazil due to their high nutritious value comprised basically by starch. The literature on the technological aspects of this seed is still very scarce. Moisture adsorption isotherms of pinhão starch were determined at 10, 20, 30 and 40 °C using the gravimetric method. Results show that the Peleg model most appropriately represents the experimental data. Other models (Chung–Pfost, GAB, Henderson, BET and Chirife) also were found to adjust well. The isosteric heat of sorption (differential enthalpy) was calculated by using the moisture adsorption isotherm and decreased as moisture content increased. The enthalpy–entropy compensation theory was applied to adsorption isotherms and the isokinetic temperature for pinhão starch was calculated by plotting the differential enthalpy versus differential entropy. It was found that the adsorption process investigated was enthalpy-controlled and spontaneous.

SORPTION ISOTHERMS AND THERMODYNAMIC PROPERTIES OF POWDERED MILK

Moisture sorption isotherms of powdered milk were obtained using the gravimetric static method at 30°, 40°, and 50°C. Peleg and Enderby equations were found to be the most suitable models for describing the sorption curves among six well-known tested equations. Thermodynamic properties such as differential enthalpy and entropy of sorption were determined from moisture adsorption and desorption data, using the Clausius-Clapeyron equation. The experimental data showed that enthalpy-entropy compensation theory was applicable to the moisture sorption behavior of powdered milk.

Predicting suitable storage conditions for spray-dried microcapsules formed with different biopolymer matrices

Canola oil (CO)-in-soy protein isolate (SPI, 12.5 g per 100 ml of solution), CO-in-whey protein concentrate (WPC, 30 g per 100 ml of solution) and CO-in-mesquite gum (MG, 30 g per 100 ml of solution) emulsions were obtained (all with CO to biopolymers solids ratio of 25 g of canola oil per 100 g of wall material), spray dried and stored at water activities ( a w) of 0.12–0.89 at temperatures of 15, 25 and 35 °C. The powders adsorption isotherms experimental data were fitted to the GAB model. Their differential and integral enthalpies and entropies were estimated. The microcapsules point of minimum integral entropy (maximum stability) kept at 25 °C occurred at 10.40 g water per 100 g of dry solids ( a w of 0.55) for MG, 10.59 g water per 100 g of dry solids ( a w of 0.68) for SPI, and 6.38 g water per 100 g of dry solids ( a w of 0.46) for WPC. The integral enthalpy–entropy compensation indicated that the water vapour adsorption was controlled by entropic mechanisms at low a w, but by enthalpic mechanisms at high a w.

Study of the Heat of Absorption of CO2 in Aqueous Ammonia: Comparison between Experimental Data and Model Predictions

Differential enthalpies of absorption of CO2 in aqueous ammonia were predicted based on reaction equilibrium constants using the Gibbs−Helmholtz equation. The reaction equilibrium constants were selected from the literature and integrated into an electrolyte-NRTL model and the model proposed by Edwards, in which the interaction parameters were previously and solely fitted from the NH3−CO2−H2O vapor−liquid equilibrium (VLE) data. The heat contributions of the individual reactions were taken into account in the total heat of absorption in both of the models. The heat of absorption was presented as a function of the CO2 loading and temperature. The predicted heats of absorption were compared with experimental data for temperatures ranging from 35 to 80 °C obtained in this work and also some other modeling results. The predicted results fit the experimental data well at lower temperatures, and also well at lower loadings when the temperature was higher, but the model was not good at high loadings and high tem...

Investigation of the Behavior of Ethylene Molecular Films Using High Resolution Adsorption Isotherms and Neutron Scattering

The wetting behavior of ethylene adsorbed on MgO(100) was investigated from 83-135 K using high resolution volumetric adsorption isotherms. The results are compared to ethylene adsorption on graphite, a prototype adsorption system, in an effort to gain further insight into the forces that drive the observed film growth. Layering transitions for ethylene on MgO(100) are observed below the bulk triple point of ethylene (T = 104.0 K). The formation of three discrete adlayers is observed on the MgO(100) surface; onset of the second and third layers occurs at 79.2 +/- 1.3 K and 98.3 +/- 0.9 K, respectively. Thermodynamic quantities such as differential enthalpy and entropy, heat of adsorption, and isosteric heat of adsorption are determined and compared to the previously published values for ethylene on graphite. The average area occupied by a ethylene molecule on MgO(100) is 22.6 +/- 1.1 A2 molecule(-1). The locations of two phase transitions are identified (i.e., layer critical temperatures at T(c2)(n=1) at 108.6 +/- 1.7 K and T(c2)(n=2) at 116.5 +/- 1.2 K) and a phase diagram is proposed. Preliminary neutron diffraction measurements reveal evidence of a monolayer solid with a lattice constant of approximately 4.2 A. High resolution INS measurements show that the onset to dynamical motion and monolayer melting take place at approximately 35 K and approximately 65 K, respectively. The data reported here exhibit a striking similarity to ethylene on graphite which suggests that molecule-molecule interactions play an important role in determining the physical properties and growth of molecularly thin ethylene films.

A study of the pore size distribution for activated carbon monoliths and their relationship with the storage of methane and hydrogen

By adsorption of different gases and simulation methods it was studied the characterization of microporous monoliths in activated carbons from coconut shells in relation to the storage capacity of gases that present energetic interest. Adsorption isotherms of nitrogen, methane, carbon dioxide and hydrogen at different temperatures were measured at sub-atmospheric pressures. Additional adsorption isotherms of methane were performed at room temperature and high pressures (up to 4.5 MPa). A Grand Canonical Monte Carlo simulation of adsorption on slit pores was carried out for these gases. The simulated data were adjusted to experimental data to optimize the models. Different parameters such as micropore volume, pore size distribution and differential isosteric enthalpy of adsorption, were studied and related to the hydrogen and methane storage capacity for these materials.

Enthalpies of interaction of water with microcrystalline cellulose having different degrees of dispersion

Changes in enthalpy during the interaction of different kinds of microcrystalline cellulose and water were determined. The integral and differential enthalpies of polysaccharide interactions with water were calculated. The amount of water retained by the cellulose was determined. The effect of mechanical processing on these characteristics was demonstrated.

Solubility of Acetamide, Propionamide, and Butyramide in Water at Temperatures between (278.15 and 333.15) K

The aqueous solubilities of acetamide, propionamide, and butyramide were measured from (278.15 to 333.15) K at intervals of 5.00 K using the gravimetric method. The temperature dependence of the solubility of acetamide, propionamide, and butyramide in water is described by the van’t Hoff equation. Linear van’t Hoff plots were found for amides in water, and the differential enthalpy of solution was calculated.

Thermodynamic Analysis of Water Vapor Sorption Isotherms and Mechanical Properties of Selected Paper‐Based Food Packaging Materials

Adsorption isotherms of 3 selected paper-based packaging materials, that is, vegetable parchment (VP) paper, Kraft paper, and solid-bleached-sulfate (SBS) paperboard, were determined at 3 different temperatures (25, 40, and 50 degrees C). The GAB isotherm model was found to fit adequately for describing experimental adsorption isotherm data for the paper samples. The monolayer moisture content of the paper samples decreased with increase in temperature, which is in the range of 0.0345 to 0.0246, 0.0301 to 0.0238, and 0.0318 to 0.0243 g water/g solid for the MG paper, the Kraft paper, and the SBS paperboard, respectively. The net isosteric heats of sorption (q(st)) for the paper samples decreased exponentially with increase in moisture content after reaching the maximum values of 18.51, 27.39, and 26.80 kJ/mol for the VP paper, the Kraft paper, and the SBS paperboard, respectively, at low-moisture content. The differential enthalpy and entropy of 3 paper samples showed compensation phenomenon with the isokinetic temperature of 399.7 K indicating that water vapor had been adsorbed onto the paper samples with the same mechanism. Depending on the paper material, tensile strength of paper samples was affected by moisture content.

Competitive Enantiodifferentiating Anti-Markovnikov Photoaddition of Water and Methanol to 1,1-Diphenylpropene Using A Sensitizing Cyclodextrin Host

UV-vis, circular dichroism (CD), fluorescence, and NMR spectral studies on the self-inclusion behavior of a newly synthesized sensitizing host, 6-(5-cyanonaphthyl-1-carboamido)-6-deoxy-beta-cyclodextrin (1), showed that the appended naphthalene moiety of 1 perches laterally on the cyclodextrin rim in aqueous methanol but is shallowly included and somewhat tilted in its own cavity in water. UV-vis and CD spectral examinations of the complexation of guest substrate 1,1-diphenylpropene (DPP) with host 1 revealed the formation of a stoichiometric 1:1 complex of DPP with 1. The naphthyl fluorescence of 1 was efficiently quenched by the addition of DPP in aqueous solutions of low methanol contents (<or=25%) but was less efficiently quenched in more hydrophobic solvents (>or=50% methanol), where the fluorophore is not included in the cavity and allows the external attack of DPP to form an exciplex in the bulk solution. Upon irradiation in aqueous solutions of different methanol contents, competitive photoaddition of water and methanol to DPP occurred to give chiral water adduct 3 and methanol adduct 4, favoring the latter product by a factor of 2.5 due to the higher nucleophilicity of methanol. The enantiomeric excess (ee) values of the photoadducts were generally low in highly methanolic solutions, but was greatly improved by increasing the water content to reach 18% ee for 3 and 13% ee for 4 in 10% methanol solution at -10 degrees C. Interestingly, the ee of methanol adduct 4 was consistently lower than that of water adduct 3 particularly in water-rich solvents, revealing that the product's ee is not a simple thermodynamic function of the enantioface-selectivity upon complexation of DPP by chiral host 1 but also kinetically controlled by the subsequent photoinduced enantioface-differentiating nucleophilic attack of water and methanol to radical cationic DPP generated photochemically. Compatible with this mechanism, the compensation plot of the differential activation enthalpy versus entropy, which were obtained from the van't Hoff analysis of the temperature-dependent ee's obtained in aqueous solutions of varying methanol contents, gave an excellent straight line for water adduct 3 but an unprecedented bent plot for methanol adduct 4, indicating a switching of the mechanism in between 35 and 50% methanol solution. By using high pressure, low temperature, and/or added salt, the ee of water adduct 3 was further enhanced to 24-26%.

Entropic effects and isosteric heats of nitrogen and carbon dioxide adsorption on chabazite zeolites

Equilibrium adsorption isotherms for CO 2 and N 2 were measured on a fully exchanged potassium chabazite (KCHA) zeolite, and partially exchanged sodium-chabazite (NaCHA) and lithium-chabazite (LiCHA) zeolites. This work presents integral thermodynamic functions and isosteric heats of N 2 and CO 2 adsorption equilibria on a fully exchanged potassium chabazite (KCHA) zeolite, and compares these to those functions measured on sodium exchanged chabazite (NaCHA) and lithium exchanged chabazite (LiCHA) zeolites. The thermodynamic quantities were calculated from equilibrium isotherms as function of loading. Adsorption of N 2 on KCHA was considered with distinct layers in inter-crystal spaces and mesopores volume, while CO 2 adsorption in KCHA cavities was more readily interpreted as fluid-like volume filling mechanism. The molecules comprising this fluid (CO 2) are in the dispersion energy field of the crystals and of each other, bounded also by considerable field-gradient quadrupole energy. In all cationic forms the adsorption equilibrium loading and differential enthalpies for CO 2 were considerably higher than those for N 2. The CO 2 integral entropy showed a rapid decreasing trend close to the saturation capacity of the cavities, demonstrating an appreciable loss of molecule degrees of freedom. The results of this work provide useful thermodynamic information that help in understanding the adsorption of N 2 and CO 2 on a fully exchanged KCHA zeolite.

MOISTURE ADSORPTION THERMODYNAMICS OF FRACTIONATED SESAME HULLS (SESAMUM INDICUM L.)

ABSTRACT Sesame hulls are a useful byproduct of sesame processing industry. Moisture adsorption isotherms (MSIs) for whole sesame hulls (WSHs) and powdered sesame hulls (PSHs) were obtained at 15, 30 and 45C, and 0.05 to 1.5 moisture content (decimal dry basis) using a water activity meter. Four MSI models were tested. Halsey model was found to provide the best fit for experimental data for both WSHs and PSHs. Standard error of estimate, %P and pseudo‐R2 values were: 0.00168 and 0.00248, 4.7 and 5.7%, and 0.963 and 0.974, respectively. Equilibrium relative humidity (ERH) values of PSHs were greater than those of WSHs at constant moisture content. Differential enthalpy (qst) and entropy (ΔSd) decreased exponentially with the increase in equilibrium moisture content, then became constant beyond 0.7 moisture content. qst and ΔSd values were larger for WSHs than PSHs. Enthalpy–entropy compensation was found to exist for both PSHs and WSHs. An entropy‐driven process was observed, with the free energy change (ΔG) for WSHs and PSHs of+0.0183 kJ/kg and−0.0284 kJ/kg, respectively. The spreading pressure was found to increase with the increase in ERH and decrease in temperature. The net integral enthalpy (ΔHi) decreased then reached an asymptote beyond a moisture content of 0.15 for both PSHs and WSHs. Net integral enthalpy was larger for WSHs. The net integral entropy (ΔSi) was negative for PSHs and WSHs, and ΔSi was greater in magnitude for PSHs.PRACTICAL APPLICATIONSSesame hulls are useful byproducts of sesame processing industry. Large amounts of this effluent are produced yearly in Jordan. They are used as livestock feed, but they require further dehydration to reduce moisture content and water activity into safe levels. In this project, drying thermodynamics of sesame hulls were discussed.

Propriedades termodinâmicas de adsorção de água do amido de rizomas do lírio-do-brejo (Hedychium coronarium)

Thermodynamic properties where determined (differential enthalpy, of differential entropy, integral enthalpy, and integral entropy) of the starch of rhizomes of swamp lily through water adsorption isotherms. The isotherms were determined in water activities in the range of 0.11 to 0.84, in temperatures ranging from 30 to 50 °C. The GAB equation which fits well to the experimental isotherms was used to estimate the properties of thermodynamic adsorption. The slight reversal of the isotherms indicates damaged starch. The enthalpy and entropy differential gap increased with the decrease in moisture and correlated to each other confirming the chemical linear compensation. An exponential model type Y = b.e(a/Xe) described adequately the dependence of these properties differential on the moisture content of balance. The integral enthalpy and entropy increased continuously with the moisture content of balance but presented negative values for the integral entropy. These thermodynamic properties of water adsorption showed that the starch extracted from the rhizomes of swamp lily has low hygroscopicity despite the occurrence of damaged starch granules.

Comparative thermodynamic and spectroscopic properties of water interaction with human stratum corneum

The water content of skin has a significant impact on skin properties; sufficient hydration is necessary to keep the skin supple, flexible, and smooth. To understand more completely the water retention properties of the human skin barrier, physical macroscopic properties must be related to the structural organization of the stratum corneum (SC). Water, lipids, and natural moisturizing factor (NMF) influence the molecular structures that affect the properties of SC, including water sorption and binding enthalpy. In the research reported here, isothermal microcalorimetry was used to study the interaction of water vapor with isolated human SC in intact, delipidized, and water-washed delipidized forms to identify the influences of the principal components of SC on water sorption. The calorimetric data are interpreted in conjunction with spectroscopic results to identify the conformational changes in keratins induced by lipid and NMF removal and to assess the influence of these changes on water binding in SC. Isothermal calorimetry was used to measure the integral heat of water vapor sorption on intact, delipidized, and water-washed delipidized human SC at 32 degrees C as a function of relative humidity using back and thigh skin from three donors. Calorimetric measurements were combined with water vapor sorption measurements to determine the differential thermodynamic properties of these systems. Attenuated total reflection-Fourier transform infrared spectroscopy was used to investigate effects of extraction on protein secondary structure. The magnitudes of the differential enthalpy, entropy, and free energy were greatest for intact SC and least for water-washed delipidized SC. Water sorption followed a similar trend. Delipidization led to a significantly reduced binding enthalpy at low water content; water washing the delipidized SC had only a small additional effect on binding enthalpy. Delipidization converts a fraction of keratin alpha-helixes to turns and random coils, while water sorption converts a fraction of keratin alpha-helixes to beta-sheets, turns, and random coils. The results of this study are consistent with a water sorption model in which keratin-keratin hydrogen bonds are replaced by keratin-water hydrogen bonds. Delipidization reduces the fraction of dry keratin that is in the alpha-helix conformation, suggesting that lipids hold the keratins in a conformation conducive to optimal hydration.