The standard enthalpies of formation of some dibenzoannelated cycloalkanols

The heats of combustion of trans-9,10-bis-hydroxymethyl-9,10-dihydrophenanthrene, trans-5-hydroxymethyl-5,6-dihydro-7H-dibenzo[a,c]cyclohepten-6-ol, 5-hydroxymethyl-5,6-dihydro-7H-di-benzo[a,c]cycloheptene, 6-hydroxymethyl-5,6-dihydro-7H-dibenzo[a,c]cycloheptene, 5H-dibenzo-[a,d]cyclohepten-5-ol and 5H-10,11-dihydrodibenzo[a,d]cyclohepten-5-ol were measured by means of a Gallenkamp adiabatic bomb calorimeter. Uncertainties in the determination of the heats of combustion ranged between 0.2 and 0.3%. The enthalpies of formation and atomization for the six compounds were derived. The experimental values of the heats of atomization were compared with those calculated using the Allen–Skinner bond energy scheme. Conclusions about energetic contributions which stabilize the structure of the investigated compounds were drawn.     

The effect of γ rays upon monohydrated asparagine. A DSC study

Crystalline non-irradiated and irradiated monohydrated asparagine was investigated by means of DSC. The samples were irradiated at room temperature with gamma radiations using a ¹³⁷Cs source. The exposure doses ranged between 1 and 12 kGy. All samples were scanned in non-sealed pans, from room temperature to a temperature beyond the melting point. The change of registered DSC thermograms for the irradiated samples compared to those of non-irradiated ones and the variation of the parameters associated to dehydration and melting—decomposition with the cumulative dose were analyzed. The study has put in evidence transformations related to the values of characteristic temperatures of peaks and to the thermal effects. The diffusion and desorption of water molecules is hindered by the free radicals formed by irradiation. The most stable free radical species is formed by the extraction of a hydrogen atom from the methylene group of the amino acid chain, done by another hydrogen atom, probably derived from a water molecule.     

Interplay between composition,structural dynamics and thermodynamic data in amino acid nitrates

Journal of Thermal Analysis and Calorimetry - A systematic thermodynamic study has been performed for a series of nitrates having cations derived from the α-amino acids glycine (Gly),...     

Estimation of Solubility of Carbon Dioxide in Polar Solvents

The solubility of CO₂ in polar solvents is poorly predicted by all estimation methods that use only properties of the pure components. It is thought that this is because CO₂ molecules, although they do not have a permanent dipole moment, behave like electrical multipoles as a consequence of their strongly polar bonds. An equation, proposed in a previous paper, for estimating the activity coefficient of a nonpolar gas dissolved in a polar liquid is modified by adding a term containing the quadrupole moment of the gas molecule. Errors in estimating gas solubilities on that basis are less than 20%, except for the solvents in which specific interactions (e.g., acid–base interactions) are present.     

The effects of gamma rays upon monohydrated and anhydrous asparagine: a DSC study in sealed pans

Non-irradiated and gamma irradiated monohydrated (l Asn·H₂O) and anhydrous (l Asn) asparagines, in solid state, were studied by means of DSC. The samples were irradiated at room temperature with gamma radiations using a ¹³⁷Cs source. The exposure doses ranged between 1 and 10 kGy. All samples were scanned in sealed pans, from room temperature to a temperature beyond the melting point. The DSC scans of l Asn·H₂O samples in sealed crucibles revealed the presence of two dehydration processes and one of decomposition and only decomposition in the case of l Asn. The influence of gamma irradiation consisted in decreasing the enthalpy of dehydration and of decomposition. A decomposition mechanism is proposed.     

The standard enthalpies of formation of l-asparagine and l-α-glutamine

The energies of combustion of l-asparagine and l-α-glutamine were measured in a static bomb adiabatic calorimeter. Corrections were made for the heats due to the ignition of sample and for the nitric acid formation. The derived enthalpies of formation in solid state of asparagine monohydrate, nonhydrated asparagine and glutamine are respectively ?1084.1 ± 3.0, ?788.1 ± 4.7 and ?834.3 ± 4.6 kJ mol^?1. The data of enthalpy of formation are compared with the literature values and with estimated values by means of group additivity, using parameters recommended by Domalski and Hearing. The discrepancies between experimental and calculated values are explained by considering the number and strength of intermolecular hydrogen bonds. The dehydration of asparagine monohydrate and the possible melting of the three amino acids were investigated by means of DSC. Glutamine melts without considerable decomposition at about 182 °C, while asparagines decompose during the fusion process (208 °C).     

The calorimetric study of some guanidine derivatives involved in living bodies nitrogen metabolism

The energies of combustion of creatine (anhydrous and monohydrate), creatinine, and arginine were measured in a static bomb adiabatic calorimeter, in pure oxygen at 3,040 kPa. The derived standard enthalpies of formation in solid state of the above-mentioned compounds are, respectively, −520.4 ± 4.3, −809.7 ± 1.3, −204.2 ± 7.0, and −634.8 ± 2.3 kJ mol⁻¹ . The data of enthalpy of formation are compared with literature values and with estimated values by means of group additivity. The dehydration of creatine monohydrate and the processes occurring in the three guanidine derivatives at temperatures exceeding 200 °C were investigated by means of DSC.     

Thermochemical and structural study of a dibenzocycloheptane cyanoenamine

The crystalline and gas phase enthalpy of formation of 5-cyano-7H-dibenzo-[a,c]-cyclohepten-6-amine (1) (142.0 ± 11.6 and 264 ± 20 kJ mol^?1, respectively) are reported. The sublimation enthalpy at T = 298.15 K for this compound was evaluated by combining the fusion enthalpy from DSC measurements adjusted to 298 K with estimated vaporization enthalpy. The experimental enthalpy of formation is discussed in relationship with values calculated at the G3(MP2)//B3LYP level of quantum chemical theory and by means of group additivity. The crystal structure of this compound was determined by X-ray crystallography and shown to exist entirely in the cyanoenamine form 1, i.e. not the tautomeric α-cyanoimine 2.     

The enthalpies of formation of two dibenzocyclooctadienones

The standard molar enthalpies of formation (Δ_fH_m⁰(s)/kJmol⁻¹) for 2,3:6,7-dibenzocycloocta-2,6-dien-1-one and 2,3:7,8-dibenzocycloocta-2,7-dien-1-one [6H-11,12-dihydro-dibenzo[a,e]cycloocten-5-one (ketone 1) and 10H-11,12-dihydrodibenzo[a,d]-cycloocten-5-one (ketone 2), respectively] were derived from enthalpies of combustion, measured by means of a microbomb calorimeter. The fusion and vaporization enthalpies of these compounds were obtained from DSC and correlation gas chromatography measurements. The standard molar enthalpies of formation in the gas phase were calculated by combining the condensed phase standard molar enthalpies of formation with the fusion and vaporization enthalpies adjusted to 298.15 K. Values for Δ_fH_m⁰(g) of (−39.9±5.5) and (−14.8±5.3) kJ mol⁻¹ were obtained for 2,3:6,7-dibenzocycloocta-2,6-dien-1-one and 2,3:7,8-dibenzocycloocta-2,7-dien-1-one, respectively. Quantum chemical calculations are reported for the compounds investigated experimentally and an additional four isomers. Isomerization enthalpies are derived from computed energies. The enthalpies of formation are also calculated by group additivity, compared with the experimental values and then correlated with the structure of the molecules investigated. The X-ray analysis of ketone 1 is also reported.