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),...     

Simultaneous thermal and contraction/expansion analyses of cast iron solidification process

Journal of Thermal Analysis and Calorimetry - Simultaneous thermal and contraction/expansion analysis of hypoeutectic grey (lamellar graphite) and ductile (nodular graphite) cast irons...     

Spontaneous radial capillary impregnation across a bank of aligned micro-cylinders. Part II: Experimental investigations

This paper presents an experimental approach to study the capillary impregnation of a liquid across an array of parallel micro-cylinders. The technique presented successfully validates the theoretical findings of part I, and provides a methodology to calculate the fill time and the overall capillary impregnation dynamics for any arbitrary cylindrical sample made of aligned micro-cylinders, by taking into account the role of the trapped gas, which opposes and slows down the inward capillary flow.     

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.     

Spontaneous radial capillary impregnation across a bank of aligned micro-cylinders – Part I: Theory and model development

This paper presents an analytical and numerical approach to describe the capillary infusion of a liquid across an array of parallel micro-cylinders. Based on a series of simplifying assumptions, the model proposes a method to average the varying capillary pressure and introduces a technique to assess the inhibiting effects of the gas entrapped between the micro-cylinders as the liquid radially ingresses into the micro-cylinder array. The proposed averaging scheme of the capillary pressure is an improvement over previous analytical approaches, as it accounts for the physics of wetting at the micro-scale. The equations are non-dimensionalized and the role of various parameters such as gas entrapment and average capillary pressure is explored. The inclusion of the gas displacement phenomenon requires only one parameter to be determined empirically, in order to describe the impregnation behavior of the liquid. Two limiting cases when all gas is allowed to escape through the impregnating liquid and when all the gas is entrapped within are identified. This study should prove useful in understanding the role of entrained gas and capillarity on impregnation mechanics in micro-scale porous media.     

Plasmonic light scattering from nanoscopic metal tips

Linear light scattering by individual nanoscopic metal wire tips is investigated. Using evanescent-wave excitation, the spectral and polarization dependence of the emission are addressed. Choosing gold and tungsten as representative tip materials, intense scattering and a strongly plasmon-resonant behavior observed for gold contrasts a comparatively weak and spectrally flat response for tungsten. Spectral dependence and local-field enhancement are found to be sensitive to details of the structural parameters and can be described by a simple model. The results provide selection criteria for tips to be used in scattering-type near-field microscopy or photoemission in inelastic tunneling spectroscopy.This revised version was published online in April 2005. The last name of the corresponding author M. B. Raschke was corrected.     

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.