Experimental and computational thermochemistry of the dihydroxypyridine isomers

Morais, Victor M.F.; Miranda, Margarida S.; Matos, M. Agostinha R.

doi:10.1016/j.jct.2005.06.013

Cited by 12 publications

(6 citation statements)

References 23 publications

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“…Since a substantially better agreement between theory and experiment is obtained for other methyl derivatives of tetrazole (30,32), it is probable that a large deviation for 31 results from inaccuracy of experimental value [29]. Excluding 31 from consideration, the mean absolute deviation from experiment of G4 theory for the species in Table 2 is 6.8 kJ/mol, which is appreciably less than that for nitro compounds.…”

Section: Nitro Compoundsmentioning

confidence: 99%

Assessment of Gaussian-4 theory for the computation of enthalpies of formation of large organic molecules

et al. 2011

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Section: Nitro Compoundsmentioning

confidence: 99%

Assessment of Gaussian-4 theory for the computation of enthalpies of formation of large organic molecules

et al. 2011

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“…The referral of hydroxypyridones as DHP in ruminant toxicology can be considered something of a misnomer, as many chemists have chosen more descriptively accurate abbreviations of what exists at physiological pH as 3-hydroxy-2(1H)-pyridone such as: 2,3-DOHP (Morais et al 2006); H2pp (Nurchi et al 2012); 3,2-Hopo (Scarrow et al 1985); 3,2-HOPO (Harrington et al 2010;Santos et al 2012); and vhpo (Stunzi et al 1979). Taking these into account, an abbreviation such as HPo would more descriptively represent the hydroxypyridone conformation.…”

Section: Toxicity Response To Infused 23-dhp Administered Orallymentioning

confidence: 99%

Unravelling Leucaena leucocephala toxicity: ruminant studies in eastern Indonesia and Australia

Halliday¹

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The forage tree legume leucaena [Leucaena leucocephala (Lam.) de Wit ssp. glabrata (Rose) Zarate] is a high-quality ruminant feed vitally important as a source of protein for livestock production in tropical regions. However, the presence of the acutely toxic nonprotein amino acid mimosine in leaves and seeds, and its breakdown to chronically toxic hydroxypyridones (DHP), was believed to limit its productivity and adversely affect animal health. The Australian development of a fermenter-cultured oral inoculum containing the DHP-degrading ruminal bacterium Synergistes jonesii in the 1980s was thought to overcome this issue; however, anecdotal evidence of leucaena toxicity symptoms occurring in inoculated animals remained. In response, a program of research was initiated to investigate the efficacy of S. jonesii as well as other methods of protection against toxicity in ruminants. Broadly, this involved two areas of research, namely the effectiveness of: (a) microbiological degradation via S. jonesii; and (b) non-microbial metabolic detoxification. Key objectives were to: (a) determine the efficacy of inoculation with S. jonesii both within Indonesia and Australia; (b) profile the toxicity status of ruminants in eastern Indonesia; (c) investigate the impact of mineral supplementation on 2,3-DHP toxicity; and (d) determine the extent of in vivo conjugation of DHP and its role in protecting ruminants against toxicity. Initially, an Indonesian study involving the transfer of rumen fluid from "protected" ruminants to naïve Bali bulls was conducted. Sequential monitoring of DHP levels in urine indicated that there was no effect of inoculation. Secondly, a controlled animal house experiment was conducted in Australia to measure the impact of high leucaena diets on production in naïve steers and the effect of inoculation with the commercial S. jonesii inoculum. Key findings were: (1) inoculation had no effect on total DHP excretion; (2) indigenous S. jonesii strains were present in naïve animals prior to inoculation; (3) DHP did not suppress thyroid hormone production; and (4) high levels of the isomer 2,3-DHP were present without accompanying signs of toxicity. The leucaena toxicity status of ruminants in eastern Indonesia was then assessed in a survey across the four islands of Lombok, Sumbawa, Sumba and West Timor. A number of different strains of S. jonesii, including the ATCC type strain (78.1), were detected, however S. jonesii was always at low population levels and always accompanied by high levels of undegraded 2,3-DHP in urine. Despite this apparent failure of S. jonesii to degrade DHP, there was no observed impact on animal productivity or health. Accordingly, vii Contributions by others to the thesis This thesis is the original work of Michael Halliday.

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“…The systematic study of thermochemical properties of pyridine derivatives, both in the condensed and gaseous phases, is one of the subjects of our research work. For several years we have studied the thermochemical properties of various pyridine compounds in order to establish how the transferability of bond energy contributions applies to these compounds – and, consequently, to correlate their behavior in terms of energetics, structure and reactivity. In addition we have been examining the effect of different substituents on the dissociation enthalpy of the (N−O) bond of the nitrogen N-oxide heterocycles, a study that requires the knowledge of thermochemical data of the correspondent heterocycles not having the (N−O) bond …”

Section: Introductionmentioning

confidence: 99%

Thermochemical Study of Three Hindered Pyridine Derivatives

2008

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The present work reports the values of the gaseous standard (p°) 0.1 MPa) molar enthalpy of formation of three pyridine derivatives substituted with one, two, and three tert-butyl groups, in positions para, orthoortho and ortho-para-ortho to the nitrogen, respectively. The standard molar energies of combustion of each compound, determined by static bomb calorimetry, yielded their standard molar enthalpies of formation in the condensed phase at T ) 298.15 K, which together with the values of the standard molar enthalpies of vaporization or sublimation, measured by Calvet microcalorimetry, allowed the calculation of the standard gas phase molar enthalpy of formation of each compound studied. The enthalpies of combustion for 4-tertbutylpyridine (l), 2,6-di-tert-butylpyridine (l) and 2,4,6-tri-tert-butylpyridine (cr) were found to be, respectively, -(5 370.1 ( 3.4) kJ mol -1 , -(7954.2 ( 4.0) kJ mol -1 , and -(10 542.9 ( 4.9) kJ mol -1 . The molar enthalpies of vaporization were measured as (54.4 ( 1.3) kJ mol -1 for 4-tert-butylpyridine, (56.6 ( 1.2) kJ mol -1 for 2,6-di-tert-butylpyridine, whereas the enthalpy of sublimation of 2,4,6-tri-tert-butylpyridine was found to be (78.3 ( 1.7) kJ mol -1 .

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Experimental and computational thermochemistry of the dihydroxypyridine isomers

Cited by 12 publications

References 23 publications

Assessment of Gaussian-4 theory for the computation of enthalpies of formation of large organic molecules

Assessment of Gaussian-4 theory for the computation of enthalpies of formation of large organic molecules

Unravelling Leucaena leucocephala toxicity: ruminant studies in eastern Indonesia and Australia

Thermochemical Study of Three Hindered Pyridine Derivatives

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