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Pyrolysis of proline, leucine, arginine and lysine in aqueous solution
Geochimica et Coamochimica Acta, 1968, Vol. 32,
pp. 1353
to 1356. Pergamon Preen. Printed in Northern Ireland
NOTES
Pyrolysis of proline, leucine, arginine and lysine
in aqueous solution
J. R. vuLIEN.TYNE* Division of Biological Sciences, Cornell University, Ithaca, New York 14850
equations for pyrolysis in 0.01 M solution were: proline, k = 1.5 x 10%4%4~/~T; leucine, k = 1.7 x lO%+@Q/~T; ar&;le, k = 1.2 x 1@e-lQ&WT; ly&e, non-linear. Ammonia was produced in all cases. Arginine gave rise to ornithine, proline and 811unidentifiedbaeic compound in addition.
Abstract-Am-herds
As A oontinuation of earlier studies on the relationship between the geological and thermal stability of 5rni110 acids (JONESand VALLZ~, 1960; VAIXENTYNE,1964; POVOLEDO and VALLENTYNX,1964) date we presented on the thermal reaction kinetics of four additional amino acids in 0.01 M aqueous solution. Experimental and analytical conditionswere the same as those described previously (VAGLENTYNE, 1964) i.e. heating in sealed evacuated glass tubes and analysis by automated column c~mato~aphy. The kinetic results are shown in Fig. 1, with data on individual amino acids summarized below. Proline The disappearance of proline followed first order reaction kinetios at all temperatures studied, 0.37.life values ranging from 9.1 hr at 282°C to 67.5 days at 218°C. The Arrhenius equation, determined by linear regression from three points, we k = 1.5 x lO~se_42~~~T_ Ammonia was the only ~y~-~~tive pyrolytic produ& observed on cohmtn ohromatography, its molar concentrationnever exceeding 30 per cent of the proline decomposed. During pyrolysis pH rose from initial values of 6.8 to values in the range of &O-8.4, decliningto 7.3-7.8 when most of the proline had deoomposed. Proline is the most stable of all amino acids tested to date under aqueous conditions at temperatures below 212°C.
At the four tempe~t~es studied the disappearanceof leucine followed first order ma&ion kinetics, 0*3?-life values ranging from 57 min at 282°C to 726 days (extrapolatedfrom measurements made up to 460 days) at 174°C. The Arrhenius equation determined from these values was k = 1.7 x 1Sl’s-*5~200/RT, No ninhydrin-reactive compounds other than mania were observed on column chromatography. The molar conversion of leucine to ammonia was only 26-40 per cent when 85-98 per oent of the leuoine had been deoomposed. Changes in pH during pyrolysis were not determined. Hydrolysis of pyrolyzed solutions with 6 N HCl resulted in no change of ohromatographicpatterns. * Present address: Fisheries Research Board of Canada, Freshwater Institute, 501 University Crescent, Winnipeg 19, Manitoba, Canada. 1363
1354
I 24t c150%) i@/
Fig. 1, Logarithm
I 22
t
( 2oow
i 20
I 18 t
I IF
(3OOW
Tabs
of 0*37-l& vs. the reciprocal of absolute temperature for 0.01 M solutions of four amino acids.
Pyrolyses were conducted at 216, 174”, 141” and lOl”C, with O-37-lives varying from 31 min at 216°C to values in the range of 35-60 days at 101°C. At all t,emperatures studied the reaction kinetics were first order, with the exception of one series of experiments at 141°C where there was a delay in the initiation of the reaction for some nnknown reason. This series was excluded from the present analysis since a repetition failed to corroborate the original results. The Arrhenius equation determined by linear regression from the four points was: k = 1.2 x 105e-1g>80e/BT; but since the values plotted in Fig. 1 showed a greater deviation from the regression line than is usual in such experiments the constants in the equation must be taken as only approximate. In most experiments there was a graduel rise in pH from initial values of about 76 to final values of about 8.3 when 95 per cent of the arginine had decomposed. The influence of pH on reaction kinetics was not tested. The following ninhydrin-reactive produots were detected in pyrolyzed solutions of arginine: ammonia, ornithine, proline, and an unidentified compound that appeared after arginine on oofumn separation following the standard proaedure for analysis of protein hydrolysa~s with the Spineo Amino Aeid Analyzer (33 ml effluent-ammonia; 50 ml effluent-erginina; 73 ml ef%luent-unknown). parallel experiments at the same temperatures showed that the unknown (= post-arginine) wasalso producedon pyrolysisof ornithineHC1. “Post-arginine”musttherefore be at least partly, if not totally, generated from ornitbine. The eon~entrations of arginine and its pyrolytic products are shown in Fig. 2 as a function of time at two dierent temperatures. It is apparent that the yields of ammonia and post-arginine are higher at higher temperatures, whereas the reverse is true of ornithine. Although the sequence of reactions is not known in detail, it is probable that the bulk of the ammonia and ornithine originated dire&y from arginine, post-~g~ine from ornithino, and proline possibly from argmine or ~st-argi~ine. Following complete decomposition of arginine, the nitrogen reoovered in the form of ninhydrin
1356
Notes
t.w
3 Time
in
hours
Fig. 2.‘Moles of arginine and ninhyd~in-motive pyrolytic products per 100 moles of arginino at t = 0 as a function of time at two different tompraturos. reactive compounds (assuming one atom of X por molecule for post-arginine) rangod from 40-80 per cent of that potentially availeble from arginine.
The decomposition of lysine at 249°C and 216°C followed first order resction kinetics; but at 200°C and 174°C graphs of log concentration vs. time decreased in slope during the course of pyrolysis, the main change in slope occurring when 40-60 per cent of the lysine had decomposed. The points for the lower temperatures given in Fig. 1 thus only indicete the time required at a given temperature to decrease the concentration to 37 per cent of the original, and cannot be extrapo~a~d further. For this reason, and the non-linearity of the e~erimental results (see Fig. l), an Arrhenius equation could not be calculated. Xo ninhydrin-reactive products other shen ammonia were observed on column chromatography; however, two unknowns were teported earlier on separations using paper chromatogrsphy (VALLENTYNE, 1964;. These unknowns could have appeared under the lysine or ammonia peaks on column separations. Parallel experiments were conducted at 200°C on 0.002 M, 0.01 M, and 0.05 M solutions of lysine*HCl to determine the effect of concentration on the kinetics of decomposition, Data for the two lower concentrations agreed within experimental error, whereas the 0.05 M solution yielded a curve of the Bame form but with lower rates of breakdown. In all cases the mte of decomposition decreased as a function of time of pyrolysis. The pII values increased during pyrolysis from initial values in the range of 66-7~0 to values in the range of 7.8-8.1 when 90-95 per cent of the lysine had decomposed. The effect of pH on reaction kinetics was not tested; but at least at the upper temperatures studied it did not exercise an important influence during the course of reaction. The high stability of proline and leueine was not unexpected in view of the many reported occurrences of these amino acids in fossils and sedimentary rocks with ages in excess of 60million years. From the experiments reported here it is clear that arginine could not persist in a free state for such a length of time without being protected in the form of complexes suoh as those proposed by DEGENS (1965).
1356
Notes
Acknowled~rnents-This work was supported by NASA to Mrs. PATRICIA MAHOOL for technical assistance.
Grant NGR
33-010-013.
1 am indebted
REFERENCES DE~ENS E. T. (1966) Geochemistry of Sediments, 342 pp. Prentice-Hall. JONES J. D. and VALLENTYNE J. R. (1960) Biogeochemistry of organic matter-I. Polypeptides and amino acids in fossils and sediments in relation to geothermometry. Ceochim. Cownochim. Acta 21, l-34. POVOLEDO D. and VALLENTYNE J. R. (1964) Thermal reaction kinetics of the glutamic acidpyroglutamic acid system in water. Ueochim. Cosrnochkm. Acta 22, 731.-734. VALLENTYNE J. R. (1964) Biogeochemistry of organic matter-II. Thermal reaction kinetics and transformation products of amino compounds. Cfeochim. Cosmochim. Acta 22, 157-188.
Geochlmioaet CosmochimicaAcb, 19613, Vol. 32, pp. 1356to 1363. Pergamon Press. Printed in Northern Ireland
Natural hydrothernublsystem and experimental hot-water/rock i&m&ion: Reactions with NaCl solutions and trace metal extraction Chemistry Division, (Received
13 May
A. J. ELLIS D.S.I.R., Petone, New Zealand
1968; accepted
in revised form
1 August
1968)
Abstract-Reactions of water, and NaCl solutions with andesite, and shale, at 35O-500°C are reported and the solutions compared with natural water compositions. High chloride greatly enhanced Fe, Mn, Cu, and Pb solubility in the low sulphide andesite reaction solutions. Except for Fe, extraction of metals was lower from the sulphur-rich shale. INTRODUCTION TFLERE is an increasing interest in the geochemistry of natural hydrothermal systems, arising from geothermal power developments and from enquiry into the nature of the fluids which gave rise to hydrothermal ore deposits. Concentrations of trace metals in dilute hot waters of volcanic hydrothermal areas are much lower than those which would be expected for an ore-forming solution capable of produoing major base metal ore bodies. During hydrothermal alteration of rock by these dilute waters, chemical equilibria evidently favour the retention of minor metals in the rock minerals, rather than their solution in the hot water. However, a high temperature (300”350°C) 26 % salt brine tapped by drillholes near Salton Sea, California, contained unusually high concentrations of elements such as lead, zinc, copper and silver (SKINNER et al., 1967). Isotope analysis (DOE et aE., 1966) showed that most of the lead was derived from the local sedimentery rooks of the aquifer. LEBEDEV (1967) reported high lead concentrations (up to 77 ppm) in N&l-CaCl, brines tapped at 80°C by deep drillholes in the Cheleken peninsula on the Eastern Caspian Sea shore. A hot brine enriched in minor metallic constituents was also reported to occur in the Atlantis II Deep in the bed of the Red Sea (MILLER et aE., 1966). It appears that under certain solution composition and temperature conditions ion complexing equilibria allow minor heavy metals to bo concentrated into solution during hydrothermal alteration or metamorphism of rocks. The present note gives information on the minor metal concentrations present in solutions after the reaotion of water and of sodium chloride solutions with an andesite and a shale at 360-600°C.
pp. 1353
to 1356. Pergamon Preen. Printed in Northern Ireland
NOTES
Pyrolysis of proline, leucine, arginine and lysine
in aqueous solution
J. R. vuLIEN.TYNE* Division of Biological Sciences, Cornell University, Ithaca, New York 14850
equations for pyrolysis in 0.01 M solution were: proline, k = 1.5 x 10%4%4~/~T; leucine, k = 1.7 x lO%+@Q/~T; ar&;le, k = 1.2 x 1@e-lQ&WT; ly&e, non-linear. Ammonia was produced in all cases. Arginine gave rise to ornithine, proline and 811unidentifiedbaeic compound in addition.
Abstract-Am-herds
As A oontinuation of earlier studies on the relationship between the geological and thermal stability of 5rni110 acids (JONESand VALLZ~, 1960; VAIXENTYNE,1964; POVOLEDO and VALLENTYNX,1964) date we presented on the thermal reaction kinetics of four additional amino acids in 0.01 M aqueous solution. Experimental and analytical conditionswere the same as those described previously (VAGLENTYNE, 1964) i.e. heating in sealed evacuated glass tubes and analysis by automated column c~mato~aphy. The kinetic results are shown in Fig. 1, with data on individual amino acids summarized below. Proline The disappearance of proline followed first order reaction kinetios at all temperatures studied, 0.37.life values ranging from 9.1 hr at 282°C to 67.5 days at 218°C. The Arrhenius equation, determined by linear regression from three points, we k = 1.5 x lO~se_42~~~T_ Ammonia was the only ~y~-~~tive pyrolytic produ& observed on cohmtn ohromatography, its molar concentrationnever exceeding 30 per cent of the proline decomposed. During pyrolysis pH rose from initial values of 6.8 to values in the range of &O-8.4, decliningto 7.3-7.8 when most of the proline had deoomposed. Proline is the most stable of all amino acids tested to date under aqueous conditions at temperatures below 212°C.
At the four tempe~t~es studied the disappearanceof leucine followed first order ma&ion kinetics, 0*3?-life values ranging from 57 min at 282°C to 726 days (extrapolatedfrom measurements made up to 460 days) at 174°C. The Arrhenius equation determined from these values was k = 1.7 x 1Sl’s-*5~200/RT, No ninhydrin-reactive compounds other than mania were observed on column chromatography. The molar conversion of leucine to ammonia was only 26-40 per cent when 85-98 per oent of the leuoine had been deoomposed. Changes in pH during pyrolysis were not determined. Hydrolysis of pyrolyzed solutions with 6 N HCl resulted in no change of ohromatographicpatterns. * Present address: Fisheries Research Board of Canada, Freshwater Institute, 501 University Crescent, Winnipeg 19, Manitoba, Canada. 1363
1354
I 24t c150%) i@/
Fig. 1, Logarithm
I 22
t
( 2oow
i 20
I 18 t
I IF
(3OOW
Tabs
of 0*37-l& vs. the reciprocal of absolute temperature for 0.01 M solutions of four amino acids.
Pyrolyses were conducted at 216, 174”, 141” and lOl”C, with O-37-lives varying from 31 min at 216°C to values in the range of 35-60 days at 101°C. At all t,emperatures studied the reaction kinetics were first order, with the exception of one series of experiments at 141°C where there was a delay in the initiation of the reaction for some nnknown reason. This series was excluded from the present analysis since a repetition failed to corroborate the original results. The Arrhenius equation determined by linear regression from the four points was: k = 1.2 x 105e-1g>80e/BT; but since the values plotted in Fig. 1 showed a greater deviation from the regression line than is usual in such experiments the constants in the equation must be taken as only approximate. In most experiments there was a graduel rise in pH from initial values of about 76 to final values of about 8.3 when 95 per cent of the arginine had decomposed. The influence of pH on reaction kinetics was not tested. The following ninhydrin-reactive produots were detected in pyrolyzed solutions of arginine: ammonia, ornithine, proline, and an unidentified compound that appeared after arginine on oofumn separation following the standard proaedure for analysis of protein hydrolysa~s with the Spineo Amino Aeid Analyzer (33 ml effluent-ammonia; 50 ml effluent-erginina; 73 ml ef%luent-unknown). parallel experiments at the same temperatures showed that the unknown (= post-arginine) wasalso producedon pyrolysisof ornithineHC1. “Post-arginine”musttherefore be at least partly, if not totally, generated from ornitbine. The eon~entrations of arginine and its pyrolytic products are shown in Fig. 2 as a function of time at two dierent temperatures. It is apparent that the yields of ammonia and post-arginine are higher at higher temperatures, whereas the reverse is true of ornithine. Although the sequence of reactions is not known in detail, it is probable that the bulk of the ammonia and ornithine originated dire&y from arginine, post-~g~ine from ornithino, and proline possibly from argmine or ~st-argi~ine. Following complete decomposition of arginine, the nitrogen reoovered in the form of ninhydrin
1356
Notes
t.w
3 Time
in
hours
Fig. 2.‘Moles of arginine and ninhyd~in-motive pyrolytic products per 100 moles of arginino at t = 0 as a function of time at two different tompraturos. reactive compounds (assuming one atom of X por molecule for post-arginine) rangod from 40-80 per cent of that potentially availeble from arginine.
The decomposition of lysine at 249°C and 216°C followed first order resction kinetics; but at 200°C and 174°C graphs of log concentration vs. time decreased in slope during the course of pyrolysis, the main change in slope occurring when 40-60 per cent of the lysine had decomposed. The points for the lower temperatures given in Fig. 1 thus only indicete the time required at a given temperature to decrease the concentration to 37 per cent of the original, and cannot be extrapo~a~d further. For this reason, and the non-linearity of the e~erimental results (see Fig. l), an Arrhenius equation could not be calculated. Xo ninhydrin-reactive products other shen ammonia were observed on column chromatography; however, two unknowns were teported earlier on separations using paper chromatogrsphy (VALLENTYNE, 1964;. These unknowns could have appeared under the lysine or ammonia peaks on column separations. Parallel experiments were conducted at 200°C on 0.002 M, 0.01 M, and 0.05 M solutions of lysine*HCl to determine the effect of concentration on the kinetics of decomposition, Data for the two lower concentrations agreed within experimental error, whereas the 0.05 M solution yielded a curve of the Bame form but with lower rates of breakdown. In all cases the mte of decomposition decreased as a function of time of pyrolysis. The pII values increased during pyrolysis from initial values in the range of 66-7~0 to values in the range of 7.8-8.1 when 90-95 per cent of the lysine had decomposed. The effect of pH on reaction kinetics was not tested; but at least at the upper temperatures studied it did not exercise an important influence during the course of reaction. The high stability of proline and leueine was not unexpected in view of the many reported occurrences of these amino acids in fossils and sedimentary rocks with ages in excess of 60million years. From the experiments reported here it is clear that arginine could not persist in a free state for such a length of time without being protected in the form of complexes suoh as those proposed by DEGENS (1965).
1356
Notes
Acknowled~rnents-This work was supported by NASA to Mrs. PATRICIA MAHOOL for technical assistance.
Grant NGR
33-010-013.
1 am indebted
REFERENCES DE~ENS E. T. (1966) Geochemistry of Sediments, 342 pp. Prentice-Hall. JONES J. D. and VALLENTYNE J. R. (1960) Biogeochemistry of organic matter-I. Polypeptides and amino acids in fossils and sediments in relation to geothermometry. Ceochim. Cownochim. Acta 21, l-34. POVOLEDO D. and VALLENTYNE J. R. (1964) Thermal reaction kinetics of the glutamic acidpyroglutamic acid system in water. Ueochim. Cosrnochkm. Acta 22, 731.-734. VALLENTYNE J. R. (1964) Biogeochemistry of organic matter-II. Thermal reaction kinetics and transformation products of amino compounds. Cfeochim. Cosmochim. Acta 22, 157-188.
Geochlmioaet CosmochimicaAcb, 19613, Vol. 32, pp. 1356to 1363. Pergamon Press. Printed in Northern Ireland
Natural hydrothernublsystem and experimental hot-water/rock i&m&ion: Reactions with NaCl solutions and trace metal extraction Chemistry Division, (Received
13 May
A. J. ELLIS D.S.I.R., Petone, New Zealand
1968; accepted
in revised form
1 August
1968)
Abstract-Reactions of water, and NaCl solutions with andesite, and shale, at 35O-500°C are reported and the solutions compared with natural water compositions. High chloride greatly enhanced Fe, Mn, Cu, and Pb solubility in the low sulphide andesite reaction solutions. Except for Fe, extraction of metals was lower from the sulphur-rich shale. INTRODUCTION TFLERE is an increasing interest in the geochemistry of natural hydrothermal systems, arising from geothermal power developments and from enquiry into the nature of the fluids which gave rise to hydrothermal ore deposits. Concentrations of trace metals in dilute hot waters of volcanic hydrothermal areas are much lower than those which would be expected for an ore-forming solution capable of produoing major base metal ore bodies. During hydrothermal alteration of rock by these dilute waters, chemical equilibria evidently favour the retention of minor metals in the rock minerals, rather than their solution in the hot water. However, a high temperature (300”350°C) 26 % salt brine tapped by drillholes near Salton Sea, California, contained unusually high concentrations of elements such as lead, zinc, copper and silver (SKINNER et al., 1967). Isotope analysis (DOE et aE., 1966) showed that most of the lead was derived from the local sedimentery rooks of the aquifer. LEBEDEV (1967) reported high lead concentrations (up to 77 ppm) in N&l-CaCl, brines tapped at 80°C by deep drillholes in the Cheleken peninsula on the Eastern Caspian Sea shore. A hot brine enriched in minor metallic constituents was also reported to occur in the Atlantis II Deep in the bed of the Red Sea (MILLER et aE., 1966). It appears that under certain solution composition and temperature conditions ion complexing equilibria allow minor heavy metals to bo concentrated into solution during hydrothermal alteration or metamorphism of rocks. The present note gives information on the minor metal concentrations present in solutions after the reaotion of water and of sodium chloride solutions with an andesite and a shale at 360-600°C.