A natureza fractal de ácidos húmicos

Silva, A. C.; Mendonça, E. S.; Martins, M. L.; Reis, C.

doi:10.1590/S0100-06832000000400008

Resumos

Dentre as ferramentas usadas para descrever a estrutura ramificada ou a superfície rugosa e distorcida de ácidos húmicos (AH), a geometria fractal aparece como uma das mais adequadas para explicar a conformação de partículas húmicas (agregados moleculares). Do ponto de vista experimental, a dimensão fractal (D) de sistemas naturais pode ser determinada a partir do monitoramento da luz transmitida, não espalhada e não absorvida (turbidimetria 'τ'). A presença de fractais implica que o sistema pode ser decomposto em partes, em que cada uma, subseqüentemente, é cópia do todo. A determinação do valor 'D' dessas partículas foi conseguida pela utilização de turbidimetria, em que suspensões de AH-comercial e de AH-Espodossolo foram analisadas por espectrofotometria UV-Vis. O fundamento matemático utilizado foi a lei de potência τ ∝ λβ, em que β < 3 indica a presença de fractal de massa (Dm); 3 < β < 4 indica fractal de superfície (Ds), e β ≅ 3 indica não-fractal (NF). A declividade das retas (β) por meio do gráfico (logτ vs logλ) permitiu a obtenção de 'D'. Segundo os resultados, partículas de AH em suspensões aquosas diluídas formam estruturas fractais, cuja geometria pode ser caracterizada por meio de turbidimetria. Entretanto, a faixa de comprimento de onda usada (400 a 550 nm) ainda é pequena para se afirmar sobre a natureza fractal de AH e determinar suas dimensões fractais com precisão.

substâncias húmicas; conformação; turbidimetria

Among the tools used to describe the ramified structure or the rugged and distorted surface of humic acids (HA), fractal geometry seems to be one of the most adequate to explain the conformation of humic particles (molecular aggregates). From the experimental point of view, fractal dimension (D) of natural systems may be measured through the transmitted light, not scattered or absorved (turbidimetry'τ'). The presence of fractals indicates that the system may be decomposed in parts, each part being a copy of the whole. The determination of the fractal dimension (D) of these particles was achieved by the turbidimetric technique, where diluted solutions of commercial-HA and Espodossolo-HA were analyzed by spectrophotometry UV-Vis. The mathematical base used was the potential law τ ∝ λβ, where β < 3 indicates the presence of mass fractal (Dm); 3 < β < 4 of surface fractal (Ds) and β ≅ 3, of non-fractal (NF). The slope of the lines (β) was taken from the graphics (logτ vs logλ) to obtain D. The results show that the HA particles in diluted aqueous suspension form fractals structures, whose geometry may be characterized by turbidimetry. However, the wavelength range used (400 to 550 nm) is still small to make statements about the fractal nature of HA and determine its fractal dimensions with precision.

humic substances; conformation; turbidimetry

SEÇÃO III - BIOLOGIA DO SOLO

A natureza fractal de ácidos húmicos

Fractal nature of humic acids

A. C. Silva^I; E. S. Mendonça^II; M. L. Martins ^III; C. Reis^IV

^IDoutorando em Solos e Nutrição de Plantas, Universidade Federal de Viçosa - UFV. Av. PH Rolfs s/n, 36571-000 Viçosa (MG). E-mail: ale@alunos.ufv.br

^IIProfessor de Departamento de Solos - UFV. Bolsista do CNPq. E-mail: esm@alunos.ufv.br

^IIIProfessor de Departamento de Física - UFV. E-mail: mmartins@mail.ufv.br

^IVProfessor de Departamento de Química - UFV. E-mail: cesar@mail.ufv.br

RESUMO

Dentre as ferramentas usadas para descrever a estrutura ramificada ou a superfície rugosa e distorcida de ácidos húmicos (AH), a geometria fractal aparece como uma das mais adequadas para explicar a conformação de partículas húmicas (agregados moleculares). Do ponto de vista experimental, a dimensão fractal (D) de sistemas naturais pode ser determinada a partir do monitoramento da luz transmitida, não espalhada e não absorvida (turbidimetria 'τ'). A presença de fractais implica que o sistema pode ser decomposto em partes, em que cada uma, subseqüentemente, é cópia do todo. A determinação do valor 'D' dessas partículas foi conseguida pela utilização de turbidimetria, em que suspensões de AH-comercial e de AH-Espodossolo foram analisadas por espectrofotometria UV-Vis. O fundamento matemático utilizado foi a lei de potência τ ∝ λ^β, em que β < 3 indica a presença de fractal de massa (D_m); 3 < β < 4 indica fractal de superfície (D_s), e β ≅ 3 indica não-fractal (NF). A declividade das retas (β) por meio do gráfico (logτ vs logλ) permitiu a obtenção de 'D'. Segundo os resultados, partículas de AH em suspensões aquosas diluídas formam estruturas fractais, cuja geometria pode ser caracterizada por meio de turbidimetria. Entretanto, a faixa de comprimento de onda usada (400 a 550 nm) ainda é pequena para se afirmar sobre a natureza fractal de AH e determinar suas dimensões fractais com precisão.

Termos de indexação: substâncias húmicas, conformação, turbidimetria.

SUMMARY

Among the tools used to describe the ramified structure or the rugged and distorted surface of humic acids (HA), fractal geometry seems to be one of the most adequate to explain the conformation of humic particles (molecular aggregates). From the experimental point of view, fractal dimension (D) of natural systems may be measured through the transmitted light, not scattered or absorved (turbidimetry'τ'). The presence of fractals indicates that the system may be decomposed in parts, each part being a copy of the whole. The determination of the fractal dimension (D) of these particles was achieved by the turbidimetric technique, where diluted solutions of commercial-HA and Espodossolo-HA were analyzed by spectrophotometry UV-Vis. The mathematical base used was the potential law τ ∝ λ^β, where β < 3 indicates the presence of mass fractal (D_m); 3 < β < 4 of surface fractal (D_s) and β ≅ 3, of non-fractal (NF). The slope of the lines (β) was taken from the graphics (logτ vs logλ) to obtain D. The results show that the HA particles in diluted aqueous suspension form fractals structures, whose geometry may be characterized by turbidimetry. However, the wavelength range used (400 to 550 nm) is still small to make statements about the fractal nature of HA and determine its fractal dimensions with precision.

Index terms: humic substances, conformation, turbidimetry.

Texto completo disponível apenas em PDF.

Full text available only in PDF format.

LITERATURA CITADA

Recebido para publicação em dezembro de 1999

Aprovado em julho de 2000

AIKEN, G.R.; MCKNIGHT, D.M.; WERSHAW, R.L. & MacCARTHY, P. An introduction to humic substances in soil, sediment, and water. In: AIKEN, G.R., MCKNIGHT, D.M. & WERSHAW, R.L., eds. Humic substances in soil, sediment and water: geochemistry, isolation and characterization. New York, John Wiley & Sons, 1985. 692p.
BARTON, C.C. & LA PONTE, P.R. Fractais in the earth sciences. New York, Plennum Press, 1995. 265p.
BENITES, V.M.; MENDONÇA, E.S.; SCHAEFER, C.E.R. & MARTIN-NETO, L. Caracterização dos ácidos húmicos extraídos de um Latossolo Vermelho-Amarelo e de um Podzol por análise termodiferencial e pela espectroscopia de absorção no infravermelho. R. Bras. Ci. Solo, 23:543-551, 1999.
BURROUGH, P.A. Multiscale source of spacial variation in soil. The aplication of fractal concepts to nested levels of soil variation. J. Soil. Sci., 34:577-597, 1983.
CHAVES, C.M.G.F. Fenômenos de agregação. Ci. Hoje, 10:27-32, 1989.
CHEN, Y.; SENESI, N. & SCHNITZER, M. Information provided on humic substances by E4/E6 ratios. Soil Sci. Soc. Am. J., 41:352-358, 1977.
GHOSH, K. & SCHNITZER, M. Macromolecular structures of humic substances. Soil Sci. 129:266-276, 1980.
GUZMAN.; M.; MARTIN, M.A.; MORÁN, M. & REYES, M. Estructuras fractales y sus aplicaciones. Barcelona, Labor, 1993. 279p.
HARRISON, A. Fractals in chemistry. Oxford, Science Publications, 1992. 90p.
HAYES, M.H.B.; MaCARTHY, P.; MALCOLM, R.L. & SWIFT, R.S. Structures of humic substances: the emergence of forms (3-31). In: HAYES, M.H.B.; MaCARTHY, P.; MALCOLM, R.L. & SWIFT, R.S. Humic Substance II: In search of structure: setting the scene. New York, John Wiley & Sons, 1989. p.
HORNE, D.S. Determination of the fractal dimension using turbidimetric techniques. Faraday Discuss. Chem. Soc., 83:259-270, 1987.
LOBARTINI, J.C.; TAN, K.H.; ASMUSSEN, L.E.; LEONARD, R.A.; HIMMELSBACH, D. & GINGLE, A.R. Chemical and spectral diferences in humic matter from swamps, streams and soils in the southeastern United States. Geoderma, 49:241-254, 1991.
MacCARTHY, P. & RICE, J. Spectroscopic methods for determining functionality in humic substances. In: AIKEN, G.R., MCKNIGHT, D.M.; WERSHAW, R.L. & MacCARTHY, P. Humic substances in soil, sediment, and water. New York, John Wiley & Sons, 1985. p.527-559.
MANDELBROT, B.B. The fractal geometry of nature - update and augmented. New York, Freeman, 1983. 568p.
ÖSTERBERG, R. & MORTENSEN, K. Fractal dimension of humic acids. Eur. Biophys J., 21:163-167, 1992.
ÖSTERBERG, R. & MORTENSEN, K. Fractal geometry of humic acids, temperature-dependent restructuring studied by small-angle neutron scattering. In: SENESI, N. & MIANO, T.M. Humic substances in the global environment and implications on human health. Amsterdam, Elsevier Science, 1994. p.127-132.
ÖSTERBERG, R.; SZAJADAK, L. & MORTENSEN, K. Temperature-dependent restruring of fractal humic acids: A proton-dependent process. Environ. Int., 20:77-88, 1994.
PIRES, A.S.T. & COSTA, B.V.A. A desordem inevitável. Ci. Hoje, 14:35-39, 1992.
RICE, J.A. & LIN, J.S. Fractal dimensions of humic materials. In: SENESI, N. & MIANO, T.M., eds. Humic substances in the global environment and implications on human health. Amsterdam, Elsevier Science, 1994. p.115-120.
RICE, J.A. & LIN, J.S. Fractal nature of humic materials. Environ. Sci. Tecnhol., 27:413-414,1993.
SENESI, N. The fractal approach to the study of humic substances. In: SENESI, N. & MIANO, T.M., eds. Humic substances in the global environment and implications on human health. Amsterdam, Elsevier Science. 1994. p.3-41.
SENESI, N.; LOURUSOO, G.F.; MIANO, T.M.; MAGGIPINTO, G.; RIZZI, F.R. & CAPOZZI, V. The fractal dimension of humic substances as function of pH by turbidity measurements. In: SENESI, N. & MIANO, T.M., eds. Humic substances in the global environment and implications on human health. Amsterdam, Elsevier Science, 1994. p.121-126.
SENESI, N.; RIZZI, F.R.; DELLINO, P. & ACQUAFREDDA, P. Fractal dimension of humic acids in aquandous suspension as a function of pH and time. Soil Sci. Soc. Am. J., 60:1773-1780, 1996.
SENESI, N.; RIZZI, F.R.; DELLINO, P. & ACQUAFREDDA, P. Fractal humic acids in aqueous suspensions at various concentrations, ionic strengths, and pH values. Coll. Surf., 127:57-68, 1997.
SKOOG, D.A.; HOLLER, F.J. & NIEMAN, T. A Principles of instrumental analysis. 5.ed. Philadelphia, Sauder Golden, 1992. 849p.
SPARK, K.M.; WELLS, J.D. & JOHNSON, B.B. The interaction of a humic acid with heavy metals. Aust. J. Soil Res., 35:89-101, 1997.
STEVENSON, J.F. Humus chemistry - Genesis, composition, reactions 2.ed. New York, John Wiley & Sons, 1994. 496p.
SWIFT, R.S. Method for extraction of IHSS soil fulvic and humic acids. In: SPARK, K.M.; WELLS, J.D. & JOHNSON, B.B Methods of soil analysis. Madison, Soil Science of Society of Americam, 1996. p.1018-1020.
SWIFT, R.S. Molecular weight, size, shape, and charge characteristics of humic substances: some basic considerations. In: HAYES, M.H.B., eds. Humic substance II: In search of structure. New York, John Wiley & Sons, 1989. p.449-465.
VICSEK, T. Fractal growth fenomena 2.ed. Singapore, World Scientic Publishing, 1992. 488p.
WERSHAW, R.L. Sizes and shapes of humic substances by scattering techniques. In: HAYES, M.H.B.; MacCHARTY, P.; MALCOLM., R.L. & SWIFT, R.S. Humic Substance II. New York, John Wiley & Sons, 1989. p.540-591.

Datas de Publicação

Publicação nesta coleção
06 Out 2014
Data do Fascículo
Dez 2000

Histórico

Recebido
Dez 1999
Aceito
Jul 2000

This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

[1] AIKEN, G.R.; MCKNIGHT, D.M.; WERSHAW, R.L. & MacCARTHY, P. An introduction to humic substances in soil, sediment, and water. In: AIKEN, G.R., MCKNIGHT, D.M. & WERSHAW, R.L., eds. Humic substances in soil, sediment and water: geochemistry, isolation and characterization. New York, John Wiley & Sons, 1985. 692p.

[2] BARTON, C.C. & LA PONTE, P.R. Fractais in the earth sciences. New York, Plennum Press, 1995. 265p.

[3] BENITES, V.M.; MENDONÇA, E.S.; SCHAEFER, C.E.R. & MARTIN-NETO, L. Caracterização dos ácidos húmicos extraídos de um Latossolo Vermelho-Amarelo e de um Podzol por análise termodiferencial e pela espectroscopia de absorção no infravermelho. R. Bras. Ci. Solo, 23:543-551, 1999.

[4] BURROUGH, P.A. Multiscale source of spacial variation in soil. The aplication of fractal concepts to nested levels of soil variation. J. Soil. Sci., 34:577-597, 1983.

[5] CHAVES, C.M.G.F. Fenômenos de agregação. Ci. Hoje, 10:27-32, 1989.

[6] CHEN, Y.; SENESI, N. & SCHNITZER, M. Information provided on humic substances by E4/E6 ratios. Soil Sci. Soc. Am. J., 41:352-358, 1977.

[7] GHOSH, K. & SCHNITZER, M. Macromolecular structures of humic substances. Soil Sci. 129:266-276, 1980.

[8] GUZMAN.; M.; MARTIN, M.A.; MORÁN, M. & REYES, M. Estructuras fractales y sus aplicaciones. Barcelona, Labor, 1993. 279p.

[9] HARRISON, A. Fractals in chemistry. Oxford, Science Publications, 1992. 90p.

[10] HAYES, M.H.B.; MaCARTHY, P.; MALCOLM, R.L. & SWIFT, R.S. Structures of humic substances: the emergence of forms (3-31). In: HAYES, M.H.B.; MaCARTHY, P.; MALCOLM, R.L. & SWIFT, R.S. Humic Substance II: In search of structure: setting the scene. New York, John Wiley & Sons, 1989. p.

[11] HORNE, D.S. Determination of the fractal dimension using turbidimetric techniques. Faraday Discuss. Chem. Soc., 83:259-270, 1987.

[12] LOBARTINI, J.C.; TAN, K.H.; ASMUSSEN, L.E.; LEONARD, R.A.; HIMMELSBACH, D. & GINGLE, A.R. Chemical and spectral diferences in humic matter from swamps, streams and soils in the southeastern United States. Geoderma, 49:241-254, 1991.

[13] MacCARTHY, P. & RICE, J. Spectroscopic methods for determining functionality in humic substances. In: AIKEN, G.R., MCKNIGHT, D.M.; WERSHAW, R.L. & MacCARTHY, P. Humic substances in soil, sediment, and water. New York, John Wiley & Sons, 1985. p.527-559.

[14] MANDELBROT, B.B. The fractal geometry of nature - update and augmented. New York, Freeman, 1983. 568p.

[15] ÖSTERBERG, R. & MORTENSEN, K. Fractal dimension of humic acids. Eur. Biophys J., 21:163-167, 1992.

[16] ÖSTERBERG, R. & MORTENSEN, K. Fractal geometry of humic acids, temperature-dependent restructuring studied by small-angle neutron scattering. In: SENESI, N. & MIANO, T.M. Humic substances in the global environment and implications on human health. Amsterdam, Elsevier Science, 1994. p.127-132.

[17] ÖSTERBERG, R.; SZAJADAK, L. & MORTENSEN, K. Temperature-dependent restruring of fractal humic acids: A proton-dependent process. Environ. Int., 20:77-88, 1994.

[18] PIRES, A.S.T. & COSTA, B.V.A. A desordem inevitável. Ci. Hoje, 14:35-39, 1992.

[19] RICE, J.A. & LIN, J.S. Fractal dimensions of humic materials. In: SENESI, N. & MIANO, T.M., eds. Humic substances in the global environment and implications on human health. Amsterdam, Elsevier Science, 1994. p.115-120.

[20] RICE, J.A. & LIN, J.S. Fractal nature of humic materials. Environ. Sci. Tecnhol., 27:413-414,1993.

[21] SENESI, N. The fractal approach to the study of humic substances. In: SENESI, N. & MIANO, T.M., eds. Humic substances in the global environment and implications on human health. Amsterdam, Elsevier Science. 1994. p.3-41.

[22] SENESI, N.; LOURUSOO, G.F.; MIANO, T.M.; MAGGIPINTO, G.; RIZZI, F.R. & CAPOZZI, V. The fractal dimension of humic substances as function of pH by turbidity measurements. In: SENESI, N. & MIANO, T.M., eds. Humic substances in the global environment and implications on human health. Amsterdam, Elsevier Science, 1994. p.121-126.

[23] SENESI, N.; RIZZI, F.R.; DELLINO, P. & ACQUAFREDDA, P. Fractal dimension of humic acids in aquandous suspension as a function of pH and time. Soil Sci. Soc. Am. J., 60:1773-1780, 1996.

[24] SENESI, N.; RIZZI, F.R.; DELLINO, P. & ACQUAFREDDA, P. Fractal humic acids in aqueous suspensions at various concentrations, ionic strengths, and pH values. Coll. Surf., 127:57-68, 1997.

[25] SKOOG, D.A.; HOLLER, F.J. & NIEMAN, T. A Principles of instrumental analysis. 5.ed. Philadelphia, Sauder Golden, 1992. 849p.

[26] SPARK, K.M.; WELLS, J.D. & JOHNSON, B.B. The interaction of a humic acid with heavy metals. Aust. J. Soil Res., 35:89-101, 1997.

[27] STEVENSON, J.F. Humus chemistry - Genesis, composition, reactions 2.ed. New York, John Wiley & Sons, 1994. 496p.

[28] SWIFT, R.S. Method for extraction of IHSS soil fulvic and humic acids. In: SPARK, K.M.; WELLS, J.D. & JOHNSON, B.B Methods of soil analysis. Madison, Soil Science of Society of Americam, 1996. p.1018-1020.

[29] SWIFT, R.S. Molecular weight, size, shape, and charge characteristics of humic substances: some basic considerations. In: HAYES, M.H.B., eds. Humic substance II: In search of structure. New York, John Wiley & Sons, 1989. p.449-465.

[30] VICSEK, T. Fractal growth fenomena 2.ed. Singapore, World Scientic Publishing, 1992. 488p.

[31] WERSHAW, R.L. Sizes and shapes of humic substances by scattering techniques. In: HAYES, M.H.B.; MacCHARTY, P.; MALCOLM., R.L. & SWIFT, R.S. Humic Substance II. New York, John Wiley & Sons, 1989. p.540-591.

Brasil

Brasil

A natureza fractal de ácidos húmicos

Fractal nature of humic acids

Resumos

Datas de Publicação

Histórico