Detail publikace

Lignite humic acids aggregates studied by high resolution ultrasonic spectroscopy. Thermodynamic stability and molecular feature.

KUČERÍK, J. ČECHLOVSKÁ, H. BURSÁKOVÁ, P. PEKAŘ, M.

Originální název

Typ

článek v časopise ve Web of Science, Jimp

Jazyk

angličtina

Originální abstrakt

The thermodynamic stability of lignite humic acids (sodium salt) aggregates was studied by high resolution ultrasonic spectroscopy within the temperature interval from 5 to 90C. The changes in differential ultrasonic velocity (U12) showed strong differences among humic solutions within the concentration range from 0.005 to 10 g/L. Measurement revealed several transitions which were attributed to the weakening of humic secondary structure. Concentration around 1 g/L seemed to be a limit under which the change of the prevalence and importance of hydration occurred. Above this concentration the difference in U12 decreased following the temperature increase which was explained as a dominance of hydrophilic hydration. In contrast, below this concentration, the temperature dependence of U12 resulted in increasing tendency which was attributed to the prevalence of hydrophobic hydration, i.e. uncovering of apolar groups towards surrounding water. Additional experiments in which the humic sample was modified by hydrochloric acid resulted in a slight structural stabilization which lead to the conclusion that humic micelle-like subaggregates form an open-layer assemblies easily accessible for interaction with an extraneous molecule. That was partly verified by addition of propionic acid which brought about even larger reconformation of humic aggregates and exhibition of polar groups towards hydration water. The reversible changes in humate solutions induced by elevated temperatures provided the evidence about the existence of significant physical interactions among humic molecules resulting in formation of various kinds of aggregates. The nature of aggregates, mainly the stability and conformation, strongly depends on the concentration. Evidently, the changes observed in this work cannot be simply explained as expansions or conformational changes of macromolecular coils.

Klíčová slova

aggregation; hydrophilic hydration; hydrophobic hydration; lignite humic acids; stability; ultrasonic spectroscopy

Autoři

KUČERÍK, J.; ČECHLOVSKÁ, H.; BURSÁKOVÁ, P.; PEKAŘ, M.

Rok RIV

2009

Vydáno

2. 8. 2009

Nakladatel

Springer

Místo

Nizozemí

ISSN

1388-6150

Periodikum

Journal of Thermal Analysis and Calorimetry

Ročník

Číslo

Stát

Maďarsko

Strany od

637

Strany do

643

Strany počet

BibTex

@article{BUT48901,
  author="Jiří {Kučerík} and Hana {Čechlovská} and Petra {Bursáková} and Miloslav {Pekař}",
  title="Lignite humic acids aggregates studied by high resolution ultrasonic spectroscopy. Thermodynamic stability and molecular feature.",
  journal="Journal of Thermal Analysis and Calorimetry",
  year="2009",
  volume="96",
  number="2",
  pages="637--643",
  issn="1388-6150"
}