TY - JOUR

T1 - Self-Association of the Macromolecules of Aldrich Humic Acid in Aqueous Solutions Using Ultraviolet–Visible (UV–Vis) Absorption Spectroscopy

AU - Lavrik, Nikolay L.

AU - Bazhin, Nikolay M.

PY - 2019/7/1

Y1 - 2019/7/1

N2 - The ultraviolet–visible (UV–Vis) spectra of the aqueous solutions of humic acids (HA) Aldrich were obtained within the concentration range 1–20 mg/L (0.1–2ċ10–6mol/L). A conclusion on the existence of the self-association (dimer formation) of HA macromolecules is based on the deviation of the concentration dependence of optical density (OD) from the linear one at [HA] > 10 mg/L (>10–6mol/L). An original, mathematical algorithm is proposed to determine a dimerization constant K and a molar coefficient of dimer absorption εD(λ) The value of K was (2.56 ± 0.07) ċ 106L/mol. The calculated molar coefficients of HA macromolecule dimer absorption, εD(λ), indicate an increase in the dimer extinction coefficient εD(λ) compared to the double value of the molar monomer absorption 2εM(λ). It was established that the spectral dependence of the value β = εD(λ) / εM(λ) exhibits a minimum within a wavelength range of 300–450 nm, which is due to the difference in the efficiency of the interaction of various sites upon HA macromolecule dimerization. Thus, an approach of studying the processes of self-association is proposed using the method of UV–Vis absorption spectroscopy. This method is implemented for molecules that do not have characteristic absorption bands. The proposed method can also be successfully applied to molecules with characteristic absorption bands.

AB - The ultraviolet–visible (UV–Vis) spectra of the aqueous solutions of humic acids (HA) Aldrich were obtained within the concentration range 1–20 mg/L (0.1–2ċ10–6mol/L). A conclusion on the existence of the self-association (dimer formation) of HA macromolecules is based on the deviation of the concentration dependence of optical density (OD) from the linear one at [HA] > 10 mg/L (>10–6mol/L). An original, mathematical algorithm is proposed to determine a dimerization constant K and a molar coefficient of dimer absorption εD(λ) The value of K was (2.56 ± 0.07) ċ 106L/mol. The calculated molar coefficients of HA macromolecule dimer absorption, εD(λ), indicate an increase in the dimer extinction coefficient εD(λ) compared to the double value of the molar monomer absorption 2εM(λ). It was established that the spectral dependence of the value β = εD(λ) / εM(λ) exhibits a minimum within a wavelength range of 300–450 nm, which is due to the difference in the efficiency of the interaction of various sites upon HA macromolecule dimerization. Thus, an approach of studying the processes of self-association is proposed using the method of UV–Vis absorption spectroscopy. This method is implemented for molecules that do not have characteristic absorption bands. The proposed method can also be successfully applied to molecules with characteristic absorption bands.

KW - Aldrich humic acid

KW - dimerization constant

KW - molar dimer absorption coefficient

KW - Ultraviolet–Visible

KW - UV–Vis absorption spectra

KW - MOLECULAR-WEIGHT

KW - Ultraviolet-Visible

KW - FLUORESCENCE

KW - UV-Vis absorption spectra

UR - http://www.scopus.com/inward/record.url?scp=85068859625&partnerID=8YFLogxK

U2 - 10.1177/0003702819829809

DO - 10.1177/0003702819829809

M3 - Article

C2 - 30700093

AN - SCOPUS:85068859625

VL - 73

SP - 810

EP - 815

JO - Applied Spectroscopy

JF - Applied Spectroscopy

SN - 0003-7028

IS - 7

ER -