Adsorption of Aqueous Nucleobases, Nucleosides, and Nucleotides on Compost-Derived Humic Acid. 2. Naturally Occurring Purines

Abstract

This paper describes adsorption of the aqueous purines adenine (10), adenosine (11), adenosine 5′monophosphate (12), guanosine (13), and guanosine 5′-monophosphate (14) on compost-derived humic acid (HA) over the solute concentration (12-1200 µM) and temperature (10.0-40.0°C) ranges used with pyrimidine solutes in Part 1. Nucleobase 10 and nucleosides 11 and 13 are neutral under the experimental conditions, while nucleotides 12 and 14 are monoanions. All the purines interact with HA, but only adenine causes HA dissolution at pH 5-6 and temperatures above 25.0°C, as found with cytosine and (-)nicotine. The IR spectrum of the soluble adenine-HA product indicates strong interaction with carboxylic and phenolic HA groups that is not due to simple proton transfer. Pyrimidines and purines are adsorbed in sequence on three HA sites A, B, and C. Most of the data fit the Langmuir model to generate site capacities V A , V B and V C and equilibrium constants K A , K B , and K C for each solute and site. Average site capacities increase 〈V A 〉 < 〈V B 〉 < 〈V C 〉, while equilibrium constants at 25.0°C decrease K A > K B > K C . Site capacities V i are independent of temperature and solute molar mass or charge, indicating adsorption through solute nucleobase units. Adenine has unusually high average 〈V A 〉 and 〈V B 〉 related to its ability to dissolve HA at pH 6, but 〈V C 〉 is unexceptional. The equilibrium constant data show that compost-derived HA sites have quite different solute selectivities. For example, site A discriminates poorly between the solutes thymine (4), thymidine (5), and 11 while site C has a strong preference for 4. These selectivities could influence animal, plant, soil, and sediment biochemistry. Linear correlation of the enthalpies and entropies for adsorption of every solute at each HA site points to a common underlying adsorption mechanism.

Adsorption of Aqueous Nucleobases, Nucleosides, and Nucleotides on Humic Acids. 3. Adsorption of Uracil, Uridine, and Uridine-5‘-Monophosphate on a German Peat-Derived Humic Acid and Its Tightly Bound Mercury(II) Form

“…Equilibrium Constants. Equilibrium constants K i for uracil adsorption on GHA follow the general trend found with CHA: K C < K B < K A . , Notable is that K A for uracil adsorption on CHA at 25.0 °C is about 13 times larger than with adsorbent GHA (Table ). Otherwise, there is remarkable similarity of K i at 25.0 °C for uracil adsorption on CHA and GHA.…”

“…Like uracil, uridine is a neutral molecule in the pH range 4.6−5.1 used for the measurements, while uridine-5‘-monophosphate is a monoanion 30 in the pH range 3.4−4.6 used to measure its isotherms. These differences check the effects of solute charge and molar mass on the adsorption parameters. − …”

“…Total average site capacities ∑〈 v i 〉 are useful for comparison of data for different solutes with a fixed adsorbent. − If we add v A = 0.09 mmol/g MGHA (at 25.0 °C and representative of very strong uracil binding in step A) to 〈 v B 〉 = 0.15 mmol/g MGHA and 〈 v C 〉 = 0.40 mmol/g MGHA from Table , the result is 0.64 mmol uracil/g MGHA, to be compared with ∑〈 v i 〉 = 0.21 mmol uracil/g GHA. The difference between these sums, 0.43 mmol uracil/g adsorbent, is the same, within experimental precision, as the mercury(II) content of MGHA (0.45 mmol Hg/g MGHA, Table ).…”

Temperature and soil organic matter decomposition rates - synthesis of current knowledge and a way forward

“…Marschner & Bredow () and Khairy et al . (,b) have both observed that a rise in temperature moves the system toward a higher share of non‐sorbed reactants, and temperature has a progressively larger effect as more energy is needed to desorb reaction partners. Temperature also increases diffusion and dissolution, both of which increase substrate availability to soil microbes and leaching losses of soil carbon (Xu & Saiers, ).…”

Tight metal binding by humic acids and its role in biomineralization †

“…2(c) likely reflects the macroscopic framework of the original aqueous gel and those of waterlogged HAs in soils and sediments. 23 for adsorption of 14 nucleic acid constituents (NACs) on a solid compost-derived HA and on solid HA particles from different soil sources without or with added Hg II 24 show that HAs can be purified to the point where they become understandable. The data fit the Langmuir model for reversible solute adsorption in sequential steps labelled i = A, B and C. 14,[22][23][24] Analysis gives the stoichiometric site capacity ν i and the equilibrium constant K i for each solute and step.…”