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Interaction Mechanisms Between Biochar and Herbicides
Published in Kassio Ferreira Mendes, Interactions of Biochar and Herbicides in the Environment, 2022
Rodrigo Nogueira de Sousa, Matheus Bortolanza Soares, Felipe Hipólito dos Santos, Camille Nunes Leite, Kassio Ferreira Mendes
Protonation is the addition of H+ protons to a molecule or ion giving rise to a conjugate acid that is poorer in electrons than the parent molecule. This protonation effect can create different electrically positive sites on the herbicide molecules, as occurs for glyphosate (strong acid) (Figure 4.9), increasing the electrostatic attraction with the biochar. Protonation easily occurs in different environments (soil, water, etc.) as a result of changes in the pH of the medium, acid–base reaction, and microbial decomposition action (Villaverde et al. 2018). Naturally acidic soils, as they occur in tropical regions, have the strong protonation effect of herbicide molecules of the chemical group of triazines, increasing their sorption to soil organic matter and reducing the availability of the herbicide in the soil solution for absorption by the plant (Fuscaldo et al. 1999). The effect of this addition of protons can result in quite different behavior, such as increased solubility, greater potential for sorption to organic matter, variation in the herbicide degradation time, and reactivity of its decomposition by-products (Colombini et al. 1998; Song et al. 2018). The result of the Coulomb attraction between the opposite charges of the herbicide–biochar interaction often results in the formation of a covalent bond, establishing chemical sorption.
N-(2-hydroxypropyl)-methacrylamide] for Biomedical Applications
Published in Raphael M. Ottenbrite, Sung Wan Kim, Polymeric Drugs & Drug Delivery Systems, 2019
Rong-Zheng Lu, Pavla Kopečková, Jindrich Kopeček
α-Chymotrypsin (CT) was used as the model protein to evaluate the consequences of its modification with the ST HPMA polymers. There are 17 carboxyl groups and 17 amino groups in a-chymotrypsin. The amino and carboxyl groups of the protein were modified with ST-PHPMA-COOSu and ST-PHPMA-CONHNH2, respectively. The amino-directed modification of CT was performed by directly reacting the protein with excess ST-PHPMA-COOSu at neutral pH (7.0–7.5) and 4°C in 20 mM in CaCl2 aqueous solution. The carboxyl group-directed modification with polymers containing hydrazo was performed by reacting the protein with an excess of ST-PHPMA-CONHNH2 at pH 4.5–5.0 in the presence of l-ethyl-3-(3-di-methylaminopropyl)carbodiimide hydrochloride (EDC). At the acidic pH used, the amino groups (pKa = 6.8–8.0 for α-amino, 10.4–11.1 for ∊-amino of lysine) on proteins are deactivated due to protonation. However, the hy-drazo groups (pKa ≈ 3.0) remain active to react with the carboxyl groups of the same proteins in the presence of a coupling agent (EDC). The pH of the reaction mixture during both modifications may change, and dilute NaOH or HCl should be added to maintain suitable pH [20].
Polymeric Indicator Substrates for Fiber Optic Chemical Sensors
Published in Richard P. Buck, William E. Hatfield, Mirtha UmañA, Edmond F. Bowden, Biosensor Technology Fundamentals and Applications, 2017
W. Rudolf Seitz, Yunke Zhang, Zhang Zhujun, Amy Sommers, Chen Jian, Richard Russell, Donald C. Sundberg
PEI differs from PVOH in that the amine groups on PEI can be protonated. As the pH is reduced, the extent of protonation increases. Electrostatic repulsion between positively charged sites on the PEI causes the PEI to adopt an extended conformation. This effect is believed to account for the pH effect on the mechanical properties of crosslinked PEI. It will also be an important effect for sensor applications since it will cause pH dependent swelling of the gel.
Real-time liquid crystal-based creatinine sensor using a micro-patterned flexible substrate
Published in Liquid Crystals, 2021
Chih-Teng Lin, Wen-Tung Hsu, Shug-June Hwang
We utilised the strategy that the protonation and deprotonation of HBA can tune orientational transitions of 5CB at the aqueous-LC interface during enzymatic hydrolysis of creatinine by CD to ammonia [10,11]. The carboxylic acid molecules of HBA are affected by the local pH value in the solution and deprotonated, resulting in a change in the alignment of LC molecules. Following treatment of the substrate with DMOAP, the micro-grids were filled with approximately 2 μL of 0.3 wt% HBA-doped nematic 5CB, and the excess LC was removed using a syringe. A top-cover with microfluidic channels was then placed on the coated substrate, and 35 μl of creatinine solution and 15 μl of creatinine deiminase (CD) were separately introduced into the sensor using a micro-pump at a flow rate of 2 ml/min. Here the injection direction of creatinine and creatinine deaminase solutions was controlled to be parallel to the transmittance axis of the polariser. (The nematic LC 5CB, creatinine, CD, DMOAP, and HBA were from Sigma-Aldric Corp, Germany.).
Modelling adiabatic cusps in
Published in Molecular Physics, 2021
F George D. Xavier, A. J. C. Varandas
In Figure 2, to show the presence of two crossing points in the finite seam in the linear geometry in the same curve, two cuts are visible at and with the crossing points encircled with the corresponding model. The plot as a function of R signifies two channels of dissociation as defined in Equations (1a) and (2a) and the process involved undergoes charge transfer from one species to another, , an exoergic (exothermic) process. This protonation and deprotonation was measured experimentally in the nineties [38, 39] and reported as . This work predicts for such a process, in fairly close agreement, and hence the model predicts well the experimental curve along this dissociation. The cuts to measure this value were chosen at the equilibrium bond length of and . For the other channel defined in Equations (1b) and (2b), the actual process, involves atomic excitation along with elastic and inelastic rovibrational energy transfer.
Pnicogen bonds in complexes with CO and CS: differentiating properties
Published in Molecular Physics, 2019
Janet E. Del Bene, Ibon Alkorta, José Elguero
Carbon monoxide (CO) and carbon monosulfide (CS) are molecules with very different properties, even though oxygen and sulfur are contiguous in Group 16. This difference has been attributed to what has been called the anomalous behaviour of the elements of the second row of the Periodic Table, from Li to F [1,2]. CO is produced by the incomplete combustion of fossil fuels. It is a stable but highly toxic gas, and has a variety of applications, including its use in metal fabrication. It is also found with H2 in fuel gas mixtures which are used for heating. CO is a common ligand in transition-metal complexes. It is known experimentally that the gas-phase protonation of CO occurs at the C atom [3]. In contrast, CS is unstable as a monomer since it polymerises. It is found as an isolated monomer mainly in the interstellar medium [4]. Like CO, CS has been used as a ligand in transition-metal complexes [5].