Biology subjects

Bonn, D.

Publications and source records attributed to Bonn, D..

5 recordsLinked to original sources

bioRxiv2025

Influence of Surfactant HLB Values and Agricultural Adjuvants on Pesticide Penetration in Plant Leaves

BACKGROUNDEffective pesticide action is crucial for optimizing efficacy and minimizing environmental impact, particularly with the increasing reliance on systemic pesticides. Surfactants and adjuvants are commonly used to enhance penetration, but their performance depends on the physicochemical properties of both the pesticide and the surfactants used in the formulations. This study examines how surfactant hydrophilic-lipophilic balance (HLB) values and commercial adjuvants affect pesticide penetration through plant cuticles. RESULTSWe assessed the penetration of two fluorescent pesticide mimics, Rhodamine B (hydrophilic) and Nile Red (lipophilic), into spring onion leaves using confocal laser scanning microscopy. High HLB surfactants significantly enhanced the uptake of Rhodamine B, while low HLB surfactants promoted Nile Red penetration. Surfactants with intermediate HLB values had minimal effect on either compound. Among seven commercial adjuvants tested, only Squall and Prolong significantly improved the penetration of both mimics. Other adjuvants, despite their common use in agriculture, showed limited or no effect on pesticide uptake. CONCLUSIONThe HLB value of surfactants strongly influences pesticide penetration, with optimal uptake achieved when the surfactant HLB aligns with the pesticides polarity. The penetration mechanisms differ: hydrophilic compounds benefit from increased cuticle hydration with high HLB surfactants, while lipophilic compounds penetrate more effectively with low HLB surfactants that enhance wax fluidity. The limited efficacy of most commercial adjuvants suggests that formulation selection should be based on compound-specific properties rather than generalized claims. These findings emphasize the need for targeted adjuvant selection based on the properties of the active ingredient, providing a practical strategy to optimize pesticide formulations for improved efficacy and reduced environmental impacts.

plant biology↗

bioRxiv2025

Optically driven control of mechanochemistry and fusion dynamics of biomolecular condensates via thymine dimerization

Phase-separated biomolecular condensates serve as functional elements of biological cells, contribute to protocell formation in prebiotic systems during early life, and represent a distinct class of soft matter with a broad range of potential applications. Understanding and controlling condensate mechanochemistry is critical for their function and material properties. Photochemical processes, such as UV-induced chemical modifications, are ubiquitous in nature and can have both detrimental and constructive impacts on living systems, and are also readily implemented in engineering applications. However, how phase-separated condensate formation influences photochemical processes, and conversely, how photochemical reactions impact condensate dynamics, remains an open question. Combining scanning probe microscopy with optical imaging and control, we developed assays that enable the study of mechanical transitions and fusion dynamics in condensate droplets, revealing that UV-induced thymine dimerization alters condensate nucleation and coalescence. Depending on the frequency and topological arrangement of thymine dimers, particularly the balance between inter- and intrachain crosslinks, UV can induce a transition from liquid-like to solid-like behaviours or lead to aggregate formation. UV treatment also leads to compartmentalization in condensate systems by e.g., promoting the formation of arrested fusion droplets, which are stable against environmental changes. UV illumination can thus be leveraged to program the architecture and material properties of DNA-based biomolecular condensates, with implications for prebiotic chemistry, and bio-inspired engineering.

biophysics↗

bioRxiv2024

Eco-toxicity of different agricultural tank-mix adjuvants

Adjuvants are often used to improve the efficiency of plant protection products. However, there is concern that these compounds themselves might result in ecotoxicological effects. To investigate this concern, we compare the toxicity of different agricultural tank-mix adjuvants for two standard test organisms, i.e. the water flea Daphnia magna and the honey bee Apis mellifera. Daphnia trials comprised tests at 1, 5 and 20 times the normal prescribed label dosage. It is found that at 48h, the novel polymer-based adjuvant Squall is significantly less harmful to D. magna compared to traditional surfactant or oil-based adjuvants. For A. mellifera, we tested topical exposure to label-rate, five and twenty times label-rate. After 96h exposure to polymer- and oil based adjuvants no statistically significant harmful effects were observed. The trisiloxane-based adjuvants, however, did significantly increase bee mortality at higher dose rates, indicating a higher toxicity of these specific compounds.

ecology↗

bioRxiv2023

Elucidating the role of water in collagen self assembly by isotopically modulating collagen hydration

Water is known to play an important role in collagen self assembly, but it is still largely unclear how water-collagen interactions influence the assembly process and determine the fibril network properties. Here, we use the H2O/D2O isotope effect on the hydrogen-bond strength in water to investigate the role of hydration in collagen self assembly. We dissolve collagen in H2O and D2O, and compare the growth kinetics and the structure of the collagen assemblies formed in these water isotopomers. Surprisingly, collagen assembly occurs ten times faster in D2O than in H2O, and collagen in D2O self assembles into much thinner fibrils, that form a more inhomogeneous and softer network, with a fourfold reduction in elastic modulus compared to H2O. Combining spectroscopic measurements with atomistic simulations, we show that collagen in D2O is less hydrated than in H2O. This partial dehydration lowers the enthalpic penalty for water removal and reorganization at the collagen-water interface, increasing the self assembly rate and the number of nucleation centers, leading to thinner fibrils and a softer network. Coarse-grained simulations show that the acceleration in the initial nucleation rate can be reproduced by the enhancement of electrostatic interactions, which appear to be crucial in determining the acceleration of the initial nucleation rate. These results show that water acts as a mediator between collagen monomers, by moderating their interactions so as to optimize the assembly process and, thus, the final network properties. We believe that isotopically modulating the hydration of proteins can be a valuable method to investigate the role of water in protein structural dynamics and protein self assembly.

biophysics↗

bioRxiv2022

Rheo-2DIR spectroscopy reveals strain-induced hydrogen-bond redistribution in polyurethane

The remarkable elastic properties of polymers are ultimately due to their molecular structure, but the relation between the macroscopic and molecular properties is often difficult to establish, in particular for (bio)polymers that contain hydrogen bonds, which can easily rearrange upon mechanical deformation. Here we show that two-dimensional infrared spectroscopy on polymer films in a miniature stress tester sheds new light on how the hydrogen-bond structure of a polymer is related to its visco-elastic response. We study thermoplastic polyurethane, a block copolymer consisting of hard segments of hydrogen-bonded urethane groups embedded in a soft matrix of polyether chains. The conventional infrared spectrum shows that upon deformation, the number of hydrogen bonds increases, a process that is largely reversible. However, the 2DIR spectrum reveals that the distribution hydrogen-bond strengths becomes slightly narrower after a deformation cycle, due to the disruption of weak hydrogen bonds, an effect that could explain the strain-cycle induced softening (Mullins effect) of polyurethane. These results show how rheo-2DIR spectroscopy can bridge the gap between the molecular structure and the macroscopic elastic properties of (bio)polymers.

biochemistry↗