Novel Lignin Nanocarriers for Smart Drug Delivery in Crop Protection

Various fungi and bacteria degrade dead plants, however, these microorganisms may also affect the xylem of living plants. The Esca syndrome of vine plants and the sudden death syndrome of soybean are two examples of diseases affecting agriculturally important plants leading to withering of the plants and crop failures.
These diseases are caused by an imbalance of microorganisms degrading lignin and other components of the xylem, which itself is triggered by stress, like heat and dry spell.
At the same time, microorganisms like fungi and bacteria are not harmful per se, they are even known to be important for plant growth. Thus, a general and undirected application of pesticides might have unfavourable results.

In human medicine, the controlled and site specific delivery of drugs is a hot topic and this smart approach can be used for plants as well. A novel nanocarrier suitable for drug delivery in plants is made from chemically modified lignin: By esterification of lignin with methacrylic anhydride a polymerisable but bio-degradable macromonomer is prepared, which is polymerised in a miniemulsion. The miniemulsion polymerisation gives access to nanoparticles of controlled size and morphology and allows easy addition of different pesticides into the lignin matrix.

The nanocarriers loaded with 5 to 35 % pesticides can be injected to the xylem of plants. If the plant is weakened, microorganisms infest the xylem and degrade lignin. Untreated, this leads to apoplectic wither of sprout and leafs. However, if the lignin nanocarriers have been injected to the xylem, the microorganisms degrade these too, releasing the pesticide. Thus, the pesticide is released only in case of infestation making the lignin nanocarrier act like a vaccination. Furthermore, by this strategy the amounts of pesticides used is decreased to less than 3 % of the typical amount used in spraying.

The efficacy of the lignin nanocarriers to fend the Esca syndrome has been tested successfully in a field study with 80 vine plants. Half of these had been treated with a single dose lignin nanocarriers loaded with 20 wt% fungicide (<10 mg pyraclostgrobin per plant injected in the trunk) in 2014 while the other half has not been treated. The first group showed significant less severe Esca symptoms compared to the second one. After three years without further treatment, the difference in severeness has even increased. No pyraclostgrobin was detected in the grapes of the plants, presumably due to the size (200-500 nm) of the nanoparticles.

• safe storage of pesticide
• in situ release of pesticide by lignin degrading microorganisms
• necessary amount of fungicides strongly reduced
• no fungicide found in vine grapes
• long-term effective against Esca syndrome

The recycling of gold catalyst 19 has been studied using the cycloisomerization of enyne 25 as a model reaction. Due to its cationic nature complex 19 is insoluble in diethyl ether, whereas diene 26 can be easily dissolved in this medium. Therefore, after full conversion, the reaction solvent was removed in vacuum, and diethyl ether was added. The catalyst precipitated, and it was separated from the product by simple filtration and reused for the next synthesis cycle. As shown in Fig 4, the test reaction could be performed up to four times with consistent excellent yields.

D. Yiamsawas, S.J. Beckers, H. Lu, K. Landfester, F.R. Wurm: "Morphology-Controlled Synthesis of Lignin Nanocarriers for Drug Delivery and Carbon Materials",
ACS Biomater. Sci. Eng. 2017, 3, 2375−2383

EP priority application filed February 2016.
PCT application filed February 2017, nationalized in EP, US, CN, AU.