Detailed characterization of Pinus ponderosa sporopollenin by infrared spectroscopy

Evaluation of the antibacterial and inhibitory activity of the NorA and TetK efflux pumps of Staphylococcus aureus by p-coumaric acid

The NorA and TetK efflux pumps mediate resistance to fluoroquinolone and tetracycline antibiotics by actively extruding these compounds and reducing their intracellular concentrations. Consequently, intense research has focused on inhibiting these efflux mechanisms using antimicrobial agents derived from natural or synthetic sources. This study used Fourier transform infrared spectroscopy (ATR-FTIR) to analyze the various functional groups present in p-coumaric acid. We also investigated the antibacterial activity of p-coumaric acid on strains of Staphylococcus aureus carrying the NorA and TetK efflux pumps, as well as the compound's ability to increase the fluorescence of ethidium bromide (EtBr) and Sytox Green. In addition, the interactions of this compound with NorA were analyzed using molecular docking, and its pharmacokinetic properties were evaluated using ADMET (Absorption, Distribution, Metabolism, Excretion and Toxicity) modeling. The results revealed that p-coumaric acid exhibited no direct antibacterial activity against the tested Staphylococcus aureus strains. However, significant reductions in the minimum inhibitory concentrations (MICs) of norfloxacin and EtBr, both used as NorA substrates, were observed when combined with p-coumaric acid. It was also observed that p-coumaric acid increased the fluorescence emission of EtBr and Sytox Green in strains 1199 and 1199B, suggesting the inhibition of the efflux mechanism and enhanced membrane permeabilization in S. aureus. The in silico analysis demonstrated that p-coumaric acid exhibits a favorable binding energy with NorA, comparable to that of chlorpromazine. These results position p-coumaric acid as a promising antibiotic adjuvant and efflux inhibitor in strains harboring NorA.

Correia V, Silva Pereira C. The Chemistry of Sporopollenin Ektexine and Endexine Layers Isolated from Sunflower Pollen through an Ionic Liquid-Mediated Process

Sporopollenin is a plant polymer present in the exine of the pollen grains that comprises two layers: the endexine and the ektexine. It possesses remarkable mechanical, thermal, and chemical stability and is also highly recalcitrant to hydrolysis. The chemical backbone of sporopollenin mostly consists of a polyhydroxylated aliphatic component and polyketide-derived aliphatic α-pyrone elements. Recent works have provided important insights into its molecular structure, yet due to the extreme inertness of the polymer, outstanding questions still exist. In this work, we produced and characterized sporopollenin enriched materials obtained from dewaxed sunflower pollen using conventional acetolysis and two ionic liquid solvents or combinations of both. Microscopic (SEM) and spectroscopic analyses (mostly NMR) showed that either method alone could render sporopollenin enriched fractions. Only the acetolyzed materials showed an increase in acetate content. Ionic liquids used alone led to the isolation of naked spore capsules containing only the endexine layer, suggesting that the ektexine layer could be solubilized by the ionic liquid. On the contrary, the acetolyzed sporopollenin capsules could not be further modified by the ionic liquid treatment, preserving the two exine layers and an echinate surface. Our results suggest that the acetolysis altered the surface hydrophobicity of sporopollenin due to the introduction of acetate. The ionic liquid process led to the isolation of either exine layer, with both showing virtually the same chemistry.

Identification of Marker Molecules in Aqueous Plant Extracts Affecting the Gold Nanostructures' Morphology and Size

This work was performed as a comparative study using nine different aqueous pollen grain extracts from eight different genera (Juniperus, Biota, Cupressus, Abies, Pinus, Cedrus, Populus and Corylus) to synthesize gold nanostructures (AuNSs) to understand if there is any possible marker that helps to predict the final morphology and size of the AuNSs. Principal component analysis (PCA) revealed that Apigenin and Pinoresinol compounds are the marker molecules in determination of the AuNSs physical characteristics while total protein, reducing carbohydrate, flavonoid and phenol contents did not show any statistically meaningful outcome. The "dominancy hypothesis" was tested by paying attention to the most concentrated phenolic acids and flavonoids in the control of AuNSs morphology and size, for which correlation analysis were performed. The statistical findings were tested using two new more pollen extracts to validate the models. Three main findings of the study were (i) determination of Apigenin and Pinoresinol levels in pollen extract can give an insight into the AuNSs physical characters, (ii) the most concentrated phenolic acids and flavonoids don't need to be same to pose same dictative effect on AuNSs morphology and size, rather relatively abundant ones in the extract play the key role and (iii) differences in the polymeric structures (e. g. lignin, cellulosic compounds etc.) have minor effect on the final morphology and size of the AuNSs.

Multifaceted roles of pollen in the management of cancer

Oral drug delivery of microparticles demonstrates shortcomings like aggregation, decreased loading capacity and batch-to-batch variation, which limits its scale-up. Later, porous structures gained attention because of their large surface-to-volume ratio, high loading capacity and ability to carry biomacromolecules, which undergo degradation in GIT. But there are pitfalls like non-uniform particle size distribution, the impact of porogen properties, and harsh chemicals. To circumvent these drawbacks, natural carriers like pollen are explored in drug delivery, which withstands harsh environments. This property helps to subdue the acid-sensitive drug in GIT. It shows uniform particle size distribution within the species. On the other side, they contain phytoconstituents like flavonoids and polysaccharides, which possess various pharmacological applications. Therefore, pollen has the capability as a carrier system and therapeutic agent. This review focuses on pollen's microstructure, composition and utility in cancer management. The extraction strategies, characterisation techniques and chemical structure of sporopollenin exine capsule, its use in the oral delivery of antineoplastic drugs, and emerging cancer treatments like photothermal therapy, immunotherapy and microrobots have been highlighted. We have mentioned a note on the anticancer activity of pollen extract. Further, we have summarised the regulatory perspective, bottlenecks and way forward associated with pollen.

Microspore-expressed SCULP1 is required for p-coumaroylation of sporopollenin, exine integrity, and pollen development in wheat

Sporopollenin is one of the most structurally sophisticated and chemically recalcitrant biopolymers. In higher plants, sporopollenin is the dominant component of exine, the outer wall of pollen grains, and contains covalently linked phenolics that protect the male gametes from harsh environments. Although much has been learned about the biosynthesis of sporopollenin precursors in the tapetum, the nutritive cell layer surrounding developing microspores, little is known about how the biopolymer is assembled on the microspore surface. We identified SCULP1 (SKS clade universal in pollen) as a seed plant conserved clade of the multicopper oxidase family. We showed that SCULP1 in common wheat (Triticum aestivum) is specifically expressed in the microspore when sporopollenin assembly takes place, localized to the developing exine, and binds p-coumaric acid in vitro. Through genetic, biochemical, and 3D reconstruction analyses, we demonstrated that SCULP1 is required for p-coumaroylation of sporopollenin, exine integrity, and pollen viability. Moreover, we found that SCULP1 accumulation is compromised in thermosensitive genic male sterile wheat lines and its expression partially restored exine integrity and male fertility. These findings identified a key microspore protein in autonomous sporopollenin polymer assembly, thereby laying the foundation for elucidating and engineering sporopollenin biosynthesis.

Sporopollenin-inspired design and synthesis of robust polymeric materials

Sporopollenin is a mechanically robust and chemically inert biopolymer that constitutes the outer protective exine layer of plant spores and pollen grains. Recent investigation of the molecular structure of pine sporopollenin revealed unique monomeric units and inter-unit linkages distinct from other previously known biopolymers, which could be harnessed for new material design. Herein, we report the bioinspired synthesis of a series of sporopollenin analogues. This exercise confirms large portions of our previously proposed pine sporopollenin structural model, while the measured chemical, thermal, and mechanical properties of the synthetic sporopollenins constitute favorable attributes of a new kind of robust material. This study explores a new design framework of robust materials inspired by natural sporopollenins, and provides insights and reagents for future elucidation and engineering of sporopollenin biosynthesis in plants.

The Toughest Material in the Plant Kingdom: An Update on Sporopollenin

The extreme chemical and physical recalcitrance of sporopollenin deems this biopolymer among the most resilient organic materials on Earth. As the primary material fortifying spore and pollen cell walls, sporopollenin is touted as a critical innovation in the progression of plant life to a terrestrial setting. Although crucial for its protective role in plant reproduction, the inert nature of sporopollenin has challenged efforts to determine its composition for decades. Revised structural, chemical, and genetic experimentation efforts have produced dramatic advances in elucidating the molecular structure of this biopolymer and the mechanisms of its synthesis. Bypassing many of the challenges with material fragmentation and solubilization, insights from functional characterizations of sporopollenin biogenesis in planta, and in vitro, through a gene-targeted approach suggest a backbone of polyhydroxylated polyketide-based subunits and remarkable conservation of biochemical pathways for sporopollenin biosynthesis across the plant kingdom. Recent optimization of solid-state NMR and targeted degradation methods for sporopollenin analysis confirms polyhydroxylated α-pyrone subunits, as well as hydroxylated aliphatic units, and unique cross-linkage heterogeneity. We examine the cross-disciplinary efforts to solve the sporopollenin composition puzzle and illustrate a working model of sporopollenin's molecular structure and biosynthesis. Emerging controversies and remaining knowledge gaps are discussed, including the degree of aromaticity, cross-linkage profiles, and extent of chemical conservation of sporopollenin among land plants. The recent developments in sporopollenin research present diverse opportunities for harnessing the extraordinary properties of this abundant and stable biomaterial for sustainable microcapsule applications and synthetic material designs.

An organic-inorganic hybrid birefringent material with diverse functional groups

Birefringent materials are vital materials to modulate the polarization of light, and play a key role in plorization devices such as linear optical devices, optical communication devices, and fiber optic sensors. It is still a challenge to design excellent birefringent materials. Herein, we report an organic-inorganic hybrid oxalate birefringent material, (CN4H7)SbC2O4F2(H2O)0.5, by introducing organic delocalized π-conjugated [CN4H7]+ and [C2O4]2- groups, and stereochemical active inorganic SbO4F2 polyhedra. (CN4H7)SbC2O4F2(H2O)0.5 exhibits a large birefringence (Δn = 0.126@546 nm) that is almost equal to that of the well-known birefringent material α-BaB2O4. Theoretical calculations reveal that the distinguished birefringence should stem from the synergistic arrangement of π-conjugated [CN4H7]+ and [C2O4]2- planar groups, and highly distorted SbO4F2 polyhedra with a stereochemically active lone pair. The synergistic effect of π-conjugated systems and the lone pair electrons greatly boosts the birefringence, which is helpful for the development of high-performance birefringent materials.

Purification of Hollow Sporopollenin Microcapsules from Sunflower and Chamomile Pollen Grains

Pollen grains are natural microcapsules comprised of the biopolymer sporopollenin. The uniformity and special tridimensional architecture of these sporopollenin structures confer them attractive properties such as high resistance and improved bioadhesion. However, natural pollen can be a source of allergens, hindering its biomedical applicability. Several methods have been developed to remove internal components and allergenic compounds, usually involving long and laborious processes, which often cannot be extended to other pollen types. In this work, we propose an abridged protocol to produce stable and pristine hollow pollen microcapsules, together with a complete physicochemical and morphological characterization of the intermediate and final products. The optimized procedure has been validated for different pollen samples, also producing sporopollenin microcapsules from Matricaria species for the first time. Pollen microcapsules obtained through this protocol presented low protein content (4.4%), preserved ornamented morphology with a nanoporous surface, and low product density (0.14 g/cm3). These features make them interesting candidates from a pharmaceutical perspective due to the versatility of this biomaterial as a drug delivery platform.

An FT-IR and XPS spectroscopy dataset of Pinus ponderosa sporopollenin and related samples to elucidate sporopollenin structural features

The ATR FT-IR spectra of Pinus ponderosa sporopollenin isolated from pollen spores by enzymatic digestion. Sporopollenin is also isolated by solvent extraction, followed by either acidolysis with phosphoric acid, and acetolysis is reported [1]. The FT-IR spectra are supplemented by XPS data of the isolated sporopollenin samples. The enzymatically isolated sporopollenin is subjected to a variety of chemical treatments and modifications, including alkaline hydrolysis, deuteration (by both D₂0 and methanol-d₄), sodium cyanoborohydride reduction, hydrolysis by peracetic acid, bromination, acetylization with acetone and octanal, and acid-catalyzed ketal cleavage. The sporopollenin isolated by acidolysis and acetolysis are also subjected to alkaline hydrolysis. The sporopollenin samples are compared to a variety of model compounds representative of putative structural constituents and functional groups.