Salicylic Acid Molecules Research Articles

The role of strigolactones in resistance to environmental stress in plants.

Abiotic stress impairs plant growth and development, thereby causing low yield and inferior quality of crops. Increasing studies reported that strigolactones (SL) are plant hormones that enhance plant stress resistance by regulating plant physiological processes and gene expressions. In this review, we introduce the response and regulatory role of SL in salt, drought, light, heat, cold and cadmium stresses in plants. This review also discusses how SL alleviate the damage of abiotic stress in plants, furthermore, introducing the mechanisms of SL enhancing plant stress resistance at the genetic level. Under abiotic stress, the exogenous SL analog GR24 can induce the biosynthesis of SL in plants, and endogenous SL can alleviate the damage caused by abiotic stress. SL enhanced the stress resistance of plants by protecting photosynthesis, enhancing the antioxidant capacity of plants and promoting the symbiosis between plants and arbuscular mycorrhiza (AM). SL interact with abscisic acid (ABA), salicylic acid (SA), auxin, cytokinin (CK), jasmonic acid (JA), hydrogen peroxide (H2O2) and other signal molecules to jointly regulate plant stress resistance. Lastly, both the importance of SL and their challenges for future work are outlined in order to further elucidate the specific mechanisms underlying the roles of SL in plant responses to abiotic stress.

Controlled Sublimation Rate of Guest Drug from Polymorphic Forms of a Cyclodextrin-Based Polypseudorotaxane Complex and Its Correlation with Molecular Dynamics as Probed by Solid-State NMR.

Encapsulation of active pharmaceutical ingredients (APIs) in confined spaces has been extensively explored as it dramatically alters the molecular dynamics and physical properties of the API. Herein, we explored the effect of encapsulation on the molecular dynamics and physical stability of a guest drug, salicylic acid (SA), confined in the intermolecular spaces of γ-cyclodextrin (γ-CD) and poly(ethylene glycol) (PEG)-based polypseudorotaxane (PPRX) structure. The sublimation tendency of SA encapsulated in three polymorphic forms of the γ-CD/PEG-based PPRX complex, monoclinic columnar (MC), hexagonal columnar (HC), and tetragonal columnar (TC), was investigated. The SA sublimation rate was decreased by 3.0-6.6-fold and varied in the order of MC form > HC form > TC form complex. The 13C and 1H magic-angle spinning (MAS) solid-state nuclear magnetic resonance (NMR) spectra and 13C spin-lattice relaxation time (T1) indicated that the encapsulated SA molecules existed as the monomeric form, and its molecular mobility increased in the order of MC form > HC form > TC form complex. In the complexes, a rapid chemical exchange between two dynamic states of SA (free and bound) was suggested, with varying adsorption/desorption rates accounting for its distinct molecular mobility. This adsorption/desorption process was influenced by proton exchange at the interaction site and interaction strength of SA in the complexes, as evidenced by 1H MAS spectra and temperature dependency of the 13C carbonyl chemical shift. A positive correlation between the molecular mobility of SA and its sublimation rate was established. Moreover, the molecular mobility of γ-CD and PEG in the complexes coincided with that of SA, which can be explained by fast guest-driven dynamics. This is the first report on the stability improvement of an API through complexation in polymorphic supramolecular host structures. The relationship between the molecular dynamics and physical properties of encapsulated API will aid in the rational design of drug delivery systems.

Raman spectroscopy investigations of hydrated hydroxypropyl cellulose mixtures with low-soluble salicylic acid: Molecular interactions and the water-binding structure

Highly hydrophilic polymer matrices are limited their in use to the delivery of hydrophilic drugs, and are ineffective for hydrophobic compounds. Therefore, studying hydrogels that can effectively deliver hydrophobic drugs is still an important challenge. The molecular interactions occurring in model hydrated binary mixtures of hydroxypropyl cellulose (HPC) and low-soluble and hydrophobic salicylic acid (SA) (1:1 w/w) were investigated by means of Raman spectroscopy. During the study, the OH stretching vibrations region (in the 3600–3100 cm−1 range) was examined and bands for the three assessed fractions of water were assigned at the wavenumbers 3400 cm−1 (non-freezing water), 3320 cm−1 (freezing bound water) and 3220 cm−1 (free water). The contribution of the OH vibrations of SA (3205 cm−1) was also considered. A significant area for the analysis of changes in the HPC polymer is the glycosidic linkage vibration region ranging from 1250 cm−1 to 1000 cm−1 (at ∼1151 cm−1 and at ∼1093 cm−1) and the 3000–2850 cm−1 region due to the CH stretching of the CH2 and CH3 groups. SA is able to form hydrogen bonds to polymer chains and to water, as well as to another SA molecule to form a dimer. Therefore, bands derived from SA were observed to monitor these interactions (in the 1600–1500 cm−1 range).The obtained results were discussed and partially compared to the corresponding previously published spectroscopic and theoretical outcomes. All observed interactions between the components of the mixture and water molecules were also analyzed as a function of time, which is a novel approach providing a large amount of valuable information about the system. The applied methodology allowed for establishing that the stabilization of the hydrated HPC/SA system took place after one week. The greatest dynamics of changes were observed for the lowest studied water concentration. For the highest water concentration, several low-intensity bands in the CO vibration range seemed to indicate dimer-type interactions.

Salicylic Acid Release from Syndiotactic Polystyrene Staple Fibers

Films and fibers of syndiotactic polystyrene (sPS), being amorphous or exhibiting nanoporous crystalline (NC) or dense crystalline phases, were loaded with salicylic acid (SA), a relevant non-volatile antimicrobial molecule. In the first section of the paper, sPS/SA co-crystalline (CC) δ form is characterized, mainly by wide angle X-ray diffraction (WAXD) patterns and polarized Fourier transform infrared (FTIR) spectra. The formation of sPS/SA δ CC phases allows the preparation of sPS fibers even with a high content of the antibacterial guest, which is also retained after repeated washing procedures at 65 °C. A preparation procedure starting from amorphous fibers is particularly appropriate because involves a direct formation of the CC δ form and a simultaneous axial orientation. The possibility of tuning drug amount and release kinetics, by simply selecting suitable crystalline phases of a commercially available polymer, makes sPS fibers possibly useful for many applications. In particular, fibers with δ CC forms, which retain SA molecules in their crystalline phases, could be useful for antimicrobial textiles and fabrics. Fibers with the dense γ form which easily release SA molecules, because they are only included in their amorphous phases, could be used for promising SA-based preparations for antibacterial purposes in food processing and preservation and public health. Finally, using a cell-based assay system and antibacterial tests, we investigated the cellular activity, toxicity and antimicrobial properties of amorphous, δ CC forms and dense γ form of sPS fibers loaded with different contents of SA.

Synthesis of the first remdesivir cocrystal: design, characterization, and therapeutic potential for pulmonary delivery

While cocrystal engineering is an emerging formulation strategy to overcome drug delivery challenges, its therapeutic potential in non-oral applications remains not thoroughly explored. We herein report for the first time the successful synthesis of a cocrystal for remdesivir (RDV), an antiviral drug with broad-spectrum activities against RNA viruses. The RDV cocrystal was prepared with salicylic acid (SA) via combined liquid-assisted grinding (LAG) and thermal annealing. Formation of RDV-SA was found to be a thermally activated process, where annealing at high temperature after grinding was a prerequisite to facilitate the cocrystal growth from an amorphous intermediate, rendering it elusive under ambient preparing conditions. Through powder X-ray analysis with Rietveld refinement, the three-dimensional molecular structure of RDV-SA was resolved. The thermally annealed RDV-SA produced by LAG crystalized in a non-centrosymmetric monoclinic space group P21 with a unit cell volume of 1826.53(17) Å3, accommodating one pair of RDV and SA molecules in the asymmetric unit. The cocrystal formation was also characterized by differential scanning calorimetry, solid-state nuclear magnetic resonance, and Fourier-transform infrared spectroscopy. RDV-SA was further developed as inhaled dry powders by spray drying for potential COVID-19 therapy. The optimized RDV-SA dry powders exhibited a mass median aerodynamic diameter of 4.33 ± 0.2 μm and fine particle fraction of 41.39 ± 4.25 %, indicating the suitability for pulmonary delivery. Compared with the raw RDV, RDV-SA displayed a 15.43-fold higher fraction of release in simulated lung fluid at 120 min (p = 0.0003). RDV-SA was safe in A549 cells without any in vitro cytotoxicity observed in the RDV concentration from 0.05 to 10 µM.

UV-resistant salicylic acid as interface modifier for efficient and stable perovskite solar cells

Interfacial defect is one of the main hurdles to impede the improvement of efficiency and stability of perovskite solar cells (PSCs). Additionally, the ultraviolet (UV) irradiate induces the generation of deep defects, and further accelerate the decomposition of perovskite films. Thus, the interfacial modification is crucial to improve the efficiency and stability of PSCs. Here, the salicylic acid (SA) as a multifunctional interface material is employed to modify the interface of mesoporous cerium oxide (m-CeOx) and perovskite. The introduced SA molecules can interact with Ce in m-CeOx and Pb in perovskite through carboxylic acid functional groups to passivate interfacial defects and promote interfacial electron extraction and transport. The PSC with SA modification exhibits an improved power conversion efficiency (PCE) of 23.33%. More importantly, the SA can absorb UV light and reduce the damage of UV light to perovskite film, then improving the UV stability and overall stability of devices. This work provides a novel insight to design the interfacial modification materials for preparing efficient and stable PSCs.

Electromagnetic Activation of Salicylic Acid in a Complex with Oxidized Zinc-graphene Structure

This work aims at the development of a method of electromagnetic activation of salicylic acid molecules per se (SA) through the ultrasonic (20 kHz) complexation with oxidized zinc-graphene structure. The result of this work implies synthesized nanopartiсles “ZnO – partially restored graphene oxide (rGO) – SA” with the average size of (5.53 ± 0.11) nm and hexagonal wurtzite zinc oxide structure with complexed SA molecules. Complexation of SA with “ZnO – rGO” matrix causes magnification of electromagnetic field of SA by 102 times with the local enhancement at the contact with ZnO by 103 times, and therefore allowing selective electromagnetic activation of drug molecules. The developed method of “ZnO – rGO – SA” nanoparticles formation can be applied to many different drugs and drug-based devices, thereby introducing a great interest in medicinal electronics and nanomedicine.

Insight into the release mechanisms of diflunisal and salicylic acid from poly(vinyl alcohol). The role of hydrogen bonding interactions.

Diflunisal (5-(2,4-Difluorophenyl)salicylic acid, DIF), salicylic acid (SAL) derivative, which, on the one hand, is active pharmaceutical ingredient, on the other hand, belongs to the compounds exhibiting excited-state intramolecular proton transfer (ESIPT) behaviour was used to study the drug interactions with poly(vinyl alcohol) (PVA) matrix. For clarifying the nature and mechanisms of the drug-matrix interactions the salicylic acid (SAL) molecule was selected as the model active ESIPT compound, whose physicochemical properties in different media are well understood. The solute–solvent interactions (non-specific (dipole–dipole) versus specific (hydrogen bonding)) of DIF and SAL with different neat solvents were investigated using the steady-state spectroscopic technique. The solvent effect on spectral behaviours of DIF and SAL was analyzed based on the parametric solvent scales. In order to identify functional groups in the PVA matrices, determine the structure present in the studied molecule-PVA system and thus obtain information about the potential interactions between PVA and the studied molecules, the Raman spectra of pure PVA, SAL-PVA and DIF-PVA systems were measured. It has been shown that the molecular structure of the active substance entrapped in the polymer matrix affects the structure of the polymer, i.e., isotactic (SAL-PVA) versus syndiotactic (DIF-PVA) structure. The analysis of drug release kinetics revealed that the DIF is more strongly bound to PVA in comparison to SAL, which confirms conclusions drawn from the analysis of the Raman spectra i.e., the isotactic structure of SAL-PVA material results in a faster initial release process of weakly bound, located on the surface of the polymer SAL molecules.

Selective detection of iron (III) using salicylic acid capped Tb3+-doped CaF2 colloidal nanoparticles

Lanthanide (Ln3+) doped nanoparticles (NPs) possess sharp luminescence peaks with long excited state lifetimes. In this manuscript we have utilized these features for the selective detection of Fe3+ ions through resonance energy transfer approach. This is achieved using salicylic acid (SA) capped Tb3+-doped CaF2 (SA@CaF2:Tb3+) NPs. These nanoparticles exhibit bright green color emission upon ultraviolet (U.V.) excitation due to the strong energy transfer from the salicylic acid molecules to Tb3+ ions. An enhancement in the green emission intensity close to 40 times is noted. Upon addition of ferric ions, the emission intensity of the green emission is greatly reduced. The spectral overlap of the SA emission with the absorption of the analyte is assumed to be the reason for the selective quenching of the luminescence intensity. As a consequence, the overall energy transfer efficiency from salicylic acid to terbium ions (Tb3+) is reduced resulting in the lowering of Tb3+ emission intensity. The calculated detection limit for the ferric ions is 8.7 μM. The selective decrease in the green emission intensity upon Fe3+ is confirmed by the introduction of other cations like Ni2+, Mn2+, Cu2+, Co2+, Cr2+, Pb2+, Zn2+ and Mg2+ resulting hardly in any alteration to the Tb3+ emission intensity. This work clearly directs that the resonance energy transfer (RET) using Tb3+-doped NPs can be used as a technique to detect ferric ions.

Ultrasonic Formation of Fe3O4-Reduced Graphene Oxide-Salicylic Acid Nanoparticles with Switchable Antioxidant Function.

We demonstrate a single-step ultrasonic in situ complexation of salicylic acid during the growth of Fe3O4-reduced graphene oxide nanoparticles (∼10 nm) to improve the antioxidant and antiproliferative effects of pristine drug molecules. These nanoparticles have a precisely defined electronic molecular structure with salicylic acid ligands specifically complexed to Fe(III)/Fe(II) sites, four orders of magnitude larger electric surface potential, and enzymatic activity modulated by ascorbic acid molecules. The diminishing efficiency of hydroxyl radicals by Fe3O4-rGO-SA nanoparticles is tenfold higher than that by pristine salicylic acid in the electro-Fenton process. The H+ production of these nanoparticles can be switched by the interaction with ascorbic acid ligands and cause the redox deactivation of iron or enhanced antioxidation, where rGO plays an important role in enhanced charge transfer catalysis. Fe3O4-rGO-SA nanoparticles are nontoxic to erythrocytes, i.e., human peripheral blood mononuclear cells, but surpassingly inhibit the growth of three cancer cell lines, HeLa, HepG2, and HT29, with respect to pristine salicylic acid molecules.

Phytohormones Trigger Drought Tolerance in Crop Plants: Outlook and Future Perspectives.

In the past and present, human activities have been involved in triggering global warming, causing drought stresses that affect animals and plants. Plants are more defenseless against drought stress; and therefore, plant development and productive output are decreased. To decrease the effect of drought stress on plants, it is crucial to establish a plant feedback mechanism of resistance to drought. The drought reflex mechanisms include the physical stature physiology and biochemical, cellular, and molecular-based processes. Briefly, improving the root system, leaf structure, osmotic-balance, comparative water contents and stomatal adjustment are considered as most prominent features against drought resistance in crop plants. In addition, the signal transduction pathway and reactive clearance of oxygen are crucial mechanisms for coping with drought stress via calcium and phytohormones such as abscisic acid, salicylic acid, jasmonic acid, auxin, gibberellin, ethylene, brassinosteroids and peptide molecules. Furthermore, microorganisms, such as fungal and bacterial organisms, play a vital role in increasing resistance against drought stress in plants. The number of characteristic loci, transgenic methods and the application of exogenous substances [nitric oxide, (C28H48O6) 24-epibrassinolide, proline, and glycine betaine] are also equally important for enhancing the drought resistance of plants. In a nutshell, the current review will mainly focus on the role of phytohormones and related mechanisms involved in drought tolerance in various crop plants.

Salt formation, hydrogen-bonding patterns and supramolecular architectures of acridine with salicylic and hippuric acid molecules.

The intermolecular interactions and salt formation of acridine with 4-aminosalicylic acid, 5-chlorosalicylic acid and hippuric acid were investigated. The salts obtained were acridin-1-ium 4-aminosalicylate (4-amino-2-hydroxybenzoate), C13H10N+·C7H6NO3- (I), acridin-1-ium 5-chlorosalicylate (5-chloro-2-hydroxybenzoate), C13H10N+·C7H4ClO3- (II), and acridin-1-ium hippurate (2-benzamidoacetate) monohydrate, C13H10N+·C9H8NO3-·H2O (III). Acridine is involved in strong intermolecular interactions with the hydroxy group of the three acids, enabling it to form supramolecular assemblies. Hirshfeld surfaces, fingerprint plots and enrichment ratios were generated and investigated, and the intermolecular interactions were analyzed, revealing their quantitative contributions in the crystal packing of salts I, II and III. A quantum theory of atoms in molecules (QTAIM) analysis shows the charge-density distribution of the intermolecular interactions. The isosurfaces of the noncovalent interactions were studied, which allows visualization of where the hydrogen-bonding and dispersion interactions contribute within the crystal.

Selective Enhancement of SERS Spectral Bands of Salicylic Acid Adsorbate on 2D Ti3C2Tx-Based MXene Film

In this research, we have demonstrated that 2D Ti3C2Xn-based MXene (MXene) films are suitable for the design of surface-enhanced Raman spectroscopy (SERS)-based sensors. The enhanced SERS signal was observed for a salicylic acid molecule on Ti3C2Tx-based MXene film. Confirmation of the adsorption of the salicylic acid molecule and the formation of a salicylic acid–MXene complex were determined by experimental SERS-based spectral observations such as greatly enhanced out-of-plane bending modes of salicylic acid at 896 cm−1 and a band doublet at 681 cm−1 and 654 cm−1. Additionally, some other spectral features indicate the adsorption of salicylic acid on the MXene surface, namely, a redshift of vibrational modes and the disappearance of the carboxyl deformation spectral band at 771 cm−1. The determined enhancement factor indicates the value that can be expected for the chemical enhancement mechanism in SERS of 220 for out-of-plane vibrational modes. Theoretical modeling based on density functional theory (DFT) calculations using B3LYP/6311G++ functional were performed to assess the formation of the salicylic acid/MXene complex. Based on the calculations, salicylic acid displays affinity of forming a chemical bond with titanium atom of Ti3C2(OH)2 crystal via oxygen atom in hydroxyl group of salicylic acid. The electron density redistribution of the salicylic acid–MXene complex leads to a charge transfer effect with 2.2 eV (428 nm) and 2.9 eV (564 nm) excitations. The experimentally evaluated enhancement factor can vary from 220 to 60 when different excitation wavelengths are applied.

Salsalate reverses metabolic disorders in a mouse model of non-alcoholic fatty liver disease through AMPK activation and caspase-6 activity inhibition.

Salsalate, an ester formed by 2 salicylic acid molecules, has beneficial effect against metabolic disorders in clinical trials and in animal studies. This study focused on the mechanistic aspects of salsalate activity against non-alcoholic fatty liver disease (NAFLD). Using high-fat diet (HFD) fed mice, we showed that salsalate treatment decreased body-weight gains, reduced white adipose tissue mass and improved glycaemic control. Mice in salsalate-treated group also had reduced obese adipose tissue and hepatic macrophage infiltration and inflammation and adipogenesis gene expression. Histology analysis revealed predominant decreases in hepatosteatosis, including both macrovesicular and microvesicular steatoses. The treatment reversed AMPK activity repression that was accompanied by reduced caspase-6 activity and cleavage. Enzymatic assay and cell culture studies showed that salsalate promoted AMPK activation by directly activating AMPK. This study links salsalate effect against metabolic disorders to its activity on reversion of AMPK repression in NAFLD mice and on suppression of adipogenic gene induction.

Improving charge separation, photocurrent and photocatalytic activities of Dy-doped TiO2 by surface modification with salicylic acid

Salicylic acid-modified Dy-TiO2 (Dy-TiO2/SA), novel visible light-sensitive material was synthesized via a sol–gel followed by impregnation method. Salicylic acid (SA) molecules are mixed with the TiO2 and Dy-TiO2 samples in hexane which promotes their direct adsorption. SA-modified TiO2 particles (TiO2/SA and Dy-TiO2/SA) were finally obtained after drying at 120 °C. FTIR spectroscopy shows the formation of a fairly stable complex between Ti4+ surface ions and salicylic acid. In Dy-TiO2/SA complex, a ligand-to-metal charge transfer (LMCT) is active giving light absorption in the visible region (500–600 nm) indicating a bandgap of ~ 2.24 eV, lower than unmodified TiO2 samples. Electron paramagnetic resonance (EPR) and photoluminescence analyses demonstrate that LMCT process stabilizes the defect states within TiO2 bandgap, suppressing the electron–hole recombination process. The charge separation of SA-modified TiO2 complexes was evaluated through the photocurrent and the photocatalytic performances of Dy-TiO2/SA under visible light irradiation.

Binding interactions of salicylic acid with chitosan and its N-alkylated derivative in solutions: An equilibrium dialysis study

Dissolved natural or modified chitosans are used as the carriers of bioactive compounds which demands knowledge on how these macromolecules bind chemicals in solutions. This work examines binding of ionizable salicylic acid (SA), a medicine chemical and plant hormone, to chitosan and its derivative obtained by amine N alkylation with n-C6H13. Binding was studied at two pHs, below the chitosan's pKa, by performing dialysis with a 3500 Da cut-of membrane, followed by a spectrophotometric determination of SA concentrations in the membrane-separated compartments. SA-chitosan binding obeys reversible linear isotherms showing distinct preferences for SA to distribute from water to macromolecules with a coefficient reaching up to few hundreds (L kg−1), depending on pH and NaCl concentration. Both SA molecules and anions bind to dissolved chitosan. Although the SA anion-chitosan interactions tend to dominate, they can be suppressed by competing anions. Chitosan N-alkylation is associated with a modest decreasing effect on SA binding. For water-soluble formulations of bioactive substances, binding quantification may help to differentiate between the effects of concentration of chitosan-bound active chemicals and the ability of complexes to pass biological barriers.

A Comprehensive Study of a New 1.75 Hydrate of Ciprofloxacin Salicylate: SCXRD Structure Determination, Solid Characterization, Water Stability, Solubility, and Dissolution Study

One problem that often arises during the formulation of a dosage form is the solubility and dissolution of the active ingredients. This problem arises in ciprofloxacin, which is a BCS class IV fluoroquinolone antibiotic. A pseudopolymorph is a kind of polymorph in which the number of hydrates is different. In this study, a new pseudopolymorph comprised of ciprofloxacin and salicylic acid was found, namely the salt ciprofloxacin salicylate 1.75 hydrate form. This new solid phase was analyzed by Fourier-transform infrared spectroscope (FTIR), Raman spectroscopy, and thermal analysis and proven by Powder X-ray Diffractometry (PXRD) analysis. The crystal structure was successfully determined by Single Crystal X-ray Diffractometry (SCXRD) analysis. It was found that the piperazinyl group of ciprofloxacin is protonated by H+ from the carboxylic group of salicylic acid. In the unit cell, two ciprofloxacin and two salicylic acid molecules were independent with four water molecules, in which one water molecule had 0.5 occupancy due to inversion symmetry. Interestingly, this hydrate crystal dehydrated by grinding for 105 minutes forms an anhydrous crystalline phase, which was analyzed with FTIR, Raman spectroscopy, thermal analysis, and PXRD. The solubility and dissolution tests were carried out using UV-Visible spectrophotometry and a multiple linear regression method. This new hydrate solid phase has a better profile than the original ciprofloxacin crystal, according to the solubility and dissolution tests.

Study on the Effect of Exogenous Salicylic Acid on Algae Growth in the Environment

With the development of industry, synthetic drugs and their secondary metabolites bring some hidden dangers to environmental safety. As an excellent drug, salicylic acid is widely used in cardiovascular drugs, industrial dyes, skin care and acne products, etc. Therefore, it is possible to detect salicylic acid molecules, its derivatives or secondary metabolites in the natural environment. It should be noted that salicylic acid, as an endogenous signal molecule, can greatly affect plant growth. In this study, the common algal Spirogyra in fresh water was taken as the research object. The effects of exogenous salicylic acid on the growth of Spirogyra were analyzed through the changes of chlorophyll content and plant cross section during the growth of Spirogyra. It is found that the concentration of salicylic acid in the natural environment generally promotes the development of algae and improves their resistance to environmental stress. Therefore, as a possible correlation index of algal blooms, it deserves our attention.

Exploiting Covalent, H-Bonding, and π-π Interactions to Design Antibacterial PDMS Interfaces That Load and Release Salicylic Acid.

Smart antimicrobial surfaces are a powerful tool to prevent bacterial colonization at surfaces. In this work, we report a successful strategy for the functionalization of polydimethylsiloxane (PDMS) surfaces, widely used in medical devices, with salicylic acid (SA), a biocide approved for use in humans. Antimicrobial PDMS surfaces were fabricated via a rational design in which bifunctional silane linker molecules were covalently grafted onto the PDMS via one end, while soft intermolecular interactions with SA were generated at the other end to enable reversible load and release of the biocide. A molecular level understanding of the interface was obtained using attenuated total reflectance Fourier transform infrared, Raman, and X-ray photoelectron spectroscopies, alongside density functional theory calculations. These reveal that the linker molecules dock the SA molecules at the surface via a 1:1 complexation interaction. Furthermore, each 1:1 complex acts as a nucleation point onto which multiple stacks of the biocide are subsequently stabilized via a combination of H-bonding and π-π stacking interactions, thus significantly enhancing SA uptake at the interface. The antimicrobial activity of these surfaces against model Gram-negative and Gram-positive bacteria represented by Escherichia coli, Staphylococcus aureus, and Staphylococcus epidermidis is demonstrated by a log 6 reduction of planktonic bacterial populations and an efficient anti-biofilm activity at the surface.

Reverse Engineering of an Aspirin-Responsive Transcriptional Regulator in Escherichia coli.

Bacterial transcription factors (TFs) are key devices for the engineering of complex circuits in many biotechnological applications, yet there are few well-characterized inducer-responsive TFs that could be used in the context of an animal or human host. We have deciphered the inducer recognition mechanism of two AraC/XylS regulators from Pseudomonas putida (BenR and XylS) for creating a novel expression system responsive to acetyl salicylate (i.e., aspirin). Using protein homology modeling and molecular docking with the cognate inducer benzoate and a suite of chemical analogues, we identified the conserved binding pocket of BenR and XylS. By means of site-directed mutagenesis, we identified a single amino acid position required for efficient inducer recognition and transcriptional activation. Whereas this modification in BenR abolishes protein activity, in XylS, it increases the response to several inducers, including acetyl salicylic acid, to levels close to those achieved by the canonical inducer. Moreover, by constructing chimeric proteins with swapped N-terminal domains, we created novel regulators with mixed promoter and inducer recognition profiles. As a result, a collection of engineered TFs was generated with an enhanced response to benzoate, 3-methylbenzoate, 2-methylbenzoate, 4-methylbenzoate, salicylic acid, aspirin, and acetylsalicylic acid molecules for eliciting gene expression in E. coli.