2D Nuclear Magnetic Resonance Research Articles

Carrier-Free Deferoxamine Nanoparticles against Iron Overload in Brain

Carrier-Free Deferoxamine Nanoparticles against Iron Overload in Brain

Guaiane-type sesquiterpenes from Curcumawenyujin

Eight undescribed sesquiterpenes including seven guaianes and one pseudoguaiane which were named as wenyujinols A-H, along with ten known guaianes, were isolated from rhizomes of Curcuma wenyujin Y. H. Chen et C. Ling. The structures of wenyujinols A-H were elucidated by 1D and 2D nuclear magnetic resonance (NMR) data, high resolution mass spectrum (HRMS), electronic circular dichroism (ECD) spectra, and X-ray single crystallographic analysis. All of the isolated compounds were evaluated for antioxidant activity via activation of the Nrf2-ARE pathway in human embryonic kidney (HEK) 293 cells, for inhibitory effects on NO production in RAW 264.7 cells, and for cytotoxicity against three human cancer cell lines A549, HL60, and MCF7 in vitro. The results indicated that procurcumenol (50–200 μM) and 9-oxo-neoprocurcumenol (25–200 μM) exhibited antioxidant activity via activation of the Nrf2-ARE pathway in a dose-dependent manner.

Isolation, Structural Characterization and Macrophage Activation Activity of an Acidic Polysaccharide from Raspberry Pulp.

The discovery of safe and effective plant polysaccharides with immunomodulatory effects has become a research hotspot. Raspberry is an essential commercial fruit and is widely distributed, cultivated, and consumed worldwide. In the present study, a homogeneous acidic polysaccharide (RPP-2a), with a weight-average molecular weight (Mw) of 55582 Da, was isolated from the pulp of raspberries through DEAE-Sepharose Fast Flow and Sephadex G-200 chromatography. RPP-2a consisted of rhamnose, arabinose, galactose, glucose, xylose, galacturonic acid and glucuronic acid, with a molar ratio of 15.4:9.6:7.6:3.2:9.1:54.3:0.8. The results of Fourier transform infrared spectroscopy (FT-IR), gas chromatography-mass spectrometer (GC-MS), 1D-, and 2D-nuclear magnetic resonance (NMR) analyses suggested that the backbone of RPP-2a was primarily composed of →2)-α-L-Rhap-(1→, →2,4)-α-L-Rhap-(1→, →4)-α-D-GalAp-(1→, and →3,4)-α-D-Glcp-(1→ sugar moieties, with side chains of α-L-Araf-(1→, α-L-Arap-(1→, and β-D-Galp-(1→3)-β-D-Galp-(1→ residues linked to the O-4 band of rhamnose and O-3 band of glucose residues. Furthermore, RPP-2a exhibited significant macrophage activation activity by increasing the production of nitric oxide (NO), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1β (IL-1β), and the expression of inducible nitric oxide synthase (iNOS) and cytokines at the transcriptional level in RAW264.7 cells. Overall, the results indicate that RPP-2a can be utilized as a potential natural immune-enhancing agent.

Steroidal saponins with anti-inflammatory activity from Tribulus terrestris L.

Abstract Objective: Tribulus terrestris L. (T. terrestris) is a highly valuable traditional Chinese medicine used to treat stroke, inflammation, pulmonary fibrosis, liver cancer, and urolithiasis. To identify the basic substance responsible for the anti-inflammatory effect of TST (total saponins of Tribulus), its chemical composition was systematically studied, and its effect of inhibiting nitric oxide generation and the expression of related inflammatory factors were determined. Methods: To separate chemical constituents from T. terrestris by column chromatography. Spectroscopic methods, including 1D and 2D nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS) techniques, were used to elucidate the isolated compounds. The anti-inflammatory activities of TST and several compounds were evaluated in vitro. Results: Fifteen steroidal saponins, including 9 furostanol steroidal saponins (1, 2, 3, 4, 5, 6, 7, 8, and 15) and 6 isospirostanol steroidal saponins (9, 10, 11, 12, 13, and 14), were isolated from T. terrestris. TST significantly decreased the expression of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in RAW 264.7 cells stimulated by lipopolysaccharides. Compounds 13 and 15 evidently reduced TNF-α expression. Compounds 6, 10, 12, 13, and 15 markedly reduced IL-6 expression. Conclusions: Compounds 1 was a novel furostanol steroidal saponin, named 26-O-β-D-glucopyranosyl-(25R)-5α-furostan-12-carbonyl-20(22)-en-3β, 26-diol-3-O-{β-D-xylopyranosyl-(1→2)-[β-D-xylopyranosyl-(1→3)]-β-D-glucopyranosyl-(1→4)-[α-L-rhamnopyranosyl-(1→2)]-β-D-galactopyranoside}. Compounds 2 was isolated from the family Zygophyllaceae for the first time, and 5 and 6 were isolated from the Tribulus genus. TST and compounds 6, 10, 12, 13, and 15 exerts anti-inflammatory activity.

Sarubicinols A-C, Cytotoxic Benzoxazoles from a Streptomyces.

A chemical investigation of Streptomyces sp. Hu186 afforded two known quinone antibiotics, sarubicin A (1) and sarubicin B (2), together with three unusual variants, sarubicinols A-C (3-5), and two new 1,4-naphthoquinone metabolites, sarubicin B1 (6) and sarubicin B2 (7). Compounds 3-5 possess a rare 2-oxabicyclo [2.2.2] substructure and a benzoxazole ring system. Their structures were elucidated using 1D and 2D nuclear magnetic resonance and high-resolution electrospray ionization mass spectrometry data. The absolute configurations of the side-chain moieties in 4 and 5 were solved by electronic circular dichroism calculations. Compounds 1-7 showed moderate cytotoxic activity against four tumor cell lines.

Lupeol and pristimerin do not inhibit activation of the human sperm CatSper Ca(2+)-channel

Opposing findings have been published on the regulation of the sperm-specific Ca 2+ channel CatSper (cation channel of sperm) in human sperm cells by the plant triterpenoids lupeol and pristimerin. While the original study on this topic found these triterpenoids to act as potent inhibitors of human CatSper, subsequent studies have failed to replicate such an inhibitory effect. It has been suggested that these issues could in part be due to purity issues and/or batch variation between the plant-derived extracts of lupeol and pristimerin obtained for the studies. The aim of this study was to elucidate this controversy by investigating the batches of lupeol and pristimerin used in our previous study with state-of-the-art 1H-, 13C- and 2D-nuclear magnetic resonance (NMR) methods to reveal potential purity and/or batch variation issues. When comparing the NMR-spectra obtained from 1H-NMR and 13C-NMR with previously published NMR-spectra for lupeol and pristimerin, we could confirm that both the lupeol and pristimerin batch were ≥95 % pure. These results confirm the validity of the findings in our previous study for lupeol and pristimerin, showing that lupeol and pristimerin do not inhibit activation of CatSper in human sperm. In conclusion, using 1H-, 13C- and 2D-NMR methods, we confirm that the lupeol and pristimerin batches used in our previous study were ≥95 % pure and thereby fail to identify any purity issues and/or batch variation that could explain the observed inability of lupeol and pristimerin to inhibit activation of CatSper in human sperm.

Structural basis of lignocellulose deconstruction by the wood-feeding anobiid beetle Nicobium hirtum

The details of the lignocellulose deconstruction processes in the digestive systems of wood-feeding insects remain elusive. This study aimed to examine the biochemical conversion of lignocellulose in the digestive system of a wood-feeding anobiid beetle, Nicobium hirtum, one of the most important pests of wooden products in Japan. To this end, N. hirtum larvae were fed with Japanese red pine (softwood) and Japanese beech (hardwood) sapwood diets, as well as an artificial diet containing Shorea wood (hardwood) sapwood sawdust. The structural differences between the original and digested (feces) lignocellulose samples were examined using wet-chemical and two-dimensional (2D) nuclear magnetic resonance (NMR) methods. Cellulose and hemicelluloses, especially mannan in the softwood diet, were preferentially degraded over lignin in the larval digestive system. As a result, lignin was enriched in the digested lignocellulose residues. Lignin compositional analyses based on thioacidolysis and 2D NMR determined that the proportions of oxidized lignin aromatic units were notably increased after digestion. Further, the 2D NMR analyses revealed the accumulation of aldehyde and hydroxypropiovanillone/syringone end-unit structures in lignin, indicating that oxidative and/or reductive modifications of lignin polymers occur in the larval digestive system. Such structural alterations of lignin may facilitate the dissociation of the lignin barrier, thereby liberating polysaccharides for subsequent enzymatic conversion for assimilation and energy.

Triterpenoid Saponins From the Fruit of Acanthopanax senticosus (Rupr. & Maxim.) Harms.

Five new oleanane-type triterpenoid saponins (1–5), together with 24 known saponins (6–29) were isolated from the fruit of Acanthopanax senticosus. Their structures were determined by extensive spectroscopic analysis, including 1D, 2D nuclear magnetic resonance (NMR), and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS), in combination with chemical methods (acid hydrolysis). The neuroinflammation model was established by lipopolysaccharide (LPS)-induced BV2 microglia, and the neuroprotective effects of all compounds (1–29) were evaluated.

Terminalin from African Mango (Irvingia gabonensis) Stimulates Glucose Uptake through Inhibition of Protein Tyrosine Phosphatases.

Protein tyrosine phosphatases (PTPs), along with protein tyrosine kinases, control signaling pathways involved in cell growth, metabolism, differentiation, proliferation, and survival. Several PTPs, such as PTPN1, PTPN2, PTPN9, PTPN11, PTPRS, and DUSP9, disrupt insulin signaling and trigger type 2 diabetes, indicating that PTPs are promising drug targets for the treatment or prevention of type 2 diabetes. As part of an ongoing study on the discovery of pharmacologically active bioactive natural products, we conducted a phytochemical investigation of African mango (Irvingia gabonensis) using liquid chromatography–mass spectrometry (LC/MS)-based analysis, which led to the isolation of terminalin as a major component from the extract of the seeds of I. gabonensis. The structure of terminalin was characterized by spectroscopic methods, including one-dimensional (1D) and two-dimensional (2D) nuclear magnetic resonance (NMR) and high-resolution (HR) electrospray ionization (ESI) mass spectroscopy. Moreover, terminalin was evaluated for its antidiabetic property; terminalin inhibited the catalytic activity of PTPN1, PTPN9, PTPN11, and PTPRS in vitro and led to a significant increase in glucose uptake in differentiated C2C12 muscle cells, indicating that terminalin exhibits antidiabetic effect through the PTP inhibitory mechanism. These findings suggest that terminalin derived from African mango could be used as a functional food ingredient or pharmaceutical supplement for the prevention of type 2 diabetes.

Time- and site-resolved kinetic NMR for real-time monitoring of off-equilibrium reactions by 2D spectrotemporal correlations

Nuclear magnetic resonance (NMR) spectroscopy provides detailed information about dynamic processes through line-shape changes, which are traditionally limited to equilibrium conditions. However, a wealth of information is available by studying chemical reactions under off-equilibrium conditions—e.g., in states that arise upon mixing reactants that subsequently undergo chemical changes—and in monitoring the reactants and products in real time. Herein, we propose and demonstrate a time-resolved kinetic NMR experiment that combines rapid mixing techniques, continuous flow, and single-scan spectroscopic imaging methods, leading in unison to a 2D spectrotemporal NMR correlation that provides high-quality kinetic information of off-equilibrium chemical reactions. These kinetic 2D NMR spectra possess a high-resolution spectral dimension revealing the individual chemical sites, correlated with a time-independent, steady-state spatial axis that delivers information concerning temporal changes along the reaction coordinate. A comprehensive description of the kinetic, spectroscopic, and experimental features associated with these spectrotemporal NMR analyses is presented. Experimental demonstrations are carried out using an enzymatically catalyzed reaction leading to site- and time-resolved kinetic NMR data, that are in excellent agreement with control experiments and literature values.

Structural analysis of unstable norbixin isomers guided by pure shift nuclear magnetic resonance.

We report the analysis of complex samples obtained during the microwave irradiation/heating of norbixin, which has been identified as a potential therapeutic target for age-related macular degeneration (AMD). In this context, identifying the different isomers that are obtained during its degradation is of primary importance. However, this characterization is challenging because, on the one hand, some of these isomers are unstable, and on the other hand, the 1 H spectra of these isomeric mixtures are poorly resolved. We could successfully apply 1D pure shift experiments to obtain ultrahigh-resolution 1 H nuclear magnetic resonance (NMR) spectra of the norbixin isomer samples and exploit their information content to analyze complementary 2D NMR data and describe accurately their isomeric composition.

Inversion of Supramolecular Chirality by In Situ Hydrolyzation of Achiral Diethylene Glycol Motifs.

Chiral inversion of supramolecular assemblies is of great research interest due to its broad practical applications. However, chiral structure transition induced by in situ regulation of building molecules has remained a challenge. Herein, left-handed fibrous assemblies were constructed by C2-symmetic l-phenylalanine coupled with diethylene glycol (LPFEG) molecules. In situ hydrolyzing terminal diethylene glycol motifs in LPFEG successfully inverted the chirality of the nanofibers from left- to right-handedness. The transition of right-handed fibers into left-handed fibers could also be achieved via hydrolyzing DPFEG molecules. Circular dichroism (CD) spectroscopy, 1D and 2D nuclear magnetic resonance (NMR) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy revealed that the back-folded achiral diethylene glycol played a vital role in L/DPFEG molecular arrangements and removing terminal diethylene glycol could induce the opposite rotation of molecular assemblies. Thanks to this merit, the enantioselective separation of racemic phenylalanine was obtained and the enantiomeric excess (ee) values could achieve around ±20% after separation. This study not only provides a new strategy to regulate the chiral structure via dynamic modulation of terminal substituents but also presents a promising application in the field of enantioselective separation.

Mineralogy, organic geochemistry, and microstructural characterization of lacustrine Shahejie Formation, Qikou Sag, Bohai Bay Basin: Contribution to understanding microcosmic storage mechanism of shale oil

Shale samples of lacustrine Shahejie Formation from the Well F39X1 drilled in Qikou sag were used to study microstructures, mineralogy, and organic geochemistry and their impacts on oil storage response. Samples are quartz and clay rich and contain a variable amount of calcite, dolomite, plagioclase, and pyrite minerals. The TOC content ranges between 0.33 and 2.59 wt %, Rock-Eval S 1 and S 2 values range from 0.05 to 1.07 mg/g and 0.12–9.57 mg/g, respectively. The maximum yield temperature (T max ) of pyrolysate ranges from 440 °C to 467 °C, and vitrinite reflectance calculated based on T max between 0.76 and 1.25%. High frequency 2D nuclear magnetic resonance (NMR) results show free oil contents are 1.176–1.909 μl/g, with an average of 1.542 μl/g. Mineral-related pores are dominant and volumetrically significant with a multimodal pore-throat size distribution, they could provide significant storage space and have good microstructural connectivity. Their roles in microscopic storage of oil molecules mainly depends on two mechanisms: (1) rigid mineral grains preserve large pore networks, within which residing a very large volume of free oil, and (2) clay particles existed within large interparticle pores alter pore throat size distribution, resulting in a slight increasing of adsorbed oil onto pore walls. The Well F39X1 is an important shale oil exploration well for Shahejie Formation. To reduce exploration risk and determine economic feasibility, knowledge of liquid hydrocarbon molecule microscopic storage mechanism is required so producible shale oil resources can be quantified. The investigation of oil-bearing shale mineralogy, organic geochemistry, and microstructures is an important step in better understanding of the pore network development and their related microscopic storage mechanism for oil in lacustrine shale. We suggested that siliceous Shahejie shales in Qikou sag with moderate TOC and suitable thermal maturity have well-developed pore networks and high residual hydrocarbons, which should be the important target for lacustrine shale oil exploration. Also, the well-developed mineral-related pore networks should be included in attempts to build realistic microscopic storage models of shales. • Four typical pore types in Shahejie Formation of Well F39X1 are identified. • Mineral-related pores are dominant and volumetrically significant in pore networks. • Oil molecule type, distribution, and content are identified by high-frequency 2D NMR. • Two microstructural models are proposed to reveal shale oil storage mechanism.

Exploring correlations between MS and NMR for compound identification using essential oils: A pilot study.

In this era of 'omics' technology in natural products studies, the complementary aspects of mass spectrometry (MS)- and nuclear magnetic resonance (NMR)-based techniques must be taken into consideration. The advantages of using both analytical platforms are reflected in a higher confidence of results especially when using replicated samples where correlation approaches can be used to statistically link results from MS to NMR. Demonstrate the use of Statistical Total Correlation (STOCSY) for linking results from MS and NMR data to reach higher confidence in compound identification. Essential oil samples of Melaleuca alternifolia and M. rhaphiophylla (Myrtaceae) were used as test objects. Aliquots of 10 samples were collected for GC-MS and NMR data acquisition [proton (1 H)-NMR, and carbon-13 (13 C)-NMR as well as two-dimensional (2D) heteronuclear single quantum correlation (HSQC), heteronuclear multiple-bond correlation (HMBC), and HSQC-total correlated spectroscopy (TOCSY) NMR]. The processed data was imported to Matlab where STOCSY was applied. STOCSY calculations led to the confirmation of the four main constituents of the sample-set. The identification of each was accomplished using; MS spectra, retention time comparison, 13 C-NMR data, and scalar correlations of the 2D NMR spectra. This study provides a pipeline for high confidence in compound identification using a set of essential oils samples as test objects for demonstration.

Two New Fatty Acid Derivatives, Omphalotols A and B and Anti-Helicobacter pylori Fatty Acid Derivatives from Poisonous Mushroom Omphalotus japonicus.

As part of ongoing systematic research into the discovery of bioactive secondary metabolites with novel structures from Korean wild mushrooms, we investigated secondary metabolites from a poisonous mushroom, Omphalotus japonicus (Kawam.) Kirchm. & O. K. Mill. belonging to the family Marasmiaceae, which causes nausea and vomiting after consumption. The methanolic extract of O. japonicus fruiting bodies was subjected to the fractionation by solvent partition, and the CH2Cl2 fraction was analyzed for the isolation of bioactive compounds, aided by an untargeted liquid chromatography mass spectrometry (LC–MS)-based analysis. Through chemical analysis, five fatty acid derivatives (1–5), including two new fatty acid derivatives, omphalotols A and B (1 and 2), were isolated from the CH2Cl2 fraction, and the chemical structures of the new compounds were determined using 1D and 2D nuclear magnetic resonance (NMR) spectroscopy and high resolution electrospray ionization mass spectrometry (HR-ESIMS), as well as fragmentation patterns in MS/MS data and chemical reactions followed by the application of Snatzke’s method and competing enantioselective acylation (CEA). In the anti-Helicobacter pylori activity test, compound 1 showed moderate antibacterial activity against H. pylori strain 51 with 27.4% inhibition, comparable to that of quercetin as a positive control. Specifically, compound 3 exhibited the most significant antibacterial activity against H. pylori strain 51, with MIC50 and MIC90 values of 9 and 20 μM, respectively, which is stronger inhibitory activity than that of another positive control, metronidazole (MIC50 = 17 μM and MIC90 = 46 μM). These findings suggested the experimental evidence that the compound 3, an α,β-unsaturated ketone derivative, could be used as a moiety in the development of novel antibiotics against H. pylori.

Hemoglobin–Laccase Modifications of Ligninsulfonate: A Promising Synergistic Stratagem for Lignin Biodegradation

AbstractMulticomponent systems, such as laccase cooperating with other proteins in ligninase, are able to modify the chemical structure of lignin efficiently and opens the door to potential applications. Here, an in‐depth investigation of hemoglobin‐assisted laccase oxidation of soluble lignosulfonate is carried out, using a combination of UV–visible spectroscopy, isothermal titration calorimetry, gel permeation chromatography, Raman spectroscopy, 2D nuclear magnetic resonance spectroscopy, and high‐performance liquid chromatography–mass spectrometry. Intriguingly, hemoglobin enhances the exothermically oxidative process of the laccase reaction. Product characterizations suggest that hemoglobin may preferentially reduce the ratio of guaiacyl/syringyl subunits and promote phenylcoumaran formation simultaneously. The complicated interactions among hemoglobin, laccase, and lignin make a multiple‐component reaction, suggesting that Fe‐containing macromolecules have the capacity to mediate laccase based chemical modifications of lignin.

Bioactive Monomer and Polymer Polyketides from Edible Mushroom Cortinarius caerulescens as Glutamate Dehydrogenase Inhibitors and Antioxidants.

Two new polyketides named rufoolivacin E and viocristin B, a new natural product named 1-hydroxy-3,6,8-trimethoxyanthraquinone, and 13 known compounds were isolated from edible mushroom Cortinarius purpurascens in this work. Their structures were assigned on the basis of high-resolution electrospray ionization mass spectrometry, 1D and 2D nuclear magnetic resonance, and electronic circular dichroism data. Notably, the enzyme activity test on glutamate dehydrogenase indicated that 1, 3, 4, 5, 6, 10, 11, and 15 displayed an excellent inhibition effect. Further kinetic studies showed that the most potent compounds, 4 and 10, possess great potential as competitive inhibitors of glutamate dehydrogenase. Molecular docking and computational chemistry were applied to illustrate the binding mechanism in detail. 2,2-Diphenyl-1-picrylhydrazyl and reactive oxygen species assay results showed that compounds 1, 2, 3, and 8 exhibited significant antioxidant activities with IC50 values of 7.0 ± 0.3, 8.6 ± 0.1, 7.5 ± 0.1, and 2.8 ± 0.2 μg mL-1, respectively. Thus, Cortinarius caerulescens represents a novel resource of these polyketides to be utilized in food selection and drug discovery.

Antibacterial activity of endophytic fungi isolated from the stem bark of jambu mawar (Syzygium jambos)

Abstract. ‘Aini K, Elfita, Widyajanti H, Setiawan A, Kurniawati AR. 2021. Antibacterial activity of endophytic fungi isolated from the stem bark of jambu mawar (Syzygium jambos). Biodiversitas 23: 521-532. Syzygium jambos (jambu mawar) is widely used in South Sumatra as a traditional medicine to treat various diseases, including pathogenic bacterial infections. Literature studies report that parts of S. jambos have been used worldwide for treating diarrhea accompanied by fever, dysentery, sore throat, diabetes, and other infectious diseases. Endophytic fungi isolated from medicinal plants have high diversity, and the biological activity of their secondary metabolites is associated with their host. Therefore, this study aimed to determine the diversity of endophytic fungi from the stem bark of S. jambos and the antibacterial activity of secondary metabolites of endophytic fungi. Fungal isolates with high antibacterial activity were identified to obtain fungal species, and the structure of their compounds was determined. The disc diffusion method carried the antibacterial activity test against Gram-positive (Staphylococcus aureus and Bacillus subtilis) and Gram-negative (Escherichia coli and Salmonella typhi) bacteria. Characteristics of endophytic fungi were identified microscopically and macroscopically. Active endophytic fungi were identified by molecular analysis of the internal transcribed region (ITS) of the ribosomal DNA. Isolation of antibacterial compounds using chromatographic techniques and determination of chemical structures using spectroscopy was performed. Eight endophytic fungi were obtained from the stem bark of S. jambos, namely SJ1–SJ8. The endophytic fungus SJ6 showed the highest activity and base on phylogenetic analysis, was identified as Fusarium verticillioides. Pure compounds isolated as yellowish-white solids showed good antibacterial activity against S. aureus and S. typhi with minimum inhibitory concentration values of 64 g/mL each. Based on 1D and 2D nuclear magnetic resonance spectroscopic analysis, compound 1 was identified as 3-hydroxy-4-(hydroxy(4-hydroxyphenyl)methyl)dihydrofuran-2-on.

Nuclear magnetic resonance reveals a two hairpin equilibrium near the 3'-splice site of influenza A segment 7 mRNA that can be shifted by oligonucleotides.

Influenza A kills hundreds of thousands of people globally every year and has the potential to generate more severe pandemics. Influenza A's RNA genome and transcriptome provide many potential therapeutic targets. Here, nuclear magnetic resonance (NMR) experiments suggest that one such target could be a hairpin loop of 8 nucleotides in a pseudoknot that sequesters a 3' splice site in canonical pairs until a conformational change releases it into a dynamic 2 × 2-nt internal loop. NMR experiments reveal that the hairpin loop is dynamic and able to bind oligonucleotides as short as pentamers. A 3D NMR structure of the complex contains 4 and likely 5 bp between pentamer and loop. Moreover, a hairpin sequence was discovered that mimics the equilibrium of the influenza hairpin between its structure in the pseudoknot and upon release of the splice site. Oligonucleotide binding shifts the equilibrium completely to the hairpin secondary structure required for pseudoknot folding. The results suggest this hairpin can be used to screen for compounds that stabilize the pseudoknot and potentially reduce splicing.

Poloxamer-enhanced solubility of griseofulvin and its related antifungal activity against Trichophyton spp.

Poorly water-soluble drugs, such as the antifungal drug griseofulvin (GF), exhibit limited bioavailability, despite their high membrane permeability. Several technological approaches have been proposed to enhance the water solubility and bioavailability of GF, including micellar solubilization. Poloxamers are amphiphilic block copolymers that increase drug solubility by forming micelles and supra-micellar structures via molecular self-association. In this regard, the aim of this study was to evaluate the water solubility increment of GF by poloxamer 407 (P407) and its effect on the antifungal activity against three Trichophyton mentagrophytes and two T. rubrum isolates. The GF water solubility profile with P407 revealed a non-linear behavior, well-fitted by the sigmoid model of Morgan-Mercer-Flodin. The polymer promoted an 8-fold increase in GF water solubility. Fourier-transform infrared (FT-IR) spectroscopy, differential scanning calorimetry (DSC), and 2D nuclear magnetic resonance (NMR Roesy) spectroscopy suggested a GF-P407 interaction, which occurs in the GF cyclohexene ring. These results were supported by an increase in the water solubility of the GF impurities with the same molecular structure. The MIC values recorded for GF ranged from 0.0028 to 0.0172 mM, except for T. Mentagrophytes TME34. Notably, the micellar solubilization of GF did not increase its antifungal activity, which could be related to the high binding constant between GF and P407.