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The aim of this work was to evaluate two kaolin clays from the southern part of Ghana, Assin-Fosu and Kumasi clays, as source clays for the fabrication of electroporcelain insulators. X-ray diffraction, differential thermal analysis, thermogravimetric analysis, chemical analyses and scanning electron microscopy observations showed the fired clay minerals have broadly similar characteristics, but with significant differences in their chemical composition. The alumina contents were determined to be 35 ± 2 wt% and 22 ± 2 wt% respectively for the two kaolins and the silica contents 49 ± 3 wt% and 58 ± 3 wt% respectively. It is concluded that Assin-Fosu kaolin is a reliable local source material for electroporcelain fabrication, while Kumasi kaolin is more suitable for making wall and floor tiles. [ABSTRACT FROM AUTHOR]

This work was intended to develop self-assembly lipids for incorporating G-protein coupled receptors (GPCRs) in order to improve the success rate for nuclear magnetic resonance spectroscopy (NMR) structural elucidation. We hereby report the expression and purification of uniformly 15N-labeled human cannabinoid receptor-2 domain in insect cell media. The domain was refolded by screening several membrane mimetic environments. Different q ratios of isotropic bicelles were screened for solubilizing transmembrane helix 6, 7 and 8 (TMH67H8). As the concentration of dimyristoylphosphocholine (DMPC) was increased such that the q ratio was between 0.16 and 0.42, there was less crowding in the cross peaks with increasing q ratio. In bicelles of q = 0.42, the maximum number of cross peaks were obtained and the cross peaks were uniformly dispersed. The receptor domain in bicelles beyond q = 0.42 resulted in peak crowding. These studies demonstrate that GPCRs folding especially in bicelles is protein-specific and requires the right mix of the longer chain and shorter chain lipids to provide the right environment for proper folding. These findings will allow further development of novel membrane mimetics to provide greater diversity of lipid mixtures than those currently being employed for GPCR stability and folding, which are critical for both X-ray and NMR studies of GPCRs. [ABSTRACT FROM AUTHOR]

Abstract: We report the NMR solution structure of a synthetic 40-mer (T377–E416) that encompasses human cannabinoid receptor-1 (hCB1) transmembrane helix 7 (TMH7) and helix 8 (H8) [hCB1(TMH7/H8)] in 30% trifluoroethanol/H2O. Structural features include, from the peptide’s amino terminus, a hydrophobic α-helix (TMH7); a loop-like, 11 residue segment featuring a pronounced Pro-kink within the conserved NPxxY motif; a short amphipathic α-helix (H8) orthogonal to TMH7 with cationic and hydrophobic amino-acid clusters; and an unstructured C-terminal end. The hCB1(TMH7/H8) NMR solution structure suggests multiple electrostatic amino-acid interactions, including an intrahelical H8 salt bridge and a hydrogen-bond network involving the peptide’s loop-like region. Potential cation–π and cation–phenolic OH interactions between Y397 in the TMH7 NPxxY motif and R405 in H8 are identified as candidate structural forces promoting interhelical microdomain formation. This microdomain may function as a flexible molecular hinge during ligand-induced hCB1 conformer transitions. [Copyright &y& Elsevier]

Abstract: We detail the structure and dynamics of a synthetic peptide corresponding to transmembrane helix 6 (TMH6) of human cannabinoid receptor-2 (hCB2) in biomembrane-mimetic environments. The peptide’s NMR structural biology is characterized by two α-helical domains bridged by a flexible, nonhelical hinge region containing a highly-conserved CWFP motif with an environmentally sensitive, Pro-based conformational switch. Buried within the peptide’s flexible region, W258 may hydrogen-bond with L255 to help stabilize the Pro-kinked hCB2 TMH6 structure and position C257 advantageously for interaction with agonist ligands. These characteristics of hCB2 TMH6 are potential structural features of ligand-induced hCB2 activation in vivo. [Copyright &y& Elsevier]

The influence of membrane environment on human cannabinoid 1 (hCB1) receptor transmembrane helix (TMH) conformational dynamics was investigated by solid-state NMR and site-directed spin labeling/EPR with a synthetic peptide, hCB1(T377-E416), corresponding to the receptor's C-terminal component, i.e., TMH7 and its intracellular a-helical extension (H8) (TMH7/H8). Solid-state NMR experiments with mechanically aligned hCB1(T377-E416) specifically 2H- or 15N-labeled at A1a380 and reconstituted in membrane-mimetic dimyristoylphosphocholine (DMPC) or 1-palmitoyl-2-oleoyl-sn-glycerophosphocholine (POPC) bilayers demonstrate that the conformation of the TMH7/H8 peptide is more heterogeneous in the thinner DMPC bilayer than in the thicker POPC bilayer. As revealed by EPR studies on hCB1(T377-E416) spin-labeled at Cys382 and reconstituted into the phospholipid bilayers, the spin label partitions actively between hydrophobic and hydrophilic environments. In the DMPC bilayer, the hydro-phobic component dominates, regardless of temperature. Mobility parameters (ΔH0-1) are 0.3 and 0.73 G for the peptide in the DMPC or POPC bilayer environment, respectively. Interspin distances of doubly labeled hCB1(T377-E416) peptide reconstituted into a TFE/H2O mixture or a POPC or DMPC bilayer were estimated to be 10.6 ± 0.5, 16.8 ± 1, and 11.6 ± 0.8 A, respectively. The extent of coupling (≥50%) between spin labels located at 1 and 1 + 4 in a TFE/H2O mixture or a POPC bilayer is indicative of an a-helical TMH conformation, whereas the much lower coupling (14%) when the peptide is in a DMPC bilayer suggests a high degree of peptide conformational heterogeneity. These data demonstrate that hCB1(T377-E416) backbone dynamics as well as spin-label rotameric freedom are sensitive to and altered by the peptide's phospholipid bilayer environment, which exerts a dynamic influence on the conformation of a TMH critical to signal transmission by the hCB1 receptor. [ABSTRACT FROM AUTHOR]

Abstract: Little direct information is available regarding the influence of membrane environment on transmembrane (TM) G-protein-coupled receptor (GPCR) conformation and dynamics. The human CB1 cannabinoid receptor (hCB1) is a prominent GPCR pharmacotherapeutic target in which helix 7 appears critical to ligand recognition. We have chemically synthesized a hCB1 peptide corresponding to a segment of TM helix 7 and the entire contiguous helix 8 domain (fourth cytoplasmic loop) and reconstituted it in defined phospholipid-bilayer model membranes. Using an NMR-based strategy combined with molecular dynamics simulations, we provide the first direct experimental description of the orientation of hCB1 helix 7 in phospholipid membranes of varying thickness and the mechanism by which helix-7 conformation adjusts to avoid hydrophobic mismatch. Solid-state 15N NMR data show that hCB1 helices 7 and 8 reconstituted into phospholipid bilayers are oriented in a TM and in-plane (i.e., parallel to the phospholipid membrane surface) fashion, respectively. TM helix orientation is influenced by the thickness of the hydrophobic membrane bilayer as well as the interaction of helix 8 with phospholipid polar headgroups. Molecular dynamics simulations show that a decrease in phospholipid chain-length induces a kink at P394 in TM helix 7 to avoid hydrophobic mismatch. Thus, the NP(X)nY motif found in hCB1 and highly conserved throughout the GPCR superfamily is important for flexing helix 7 to accommodate bilayer thickness. Dynamic modulation of hCB1-receptor TM helix conformation by its membrane environment may have general relevance to GPCR structure and function. [Copyright &y& Elsevier]

Abstract: Cannabinoids are compounds that can modulate neuronal functions and immune responses via their activity at the CB1 receptor. We used 2H NMR order parameters and relaxation rate determination to delineate the behavior of magnetically aligned phospholipid bilayers in the presence of several structurally distinct cannabinoid ligands. THC (Δ9-Tetrahydrocannabinol) and WIN-55,212-2 were found to lower the phase transition temperature of the DMPC and to destabilize their acyl chains leading to a lower average S CD (≈0.13), while methanandamide and CP-55,940 exhibited unusual properties within the lipid bilayer resulting in a greater average S CD (≈0.14) at the top of the phospholipid upper chain. The CB1 antagonist AM281 had average S CD values that were higher than the pure DMPC lipids, indicating a stabilization of the lipid bilayer. R 1Z versus |S CD|2 plots indicated that the membrane fluidity is increased in the presence of THC and WIN-55,212-2. The interaction of CP-55,940 with a variety of zwitterionic and charged membranes was also assessed. The unusual effect of CP-55,940 was present only in bicelles composed of DMPC. These studies strongly suggest that cannabinoid action on the membrane depends upon membrane composition as well as the structure of the cannabinoid ligands. [Copyright &y& Elsevier]

Cannabinoid receptors are G-protein-coupled receptors comprised of seven transmembrane helices. We hypothesized that the extended helix of the receptor interacts differently with POPC bilayers due to the differing distribution of charged amino acid residues. To test this, hCB1(T377—E416) and hCB2(K278—H316) peptides were studied with 31P and 2H solid-state NMR spectroscopy by incorporating them into 1-palmitoyl-2-oleoyl-sn-glycerophosphocholine bilayers. Lipid affinities of the 40- and 39- residue peptides were analyzed on the basis of 31P and 2H spectral line shapes, order parameters, and T1 relaxation measurements of the POPC bilayers. Lipid headgroup perturbations were noticed in the 31P NMR spectra in the lipid/peptide mixtures when compared with the pure lipids. 2H order parameters were calculated from the quadrupolar splitting of the de-Paked 2H NMR spectra. At the top of the acyl chain, pure lipids had an average SCD ≈ 0.20, whereas SCD ≈ 0.16 and SCD ≈ 0.18 were found in the presence of hCB1 (T377–E416) and hCB2(K278–H316), respectively. SCD values decreased in the central part of the acyl chains when compared to the pure POPC lipids, indicating a change in the dynamic properties of the lipid membrane in the presence of the cannabinoid peptides. R1z vs S2CD plots exhibited a linear dependency with and without the peptides, with an increase in slope upon addition of the peptides to the POPC, indicating that the dynamics of the lipid bilayer is dominated by fast axially symmetric motion. This study provides insights into the interaction of cannabinoid peptides with the membrane bilayer by investigating the headgroup and acyl chain dynamics. [ABSTRACT FROM AUTHOR]

Abstract: Solid-state NMR spectroscopic techniques were used to investigate the secondary structure of the transmembrane peptide phospholamban (TM-PLB), a sarcoplasmic Ca2+ regulator. 13C cross-polarization magic angle spinning spectra of 13C carbonyl-labeled Leu39 of TM-PLB exhibited two peaks in a pure 1-palmitoyl-2-oleoyl-phosphocholine (POPC) bilayer, each due to a different structural conformation of phospholamban as characterized by the corresponding 13C chemical shift. The addition of a negatively charged phospholipid (1-palmitoyl-2-oleoylphosphatidylglycerol (POPG)) to the POPC bilayer stabilized TM-PLB to an α-helical conformation as monitored by an enhancement of the α-helical carbonyl 13C resonance in the corresponding NMR spectrum. 13C–15N REDOR solid-state NMR spectroscopic experiments revealed the distance between the 13C carbonyl carbon of Leu39 and the 15N amide nitrogen of Leu42 to be 4.2±0.2Å indicating an α-helical conformation of TM-PLB with a slight deviation from an ideal 3.6 amino acid per turn helix. Finally, the quadrupolar splittings of three 2H labeled leucines (Leu28, Leu39, and Leu51) incorporated in mechanically aligned DOPE/DOPC bilayers yielded an 11°±5° tilt of TM-PLB with respect to the bilayer normal. In addition to elucidating valuable TM-PLB secondary structure information, the solid-state NMR spectroscopic data indicates that the type of phospholipids and the water content play a crucial role in the secondary structure and folding of TM-PLB in a phospholipid bilayer. [Copyright &y& Elsevier]

²H and 15N solid-state NMR spectroscopic techniques were used to investigate the membrane composition, orientation, and side-chain dynamics of the transmembrane segment of phospholamban (TM- PLB), a sarcoplasmic Ca2+-regulator protein. ²H NMR spectra of ²H-labeled leucine (deuterated at one terminal methyl group) incorporated at different sites (CD3-Leu28, CD3-Leu39, and CD3-Leu51) along the TM-PLB peptide exhibited line shapes characteristic of either methyl group reorientation about the Cγ-Cδ bond axis or by additional librational motion about the Cα-Cβ and Cβ-Cγ bond axes. The ²H NMR line shapes of all CD3-labeled leucines are very similar below 0°C, indicating that all of the residues are located inside the lipid bilayer. At higher temperatures, all three labeled leucine residues undergo rapid reorientation about the Cα-Cβ, Cβ-Cγ and Cγ-Cδ bond axes as indicated by ²H line-shape simulations and reduced quadrupolar splittings. At all of the temperatures studied, the ²H NMR spectra indicated that the Leu51 side chain has less motion than Leu39 or Leu28, which is attributed to its incorporation in the pentameric PLB leucine zipper motif. The 15N powder spectra of Leu39 and Leu42 residues indicated no backbone motion, while Leu28 exhibited slight backbone motion. The chemical- shift anisotropy tensor values for 15N-labeled Leu TM-PLB were σ11 = 50.5 ppm, σ22 = 80.5 ppm, and σ33 = 229 ppm within ±3 ppm experimental error. The 15N chemical-shift value from the mechanically aligned spectrum of 15N-labeled Leu39 PLB in DOPCIDOPE phospholipid bilayers was 220 ppm and is characteristic of a TM peptide that is nearly parallel with the bilayer normal. [ABSTRACT FROM AUTHOR]

This is the first time 2H solid-state NMR spectroscopy and spin-labeled EPR spectroscopy have been utilized to probe the structural orientation and dynamics of a stearic acid incorporated into magnetically aligned phospholipid bilayers or bicelles. The data gleaned from the two different techniques provide a more complete description of the bilayer membrane system. Both methods provided similar qualitative information on the phospholipid bilayer, high order, and low motion for the hydrocarbon segment close to the carboxyl groups of the stearic acid and less order and more rapid motion at the end towards the terminal methyl groups. However, the segmental order parameters differed markedly due to the different orientations that the nitroxide and C–D bond axes transform with the various stearic acid acyl chain conformations, and because of the difference in dynamic sensitivity between NMR and EPR over the timescales examined. 5-, 7-, 12-, and 16-doxylstearic acids spin-labels were used in the EPR experiments and stearic acid-d35 was used in the solid-state NMR experiments. The influence of the addition of cholesterol and the variation of temperature on the fatty acid hydrocarbon chain ordering in the DMPC/DHPC phospholipid bilayers was also studied. Cholesterol increased the degree of ordering of the hydrocarbon chains. Conversely, as the temperature of the magnetically aligned phospholipid bilayers increased, the order parameters decreased due to the higher random motion of the acyl chain of the stearic acid. The results indicate that magnetically aligned phospholipid bilayers are an excellent model membrane system and can be used for both NMR and EPR studies. [Copyright &y& Elsevier]

Solid-state deuterium NMR spectroscopy was used to study the structural and dynamic properties of stearic acid-d35 in magnetically aligned phospholipid bilayers as a function of temperature. Magnetically aligned phospholipid bilayers or bicelles are model systems, which mimic biological membranes for magnetic resonance studies. Paramagnetic lanthanide ions (Yb3+) were added to align the bicelles such that the bilayer normal is colinear with the direction of the static magnetic field. The corresponding order parameters of the stearic acid-d35 probe were calculated and compared with values obtained from unoriented samples in the literature. The addition of cholesterol to the bicelle system decreases the fluidity of the phospholipid bilayers and increases the ordering of the acyl chains of stearic acid-d35. This study demonstrates the feasibility of utilizing magnetically aligned bicelles for calculating 2H order parameter profiles for non-biological systems such as polymer-grafted membranes and Schiff''s base complexes. [Copyright &y& Elsevier]

Our lab is developing a spin-labeled EPR spectroscopic technique complementary to solid-state NMR studies to study the structure, orientation, and dynamics of uniaxially aligned integral membrane proteins inserted into magnetically aligned discotic phospholipid bilayers, or bicelles. The focus of this study is to optimize and understand the mechanisms involved in the magnetic alignment process of bicelle disks in weak magnetic fields. Developing experimental conditions for optimized magnetic alignment of bicelles in low magnetic fields may prove useful to study the dynamics of membrane proteins and its interactions with lipids, drugs, steroids, signaling events, other proteins, etc. In weak magnetic fields, the magnetic alignment of Tm3+-doped bicelle disks was thermodynamically and kinetically very sensitive to experimental conditions. Tm3+-doped bicelles were magnetically aligned using the following optimized procedure: the temperature was slowly raised at a rate of 1.9 K/min from an initial temperature being between 298 and 307 K to a final temperature of 318 K in the presence of a static magnetic field of 6300 G. The spin probe 3β-doxyl-5α-cholestane (cholestane) was inserted into the bicelle disks and utilized to monitor bicelle alignment by analyzing the anisotropic hyperfine splitting for the corresponding EPR spectra. The phases of the bicelles were determined using solid-state 2H NMR spectroscopy and compared with the corresponding EPR spectra. Macroscopic alignment commenced in the liquid crystalline nematic phase (307 K), continued to increase upon slowly raising the temperature, and was well-aligned in the liquid crystalline lamellar smectic phase (318 K). [Copyright &y& Elsevier]

Healing clay is a rich source of diverse minerals. The relevance of these indigenous minerals in the improvement of antibiotic chemotherapy against prevailing bacterial pathogens is yet to be thoroughly explored. In the present study, healing clay from archaeological context was characterized and used in combination with 19 different antibacterial drugs to test their combined in vitro activity against Mycobacterium smegmatis mc2 155 and a multidrug-resistant (MDR) Mycobacterium smegmatis strain. Among the antibiotics tested, the anti-tuberculosis drug, pyrazinamide (Pzd), showed a drastic antimycobacterial activity against Mycobacterium smegmatis mc2 155 in the presence of 5 µg/µL of the healing clay, whereas ribosome targeted inhibitors such as gentamicin showed significant reduction in activity in the presence of the healing clay. The resistance phenotype of the MDR Mycobacterium smegmatis strain to ampicillin and isoniazid was reversed in the presence of the healing clay. The activity of the other antibiotics was either unaffected, enhanced or reduced in the presence of the healing clay. The activity of ampicillin and isoniazid against the MDR strain in the presence of the healing clay suggest that healing clay might be a useful synergy for these antibiotics against MDR Mycobacterium tuberculosis. [ABSTRACT FROM AUTHOR]

In this study, a clay sample recovered from an archaeological excavation from the Krobo Mountains in Ghana was examined for its potential to decolorize and adsorb cationic methylene blue. The raw and calcined clay samples were characterized with XRD, SEM, FTIR and EDX. The supernatant obtained by washing the raw clay with 70% ethanol solution decolorized methylene blue. The decolorization of methylene blue was independent of calcination temperature up to 300°C. The clay material subjected to calcination temperature at 600°C showed strong adsorption towards cationic methylene blue. The equilibrium adsorption data fitted well with the Freundlich isotherm indicating adsorption unto heterogeneous surface with the interaction between the adsorbed molecules which is not restricted to the formation of a monolayer. The data also fitted well with the Weber and Morris model which described the rate-controlling steps. The intra-particle diffusion was controlled by pore and surface diffusion. In addition, the adsorption data followed a pseudo-second-order kinetic model, indicating a chemisorption process. The results highlight a unique property of the clay material as an effective decolorizing and adsorption agent for the removal of water-soluble dyes from contaminated water bodies. [ABSTRACT FROM AUTHOR]

Temperature-dependent zeolite synthesis has revealed a unique surface morphology, surface area and pore size which influence the immobilization of urease on gold electrode supports for biosensor fabrication. XRD characterization has identified zeolite X (Na) at all crystallization temperatures tested. However, N2 adsorption and desorption results showed a pore size and pore volume of zeolite X (Na) 60 °C, zeolite X (Na) 70 °C and zeolite X (Na) 90 °C to range from 1.92 nm to 2.45 nm and 0.012 cm3/g to 0.061 cm3/g, respectively, with no significant differences. The specific surface area of zeolite X (Na) at 60, 70 and 90 °C was 64 m2/g, 67 m2/g and 113 m2/g, respectively. The pore size, specific surface area and pore volumes of zeolite X (Na) 80 °C and zeolite X (Na) 100 °C were dramatically increased to 4.21 nm, 295 m2/g, 0.762 cm3/g and 4.92 nm, 389 m2/g, 0.837 cm3/g, in that order. The analytical performance of adsorbed urease on zeolite X (Na) surface was also investigated using cyclic voltammetry measurements, and the results showed distinct cathodic and anodic peaks by zeolite X (Na) 80 °C and zeolite X (Na) 100 °C. These zeolites' molar conductance was measured as a function of urea concentration and gave an average polynomial regression fit of 0.948. The findings in this study suggest that certain physicochemical properties, such as crystallization temperature and pH, are critical parameters for improving the morphological properties of zeolites synthesized from natural sources for various biomedical applications. [ABSTRACT FROM AUTHOR]

This work reports on the use of low-cost pineapple leaf fiber (PALF) as an alternative reinforcing material to the established, commonly used material for prosthetic socket fabrication which is carbon-fiber-reinforced composite (CFRC) due to the high strength and stiffness of carbon fiber. However, the low range of loads exerted on a typical prosthetic socket (PS) in practice suggests that the use of CFRC may not be appropriate because of the high material stiffness which can be detrimental to socket-limb load transfer. Additionally, the high cost of carbon fiber avails opportunities to look for an alternative material as a reinforcement for composite PS development. PALF/Methyl Methacrylate-based (MMA) composites with 0°, 45° and 90° fiber orientations were made with 5–50 v/v fiber volume fractions. The PALF/MMA composites were subjected to a three-point flexural test to determine the effect of fiber volume fraction and fiber orientation on the flexural properties of the composite. The results showed that 40% v/v PALF/MMA composite with 0° fiber orientation recorded the highest flexural strength (50 MPa) and stiffness (1692 MPa). Considering the average load range exerted on PS, the flexural performance of the novel composite characterized in this work could be suitable for socket-limb load transfer for PS fabrication. [ABSTRACT FROM AUTHOR]

The aim of the work is to improve the release properties of curcumin onto human breast cancer cell lines using coated halloysite nanotubes (HNTs) with chitosan as a polycation. A loading efficiency of 70.2% (w/w) was attained for loading 4.9 mg of the drug into 0.204 g bed volume of HNTs using the vacuum suction method. Results acquired from Brunauer-Emmett-Teller (BET), Fourier-transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), scanning electron spectroscopy (SEM), zeta potential, and thermogravimetric analysis (TGA) indicated the presence of the drug and the biopolymer in and around the nanotubes. The release properties of drug-loaded HNTs (DLHNTs) and chitosan-coated drug-loaded HNTs (DLHNTs-CH) were evaluated. The release percentages of DLHNTs and DLHNTs-CH after 6 h were 50.7 and 37%, respectively. Based on the correlation coefficients obtained by fitting the release nature of curcumin from the two samples, the Korsmeyer-Peppas model was found to be the best-fitted model. In vitro cell viability studies were carried out on the human breast cancer cell line MCF-7, using the MTT and trypan blue exclusion assays. Prior to the Trypan blue assay, the IC50 of curcumin was determined to be ~ 30 µM. After 24 h of incubation, the recorded cell viability values were 94, 68, 57, and 51% for HNTs, DLHNTs-CH, DLHNTs, and curcumin, respectively. In comparison to the release studies, it could be deducted that sustained lethal doses of curcumin were released from the DLHNTs-CH within the same time. It is concluded from this work that the "burst release" of naked drugs could be slowly administered using chitosan-coated HNTs as potential drug carriers. [ABSTRACT FROM AUTHOR]

The coronavirus disease 2019 (COVID-19) pandemic caused by the severe acute respiratory syndrome virus 2 (SARS-CoV-2) has impacted negatively on public health and socioeconomic status, globally. Although, there are currently no specific drugs approved, several existing drugs are being repurposed, but their successful outcomes are not guaranteed. Therefore, the search for novel therapeutics remains a priority. We screened for inhibitors of the SARS-CoV-2 main protease and the receptor-binding domain of the spike protein from an integrated library of African natural products, compounds generated from machine learning studies and antiviral drugs using AutoDock Vina. The binding mechanisms between the compounds and the proteins were characterized using LigPlot+ and molecular dynamics simulations techniques. The biological activities of the hit compounds were also predicted using a Bayesian-based approach. Six potential bioactive molecules NANPDB2245, NANPDB2403, fusidic acid, ZINC000095486008, ZINC0000556656943 and ZINC001645993538 were identified, all of which had plausible binding mechanisms with both viral receptors. Molecular dynamics simulations, including molecular mechanics Poisson-Boltzmann surface area (MM/PBSA) computations revealed stable protein-ligand complexes with all the compounds having acceptable free binding energies <−15 kJ/mol with each receptor. NANPDB2245, NANPDB2403 and ZINC000095486008 were predicted as antivirals; ZINC000095486008 as a membrane permeability inhibitor; NANPDB2403 as a cell adhesion inhibitor and RNA-directed RNA polymerase inhibitor; and NANPDB2245 as a membrane integrity antagonist. Therefore, they have the potential to inhibit viral entry and replication. These drug-like molecules were predicted to possess attractive pharmacological profiles with negligible toxicity. Novel critical residues identified for both targets could aid in a better understanding of the binding mechanisms and design of fragment-based de novo inhibitors. The compounds are proposed as worthy of further in vitro assaying and as scaffolds for the development of novel SARS-CoV-2 therapeutic molecules. [ABSTRACT FROM AUTHOR]

Buruli ulcer is a neglected tropical disease caused by the bacterium Mycobacterium ulcerans. Its virulence is attributed to the dermo-necrotic polyketide toxin mycolactone, whose synthesis is regressed when its iron acquisition system regulated by the iron-dependent regulator (ideR) is deactivated. Interfering with the activation mechanism of ideR to inhibit the toxin's synthesis could serve as a possible cure for Buruli ulcer. The three-dimensional structure of the ideR for Mycobacterium ulcerans was generated using homology modeling. A library of 832 African natural products (AfroDB), as well as five known anti-mycobacterial compounds were docked against the metal binding site of the ideR. The area under the curve (AUC) values greater than 0.7 were obtained for the computed Receiver Operating Characteristics (ROC) curves, validating the docking protocol. The identified top hits were pharmacologically profiled using Absorption, Distribution, Metabolism, Elimination and Toxicity (ADMET) predictions and their binding mechanisms were characterized. Four compounds with ZINC IDs ZINC000018185774, ZINC000095485921, ZINC000014417338 and ZINC000005357841 emerged as leads with binding energies of −7.7 kcal/mol, −7.6 kcal/mol, −8.0 kcal/mol and −7.4 kcal/mol, respectively. Induced Fit Docking (IFD) was also performed to account for the protein's flexibility upon ligand binding and to estimate the best plausible conformation of the complexes. Results obtained from the IFD were consistent with that of the molecular docking with the lead compounds forming interactions with known essential residues and some novel critical residues Thr14, Arg33 and Asp17. A hundred nanoseconds molecular dynamic simulations of the unbound ideR and its complexes with the respective lead compounds revealed changes in the ideR's conformations induced by ZINC000018185774. Comparison of the lead compounds to reported potent inhibitors by docking them against the DNA-binding domain of the protein also showed the lead compounds to have very close binding affinities to those of the potent inhibitors. Interestingly, structurally similar compounds to ZINC000018185774 and ZINC000014417338, as well as analogues of ZINC000095485921, including quercetin are reported to possess anti-mycobacterial activity. Also, ZINC000005357841 was predicted to possess anti-inflammatory and anti-oxidative activities, which are relevant in Buruli ulcer and iron acquisition mechanisms, respectively. The leads are molecular templates which may serve as essential scaffolds for the design of future anti-mycobacterium ulcerans agents. [ABSTRACT FROM AUTHOR]

The sol-gel and cross-linking processes have been used by researchers to synthesize silica-based nanostructures and optimize their size and morphology by changing either the material or the synthesis conditions. However, the influence of the silica nanostructures on the overall physicochemical and mechanistic properties of organic biopolymers such as chitosan has received limited attention. The present study used a one-step synthetic method to obtain chitosan composites to monitor the uptake and release of a basic cationic dye (methylene blue) at two different pH values. Firstly, the composites were synthesized and characterized by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD) to ascertain their chemical identity. Adsorption studies were conducted using methylene blue and these studies revealed that Acetic Acid-Chitosan (AA-CHI), Tetraethylorthosilicate-Chitosan (TEOS-CHI), Acetic Acid-Tetraethylorthosilicate-Chitosan (AA-TEOS-CHI), and Acetic Acid-Chitosan-Tetraethylorthosilicate (AA-CHI-TEOS) had comparatively lower percentage adsorbances in acidic media after 40 h, with AA-CHI adsorbing most of the methylene blue dye. In contrast, these materials recorded higher percentage adsorbances of methylene blue in the basic media. The release profiles of these composites were fitted with an exponential model. The R-squared values obtained indicated that the AA-CHI at pH ~ 2.6 and AA-TEOS-CHI at pH ~ 7.2 of methylene blue had steady and consistent release profiles. The release mechanisms were analyzed using Korsmeyer-Peppas and Hixson-Crowell models. It was deduced that the release profiles of the majority of the synthesized chitosan beads were influenced by the conformational or surface area changes of the methylene blue. This was justified by the higher correlation coefficient or Pearson’s R values (R ≥ 0.5) computed from the Hixson-Crowell model. The results from this study showed that two of the novel materials comprising acetic acid-chitosan and a combination of equimolar ratios of acetic acid-TEOS-chitosan could be useful pH-sensitive probes for various biomedical applications, whereas the other materials involving the two-step synthesis could be found useful in environmental remediation of toxic materials. [ABSTRACT FROM AUTHOR]