Understanding the Anion-Templated, OSDA-Free, Interzeolite Conversion Synthesis of High Silica Zeolite ZK-5.

High silica zeolite ZK-5 (framework Si/Al=4.8) has been prepared by interzeolite conversion from ultrastable zeolite Y via a co-templating route using alkali metal cations and nitrate anions but without organic structure directing agents. The mechanism, which involves zeolite framework - alkali metal cation - nitrate anion ordering, has been established by a combination of chemical and thermal analyses, Raman spectroscopy, computational modelling, and X-ray powder diffraction. Ammonium exchange gives ZK-5 with occluded ammonium nitrate and subsequent heating gives microporous zeolite ZK-5.

A zeolite family with expanding structural complexity and embedded isoreticular structures.

The prediction and synthesis of new crystal structures enable the targeted preparation of materials with desired properties. Among porous solids, this has been achieved for metal-organic frameworks, but not for the more widely applicable zeolites, where new materials are usually discovered using exploratory synthesis. Although millions of hypothetical zeolite structures have been proposed, not enough is known about their synthesis mechanism to allow any given structure to be prepared. Here we present an approach that combines structure solution with structure prediction, and inspires the targeted synthesis of new super-complex zeolites. We used electron diffraction to identify a family of related structures and to discover the structural 'coding' within them. This allowed us to determine the complex, and previously unknown, structure of zeolite ZSM-25 (ref. 8), which has the largest unit-cell volume of all known zeolites (91,554 cubic ångströms) and demonstrates selective CO2 adsorption. By extending our method, we were able to predict other members of a family of increasingly complex, but structurally related, zeolites and to synthesize two more-complex zeolites in the family, PST-20 and PST-25, with much larger cell volumes (166,988 and 275,178 cubic ångströms, respectively) and similar selective adsorption properties. Members of this family have the same symmetry, but an expanding unit cell, and are related by hitherto unrecognized structural principles; we call these family members embedded isoreticular zeolite structures.

Site-Specific Iron Substitution in STA-28, a Large Pore Aluminophosphate Zeotype Prepared by Using 1,10-Phenanthrolines as Framework-Bound Templates.

An AlPO4 zeotype has been prepared using the aromatic diamine 1,10-phenanthroline and some of its methylated analogues as templates. In each case the two template N atoms bind to a specific framework Al site to expand its coordination to the unusual octahedral AlO4 N2 environment. Furthermore, using this framework-bound template, Fe atoms can be included selectively at this site in the framework by direct synthesis, as confirmed by annular dark field scanning transmission electron microscopy and Rietveld refinement. Calcination removes the organic molecules to give large pore framework solids, with BET surface areas up to 540 m2 g-1 and two perpendicular sets of channels that intersect to give pore space connected by 12-ring openings along all crystallographic directions.

Inhibition of homologous phosphorolytic ribonucleases by citrate may represent an evolutionarily conserved communicative link between RNA degradation and central metabolism.

Ribonucleases play essential roles in all aspects of RNA metabolism, including the coordination of post-transcriptional gene regulation that allows organisms to respond to internal changes and environmental stimuli. However, as inherently destructive enzymes, their activity must be carefully controlled. Recent research exemplifies the repertoire of regulatory strategies employed by ribonucleases. The activity of the phosphorolytic exoribonuclease, polynucleotide phosphorylase (PNPase), has previously been shown to be modulated by the Krebs cycle metabolite citrate in Escherichia coli. Here, we provide evidence for the existence of citrate-mediated inhibition of ribonucleases in all three domains of life. In silico molecular docking studies predict that citrate will bind not only to bacterial PNPases from E. coli and Streptomyces antibioticus, but also PNPase from human mitochondria and the structurally and functionally related archaeal exosome complex from Sulfolobus solfataricus. Critically, we show experimentally that citrate also inhibits the exoribonuclease activity of bacterial, eukaryotic and archaeal PNPase homologues in vitro. Furthermore, bioinformatics data, showing key citrate-binding motifs conserved across a broad range of PNPase homologues, suggests that this regulatory mechanism may be widespread. Overall, our data highlight a communicative link between ribonuclease activity and central metabolism that may have been conserved through the course of evolution.

A Bifunctional MOF Catalyst Containing Metal-Phosphine and Lewis Acidic Active Sites.

Post-synthetic modification of the hafnium metal-organic framework MOF-808(Hf) to include triarylphosphine ligands is reported. Sulfonated phenylphosphines are incorporated without oxidation to give a "MOF ligand" that can complex late transition metals such as Ir and Rh to give a bifunctional catalyst containing both metal-phosphine complexes and the Lewis acidic framework hafnium metal sites. The metallated phosphine-bearing MOFs act as fully heterogeneous bifunctional catalysts for tandem reductive amination and hydroaminomethylation reactions.

Base-Catalyzed Aryl-B(OH)2 Protodeboronation Revisited: From Concerted Proton Transfer to Liberation of a Transient Aryl Anion.

Pioneering studies by Kuivila, published more than 50 years ago, suggested ipso protonation of the boronate as the mechanism for base-catalyzed protodeboronation of arylboronic acids. However, the study was limited to UV spectrophotometric analysis under acidic conditions, and the aqueous association constants (Ka) were estimated. By means of NMR, stopped-flow IR, and quenched-flow techniques, the kinetics of base-catalyzed protodeboronation of 30 different arylboronic acids has now been determined at pH > 13 in aqueous dioxane at 70 °C. Included in the study are all 20 isomers of C6HnF(5-n)B(OH)2 with half-lives spanning 9 orders of magnitude: <3 ms to 6.5 months. In combination with pH-rate profiles, pKa and ΔS⧧ values, kinetic isotope effects (2H, 10B, 13C), linear free-energy relationships, and density functional theory calculations, we have identified a mechanistic regime involving unimolecular heterolysis of the boronate competing with concerted ipso protonation/C-B cleavage. The relative Lewis acidities of arylboronic acids do not correlate with their protodeboronation rates, especially when ortho substituents are present. Notably, 3,5-dinitrophenylboronic acid is orders of magnitude more stable than tetra- and pentafluorophenylboronic acids but has a similar pKa.

Protodeboronation of Heteroaromatic, Vinyl, and Cyclopropyl Boronic Acids: pH-Rate Profiles, Autocatalysis, and Disproportionation.

pH-rate profiles for aqueous-organic protodeboronation of 18 boronic acids, many widely viewed as unstable, have been studied by NMR and DFT. Rates were pH-dependent, and varied substantially between the boronic acids, with rate maxima that varied over 6 orders of magnitude. A mechanistic model containing five general pathways (k1-k5) has been developed, and together with input of [B]tot, KW, Ka, and KaH, the protodeboronation kinetics can be correlated as a function of pH (1-13) for all 18 species. Cyclopropyl and vinyl boronic acids undergo very slow protodeboronation, as do 3- and 4-pyridyl boronic acids (t0.5 > 1 week, pH 12, 70 °C). In contrast, 2-pyridyl and 5-thiazolyl boronic acids undergo rapid protodeboronation (t0.5 ≈ 25-50 s, pH 7, 70 °C), via fragmentation of zwitterionic intermediates. Lewis acid additives (e.g., Cu, Zn salts) can attenuate (2-pyridyl) or accelerate (5-thiazolyl and 5-pyrazolyl) fragmentation. Two additional processes compete when the boronic acid and the boronate are present in sufficient proportions (pH = pKa ± 1.6): (i) self-/autocatalysis and (ii) sequential disproportionations of boronic acid to borinic acid and borane.

Grazing livestock are exposed to terrestrial cyanobacteria.

While toxins from aquatic cyanobacteria are a well-recognised cause of disease in birds and animals, exposure of grazing livestock to terrestrial cyanobacteria has not been described. This study identified terrestrial cyanobacteria, predominantly Phormidium spp., in the biofilm of plants from most livestock fields investigated. Lower numbers of other cyanobacteria, microalgae and fungi were present on many plants. Cyanobacterial 16S rDNA, predominantly from Phormidium spp., was detected in all samples tested, including 6 plant washings, 1 soil sample and ileal contents from 2 grazing horses. Further work was performed to test the hypothesis that ingestion of cyanotoxins contributes to the pathogenesis of some currently unexplained diseases of grazing horses, including equine grass sickness (EGS), equine motor neuron disease (EMND) and hepatopathy. Phormidium population density was significantly higher on EGS fields than on control fields. The cyanobacterial neurotoxic amino acid 2,4-diaminobutyric acid (DAB) was detected in plant washings from EGS fields, but worst case scenario estimations suggested the dose would be insufficient to cause disease. Neither DAB nor the cyanobacterial neurotoxins ß-N-methylamino-L-alanine and N-(2-aminoethyl) glycine were detected in neural tissue from 6 EGS horses, 2 EMND horses and 7 control horses. Phormidium was present in low numbers on plants where horses had unexplained hepatopathy. This study did not yield evidence linking known cyanotoxins with disease in grazing horses. However, further study is warranted to identify and quantify toxins produced by cyanobacteria on livestock fields, and determine whether, under appropriate conditions, known or unknown cyanotoxins contribute to currently unexplained diseases in grazing livestock.

Controlled release of 5-fluorouracil from microporous zeolites.

Zeolite particles with different pore diameter and particle size were loaded with the model anticancer drug 5-fluorouracil. The loaded zeolites were characterized by means of SEM, XRD, DSC, XPS, N2 physisorption and FT-IR. Higher loading of 5-FU was observed for NaX-FAU than BEA. Release studies were carried out in HCl 0.1N. Release of 5-FU from NaX-FAU showed exponential-type behaviour with the drug fully released within 10 min. In the case of BEA, the kinetics of 5-FU shows a multi-step profile with prolonged release over time. Molecular dynamics simulations showed that diffusion of the drug molecule through the BEA framework is lower than for NaX-FAU due to increased van der Waals interaction between the drug and the framework. The effect of zeolitic particles on the viability of Caco-2 monolayers showed that the NaX-FAU particles cause a reduction of cell viability in a more pronounced way compared with the BEA particles. FROM THE CLINICAL EDITOR: This article describes zeolite-based nanoparticles in generating time-controlled release of 5-FU from zeolite preparations for anti-cancer therapy.

An aluminophosphate molecular sieve with 36 crystallographically distinct tetrahedral sites.

The structure of the new medium-pore aluminophosphate molecular sieve PST-6 is determined by the combined use of rotation electron diffraction tomography, synchrotron X-ray powder diffraction, and computer modeling. PST-6 was prepared by calcination of another new aluminophosphate material with an unknown structure synthesized using diethylamine as a structure-directing agent, which is thought to contain bridging hydroxy groups. PST-6 has 36 crystallographically distinct tetrahedral sites in the asymmetric unit and is thus crystallographically the most complex zeolitic structure ever solved.

Synthesis of the large pore aluminophosphate STA-1 and its application as a catalyst for the Beckmann rearrangement of cyclohexanone oxime.

The preparation of stable large pore aluminophosphate (AlPO) zeotypes offers materials for applications in adsorption and catalysis. Here we report the synthesis of the pure AlPO with the SAO topology type (AlPO STA-1) using N,N'-diethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidine (DEBOP) as the organic structure directing agent in the presence of fluoride. The AlPO STA-1 can be rendered microporous (pore volume 0.36 cm3 g-1) via calcination and the calcined form remains stable in the presence of moisture. The structure of the dehydrated form has been established by Rietveld refinement (tetragonal P4̄n2, a = 13.74317(10) Å, c = 21.8131(5) Å, V = 4119.94(16) Å3). Multinuclear 27Al and 31P MAS NMR, together with 2D COSY and CASTEP NMR calculations, enables resolution and assignment of the signals from all crystallographically distinct Al and P framework sites. Structural elucidation of the as-prepared aluminophosphate-fluoride is more challenging, because of the presence of partially protonated OSDA molecules in the 3D-connected channel system and in particular because the fluoride ions coordinate with positional disorder to some of the Al atoms to give 5-fold as well as tetrahedrally-coordinated framework Al species. These are postulated to occupy Al-F-Al bridging sites, where they are responsible for distortion of the framework [P4̄n2, a = 13.3148(9) Å, c = 22.0655(20) Å, V = 3911.9(7) Å3]. Calcination and removal of fluoride ions and OSDAs allows the framework to expand to its relaxed configuration. The SAO topology type aluminophosphate can also be synthesised with small amounts of Si and Ge in the framework, and these SAPO and GeAPO STA-1 materials are also stable to template removal. IR spectroscopy with CO as a probe at 123 K indicates all have weak-to-mild acidity, increasing in the order AlPO < GeAPO < SAPO. These STA-1 materials have been investigated for their activity in the Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam at 598 K: while all are active, the AlPO form is favoured due to its high selectivity and slow deactivation, both of which are a consequence of its very weak acid strength, which is nevertheless sufficient to catalyse the reaction.

Cyanotoxin accumulation and growth patterns of biocrust communities under variable environmental conditions.

Biocrusts dominate the soil surface in deserts and are composed of diverse microbial communities that provide important ecosystem services. Cyanobacteria in biocrusts produce many secondary metabolites, including the neurotoxins BMAA, AEG, DAB, anatoxin-a(S) (guanitoxin), and the microcystin hepatotoxins, all known or suspected to cause disease or illness in humans and other animals. We examined cyanobacterial growth and prevalence of these toxins in biocrusts at millimeter-scales, under a desert-relevant illumination gradient. In contrast to previous work, we showed that hydration had an overall positive effect on growth and toxin accumulation, that nitrogen was not correlated with growth or toxin production, and that phosphorus enrichment negatively affected AEG and BMAA concentrations. Excess illumination positively correlated with AEG, and negatively correlated with all other toxins and growth. Basic pH negatively affected only the accumulation of BMAA. Anatoxin-a(S) (guanitoxin) was not correlated with any tested variables, while microcystins were not detected in any of the samples. Concerning toxin pools, AEG and BMAA were good predictors of the presence of one another. In a newly conceptualized scheme, we integrate aspects of biocrust growth and toxin pool accumulations with arid-relevant desertification drivers.

Schisandrin B Suppresses Colon Cancer Growth by Inducing Cell Cycle Arrest and Apoptosis: Molecular Mechanism and Therapeutic Potential.

Colon cancer is among the most lethal and prevalent malignant tumors in the world, and the lack of effective therapies highlights the need for novel therapeutic approaches. Schisandrin B (Sch B), a lignan extracted from the fruit ofSchisandra chinensis, has been reported for its anticancer properties. However, to date, no studies have been done to characterize the exact molecular mechanisms underlying the antitumorigenic effects of Sch B in colon cancer. This study aimed to explore the antitumorigenic effects of Sch B in colon cancer and to understand the underlying therapeutic mechanism. A comprehensive analysis of the molecular mechanism underlying the antitumorigenic effects of Sch B on human colon cancer cells was performed using a combination of Raman spectroscopy, RNA-seq, computational docking, and molecular biological experiments. The in vivo efficacy was evaluated by a mouse xenograft model. Sch B reduced cell proliferation and triggered apoptosis in human colon cancer cell lines. Raman spectroscopy, computational, RNA-seq, and molecular and cellular studies revealed that Sch B activated unfolded protein responses by interacting with CHOP and upregulating CHOP, which thereby induced apoptosis. CHOP knockdown alleviated the Sch B-induced reduction in cell viability and apoptosis. Sch B reduced colon tumor growth in vivo. Our findings demonstrated that Sch B induced apoptosis and inhibited cell proliferation and tumor growth in vitro and in vivo. These results provided an essential background for clinical trials examining the effects of Sch B in patients with colon cancer.

A Direct Analysis of ß-N-methylamino-l-alanine Enantiomers and Isomers and Its Application to Cyanobacteria and Marine Mollusks.

Of the wide variety of toxic compounds produced by cyanobacteria, the neurotoxic amino acid ß-N-methylamino-l-alanine (BMAA) has attracted attention as a result of its association with chronic human neurodegenerative diseases such as ALS and Alzheimer's. Consequently, specific detection methods are required to assess the presence of BMAA and its isomers in environmental and clinical materials, including cyanobacteria and mollusks. Although the separation of isomers such as ß-amino-N-methylalanine (BAMA), N-(2-aminoethyl)glycine (AEG) and 2,4-diaminobutyric acid (DAB) from BMAA has been demonstrated during routine analysis, a further compounding factor is the potential presence of enantiomers for some of these isomers. Current analytical methods for BMAA mostly do not discriminate between enantiomers, and the chiral configuration of BMAA in cyanobacteria is still largely unexplored. To understand the potential for the occurrence of D-BMAA in cyanobacteria, a chiral UPLC-MS/MS method was developed to separate BMAA enantiomers and isomers and to determine the enantiomeric configuration of endogenous free BMAA in a marine Lyngbya mat and two mussel reference materials. After extraction, purification and derivatization with N-(4-nitrophenoxycarbonyl)-l-phenylalanine 2-methoxyethyl ester ((S)-NIFE), both L- and D-BMAA were identified as free amino acids in cyanobacterial materials, whereas only L-BMAA was identified in mussel tissues. The finding of D-BMAA in biological environmental materials raises questions concerning the source and role of BMAA enantiomers in neurological disease.

The Effects of Long-term, Low-dose ß-N-methylamino-L-alanine (BMAA) Exposures in Adult SODG93R Transgenic Zebrafish.

ß-N-Methylamino-L-alanine (BMAA) is a non-proteinogenic amino acid produced by cyanobacteria, which has been implicated in several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). It is postulated that chronic exposure to BMAA can lead to formation of protein aggregates, oxidative stress, and/or excitotoxicity, which are mechanisms involved in the etiology of ALS. While specific genetic mutations are identified in some instances of ALS, it is likely that a combination of genetic and environmental factors, such as exposure to the neurotoxin BMAA, contributes to disease. We used a transgenic zebrafish with an ALS-associated mutation, compared with wild-type fish to explore the potential neurotoxic effects of BMAA through chronic long-term exposures. While our results revealed low concentrations of BMAA in the brains of exposed fish, we found no evidence of decreased swim performance or behavioral differences that might be reflective of neurodegenerative disease. Further research is needed to determine if chronic BMAA exposure in adult zebrafish is a suitable model to study neurodegenerative disease initiation and/or progression.

Sourcing thermotolerant poly(ethylene terephthalate) hydrolase scaffolds from natural diversity.

Enzymatic deconstruction of poly(ethylene terephthalate) (PET) is under intense investigation, given the ability of hydrolase enzymes to depolymerize PET to its constituent monomers near the polymer glass transition temperature. To date, reported PET hydrolases have been sourced from a relatively narrow sequence space. Here, we identify additional PET-active biocatalysts from natural diversity by using bioinformatics and machine learning to mine 74 putative thermotolerant PET hydrolases. We successfully express, purify, and assay 51 enzymes from seven distinct phylogenetic groups; observing PET hydrolysis activity on amorphous PET film from 37 enzymes in reactions spanning pH from 4.5-9.0 and temperatures from 30-70 °C. We conduct PET hydrolysis time-course reactions with the best-performing enzymes, where we observe differences in substrate selectivity as function of PET morphology. We employed X-ray crystallography and AlphaFold to examine the enzyme architectures of all 74 candidates, revealing protein folds and accessory domains not previously associated with PET deconstruction. Overall, this study expands the number and diversity of thermotolerant scaffolds for enzymatic PET deconstruction.

Novel biocompatible chitosan decorated single-walled carbon nanotubes (SWNTs) for biomedical applications: theoretical and experimental investigations.

Molecular mechanics and molecular dynamics simulations have been employed to characterise the interactions between SWNTs and biocompatible amphililic derivatives of chitosan, namely N-butyl-O-sulfate chitosan (NBSC), N-octyl-O-sulfate chitosan (NOSC) and N-palmitoyl-O-sulfate chitosan (NPSC). The computational simulations have shown that the affinity of the polymer for the hydrophobic surface of the nanotubes depends on the length of the chitosan hydrophobic pendant chain. Longer chains have a higher flexibility and therefore a better ability to wrap around the nanotubes. To underpin the theoretical calculations, experimental studies revealed that NPSC exhibits highest affinity for SWNTs with up to 66.9 ± 19.7% SWNTs stably suspended in an aqueous environment; this affinity was confirmed by the calculated binding energy of five polymer chains with a SWNT that was found to be -300.93 kcal mol(-1), the highest amongst the three polymers studied. Furthermore, the high value of cell viability after incubation with NPSC indicates that this is a good candidate for the preparation of biocompatible SWNTs dipersions that could be used in biomedical and pharmaceutical applications.

Formulation and characterization of a captopril ethyl ester drug-in-adhesive-type patch for percutaneous absorption.

BACKGROUND: The ethyl ester of captopril has been shown to exhibit enhanced permeation across human skin compared to the parent drug. A drug-in-adhesive patch formulation of a captopril ethyl ester was therefore developed for optimum drug release. METHOD: A wide range of transdermal patches were prepared using two commercially available bioadhesive polymers. Investigational screening was conducted on the patches using microscopy, texture profile analysis, and infrared spectroscopy. Drug release profiles of suitable patches were obtained using both polydimethylsiloxane (Silastic) and porcine skin in vitro. RESULTS: Diffusion results across Silastic showed a gradual plateau in flux with increased drug loading that may be attributable to intramolecular interactions while flux across porcine skin was seen to increase with increasing patch thickness and attained a therapeutic level. CONCLUSIONS: This study demonstrated that adhesion and drug loading are significant factors in optimizing a topical patch formulation for the delivery of a captopril prodrug.

Identification and analysis of novel small molecule inhibitors of RNase E: Implications for antibacterial targeting and regulation of RNase E.

Increasing resistance of bacteria to antibiotics is a serious global challenge and there is a need to unlock the potential of novel antibacterial targets. One such target is the essential prokaryotic endoribonuclease RNase E. Using a combination of in silico high-throughput screening and in vitro validation we have identified three novel small molecule inhibitors of RNase E that are active against RNase E from Escherichia coli, Francisella tularensis and Acinetobacter baumannii. Two of the inhibitors are non-natural small molecules that could be suitable as lead compounds for the development of broad-spectrum antibiotics targeting RNase E. The third small molecule inhibitor is glucosamine-6-phosphate, a precursor of bacterial cell envelope peptidoglycans and lipopolysaccharides, hinting at a novel metabolite-mediated mechanism of regulation of RNase E.

Metabolism of captopril carboxyl ester derivatives for percutaneous absorption.

OBJECTIVES: To determine the metabolism of captopril n-carboxyl derivatives and how this may impact on their use as transdermal prodrugs. The pharmacological activity of the ester derivatives was also characterised in order to compare the angiotensin converting enzyme inhibitory potency of the derivatives compared with the parent drug, captopril. METHODS: The metabolism rates of the ester derivatives were determined in vitro (using porcine liver esterase and porcine ear skin) and in silico (using molecular modelling to investigate the potential to predict metabolism). KEY FINDINGS: Relatively slow pseudo first-order metabolism of the prodrugs was observed, with the ethyl ester displaying the highest rate of metabolism. A strong relationship was established between in-vitro methods, while in-silico methods support the use of in-vitro methods and highlight the potential of in-silico techniques to predict metabolism. All the prodrugs behaved as angiotensin converting enzyme inhibitors, with the methyl ester displaying optimum inhibition. CONCLUSIONS: In-vitro porcine liver esterase metabolism rates inform in-vitro skin rates well, and in-silico interaction energies relate well to both. Thus, in-silico methods may be developed that include interaction energies to predict metabolism rates.