Mines Repository (Colorado School of Mines)
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Fluorite on dolomite
No full textPhotographed by Ron Wolf.Pale purple-white translucent glassy fluorite on mass of tan-white dolomite, Egremont, Cumberland, England
Covellite
No full textPhotographed by Ron Wolf.Dark grey blocky mass of covellite with faint blue resinous sheen
Structural basis and evolutionary origins of psilocybin biosynthesis, The
No full textIncludes bibliographical references.2024 Spring.doctoral dissertationsPsilocybin is the principal natural product of Psilocybe and other fungal genera, collectively referred to as “magic mushooms”.Therapeutic evaluation of psilocybin has revealed a remarkable potential to treat a variety of psychological conditions, including major depressive disorder, substance dependence, and end-of-life anxiety. As a result, psilocybin has received “breakthrough therapy” status by the US Food and Drug Administration and is currently the subject of 22 clinical trials. The rising interest in potential medical applications has prompted efforts to produce psilocybin biotechnologically, as well as to explore the properties of novel analogs. Four enzyme-encoding genes required for the biosynthetic pathway from L-tryptophan to psilocybin were recently identified in Psilocybe cubensis (P. cubensis) and other species, paving the way for large-scale heterologous production in microorganisms. Although heterologous production of psilocybin has been achieved, production of psilocybin analogs requires detailed characterization of the enzymes involved to optimize their activity on non-native substrates.
The final reaction in the psilocybin biosynthetic pathway is catalyzed by PsiM, an S-adenosyl-L-methionine (SAM) dependent methyltransferase. This enzyme carries out the final two methylations to produce the tertiary amine psilocybin. It exhibits strict substrate specificity toward its native substrate as indicated by low to no turnover of analogous substrates. However, the pertinent structural features and subsequent mechanistic implications for specificity of PsiM have not been identified. To address these fundamental gaps in our understanding of the last step in the biosynthesis of psilocybin, we structurally and biochemically characterized PsiM from P. cubensis. Using X-ray crystallography, we achieved sub-angstrom resolution of the first crystal structures of PsiM in all stages of its reaction cycle revealing geometric restraints that dictate activity and selectivity. We also include a full kinetic characterization of PsiM toward its primary amine substrate and the monomethylated intermediate. Inspection of the secondary sphere of the active site in conjunction with sequence alignments to homologous methyltransferases and phylogenetic analysis strongly suggest PsiM evolved from monomethylating RNA methyltransferases. Mutagenesis studies support our evolutionary hypothesis through the production of PsiM mutants that mimic ancestral activity through the inability to produce psilocybin. Ultimately, our findings suggest PsiM is not an ideal methyltransferase for biotechnological production of psilocybin analogs due to the delicate nature of substrate binding resulting from its evolutionary history
Rosasite
No full textPhotographed by Ron Wolf.Botryoidal rind of blue green rosasite filling cavities, Mapimi, Durango, Mexico
Gypsum
No full textPhotographed by Ron Wolf.Glassy radiating spikes of translucent white, brown and purple gypsum
Development of new coating alloys
No full textIncludes bibliographical references.2024 Spring.In the automotive industry, the transition towards lightweight steels aims to reduce exhaust emissions while ensuring crashworthiness. To provide sacrificial corrosion protection, Zn-based coatings are applied to these carbon steels via hot-dip galvanizing (HDG). However, the high temperatures involved in HDG (460 °C) can undesirably alter the microstructure of substrate steels. Therefore, the study introduces novel coating alloys with lower liquidus temperatures (TL), aimed at preserving the substrate microstructure during HDG. These alloys offer metallurgical advantages in a variety of steels that benefit from reduced exposure of the annealed microstructure to the “elevated” temperatures associated with molten Zn.
New coating alloy development started with the creation of a comprehensive database, including coating alloy composition, corrosion current density (Icorr), corrosion potential (Ecorr), types of electrolytes, and their concentrations extracted from the literature and computed TL for each alloy, to train machine learning (ML) models. ML tools including the Citrination platform® and various open-source Python libraries were employed to develop Icorr, Ecorr, and TL models. A materials selection chart was also developed to visualize the current state and potential future opportunities, focusing on optimizing Icorr, Ecorr, and TL attributes of coatings.
For CALPHAD (Calculation of Phase Diagrams) modeling, elements such as Zn, Mg, Al, Sn, Bi, Ga, and In were chosen after an initial screening. This screening assessed factors like the availability of thermodynamic databases, toxicity, flammability, and their capacity to offer sacrificial protection to steels while lowering the TL of an alloy. Over 300,000 unique conditions were assessed, analyzing more than twenty-one binary systems, thirty five ternary systems, four quaternary systems, and six quinary systems. This analysis aimed to identify suitable coating alloy compositions with low TL. Consequently, four alloys – Zn 2.17Mg 3.95Al, Zn 3.25Mg 3.61Al 20.18Sn, Zn 2.61Mg 3.96Al 10.26Sn 9.18Ga, and Zn 2.84Mg 3.48Al 10.07Sn 9.4Bi (wt%), – were selected for experimental studies.
Differential scanning calorimetry (DSC) and potentiodynamic polarization testing were used to experimentally validate the corrosion and transformation behavior of these alloys. Further, the study delved into applying these alloys to substrate steels, analyzing the phase transformations and microstructures through computed phase diagrams, DSC, scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), scanning transmission electron microscopy (STEM), and X ray diffraction (XRD).
The findings of the study demonstrate that the novel alloys provide effective sacrificial protection to the substrate and exhibit significantly lower TL than pure Zn. A unique phenomenon of liquid phase separation was observed in ZnMgAlSnGa alloy at room temperature, therefore, this alloy was not further considered for application to steel. The ZnMgAl coating showed pro-eutectic Zn dendrites and a ternary eutectic comprising lamellae of Zn (η hcp), Cubic MgZn2-based solution, and binary Zn (η-hcp)/Al (? fcc) regions. The ZnMgAlSnBi coating exhibited Zn (η hcp), Al (? fcc), tetragonal Sn, orthorhombic Mg2Sn, and hexagonal Mg3Bi2-based solutions. The ZnMgAlSnBi coating showed significant dross formation in the coating alloy bath. The ZnMgAlSn coating showed the best combination of sacrificial substrate protection, low TL, and coating uniformity. The coating microstructure involved the Zn phase, an Al matrix with Zn precipitates, a Mg2Sn-based solution, and a Sn-rich phase. There was a uniform intermetallic layer at the ZnMgAlSn coating substrate interface with minimal Fe diffusion into the coating, and Al segregation at the interface.
This study highlighted the significance of low TL coatings that could enable new substrate concepts, presenting a novel approach for steel processing during HDG, without the extra costs associated with modifying existing galvanizing lines