Design of hetero tri metallic molecules, especially those containing at least two different metals with close atomic numbers, radii, and the same coordination number/environment is a challenging task. This quest is greatly facilitated by having a heterobimetallic parent molecule that features multiple metal sites with only some of those displaying substitutional flexibility. Recently, a unique heterobimetallic complex LiMn 2 (thd) 5 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) has been introduced as a single-source precursor for the preparation of a popular spinel cathode material, LiMn 2 O 4 . Theoretical calculations convincingly predict that in the above trinuclear molecule only one of the Mn sites is sufficiently flexible to be substituted with another 3d transition metal. Following those predictions, two hetero tri metallic complexes, LiMn 2−x Co x (thd) 5 ( x = 1 ( 1a ) and 0.5 ( 1b )), that represent full and partial substitution, respectively, of Co for Mn in the parent molecule, have been synthesized. X-ray structural elucidation clearly showed that only one transition metal position in the trinuclear molecule contains Co, while the other site remains fully occupied by Mn. A number of techniques have been employed for deciphering the structure and composition of hetero tri metallic compounds. Synchrotron resonant diffraction experiments unambiguously assigned 3d transition metal positions as well as provided a precise “site-specific Mn/Co elemental analysis” in a single crystal, even in an extremely difficult case of severely disordered structure formed by the superposition of two enantiomers. DART mass spectrometry and magnetic measurements clearly confirmed the presence of hetero tri metallic species LiMnCo(thd) 5 rather than a statistical mixture of two hetero bi metallic LiMn 2 (thd) 5 and LiCo 2 (thd) 5 molecules. Heterometallic precursors 1a and 1b were found to exhibit a clean decomposition yielding phase-pure LiMnCoO 4 and LiMn 1.5 Co 0.5 O 4 spinels, respectively, at the relatively low temperature of 400 °C. The latter oxide represents an important “5 V spinel” cathode material for the lithium ion batteries. Transmission electron microscopy confirmed a homogeneous distribution of transition metals in quaternary oxides obtained by pyrolysis of single-source precursors.
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Precursor-Directed Biosynthesis of Aminofulvenes: New Chalanilines from Endophytic Fungus Chalara sp.
The plant endophyte Chalara sp. is able to biotransform the epigenetic modifier vorinostat to form unique, aniline-containing polyketides named chalanilines. Here, we sought to expand the chemical diversity of chalaniline A-type molecules by changing the aniline moiety in the precursor vorinostat. In total, twenty-three different vorinostat analogs were prepared via two-step synthesis, and nineteen were incorporated by the fungus into polyketides. The highest yielding substrates were selected for large-scale precursor-directed biosynthesis and five novel compounds, including two fluorinated chalanilines, were isolated, purified, and structurally characterized. Structure elucidation relied on 1D and 2D NMR techniques and was supported by low- and high-resolution mass spectrometry. All compounds were tested for their bioactivity but were not active in antimicrobial or cell viability assays. Aminofulvene-containing natural products are rare, and this high-yielding, precursor-directed process allows for the diversification of this class of compounds.
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- Award ID(s):
- 2020110
- NSF-PAR ID:
- 10335232
- Date Published:
- Journal Name:
- Molecules
- Volume:
- 26
- Issue:
- 15
- ISSN:
- 1420-3049
- Page Range / eLocation ID:
- 4418
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Yarrowia lipolytica is an oleaginous yeast that is recognized for its ability to accumulate high levels of lipids, which can serve as precursors to biobased fuels and chemicals. Polyketides, such as triacetic acid lactone (TAL), can also serve as a precursor for diverse commodity chemicals. This study usedY. lipolytica as a host organism for the production of TAL via expression of the 2‐pyrone synthase gene fromGerbera hybrida . Induction of lipid biosynthesis by nitrogen‐limited growth conditions increased TAL titers. We also manipulated basal levels of TAL production using a DNA cut‐and‐paste transposon to mobilize and integrate multiple copies of the 2‐pyrone synthase gene. Strain modifications and batch fermentation in nitrogen‐limited medium yielded TAL titers of 2.6 g/L. Furthermore, we show that minimal medium allows TAL to be readily concentrated at >94% purity and converted at 96% yield to pogostone, a valuable antibiotic. Modifications of this reaction scheme yielded diverse related compounds. Thus, oleaginous organisms have the potential to be flexible microbial biofactories capable of economical synthesis of platform chemicals and the generation of industrially relevant molecules. -
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Animal cytoplasmic fatty acid synthase (FAS) represents a unique family of enzymes that are classically thought to be most closely related to fungal polyketide synthase (PKS). Recently, a widespread family of animal lipid metabolic enzymes has been described that bridges the gap between these two ubiquitous and important enzyme classes: the animal FAS–like PKSs (AFPKs). Although very similar in sequence to FAS enzymes that produce saturated lipids widely found in animals, AFPKs instead produce structurally diverse compounds that resemble bioactive polyketides. Little is known about the factors that bridge lipid and polyketide synthesis in the animals. Here, we describe the function of EcPKS2 from
Elysia chlorotica , which synthesizes a complex polypropionate natural product found in this mollusc. EcPKS2 starter unit promiscuity potentially explains the high diversity of polyketides found in and among molluscan species. Biochemical comparison of EcPKS2 with the previously described EcPKS1 reveals molecular principles governing substrate selectivity that should apply to related enzymes encoded within the genomes of photosynthetic gastropods. Hybridization experiments combining EcPKS1 and EcPKS2 demonstrate the interactions between the ketoreductase and ketosynthase domains in governing the product outcomes. Overall, these findings enable an understanding of the molecular principles of structural diversity underlying the many molluscan polyketides likely produced by the diverse AFPK enzyme family. -
The effect of precursor molecular structural features on secondary organic aerosol (SOA) growth was investigated for a number of precursor functional groups. SOA yields were determined for straight chain alkanes, some oxygenated, up to highly functionalized hydrocarbons, the largest being β-caryophyllene. Organic SOA yield was determined by comparing to standard particle size changes with SO 2 in a photolytic flow reactor. SOA formation was initiated with OH radicals from HONO photolysis and continued with NO and NO 2 present at single-digit nmol/mol levels. Seed particles of ∼10 nm diameter grew by condensation of SOA material and growth was monitored with a nanoparticle sizing system. Cyclic compounds dominate as the highest SOA yielding structural feature, followed by C-10 species with double bonds, with linear alkanes and isoprene most ineffective. Carbonyls led to significant increases in growth compared to the alkanes while alcohols, triple-bond compounds, aromatics, and epoxides were only slightly more effective than alkanes at producing SOA. When more than one double bond is present, or a double bond is present with another functional group as seen with 1, 2-epoxydec-9-ene, SOA yield is notably increased. Placement of the double bond is important as well with β-pinene having an SOA yield approximately 5 times that of α-pinene. In our photolytic flow reactor, first-generation oxidation products are presumed to be the primary species contributing to SOA thus the molecular structure of the precursor is determinant. We also conducted proton-transfer mass spectrometry measurements of α-pinene photooxidation and significant signals were observed at masses for multifunctional nitrates and possibly peroxy radicals. The mass spectrometer measurements were also used to estimate a HONO photolysis rate.more » « less
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Abstract Cyclophanes are an admirable class of macrocyclic and cage compounds that often display unusual properties due to their high strain and unusual conformations. However, the exploration of new, complex cyclophanes has been encumbered by syntheses that can be low yielding, require harsh reaction conditions, and arduous purification steps. Herein, we discuss our work using metalloid-directed self-assembly and dynamic covalent chemistry to form cryptands. These were then subjected to mild conditions to produce discrete disulfide, thioether and hydrocarbon macrocycles in high yields. ‘Design of Experiments’ was then used to selectively synthesize targeted macrocycles from complex mixtures. 1 Introduction 2 Cryptands to Cyclophanes 3 Functionalizable Macrocycles 4 ‘Design of Experiments’ Targeted Synthesis 5 Conclusions and Outlookmore » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3390/molecules26154418
