Ketoreductases from Klebsiella pneumoniae (NBRC 3319) selectively reduce several 2-substituted ethyl 3-oxobutyrates to yield the corresponding syn-β-hydroxy esters with remark-
Biocatalytically derived enantiopure α‐substituted β‐hydroxy esters serve as excellent chirons for the synthesis of a diverse set of structures such as oxetanes, a carbohydrate mimic, an ϵ‐lactone, and carbocyclic and aromatic cyclitols. The starting materials can be easily accessed in enantiopure form from α‐substituted β‐keto esters by biocatalytic reduction with Klebsiella pneumoniae (NBRC 3319). Ring‐closing metathesis (RCM) is one of the key transformations used to create the carbocyclic/heterocyclic frameworks reported in this article. The synthesized cyclitols were screened for their inhibitory effect on α‐ and β‐glucosidases.
The optical transformation and thermal stability of Ag centres in KCI:Ag crystals stabilized in different valence states after 5-irradiation are studied using thermoluminescence (TL) as the tool. The much higher sensitivity of TL over optical absorption enables to monitor the transformation processes with the help of the data obtained from TL spectra. It is shown t h a t the 555 nm recombination luminescence emission predominant in the 90 "C glow peak is due to Ago atoms at cation sites while the 543 nm emission predominant in the 135 "C glow peak is due t o Agi:F centre complex. The results further reveal that electrons trapped by Ag' ions during X-irradiation are mostly not destroyed during optical bleaching but undergo transformation and stabilize the Ag' ions in different valence states both in cationic and anionic sites. Results also indicate that Ago atoms in anion sites are non-thermoluminescent.Die optischen Ubergange und die thermische Stabilitat der Ag-Zentren in KC1: Ag-Bristallen, die nach Rontgeneinstrahlung in verschiedenen Valenzzustlnden stabilisiert wurden, werden mit Thermolumineszenz (TL) untersucht. Die vie1 hohere Empfindlichkeit der TL gegenuber optischer Absorption ermoglicht die Ubergangsprozesse mit den Werten der TL-Spektren zu verfolgen. E s wird gezeigt, dal3 die 555 nm-Rekombinationslumineszenzernission, die im 90 oC-Glowmaximnm iiberwiegt, durch Ago-Atome auf KationenplLtze hervorgerufen wird, wahrend die im 135 "CGlowmaximum dominierende 543 nm-Emission durch cinen A&: F-Zontrcn-Komplex verursacht wird. Die Ergebnisse zeigen weiter, daB a n Ag+-lonen wahrend der Rontgenstrahlung angehaftete Elektronen fast nicht beseitigt werden wahrend des optischen Bleichens, jedoch einen tfbergang durchfiihren und die Ag+-Ionen in verschiedenen Valenzzustanden sowohl auf Kationen-als auch auf Anionenplatzen stabilisieren. Die Ergebnisse zeigen auch, daB Ago-Atome auf Anionenplatzen nicht-thermolumineszent sind.
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