Classification of finite congruence-simple semirings with zero

Our main result states that a finite semiring of order >2 with zero which is not a ring is congruence-simple if and only if it is isomorphic to a `dense' subsemiring of the endomorphism semiring of a finite idempotent commutative monoid. We also investigate those subsemirings further, addressing e.g. the question of isomorphy.Comment: 16 page

Distance Properties of Short LDPC Codes and their Impact on the BP, ML and Near-ML Decoding Performance

Parameters of LDPC codes, such as minimum distance, stopping distance, stopping redundancy, girth of the Tanner graph, and their influence on the frame error rate performance of the BP, ML and near-ML decoding over a BEC and an AWGN channel are studied. Both random and structured LDPC codes are considered. In particular, the BP decoding is applied to the code parity-check matrices with an increasing number of redundant rows, and the convergence of the performance to that of the ML decoding is analyzed. A comparison of the simulated BP, ML, and near-ML performance with the improved theoretical bounds on the error probability based on the exact weight spectrum coefficients and the exact stopping size spectrum coefficients is presented. It is observed that decoding performance very close to the ML decoding performance can be achieved with a relatively small number of redundant rows for some codes, for both the BEC and the AWGN channels

Structural Characterization of an S enantioselective Imine Reductase from Mycobacterium Smegmatis

NADPH-dependent imine reductases (IREDs) are enzymes capable of enantioselectively reducing imines to chiral secondary amines, which represent important building blocks in the chemical and pharmaceutical industry. Since their discovery in 2011, many previously unknown IREDs have been identified, biochemically and structurally characterized and categorized into families. However, the catalytic mechanism and guiding principles for substrate specificity and stereoselectivity remain disputed. Herein, we describe the crystal structure of S-IRED-Ms from Mycobacterium smegmatis together with its cofactor NADPH. S-IRED-Ms belongs to the S-enantioselective superfamily 3 (SFam3) and is the first IRED from SFam3 to be structurally described. The data presented provide further evidence for the overall high degree of structural conservation between different IREDs of various superfamilies. We discuss the role of Asp170 in catalysis and the importance of hydrophobic amino acids in the active site for stereospecificity. Moreover, a separate entrance to the active site, potentially functioning according to a gatekeeping mechanism regulating access and, therefore, substrate specificity is described

Segmentierte Flow‐Prozesse zur Überwindung von Limitierungen der Ganzzell‐Biokatalyse in Gegenwart von organischen Lösungsmitteln

Adebar N, Nastke A, Löwe J, Gröger H. Segmentierte Flow‐Prozesse zur Überwindung von Limitierungen der Ganzzell‐Biokatalyse in Gegenwart von organischen Lösungsmitteln. Angewandte Chemie. 2021;133(29):15997-16004.In der modernen Prozessentwicklung spielt Biokatalyse eine immer gewichtigere Rolle, wobei die Benutzung von Ganzzellkatalysatoren häufig eine bevorzugte Form dieser Biokatalysatoren darstellt. Die Anwendung von Ganzzellkatalysatoren in organischen zweiphasigen Batch-Synthesen ist jedoch oft durch Einschränkungen im Hinblick auf Stofftransfer, Emulsionsbildung, aufwändiger Aufarbeitung und damit verbundenen geringen Ausbeuten beeinträchtigt. In diesem Beitrag zeigen wir, dass unter Zuhilfenahme von segmentierten Flow-Prozessen eine effiziente Ganzzellkatalyse in zweiphasigen Medien ermöglicht wird. Die Leistungsfähigkeit solcher segmentierter Flow-Prozesse ist dabei exemplarisch an drei unterschiedlichen Biotransformationen dargestellt. Zum Beispiel wurde in einem solchen Flow-Prozess eine 3-fache Steigerung des Umsatzes von 34 % auf >99 % verbunden mit einer erheblich vereinfachten Aufarbeitung erzielt, die zu einer 1.5-fachen Steigerung der Ausbeute von 44 % auf 65 % im Vergleich zum analogen Batch-Prozess führte