Development of New Homogeneous (Enantioselective): Hydrogenation Catalysts Based on Bio‐relevant Metals

This thesis presents the study and development of new catalysts based on first row transition metals for the (asymmetric) reduction of different C=O and C=N bonds. An iron cluster catalyst with a chiral tetradentate P2N2 ligand was discovered to catalyze the asymmetric transfer hydrogenation of N-diphenylphosphinylketimines. Subsequently the combination of a chiral Brønsted acid with a well-defined Shvo type iron complex creates an active catalyst which could hydrogenate a variety of N-aryl ketimines to amines using molecular hydrogen. Finally, an iron cluster catalyst was discovered to catalyze the reduction of amides with inexpensive PMHS

Process Simulation and Optimization of Fluid Catalytic Cracking Unit’s Rich Gas Compression System and Absorption Stabilization System

In a fuel-based refinery, rich gas in the fluid catalytic cracking (FCC) unit is further processed to separate dry gas and refinery products (i.e., stabilized gasoline and liquified petroleum gas). The process is utility-intensive and costly and includes a two-stage compressor, pumps, an absorber, a stripper, a stabilizer, and a re-absorber. The optimization was conducted with respect to the compressor outlet pressure from the gas compression system (GCS) and the flow rate of absorbent and supplementary absorbent from the Absorption-stabilization System (ASS) using the process simulation software Aspen Plus. Compared to the base case of a 725 kt/a rich gas FCC unit, a refinery can save 2.42% of utility costs under optimal operation. Through optimized operation, medium-pressure steam consumption has been reduced by 2.4% compared to the base case, resulting in a significant improvement in total operational cost. The optimization strategy can provide insightful guidance for the practical operation of GCS and ASS.</p

The role of functional strategies in global plant distribution

© 2020 The Authors. Ecography published by John Wiley & Sons Ltd on behalf of Nordic Society Oikos Understanding the determinants of species distributions is a central topic in ecology. Competition, stress tolerance and colonization, respectively represented by Grime\u27s competitor (C), stress-tolerator (S) and ruderal (R) schemes, are three important functions that interactively influence plant distributions. In this study, we compiled a dataset of 2645 vascular plant species to explore the roles of the CSR strategies in global plant distribution. We analyzed the associations between the CSR scores and species range size with phylogenetic generalized least square (PGLS) models and phylogenetic path analysis, both of which accounted for the effects of species phylogenetic relatedness, longevity and growth form. The functional strategy-range size associations differed across different distributional ranges and growth forms. Specifically, species global and native range sizes were positively associated with the R score; species naturalized range size was positively associated with the C score; and all range-size measurements were negatively associated with the S score. These patterns were mostly driven by herbs but not shrubs or trees. For species global and native-range distributions, the patterns of shrubs were even opposite to those of herbs. Our work emphasizes the importance of distinguishing the functional strategy-distribution associations between different distributional ranges and growth forms for ecosystem conservation and invasion risk prediction, because of the trade-offs among the CSR strategies

Heterogeneous and flexible transmission of mcr-1 in hospital-associated escherichia coli

The recent emergence of a transferable colistin resistance mechanism, MCR-1, has gained global attention because of its threat to clinical treatment of infections caused by multidrug-resistant Gram-negative bacteria. However, the possible transmission route of mcr-1 among Enterobacteriaceae species in clinical settings is largely unknown. Here, we present a comprehensive genomic analysis of Escherichia coli isolates collected in a hospital in Hangzhou, China. We found that mcr-1-carrying isolates from clinical infections and feces of inpatients and healthy volunteers were genetically diverse and were not closely related phylogenetically, suggesting that clonal expansion is not involved in the spread of mcr-1. The mcr-1 gene was found on either chromosomes or plasmids, but in most of the E. coli isolates, mcr-1 was carried on plasmids. The genetic context of the plasmids showed considerable diversity as evidenced by the different functional insertion sequence (IS) elements, toxin-antitoxin (TA) systems, heavy metal resistance determinants, and Rep proteins of broad-host-range plasmids. Additionally, the genomic analysis revealed nosocomial transmission of mcr-1 and the coexistence of mcr-1 with other genes encoding β-lactamases and fluoroquinolone resistance in the E. coli isolates. These findings indicate that mcr-1 is heterogeneously disseminated in both commensal and pathogenic strains of E. coli, suggest the high flexibility of this gene in its association with diverse genetic backgrounds of the hosts, and provide new insights into the genome epidemiology of mcr-1 among hospital-associated E. coli strains. IMPORTANCE Colistin represents one of the very few available drugs for treating infections caused by extensively multidrug-resistant Gram-negative bacteria. The recently emergent mcr-1 colistin resistance gene threatens the clinical utility of colistin and has gained global attention. How mcr-1 spreads in hospital settings remains unknown and was investigated by whole-genome sequencing of mcr-1-carrying Escherichia coli in this study. The findings revealed extraordinary flexibility of mcr-1 in its spread among genetically diverse E. coli hosts and plasmids, nosocomial transmission of mcr-1-carrying E. coli, and the continuous emergence of novel Inc types of plasmids carrying mcr-1 and new mcr-1 variants. Additionally, mcr-1 was found to be frequently associated with other genes encoding β-lactams and fluoroquinolone resistance. These findings provide important information on the transmission and epidemiology of mcr-1 and are of significant public health importance as the information is expected to facilitate the control of this significant antibiotic resistance threat