Alteration of the Route to Menaquinone towards Isochorismate-Derived Metabolites

Chorismate and isochorismate constitute branch-point intermediates in the biosynthesis of many aromatic metabolites in microorganisms and plants. To obtain unnatural compounds, we modified the route to menaquinone in Escherichia coli. We propose a model for the binding of isochorismate to the active site of MenD ((1R,2S, 5S,6S)-2-succinyl-5-enolpyruvyl-6-hydroxycyclohex-3-ene-1-carboxylate (SEPHCHC) synthase) that explains the outcome of the native reaction with α-ketoglutarate. We have rationally designed variants of MenD for the conversion of several isochorismate analogues. The double-variant Asn117Arg–Leu478Thr preferentially converts (5S,6S)-5,6-dihydroxycyclohexa-1,3-diene-1-carboxylate (2,3-trans-CHD), the hydrolysis product of isochorismate, with a >70-fold higher ratio than that for the wild type. The single-variant Arg107Ile uses (5S,6S)-6-amino-5-hydroxycyclohexa-1,3-diene-1-carboxylate (2,3-trans-CHA) as substrate with >6-fold conversion compared to wild-type MenD. The novel compounds have been made accessible in vivo (up to 5.3 g L⁻¹). Unexpectedly, as the identified residues such as Arg107 are highly conserved (>94 %), some of the designed variations can be found in wild-type SEPHCHC synthases from other bacteria (Arg107Lys, 0.3 %). This raises the question for the possible natural occurrence of as yet unexplored branches of the shikimate pathway.     

Effect of processing on the microbiological quality and safety of chicken carcasses at slaughterhouse

Microbiological contamination of chicken meat depends on the conditions under which the animals are reared, slaughtered and processed. The aim of this study was to determine the influence of farm origin and processing stages at slaughterhouse on the microbial safety and quality of chicken. Samples of chicken carcasses from three different farms were taken from a slaughterhouse. Mesophiles, Escherichia coli, coagulase positive Staphylococcci counts, presence of Listeria monocytogenes,Campylobacter and Salmonella were determined at five sampling points: after defeathering, after evisceration, after washing, after chilling and after cutting. Chilling reduced log numbers of mesophiles, coagulase positive Staphylococci and E. coli by 0.85, 1.52 and 2.2 log units, respectively. Salmonella was not detected after chilling. High prevalence of Campylobacter spp was observed at all the stages ranging between 84% and 100%. L. monocytogenes was not detected in chicken carcasses after defeathering. However, it was detected after evisceration and after washing and chilling. The most critical stage for L. monocytogenes contamination was the portioning operation, the prevalence in breast and legs being 88% and 84%, respectively.     

Evaluation of bismuth doped La2-xBixNiO4+δ (x = 0, 0.02 and 0.04) as cathode materials for solid oxide fuel cells

Bismuth doped La_2-xBi_xNiO_4+δ (x = 0, 0.02 and 0.04) oxides are investigated as SOFC cathodes. The effects of Bi doping on the phase structure, thermal expansion, electrical conduction behavior as well as electrochemical performance are studied. All the samples exist as a tetragonal Ruddlesden-Popper structure. Bi-doped LBNO-0.02 and LBNO-0.04 have good chemical and thermal compatibility with LSGM electrolyte. The average TEC over 20–900°С was 13.4 × 10^?6 and 14.2 × 10^?6 K^?1 for LBNO-0.02 and LBNO-0.04, respectively. The electrical conductivity was decreasing with the rise of Bi doping content. EIS measurement indicates Bi doping can decrease the ASR values. At 750 °C, the obtained ASR for LBNO-0.04 is 0.18 Ωcm², which is 56% lower than that of the sample without Bi doping, suggesting Bi doping is beneficial to the electrochemical catalytic activity of LBNO cathodes.     

The generalized discrete ‐centroid problem

The ‐centroid problem or leader–follower problem is generalized considering different customer choice rules where a customer may use facilities belonging to different firms, if the difference in travel distance (or time) is small enough. Assuming essential goods, some particular customer choice rules are analyzed. Linear programming formulations for the generalized ‐medianoid and ‐centroid problems are presented and an exact solution approach is applied. Some computational examples are included.     

基于区块链技术的公益时间银行系统

在现有的时间银行系统中，时间币的发行功能和结算功能完全集中到一个中心节点上。这种极度中心化的功能结构，不仅存在容易发生中心节点单点失效、数据容易被篡改等信息安全问题，还存在着时间币的发行和流通缺乏透明度以及时间币的结算依赖中心化的结算机构等问题。针对这些问题，提出了一种基于区块链技术的解决方法。首先，将时间币的发行功能和结算功能从中心节点上分离出来；然后，利用具有分布式去中心化、集体维护和不可篡改等特性的区块链技术，将分离出来的发行功能逐步去中心化，将分离出来的结算功能去中心化，形成公益时间链（PWTB）；最终，PWTB利用区块链技术以去中心化的方式将时间银行系统由单个节点维护账本变成由集体维护一个分布式的共享账本，使时间币的发行和流通公开透明，时间币的结算不依赖某个中心化的节点。安全分析表明所设计的PWTB能够实现安全的信息传输与存储，以及数据的共享。     

Skeletal Muscle Health and Cognitive Function: A Narrative Review

Sarcopenia is the loss of skeletal muscle mass and function with advancing age. It involves both complex genetic and modifiable risk factors, such as lack of exercise, malnutrition and reduced neurological drive. Cognitive decline refers to diminished or impaired mental and/or intellectual functioning. Contracting skeletal muscle is a major source of neurotrophic factors, including brain-derived neurotrophic factor, which regulate synapses in the brain. Furthermore, skeletal muscle activity has important immune and redox effects that modify brain function and reduce muscle catabolism. The identification of common risk factors and underlying mechanisms for sarcopenia and cognition may allow the development of targeted interventions that slow or reverse sarcopenia and also certain forms of cognitive decline. However, the links between cognition and skeletal muscle have not been elucidated fully. This review provides a critical appraisal of the literature on the relationship between skeletal muscle health and cognition. The literature suggests that sarcopenia and cognitive decline share pathophysiological pathways. Ageing plays a role in both skeletal muscle deterioration and cognitive decline. Furthermore, lifestyle risk factors, such as physical inactivity, poor diet and smoking, are common to both disorders, so their potential role in the muscle–brain relationship warrants investigation.     

Assessing students' conceptual understanding using an online three‐tier diagnostic test

When solving a mathematical problem, students who do not have sufficient conceptual understanding may perform poorly and exhibit misconceptions. This study was aimed to examine students' conceptual understanding and significant misconceptions when solving number sense‐related problems. An online three‐tier diagnostic test was administered to 125 fifth‐grade students with varied socio‐economic backgrounds in Hong Kong. Only 14.40% of the students exhibited high performance with high confidence, indicating that these students had a profound conceptual understanding of number sense. In addition, the majority of the students (66.40%) did not demonstrate number sense; these students exhibited several significant misconceptions and could solve the questions only by using a rule‐based method or guessing. Accordingly, most students performed unsatisfactorily on number sense‐related problems. This study is imperative in identifying early predictors and provides information for further compatible interventions in the teaching and learning of number sense in Hong Kong in particular and worldwide in general.     

Biocatalytic Alkylation Cascades: Recent Advances and Future Opportunities for Late-Stage Functionalization

This Concept article describes the latest developments in the emerging area of late-stage biocatalytic alkylation. Central to these developments is the ability to efficiently prepare S-adenosyl methionine (SAM) cofactor analogues and couple this with enzymatic alkyl transfer. Recent developments in the enzymatic synthesis of SAM cofactor analogues are summarized first, followed by their application as alkyl transfer agents catalyzed by methyltransferases (MTases). Second, innovative methods to regenerate SAM cofactors by enzymatic cascades is reported. Finally, future opportunities towards establishing a generalized platform for late-stage alkylation are described.     

Quantitative UPLC‐MS/MS analysis of chlorogenic acid derivatives in antioxidant fractionates from dandelion (Taraxacum officinale) root

While qualitative studies have identified chlorogenic acids in antioxidant extracts, particularly ethyl acetate‐derived extracts, of Taraxacum officinale, quantitative analysis of these phenolic compounds remains largely unreported for this species. In this study, bioactivity‐guided fractionation of an antioxidant crude ethyl acetate extract (DPPH = 295.481 ± 0.955 mg TE g^?1 extract) from T. officinale root resulted in a number of reverse‐phase fractions that demonstrated high antioxidant activity (DPPH = 1058.733–1312.136 mg TE g^?1 extract), stronger than that of the synthetic antioxidant Trolox^®. UPLC‐MS/MS screening of these fractions for the presence of selected mono‐ and di‐caffeoylquinic acids revealed large quantities of 1,5‐dicaffeoylquinic acid present in several fractions (853.052–907.324 μg mg^?1), respectively. Due to the antioxidant potency and high levels of 1,5‐dicaffeoylquinic acid observed in these fractions, it was concluded that specifically this chlorogenic acid derivative is a major contributor to the antioxidant efficacy of dandelion root.