Expanding the Chemistry of Polyoxygenated Heterocycles

Heterocyclic compounds have undisputed significance in disciplines that stretch across chemistry and biology. The ever-growing utility of heterocyclic chemistry spans the development of therapeutic agents, catalysis and ligand design, to the preparation of chemical probes utilized in biological investigations. The chemistry described in this thesis focuses on reaction development for the generation of extensively functionalized polyoxygenated heterocycles and the incorporation of these synthetic tools in the arena of natural product synthesis. Chapter One introduces the dogma of discovering new pharmaceutical leads by acknowledging long-appreciated traditional medicinal knowledge in the context of ethnomycology. The biosynthetic analyses of several key bioactive fungal metabolites are subsequently discussed, underpinning the string of synthetic campaigns presented in this thesis. Chapter Two describes the evolution of a new synthetic method that strategically exploits the intrinsic reactivity of o-benzoquinones within the confines of dibenzofuran synthesis. The nascent idea was brought to maturity with the development of an unconventional approach whereby the target dibenzo[b,d]furan scaffold was directly constructed through the union of simple phenols/naphthols and o-benzoquinones through a Michael-oxidation-oxa-Michael sequence. The scope of this transformation was evaluated with a broad range of phenolic substrates and a tactical insertion of this methodology into a total synthesis endeavor led to a concise synthesis of two dibenzofuran natural products. Chapter Three details a nine-step synthesis of boletopsin 11, a polyoxygenated p-terphenyl dibenzofuran fungal metabolite. Our synthetic approach employs a one-pot oxidation-oxa-Michael sequence ensued by a palladium-catalyzed directed ortho-C(sp2)-H arylation reaction to forge efficiently the entirety of the carbon skeleton. Efforts directed at optimizing the latter reaction revealed a tandem ortho-C(sp2)-H arylation event-an unprecedented mode of reactivity which superseded the scope of the original methodology report. Chapter Four outlines the first total synthesis of suillusin. The molecular framework was constructed in one step using a multicatalytic Michael-benzoin condensation cascade followed by a Rubottom-Swern oxidation strategy to yield the requisite oxidation state of the skeletal framework. The successful completion of the synthesis enabled the investigation of the enantiopurity of the natural isolate and its unexplored biosynthetic origin

STUDENTS’ ENGAGEMENT IN COLLABORATIVE LEARNING GROUP SUPPORTED BY COMMUNICATION TOOLS: AN EMPIRICAL STUDY

Collaborative learning group in higher education is increasingly supported by communication tools, but there are still some problems regarding engagement. We examined students’ engagement in collaborative learning groups with the help of communication tool—Slack. Students’ motivation to engage in teamwork can be promoted through the openness of team members’ effort on Slack. Moreover, free-rider and sucker effect can also be relieved. Teamwork engagement can prompt students’ learning and work satisfaction. We proposed a research model and corresponding hypotheses. Surveys were issued online to graduate students at different time of our course. SmartPLS 3.0 was used to analyze data and test structure equations. We came to conclusions lastly as follows: mutual trust, social influence and reward valence are positively related to teamwork engagement, and teamwork engagement is positively related to personal success (i.e. learning and work satisfaction). However, the moderation role of task complexity between teamwork engagement and personal success is not supported. Theoretical and practical contributions are discussed. Research limitations and future research directions are also presented

Type-II Dirac points and Dirac nodal loops on the magnons of square-hexagon-octagon lattice

We study topological magnons on an anisotropic square-hexagon-octagon (SHO) lattice which has been found by a two-dimensional Biphenylene network (BPN). We propose the concepts of type-II Dirac magnonic states where new schemes to achieve topological magnons are unfolded without requiring the Dzyaloshinsky-Moriya interactions (DMIs). In the ferromagnetic states, the topological distinctions at the type-II Dirac points along with one-dimensional (1D) closed lines of Dirac magnon nodes are characterized by the $\mathbb{Z}_2$ invariant. We find pair annihilation of the Dirac magnons and use the Wilson loop method to depict the topological protection of the band-degeneracy. The Green's function approach is used to calculte chiral edge modes and magnon density of states (DOS). We introduce the DMIs to gap the type-II Dirac magnon points and demonstrate the Dirac nodal loops (DNLs) are robust against the DMIs within a certain parameter range. The topological phase diagram of magnon bands is given via calculating the Berry curvature and Chern number. We find that the anomalous thermal Hall conductivity gives connection to the magnon edge current. Furthermore, we derive the differential gyromagnetic ratio to exhibit the Einstein-de Haas effect (EdH) of magnons with topological features.Comment: arXiv admin note: text overlap with arXiv:2207.0288

Impurity effect of Lambda hyperon on collective excitations of atomic nuclei

Taking the ground state rotational band in $^{24}$Mg as an example, we investigate the impurity effect of $\Lambda$ hyperon on collective excitations of atomic nuclei in the framework of non-relativistic energy density functional theory. To this end, we take into account correlations related to the restoration of broken symmetries and fluctuations of collective variables by solving the eigenvalue problem of a five-dimensional collective Hamiltonian for quadrupole vibrational and rotational degrees of freedom. The parameters of the collective Hamiltonian are determined with constrained mean-field calculations for triaxial shapes using the SGII Skyrme force. We compare the low-spin spectrum for $^{24}$Mg with the spectrum for the same nucleus inside $^{25}_{\Lambda}$Mg. It is found that the $\Lambda$ hyperon stretches the ground state band and reduces the $B(E2:2^+_1 \rightarrow 0^+_1)$ value by $\sim 9$, mainly by softening the potential energy surface towards the spherical shape, even though the shrinkage effect on the average proton radius is only $\sim0.5$.Comment: 16 pages, 5 figures, and 1 tabl

Periodic Loop Solutions and Their Limit Forms for the Kudryashov-Sinelshchikov Equation

The Kudryashov-Sinelshchikov equation is studied by using the bifurcation method of dynamical systems and the method of phase portraits analysis. We show that the limit forms of periodic loop solutions contain loop soliton solutions, smooth periodic wave solutions, and periodic cusp wave solutions. Also, some new exact travelling wave solutions are presented through some special phase orbits

A Bootstrapping Method for Finer-Grained Opinion Mining Using Graph Model

PACLIC 23 / City University of Hong Kong / 3-5 December 200