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Graphene has attracted enormous attention over the past years in condensed matter physics. The most interesting feature of graphene is that its low-energy excitations are relativistic Dirac fermions. Such feature is the origin of many topological properties in graphene-like physics. On the other hand, ultracold quantum gas trapped in an optical lattice has become a unique setting for quantum simulation of condensed matter physics. Here, we mainly review our recent work on quantum simulation of graphene-like physics with ultracold atoms trapped in a honeycomb or square optical lattice, including the simulation of Dirac fermions and quantum Hall effect with and without Landau levels. We also present the related experimental advances. [ABSTRACT FROM AUTHOR]

The article discusses synthesis of aromatic amide foldamers which are chain of molecules and oligomers that adopts secondary structure of proteins stabilized by non covalent interactions. The molecular design and development of hydrogen bonding patterns in aromatic amide foldamers is discussed. It also refers to design principles and basic synthetic strategies that should be employed for preparation of foldamers.

Monopoles play a center role in gauge theories and topological matter. There are two fundamental types of monopoles in physics: vector monopoles and tensor monopoles. Examples of vector monopoles include the Dirac monopole in three dimensions and Yang monopole in five dimensions, which have been extensively studied and observed in condensed matter or artificial systems. However, tensor monopoles are less studied, and their observation has not been reported. Here we experimentally construct a tunable spin-1 Hamiltonian to generate a tensor monopole and then measure its unique features with superconducting quantum circuits. The energy structure of a 4D Weyl-like Hamiltonian with threefold degenerate points acting as tensor monopoles is imaged. Through quantum-metric measurements, we report the first experiment that measures the Dixmier-Douady invariant, the topological charge of the tensor monopole. Moreover, we observe topological phase transitions characterized by the topological Dixmier-Douady invariant, rather than the Chern numbers as used for conventional monopoles in odd-dimensional spaces. [ABSTRACT FROM AUTHOR]

A Berry curvature is an imaginary component of the quantum geometric tensor (QGT) and is well studied in many branches of modern physics; however, the quantum metric as a real component of the QGT is less explored. Here, by using tunable superconducting circuits, we experimentally demonstrate two methods to directly measure the quantum metric tensor for characterizing the geometry and topology of underlying quantum states in parameter space. The first method is to probe the transition probability after a sudden quench, and the second one is to detect the excitation rate under weak periodic driving. Furthermore, based on quantum metric and Berry-curvature measurements, we explore a topological phase transition in a simulated time-reversal-symmetric system. The work opens up a unique approach to explore the topology of quantum states with the QGT. [ABSTRACT FROM AUTHOR]

We experimentally explore the topological Maxwell metal bands by mapping the momentum space of condensed-matter models to the tunable parameter space of superconducting quantum circuits. An exotic band structure that is effectively described by the spin-1 Maxwell equations is imaged. Threefold degenerate points dubbed Maxwell points are observed in the Maxwell metal bands. Moreover, we engineer and observe the topological phase transition from the topological Maxwell metal to a trivial insulator, and report the first experiment to measure the Chern numbers that are higher than one. [ABSTRACT FROM AUTHOR]

We study the dynamics of a transverse-field XY chain driven across quantum critical points by noisy control fields. We characterize the defect density as a function of the quench time and the noise strength and demonstrate that the defect productions for three quench protocols with different scaling exponents exhibit the anti-Kibble-Zurek behavior, whereby slower driving results in more defects. The protocols are quenching through the boundary line between paramagnetic and ferromagnetic phases, quenching across the isolated multicritical point, and quenching along the gapless line, respectively. We also show that the optimal quench time to minimize defects scales as a universal power law of the noise strength in all three cases. Furthermore, by using quantum simulation of the quench dynamics in the spin system with well-designed Landau-Zener crossings in pseudomomentum space, we propose an experimentally feasible scheme to test the predicted anti-Kibble-Zurek behavior of this noisy transverse-field XY chain with two-level systems under controllable fluctuations. [ABSTRACT FROM AUTHOR]

Studies on periodic porosity and related properties and functions have been limited to insoluble solid-state materials. Self-assembly provides a straightforward and efficient strategy for the construction of soluble periodic porous supramolecular organic frameworks (SOFs) in water from rationally designed molecular building blocks. From rigid tri- and tetra-armed building blocks and cucurbitu[8]ril (CB[8]), a number of two-dimensional (2D) honeycomb, square and rhombic SOFs can be generated, which is driven by CB[8]-encapsulation-enhanced dimerization of two aromatic units on the periphery of the multi-armed molecules. By utilizing the same three-component host-guest motif as the driving force, three-dimensional (3D) diamondoid and cubic SOFs can be obtained from tetrahedral and [Ru(bipy)3]2+-derived octahedral monomers and CB[8]. All of the 2D and 3D periodic frameworks are soluble in water, and are able to maintain the periodicity as well as the pore sizes in the solid state. 3D SOFs are highly efficient homogeneous polycationic frameworks for reversible adsorption of anionic species including organic dyes, peptides, nucleic acids, drugs, dendrimers and Wells-Dawson-typed polyoxametallates (WD-POMs). WD-POM molecules adsorbed in the [Ru(bipy)3]2+-based SOF can catalyse the reduction of proton to H2 upon visible-light sensitization of [Ru(bipy)3]2+, which allows multiple electron transfer from [Ru(bipy)3]2+ to WD-POM.This review summarizes the design, formation and characterization of this new family of self-assembled frameworks, highlights their applications as homogeneous porous materials and finally outlines some future research directions. [ABSTRACT FROM AUTHOR]

Geometric quantum manipulation and Landau-Zener interferometry have been separately explored in many quantum systems. In this Letter, we combine these two approaches to study the dynamics of a superconducting phase qubit. We experimentally demonstrate Landau-Zener interferometry based on the pure geometric phases in this solid-state qubit. We observe the interference caused by a pure geometric phase accumulated in the evolution between two consecutive Landau-Zener transitions, while the dynamical phase is canceled out by a spin-echo pulse. The full controllability of the qubit state as a function of the intrinsically robust geometric phase provides a promising approach for quantum state manipulation. [ABSTRACT FROM AUTHOR]

The monomer 1 derived from achiral 1-(aminoxy)cyclopropanecarboxylic acid (OAcc) and oligopeptides 2-9 consisting of a chiral α-aminoxy acid and an achiral α-aminoxy acid such as OAcc were synthesized and their structures characterized. The eight-membered-ring intramolecular hydrogen bond, namely the α N-O turn, was formed between adjacent residues independent of their chirality. However, the helix formation was sequence-dependent. Dipeptide 2 bearing chiral α-aminoxy acid (D-OAA) at the N-terminus and achiral OAcc at the C-terminus preferentially adopted a right-handed 1.88 helical structure, but dipeptide 3 (OAcc-D-OAA) did not. Theoretical calculation results, in good agreement with experimental ones, revealed that the biased handedness of α N-O turn found in OAcc residue depends on its preceding chiral residue. It was then found that the helical conformation was destroyed in the case of oligopeptides 6 and 7 [OAA-(OAcc)n, n = 2, 3]. The crystal structure of tripeptide 8 (iPrCO-D-OVal-OAcc-D-OVal-NHiBu) further disclosed the helical structure formed by three consecutive homochiral α N-O turns. This study has uncovered achiral aminoxy acid residues such as the OAcc unit as a useful building block to be incorporated into chiral aminoxy peptides to mimic chiral helix structure. [ABSTRACT FROM AUTHOR]

The self-assembly of a diamondoid woven supramolecular metal-organic framework wSMOF-1 has been achieved from intertwined [Ru(tpy)2]2+ (tpy=2,2',6',2"-terpyridine) complex M1 and cucurbit[8]uril (CB[8]) in water, where the intermolecular dimers formed by the appended aromatic arms of M1 are encapsulated in CB[8]. wSMOF-1 exhibits ordered pore periodicity in both water and the solid state, as confirmed by a combination of ¹H NMR spectroscopy, UV-vis absorption, isothermal titration calorimetry, dynamic light scattering, small angle X-ray scattering and selected area electron diffraction experiments. The woven framework has a pore aperture of 2.1 nm, which allows for the free access of both secondary and primary alcohols and tert-butyl hydroperoxide (TBHP). Compared with the control molecule [Ru(tpy)2]Cl2, the [Ru(tpy)2]2+ unit of wSMOF-1 exhibits a remarkably higher heterogeneous catalysis activity for the oxidation of alcohols by TBHP in nhexane. For the oxidation of 1-phenylethan-1-ol, the yield of acetophenone was increased from 10% to 95%. [ABSTRACT FROM AUTHOR]

Morpholine and methylpiperazine are among the most important structural parts of different drugs including organic chemotherapeutic agents. In the current study we incorporated these entities as co-ligand and a series of structurally related mono- and di-metallic square planner Pt(II) complexes (Pt(II)(salicylaldimine)(morpholine)Cl C1a-C3a, Pt(II)(salicylaldimine) (methylpiperazine)Cl C1b-C3b, di-metallic Pt(II)2(bis-salicylaldimine)(morpholine)2Cl2C4a and Pt(II)2(bis-salicylaldimine)(methylpiperazine)2Cl2C4b were prepared. These complexes were characterized by ¹H, 13C, 19F, 2D NOESY NMR, HR ESI-MS and elemental analyses, while structures of C2a, C3a and C4b were determined by single crystal X-ray analysis. All these complexes were studied for their in vitro cytotoxic effect on breast (MCF-7), liver (HepG2) and lung (A549) cancer cell lines. All these complexes showed considerable cytotoxic effect on these tested cancer cell lines comparable to cisplatin. Moreover three complexes C1a, C4a and C1b were studied in details. Time- and dose-dependent study was performed for C1a, C4a and C1b. These complexes induced the expression of p53 that suppresses cancer cell growth. Induction of PUMA gene and repression of MYC oncogene suggested that these complexes targeted different genes to suppress cancer progression. TUNEL assay showed induction of apoptosis and invasion analysis showed reduction in invasion ability of breast cancer cells treated with C1a, C4a or C1b. Importantly, these novel complexes suppressed the expression of EMT and metastasis promoter genes. Similarly these complexes induced autophagy by enhancing the expression of autophagy related genes such as beclin, atg-5 and atg-7. The E. coli growth retardation study showed stronger growth inhibitory effects and subsequently resulted in filamentous morphology of bacterial cells. Gel electrophoresis study proved the interaction of these complexes with DNA. All these analysis revealed anticancer potencies of this class of complexes. [ABSTRACT FROM AUTHOR]

Two rigid N-monosulfonylated 1,3-diamine ligands have been prepared starting from commercially available d-camphor through three steps. Their reactions with [Ru(η6-arene)(μ-Cl)Cl]2 (arene = p-cymene or C6H5CO2Et) or [Ir(η5-C5Me5)(μ-Cl)Cl]2 afforded five new complexes. The structures of one monosulfonamide 1,3-diamine ligand and three organometallic complexes were confirmed by X-ray crystallography. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis of two series of rigid macrocycles from hydrogen bonding-induced folded aryl amide and hydrazone oligomers that bear two amines or one amine and one aldehyde. The diamines reacted with diacyl chloride to produce amide macrocycles, whereas the latter underwent self-coupling reactions to afford imine macrocycles. DFT calculations revealed that the new macrocycles possess rigid planar conformations and their cavity diameters were estimated to be 1.86 nm-2.75 nm. [ABSTRACT FROM AUTHOR]

This paper describes an intermolecular benzene-pentafluorobenzene stacking-promoted anti-parallel arrangement of side-chain-free γ-, δ-, and ϵ-dipeptides. Three diamides have been prepared from γ-, δ-, and ϵ-amino acids with a benzene ring and a pentafluorobenzene ring attached to their C- and N-terminals, respectively. Their crystal structures showed that all the compounds formed intermolecular benzene- pentafluorobenzene stacking, which guided the molecules to arrange in a ruler-styled pattern and the aliphatic backbones to adopt extended sheet-like conformations. Shorter control compounds also gave rise to a similar intermolecular aromatic stacking, but the central aliphatic amide chains adopted different conformations. [ABSTRACT FROM AUTHOR]

We have developed a regiospecific and highly stereoselective strategy for constructing the five-/sixmembered monocyclic and bicyclic nitrogen heterocycle skeletons using PhSe group transfer radical cyclization of α-phenylseleno amido esters promoted by a Lewis acid (e.g., Yb(OTf)3) under UV irradiation. We obtained 5-/6-exo-trig mode cyclization products for the N-allyl/homoallyl substrates, whereas the enamide substrate gave 5-endo-trig ring closure. [ABSTRACT FROM AUTHOR]

A series of chiral β³-aminoxy acids or amides with various side chains have been synthesized via two different approaches. One is the Arndt­Eistert homologation approach, using chiral aa-aminoxy acids as starting materials. The other approach, utilizing the enantioselective reduction of β-keto esters catalyzed by baker's yeast or chiral Ru(II) complexes, produces chiral β³-aminoxy acids with nonproteinaceous side chains. The oligomers of β³-aminoxy acids can be readily prepared using EDCI/HOAt as the coupling reagent. [ABSTRACT FROM AUTHOR]

We have investigated using NMR, IR, and CD spectroscopy and X-ray crystallography, the conformational properties of peptides 1-10 of β³-aminoxy acids (NH2OCHRCH2COOH) having different side chains on the β carbon atom (e.g., A = Me, Et, COOBn, CH2CH2CH=CH2, i-Bu, i-Pr). The β N-O turns and β N-O helices that involve a nine-membered-ring intramolecular hydrogen bond between NHi+2 and COi, which have been found previously in peptides of β2,2-aminoxy acids (NH2OCH2CMe2COOH) are also present in those β³-aminoxy peptides. X-ray crystal structures and NMR spectral analysis reveal that, in the β N-O turns and β N-O helices induced by β³-aminoxy acids, the N-O bond could be either anti or gauche to the Cα-Cβ bond depending on the size of the side chain; in contrast, only the anti conformation was found in β2,2-aminoxy peptides. Both diamide 1 and triamide 9 exist in different conformations in solution and in the solid state: parallel sheet structures in the solid state and Predominantly β N-O turn and β N-O helix conformations in nonpolar solvents. Theoretical studies on a series of model diamides rationalize very well the experimentally observed conformational features of these β³-aminoxy peptides. [ABSTRACT FROM AUTHOR]

The topology of quantum systems has become a topic of great interest since the discovery of topological insulators. However, as a hallmark of the topological insulators, the spin Chern number has not yet been experimentally detected. The challenge to directly measure this topological invariant lies in the fact that this spin Chern number is defined based on artificially constructed wave functions. Here we experimentally mimic the celebrated Bernevig-Hughes-Zhang model with cold atoms, and then measure the spin Chern number with the linear response theory. We observe that, although the Chern number for each spin component is ill defined, the spin Chern number measured by their difference is still well defined when both energy and spin gaps are nonvanished. [ABSTRACT FROM AUTHOR]

A chiral supramolecular alternate block copolymer has been self-assembled from a ureidopyrimidinone (UPy)-terminated arylamide-based hydrogen bonded foldamerand a structurally flexible pentamer, which is driven by the ion-pair binding of the two arylamide segments toward chiral ammonium and carboxylate guests. [ABSTRACT FROM AUTHOR]

We describe an efficient method for the oxidative cleavage of alkynes to carboxylic acids using a combination of RuO2/Oxone/NaHCO3 in a CH3CN/H2O/EtOAc solvent system. Both internal and terminal alkynes, regardless of their electron density, can be oxidized to carboxylic acids in excellent yield (up to 99%). ¹H NMR spectroscopy and ESIMS experiments provided evidence for α-diketones and anhydrides as possible intermediates in these oxidation reactions. [ABSTRACT FROM AUTHOR]

The article reports that the carboxylate group is an anionic entity of prime importance in nature. Enzymes, antibodies, amino acids, and metabolic intermediates, as well as the other natural products, contain a range of carboxylate functionalities that account for the characteristic biochemical behavior. Enantioselective recognition of carboxylates has important implications in asymmetric synthesis and drug discovery. Although many enantioselective carboxylate receptors have shown their application in chiral resolution, few such receptors can be used as chiral shift reagents to determine enantiomeric purities of chiral carboxylic acids by HNMR accurately because of either their structural complexity or their H chemical shift non equivalences that are too small to realize baseline resolution.