Resource-Efficient Direct Characterization of General Density Matrix.

Sequential weak measurements allow for the direct extraction of individual density-matrix elements, rather than relying on global reconstruction of the entire density matrix, which opens a new avenue for the characterization of quantum systems. Nevertheless, extending the sequential scheme to multiqudit quantum systems is challenging due to the requirement of multiple coupling processes for each qudit and the lack of appropriate precision evaluation. To address these issues, we propose a resource-efficient scheme (RES) that directly characterizes the density matrix of general multiqudit systems while optimizing measurements and establishing a feasible estimation analysis. In the RES, an efficient observable of the quantum system is constructed such that a single meter state coupled to each qudit is sufficient to extract the corresponding density-matrix element. An appropriate model based on the statistical distribution of errors is utilized to evaluate the precision and feasibility of the scheme. We have experimentally applied the RES to the direct characterization of general single-photon qutrit states and two-photon entangled states. The results show that the RES outperforms sequential schemes in terms of efficiency and precision in both weak- and strong-coupling scenarios. This Letter sheds new light on the practical characterization of large-scale quantum systems and the investigation of their nonclassical properties.

Concentration-Driven Evolution of Adaptive Artificial Ion Channels or Nanopores with Specific Anticancer Activities.

In nature, ceramides are a class of sphingolipids possessing a unique ability to self-assemble into protein-permeable channels with intriguing concentration-dependent adaptive channel cavities. However, within the realm of artificial ion channels, this interesting phenomenon is scarcely represented. Herein, we report on a novel class of adaptive artificial channels, Pn-TPPs, based on PEGylated cholic acids bearing triphenylphosphonium (TPP) groups as anion binding motifs. Interestingly, the molecules self-assemble into chloride ion channels at low concentrations while transforming into small molecule-permeable nanopores at high concentrations. Moreover, the TPP groups endow the molecules with mitochondria-targeting properties, enabling them to selectively drill holes on the mitochondrial membrane of cancer cells and subsequently trigger the caspase 9 apoptotic pathway. The anticancer efficacies of Pn-TPPs correlate with their abilities to form nanopores. Significantly, the most active ensembles formed by P5-TPP exhibits impressive anticancer activity against human liver cancer cells, with an IC50 value of 3.8 µM. While demonstrating similar anticancer performance to doxorubicin, P5-TPP exhibits a selectivity index surpassing that of doxorubicin by a factor of 16.8.

Non-Covalently Stapled H+ /Cl- Ion Channels Activatable by Visible Light for Targeted Anticancer Therapy.

The development of stimuli-responsive artificial H+ /Cl- ion channels, capable of specifically disturbing the intracellular ion homeostasis of cancer cells, presents an intriguing opportunity for achieving high selectivity in cancer therapy. Herein, we describe a novel family of non-covalently stapled self-assembled artificial channels activatable by biocompatible visible light at 442 nm, which enables the co-transport of H+ /Cl- across the membrane with H+ /Cl- transport selectivity of 6.0. Upon photoirradiation of the caged C4F-L for 10 min, 90 % of ion transport efficiency can be restored, giving rise to a 10.5-fold enhancement in cytotoxicity against human colorectal cancer cells (IC50 =8.5 µM). The mechanism underlying cancer cell death mediated by the H+ /Cl- channels involves the activation of the caspase 9 apoptosis pathway as well as the scarcely reported disruption of the autophagic processes. In the absence of photoirradiation, C4F-L exhibits minimal toxicity towards normal intestine cells, even at a concentration of 200 µM.

Membrane-Active Molecular Machines.

Both biological and artificial membrane transporters mediate passive transmembrane ion flux predominantly via either channel or carrier mechanisms, tightly regulating the transport of materials entering and exiting the cell. One early elegant example unclassifiable as carriers or channels was reported by Smith who derivatized a phospholipid molecule into an anion transporter, facilitating membrane transport via a two-station relay mechanism (Smith et al. J. Am. Chem. Soc. 2008, 130, 17274-17275). Our journey toward blurring or even breaking the boundaries defined by the carrier and channel mechanisms starts in January of 2018 when seeing a child swinging on the swing at the playground park. Since then, I have been wondering whether we could build a nanoscale-sized molecular swing able to perform the swing function at the molecular level to induce transmembrane ion flux. Such research journey culminates in several membrane-active artificial molecular machines, including molecular swings, ion fishers, ion swimmers, rotors, tetrapuses and dodecapuses that permeabilize the membrane via swinging, ion-fishing, swimming, rotating, or swing-relaying actions, respectively. Except for molecular ion swimmers, these unconventional membrane transporters in their most stable states readily span across the entire membrane in a way akin to channels. With built-in flexible arms that can swing or bend in the dynamic membrane environment, they transport ions via constantly changing ion permeation pathways that are more defined than carriers but less defined than channels. Applying the same benzo-crown ether groups as the sole ion-binding and -transporting units, these transporters however differ immensely in ion transport property. While the maximal K+ transport activity is achieved by the molecular swing also termed "motional channel" that displays an EC50 value of 0.021 mol % relative to lipid and transports K+ ions at rate 27% faster than gramicidin A, the highest K+/Na+ selectivity of 18.3 is attained by the molecular ion fisher, with the highest Na+/K+ selectivity of 13.7 by the molecular dodecapus. Having EC50 values of 0.49-1.60 mol % and K+/Na+ values of 1.1-6.3, molecular rotors and tetrapuses are found to be generally active but weakly to moderately K+-selective. For molecular ion swimmers that contain 10 to 14 carbon atom alkyl linkers, they all turn out to be highly active (EC50 = 0.18-0.41 mol %) and highly selective (RK+/RNa+ = 7.0-9.5) transporters. Of special note are crown ether-appended molecular dodecapuses that establish the C60-fullerene core as an excellent platform to allow for a direct translation of solution binding affinity to transmembrane ion transport selectivity, providing a de novo basis for rationally designing artificial ion transporters with high transport selectivity. Considering remarkable cytotoxic activities displayed by molecular swings and ion swimmers, the varied types of existing and emerging unconventional membrane transporters with enhanced activities and selectivities eventually might lead to medical benefits in the future.

Erratum: Quantum Radar [Phys. Rev. Lett. 124, 200503 (2020)].

This corrects the article DOI: 10.1103/PhysRevLett.124.200503.

Spin Quantum Heat Engine Quantified by Quantum Steering.

Following the rising interest in quantum information science, the extension of a heat engine to the quantum regime by exploring microscopic quantum systems has seen a boon of interest in the last decade. Although quantum coherence in the quantum system of the working medium has been investigated to play a nontrivial role, a complete understanding of the intrinsic quantum advantage of quantum heat engines remains elusive. We experimentally demonstrate that the quantum correlation between the working medium and the thermal bath is critical for the quantum advantage of a quantum Szilárd engine, where quantum coherence in the working medium is naturally excluded. By quantifying the nonclassical correlation through quantum steering, we reveal that the heat engine is quantum when the demon can truly steer the working medium. The average work obtained by taking different ways of work extraction on the working medium can be used to verify the real quantum Szilárd engine.

Aquafoldmer-Based Aquaporin-like Synthetic Water Channel.

Synthetic water channels were developed with an aim to replace aquaporins for possible uses in water purification, while concurrently retaining aquaporins' ability to conduct highly selective superfast water transport. Among the currently available synthetic water channel systems, none possesses water transport properties that parallel those of aquaporins. In this report, we present the first synthetic water channel system with intriguing aquaproin-like features. Employing a "sticky end"-mediated molecular strategy for constructing abiotic water channels, we demonstrate that a 20% enlargement in angstrom-scale pore volume could effect a remarkable enhancement in macroscopic water transport profile by 15 folds. This gives rise to a powerful synthetic water channel able to transport water at a speed of ∼3 × 109 H2O s-1 channel-1 with a high rejection of NaCl and KCl. This high water permeability, which is about 50% of aquaporin Z's capacity, makes channel 1 the fastest among the existing synthetic water channels with high selectivity.

Quantum Radar.

We propose a quantum metrology protocol for the localization of a noncooperative pointlike target in three-dimensional space, by illuminating it with electromagnetic waves. It employs all the spatial degrees of freedom of N entangled photons to achieve an uncertainty in localization that is sqrt[N] times smaller for each spatial direction than what could be achieved by N-independent photons or by classical light of the same average intensity.

Pyridine/Oxadiazole-Based Helical Foldamer Ion Channels with Exceptionally High K+ /Na+ Selectivity.

Protein channels are characterized by high transport selectivity, which is essential for maintaining cellular function. Efforts to reproduce such high selectivity over the past four decades have not been very successful. We report a novel series of aromatic foldamer-based polymeric channels where the backbone is stabilized by differential electrostatic repulsions among heteroatoms helically arrayed along the helical backbone. Nanotubes averaging 2.3 and 2.7 nm in length mediate highly efficient transport of K+ ions as a consequence of hydrophilic electron-rich hollow cavities that are 3 Šin diameter. Exceptionally high K+ and Na+ selectivity values of 16.3 and 12.6, respectively, are achieved.

Molecular Ion Fishers as Highly Active and Exceptionally Selective K+ Transporters.

We report here a unique ion-fishing mechanism as an alternative to conventional carrier or channel mechanisms for mediating highly efficient and exceptionally selective transmembrane K+ flux. The molecular framework, underlying the fishing mechanism and comprising a fishing rod, a fishing line and a fishing bait/hook, is simple yet modularly modifiable. This feature enables rapid construction of a series of molecular ion fishers with distinctively different ion transport patterns. While more efficient ion transports are generally achieved by using 18-crown-6 as the fishing bait/hook, ion transport selectivity (K+/Na+) critically depends on the length of the fishing line, with the most selective MF6-C14 exhibiting exceptionally high selectivity (K+/Na+ = 18) and high activity ( EC50 = 1.1 mol % relative to lipid).

Experimental Simultaneous Learning of Multiple Nonclassical Correlations.

Nonclassical correlations can be regarded as resources for quantum information processing. However, the classification problem of nonclassical correlations for quantum states remains a challenge, even for finite-size systems. Although there exists a set of criteria for determining individual nonclassical correlations, a unified framework that is capable of simultaneously classifying multiple correlations is still missing. In this Letter, we experimentally explored the possibility of applying machine-learning methods for simultaneously identifying nonclassical correlations. Specifically, by using partial information, we applied an artificial neural network, support vector machine, and decision tree for learning entanglement, quantum steering, and nonlocality. Overall, we found that, for a family of quantum states, all three approaches can achieve high accuracy for the classification problem. Moreover, the run time of the machine-learning methods to output the state label is experimentally found to be significantly less than that of state tomography.

Molecular Swings as Highly Active Ion Transporters.

Ions are transported across membrane mostly via carrier or channel mechanisms. Herein, a unique class of molecular-machine-inspired membrane transporters, termed molecular swings is reported that utilize a previously unexplored swing mechanism for promoting ion transport in a highly efficient manner. In particular, the molecular swing, which carries a 15-crown-5 unit as the ion-binding and transporting unit, exhibits extremely high ion-transport activities with EC50 values of 46 nm (a channel:lipid molar ratio of 1:4800 or 0.021 mol % relative to lipid) and 110 nm for K+ and Na+ ions, respectively. Remarkably, such ion transport activities remain high in a cholesterol-rich environment, with EC50 values of 130 (0.045 mol % relative to lipid/cholesterol) and 326 nm for K+ and Na+ ions, respectively.

Pore-Forming Monopeptides as Exceptionally Active Anion Channels.

We describe here a unique family of pore-forming anion-transporting peptides possessing a single-amino-acid-derived peptidic backbone that is the shortest among natural and synthetic pore-forming peptides. These monopeptides with built-in H-bonding capacity self-assemble into an H-bonded 1D columnar structure, presenting three types of exteriorly arranged hydrophobic side chains that closely mimic the overall topology of an α-helix. Dynamic interactions among these side chains and membrane lipids proceed in a way likely similar to how α-helix bundle is formed. This subsequently enables oligomerization of these rod-like structures to form ring-shaped ensembles of varying sizes with a pore size of smaller than 1.0 nm in diameter but sufficiently large for transporting anions across the membrane. The intrinsic high modularity in the backbone further allows rapid tuning in side chains for combinatorial optimization of channel's ion-transport activity, culminating in the discovery of an exceptionally active anion-transporting monopeptide 6L10 with an EC50 of 0.10 µM for nitrate anions.

Combinatorial Evolution of Fast-Conducting Highly Selective K+-Channels via Modularly Tunable Directional Assembly of Crown Ethers.

We describe here a modularly tunable molecular strategy for construction and combinatorial optimization of highly efficient K+-selective channels. In our strategy, a highly robust supramolecular H-bonded 1D ensemble was used to order the appended crown ethers in such a way that they roughly stack on top of each other to form a channel for facilitated ion transport across the membrane. Among 15 channels that all prefer K+ over Na+ ions, channel molecule 5F8 shows the most pronounced optimum for K+ while disfavoring all other biologically important cations (e.g., Na+, Ca2+ and Mg2+). With a K+/Na+ selectivity of 9.8 and an EC50 value of 6.2 µM for K+ ion, 5F8 is clearly among the best synthetic potassium channels developed over the past decades.

Surprisingly High Selectivity and High Affinity in Mercury Recognition by H-Bonded Cavity-Containing Aromatic Foldarands.

In the absence of macrocyclic ring constraints, few synthetic systems, possessing a mostly solvent-independent well-folded conformation that is predisposed for highly selective and high affinity recognition of metal ions, have been demonstrated. We report here such a unique class of conformationally robust modularly tunable folding molecules termed foldarands that can recognize Hg2+ ions surprisingly well over 22 other metal ions. Despite the lack of sulfur atoms and having only oxygen-donor atoms in its structure, the best foldarand molecule, i.e., tetramer 4, exhibits a selectivity factor of at least 19 in differentiating the most tightly bound Hg2+ ion from all other metal ions, and a binding capacity that is ≥18 times that of thio-crown ethers. These two noteworthy binding characters make possible low level removal of Hg2+ ions. With a [4]:[Hg2+] molar ratio of 5:1 and a single biphasic solvent extraction, the concentration of Hg2+ ions could be reduced drastically by 98% (from 200 to 4 ppb) in pure water. 4 could also effect a highly efficient reduction in mercury content by 98% (from 500 to 10 ppb) in artificial groundwater via multiple successive extractions with an overall consumption of 4 being 9:1 in terms of [4]:[Hg2+] molar ratio.

Rapid Room-Temperature Gelation of Crude Oils by a Wetted Powder Gelator.

Phase-selective organogelators (PSOGs) not only exhibit ability to phase-selectively congeal oil from oily water but also allow easy separation of gelled oil from the body of water. However, all hitherto reported PSOGs either necessitate carrier solvents for their dissolution or suffer from an extremely slow action in gelling oil in the powder form. A previously unexplored generally applicable wetting strategy is now described to dramatically enhance, by up to two orders of magnitude, gelling speed of the resultant wet but non-sticky gelator in the powder form in crude oils of widely ranging viscosities. Such unprecedented rapid gelling speeds enable rapid gelation of six types of (un)weathered crude oils within minutes at room temperature, making PSOGs one step closer to their eventual practical uses as one of important oil spill control technologies.

Low-Cost Phase-Selective Organogelators for Rapid Gelation of Crude Oils at Room Temperature.

Frequent marine oil spills pose a significant threat to the environment and marine's ecosystem. We have recently reported a highly tunable molecular gelling scaffold, which enables us to identify a few first examples of phase-selective organogelators (PSOGs) that can instantly gel the crude oil of various types with room-temperature operation. In this study, we demonstrate the high robustness and reliability of this modular gelling scaffold in consistently and combinatorially producing high capacity PSOGs. Such a unique feature has allowed us to carry out a systematic study of 48 gelators via a two-step screening process and to discover another powerful carboxybenzyl-based gelator with comparable gelling properties but with a cost lowered by more than 300%, pointing to a good commercial potential for rapid cleanup of oil spills while effectively eliminating environmental pollution caused by the spilled oil.

Silica-based nanocapsules: synthesis, structure control and biomedical applications.

Synergistically combining the merits of silica (e.g., mechanical robustness, biocompatibility and great versatility in surface functionalization) and capsular configurations (e.g., a large inner cavity, low density and favourable colloidal properties), silica-based nanocapsules (SNCs) with a size cutoff of ∼100 nm have gained growing interest in encapsulating bioactive molecules for bioimaging and controlled delivery applications. Within this context, this review provides a comprehensive overview of the synthetic strategies, structural control and biomedical applications of SNCs. Special emphasis is placed on size control at the nanoscale and material composition manipulation of each strategy and the newly emerging synthetic strategies. The applications of SNCs in bioimaging/diagnosis and drug delivery/therapy and the structure engineering that is critically important for the bio-performance of SNCs are also addressed in this review.

Intramolecularly Hydrogen-Bonded Aromatic Pentamers as Modularly Tunable Macrocyclic Receptors for Selective Recognition of Metal Ions.

Despite the tremendous progress that has been made in macrocyclic chemistry since the discovery of corands, cryptands, and spherands more than four decades ago, macrocyclic systems possessing a high level of controllability in structural configuration concurrent with a systematic tunability in function are still very rare. Employing an inner design strategy to orient H-bonding forces toward a macrocyclic cavity interior while convergently aligning exchangeable ion-binding building blocks that dictate a near-identical backbone curvature, we demonstrate here a novel pentagonal framework that not only enables its variable interior cavity to be maintained at near-planarity but also allows its ion-binding potential to be highly tunable. The H-bonded macrocyclic pentamers thus produced have allowed a systematic and combinatorial evolution of ion-selective pentamers for preferential recognition of Cs(+), K(+), or Ag(+) ions.

An artificial tongue fluorescent sensor array for identification and quantitation of various heavy metal ions.

Herein, a small-molecule fluorescent sensor array for rapid identification of seven heavy metal ions was designed and synthesized, with its sensing mechanism mimicking that of a tongue. The photoinduced electron transfer and intramolecular charge transfer mechanism result in combinatorial interactions between sensor array and heavy metal ions, which lead to diversified fluorescence wavelength shifts and emission intensity changes. Upon principle component analysis (PCA), this result renders clear identification of each heavy metal ion on a 3D spatial dispersion graph. Further exploration provides a concentration-dependent pattern, allowing both qualitative and quantitative measurements of heavy metal ions. On the basis of this information, a "safe-zone" concept was proposed, which provides rapid exclusion of versatile hazardous species from clean water samples based on toxicity characteristic leaching procedure standards. This type of small-molecule fluorescent sensor array could open a new avenue for multiple heavy metal ion detection and simplified water quality analysis.