How Resonance Modulates Multiple Hydrogen Bonding in Self-Assembled Systems.

The secondary electrostatic interaction (SEI) has been regarded as the fundamental cause for the relative strengths of multiple hydrogen bonds for decades, though recent studies challenged its validation. Here, we used our developed block-localized wave function (BLW) method, which is a variant of ab initio valence bond (VB) theory and can self-consistently derive the wave function for a strictly electron-localized state, to study a series of exemplary multiply hydrogen-bonded complexes and critically examine the role of SEI in the binding. Our computations show that the multiple hydrogen bond in self-assembled complexes is a kind of resonance-assisted hydrogen bond (RAHB) in nature, and the π resonance which moves electron density from the hydrogen bond donor to the acceptor is the true origin of the different hydrogen bond strengths. By quenching the π resonance effect, the hydrogen bond strengths become nearly identical for various neutral doubly, triply, and quadruply hydrogen-bonded dimers where in general the SEI model works. In other words, the SEI plays only a minor role in multiply hydrogen-bonded complexes, and the π resonance, which changes not only electron densities but also molecular polarities (dipole moments), is the major force

Real-space sampling of terahertz waveforms with sub-nanometer spatial resolution

Terahertz scanning tunneling microscopy (THz-STM) has emerged as a potent technique for probing ultrafast nanoscale dynamics with exceptional spatiotemporal precision, whereby the acquisition of THz near-field waveforms holds paramount significance. While substantial efforts have been dedicated to retrieving the waveform utilizing the photoemission current or a molecular sensor, these methods are challenged by intensive thermal effects or complex sample preparations. In this study, we introduce a universal approach for real-time characterization of THz near-field waveforms within the tunnel junction, achieving sub-nanometer spatial resolution. Utilizing the gating mechanism intrinsic to the STM junction, coherent scanning of a gated strong THz pulse over a weak THz pulse is achieved, facilitating direct measurement of the waveform. Notably, employing a custom-built Carrier-Envelope Phase (CEP) shifter, THz-CEP has been successfully characterized in the tunnel junction. Furthermore, THz spectral imaging through point-to-point sampling of THz waveforms on a triatomic Au (111) step has been demonstrated, highlighting the sub-nanometer spatial resolution of our sampling methodology.Comment: 26 pages and 4 figures for the manuscript; 16 pages and 7 figures for the Supporting Informatio

Two Push-Pull Channels Enhance the Dinitrogen Activation by Borylene Compounds.

Recently, Braunschweig et al found that borylene (CAAC)DurB, where CAAC is a cyclic alkyl(amino) carbene and Dur refers to 2,3,5,6-tetramethylphenyl, can bind and activate N2, and the resulting [(CAAC)DurB]2N2 is of a bent BNNB core. Since the N2 ligand in transition metal complexes is generally linear, here we probed the bonding nature of both terminal end-on and end-on bridging borylene-N2 complexes with the valence bond (VB) theory. In the terminal end-on (CAAC)HBN2 the bonding follows the mechanism in transition metals with a σ donation and a π back-donation, but in the end-on bridging borylene-N2 complex, the σ donation comes from the π orbitals of N2 and thus there are two opposite and perpendicular push-pull channels. It is the push-pull interaction that governs the enhanced activation of N2 and the BNNB bent geometry. It is expected that the substituents bonded to B can modulate the bent angle and the strength of the push-pull interaction. Indeed, (CAAC)FB exhibits enhanced catalytic capacity for the activation of N2

Cloud-Magnetic Resonance Imaging System: In the Era of 6G and Artificial Intelligence

Magnetic Resonance Imaging (MRI) plays an important role in medical diagnosis, generating petabytes of image data annually in large hospitals. This voluminous data stream requires a significant amount of network bandwidth and extensive storage infrastructure. Additionally, local data processing demands substantial manpower and hardware investments. Data isolation across different healthcare institutions hinders cross-institutional collaboration in clinics and research. In this work, we anticipate an innovative MRI system and its four generations that integrate emerging distributed cloud computing, 6G bandwidth, edge computing, federated learning, and blockchain technology. This system is called Cloud-MRI, aiming at solving the problems of MRI data storage security, transmission speed, AI algorithm maintenance, hardware upgrading, and collaborative work. The workflow commences with the transformation of k-space raw data into the standardized Imaging Society for Magnetic Resonance in Medicine Raw Data (ISMRMRD) format. Then, the data are uploaded to the cloud or edge nodes for fast image reconstruction, neural network training, and automatic analysis. Then, the outcomes are seamlessly transmitted to clinics or research institutes for diagnosis and other services. The Cloud-MRI system will save the raw imaging data, reduce the risk of data loss, facilitate inter-institutional medical collaboration, and finally improve diagnostic accuracy and work efficiency.Comment: 4pages, 5figures, letter