Artificial intelligence (AI), and, in particular, deep learning as a subcategory of AI, provides opportunities for the discovery and development of innovative drugs. Various machine learning approaches have recently (re)­emerged, some of which may be considered instances of domain-specific AI which have been successfully employed for drug discovery and design. This review provides a comprehensive portrayal of these machine learning techniques and of their applications in medicinal chemistry. After introducing the basic principles, alongside some application notes, of the various machine learning algorithms, the current state-of-the art of AI-assisted pharmaceutical discovery is discussed, including applications in structure- and ligand-based virtual screening, de novo drug design, physicochemical and pharmacokinetic property prediction, drug repurposing, and related aspects. Finally, several challenges and limitations of the current methods are summarized, with a view to potential future directions for AI-assisted drug discovery and design.

Ti2C is one of the thinnest layers in MXene family with high potential for applications. In the present study, the adsorption of NH3, H2, CH4, CO, CO2, N2, NO2, and O2 on monolayer Ti2CO2 was investigated by using first-principles simulations to exploit its potential applications as gas sensor or capturer. Among all the gas molecules, only NH3 could be chemisorbed on Ti2CO2 with apparent charge transfer of 0.174 e. We further calculated the current-voltage (I-V) relation using the nonequilibrium Green's function (NEGF) method. The transport feature exhibits distinct responses with a dramatic change of I-V relation before and after NH3 adsorption on Ti2CO2. Thus, we predict that Ti2CO2 could be a promising candidate for the NH3 sensor with high selectivity and sensitivity. On the other hand, the adsorption of NH3 on Ti2CO2 could be further strengthened with the increase of applied strain on Ti2CO2, while the adsorption of other gases on Ti2CO2 is still weak under the same strain, indicating that the capture of NH3 on Ti2CO2 under the strain is highly preferred over other gas molecules. Moreover, the adsorbed NH3 on Ti2CO2 could be escapable by releasing the applied strain, which indicates the capture process is reversible. Our study widens the application of monolayer Ti2CO2 not only as the battery material, but also as the potential gas sensor or capturer of NH3 with high sensitivity and selectivity.

We review the literature on the use of computational methods to study the reactions between carbon dioxide and aqueous organic amines used to capture CO prior to storage, reuse, or sequestration. The focus is largely on the use of high level quantum chemical methods to study these reactions, although the review also summarizes research employing hybrid quantum mechanics/molecular mechanics methods and molecular dynamics. We critically review the effects of basis set size, quantum chemical method, solvent models, and other factors on the accuracy of calculations to provide guidance on the most appropriate methods, the expected performance, method limitations, and future needs and trends. The review also discusses experimental studies of amine-CO equilibria, kinetics, measurement and prediction of amine pK values, and degradation reactions of aqueous organic amines. Computational simulations of carbon capture reaction mechanisms are also comprehensively described, and the relative merits of the zwitterion, termolecular, carbamic acid, and bicarbonate mechanisms are discussed in the context of computational and experimental studies. Computational methods will become an increasingly valuable and complementary adjunct to experiments for understanding mechanisms of amine-CO reactions and in the design of more efficient carbon capture agents with acceptable cost and toxicities.

A single-electron tetrel bond was predicted and characterized in FXH3···CH3 (X = C, Si, Ge, and Sn) complexes by performing quantum chemical calculations, where the methyl radical acts as the Lewis base and the σ-hole on the X atom in FXH3 as the Lewis acid. The interaction between the methyl radical and FXH3 is characterized by a red shift of F-X stretching frequency. The strength of the tetrel bond becomes stronger by not only increasing the atomic number of the central atom X (X = C, Si, Ge, and Sn) but also by enhancing the electron-withdrawing ability of substituents in the Lewis acid. The energy decomposition analysis highlights the importance of the electrostatic interaction in the formation of the tetrel bond, although the dispersion part is also non-negligible for the weak tetrel bond. There is a competition between the formation of single-electron tetrel bonds and hydrogen bonds for the complexes composed of the methyl radical and CNCH3 or NCCH3. Furthermore, the single-electron tetrel bond exhibits the cooperative effect not only with the hydrogen bond in the complex of NCH···NCCH3···CH3, but also with the conventional tetrel bond in NCCH3···NCCH3···CH3.

Abstract-We demonstrate single laser 32.5 Tbit/s 16QAM Nyquist WDM transmission over a total length of 227 km of SMF-28 without optical dispersion compensation. A number of 325 optical carriers are derived from a single laser and encoded with dualpolarization 16QAM data using sinc-shaped Nyquist pulses. As we use no guard bands, the carriers have a spacing of 12.5 GHz equal to the symbol rate or Nyquist bandwidth of the data. We achieve a net spectral efficiency of 6.4 bit/s/Hz using a softwaredefined transmitter, which generates the electric drive-signals for the electro-optic modulator in realtime.

No abstract

We demonstrate a dual-wavelength passively mode-locked soliton fiber laser based on the single-wall carbon nanotube saturable absorber. By using a simple scheme of adjusting the intracavity loss, the gain profile of the erbium-doped fiber laser is effectively controlled. Besides operating at a single wavelength, the laser is able to simultaneously generate sub-picosecond pulses at both ~1532 and 1557 nm wavelength. The mode-locking wavelength can also be quickly switched from one wavelength to the other by changing the intracavity loss with a tunable attenuator.

Adiabatic and diabatic potential energy surfaces (PES’s) for the interaction of Ar(1S0) with the CN molecule in its ground (X 2Σ+) and first excited (A 2Π) electronic states were determined using multireference configuration-interaction calculations. The three electronically adiabatic potential energy surfaces (PES’s 2A′ and 1A″) are transformed to three diabatic PES’s plus one additional PES which describes the coupling between the two diabatic PES’s of A′ symmetry which correlate asymptotically with the X 2Σ+ and A 2Π states of CN. The appropriate diabatic PES’s are then used in the study of rotationally inelastic scattering of CN(A 2Π) in collisions with Ar. Experimental state-to-state rate constants were measured with an optical–optical double resonance technique. The CN radical was prepared by 193 nm photolysis of BrCN diluted in slowly flowing argon at a total pressure of ∼0.5 Torr. Specific fine-structure Λ-doublet levels of CN(A 2Π,v=3) were prepared by excitation with a pulsed dye laser on various rotational lines in the A 2Π–X 2Σ+(3,0) band, and collisionally populated levels were probed after a short delay by laser fluorescence excitation in the B 2Σ+–A 2Π(3,3) band. State-to-state rate constants, both relative and absolute, were determined for several rotational levels with J=6.5 and 7.5. The final state distributions displayed an even–odd alternation as a function of the final angular momentum J for scattering into certain fine-structure Λ-doublet manifolds. The measured state-to-state rate constants agreed quite well with rate constants derived from quantum scattering calculations with the ab initio CN(A 2Π)–Ar PES’s. The even–odd oscillation in final state populations is ascribed to the near homonuclear character of the PES’s.