In this paper, the origins of enantioselectivity in asymmetric ketone hydrogenation catalyzed by RuH(2)(binap)(cydn) (cydn = trans-1,2-diaminocyclohexane) were discussed. Fifteen substrates involving aromatic, heteroaromatic, olefinic and dialkyl prochiral ketones were used to probe the catalytic mechanism and find an effective way to predict the chirality of the products. The calculated results demonstrate that the hydrogen transfer (HT) step from the Ru complex to the ketone substrate is the chirality-determining step in the H(2)-hydrogenation of ketones. The hydrogenation of aromatic-alkyl ketones can give higher enantiomeric excess (ee) values than that of dialkyl ketones. An interesting intermediate (denoted as ) could be formed if there is an α-hydrogen for R/R' groups of the ketone due to the H(2)-H(α) interaction. Two substituent groups of the ketone could rotate around the C=O axis in two directions, clockwise or counter-clockwise. This rotation, with the big or conjugative substituent group away from/toward the closer binap ligand of the Ru catalyst, will form favorable/unfavorable chiral products with an Re-/Si- intermediate structure. On the contrary, if there is no such α-hydrogen in any substituent group of the ketone, ABS and another intermediate (denoted as INT) would not exist. This study indicates that the conjugative effect of the substituent groups of the ketone play an important role in differentiating the R/R' groups of the ketone, while steric and electrostatic effects contribute to a minor extent. Furthermore, the disparity of the R and R' groups of the ketone is of importance in the enantioselectivity and the favorable chiral alcohol is formed when the structure of the conjugative/big substituent group is away from the closer binap ligand of the RuH(2)(binap)(cydn) catalyst. According to the three factors of the substituent group and the fourth quadrant theory, the enantioselectivity of 91 prochiral ketones catalyzed by a series of Ru catalysts were predicted. All of the predictions are consistent with the experimental results.

Two novel complexes were constructed by adsorption of two typical organic molecules, including one electron-donating molecule (TTF = tetrathiafulvalene) and one electron-withdrawing molecule (TCNQ = tetracyanoquinodimethane), on the surface of...

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Using density functional theory calculations, we have analyzed second-order nonlinear optical (NLO) properties of a series of 1À 6, 9, 12). This type of modification can induce evident electron transfer between the graphyne and conjugated chain and decrease the transition energy, resulting in the system exhibiting a large static first hyperpolarizability (β 0 ). The β 0 values of the GY[n]À (CH=CH) m À NH 2 /NO 2 show a monotonously increasing trend with lengthening the À (CH=CH) m À NH 2 /NO 2 chain from m = 1 to 12. Further, the NO 2 -modified system has a higher β 0 value than the corresponding NH 2 -modified system with the same π-conjugated length. Compared with the singlemodified GY[1], the À (CH=CH) m À NH 2 /NO 2 co-modified GY[1] systems exhibit better NLO responses. For GY-[n]À (CH=CH) m À NO 2 , when m = 1À 4, the β 0 value increases with increasing the size of graphyne, while for m = 5, 6, 9, 12, the varying order is reversed. Solvent and frequency dispersion effects are also analyzed. The polarizable environment has a significant influence on hyper-Rayleigh scattering first hyperpolarizability (β HRS ).

Surface enhanced Raman scattering (SERS) is a rapid and nondestructive technique that is capable of detecting and identifying chemical or biological compounds. Sensitive SERS quantification is vital for practical applications, particularly for portable detection of biomolecules such as amino acids and nucleotides. However, few approaches can achieve sensitive and quantitative Raman detection of these most fundamental components in biology. Herein, a noble-metal-free single-atom site on a chip strategy was applied to modify single tungsten atom oxide on a lead halide perovskite, which provides sensitive SERS quantification for various analytes, including rhodamine, tyrosine and cytosine. The single-atom site on a chip can enable quantitative linear SERS responses of rhodamine (10 −6 −1 mmol L −1 ), tyrosine (0.06–1 mmol L −1 ) and cytosine (0.2–45 mmol L −1 ), respectively, which all achieve record-high enhancement factors among plasmonic-free semiconductors. The experimental test and theoretical simulation both reveal that the enhanced mechanism can be ascribed to the controllable single-atom site, which can not only trap photoinduced electrons from the perovskite substrate but also enhance the highly efficient and quantitative charge transfer to analytes. Furthermore, the label-free strategy of single-atom sites on a chip can be applied in a portable Raman platform to obtain a sensitivity similar to that on a benchtop instrument, which can be readily extended to various biomolecules for low-cost, widely demanded and more precise point-of-care testing or in-vitro detection. Electronic Supplementary Material Supplementary material is available in the online version of this article at 10.1007/s40843-022-1968-5.