Although several groups have synthesized dual-emission carbon dots (D-CDs) and paid more attention to their emission centers in recent years, the luminescence mechanism of D-CDs is still unclear. Here, we synthesized multiemission CDs via the one-pot hydrothermal method. The prepared CDs exhibit three fluorescence (FL) emissions (370, 425, and 505 nm) under one-wavelength excitation of 320 nm. In addition, various emission origins dominate the unique multiemission property, which is illuminated by means of the radiation decay process, CD internal graphite domains, and abundant functional group characterization. The characterization results fully indicate that there are three energy states: band gap state (carbon-core state), surface defect state, and molecular state. In addition, the peculiar concentration-dependent and polarity-modulated properties further support the explanation of CD multienergy states. Strikingly, the CD FL quantum yield is up to 50.68%. As CDs can show bright green FL excited over 400 nm, the color of concentrated CD solution incredibly turns from maroon to green in visible light observed from different angles. Our findings mainly account for this luminescence mechanism of CDs. This work utilizes time-resolved emission spectra for the first time to distinguish and identify multiemission origins, which would provide scientific inspiration for finding effective ways to regulate or control these luminescence processes.

Oligosaccharide synthesis is hindered by the need for multiple steps as well as numerous selective protections and deprotections. Herein we report a highly efficient de novo route to various oligosaccharide motifs, of use for biological and medicinal structure activity studies. The key to the overall efficiency is the judicious use of asymmetric catalysis and synthetic design. These green principles include the bidirectional use of highly stereoselective catalysis (Pd(0)-glycosylation/post-glycosylation). In addition, the chemoselective use of C-C and C-O π-bonds functionality, as atom-less protecting groups as well as an anomeric directing group (via a Pd-π-allyl), highlights the atom economical aspects of the route to a divergent set of natural and unnatural oligosaccharides (i.e., various D-/L-diastereomers of oligosaccharide as well as deoxysugars which lack C-2 anomeric directing groups). For example, in only 12 steps, the construction of a highly branched hepta-saccharide with 35 stereocenters was accomplished from an achiral acylfuran.

We demonstrate that incorporation of MnSalen into a protein scaffold enhances the chemoselectivity in sulfoxidation of thioanisole and found that both the polarity and hydrogen bonding of the protein scaffold play an important role in tuning the chemoselectivity.Metalloenzymes have set a golden standard for carrying out reactions with high reactivity and selectivity. Understanding how proteins confer such reactivity and selectivity is important not only to providing deeper insight in biological functions, but also to its application in chemical transformations. [1][2][3][4][5][6][7][8][9][10][11] Toward this goal, much work has focused on the study of native metalloenzymes, such as cytochrome P-450s, a metalloenzyme with high chemoselectivity in the oxidation of C-H bonds. [12][13][14] These studies indicate that the protein scaffold is capable of creating the proper environment to modulate the reactive pathways of active intermediates so as to inhibit side reactions such as over oxidization. In contrast to the tremendous progress made in biochemical and biophysical studies of native metalloenzymes and their variants, much less has been reported regarding the application of the insight gained from such studies for designing artificial enzymes. In addition to testing our knowledge of metalloenzymes, designing artificial enzymes can provide new information that otherwise may be difficult to obtain from studying native enzymes. 1-8, 12, 15 By carefully choosing protein scaffolds that are small, stable and easy to produce, such artificial enzymes may find interesting applications in chemical transformations to generate fine chemical intermediates. An emerging area in artificial enzyme design is the incorporation of non-native metal catalysts into proteins to expand the reactivity and functionality of metalloenzymes, thus transforming achiral and water-insoluble metal catalysts into asymmetric aqueous solution catalysts for reactions such as sulfoxidation, hydrogenation, and cycloaddition (Diels-Alder reaction). 7,8,[16][17][18][19][20][21][22][23][24] A notable bonus to such an approach is the opportunity to compare how the selectivity of the metal catalyst can be fine-tuned using biological and chemical approaches. 7 Understanding how such systems control catalysis can enrich our knowledge of catalyst design, generating more selective catalysts. The majority of artificial metalloenzyme design studies have been devoted to exploring the use of the protein scaffold to tune enantioselectivity. 7,8,[16][17][18][19] However, learning to control chemoselectivity in these artificial biocatalysts, especially in catalytic oxidation, is equally important. To demonstrate the ability of the protein scaffold to tune the oxidative reactivity of metal catalysts and to discover factors involved in tuning such chemoslectivity, we report here that introducing manganese salen (salen=N,N′-bissalicylidene-1,2-ethanediamino anion, MnSalen, 1) as a non-native metal cofactor into apo NIH-PA Author ManuscriptNIH-PA Author Manuscri...

New Cu-doped dual-emission carbon dots (D-CDs) were synthesized rapidly and simply via a one-pot solvothermal method, and its special photoluminescence mechanism was studied. D-CDs have two fluorescence (FL) emission peaks under one-wavelength excitation and can be used as dual-signal sensor which is usually designed with two or more substances. The prepared CDs show excellent water solubility, photostability, salt tolerance, oxidation resistance, and special optical properties. The raw material ratio, solvent, pH, time, and synthesis temperature were optimized. The characterizations of CDs including transmission electron microscopy, X-ray photoelectron spectroscopy, inductively coupled plasma spectroscopic analysis, X-ray diffraction assignation of phases, thermogravimetric analysis and differential scanning calorimetry, Fourier transform infrared (FTIR) spectroscopy, FL spectrum, and ultraviolet-visible spectrum (UV-vis) were conducted. The investigation on mechanism indicates that the unique dual-emissive property is mainly caused by the energy-level gaps generated by the surface defects of CDs. The prepared D-CDs have good potential in dual-signal analysis and visualization sensing. To demonstrate the practical application, ferric ions, vitamin A acetate, and pH have been determined successfully.

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