Designed synthesis of TS-1 crystals with controllable b-oriented length

TS-1 crystals with controllable b-oriented length (sheet-like morphology, TS-1-S; chain-like morphology, TS-1-C) have been rationally synthesized from addition of organic additives (urea and fluorinated surfactant of FC-4) in the starting titanosilicate gels, and catalytic and adsorptive measurements show that TS-1-S samples are very active in Beckmann rearrangement of cyclohexanone oxime, whereas TS-1-C samples are selective in adsorption for para-xylene.     

Three-dimensional clogging structures of granular spheres near hopper orifice

The characteristic clogging structures of granular spheres blocking three-dimensional granular flow through hopper outlet are analyzed based on packing structures reconstructed using magnetic resonance imaging techniques.Spheres in clogging structures are arranged in a way with typical features of load-bearing,such as more contacting bonds close to the horizontal plane and more mutually-stabilized contact configurations than packing structures away from the orifice.The requirement of load-bearing inevitably leads to the cooperativity of clogging structures with a correlation length of several particle diameters.This correlation length being comparable with the orifice diameter suggests that a clogging structure is composed of several mutually-stabilized structural motifs to span the orifice perimeter,instead of a collection of independent individual spheres to cover the whole orifice area.Accordingly,we propose a simple geometric model to explain the unexpected linear dependence of the average size of three-dimensional clogging structures on orifice diameter.     

Plasmonic Ag/AgBr nanohybrid: synergistic effect of SPR with photographic sensitivity for enhanced photocatalytic activity and stability

A plasmonic Ag/AgBr nanohybrid has been synthesized by in situ thermal reduction of AgBr nanoparticles in polyols. This directly converted Ag/AgBr shows significant absorption over the full visible spectrum. The enhanced light absorption in the spectral region of 450 nm to 800 nm was due to the plasmonic nanosized Ag grown on the surface of AgBr nanoparticles with mixed morphologies and increased sizes. Under visible light irradiation, the plasmonic Ag/AgBr exhibits high activity and stability for the photodegradation of organic pollutants, e.g. methylene blue. The contribution of the SPR and its synergistic effect with the photosensitive AgBr in the photocatalytic activity were verified. Based on the plasmon-mediated charge injection and the band structure of the metal-semiconductor heterojunction, a mechanism of the plasmon synergistically enhanced photocatalytic process was proposed.     

Simultaneous Identification and Quantitative Determination of Amino Acids in Mixture by NMR Spectroscopy Using Chemometric Resolution

Nuclear magnetic resonance (NMR) spectroscopy receives increasing interest in biological and metabolomic studies. It is still, however, a great challenge to analyze the NMR spectra of multicomponent samples, containing overlapping responses of the compositions. In this work, nonnegative independent component analysis (nonnegative ICA) and immune algorithm (IA) were employed for simultaneous identification and quantitative determination of three amino acids in mixture samples from measured multicomponent NMR signals. Results show that the correlation coefficients (R) between the extracted and measured spectra are higher than 0.97 and that those between the calculated relative contents and experimental ones are higher than 0.99. The method may provide an alternative technique for analyzing multicomponent samples like biofluids by using NMR spectroscopy.     

Assembly of multicyclic isoquinoline scaffolds from pyridines: formal total synthesis of fredericamycin A

The construction of an isoquinoline skeleton typically starts with benzene derivatives as substrates with the assistance of acids or transition metals. Disclosed here is a concise approach to prepare isoquinoline analogues by starting with pyridines to react with β-ethoxy α,β-unsaturated carbonyl compounds under basic conditions. Multiple substitution patterns and a relatively large number of functional groups (including those sensitive to acidic conditions) can be tolerated in our method. In particular, our protocol allows for efficient access to tricyclic isoquinolines found in hundreds of natural products with interesting bioactivities. The efficiency and operational simplicity of introducing structural complexity into the isoquinoline frameworks can likely enable the collective synthesis of a large set of natural products. Here we show that fredericamycin A could be obtained via a short route by using our isoquinoline synthesis as a key step.

A concise approach for rapid assembly of multicyclic isoquinoline scaffolds from pyridines and β-ethoxy α,β-unsaturated carbonyl compounds was developed, which enabled the formal total synthesis of fredericamycin A.

Isoquinolines and their derivatives are common structural motifs in numerous natural products. Among them, the analogues of isoquinolines fused with rings from the benzene side such as 8-hydroxyisoquinolin-1[2H]-one (Fig. 1a) have been found in hundreds of natural products with interesting bioactivities.¹ For example, fredericamycin A and the related family members, isolated from Streptomyces griseus, show both antimicrobial and anti-tumor activities.² Ericamycin is a natural product isolated in the culture of Streptomyces varius n. sp. with anti-staphylococcal activities.³ Due to the widespread presence of isoquinolines in both natural and synthetic molecules, numerous approaches have been developed to assemble this class of scaffolds.⁴ The dominated strategies reported to date focus on forming the new pyridine ring of isoquinolines (Fig. 1b, left part). Classic methods include Bischler–Napieralski isoquinoline synthesis,^4a,b Pictet–Gams isoquinoline synthesis,^4a and Pomeranz–Fritsch reaction.^4a These reactions, proven to be useful since as early as 1893,⁵ have their own merits and limitations. For instance, high reaction temperature (e.g. reflux in toluene) and strong acids are typically required and thus functional group tolerance can become challenging. On the other side, the introduction of structural complexities and substitution patterns is constrained as the substrates have to be pre-settled to favor the formation of pyridine moieties. Here we report a new approach to prepare isoquinoline scaffolds by constructing a new benzene ring (Fig. 1b, right part).⁶ Our method starts with pyridine derivatives as the substrates to react with readily available β-ethoxy α,β-unsaturated carbonyl compounds. The reaction cascade involves five main plausible mechanistic processes (Michael addition, Dieckmann condensation, elimination, aromatization and in situ methylation) to furnish isoquinoline-based products with medium to good yields. The tricyclic isoquinoline-containing products might serve as formal common starting points for rapid total synthesis of a large number of natural products, such as those exemplified in Fig. 1a. In the present study, we demonstrate that starting from the tricyclic isoquinoline adduct 6a prepared using our method, fredericamycin A can be synthesized in 8 steps (Fig. 1c). Our strategy for isoquinoline assembly offers complementary and in certain cases better solutions not readily provided by the classic methods. We expect our method to find impressive applications in concise modular synthesis of complex natural products and molecular libraries, especially those bearing isoquinoline units fused with additional cyclic structures.Open in a separate windowFig. 1Isoquinoline analogues and their synthesis.Our design and initial studies are illustrated in Scheme 1.⁷ We first used pyridine 1a to react with α-substituted cycloenones (2a–2d), in the hope of obtaining isoquinoline 3a as the target product (Scheme 1a). The use of 2a and 2b was inspired by studies from Tamura, in which α-Br in 1,4-naphthoquinone was used as a leaving group to form an aromatic ring.⁸ Unfortunately, no product was formed and most of the starting materials were recovered. When SPh (2c) or SOPh (2d) was incorporated at the α site of the cycloenone, side products 4a and 4b were isolated respectively in moderate yields. The Michael products 4a and 4b could not be further transformed into our desired cyclic product 3a under various conditions. We then studied the use of β-substituted cycloenones (2e–2g) to react with 1a (Scheme 1b). No reactions were observed when 2e or 2f was used. To our delight, when the halogen of 2e/2f was replaced with a methoxy unit (OCH₃, substrate 2g), an encouraging amount of annulation product 3a was detected (10% yield). A side product 5a was also obtained (5% yield) in this initial study and it couldn''t be further transformed into the annulation product 3a under various alkaline conditions. It is noteworthy that, while β-alkoxy cycloenones (specifically, only β-alkoxy cyclohexenones) have been used in Staunton–Weinreb annulation⁹ to prepare fused aromatic compounds, no examples for those containing a heterocyclic aromatic ring were reported.¹⁰ Even for the construction of an aromatic ring without any heteroatom, low yields (mostly ranging from 0 to 30%) often occurred for this type of annulation starting with β-alkoxy cycloenones,⁹ which severely hampered its usage in Staunton–Weinreb annulation for the total synthesis of natural products. Our initial results showcased the possibility of direct assembly of isoquinoline scaffolds from β-methoxy cyclopentenone for the first time, though also in a low yield of 10%.Open in a separate windowScheme 1Proposed routes and initial studies for isoquinoline synthesis.With the initial results in hand, we performed additional condition optimization (11 The β-methoxy cyclopentenone 2g could also react to give 6a in a lower yield of 65% (entry 3). Other bases [such as triethylenediamine (DABCO), diazabicyclo[5.4.0]undec-7-ene (DBU), 4-dimethylaminopyridine (DMAP), lithium bis(trimethylsilyl)amide (LiHMDS) and potassium bis(trimethylsilyl)amide (KHMDS)] gave poorer results with yields ranging from 0 to 42% (entry 4). When THF was changed to other solvents, lower yields (<41%) were obtained (entry 5). Revising the ratio of 1a to 2h from 1 : 1.5 to 1.5 : 1 delivered 6a in 39% to 54% yields (entries 6–8). Lower reaction temperature (e.g. −78 °C) could not improve the outcome of this cascade transformation, but gave 23% yield of 6a together with 16% yield of recovered starting material 2h (entry 9). Long exposure to low temperature in step 1 could also lead to a considerable amount of the undesired elimination product 5a (ca. 29% yield), which was decomposed under the following methylation conditions (step 2). No product was observed in the absence of the methoxy group in 1a as it could stabilize the transition state via the formation of a metallate complex (entry 10).Screening of conditions^a

Voter model in a random environment in ? d

We consider the voter model with flip rates determined by {?? _e , e ?? E _d }, where E _d is the set of all non-oriented nearest-neighbour edges in the Euclidean lattice ? ^d . Suppose that {?? _e , e ?? E _d } are independent and identically distributed (i.i.d.) random variables satisfying ?? _e ? 1. We prove that when d = 2, almost surely for all random environments, the voter model has only two extremal invariant measures: ?? ₀ and ?? ₁.     

Regioselective Acylation of 2＇- or 3＇-Hydroxyl Group in Salicin： Hemisynthesis of Acylated Salicins

Salicin-based phenolic glycosides（PGs） are important defensive substances against herbivore feeding and have good bioactivities. In this work, a novel approach for the synthesis of salicin-based PGs has been developed, by which PGs of 2＇-O-acetylsaliein（5a）, 3＇-O-acetylsalicin（gb） and 3＇-O-benzoylsalicin（Sd） were hemisynthesized. The effects of acylation reagent, solvent and temperature on the regioselective acylation of 2＇- or 3＇-hydroxyl groups of salicin mediated by dibutyltin oxide were investigated. The optimal conditions under which the best regioselectivity reached for 5a-5d were discovered, respectively. Moreover, a tentative tin-oxygen coordination mechanism was put forward to explain the different regioselectivities shown under different conditions.     

Postbuckling analysis and its application to stretchable electronics

A versatile strategy for fabricating stretchable electronics involves controlled buckling of bridge structures in circuits that are configured into open, mesh layouts (i.e. islands connected by bridges) and bonded to elastomeric substrates. Quantitative analytical mechanics treatments of the responses of these bridges can be challenging, due to the range and diversity of possible motions. Koiter (1945) pointed out that the postbuckling analysis needs to account for all terms up to the 4th power of displacements in the potential energy. Existing postbuckling analyses, however, are accurate only to the 2nd power of displacements in the potential energy since they assume a linear displacement–curvature relation. Here, a systematic method is established for accurate postbuckling analysis of beams. This framework enables straightforward study of the complex buckling modes under arbitrary loading, such as lateral buckling of the island-bridge, mesh structure subject to shear (or twist) or diagonal stretching observed in experiments. Simple, analytical expressions are obtained for the critical load at the onset of buckling, and for the maximum bending, torsion (shear) and principal strains in the structure during postbuckling.     

超细荧光聚合物纳米微球的制备

合成了具有较高荧光量子产率(0.69)和良好光稳定性的可聚合荧光染料单体,该荧光染料的光稳定性高于商品化的染料罗丹明B。 通过氧化还原引发剂引发乳液聚合制备了超细荧光聚合物纳米微球,将染料分子共价连接在聚合物链上。 使用非离子表面活性剂Triton X-100作为乳化剂、甲基丙烯酸甲酯(MMA)作为单体和助乳化剂,制备的超细纳米微球平均粒径为22 nm,而不加MMA时制备出的纳米微球平均粒径在150 nm左右。 由于微球表面带有苄氯基团,为进一步的微球功能化提供了途径。