The anti-hyperglycemic effect of metformin is believed to be caused by its direct action on signaling processes in hepatocytes, leading to lower hepatic gluconeogenesis. Recently, metformin was reported to alter the gut microbiota community in humans, suggesting that the hyperglycemia-lowering action of the drug could be the result of modulating the population of gut microbiota. However, the critical microbial signaling metabolites and the host targets associated with the metabolic benefits of metformin remained elusive. Here, we performed metagenomic and metabolomic analysis of samples from individuals with newly diagnosed type 2 diabetes (T2D) naively treated with metformin for 3 d, which revealed that Bacteroides fragilis was decreased and the bile acid glycoursodeoxycholic acid (GUDCA) was increased in the gut. These changes were accompanied by inhibition of intestinal farnesoid X receptor (FXR) signaling. We further found that high-fat-diet (HFD)-fed mice colonized with B. fragilis were predisposed to more severe glucose intolerance, and the metabolic benefits of metformin treatment on glucose intolerance were abrogated. GUDCA was further identified as an intestinal FXR antagonist that improved various metabolic endpoints in mice with established obesity. Thus, we conclude that metformin acts in part through a B. fragilis–GUDCA–intestinal FXR axis to improve metabolic dysfunction, including hyperglycemia.

Thermal stability of CO2 adducts of N-heterocyclic carbenes (NHCs) was studied by means of in situ FTIR method with monitoring of the nu(CO2) region of the infrared spectra under various conditions. 1,3-Bis(2,6-diisopropylphenyl)imidazolinium-2-carboxylate (SIPr-CO2) shows higher thermal stability compared with 1,3-bis(2,6-diisopropylphenyl)imidazolium-2-carboxylate (IPr-CO2). The presence of free CO2 can significantly inhibit the decomposition of NHC-CO2 adducts, while the addition of an epoxide such as propylene oxide has a negative effect on stabilizing these adducts. As zwitterionic compounds, NHC-CO2 adducts were also proved to be effective organic catalysts for the coupling reaction of CO2 and epoxides to afford cyclic carbonates, for which a possible mechanism was proposed. Among these NHC-CO2 adducts, the relatively unstable IPr-CO2 exhibits the highest catalytic activity. The presence of an electrophile such as SalenAlEt could greatly improve the catalytic activity of IPr-CO2 due to intermolecular cooperative catalysis of the binary components.

Volatiles of a wild mandarin, Mangshanyegan (Citrus nobilis Lauriro), were characterized by GC-MS, and their aroma active compounds were identified by aroma extract dilution analysis (AEDA) and gas chromatography-olfactometry (GC-O). The volatile profile of Mangshanyegan was compared with those of other four citrus species, Kaopan pummelo (Citrus grandis), Eureka lemon (Citrus limon), Huangyanbendizao tangerine (Citrus reticulata), and Seike navel orange (Citrus sinensis). Monoterpene hydrocarbons predominated in Mangshanyegan, in particular d-limonene and β-myrcene, which accounted for 85.75 and 10.89% of total volatiles, respectively. Among the 12 compounds with flavor dilution factors (FD) = 27, 8 oxygenated compounds, including (Z)- and (E)-linalool oxides, were present only in Mangshanyegan. The combined results of GC-O, quantitative analysis, odor activity values (OAVs), and omission tests revealed that β-myrcene and (Z)- and (E)-linalool oxides were the characteristic aroma compounds of Mangshanyegan, contributing to the balsamic and floral notes of its aroma.

No abstract

We developed an in vitro DNA detection system using a pair of dCas9 proteins linked to split halves of luciferase. Luminescence was induced upon colocalization of the reporter pair to a ∼44 bp target sequence defined by sgRNAs. We used the system to detect Mycobacterium tuberculosis DNA with high specificity and sensitivity. The reprogrammability of dCas9 was further leveraged in an array design that accesses sequence information across the entire genome.

A novel synergistic effect during supramolecular host-guest encapsulations of core-shell amphiphilic hyperbranched polymers to two kinds of dyes was reported. Two kinds of palmityl chloride-modified hyperbranched polymer, polyamidoamine (HPAMAM10K-C16) and poly(sulfone-amine) (HPSA11K-C16), were used as the hosts of supramolecular encapsulations, and water-soluble dyes such as methyl orange (MO) and methyl blue (MB) were selected as the corresponding guests. In cases of single-dye encapsulations, each host can extract one kind of guest from water phase into chloroform phase with a certain loading capacity (C load ). In the double-dye encapsulations, a pair of dyes, MO and MB, was employed as the guests. The C load increased significantly for one or both of the pair dyes with the C load of the single-dye encapsulation as the reference. This is defined as synergistic encapsulation in this paper. For the HPAMAM10K-C16, C load of MO can be increased by about 100% with the cooperation of MB. For HPSA11K-C16, C load of MB can be raised to a 40-100-fold level of single-dye encapsulation without loss of MO. Experiments with different encapsulating sequence showed that the synergistic encapsulation for HPAMAM10K-C16 is a parallel-type process because the sequence has no significant impact on the C load of each dye, while the case of HPSA11K-C16 is a cascade-type process since the results with different encapsulating order were different. The synergistic encapsulation phenomenon was confirmed by the measurements of 1 H NMR, DSC, and TGA on the resulting dye-encapsulated hyperbranched polymers. In addition, investigations on the guest-host supramolecular systems with different pH indicated that the pH value has certain influence on the synergistic encapsulation C load , but it was not the dominating factor for the synergistic encapsulation. The synergistic effect was found simultaneously in the supramolecular encapsulation of two hosts, indicating this effect is not limited to a peculiar dendritic polymer. The phenomenon presented here will trigger further application of dendritic and other complex polymeric materials in the supramolecular host-guest chemistry.

Footprinting, fluorescence, and x-ray structural information from the initial, promoter-bound complex of T7 RNA polymerase describes the very beginning of the initiation of transcription, whereas recent fluorescence and biochemical studies paint a preliminary picture of an elongation complex. The current work focuses on the transition from an initially transcribing, promoterbound complex to an elongation complex clear of the promoter. Fluorescence quenching is used to follow the melted state of the DNA bubble, and a novel approach using a locally mismatched fluorescent base analog reports on the local structure of the heteroduplex. Fluorescent base analogs placed at positions ؊2 and ؊1 of the promoter indicate that this initially melted, nontranscribed region remains melted as the polymerase translocates through to position ؉8. In progressing to position ؉9, this region of the DNA bubble begins to collapse. Probes placed at positions ؉1 and ؉2 of the template strand indicate that the 5 end of the RNA remains in a heteroduplex as the complex translocates to position ؉10. Subsequent translocation leads to sequential dissociation of the first 2 bases of the RNA. These results show that the initially transcribing complex bubble can reach a size of up to 13 base pairs and a maximal heteroduplex length of 10 base pairs. They further indicate that initial bubble collapse precedes dissociation of the 5 end of the RNA.The recent past has seen a number of structures of RNA polymerases, ranging from RNA polymerase II (1, 2) to a smaller bacterial RNA polymerase (3) to the simplest well studied system: the single-subunit T7 RNA polymerase (4 -7). Structures are available for polymerases without DNA, with DNA bound, and with either a very short initial transcript or with longer transcripts, corresponding to elongation. Lacking in any system, however, is x-ray structural information on the critical transition from an unstable initially transcribing complex (ITC) 1 to a stable elongation complex. This transition occurs at about 10 base pairs (bp) in all RNA polymerases, suggesting that the transition is a fundamental feature of transcription, independent of the specific system (8). What is the nature of the transcription bubble at this critical, early transition point?For the single-subunit RNA polymerase from T7, a crystal structure is available with a 3-base RNA transcript at the active site (7). Modeling from that structure, Cheetham and Steitz (7) predicted that as the polymerase transcribes forward, the enzyme could accommodate no more than a 3-base heteroduplex. Recent results have shown, however, that in a stably elongating complex stalled clear of the promoter, near position ϩ15, the transcription bubble extends about 8 -9 bp upstream of the stall site, consistent with a heteroduplex size of ϳ8 bp (9 -11). Cross-linking studies report that in a complex stalled at position ϩ23, RNA at position Ϫ9 relative to the stall site cross-links to RNA polymerase but not to DNA, whereas RNA at positions closer to the last incorp...

Honeycomb-patterned films made by the self-assembly of polymers have aroused increasing interest because of their fascinating morphology and potential applications. [1][2][3] Although much of the work has focused on linear [1][2][3][4][5][6][7][8][9][10][11][12][13] and star-shaped [1,4] macromolecules, the use of dendritic polymers, with their three-dimensional architectures and unique properties, significantly enlarges the structural diversity and makes multifunctional self-assembly accessible.[14] The combination of supramolecular chemistry and nanotechnology has recently offered an alternative approach to functional selfassembly. Quantum dots (for example, CdSe) [3] and fullerenes [15] have been mixed with polymers to fabricate luminescent honeycomb films. However, the dispersibility of nanomaterials in a polymer matrix is limited, which results in their random distribution in the organized films. It is quite difficult to achieve a dispersion of one substance in another one at a molecular level simply by mixing because of aggregation. To meet this challenge and explore a new area of functional self-assembly, we have shifted our attention from conventional linear macromolecules to hyperbranched polymers.Hyperbranched polymers play a very important role in self-assembly and greatly enrich the range of host materials and building blocks that can be used in supramolecular chemistry. [14,[16][17][18] So far, nanofibers, [16] giant vesicles, [17] and visible tubes [18] have been obtained by the self-assembly of amphiphilic hyperbranched polymers in a solvent. Intriguingly, a core-shell amphiphilic dendritic macromolecule can be regarded as a unimolecular micelle or nanobox [19][20][21] in which small guests, such as dyes, quantum dots, and noble metals, can be loaded. [21][22][23] This property generates the ability for the molecular-level dispersion and distribution of one or even more substances in another one. Accordingly, multifunctional assembled structures would be expected to have applications as the junctions of honeycomb patterned films, in dendritic polymers, and in host-guest chemistry. Herein, we report that honeycomb-patterned films with thicknesses ranging from tens of nanometers to micrometers can be prepared by the molecular self-assembly of amphiphilic hyperbranched poly(amidoamine)s (HPAMAMs). Moreover, the HPAMAMs can encapsulate dye molecules to form colorful host-guest supramolecular complexes. Various luminescent honeycomb-patterned films with tunable emission wavelengths (l em ) were prepared by subsequent nonmolecular self-assembly of the complex on substrates.An amphiphilic hyperbranched polymer, poly(amidoamine) modified with palmitoyl chloride (HPAMAM10K-C16; see the Supporting Information), [23] was chosen as the first material for the construction of the porous films. The films were prepared by dropping a solution of the HPA-MAM10K-C16 in chloroform on to a cleaned substrate (for example, a silicon wafer, quartz, mica, etc.) and then analyzed by SEM, AFM, TEM, and optical fluorescence m...