Search

Flexible ligands and multinuclear complexes were assembled into nanoscale {P2W18O62} polyoxometalates (POMs) to generate two phosphotungstate hybrid derivatives, (H2bip)2{H2P2 W18O62}·2H2O (1) and (bipy)0.5{Ag-(bipy)2}-{Ag4(bipy)7}-{NaP2W18O62}·H2O (2) (bip = 1,5-bis-(imidazole-1-yl)-pentane; bipy = 2,2′-bipy), via a precursor hydrothermal method. Compound 1 is a bip ligand modified 4,8-connected supramolecular net with {415;612;8}-{45;6}2 topology. In compound 2, the monocore complexes {Ag-(bipy)2} and tetranuclear complexes {Ag4(bipy)7} self-associate to generate two supramolecular chains A and B, respectively, which are further alternately joined together to form a unique metal–organic framework with irregular cavities via weak actions and π–π stacking. The Na-linked {P2W18O62} dipolymers as guest units were embedded into the holes, leading to a 3D supramolecular host–guest assemblies. The capacitive performance test reveals that 2-GCE/-CPE presents improved specific capacitance (802.4 and 752.1 F/g at 3 A/g), cycle efficiency (93.6 and 94.8% after the 5000th cycle), and electrical conductivity compared to the precursor and bip ligand modified compound 1. The electrocatalytic comparative data shows that 2-GCE has enhanced electrochemical redox capacity compared to the precursor and compound 1. Further sensing tests display that 2-GCE shows strong electrochemical responses to H2O2/AA at voltages of −0.41/0.36 V with a lower detection line of 0.33/0.05 μM, a wider linear range of 1.0 μM to 3.18 mM/0.15 μM to 2.33 mM, merit selectivity, and reproducibility. The excellent capacitive and sensing performances are related to increased redox centers, improved ion/electron conversion efficiency, and host–guest structural stability resulting from the introduction of multinuclear complexes, irregular holes, and abundant π–π stacking. This study not only enriches the variety of Dawson-type POMs but also provides a feasible idea for enhancing their electrochemical capacitance and sensing performance. [ABSTRACT FROM AUTHOR]

{P 6 Mo 18 } poly(oxometalate) (POM) clusters have huge steric hindrance and limited active oxygen atoms, which make them difficult to combine with metal-organic units to form three-dimensional (3D) porous structures. Therefore, functionalization of such POMs has always been a bottleneck that is difficult to break through. In this study, {P 6 Mo 18 } POM was successfully grafted on a lock-like metal-organic chain to generate a multiporous coordination polymer, [{Na(H 2 O)(H 2 btb)}{Cu 4 I (H 2 O)(pz) 5 Cl}{H 2 Sr⊂P 6 Mo 2 V Mo 16 VI O 73 }]·3H 2 O ( 1 ) (pz = pyrazine; btb = 1,4-bis(1,2,4-triazole) butane). Meanwhile, a zero-dimensional (0-D) control compound with only btb ligands as counterions, (H 4 btb)[H 4 Sr⊂P 6 Mo 2 V Mo 16 VI O 73 ]·3H 2 O ( 2 ), was also obtained via a hydrothermal reaction. Compound 1 represents the first basket-type 3D poly(oxometalate) metal-organic framework (POMOF) assembly, which possesses interpenetrating pores and complex topology. 1 -GO-CPE displays improved supercapacitor (SC) performance (the specific capacitance of 929.4 F g -1 at a current density of 3 A g -1 with 94.1% of cycle efficiency after 5000 cycles) compared with 2 -GO-CPE and most reported POMOF electrode materials, which may be due to the outstanding redox capability of basket-POM, introduction of metal-organic chains, intersecting pores, and excellent conductivity of graphene. An asymmetric SC device with 1 -GO-CPE as the negative electrode exhibits an energy density of 29.7 Wh kg -1 with a power density of 3148.2 W kg -1 and long-lasting cycling life. In addition, 1 -GO-GCE as an electrochemical sensor responds to dopamine (DA) at a voltage of 0.40 V and shows lower detection limits (0.19 μM (signal-to-noise ratio (SNR) = 3)), higher selectivity, and good reproducibility in the linear range of 0.56 μM to 0.24 mM. The ability to accurately detect the content of DA in biological samples further proves the feasibility of the sensor in practical applications.

This study aims to determine whether sodium butyrate (SB) could antagonize deoxynivalenol (DON)-induced intestinal epithelial dysfunction. In a four-week feeding trial, twenty-eight barrows were randomly divided into four treatments: (1) uncontaminated basal diet (control); (2) 4 mg/kg DON-contaminated diet (DON); (3) basal diet supplemented with 0.2% SB (SB); and (4) 4 mg/kg DON + 0.2% SB (DON + SB). A decrease in performance was observed in DON-exposed animals, which was prevented by the dietary SB supplementation. DON exposure also depressed the expression of host defense peptides (HDPs) in the intestine, impaired the intestinal barrier integrity, and disturbed the gut microbiota homeostasis. These alterations induced by DON were attenuated by SB supplementation. The supplementation of 0.2% SB ameliorated the adverse effects of DON on the liver in terms of hepatic lesions as well as serum concentrations of alkaline phosphatase and aspartate aminotransferase. In IPEC-J2 cells, pretreatment with SB alleviated the DON-induced decreased cell viability. Additionally, the NOD2/caspase-12 pathway participated in the alleviation of SB on DON-induced diminished HDP expression. Taken together, these data demonstrated that SB protected piglets from DON-induced intestinal barrier dysfunction potentially through stimulation of intestinal HDP assembly and regulation in gut microbiota.

This study investigated the potential link between gut microbiota and deoxynivalenol (DON)-induced feed refusal. A total of 24 barrows were randomly divided into one of three diets containing 0.61 (control diet), 1.28, or 2.89 mg DON/kg feed for 28 days. Dietary exposure to DON at 2.89 mg/kg significantly decreased the relative abundances of unclassified_f_Lachnospiraceae, Phascolarctobacterium and Ruminococcaceae_UCG-014, whereas it increased Prevotella_9 and norank_f_Prevotellaceae in the cecal digesta. Moreover, the decreased relative abundance of unclassified_f_Lachnospiraceae induced by DON exposure was positively correlated with average daily feed intake. Exposure to DON increased the serum concentrations of glucagon-like peptide-1 and peptide YY but reduced the levels of serum growth hormone and insulin-like growth factor 1. In summary, these findings suggest that chronic dietary exposure to DON induces disturbances of intestinal microbiota. Disturbed appetite-regulating hormones and somatotropic-axis-hormone secretion induced by negative microbial changes could be the potential mechanisms for DON-induced anorexia.

Recycling of RNA polymerase II (RNAPII) requires dephosphorylation of the C-terminal domain (CTD) of the largest subunit of the polymerase. FCP1 enables the recycling of RNAPII via its CTD-specific phosphatase activity, which is stimulated by the RAP74 subunit of the general transcription factor TFIIF. Both the central (centFCP1) and C-terminal (cterFCP1) domains of FCP1 interact independently and specifically with the C-terminal domain of RAP74 (cterRAP74), suggesting that these interactions mediate the stimulatory effect of TFIIF on the CTD phosphatase activity of FCP1. Phosphorylation of FCP1 by casein kinase 2 on residues in its central (T584) and C-terminal (S942 and S944) domains stimulates its binding to RAP74 and its CTD phosphatase activity. To improve our understanding of the FCP1-RAP74 interactions, we previously determined the NMR structure of a complex formed by human cterRAP74 and cterFCP1. We now present the high-resolution NMR structure and thermodynamic characterization by isothermal titration calorimetry of a complex formed by the same cterRAP74 domain and a phosphorylated peptide from the central domain of human FCP1 (centFCP1-PO(4)). Comparison of the cterFCP1-cterRAP74 and centFCP1-PO(4)-cterRAP74 complexes indicates that centFCP1 and cterFCP1 both utilize hydrophobic and acidic residues to recognize the same groove of RAP74, but there are significant differences in the details of their interactions. These differences point to the adaptability of RAP74 to recognize the two regions of FCP1. Our NMR and thermodynamic studies further elucidate the complex molecular mechanism by which TFIIF and FCP1 cooperate for RNAPII recycling.

Two concise, high-yielding syntheses of enantioenriched (-)-kainic acid are presented. Both routes feature a Pd-catalyzed Zn-ene cyclization that proceeds with complete diastereoselectivity. The key step can be carried out on a multigram scale, and the overall yields are among the highest to date for this marine alkaloid.

Human centrin 2 is a component of the nucleotide excision repair system, as a subunit of the heterotrimer including xeroderma pigmentosum group C protein (XPC) and hHR23B. The C-terminal domain of centrin (C-HsCen2) binds strongly a peptide from the XPC protein (P1-XPC: N(847)-R(863)). Here, we characterize the solution Ca(2+)-dependent structural and molecular features of the C-HsCen2 in complex with P1-XPC, mainly using NMR spectroscopy and molecular modeling. The N-terminal half of the peptide, organized as an alpha helix is anchored into a deep hydrophobic cavity of the protein, because of three bulky hydrophobic residues in position 1-4-8 and electrostatic contacts with the centrin helix E. Investigation of the whole centrin interactions shows that the N-terminal domain of the protein is not involved in the complex formation and is structurally independent from the peptide-bound C-terminal domain. The complex may exist in three different binding conformations corresponding to zero, one, and two Ca(2+)-bound states, which may exchange with various rates and have distinct structural stability. The various features of the intermolecular interaction presented here constitute a centrin-specific mode for the target binding.

Centrins are well-conserved calcium binding proteins from the EF-hand superfamily implicated in various cellular functions, such as centrosome duplication, DNA repair, and nuclear mRNA export. The intrinsic molecular flexibility and the self-association tendency make difficult the structural characterization of the integral protein. In this paper we report the solution structure, the Ca2+ binding properties, and the intermolecular interactions of the N-terminal domain of two human centrin isoforms, HsCen1 and HsCen2. In the absence of Ca2+, the N-terminal construct of HsCen2 revealed a compact core conformation including four almost antiparallel alpha-helices and a short antiparallel beta-sheet, very similar to the apo state structure of other calcium regulatory EF-hand domains. The first 25 residues show a highly irregular and dynamic structure. The three-dimensional model for the N-terminal domain of HsCen1, based on the high sequence conservation and NMR spectroscopic data, shows very close structural properties. Ca2+ titration of the apo-N-terminal domain of HsCen1 and HsCen2, monitored by NMR spectroscopy, revealed a very weak affinity (10(2)-10(3) M(-1)), suggesting that the cellular role of this domain is not calcium dependent. Isothermal calorimetric titrations showed that an 18-residue peptide, derived from the N-terminal unstructured fragment, has a significant affinity (approximately 10(5) M(-1)) for the isolated C-terminal domain, suggesting an active role in the self-assembly of centrin molecules.

Easily prepared allyl phenyl sulfones, capable of introduction of the alkene by electrophilic alpha-substitution, are superior to allyl acetates as substrates for Pd-catalyzed Zn-ene cyclizations, providing C5 or C(4)N rings with cis-1,2-vinyl and -CH(2)Zn substituents. Several examples, with different methods of substrate preparation, are presented. [reaction: see text]