CoH-catalyzed asymmetric remote hydroalkylation of heterocyclic alkenes: a rapid approach to chiral five-membered S- and O-heterocycles.

Saturated heterocycles, which incorporate S and O heteroatoms, serve as fundamental frameworks in a diverse array of natural products, bioactive compounds, and pharmaceuticals. Herein, we describe a unique cobalt-catalyzed approach integrated with a desymmetrization strategy, facilitating precise and enantioselective remote hydroalkylation of unactivated heterocyclic alkenes. This method delivers hydroalkylation products with high yields and excellent stereoselectivity, representing good efficiency in constructing alkyl chiral centers at remote C3-positions within five-membered S/O-heterocycles. Notably, the broad scope and good functional group tolerance of this asymmetric C(sp3)-C(sp3) coupling enhance its applicability.

Metal-Catalyst-Controlled Divergent Synthesis of γ-Butyrolactones via Intramolecular Coupling of Epoxides with Alcohols.

A metal-controlled divergent protocol for the synthesis of α- and ß-substituted γ-butyrolactones was developed through intramolecular coupling of epoxides with alcohols. This method provides an efficient and practicable way to afford γ-butyrolactones with good efficiency, excellent regioselectivity, and broad substrate scope.

Conformational sampling of the intrinsically disordered dsRBD-1 domain from Arabidopsis thaliana DCL1.

DCL1 is the ribonuclease that carries out miRNA biogenesis in plants. Substrate pri-miRNA recognition by DCL1 requires two double stranded RNA binding domains located at the C-terminus of the protein. We have previously shown that the first of these domains, DCL1-A, is intrinsically disordered and folds upon binding pri-miRNA. Integrating NMR and SAXS data, we study here the conformational landscape of free DCL1-A through an ensemble description. Our results reveal that secondary structure elements, corresponding to the folded form of the protein, are transiently populated in the unbound state. The conformation of one of the dsRNA binding regions in the free protein shows that, at a local level, RNA recognition proceeds through a conformational selection mechanism. We further explored the stability of the preformed structural elements via temperature and urea destabilization. The C-terminal helix is halfway on the folding pathway in free DCL1-A, constituting a potential nucleation site for the final folding of the protein. In contrast, the N-terminal helix adopts stable non-native structures that could hinder the correct folding of the protein in the absence of RNA. This description of the unfolded form allows us to understand details of the mechanism of binding-induced folding of the protein.

Alteration in methylation pattern of GATA-4 promoter region in vitamin A-deficient offspring's heart.

Epigenetics might explain correlations between lifestyle and risk of disease. Maternal diet has been shown to dynamically alter epigenetic regulation, including affecting DNA methylation status. This study was designed to test the hypothesis that GATA-4 gene methylation would lead to congenital heart defects in vitamin A-deficient offspring. Ten weaning female rats (VAN group) were fed with a diet which contents 4 IU vitamin A/g diet, while 20 rats (VAD group) were maintained on a diet without vitamin A. After 10 weeks of feeding, all the female rats were mated with normal male rats. The VAN group and a portion of VAD group rats were still given the same diet as before mating, while the rest of the rats from the VAD group (VADS group) were transferred to a diet with enough added vitamin A (10 IU/g diet) for the pregnancy cycle. The embryo hearts were dissected out at embryonic day 13.5 (E13.5) for observation of cardiac development, GATA-4 gene methylation status and the expression of DNA methyltransferases (DNMTs). Embryos from vitamin A-deficient group exhibited a high incidence of cardiac defects. High methylation was present in the CpG loci of GATA-4 gene with a low expression of GATA-4 mRNA from vitamin A-deficient group embryos. Moreover, up-regulation of DNMT1 and down-regulation of DNMT3a and DNMT3b expression were found in this group embryo. These findings show that aberrant methylation is one of key mechanisms to heart defects in vitamin A-deficient offspring. DNMTs play a critical role in this process.

New strategy for the evaluation of CdTe quantum dot toxicity targeted to bovine serum albumin.

The biological toxicity of CdTe quantum dots (QDs) to bovine serum albumin (BSA) has been investigated mainly by fluorescence spectra, UV-vis absorption spectra and circular dichroism (CD) under simulative physiological conditions. Fluorescence data revealed that the quenching mechanism of BSA by CdTe QDs was a static quenching process and the binding constant is 6.05x10(3) and the number of binding sites is 0.7938. The thermodynamic parameters (DeltaH=-62.33 kJ mol(-1), DeltaG=-21.21 kJ mol(-1), and DeltaS=-140.3 J mol(-1) s(-1)) indicate that hydrogen bonds and van der Waals forces between the protein and the QDs are the main binding forces stabilizing the complex. In addition, UV-vis and CD results showed that the addition of CdTe QDs changed the conformation of BSA.

Protective effects of DIDS against ethanol-induced gastric mucosal injury in rats.

The compound 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) is an efficient anion exchanger inhibitor that can block the activities of anion exchanger 2 (AE2), which plays an indispensable role in gastric acid secretion. DIDS also has potent anti-oxidative and antiapoptosis activities. This study aimed to investigate the effect of DIDS on ethanol-induced mucosal damage in rats and to evaluate the underlying mechanisms that mediate the action of the compound. The rats received 1 ml of absolute ethanol or saline orally. DIDS [50 mg/kg intravenous (i.v.)] was given 5 min before ethanol administration. Gastric lesions were evaluated macroscopically, microscopically, and electron microscopically at 60 min after ethanol challenge. Gastric myeloperoxidase (MPO) activity, malonyldialdehyde (MDA) level, prostaglandin E2 (PGE2) synthesis, and cyclooxygenase-2 (COX-2) expression were assessed. For the evaluation of the effect of DIDS on gastric acid secretion, histamine-stimulatory gastric acid secretion was examined with or without pretreatment of DIDS (50 mg/kg; i.v.). Ethanol-induced gastric lesions were characterized by increasing gastric MDA level, MPO activity, and COX-2 expression, and decreasing PGE2 synthesis. It was found that DIDS significantly reduced the extent of gastric mucosal damage and reversed tissue MDA level and MPO activity. DIDS further enhanced the expression of COX-2 and reversed the decrease of PGE2. Our results suggested that DIDS is beneficial in rat model of gastric injury through mechanisms that involve inhibiting inflammatory cell infiltration and lipid peroxidation and up-regulating the COX-2/PGE2 pathway.

Side-chain oxidative damage to cysteine on a glassy carbon electrode.

In this paper, oxidative damage to the cysteine (CySH) side-chain on a glassy carbon electrode (GCE) was investigated. Voltammetric studies show that there are three anodic peaks for the oxidation of CySH, which arise from (1) the oxidation of the -SH side-chain, forming cystine (0.71 V, vs. SCE) and (2) CySO( x )H, x = 2, 3 (0.98 V vs. SCE), and (3) the oxidation of the amino acid carboxyl group (around 1.51 V vs. SCE). The influence of dissolved oxygen, pH, scan rate, scan time, temperature and CySH concentration were investigated and the oxidative mechanism proposed. The peaks near 0.71 and 0.98 V are the promising candidates for measuring the oxidation of CySH on the GCE. This paper provides a new strategy for researching oxidative damage of amino acids, sulfur-containing peptides and proteins.

A new strategy to probe the genotoxicity of silver nanoparticles combined with cetylpyridine bromide.

The environmental genotoxic behavior of silver nanoparticles (nanoAg) combined with the detergent cetylpyridine bromide (CPB) was examined in vitro. The experimental results showed that the genotoxicity of nanoAg itself is weak, but nanoAg shows obvious genotoxicity after combined with CPB. The combined materials have a strong coeffect on calf thymus DNA (ctDNA) at a concentration of 3.3 x 10(-6 )gmL(-1) nanoAg and 6.0 x 10(-6) molL(-1) CPB. After the addition of ctDNA to the nanoAg-CPB system, the particles are scattered and the diameter decreases, which indirectly reveal that nanoAg-CPB has genotoxicity.