Biography:

One of their most recent publications is NMR studies of aurein 1.2 analogs. Which was published in journal Biochimica et Biophysica Acta (BBA) - Biomembranes.

More information about Xia Li research including statistics on their citations can be found on their Copernicus Academic profile page.

Xia Li's Articles: (45)

NMR studies of aurein 1.2 analogs

AbstractAurein 1.2 is an antimicrobial and anticancer peptide isolated from an Australian frog. To improve our understanding of the mechanism of action, two series of peptides were designed. The first series includes the N-terminal membrane anchor of bacterial glucose-specific enzyme IIA, aurein 1.2, and a newly identified aurein 1.2 analog from human LL-37 (LLAA). The order of antibacterial activity is LLAA > aurein 1.2 >> the membrane anchor (inactive). The structure of LLAA in detergent micelles was determined by 1H NMR spectroscopy, including structural refinement by natural abundance 13Cα, 13Cβ, and 15N chemical shifts. The hydrophobic surface area of the 3D structure is related to the retention time of the peptide on a reverse-phase HPLC column. The higher activity of LLAA compared to aurein 1.2 was attributed to additional cationic residues that enhance the membrane perturbation potential. The second peptide series was created by changing the C-terminal phenylalanine (F13) of aurein 1.2 to either phenylglycine or tryptophan. A closer or further location of the aromatic rings to the peptide backbone in the mutants relative to F13 is proposed to cause a drop in activity. Phenylglycine with unique chemical shifts may be a useful NMR probe for structure–activity relationship studies of antimicrobial peptides. To facilitate potential future use for NMR studies, random-coil chemical shifts for phenylglycine (X) were measured using the synthetic peptide GGXGG. Aromatic rings of phenylalanines in all the peptides penetrated 2–5 Å below the lipid head group and are essential for membrane targeting as illustrated by intermolecular peptide–lipid NOE patterns.

Improving lycopene production in Saccharomyces cerevisiae through optimizing pathway and chassis metabolism

Highlights•Lycopene production was significantly improved through optimizing pathway and chassis metabolism.•GGPP was the rate-controlling metabolite for lycopene production.•Expanding GGPP pool and MVA pathway significantly increased the flow of lycopene synthesis.•Citric acid fed-batch fermentation greatly improved the titer of lycopene.•Constitutive promoter was more efficient for balancing the expression of lycopene biosynthesis pathway.

Cysteine-25 of adenylate kinase reacts with dithiothreitol to form an adduct upon aging of the enzyme

AbstractAdenylate kinase (AK) ages in solution in the presence of DL-dithiothreitol (DTT) with a gradual activity decrease. Upon dilution with 4 M guanidine hydrochloride denatured native and aged AK, both recover to the same activity as the fresh enzyme. Mass spectroscopy and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole chloride modification kinetics studies identify that the residue cysteine-25 of the enzyme reacts with DTT to form an adduct. The formation of the unusual bridging DTT adduct of AK appears to be the result of a stable DTT–protein complex. The KM for AMP, ADP and MgATP of the DTT-modified enzyme does not differ significantly from that of the intact enzyme, whereas the secondary and tertiary structures of the enzyme change obviously. These results indicate that cysteine-25 may not be involved directly in substrate binding, but may play an important role in maintaining secondary and tertiary structures of native AK, as well as the conformation interconversion in the catalytic cycle.

Interior W2,p(x)-regularity for elliptic equations of nondivergence form☆

AbstractIn this paper, we consider the following elliptic equations of nondivergence form∑i,j=1naij∂2u∂xi∂xj=f,in Ω⊂Rn, where the coefficients aij are real valued bounded measurable functions defined in Ω⊂Rn, belong to VMOloc (see Definition 2.5) and satisfy the uniformly elliptic condition. Under the assumption that p(⋅) satisfies the log-Hölder continuity condition, we will establish the interior W2,p(x)-regularity for strong solutions to the elliptic equations of nondivergence form.

Crystal structure of N,N-bis(2-oxopyrrolidin-1-ylmethyl)leucine and photochromism of the Eu3+–PML–phen complex

AbstractThe title compound N,N-bis(2-oxopyrrolidin-1-ylmethyl)leucine (PML) has been prepared, and its crystal structure was determined by single crystal X-ray diffraction. The molecule has four conformations differing from each other in the corresponding bond lengths and angles, which may arise from steric effect of the bulky groups. The europium(III) complex with PML and 1,10-phenanthroline(phen) has photochromic reactivity in aqueous medium, which was studied spectroscopically.

Hydrothermal synthesis, crystal structure, and luminescence of lanthanide(III) coordination polymers with tetrafluorosuccinate and 1,10-phenanthroline

AbstractThree new coordination polymers [Nd2(TFSA)3(phen)2]n (1) and {[Ln(TFSA)(phen)(H2O)4]·0.5(TFSA)·2(phen) H2O}n (Ln = Sm, 2 and Dy, 3; TFSA = tetrafluorosuccinate; phen = 1,10-phenanthroline) were synthesized and characterized using X-ray structure analyses and luminescence spectroscopy. The 1 has a 2-D network structure through TFSA ligands via bridging/chelating-bridging pentadentate and bridging/bridging tetradentate coordination modes. The 2 and 3 have novel 1-D chain structures, in which adjacent Ln(III) ions are linked though the single μ2-bridging TFSA ligands as linkages. The emission spectrum in the NIR of 1 corresponds to the 4F3/2 → 4I9/2, 11/2, 13/2 transitions of Nd(III) ion. The emission spectra of 2 and 3 indicate the typical luminescence characteristics of the Sm(III) and Dy(III) ions, respectively.

Synthesis, structures and photocatalytic properties of two new Co(II) coordination polymers based on 5-(benzyloxy)isophthalate ligand

Highlights•Two new Co(II) coordination polymers constructed from 5-(benzyloxy)isophthalic acid.•Compound 1 is a 3D complicated framework, and compound 2 is a 1D chain structure.•These two compounds display excellent photocatalytic properties.

The efficacy and safety of aspirin plus dipyridamole versus aspirin in secondary prevention following TIA or stroke: A meta-analysis of randomized controlled trials

AbstractObjectiveStroke is becoming a common disease worldwide, and has an increased rate of recurrence yearly after a transient ischemic attack (TIA) or stroke. Aspirin, dipyridamole, clopidogrel and aspirin plus dipyridamole combination therapy have been recommended for the secondary prevention of stroke in Americans.DesignWe performed meta-analyses to assess the effectiveness and safety of combination therapy with aspirin and dipyridamole (A + D) versus aspirin (A) alone in secondary prevention after transient ischemic attack (TIA) or stroke of presumed arterial origin within one week and six months.Data sourcesMedline, Embase, and the Cochrane Library.Selection of studiesEligible studies were completed randomized controlled trials investigating the effect of aspirin plus dipyridamole versus aspirin in patients with previous TIA or stroke.ResultsFive trials involving the use of aspirin and dipyridamole were included, 4318 allocated to A + D and 4304 to A alone. Meta-analysis of trials showed a significant protective effect of reducing or preventing recurrence of stroke (P = 0.01), and ischemic event (P = 0.003). The statistics showed no significant difference in vascular event, death from all cause and myocardial infarction (P > 0.05). There were similarities with all bleeding events, major bleeding and intracranial hemorrhage was significant (P > 0.05) between two groups.ConclusionsAspirin plus dipyridamole combination therapy was beneficial in reducing the recurrence of stroke, and did not increase the bleeding event. Hence, aspirin plus dipyridamole combination therapy is effective and safe for the secondary prevention of stroke.

Effects of metabotropic glutamate receptor ligands on male sexual behavior in rats

AbstractMetabotropic glutamate receptors (mGluRs), particularly mGluR2/3, mGluR5 and mGluR7, have received much attention in medication development for the treatment of drug addiction and other neuropsychiatric diseases. However, little is known as to whether mGluR ligands also alter natural sexual behavior, a possible unwanted effect when used in humans. In the present study, we used classical copulatory behaviors to evaluate the effects of LY379268 (a selective mGluR2/3 agonist), MPEP (a selective mGluR5 antagonist) and AMN082 (a selective mGluR7 agonist), on male sexual performance in rats. We found that systemic administration of LY379268 (1, 3 mg/kg, i.p.) had no effect, while MPEP (20 mg/kg, but not 10 mg/kg, i.p.) and AMN082 (10, 20 mg/kg, but not 3 mg/kg) produced a significant and dose-dependent reduction in both sex-seeking and sex-performance behaviors, manifested as an increase in mount or intromission latency and time required for ejaculation, and a reduction in mount or intromission frequency. This inhibition lasted for about 30–60 min. These findings suggest that compounds that target mGluR5 or mGluR7, but not mGluR2/3, may have short-term inhibitory effects on male sexual performance.This article is part of a Special Issue entitled ‘Metabotropic Glutamate Receptors’.

Comparison of the effects of the GABAB receptor positive modulator BHF177 and the GABAB receptor agonist baclofen on anxiety-like behavior, learning, and memory in mice

Abstractγ-Aminobutyric acid B (GABAB) receptor activation is a potential therapeutic approach for the treatment of drug addiction, pain, anxiety, and depression. However, full agonists of this receptor induce side-effects, such as sedation, muscle relaxation, tolerance, and cognitive disruption. Positive allosteric modulators (PAMs) of the GABAB receptor may have similar therapeutic effects as agonists with superior side-effect profiles. The present study behaviorally characterized N-([1R,2R,4S]-bicyclo[2.2.1]hept-2-yl)-2-methyl-5-(4-[trifluoromethyl]phenyl)-4-pyrimidinamine (BHF177), a GABAB receptor PAM, in mouse models of anxiety-like behavior, learning and memory. In addition, the effects of BHF177 were compared with the agonist baclofen. Unlike the anxiolytic chlordiazepoxide, baclofen (0.5, 1.5, and 2.5 mg/kg, intraperitoneally) and BHF177 (10, 20, and 40 mg/kg, orally) had no effect on anxiety-like behavior in the elevated plus maze, light/dark box, or Vogel conflict test. Baclofen increased punished drinking in the Vogel conflict test, but this effect may be attributable to the analgesic actions of baclofen. At the highest dose tested (2.5 mg/kg), baclofen-treated mice exhibited sedation-like effects (i.e., reduced locomotor activity) across many of the tests, whereas BHF177-treated mice exhibited no sedation-like effects. BHF177 exhibited pro-convulsion properties only in mice, but not in rats, indicating that this effect may be species-specific. At doses that were not sedative or pro-convulsant, baclofen and BHF177 had no selective effects on fear memory retrieval in contextual and cued fear conditioning or spatial learning and memory in the Barnes maze. These data suggest that BHF177 has little sedative activity, no anxiolytic-like profile, and minimal impairment of learning and memory in mice.

Invited reviewInvolvement of glutamatergic and GABAergic systems in nicotine dependence: Implications for novel pharmacotherapies for smoking cessation

Highlights•Blockade of glutamatergic transmission inhibited nicotine reward.•Facilitation of GABAergic transmission inhibited nicotine reward.•Blockade of glutamatergic transmission inhibited nicotine-seeking behavior.•Facilitation of GABAergic transmission inhibited nicotine-seeking behavior.•Glutamatergic and GABAergic medications may be promising for smoking cessation.

Short communicationSynthesis and enantioseparation characteristics of a novel mono-6-deoxy-(2,4-dihydroxybenzimide)-β-cyclodextrin as a chiral stationary phase in high-performance liquid chromatography

AbstractA novel chiral selector mono-6-deoxy-(2,4-dihydroxybenzimide)-β-CD (MDHB-β-CD) in which the derivatized group and the cavity of CD is linked by CH2–NC group, was successfully prepared, and the structural characteristics were determined by FT-IR, 1H and 13C NMR, MALDITOF-MS and element analysis. The corresponding stationary phase (CSP) was used in HPLC and the enantioseparation performance was investigated using chiral 1-phenyl-2-nitroethanol derivatives as test samples in the reverse-phase mode composed of methanol/water and acetonitrile/TEAA. Better separation abilities and excellent enantioselectivities (α > 1.26, RS > 1.73) were obtained on MDHB-β-CD CSP for these chiral compounds in the methanol/water mobile phase.

Dihydroptychantol A, a macrocyclic bisbibenzyl derivative, induces autophagy and following apoptosis associated with p53 pathway in human osteosarcoma U2OS cells

AbstractDihydroptychantol A (DHA), a novel macrocyclic bisbibenzyl compound extracted from liverwort Asterella angusta, has antifungal and multi-drug resistance reversal properties. Here, the chemically synthesized DHA was employed to test its anti-cancer activities in human osteosarcoma U2OS cells. Our results demonstrated that DHA induced autophagy followed by apoptotic cell death accompanied with G2/M-phase cell cycle arrest in U2OS cells. DHA-induced autophagy was morphologically characterized by the formation of double membrane-bound autophagic vacuoles recognizable at the ultrastructural level. DHA also increased the levels of LC3-II, a marker of autophagy. Surprisingly, DHA-mediated apoptotic cell death was potentiated by the autophagy inhibitor 3-methyladenine, suggesting that autophagy may play a protective role that impedes the eventual cell death. Furthermore, p53 was shown to be involved in DHA-meditated autophagy and apoptosis. In this connection, DHA increased nuclear expression of p53, induced p53 phosphorylation, and upregulated p53 target gene p21Waf1/Cip1. In contrast, cytoplasmic p53 was reduced by DHA, which contributed to the stimulation of autophagy. In relation to the cell cycle, DHA decreased the expression of cyclin B1, a cyclin required for progression through the G2/M phase. Taken together, DHA induces G2/M-phase cell cycle arrest and apoptosis in U2OS cells. DHA-induced apoptosis was preceded by the induction of protective autophagy. DHA-mediated autophagy and apoptosis are associated with the cytoplasmic and nuclear functions of p53.

Preparation and physicochemical properties of carboxymethyl Fritillaria ussuriensis Maxim. starches

AbstractStarch isolated from an under-utilized Liliaceae plant (Fritillaria ussuriensis Maxim.) was carboxymethylated. Influences of reaction parameters were investigated on the degree of substitution (DS). The optimal molar ratio of NaOH/AGU and MCA/AGU is 2.43 and 1.03, respectively. The highest values of the DS obtained when the carboxymethylation was performed at 60 °C for 2.5 h. Scanning electron microscopy (SEM) showed that after carboxymethylation, the granular appearance of the native starch was distorted and many alveolate holes were seen. The new bands at 1608 cm−1 and 1426 cm−1 in Fourier transform infrared (FT-IR) indicated that the starch granules were substituted. Wide-angle X-ray diffractometry revealed that crystallinity was reduced significantly after carboxymethylation. Differential scanning calorimetry (DSC) suggests loss of crystallinity after carboxymethylation. The thermal behavior of the starches was investigated using thermogravimetric analysis (TGA). The results revealed that the decomposition temperature of the starch decreased from 316 °C to 252 °C and at a low decomposition speed.

Adsorption characteristics of Copper (Ⅱ), Zinc (Ⅱ) and Mercury (Ⅱ) by four kinds of immobilized fungi residues

Highlights•We used fungi residues to reduce Cu2+, Zn2+ and Hg2+ in water.•Our study focused on the removal of lower concentration metal ions in water.•Functional groups of fungi residues in metal ions adsorbents were analyzed.•We proved metal ions could be efficiently removed by fungi residue.

Research reportDecreased platelet 5-hydroxytryptamin (5-HT) levels: a response to antidepressants

Highlights•In comparison with control and drug-naïve depressed patients, citalopram-treated patients had significantly lower 5-HT Levels, While Drug-naïve patients had similar 5-HT platelet concentrations as controls.•Consistent with clinical results, the platelet 5-HT level decreased in chronic unpredictable mild stress (CUMS) citalopram-treated rats, in comparison with control and drug-naive CUMS rats.•CUMS+saline rats had high 5-HT level in hippocampus.•The levels of platelet 5-HT did not correlate with neuronal 5-HT levels.•Platelet 5-HT could response to SSRI treatment.

Contact metamorphism of shales intruded by a granite dike: Implications for shale gas preservation

Highlights•The granite dike has strong effect on mineralogy, organic geochemistry and pore structure of black shales.•There is no evident relationship between TOC content and the distance to the dike.•Contact metamorphism formed macropores and microcracks in the shales near the contact boundary.•Intrusion of granites will cause a fast escape of shale gas in shales within the contact aureole.•The results provide new insights on shale gas preservation in basins with magmatic activities.

Rapid synthesis of YAG nano-sized powders by a novel method

AbstractNano-sized powders of aluminum yttrium garnet (YAG) have been successfully synthesized by a mixed solvo-thermal method at low temperature (300 °C) and low pressure (10 MPa). The phase transformation, composition and micro-structural features of the crystalline samples were characterized by X-ray powder diffraction, IR and TEM techniques. It was found that type of solvent, reaction temperature and time were important factors in the YAG synthesis process. X-ray powder diffraction pattern indicated that the pure phase YAG was synthesized in mixed solvent at 300 °C. The transmission electron microscopy (TEM) revealed the averaged size of crystallite was 20 nm and well dispersed. Moreover, the mechanism for solvo-thermal crystallization of YAG is proposed based on IR results.

Polyaniline/CuCl nanocomposites prepared by UV rays irradiation

AbstractIn present paper, polynailine (PANI)/CuCl nanocomposites were prepared by UV rays irradiation method. In this method, photons in the UV rays and Cu2+ ions replaced conventional oxidant such as ammonium persulfate (APS) to promote polymerization of aniline monomer. The PANI/CuCl nanocomposites were characterized by infrared spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscope (HRTEM), and electron diffraction (ED). The results indicated that aniline could polymerize to PANI by UV rays irradiation. Meanwhile, the results of HRTEM and ED confirmed that the CuCl dispersed into PANI was single crystal with cubic crystal structure. A potential formation mechanism of PANI/CuCl nanocomposites was investigated and suggested.

Evaluation of three traditional Chinese medicine (TCM) starches and potential application in health product industry

Highlights•We investigated the composition and properties of three TCM starches.•Ginkgo starch showed excellent paste clarity.•Ginkgo and Angelica starches possessed high slowly digested starch content.•The three starches showed lower enthalpy values than most of conventional starch.

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