Search

As a quinazolinocarboline alkaloid, dehydroevodiamine (DHED) derived from Evodia rutaecarpa has recently gained attention because it improves memory failure in Alzheimer's mice. However, its solid forms, which have not yet been elucidated, could be a vital factor affecting its bioactivity and dosage form design. In this study, five DHED-related crystals, including DHED, its hydrochloride anhydrate (DHED·HCl), methanol solvate (DHED·HCl·CH3OH), dihydrate (DHED·HCl·2H2O) and trihydrate (DHED·HCl·3H2O), were obtained via re-crystallization. The five crystals fell into four distinct structural types based on the analysis of their similarities, and DHED·HCl·CH3OH and DHED·HCl·2H2O were proven to be isostructural. The water or solvent molecules incorporated into the crystal lattices via hydrogen bonds and π–π interactions were the main causes of formation of the distinct solid DHED hydrochloride forms. After dehydration at a high temperature, DHED·HCl·3H2O was transformed into an amorphous form (DHED·HCl-AM). Stability tests showed that the two isostructural crystals exhibited the same solid forms under all investigated conditions, and the humidity-induced phase transformation of DHED·HCl was closely tied to the moisture content. Solubility experiments showed that DHED achieved the highest solubility of approximately 3.6 μg ml−1, because of the loose molecular arrangements in DHED with the smallest packing coefficient and lack of π–π interactions. Additionally, transformations among evodiamine (EVO), DHED, DHED·HCl·2H2O and rutaecarpine (RUT) were also revealed: EVO was transformed into DHED·HCl·2H2O in hydrochloric acid-acidified acetone, and all of the solid forms of DHED hydrochloride were converted to RUT at 523 K. The transformations provided a novel and reliable approach to prepare these compounds. [ABSTRACT FROM AUTHOR]

The remarkable catalytic properties of enzymes contribute to their unique 3D structures and arrangement of amino acid residues, which provide a blueprint for the design of artificial enzymes. Here, a series of peptide catalysts (PCs) that mimic the unique orientation and function of β-glycosyl hydrolases were designed. Transmission electron microscopy (TEM), fluorescence analysis, circular dichroism spectroscopy, X-ray diffraction and computational modeling were used to investigate and compare the relationship of the fibrinous structure of PCs with its glycoside hydrolysis activity. These results indicated that the catalytic activity of PCs was not only related to their amyloid-like structures, but it can also be influenced by the site, species, molecular arrangement and steric hindrance of the amino acid sequence. What's more, this is the first report on peptide-inspired catalysts that mimic the natural cellobiose hydrolases. All this provided insights into the potential use of peptide nanoenzymes in the generation of efficient artificial enzymes. [ABSTRACT FROM AUTHOR]

A fluorescence magnetic biosensor for the DNA methyltransferase activity was developed based on the cooperative amplification by combining the magnetic nanoparticles synergistic exonuclease III (Exo III)-assisted circular exponential amplification and a supramolecular structure ZnPPIX/G-quadruplex. First, a duplex DNA probe, which was constructed by the hybridization of a quadruplex-forming oligomer with a molecular beacon, was assembled on the magnetic nanoparticles (MNPs) as a reporter. A hairpin probe (HP)-containing sequence of GATC was used as the methylation substrate of DNA adenine methyltransferase (DAM). Once HP was methylated by DAM, it could be recognized and cleaved by Dpn I, which allows the release of a single-stranded DNA. The DNA (tDNA1) then hybridizes to the MNP probe, which then triggers the exonuclease III-mediated target exponential recycling reaction. Simultaneously, numerous quadruplex forming oligomers are liberated and folded into the G-quadruplex-ZnPPIX complexes with the help of zinc(ii)-protoporphyrin IX(ZnPPIX) on the MNP surface to give a remarkable fluorescence response. In the developed sensor, a small amount of target DAM can be converted to a large number of stable DNA triggers, leading to remarkable amplification of the target. Moreover, using MNPs as a vector of the sensor may reduce the interference from the real samples, which increases the anti-interference of the sensing system. Based on this unique amplification strategy, a very low detection limit down to 2.0 × 10−4 U mL−1 was obtained. Furthermore, the sensor could be used to evaluate the DAM activity in different growth stages of E. coli cells and screen Dam MTase inhibitors. Therefore, the strategy proposed here provides a promising platform for monitoring the activity and inhibition of DNA MTases and has great potential to be applied further in early clinical diagnostics and medical research. [ABSTRACT FROM AUTHOR]

A simple, label-free and sensitive fluorescence protein assay has been developed on the basis of aptamer exonuclease protection and exonuclease III (Exo III)-assisted recycling amplification-responsive cascade ZnPPIX/G-quadruplex supramolecular fluorescent labels. In the sensing system, a special aptamer probe containing the aptamer sequence at the 3′-terminus and the DNAzyme sequence at the 5′-terminus was applied, which has the capacity to recognize a protein target with high affinity and specificity. Exonuclease I (Exo I) can efficiently catalyze the degradation of free single stranded DNA probes in the 3′ to 5′ direction. In the presence of the target protein, the strong binding between the target protein and its aptamer can protect aptamer probes from degradation. Subsequently, the protected aptamer probes act as catalysators to trigger hybridization with the hairpin DNA probe that contains a partially “caged” G-quadruplex sequence. Upon interaction with the protected aptamer probes, the hairpin opens to yield the active G-quadruplex structure. In the presence of exonuclease III (Exo III), Exo III-assisted recycling amplification occurs generating numerous G-quadruplex supramolecular structures. The zinc(ii)-protoporphyrin IX (ZnPPIX) fluorophore binds to the G-quadruplexes and this results in the enhanced fluorescence of the fluorophore. The resulting fluorescence of the ZnPPIX/G-quadruplex provides the readout signal for the sensing event. Thrombin is used as the model analyte in the current proof-of-concept. The developed method was demonstrated to have very high sensitivity for the detection of proteins with a limit of detection of 0.2 pM without using washes or separations. In addition, this new method for protein detection is simple and inherits all the advantages of aptamers. The mechanism, moreover, may be generalized and used for other forms of protein analysis. [ABSTRACT FROM AUTHOR]

In this work, ZnO nano-needles were electrochemically deposited onto the surface of single carbon fiber. The influence of deposition condition on the surface morphology of ZnO nanostructures was investigated. A growth mechanism was suggested to elucidate the deposition process. Electrochemiluminescence conducted in 0.1 M KOH solution containing 0.1 M K2S2O8 and 0.1 M KCl displayed the stable and sensitive luminescent property of as-prepared ZnO nano-needles. The electrochemiluminescence intensity per projection area from ZnO nano-needles deposited on single carbon fiber was almost five orders of magnitude larger than that from ZnO nanostructures deposited on ITO and ZnO dip-coated on ITO. It demonstrated the high electrochemiluminescence efficiency of ZnO nano-needles deposited on single carbon fiber and the remarkable electrical conductivity of carbon fiber. This work presented a new strategy to deposit oxides on carbon fiber with tunable coverage and nanostructure. Furthermore, the excellent electrochemiluminescence property of ZnO nano-needles on carbon fiber highlights the importance and potential utility of such nanostructures in the development of optoelectronic and biomedical devices. [ABSTRACT FROM AUTHOR]

Novel three-dimensional Ag nanoflowers (3DAN) were successfully synthesized through a facile Cu2+ mediated solution method using N,N-dimethylformamide (DMF), which serves as both a reducing agent and a solvent at room temperature. It was found that the introduction of a trace amount of Cu2+ could greatly slow the rate of the Ag+ reaction and thus this process effectively reduced the growth speed of Ag nanoparticles allowing 3DAN to be formed. The mechanism underlying the self-assembly process and shape evolution of 3DAN were systematically investigated by varying reaction time. X-Ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) were used to characterize the structure and morphology of the obtained products. X-Ray photoelectron spectroscopy (XPS) was used to assess the chemical state and surface composition of the 3DAN. UV-vis absorption spectra of the products collected from the reaction solution at various stages were taken to study their optical properties. In the measurement of surface-enhanced Raman scattering using rhodamine 6G (R6G) as the probe, the 3DAN exhibited a significant enhancement factor, indicating their potential applications in biosensing and nanodevices. [ABSTRACT FROM AUTHOR]

An antioxidant (AO) amperometric technique based on guanine attached to graphene and Fe(3)O(4) nanoparticles (NPs) magnetic materials was developed. Guanine molecules acted as an antioxidant competitor were bonded with graphene nanosheets, onto which magnetic Fe(3)O(4) NPs were attached and the as-prepared magnetic composite can be attracted to the electrode surface by an external magnetic field. When applied with negative potentials, the dissolved oxygen was reduced to H(2)O(2) at the electrode surface, and then reacted with the EDTA-Fe(ii) complex via a Fenton-like reaction to produce OH radicals. After oxidation damage by OH radicals, the electrochemical oxidation of guanine gave a decreased current. In the presence of AOs, the reactive oxygen species (ROS, e.g. OH radicals and H(2)O(2)) were scavenged by AOs and fewer guanine probe molecules were oxidized, thus inducing a higher electrochemical oxidation current of guanine. So AOs competed with the guanine probe molecules toward oxidation by ROS. The current signals of the guanine probe molecules were proportional to the concentrations of AOs. A kinetic model was proposed to quantify the ROS scavenging capacities of the AOs. Using guanine as an oxidizable probe and OH radicals and H(2)O(2) as endogenous ROS, this kind of AO detection technique mimicks the antioxidant protection mechanism by small AO molecules in the human body.