Tetrabutylammonium Bromide-Catalyzed Transfer Hydrogenation of Quinoxaline with HBpin as a Hydrogen Source.

A metal-free environmentally benign, simple, and efficient transfer hydrogenation process of quinoxaline has been developed using the HBpin reagent as a hydrogen source. This reaction is compatible with a variety of quinoxalines offering the desired tetrahydroquinoxalines in moderate-to-excellent yields with Bu4NBr as a noncorrosive and low-cost catalyst.

Zinc salt-catalyzed reduction of α-aryl imino esters, diketones and phenylacetylenes with water as hydrogen source.

The zinc salt-catalyzed reduction of α-aryl imino esters, diketones and phenylacetylenes with water as hydrogen source and zinc as reductant was successfully conducted. The presented method provides a low-cost, environmentally friendly and practical preparation of α-aryl amino esters, α-hydroxyketones and phenylethylenes. By using D2O as deuterium source, the corresponding products were obtained in high efficiency with excellent deuterium incorporation rate, which gives a cheap and safe tool for access to valuable deuterium-labelled compounds.

Rhodium-catalyzed transfer hydrogenation of quinoxalines with water as a hydrogen source.

Rhodium-catalyzed transfer hydrogenation of quinoxalines with water as a hydrogen source was reported. The reaction allowed the simple preparation of tetrahydroquinoxalines under mild conditions. The deuterium-labelling experiment confirmed that water is the sole hydrogen source in the transfer hydrogenation reaction.

[Experimental Study on Migration Parameters of DEHP in PVC Infusion].

The work explored the DEHP migration parameters in PVC infusion in clinic,based on the previous research on the test model of DEHP migrated from PVC infusion,to assess the safety of PVC infusion.The leaching solution samples in different conditions were evaluated by analysis of the DEHP in leaching solution using GC-MS under simulated clinical transfusion way.The release behavior of DEHP was significantly affected by the storage time,storage temperature,surrounding temperature,dripping speed,sterilization process,volume of the leaching solution,and the property of the leaching solution.

[Research on Experimental Model of Security Assessment of DEHP Migration from PVC-Tubes Medical Devices].

As we all know, DEHP is seriously harmful to human health and consequently has been acquired critical attention. DEHP is able to migrate from PVC medical devices for the non-chemically bound to PVC, thus contact with user and patient. The DEHP migration is influenced by various parameters. In order to assess the security of PVC-tubes medical devices scientifically of DEHP migration, we develop an experimental model by analyzing the parameters comprehensively and systematically, taking into account the clinical practices. For example, assessing the security of DEHP migration from infusion sets by utilizing this model.

Electrochemical immunosensor based on Pd-Au nanoparticles supported on functionalized PDDA-MWCNT nanocomposites for aflatoxin B1 detection.

This paper reports a label-free electrochemical immunosensor for the determination of aflatoxin B1 (AFB1), which is based on a gold electrode modified by a biocompatible film of carbon nanotubes/poly(diallyldimethylammoniumchloride)/Pd-Au nanoparticles (CNTs/PDDA/Pd-Au). The nanocomposite was characterized by transmission electron microscopy and the electrochemical behavior of modified electrodes was investigated by cyclic voltammetry. The CNTs/PDDA/Pd-Au nanocomposites film showed good electron transfer ability, which ensured high sensitivity to detect AFB1 in a range from 0.05 to 25 ng mL(-1) with a detection limit of 0.03 ng mL(-1) obtained at 3σ (where σ is the standard deviation of the blank solution, n = 10). The proposed immunosensor provides a simple tool for AFB1 detection. This strategy can be extended to any other antigen detection by using the corresponding antibodies.

A novel logic gate based on liquid-crystals responding to the DNA conformational transition.

Described herein is a novel liquid crystal (LC)-based DNA logic gate constructed via employing the reorientation of LCs triggered by metal-ion-mediated DNA probe conformational changes.

Hydrogenation of Alkynes and Olefins Catalyzed by Quaternary Ammonium Salts.

Catalytic hydrogenation of unsaturated hydrocarbons to alkenes and alkanes using molecular hydrogen is one of the most fundamental transformations in organic synthesis. While methodologies involving transition metals as catalysts in homogeneous and heterogeneous processes have been well developed, metal-free catalytic hydrogenation offers an ideal approach for future chemistry. Herein, the common and inexpensive quaternary ammonium salts are first introduced as catalysts in the catalytic hydrogenation system for the transformations from alkynes or olefins into the corresponding olefins or alkanes. Interestingly, the hydrogenation process of alkynes can be controlled to selectively produce alkenes or alkanes under different conditions. Moreover, the possible mechanism is discussed in new insights into the catalytic behavior of quaternary ammonium salts.

A biological age model based on physical examination data to predict mortality in a Chinese population.

Biological age could be reflective of an individual's health status and aging degree. Limited estimations of biological aging based on physical examination data in the Chinese population have been developed to quantify the rate of aging. We developed and validated a novel aging measure (Balanced-AGE) based on readily available physical health examination data. In this study, a repeated sub-sampling approach was applied to address the data imbalance issue, and this approach significantly improved the performance of biological age (Balanced-AGE) in predicting all-cause mortality with a 10-year time-dependent AUC of 0.908 for all-cause mortality. This mortality prediction tool was found to be effective across different subgroups by age, sex, smoking, and alcohol consumption status. Additionally, this study revealed that individuals who were underweight, smokers, or drinkers had a higher extent of age acceleration. The Balanced-AGE may serve as an effective and generally applicable tool for health assessment and management among the elderly population.

Cooperative amplification-based electrochemical sensor for the zeptomole detection of nucleic acids.

In this work, we developed a multiple-amplification-based electrochemical sensor for ultrasensitive detection of nucleic acids using a disease-related sequence of the p53 gene as the model target. A capture probe (CP) with a hairpin structure is immobilized on the electrode surface via thiol-gold bonding, while its stem is designed to contain a restriction site for EcoRI. In the absence of target DNA, the probe keeps a closed conformation and forms a cleavable region. After treatment with EcoRI, the target binding portion (loop) plus the biotin tag can be peeled off, suppressing the background current. In contrast, the CP is opened by the target hybridization, deforming the restriction site and forcing the biotin tag away from the electrode. On the basis of the biotin-streptavidin complexation, gold nanoparticles (GNPs) modified with a large number of ferrocene-signaling probes (Fc-SPs) are captured by the resulting interface, producing an amplified electrochemical signal due to the GNP-based enrichment of redox-active moieties. Furthermore, Fc tags can be dragged in close proximity to the electrode surface via hybridization between the signaling probes and the CP residues after EcoRI treatment, facilitating interfacial electron transfer and further enhancing the signal. With combination of these factors, the present system is demonstrated to achieve an ultrahigh sensitivity of zeptomole level and a wide dynamic response range of over 7 orders of magnitude.

Target-triggered cyclic assembly of DNA-protein hybrid nanowires for dual-amplified fluorescence anisotropy assay of small molecules.

Aptamer-based fluorescence anisotropy (FA) assays have attracted great interest in recent years. However, a key factor that determines FA value is molar mass, thus limiting the utility of this assay for the detection of small molecules. To solve this problem, streptavidin, as a molar mass amplifier, was used in a hybridization chain reaction (HCR) to construct a target-triggered cyclic assembly of DNA-protein hybrid nanowires for highly sensitive detection of small molecules by fluorescence anisotropy. In this assay, one blocking DNA strand is released by target-aptamer recognition. The DNA then serves as an initiator to trigger enzyme-free autonomous cross-opening of hairpin probes via HCR to form a DNA nanowire for further assembly of streptavidin. Using adenosine triphosphate (ATP) as the small molecule target, this novel dual-amplified, aptamer-based FA assay affords high sensitivity with a detection limit of 100 nM. This limit of detection (LOD) is much lower than that of the disassembly approach without HCR amplification or the assembly strategy without streptavidin. In contrast to the previous turn-off disassembly approaches based on nonspecific interactions between the aptamer probe and amplification moieties, the proposed aptamer-based FA assay method exhibits a turn-on response to ATP, which can increase sensing reliability and reduce the risk of false hits. Moreover, because of its resistance to environmental interferences, this FA assay has been successfully applied for direct detection of 0.5 µM ATP in complex biological samples, including cell media, human urine, and human serum, demonstrating its practicality in real complex biological systems.

Label-free liquid crystal biosensor based on specific oligonucleotide probes for heavy metal ions.

In this study, to enhance the capability of metal ions disturbing the orientation of liquid crystals (LCs), we designed a new label-free LC biosensor for the highly selective and sensitive detection of heavy metal ions. This strategy makes use of the target-induced DNA conformational change to enhance the disruption of target molecules for the orientation of LC leading to an amplified optical signal. The Hg(2+) ion, which possesses a unique property to bind specifically to two DNA thymine (T) bases, is used as a model heavy metal ion. In the presence of Hg(2+), the specific oligonucleotide probes form a conformational reorganization of the oligonucleotide probes from hairpin structure to duplex-like complexes. The duplex-like complexes are then bound on the triethoxysilylbutyraldehyde/N,N-dimethyl-N-octadecyl (3-aminopropyl) trimethoxysilyl chloride (TEA/DMOAP)-coated substrate modified with capture probes, which can greatly distort the orientational profile of LC, making the optical image of LC cell birefringent as a result. The optical signal of LC sensor has a visible change at the Hg(2+) concentration of low to 0.1 nM, showing good detection sensitivity. The cost-effective LC sensing method can translate the concentration signal of heavy metal ions in solution into the presence of DNA duplexes and is expected to be a sensitive detection platform for heavy metal ions and other small molecule monitors.

Modulated dye retention for the signal-on fluorometric determination of acetylcholinesterase inhibitor.

A novel fluorometric assay method based on target-induced signal on was developed for acetylcholinesterase (AChE) inhibitor with obviously improved detection sensitivity. In this method, the AChE molecules catalyzed the hydrolysis of acetylthiocholine (ATCl) to form thiocholine, which in turn can specifically react with fluorescent squaraine derivative, a specific chemodosimeter for thiol-containing compounds, resulting in fluorescence quenching and offering a low fluorometric background for the further detection of AChE inhibitor. In the presence of AChE inhibitor, the catalytic hydrolysis of ATCl is blocked, and then the squaraine derivative remains intact and shows signal-on fluorescence. The amount of the remaining fluorescent squaraine derivative is positively correlated with that of the AChE inhibitor in solution. This new designed sensing system shows an obviously improved sensitivity toward target with a detection limit of 5 pg mL(-1) (0.018 nM) for the AChE inhibitor, comparing favorably with previously reported fluorometric methods. To our best knowledge, this new method is the first example of fluorometric enzymatic assay for AChE inhibitors based on such a signal-on principle and using a specific reaction, which has potential to offer an effective strategy for the detection of AChE inhibitors.

High-sensitivity naphthalene-based two-photon fluorescent probe suitable for direct bioimaging of H2S in living cells.

H2S is the third endogenously generated gaseous signaling compound and has also been known to involve a variety of physiological processes. To better understand its physiological and pathological functions, efficient methods for monitoring of H2S in living systems are desired. Although quite a few one photon fluorescence probes have been reported for H2S, two-photon (TP) probes are more favorable for intracellular imaging. In this work, by employing a donor-π-acceptor-structured naphthalene derivative as the two-photon fluorophore and an azide group as the recognition unit, we reported a new two-photon bioimaging probe 6-(benzo[d]thiazol-2'-yl)-2-azidonaphthalene (NHS1) for H2S with improved sensitivity. The probe shows very low background fluorescence in the absence of H2S. In the presence of H2S, however, a significant enhancement for both one photon and TP excited fluorescence were observed, resulting in a high sensitivity to H2S in aqueous solutions with a detection limit of 20 nM observed, much lower than the previously reported TP probe. The probe also exhibits a wide linear response concentration range (0-5 µM) to H2S with high selectivity. All these features are favorable for direct monitoring of H2S in complex biological samples. It was then applied for direct TP imaging of H2S in living cells with satisfactory sensitivity, demonstrating its value of practical application in biological systems.

New probe design strategy by cooperation of metal/DNA-ligation and supermolecule inclusion interaction: application to detection of mercury ions(II).

In this paper, the development is described of an efficient pyrene excimer signaling-based fluorescent sensor for the measurement of mercury ions in aqueous solutions based on thymine-Hg(2+)-thymine (T-Hg(2+)-T) coordination chemistry and the inclusion interaction of γ-cyclodextrin. Introduction of cyclodextrin can provide cooperation for the molecular level space proximity of the two labeled pyrene molecules, moreover the hydrophobic cavity of γ-cyclodextrin can also offer protection for the pyrene dimer's emission from the quenching effect of Hg(2+) and enhance the fluorescence intensity of the pyrene excimer. To demonstrate the feasibility of the design, a bis-pyrene-labeled thymine-rich DNA strand was used as the detection probe. In the presence of Hg(2+), stem-close-shaped DNA strands can be formed with the cooperation of γ-cyclodextrin and ideally predominantly emit the excimer fluorescence. The selectivity of the sensor for Hg(2+) against other biologically and environmentally related metal ions is outstanding due to the high specificity of T-Hg(2+)-T formation. In addition, the pyrene excimer has a long fluorescence lifetime, which can tolerate intense background fluorescence interference from complex biological components, making it potentially applicable in the analysis of complex biological samples.

A Hg(2+)-mediated label-free fluorescent sensing strategy based on G-quadruplex formation for selective detection of glutathione and cysteine.

A novel label-free fluorescent strategy for the detection of glutathione (GSH) and cysteine (Cys) is presented. The system consists of two single stranded DNA (ssDNA) with thymine-thymine (T-T) mismatches and used Hg(2+) as a mediator, and N-methyl mesoporphyrin IX (NMM) as the signal reporter. The assay is based on the competitive reaction of Hg(2+) with GSH/Cys and T-T mismatched double stranded DNA (dsDNA). In the absence of the target, two ssDNA containing T-T mismatches react with Hg(2+) to form a T-Hg(2+)-T dsDNA structure in the solution, which hampers the formation of a G-quadruplex structure. However, in the presence of the target, GSH/Cys reacts with Hg(2+) to keep DNA probes in a free single state, resulting in the effective formation of a G-quadruplex structure of the DNA probe (GP). Subsequently, due to the strong interaction between the G-quadruplex structure and NMM, fluorescence was greatly enhanced. This fluorescence strategy does not require any chemical modification, making the assay convenient and cost-effective. This method exhibited a linear relationship between peak fluorescence intensity and concentration of GSH in the range of 10-400 nM with a limit of detection (LOD) of 9.6 nM. A linear range for Cys detection was obtained in the concentration range of 10-500 nM with an LOD of 10 nM. Moreover, the proposed method worked well for the analysis of complex biological samples.

A label-free amplified fluorescence DNA detection based on isothermal circular strand-displacement polymerization reaction and graphene oxide.

A label-free fluorescent DNA biosensor has been presented based on isothermal circular strand-displacement polymerization reaction (ICSDPR) combined with graphene oxide (GO) binding. The proposed method is simple and cost-effective with a low detection limit of 4 pM, which compares favorably with other GO-based homogenous DNA detection methods.

Asymmetric Construction of Multifunctional γ-Lactams from 1,3-Dienes and α-Ketoamides via Pd(0)-π-Lewis Base Catalysis.

A straightforward approach for the asymmetric synthesis of multifunctionalized γ-lactams, including those bearing two tetrasubstituted stereogenic centers, has been developed through a palladium-catalyzed vinylogous addition/allylic amination process between 1,3-dienes and α-ketoamides. This protocol features advantages of ready substrate availability, broad applicability, high efficiency, and excellent stereoselectivity, making it an attractive complementary tool to the previous strategies.

Coevolution between simple sequence repeats (SSRs) and virus genome size.

BACKGROUND: Relationship between the level of repetitiveness in genomic sequence and genome size has been investigated by making use of complete prokaryotic and eukaryotic genomes, but relevant studies have been rarely made in virus genomes. RESULTS: In this study, a total of 257 viruses were examined, which cover 90% of genera. The results showed that simple sequence repeats (SSRs) is strongly, positively and significantly correlated with genome size. Certain repeat class is distributed in a certain range of genome sequence length. Mono-, di- and tri- repeats are widely distributed in all virus genomes, tetra- SSRs as a common component consist in genomes which more than 100 kb in size; in the range of genome < 100 kb, genomes containing penta- and hexa- SSRs are not more than 50%. Principal components analysis (PCA) indicated that dinucleotide repeat affects the differences of SSRs most strongly among virus genomes. Results showed that SSRs tend to accumulate in larger virus genomes; and the longer genome sequence, the longer repeat units. CONCLUSIONS: We conducted this research standing on the height of the whole virus. We concluded that genome size is an important factor in affecting the occurrence of SSRs; hosts are also responsible for the variances of SSRs content to a certain degree.

Acetylcholinesterase liquid crystal biosensor based on modulated growth of gold nanoparticles for amplified detection of acetylcholine and inhibitor.

A novel acetylcholinesterase (AChE) liquid crystal (LC) biosensor based on enzymatic growth of gold nanoparticles (Au NPs) has been developed for amplified detection of acetylcholine (ACh) and AChE inhibitor. In this method, AChE mediates the hydrolysis of acetylthiocholine (ATCl) to form thiocholine, and the latter further reduces AuCl(4)(-) to Au NPs without Au nanoseeds. This process, termed biometallization, leads to a great enhancement in the optical signal of the LC biosensor due to the large size of Au NPs, which can greatly disrupt the orientational arrangement of LCs. On the other hand, the hydrolysis of ATCl is inhibited in the presence of ACh or organophosphate pesticides (OPs, a AChE inhibitor), which will decrease the catalytic growth of Au NPs and, as a result, reduce the orientational response of LCs. On the basis of such an inhibition mechanism, the AChE LC biosensor can be used as an effective way to realize the detection of ACh and AChE inhibitors. The results showed that the AChE LC biosensor was highly sensitive to ACh with a detection limit of 15 µmol/L and OPs with a detection limit of 0.3 nmol/L. This study provides a simple and sensitive AChE LC biosensing approach and offers effective signal enhanced strategies for the development of enzyme LC biosensors.