Ratiometric Detection of microRNA Using Hybridization Chain Reaction and Fluorogenic Silver Nanoclusters

miRNA (miR)-155 is a potential biomarker for breast cancers. We aimed at developing a nanosensor for miR-155 detection by integrating hybridization chain reaction (HCR) and silver nanoclusters (AgNCs). HCR serves as an enzyme-free and isothermal amplification method, whereas AgNCs provide a built-in fluorogenic detection probe that could simplify the downstream analysis. The two components were integrated by adding a nucleation sequence of AgNCs to the hairpin of HCR. The working principle was based on the influence of microenvironment towards the hosted AgNCs, whereby unfolding of hairpin upon HCR has manipulated the distance between the hosted AgNCs and cytosine-rich toehold region of hairpin. As such, the dominant emission of AgNCs changed from red to yellow in the absence and presence of miR-155, enabling a ratiometric measurement of miR with high sensitivity. The limit of detection (LOD) of our HCR-AgNCs nanosensor is 1.13 fM in buffered solution. We have also tested the assay in diluted serum samples, with comparable LOD of 1.58 fM obtained. This shows the great promise of our HCR-AgNCs nanosensor for clinical application.     

Multiplier ideal sheaves in complex and algebraic geometry

The application of the method of multiplier ideal sheaves to effective problems in algebraic geometry is briefly discussed. Then its application to the deformational invariance of plurigenera for general compact algebraic manifolds is presented and discussed. Finally its application to the conjecture of the finite generation of the canonical ring is explored, and the use of complex algebraic geometry in complex Neumann estimates is discussed.

     

Quantitation of homoharringtonine in plasma by high-performance liquid chromatography with amperometric detection

A high-performance liquid chromatographic procedure was developed for the quantitation of homoharringtonine in plasma. Harringtonine was used as an internal standard, and 1 ml of sample was required. The single-step extraction with dichloromethane resulted in almost 100% recovery for homoharringtonine and harringtonine. Analysis was performed on a reversed-phase CN column with amperometric detection. Chromatography was completed in 12 min. At an oxidation potential of +1.0 V, the detection limit was 1 ng/ml at a signal-to-noise ratio of 2. The mean analytical recovery for homoharringtonine was 99.5%. The within-run precision and between-run precision were both less than 11%. The method is equally applicable for plasma or serum, and it has been demonstrated to be applicable for study of the pharmacokinetics of homoharringtonine in patients suffering from acute non-lymphocytic leukaemia.     

Gas-phase fragmentation of the Ag+—phenylalanine complex: Cation—π interactions and radical cation formation

Collision-induced dissociation experiments on the Ag+-phenylalanine complex using several collision energies were shown to yield ten different fragment ions. Unambiguous assignment of these fragment ions were made by careful analysis of deuterium labeling experiments. The losses of H2O, CO, CO2, and AgH were commonly observed; also encountered were the losses of H2, Ag, and H. Deuterium labeling experiments and density functional calculations have been employed to probe fragmentation mechanisms that account for all experimental results.     

Existence of doubly charged lead monohydrate: experimental evidence and theoretical examination

Despite reports to the contrary, doubly charged lead monohydrate is a stable species against both proton and charge transfers. [Pb(H(2)O)](2+) has been observed as a minor product in the ligand-exchange reaction of [Pb(CH(3)CN)](2+) with H(2)O after collisional activation. Density functional theory has been used to examine reaction profiles of [Pb(H(2)O)(n)](2+) where n = 1, 2, and 3.     

Collisional cooling enhances the ability to observe non-covalent interactions within the inducible nitric oxide synthase oxygenase domain: Dimerization,complexation, and dissociation

The investigation of protein quaternary structure, protein-cofactor, and protein-ligand interactions by mass spectrometry is often limited by the fragility of such interactions under experimental conditions. To develop more gentle conditions of perhaps general use, we used as a model for study the oxygenase domain of murine inducible nitric oxide synthase (iNOS), which is homodimeric, binds heme and tetrahydrobiopterin H(4)B cofactors, and the substrate L-arginine. The energetics of the collisions in q2 and in the lens region of the mass spectrometer were manipulated for varying the degree of solvation around the non-covalently bound ions. Furthermore, the number of low-energy collisions in the collision cell of the instrument was varied, focusing and dampening the ion beam. Under gentle source collision conditions, and using multiple low-energy collisions in the collision cell of the mass spectrometer, dimers of the iNOS oxygenase domain containing heme, H(4)B, and arginine were observed intact after electrospraying at pH values near neutrality; a mutant of this protein (Trp188 --> Phe) was monomeric and did not bind cofactors. The pH dependence of the iNOS oxygenase domain under acidic conditions was also studied; while heme remained bound to the protein between pH 2.5 and 4.0, the dimeric structure was disrupted. Our findings confirm that non-covalently bound macromolecular complexes are retained and observable using electrospray mass spectrometry under the appropriate experimental conditions.     

Thermal denaturation of some proteins and its effect on their electrospray mass spectrat

The effects of beat on the electrospray mass spectra of eight globular proteins in solution were studied. These ranged from hardly noticeable to a dramatic shift in the mass spectrometric profile and a concomitant increase in ion abundance. This change is believed to be the result of thermal denaturation of the protein species in solution resulting in a transition from a more compact to a less compact conformation. We accounted for this transition by means of a recently proposed model based on aqueous solution acid/base equilibria. For cytochrome c, profiles calculated by means of this model agree well with experimental data. The ΔH of the denaturation reaction of cytochrome c in aqueous solution containing 0.2% acetic acid was calculated from experimental data to be 103.8 ± 9.2 kJ mol^?1, in good agreement with previous measurements.     

A Construction of Partial Difference Sets in {\mathbb{Z}}_{p^{2 \times } } {\mathbb{Z}}_{p^{2 \times \cdot \cdot \cdot \times } } {\mathbb{Z}}_{p^2 }

In this paper, we give a construction of partial difference sets in _p ² x _p ² x ... x _p ²using some finite local rings.Dedicated to Hanfried Lenz on the occasion of his 80th birthdayThe work of this paper was done when the authors visited the University of Hong Kong.     

Marine biological reference materials for methylmercury: analytical methodologies used in certification

Summary The methylmercury concentrations in three existing marine biological certified reference materials — TORT-1, DORM-1 and DOLT-1 — are determined by gas chromatography with electron capture detection, cold vapour atomic absorption spectrometry and inductively coupled plasma mass spectrometry after selective isolation of methylmercury. Two such procedures were used. These and the three analytical techniques are evaluated and compared. The certified methylmercury concentrations are: TORT-1, 0.128 ± 0.014; DORM-1, 0.731±0.060; and DOLT-1, 0.080 ± 0.011 g Hg/g dry weight.

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Meeresbioligische Referenzmaterialien für Methylquecksilber: Analytische Methoden der Zertifizierung

     

Ab initio studies on Al(+)(H(2)O)(n), HAlOH(+)(H(2)O)(n-1), and the size-dependent H(2) elimination reaction

We report computational studies on Al(+)(H(2)O)(n), and HAlOH(+)(H(2)O)(n-1), n = 6-14, by the density functional theory based ab initio molecular dynamics method, employing a planewave basis set with pseudopotentials, and also by conventional methods with Gaussian basis sets. The mechanism for the intracluster H(2) elimination reaction is explored. First, a new size-dependent insertion reaction for the transformation of Al(+)(H(2)O)(n), into HAlOH(+)(H(2)O)(n-1) is discovered for n > or = 8. This is because of the presence of a fairly stable six-water-ring structure in Al(+)(H(2)O)(n) with 12 members, including the Al(+). This structure promotes acidic dissociation and, for n > or = 8, leads to the insertion reaction. Gaussian based BPW91 and MP2 calculations with 6-31G* and 6-31G** basis sets confirmed the existence of such structures and located the transition structures for the insertion reaction. The calculated transition barrier is 10.0 kcal/mol for n = 9 and 7.1 kcal/mol for n = 8 at the MP2/6-31G** level, with zero-point energy corrections. Second, the experimentally observed size-dependent H(2) elimination reaction is related to the conformation of HAlOH(+)(H(2)O)(n-1), instead of Al(+)(H(2)O)(n). As n increases from 6 to 14, the structure of the HAlOH(+)(H(2)O)(n-1) cluster changes into a caged structure, with the Al-H bond buried inside, and protons produced in acidic dissociation could then travel through the H(2)O network to the vicinity of the Al-H bond and react with the hydride H to produce H(2). The structural transformation is completed at n = 13, coincident approximately with the onset of the H(2) elimination reaction. From constrained ab initio MD simulations, we estimated the free energy barrier for the H(2) elimination reaction to be 0.7 eV (16 kcal/mol) at n = 13, 1.5 eV (35 kcal/mol) at n = 12, and 4.5 eV (100 kcal/mol) at n = 8. The existence of transition structures for the H(2) elimination has also been verified by ab initio calculations at the MP2/6-31G** level. Finally, the switch-off of the H(2) elimination for n > 24 is explored and attributed to the diffusion of protons through enlarged hydrogen bonded H(2)O networks, which reduces the probability of finding a proton near the Al-H bond.