N-Methyl-4-hydrazino-7-nitrobenzofurazan: a fluorogenic substrate for peroxidase-like DNAzyme,and its potential application

Characterization and optimization studies of N-methyl-4-hydrazino-7-nitrobenzofurazan (MNBDH) as a new fluorogenic substrate in the peroxidation reaction catalyzed by DNAzyme are reported. The effects of pH, H₂O₂ concentration, metal-cation type, and the concentration and type of surfactant on the fluorescence intensity were investigated. The optimized reaction was subsequently used for the development of an assay for DNA detection based on a molecular-beacon probe. The use of a fluorogenic substrate enabled the detection of a single-stranded DNA target with a 1 nmol L^?1 detection limit. Graphical Abstract

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Nonlinear Effects in Paul Traps Operated in the Second Stability Region: Analytical Analysis and Numerical Verification

Paul trap working in the second stability region has long been recognized as a possible approach for achieving high-resolution mass spectrometry (MS), which however is still far away from the experimental implementations because of the narrow working area and inefficient ion trapping. Full understanding of the ion motional behavior is helpful for solving the problem. In this article, the ion motion in a superimposed octopole field, which was characterized by the nonlinear Mathieu equation, was solved analytically using Poincare-Lighthill-Kuo (PLK) method. This method equivalently described the nonlinear disturbance by an effective quadrupole field with perturbed Mathieu parameters, a _u ^′ and q _u ^′ , which would bring huge convenience in the studies of nonlinear ion dynamics and was, therefore, used for rapid evaluation of the nonlinear effects of ion motion. Fourth-order Runge-Kutta method (4th R-K) indicated the error of PLK for characterizing the frequency shift of ion motion was within 15%. Figure

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Synthesis and structure of the [Co(NioxH)<Subscript>2</Subscript>(Thio)<Subscript>2</Subscript>]<Subscript>2</Subscript>SO<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O complex compound

A new Co(III) complex of 1,2-cyclohexanedionedioxime and thiocarbamide with an SO ₄ ^2? anion and solvation water molecules in the outer sphere has been synthesized and its structure has been defined. Orthorhombic crystals, a = 11.659(2) Å, b = 26.448(5) Å, c = 30.142(6) Å, V = 9295(3) Å ³, Z = 8, d_calc = 1.599 g/cm³, space group Pbca; final R index is 0.0578 for 8221 reflections with I > 2σ(I). In the octahedral Co(III) complex, two 1,2-cyclohexanedionedioxime residues lie in the equatorial plane, while two thiocarbamide molecules are in the axial plane. Intramolecular bonds: N-H…O and O-H…O type hydrogen bonds and π-π interactions that stabilize the complex cations. In crystal, the components are linked by N-H…O and O-H…O hydrogen bonds into a 3D framework.     

A Distonic Radical-Ion for Detection of Traces of Adventitious Molecular Oxygen (O2) in Collision Gases Used in Tandem Mass Spectrometers

We describe a diagnostic ion that enables rapid semiquantitative evaluation of the degree of oxygen contamination in the collision gases used in tandem mass spectrometers. Upon collision-induced dissociation (CID), the m/z 359 positive ion generated from the analgesic etoricoxib undergoes a facile loss of a methyl sulfone radical [^?SO₂(CH₃); 79-Da] to produce a distonic radical cation of m/z 280. The product-ion spectrum of this m/z 280 ion, recorded under low-energy activation on tandem-in-space QqQ or QqTof mass spectrometers using nitrogen from a generator as the collision gas, or tandem-in-time ion-trap (LCQ, LTQ) mass spectrometers using purified helium as the buffer gas, showed two unexpected peaks at m/z 312 and 295. This enigmatic m/z 312 ion, which bears a mass-to-charge ratio higher than that of the precursor ion, represented an addition of molecular oxygen (O₂) to the precursor ion. The exceptional affinity of the m/z 280 radical cation towards oxygen was deployed to develop a method to determine the oxygen content in collision gases. Figure

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Higher order structure characterization of protein therapeutics by hydrogen/deuterium exchange mass spectrometry

Characterization of therapeutic drugs is a crucial step in drug development in the biopharmaceutical industry. Analysis of protein therapeutics is a challenging task because of the complexities associated with large molecular size and 3D structures. Recent advances in hydrogen/deuterium-exchange mass spectrometry (HDX-MS) have provided a means to assess higher-order structure of protein therapeutics in solution. In this review, the principles and procedures of HDX-MS for protein therapeutics characterization are presented, focusing on specific applications of epitope mapping for protein–protein interactions and higher-order structure comparison studies for conformational dynamics of protein therapeutics. Figure

HDX of protein backbone amide hydrogen     

Synthesis of Au13(glutathionato)8@β-cyclodextrin nanoclusters and their use as a fluorescent probe for silver ions

Heating and drying of the mixture of glutathione-etched gold nanoparticles (Au-SG) and β-cyclodextrin (β-CD) results in the formation of β-CD-capped and glutathionate-protected Au₁₃ nanoclusters (Au₁₃(SG)₈@β-CD). Their particle size, composition, and number of gold atoms and the capping molecules were characterized by scanning electron microscopy, fluorescence, UV–vis absorption, FT-IR spectroscopy and mass spectrometry. The fluorescence of these nanoclusters is specifically enhanced by the addition of Ag(I) ions to the aqueous solution. This effect was exploited to develop a selective and sensitive method for the fluorometric determination of Ag(I) in water in the concentration range between 0.5 nM and 0.1 μM, with a detection limit at 0.3 nM (at a signal-to-noise ratio of 3). Graphical Abstract

β-CD-capped Au₁₃ nanoclusters has been synthesized by heating and drying the mixture of glutathione-etched gold nanoparticles and β-CD. A simple, sensitive and selective FL sensing method for Ag⁺ in environmental water has developed using the Au nanoclusters.     

<Emphasis Type="Italic">N,N</Emphasis>-diethylanilinium complex with borodicitric acid: Synthesis and crystal structure

N,N-Diethylanilinium dicitratoborate [C₆H₅NH(C₂H₅)₂][(C₆H₆O₇)₂B] (I) has been synthesized for the first time. Single crystals has been synthesized in an aqueous solution to study the crystal structure of complex I by single-crystal X-ray diffraction. Crystals are triclinic, space group Р1 a = 9.6183(2) Å, b = 10.3153(3) Å, c = 13.7364(4) Å, α = 69.0304(12)°, β = 77.0394(13)°, γ = 89.5518(10)°, V = 1236.25(6) ų, Z = 2, ρ_calcd = 1.454 g/cm³. Structural units in a crystal of complex I are large complex dicitratoborate anions with a spirane structure and N,N-diethylanilinium cations. The crystal packing is a three-dimensional framework implemented via a system of hydrogen bonds like О–Н…О, О–Н…О, ОI, and N–Н…О.     

Synthesis and structural characterization of binuclear ytterbium(III) complexes with 2-amino and 3-amino benzoic acid

Two novel homobinuclear ytterbium(III) complexes, [Yb₂(2AMB)₆(H₂O)₄] · 2C₂H₆O (I) and Yb₂(3AMB)₆(H₂O)₄] · 3H₂O (II) (2AMB = 2-aminobenzoic acid, 3AMB = 3-aminobenzoic acid) have been synthesized and characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis and X-ray crystallography (CIF files CCDC nos. 950103 (I), 921652 (II)). Complex I crystallizes in triclinic space group \(P\bar 1\) and complex II crystallizes in monoclinic space group P2₁/n. X-ray analysis shows that both complexes (I, II) have the dinuclear structure. The central Yb³⁺ ions in both complexes are eight-coordinated adopting distorted YbO₈ dodecahedral geometry. Each Yb³⁺ ion is coordinated to two O atoms from bridging carboxylate, four O atoms from the chelating carboxylate ligands and two O atoms of water molecules. The crystal structure of I and II are stabilized by N-H…O, O-H…O, O-H…N, and C-H…O hydrogen bonds, C-H…π interactions and weak π-π stacking interactions.     

Ion Funnel Augmented Mars Atmospheric Pressure Photoionization Mass Spectrometry for In Situ Detection of Organic Molecules

Laser desorption is an attractive technique for in situ sampling of organics on Mars given its relative simplicity. We demonstrate that under simulated Martian conditions (~2.5 Torr CO₂) laser desorption of neutral species (e.g., polycyclic aromatic hydrocarbons), followed by ionization with a simple ultraviolet light source such as a discharge lamp, offers an effective means of sampling organics for detection and identification with a mass spectrometer. An electrodynamic ion funnel is employed to provide efficient ion collection in the ambient Martian environment. This experimental methodology enables in situ sampling of Martian organics with minimal complexity and maximum flexibility. Figure

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Hirshfeld Surface Analysis,Crystal Structure and Spectroscopic Studies of a New Cu(II) Halocuprate Salt with Protonated N-Amino-Ethyl-Piperazine

(C₆H₁₈N₃)₄[CuCl₅]₂[CuCl₄]₃·1.42H₂O is prepared and characterized by various physicochemical techniques. The single crystal X-ray diffraction structural analysis reveals that the title compound belongs to the orthorhombic system with the space group Cmca. Its unit cell dimensions are: a = 24.286(2) Å, b = 14.3082(14) Å, c = 16.6160(16) Å, Z = 4, V = 5773.8(10) ų. Its crystal structure is determined and refined down to R = 0.024 and wR(F²) = 0.059. The structure contains three crystallographically independent Cu²⁺ ions coordinated to chlorine anions in various fashions. Cu1 is five-coordinated in a distorted square pyramidal fashion, while Cu2 and Cu3 are four-coordinated in square planar and distorted tetrahedral fashions, respectively. The entities are interconnected by means of the hydrogen bonding [O(W)–H…Cl, N–H…Cl, C–H…Cl and C–H…O(W)], forming a three-dimensional network. Intermolecular interactions are investigated by Hirshfeld surfaces and the contacts of the eight different chloride atoms are notably compared. The vibrational absorption bands are identified by infrared spectroscopy. The optical study is performed by UV-vis absorption.     

Hybrid nanonet/nanoflake NiCo2O4 electrodes with an ultrahigh surface area for supercapacitors

An integrated electrode consisting of hybrid nanonet/nanoflake NiCo₂O₄ grown on stainless steel mesh substrates exhibits a high specific capacitance while maintaining high-rate capability and good cycling stability. The specific capacitance reaches a maximum of 911 F g^?1 at a current density of 10 A g^?1, which can still retain 864 F g^?1 (94.8 % retention) after 10,000 cycles. These much-improved electrochemical performances are attributed to the unique architecture of NiCo₂O₄ electrode. The interconnected nanonet NiCo₂O₄ with an ultrahigh surface area significantly facilitates the rapid ion/electron transport and guarantees good mechanical adhesion, while the ultrathin nanoflakes further extend the active sites for fast redox reactions for efficient energy storage. Figure

Hybrid nanonet/nanoflake NiCo₂O₄ grown on stainless steel mesh exhibits superior capacitive performance and long-life stability as an integrated electrode for high-performance supercapacitors.     

Electrochemical immunoassay for the prostate specific antigen using ceria mesoporous nanospheres

We report on a sensitive electrochemical immunoassay for the prostate specific antigen (PSA). An immunoelectrode was fabricated by coating a glassy carbon electrode with multiwalled carbon nanotubes, poly(dimethyldiallylammonium chloride), CeO₂ and PSA antibody (in this order) using the layer-by-layer method. The immunosensor is then placed in a sample solution containing PSA and o-phenylenediamine (OPD). It is found that the CeO₂ nanoparticles facilitate the electrochemical oxidation of OPD, and this produces a signal for electrochemical detection of PSA that depends on the concentration of PSA. There is a linear relationship between the decrease in current and the concentration of PSA in the 0.01 to 1,000 pg mL^?1 concentration range, and the detection limit is 4 fg mL^?1. The assay was successfully applied to the detection of PSA in serum samples. This new differential pulse voltammetric immunoassay is sensitive and acceptably precise, and the fabrication of the electrode is well reproducible. Figure

A novel electrochemical immunoassay for prostate specific antigen (PSA) was developed. Ceria (CeO₂) mesoporous nanospheres facilitated the electrochemical oxidation of o-phenylenediamine (OPD). The developed immunoassay has high sensitivity and can be successfully applied for the detection of PSA in serum samples     

Thermochemistry of the Reaction of Solvated Sodium Ion Clusters with Thymine in the Gas Phase: An Example of the Reaction in Microcosmic Environment

The thermochemistry of the reaction of the microsolvated Na⁺ such as [Na(H₂O) _n ; n?=?1?6]⁺, [Na(NH₃) _n ; n?=?1?6]⁺ and [Na(H₂O) _n (NH₃) _m ; n?+?m?=?2?6]⁺ with thymine (Thy), as an example of a reaction in the microcosmic environment, have been studied in this work, theoretically. It was found that the increase of the number of solvent molecules in the structure of microsolvated Na⁺ is accompanied by the decrease of the standard enthalpy (\(\Delta H_{r}^{^\circ }\)) and Gibbs free (\(\Delta G_{r}^{^\circ }\)) energies of the reaction (Thy?+?[Na(X) _n ]⁺→Thy-Na(X) _n ⁺ ; X?=?solvent molecule). Also, the calculations showed that the electronic intermolecular interaction (?E_int) between the Thy and microslovated Na⁺ decreased with the increase of solvent molecules. For the interaction of the [Na(H₂O) _n ; n?=?4, 5 and 6]⁺ ions with the Thy, there was the probability of forming of the hydrogen bond between water molecules in the structure of solvated Na⁺ and the Thy. The gas phase infrared (IR) spectra of the complexes of the microsolvated Na⁺ with the Thy for different values of n were calculated and compared with each other to follow the change in the frequency of the stretching vibration of the interaction path between the C=O group of the Thy and Na (O…Na) with n. Using the calculated values of \(\Delta G_{r}^{^\circ }\) of the reactions, the mole fractions of the complexes of microsolvated Na⁺ ions with the Thy were calculated at different humidity.     

Crystal structures of tetrafluoroantimonates(III) of single and double protonated 3-amino-1,2,4-triazolium cations

Crystal structures are determined by X-ray crystallography for tetrafluoroantimonates(III) of single and double protonated 3-amino-1,2,4-triazolium cations of the composition (C₂H₅N₄)SbF₄ (I) (monoclinic: a = 4.7723(6) Å, b = 19.643(2) Å, c = 7.6974(9) Å, β = 97.239(2)°, Z = 4, Cc space group) and (C₂H₆N₄)(SbF₄)₂ (II) (monoclinic: a = 4.7617(3) Å, b = 15.512(1) Å c = 7.4365(5)Å β = 107.706(1)°, Z = 2, P2₁/n space group). The structure of I is built from complex [SbF₄]^? anions and single charged (C₂H₅N₄)⁺ cations; the structure of II is built from the same anion and double charged 3-amino-1,2,4-triazolium cation: (C₂H₆N₄)²⁺. In the structure, weak interactions Sb…F join the anions in polymeric layers [SbF₄] _n ^n? that are assembled in a 3D framework by N-H…F hydrogen bonds. The formation of the double protonated 3-amino-1,2,4-triazolium cation (C₂H₆N₄)²⁺, found in the crystal structure of II, is observed for the first time.     

Gas-Phase Arylmethyl Transfer and Cyclodeamination of Argentinated N-Arylmethyl-Pyridin-2-Ylmethanimine

In collisional activation of argentinated N-arylmethyl-pyridin-2-ylmethanimine, a neutral molecule of AgNH₂ is eliminated, carrying one hydrogen from the methylene and the other one from the ortho position (relative to the ipso carbon) of the aryl ring. Taking argentinated N-benzyl-pyridin-2-ylmethanimine for example, the proposition that the AgNH₂ loss results from intramolecular arylmethyl transfer combined with cyclodeamination is rationalized by deuterium labeling experiments, blocking experiments, and theoretical calculations. The structure of the final product ion from loss of AgNH₂ was confirmed further by multistage mass spectrometry.

Structure,Stability, and Fragmentation of Sodium bis(2-ethylhexyl)Sulfosuccinate Negatively Charged Aggregates In Vacuo by MD Simulations

Negatively charged supramolecular aggregates formed in vacuo by n bis(2-ethylhexyl)sulfosuccinate (AOT^–) anions and n + n _c sodium counterions (i.e., [AOT _n Na _n+nc ] ^nc ) have been investigated by molecular dynamics (MD) simulations for n = 1 to 20 and n _c = –1 to –5. By comparing the maximum excess charge values of negatively and positively charged AOTNa aggregates, it is found that the charge storage capability is higher for the latter systems, the difference decreasing as the aggregation number increases. Statistical analysis of physical properties like gyration radii and moment of inertia tensors of aggregates provides detailed information on their structural properties. Even for n _c = –5, all stable aggregates show a reverse micelle-like structure with an internal core, including sodium counterions and surfactant polar heads, surrounded by an external layer consisting of the surfactant alkyl chains. Interestingly, the reverse micelle-like structure is retained also in proximity of fragmentation. Moreover, the aggregate shapes may be approximated by elongated ellipsoids whose longer axis increases with n and |n _c |. The fragmentation patterns of a number of these aggregates have also been examined and have been found to markedly depend on the aggregate charge state. The simulated fragmentation patterns of a representative aggregate show good agreement with experimental data obtained using low collision voltages. Figure

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Soft Ionization of Saturated Hydrocarbons, Alcohols and Nonpolar Compounds by Negative-Ion Direct Analysis in Real-Time Mass Spectrometry

Large polarizable n-alkanes (approximately C18 and larger), alcohols, and other nonpolar compounds can be detected as negative ions when sample solutions are injected directly into the sampling orifice of the atmospheric pressure interface of the time-of-flight mass spectrometer with the direct analysis in real time (DART) ion source operating in negative-ion mode. The mass spectra are dominated by peaks corresponding to [M + O₂]￣^?. No fragmentation is observed, making this a very soft ionization technique for samples that are otherwise difficult to analyze by DART. Detection limits for cholesterol were determined to be in the low nanogram range.

Intramolecular Electrophilic Aromatic Substitution in Gas-phase Fragmentation of Protonated N-Benzylbenzaldimines

In this study, the gas-phase fragmentations of protonated N-benzylbenzaldimines were investigated by electrospray ionization tandem mass spectrometry (ESI-MSⁿ). Upon collisional activation, several characteristic fragment ions are produced and their fragmentation mechanisms are rationalized by electrophilic aromatic substitution accompanied by benzyl cation transfer. (1) For N-(p-methoxybenzylidene)-1-phenylmethanimine, concomitant with a loss of HCN, a product ion at m/z 121 was observed. It is proposed to be generated from electrophilic substitution at the ipso-position by transferring benzyl cation rather than cleavage of the C-N double bond. (2) For N-(m-methoxybenzylidene)-1-phenylmethanimine, a product ion at m/z 209 was obtained, corresponding to the elimination of NH₃ carrying two hydrogens from the two aromatic rings respectively. This process can be rationalized by two sequential electrophilic substitutions and cyclodeamination reaction based on the benzyl cation transfer. Deuterium-labeled experiments, density functional theory (DFT) calculation and substituent effect results also corroborate the proposed mechanism. Figure a

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Investigation of bn-44 Peptide Fragments Using High Resolution Mass Spectrometry and Isotope Labeling

An N-terminal deuterohemin-containing hexapeptide (DhHP-6) was designed as a short peptide cytochrome c (Cyt c) mimetic to study the effect of N-terminal charge on peptide fragmentation pathways. This peptide gave different dissociation patterns than normal tryptic peptides. Upon collision-induced dissociation (CID) with an ion trap mass spectrometer, the singly charged peptide ion containing no added proton generated abundant and characteristic b_n-44 ions instead of b_n-28 (a_n) ions. Studies by high resolution mass spectrometry (HRMS) and isotope labeling indicate that elimination of 44 Da fragments from b ions occurs via two different pathways: (1) loss of CH₃CHO (44.0262) from a Thr side chain; (2) loss of CO₂ (43.9898) from the oxazolone structure in the C-terminus. A series of analogues were designed and analyzed. The experimental results combined with Density Functional Theory (DFT) calculations on the proton affinity of the deuteroporphyrin demonstrate that the production of these novel b_n-44 ions is related to the N-terminal charge via a charge-remote rather than radical-directed fragmentation pathway. Graphical Abstract

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