A strategy to improve the accuracy of digital simulation for electroanalytical chemistry

A strategy for digital simulation methods was presented for solving partial differential equations, called as IPBFP which is to insert M points before the first time point of the usual way, to decrease simulation errors. The theoretical analysis and simulation results show that it can improve the fully implicit method with any dimensionless diffusion coefficient A, Crank-Nicolson method with large and Saul'yev method with small . The IPBFP is convenient to arrange the simulation time points flexibly and reduce calculation time and errors. This approach can combine the merits of non-uniform time grid and uniform time grid methods in simulation for electrochemical studies.     

Determination of the Poisson’s ratio of viscoelastic materials based on the linear rheological model using instrumented indentation

Based on the linear rheological constitutive model that is used to describe viscoelastic-plastic behavior of viscoelastic materials, a formula of the Poisson’s ratio was deduced according to the relationship between the shear creep compliance and tensile compliance. Instrumented indentation under various loading conditions and universal creep tests were performed on polyamide 12 samples to obtain the relevant rheological parameters. Results show that the Poisson’s ratio for a step load indentation can obtain a constant but overrated value. However, the Poisson’s ratio approaches an asymptotic value and an accurate value can be gained at a certain loading rate.     

A new strategy for label-free electrochemical immunoassay based on “gate-effect” of β-cyclodextrin modified electrode

A novel label-free electrochemical immunoassay was developed for prostate-specific antigen (PSA) detection via using β-cyclodextrin (β-CD) assembled layer created gates for the electron transfer of probe. To construct the sensor, a gold electrode was self-assembled with monoclonal anti-PSA antibody labeled 6-mercapto-β-cyclodextrin. Interspaces among β-CD molecules in the layer were automatically formed on gold electrode, which act as the channel of the electron transfer of [Fe(CN)₆]^3−/4− probe. When PSA bind with anti-PSA, it can block these channels on the electrode surface due to their steric hindrance effect, resulting in the decrease in redox current of the probe. Through such a gate-controlled effect, ultra trace amount of PSA may make the currents change greatly after the immunoreaction, which enhanced the signal-to-noise ratio to achieve the amplification effect. By evaluating the logarithm of PSA concentrations, the immunosensor had a good linear response to the current changes with a detection limit of 0.3 pg/mL (S/N = 3) when PSA concentration ranged from 1.0 pg/mL to 1.0 ng/mL. The label-free immunosensor exhibited satisfactory performances in sensitivity, repeatability as well as specificity.     

A synthetic approach to the phorboxazoles – A strategy for the synthesis of the C1–C19 polyketide fragment

A synthetic approach to the C1–C19 polyketide fragment of the phorboxazoles is disclosed here. While an initial two-directional approach was efficient, it did not proceed in a high enough yield to justify moving forward. A subsequent successful strategy for the generation of the C11–C15 pyrans of both of the phorboxazoles was achieved, and the installation of the C9 stereocenter was able to be demonstrated. Furthermore, an efficient route for the preparation of the C1–C8 fragment with suitable functionality to allow for elaboration into the complete C1–C19 fragment, with the capricious C2–C3 Z-geometry installed, was also achieved.     

The impact of measurement uncertainty on the producer’s and user’s risks, on classification and conformity assessment: an example based on tests on some construction products

The reliability of test results and subsequent classification statements or product certification depend on the variability of the product’s properties and on the validity of the test procedures used. With an emphasis on measurement uncertainty, producer’s and user’s risks as well as probabilities of conformance, conformity and classification are calculated exemplarily for two requirements for mineral aggregates used in construction. An important methodological basis is an international draft document on measurement uncertainty in conformity assessment. The mathematical instruments given are applied and further developed to a risk scenario for product classification. The results from a classification point of view show that the reliability of test results for acid-soluble sulphates is mostly acceptable and both the producer’s and user’s risks are quite small. In contrast, the magnesium sulphate index test produces results which are hardly usable for classification and certification purposes or for risk management in production. Product certification bodies should generally have an appropriate approach when dealing with results where precision data are poor.     

A Study on Inhibitors for the Prevention of Hydrate Formation in Gas Transmission Pipeline

Gas Hydrate is usually formed during the transportation and treatment of oil and gas, resulting in the plugging of gas pipeline and equipment. Three thermodynamic calculation formulas are analyzed to deal with this problem. The lowering of the freezing point of the inhibitors AT is used to calculate the formation temperature of natural gas hydrates. This is considered to be a good approach because it is not limited by what kind and what concentration of inhibitors one uses. Besides, the rate of lowering of the freezing point could be easily measured. The result of testing methanol and mono-ethylene glycol in a reactor shows that adding 10% inhibitors to the reactor can prevent the hydrates formation. Kinetic inhibitors are favored in the present research. They are divided into two types, polymer and surface-active agents. Their characteristics, mechanisms, and application prospect are separately discussed. Polymer inhibitors exhibit better efficiency. The result of field application of VC-713 inhibiter is also given in this article. In practice, the combination of thermodynamic inhibitors and kinetic inhibitors gives better result.     

A multifunctional probe based on the use of labeled aptamer and magnetic nanoparticles for fluorometric determination of adenosine 5’-triphosphate

A multifunctional fluorescent probe is synthesized for the determination of adenosine 5′-triphosphate (ATP). The 6-carboxyfluorescein-labeled aptamer (FAM-aptamer) was bound to the surface of magnetite nanoparticles coated with polydopamine (Fe₃O₄@PDA) by π-π stacking interaction to form the multifunctional probe. The probe has three functions including recognition, magnetic separation, and yielding a fluorescent signal. In the presence of ATP, FAM-aptamer on the surface of the probe binds to ATP and returns to the solution. Thus, the fluorescence of the supernatant is enhanced and can be related to the concentration of ATP. Fluorescence intensities were measured at excitation/emission wavelengths of 494/526 nm. Response is linear in the 0.1–100 μM ATP concentration range, and the detection limit is 89 nM. The probe was applied to the quantitation of ATP in spiked human urine and serum samples, with recoveries ranging between 94.8 and 102%.

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Graphical abstract A multifunctional fluorescent probe based on the use of FAM-aptamer and Fe₃O₄@PDA is described for the determination of ATP in spiked human urine and serum samples. FAM-aptamer: 6-carboxyfluorescein-labeled aptamer; Fe₃O₄@PDA: magnetite nanoparticles coated with polydopamine. ATP: adenosine 5′-triphosphate.

     

A note on Michael Weisberg’s: challenges to the structural conception of chemical bonding

Michael Weisberg’s recent 2007 paper on the chemical bond makes the claim that the chemical notion of the covalent bond is in trouble. This note casts doubts on that claim.

Study on the bioactivity changes of hydroxylated sulfonylureas derivatives: A possible metabolism

Some new sulfonylureas and their hydroxylation products had been synthesized from 2-amino-4-methylpyrimidine. Their bioactivities against E. coli AHAS II in vitro were tested and the results indicated that the hydroxylation decreased the inhibition activities of sulfonylureas significantly. Subsequently herbicidal tests against stem-growth of barnyard grass and root-growth of rape confirmed the above conclusion. The preliminary molecular docking studies were also carried out to investigate the binding modes of non-hydroxylated and hydroxylated sulfonylureas with AHAS.     

A computational study on the stability–aromaticity correlation of triply N-confused porphyrins: CMMSE-09

The B3LYP density functional theory methodology in conjunction with the 6-31G(d,p) basis set has been used to characterize triply N-confused meso-tetraphenylporphyrins. According to our computations, there is no a direct correlation between stability and aromaticity as already found for non-substituted confused porphyrins. The inclusion of these substituents in the calculations provokes a decrease of the planarity and aromaticity of these macrocycles along with a notable rise of their relative stability with respect to the non-substituted case. Steric repulsions, both among phenyl rings and β atoms in the pyrrolic rings, and among H atoms in the core of the macrocycles, dominate over aromaticity in the establishment of the most stable conformation of each isomer.     

Acid-catalyzed conversion of caryolan-1-ol to isoclovene: A computational investigation of the multi-step carbocation rearrangement

Acid-catalyzed conversion of caryolan-1-ol to isoclovene involves a multi-step carbocation rearrangement. Electronic structure calculations show that the pathway proceeds through an initial 3° carbocation, as well as a series of three other 3° carbocations. The key stage in which the ring structure is rearranged occurs not as might initially be imagined, in two separate steps with the intermediacy of a 2° carbocation, but rather in a single, concerted but highly asynchronous dyotropic rearrangement. The transition structure for this dyotropic rearrangement strongly resembles the 2° carbocation that would be involved in a stepwise mechanism. However, the dyotropic rearrangement is stereochemically unusual. While one of the bond migrations is suprafacial, as expected, the other is effectively antarafacial. This unusual stereochemical outcome is enforced by the geometric constraints of the polycyclic structure.     

A photoelectrochemical immunosensor based on Au-doped TiO2 nanotube arrays for the detection of α-synuclein

α‐Synuclein (α‐SYN) is a very important neuronal protein that is associated with Parkinson’s disease. In this paper, we utilized Au‐doped TiO₂ nanotube arrays to design a photoelectrochemical immunosensor for the detection of α‐SYN. The highly ordered TiO₂ nanotubes were fabricated by using an electrochemical anodization technique on pure Ti foil. After that, a photoelectrochemical deposition method was exploited to modify the resulting nanotubes with Au nanoparticles, which have been demonstrated to facilitate the improvement of photocurrent responses. Moreover, the Au‐doped TiO₂ nanotubes formed effective antibody immobilization arrays and immobilized primary antibodies (Ab₁) with high stability and bioactivity to bind target α‐SYN. The enhanced sensitivity was obtained by using {Ab₂‐Au‐GOx} bioconjugates, which featured secondary antibody (Ab₂) and glucose oxidase (GOx) labels linked to Au nanoparticles for signal amplification. The GOx enzyme immobilized on the prepared immunosensor could catalyze glucose in the detection solution to produce H₂O₂, which acted as a sacrificial electron donor to scavenge the photogenerated holes in the valence band of TiO₂ nanotubes upon irradiation of the other side of the Ti foil and led to a prompt photocurrent. The photocurrents were proportional to the α‐SYN concentrations, and the linear range of the developed immunosensor was from 50 pg mL^?1 to 100 ng mL^?1 with a detection limit of 34 pg mL^?1. The proposed method showed high sensitivity, stability, reproducibility, and could become a promising technique for protein detection.     

A facile approach to synthesize a “star-like” material based on β-cyclodextrin for enhancing the flowability of paraffinic oils

A novel compound, which exhibits “star-like” architecture and is expected to be a promising flow improver for paraffinic oils, was presented in the current work. This material was facilely synthesized based on β-cyclodextrin molecule via a catalytic esterification procedure under mild experiment conditions. The chemical formation was characterized by FT-IR, ¹H-NMR, and elemental analysis, respectively. The experimental data revealed that each β-cyclodextrin was attached by approximately seven C14 chains. This type of architecture is supposed to be appropriate to co-crystallize with paraffin melocules through taking the place of a paraffin in crystal lattic and thus disperse the agglomeration of wax crystals. This hypothesis was verified through a yield stress test and rheological analysis. It was observed that after treatment with this compound, the paraffinic oil yielded at a much lower stress value compared to the untreated oil. Moreover, a significant shift of the apparent viscosity vs. temperature curve to the left field occurred. These results demonstrated the capacity of this synthesized compound in enhancing the flowability of paraffinic oils.     

Fe/SiO_2 as an XAFS-Probe for the Study on the Effect of Sodium Promotion to the Silica Surface

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Addition of halide to π-bond directly from aqueous NaX solution: a general strategy for installation of two different functional groups

Activation of π-bond with organic Lewis acid and cationic surfactant mediated direct transfer of halides to alkyne and alkene are demonstrated to afford α,α-dihaloketones and other valuable synthons with outstanding selectivities.     

A post-modification approach to independent compo-nent analysis for resolution of overlapping GC/MS signals: from independent components to chemical components

Independent component analysis (ICA) has demonstrated its power to extract mass spectra from over-lapping GC/MS signal. However, there is still a problem that mass spectra with negative peaks at some m/z will be obtained in the resolved results when there are overlapping peaks in the mass spectra of a mixture. Based on a detail theoretical analysis of the preconditions for ICA and the non-negative property of GC/MS signals, a post-modification based on chemical knowledge (PMBK) strategy is pro-posed to solve this problem. By both simulated and experimental GC/MS signals, it was proved that the PMBK strategy can improve the resolution effectively.     

A Study on the Driving Force for Binding of Benzene Derivatives by α-and β-Cyclodextrin

WehavedemonstTatedthattheassociationconstantsfortheinclusioncomplexationofa-and6-cyclodextrin(a-and9-CD)withsubstitutedbenzene(PhX)arecorrelatedwithpropertiessuchasmolarrefraction(R.),hydrophobicity(n.)andeIectroniceffect(a.)ofsubstitUentsintheguestcompounds.Uponapplicationofanariificialneuralnetwork(ANN),theassociationconstants(Ka)fortheinclusionofa-CDand6-CDwithsubstitutedbenzenewerepredictedfromR.,rrxandG.withsatisfactoryresultSl'2.Furthermore,theeffectsofsubstituentsinbenzenederivat…     

A thiol-selective fluorogenic probe based on the cleavage of 4-methylumbelliferyl-2’,4’,6’-trinitropheyl ether

A new fluorescent probe 1,4-methylumbelliferyl-2′,4′,6′-trinitropheyl ether (Probe 1) was designed and synthesized. Probe 1 was a nonfluorescent compound and was synthesized via the one-step reaction of 4-methylumbelliferone (4-MU) with 1-chloro-2,4,6-trinitrobenzene. Upon mixing with biothiols under neutral aqueous conditions, the 2,4,6-trinitrophenyl group of 1 was efficiently removed, and the emissive free dye 4-MU was released, hence leading to a dramatic increase in fluorescence emission of the reaction mixture. A good linear relationship was obtained from 0.1 to 4.0 μmol L⁻¹ for cysteine (Cys), from 0.1 to 3.0 μmol L⁻¹ for homocysteine (Hcy), and from 0.2 to 3.0 μmol L⁻¹ for glutathione (GSH), respectively. The detection limits of Cys, Hcy, and GSH were 24.3, 35.6, and 26.8 nmol L⁻¹, respectively. Furthermore, probe 1 was highly selective for biothiols without the interference of some biologically relevant analytes and has been applied to detecting biothiols in human serum samples.     

Effects of substitution on the effective molarity (EM) for five membered ring-closure reactions – A computational approach

DFT molecular orbital calculations of kinetic parameters for ring closing reactions of substituted 4-bromobutyl alcohols 1–5 and 4-bromobutyl amines 6–10 (Brown’s system) indicate that accelerations in ring closing rate in both systems are largely the result of strain effects as opposed to the currently advanced proximity orientation. Furthermore, the calculated effective molarity (EM) values derived from the DFT data reveal that replacing the nitrogen (6–10, Brown’s system) with an oxygen (1–5, alcoholic analog) results in a decrease in demands on directional flexibility to form 5-membered ring, thus enhancing the rate of the cyclization reaction. In the absence of experimental data the DFT approach could be utilized to predict effective molarities (EM) for intramolecular processes.