Spectrophotometric investigation of the effect of beta-cyclodextrin on the intramolecular cyclization reaction of catecholamines using rank annihilation factor analysis

The catalytic effect of β-cyclodextrin (β-CD) on the intramolecular cyclization reaction of catecholamines dopamine, methyldopa and levodopa after their oxidation with periodate was investigated spectrophotometrically using rank annihilation factor analysis (RAFA). The method was based on the effect of β-CD concentration on the intramolecular cyclization reaction of the investigated catecholamines after their oxidation with potassium periodate. In order to perform RAFA, concentration profiles were calculated by optimizing the value of formation constant. The rank of original data matrix can be reduced by one by annihilating the information of the cyclization reaction in the absence of β-CD. The rate constant for the reactions in the presence and absence of β-CD was also determined. The best estimation of rate constant in the presence of β-CD reduces the rank of the system to zero (noise level). The method was evaluated using synthetic data as well as experimental data and good results were obtained.     

Interaction of β‐Cyclodextrin with Cetyltrimethylammonium Bromide in the Presence of Neutral Red and Its Application to the Spectrophotometric Determination of β‐Cyclodextrin

The effects of addition of β‐cyclodextrin (β‐CD) to the neutral red‐cetyltrimethylammonium bromide (CTAB) associates in pH 7 phosphate buffer solutions were investigated. Addition of β‐CD to neutral red‐CTAB association causes decomposition of the associate by displacement of neutral red with β‐CD. The inclusion complex of CTAB with β‐CD is more stable than that with neutral red. The results indicate that formation of inclusion complex of CTAB with β‐CD prevents its association with neutral red, and inclusion complex formation of β‐CD and neutral red in the presence of CTAB takes place after total consumption of CTAB. The competition of β‐CD and neutral red on the interaction with CTAB can be used for the simple, rapid and sensitive spectrophotometric determination of β‐CD.     

Cathodic etching for fabrication of super-hydrophobic aluminum coating with micro/nano-hierarchical structure

A facile method for fabricating super-hydrophobic surfaces on the magnetron sputtering aluminum film by cathodic electrochemical etching followed by the modification of myristic acid was presented in this article. The morphologies and the compositions of the films were characterized by means of scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), respectively. The corrosion behavior of the super-hydrophobic film was evaluated by potentiodynamic polarization measurement, linear polarization measurement, and electrochemical impedance spectroscopy. After the treatment with cathodic electrochemical etching, the thin aluminum film remained unbroken and the bulk structure of the aluminum coating maintained a microcrystalline morphology while the surface of the coating presented a petal-shaped microstructure dotted with nano-sized floccules. Aluminum myristate was formed on the nano/microstructural surface of the coating when the sample was modified in melting myristic acid. The static water contact angle on the surface was larger than 165°, which demonstrated that a super-hydrophobic film was prepared on the magnetron sputtering aluminum coating. The corrosion resistance of the aluminum coating was enhanced remarkably because of the super-hydrophobic modification.     

GaN nanowires as a reusable photoredox catalyst for radical coupling of carbonyl under blacklight irradiation

Employing photo-energy to drive the desired chemical transformation has been a long pursued subject. The development of homogeneous photoredox catalysts in radical coupling reactions has been truly phenomenal, however, with apparent disadvantages such as the difficulty in separating the catalyst and the frequent requirement of scarce noble metals. We therefore envisioned the use of a hyper-stable III–V photosensitizing semiconductor with a tunable Fermi level and energy band as a readily isolable and recyclable heterogeneous photoredox catalyst for radical coupling reactions. Using the carbonyl coupling reaction as a proof-of-concept, herein, we report a photo-pinacol coupling reaction catalyzed by GaN nanowires under ambient light at room temperature with methanol as a solvent and sacrificial reagent. By simply tuning the dopant, the GaN nanowire shows significantly enhanced electronic properties. The catalyst showed excellent stability, reusability and functional tolerance. All reactions could be accomplished with a single piece of nanowire on Si-wafer.

A highly efficient re-usable semiconductor as a radical coupling catalyst in MeOH.     

Arrest of Rolling Circle Amplification by Protein‐Binding DNA Aptamers

Certain DNA polymerases, such as ?29 DNA polymerase, can isothermally copy the sequence of a circular template round by round in a process known as rolling circle amplification (RCA), which results in super‐long single‐stranded (ss) DNA molecules made of tandem repeats. The power of RCA reflects the high processivity and the strand‐displacement ability of these polymerases. In this work, the ability of ?29DNAP to carry out RCA over circular templates containing a protein‐binding DNA aptamer sequence was investigated. It was found that protein–aptamer interactions can prevent this DNA polymerase from reading through the aptameric domain. This finding indicates that protein‐binding DNA aptamers can form highly stable complexes with their targets in solution. This novel observation was exploited by translating RCA arrest into a simple and convenient colorimetric assay for the detection of specific protein targets, which continues to showcase the versatility of aptamers as molecular recognition elements for biosensing applications.     

Synthesis,Characterization and X‐ray Crystal Structures of [Cu(ncaen)2]ClO4 and [Cu(nca2en)(PPh3)2]BPh4 Complexes

A novel ligand, N,N′‐Bis‐[3‐(2‐nitrophenyl)‐allylidene]‐ethane‐1,2‐diamine (nca₂en), and their corresponding copper(I) complexes, [Cu(ncaen)₂]ClO₄ ( 1 ), and [Cu(nca₂en)(PPh₃)₂]BPh₄ ( 2 ), have been synthesized and characterized by CHN analyses, ¹H and ¹³C‐NMR, IR, and UV‐Vis spectroscopy. The crystal and molecular structures of [Cu(ncaen)₂]ClO₄ ( 1 ), and [Cu(nca₂en)(PPh₃)₂]BPh₄ ( 2 ), were determined by X‐ray crystallography from single‐crystal data. The coordination polyhedron about the copper(I) atom in the two complexes is best described as a distorted tetrahedron. A quasireversible redox behavior is observed for complex 1 and 2 (E_1/2 = 0.55 and 0.95 V, respectively).     

Electrogenerated base-promoted synthesis of tetrahydrobenzo[b]pyran derivatives

An efficient and convenient synthesis of tetrahydrobenzo[b]pyrans is described, using an electrogenerated base of the anion of malononitrile in a one-pot, three component condensation of an aromatic aldehyde, an active methylene compound and dimedone. The reaction is carried out at room temperature in acetonitrile with the use of a sacrificial magnesium anode in a single-compartment cell.     

The effect of Doppler broadening on dispersive and absorptive properties in atomic systems with two-photon interference

The effect of Doppler broadening on dispersive and absorptive properties is theoretically investigated in the hot four-level electromagnetically induced transparency (EIT) atomic systems with two different types of two-photon interference. It is found that the dispersive behavior for the probe in the ladder-type atomic system with two-photon constructive interference will be changed from anomalous in cold atoms to normal in hot atoms, and the three-peak absorptive profile is shifted to a broadened spectrum with a shallow dip at the line center; as a comparison, there is always normal dispersion at the line center for the invert-Y-type atomic system with two-photon destructive interference, but the EIT window in the absorptive profile will be narrowed to subnatural linewidth (0.01Γ) at room temperature. The physics of those two different behaviors are discussed and compared in the dressed-state theory.     

Phenomenological characterization and thermal analysis of flame spread over jet fuel: influence of radiant exposure time

Journal of Thermal Analysis and Calorimetry - The high-temperature objects widely exist in industrial and civil building such as the nearby burning pool fires, the heated walls and the hot smoke...