Regeneration of Carbonyl Compounds by Oxidative Cleavage of Oximes with NBS in the Presence of β‐Cyclodextrin in Water

Abstract

The conversion of different oximes to the corresponding carbonyl compounds was carried out at room temperature in good to high yields with N‐bromosuccinimide in water in the presence of β‐cyclodextrin.     

Effect of 1-n-Dodecanethiol on the Molecular Weight Distribution of Poly(methyl Methacrylate) Synthesized by Suspension Polymerization

Fractionation data of two poly(methyl methacrylate) samples prepared by suspension polymerization up to limiting conversion, in the presence of different amounts of 1-n-dodecanethiol, indicate that both samples have similar polydispersity factors, although the molecular weight distribution curve for the sample obtained with the highest chain transfer agent concentration is shifted to lower molecular weight values. The results obtained are qualitatively correlated with the high conversion polymerization theory proposed by Cardenas and O'Driscoll.     

Efficient Synthesis of β‐Primeverosides as Aroma Precursors by Transglycosylation of β‐Diglycosidase from Penicillium multicolor

The enzyme activity transferring a β‐primeverosyl unit was found from culture filtrates of Penicillium multicolor IAM7153 and was useful for synthesizing a series of β‐primeverosides via a β‐primeverosyl transfer reaction in an aqueous‐organic biphasic system. With the acceptors benzyl alcohol, 2‐phenylethanol, and (Z)‐3‐hexenol, the enzyme induced the transfer products benzyl, 2‐phenylethyl, and (Z)‐3‐hexyl β‐primeverosides in high yields of 51% to 70% based on the donor added. When geraniol and eugenol were used as acceptors, the corresponding geranyl and eugenyl β‐primeverosides were obtained in lower yields of 8% to 12%. The enzyme was an excellent tool for producing naturally occurring β‐primeverosides on a mmol scale.     

Synthesis of Novel Caged Intramolecular Ketals of β‐C‐Glycopyranosidic Ketones

Novel caged intramolecular ketals of β‐C‐glycosidic ketones were prepared from pyranoses. The structures of the new compounds were elucidated by NMR and HRMS spectral analysis. Preliminary studies revealed that the intramolecular ketal could be used to protect 3‐ and 6‐hydroxyl groups of β‐C‐glycosidic ketones.     

A Study on the Optically Active Polymer Poly‐β‐pinene

Poly‐β‐pinene (PBP) was obtained by radiation‐induced polymerization of monomer with γ radiation. The polymerizations were conducted both in vacuum and in the presence of air at different radiation doses up to 1–3 MGy. It was found that the presence of oxygen retards the polymerization rate and reduces the polymer yields and the radiation chemical yield suggesting that the polymerization mechanism involves free radicals. It is shown that PBP can also be obtained in low yields from β‐(‐)pinene polymerization with a free radical initiator. The chemical structures of the PBP radiopolymer and PBP obtained by a free radical initiator were studied by FT‐IR and ¹³C CP‐MAS NMR spectroscopy. The data shows that the PBP obtained have highly ordered structures, which is manifested also by the very high specific optical rotation which is about 3 times that of the starting monomer in the case of the radiopolymer and about 5 times in the case of the PBP prepared with the free radical initiator. In contrast, PBP obtained in high yields by cationic polymerization shows a very low specific optical rotation, much lower than that of the starting monomer and low regularity in chemical structure has been attributed to this polymer by FT‐IR and ¹³C CP‐MAS NMR spectroscopy. It is shown that PBP with high optical activity racemizes over an acidic catalyst.     

The Electrochemical Behavior of Neurotransmitters at a Poly (Pyrrole‐ β‐Cyclodextrin) Modified Glassy Carbon Electrode

Abstract

A glassy carbon electrode surface was modified with an electropolymerized film made of pyrrole and β‐cyclodextrin 1∶1, in a 0.1 M LiClO₄ solution using cyclic voltammetry. The resulting modified electrode (Ppy/β‐CD) exhibits interesting electrocatalytic activity toward the electrochemical oxidation of neurotransmitters such as dopamine (DA) and norepinephrine (NE). Well‐resolved and reversible cyclic voltammograms (CVs) were obtained for these organic compounds in a 0.1 M H₂SO₄ solution. The effect of the pH on the voltammetric response of DA and NE was also investigated inside the range of pH 2.8–8.4. The oxidation current of norepinephrine increase linearly with the concentration inside the range of 4×10^?7 M–2×10^?6 M. The oxidation current of dopamine also followed the same trend range of 2×10^?6 M–10^?5 M. The detection limit was 6×10^?6 M for (DA) and 8×10^?7 M for (NE). As an example, the relative standard deviation for 1×10^?5 M of DA was 2.056%. The diffusion coefficients D for the molecules studied were determined by means of the measurement of the effect of the scan rate on the CVs of the neurotransmitters. All the results showed that the electron transfer was predominantly diffusion controlled at the conducting polymer/solution interface.

Interference phenomenon due to ascorbic acid (AA) toward the neurotransmitters was also investigated. The novel modified electrodes presented capability to resolve perfectly the AA and neurotransmitters oxidation peaks. This performance could be achieved even at a concentration 20 times higher than the neurotransmitters.

Finally, the newly fabricated Ppy/β‐CD film exhibits interesting analytical performances compared with other systems in the literature, such as higher sensitivity, rapid response, good mechanical stability and reproducibility.     

Voltammetric Determination of Hydroquinone using β‐Cyclodextrin/Poly(N‐Acetylaniline)/Carbon Nanotube Composite Modified Glassy Carbon Electrode

Abstract

An electrochemical sensor for hydroquinone (HQ) using β‐cyclodextrin/poly(N‐acetylaniline)/carbon nanotube composite (β‐CD/PAA/MWNTs) modified glassy carbon electrode has been successfully developed. Based on the synergistic effect of MWNTs and conducting PAA polymer and the accumulation effect of β‐CD, the analytical response of the β‐CD/PAA/MWNTs film to the electrochemical behavior of HQ was better than that of a β‐CD/PAA film, a PAA/MWNTs film, a PAA film, or a bare glassy carbon (GC) electrode. Under the conditions chosen, the anodic currents increased linearly with HQ concentration from 1×10^?6 to 5×10^?3 mol l^?1 and the detection limit was 8×10^?7 mol l^?1. This electrochemical sensor showed excellent reproducibility, stability and recovery for the determination of HQ.     

Flow Injection and Batch Spectrophotometric Determination of Ibuprofen Based on its Competitive Complexation Reaction with Phenolphthalein‐β‐Cyclodextrin Inclusion Complex

Abstract

Rapid, simple, and accurate spectrophotometric method is presented for the determination of ibuprofen by batch and flow injection analysis methods. The method is based on ibuprofen competitive complexation reaction with phenolphthalein‐β‐cyclodextrin (PHP‐β‐CD) inclusion complex. The increase in the absorbance of the solution at 554 nm by the addition of ibuprofen was measured. Ibuprofen can be determined in the range 8.0×10^?6 ?3.2×10^?4 and 2.0×10^?5?5.0×10^?3 mol l^?1 by batch and flow methods, respectively. The limit of detection and limit of quantification were 6.19×10^?6 and 2.06×10^?5 mol l^?1 for batch and 1.77×10^?5 and 5.92×10^?5 mol l^?1 for flow method, respectively. The sampling rate in flow injection analysis method was 120±5 samples h^?1. The method was applied to the determination of pharmaceutical formulations.