1H-NMR investigations of the conformation of aryl-(hydroxynaphthyl)-methylpiperidines. Intramolecular interactions,IV

Summary The¹H-NMR spectra of aryl-(hydroxynaphthyl)-methylpiperidines, which are model compounds for intramolecular hydrogen bonding, have been analyzed in order to investigate their conformations in solution. As dynamic phenomena can be assumed from line broadening, low temperature spectra have been measured to evaluate the coalescence temperatures and the energy barriers. The latter have been discussed with respect to the size and position of selected substituents. It can be shown that the molecules exist in one energetically favorable conformation with the aryl ring perpendicular to the plane of the naphthol ring system. The interaction between the naphthol ring and the aryl ring influences the conformation at the piperidine ring moiety. This effect leads to an increase of the inversion barrier of the piperidine residue.On Sabbatical Leave from Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan     

1,1‐Ethylboration of alkyn‐1‐yl‐chloro(methyl)silanes: alkenes with chloro(methyl)silyl and diethylboryl groups in cis positions

The 1,1‐ethylboration of alkyn‐1‐yl‐chloro(methyl)silanes, Me₂Si(Cl)? C?C? R ( 1 ) and Me(H)Si(Cl)? C?C? R ( 2 ) [R = Bu ( 2a ), CH₂NMe₂ ( 2b )] requires harsh reaction conditions (up to 20 days in boiling triethylborane), and leads to alkenes in which the boryl and silyl groups occupy cis ((E)‐isomers: 3a , 3b , 5a , 5b ) or trans positions ((Z)‐isomers in smaller quantities: 4b and 6b ). The alkenes are destabilized in the presence of SiH(Cl) and CH₂NMe₂ units ( 5b , 6b ). NMR data indicate hyper‐coordinated silicon by intramolecular N? Si coordination in 3b and 5b , by which, at the same time, weak Si? Cl? B bridges are favoured. Copyright © 2005 John Wiley & Sons, Ltd.     

An isocratic reversed-phase high-performance liquid chromatographic method for the simultaneous determination of benzoyl peroxide and the related compounds benzoic acid, benzaldehyde, ethyl benzoate, methylparaben, and propylparaben in dermal preparations

A reversed-phase high-performance liquid chromatographic method was developed for the simultaneous determination of benzoyl peroxide and the related compounds benzoic acid (BA), methylparaben, benzaldehyde, propylparaben, and ethyl benzoate. The compounds are separated on a column containing octadecyl silane chemically bonded to porous silica particles. The mobile phase is acetonitrile-buffer (45 + 55, v/v). Solutions are injected into the chromatographic system under isocratic conditions at a constant flow rate of 1.5 mL/min with UV detection at 235 nm. Analysis of stability samples showed rapid accumulation of BA by thermal degradation. A rationale has been established for the acceptable limit of BA in the formulation, which already contains BA (0.2%) as a preservative. The proposed method is efficient and determines the active compound and 5 related compounds in a run time of 20 min. The method was validated according to the guidelines of the International Conference on Harmonization and demonstrated good agreement with the validation requirements.     

A Novel Molecule 3-(1′-Methyltetrahydropyridinyl)-2,4-6-Trihydroxy Acetophenone Alleviates Ultraviolet-B-Induced Photoaging in Human Dermal Fibroblasts and BALB/c Mice

Ultraviolet radiation (UVR) is the major exogenous agent that disturbs tissue homeostasis and hastens the onset of age-related phenotypes (photoaging). Exposure to UV-B radiation promotes apoptosis in human skin cells via induction of Reactive Oxygen Species (ROS)-mediated Endoplasmic Reticulum (ER) stress by activating the PERK-eIF2α-CHOP pathway, which plays a major role in exacerbating skin photoaging. Alleviating the production of ROS and boosting the antioxidant capacity of cells is the foremost therapeutic strategy to avert the repercussions of ultraviolet radiation exposure. In this study, we investigated the role of 3-(1′-methyltetrahydropyridinyl)-2,4-6-trihydroxy acetophenone (IIIM-8) in thwarting the UV-B-induced photoaging. We observed that IIIM-8 ameliorates UV-B-induced oxidative stress, ER stress, Loss of Mitochondrial membrane potential, MAPK activation and Inflammation in irradiated skin cells. Ultraviolet radiation-related damage to fibroblasts within the dermis leads to collagen degradation-the hallmark of photoaging. IIIM-8 substantially restored the synthesis of collagen and prevented its degradation via the downregulation of matrix metalloproteinases. Topical application of IIIM-8 prevented BALB/c mice skin from UV-B-induced leukocyte infiltration, epidermal thickening and disruption of Extracellular matrix components. Implying that IIIM-8 has a strong photoprotective property and has potential to be developed as a topical therapeutic/cosmeceutical agent against UV-B-induced photoaging.     

An efficient isolation and purification of broad partition coefficient range ginsenosides from roots of Panax quinquefolium L. by linear gradient counter-current chromatography coupled with preparative high-performance liquid chromatography

As a famous health food, roots of Panax quinquefolium L. possessed immune regulation and enhancement of the central nervous system, in which ginsenosides are the main active component with different numbers and positions of sugars, causing different chemical polarities with a challenge for the separation and isolation. In this study, a fast and effective bilinear gradient counter-current chromatography was proposed for preparative isolation ginsenosides with a broad partition coefficient range from roots of Panax quinquefolium L. In terms of the established method, the mobile phases comprising n-butanol and ethyl acetate were achieved by adjusting the proportion. Coupled with the preparative HPLC, eleven main ginsenosides were successfully separated, including ginsenoside Rg₁ ( 1 ), Re ( 2 ), acetyl ginsenoside Rg₁ ( 3 ), Rb₁ ( 4 ), Rc ( 5 ), Rg₂ ( 6 ), Rb₃ ( 7 ), quinquefolium R₁ ( 8 ), Rd ( 9 ), gypenoside X VII ( 10 ) and notoginsenoside Fd ( 11 ), with purities exceeding 95% according to the HPLC results. Tandem mass spectrometry and electrospray ionization mass spectrometry were adopted for recognizing the isolated compound architectures. Our study suggests that linear gradient counter-current chromatography effectively separates the broad partition coefficient range of ginsenosides compounds from the roots of Panax quinquefolium L. In addition, it can apply to active compound isolation from other complicated natural products.     

Development and Validation of a Stability-Indicating LC Method for Simultaneous Analysis of Aceclofenac and Paracetamol in Conventional Tablets and in Microsphere Formulations

A stability-indicating reversed-phase LC method for analysis of aceclofenac and paracetamol in tablets and in microsphere formulations has been developed and validated. The mobile phase was 80:20 (v/v) methanol–phosphate buffer (10 mM at pH 2.5 ± 0.02). UV detection was at 276 nm. The method was linear over the concentration ranges 16–24 and 80–120 μg mL^?1 for aceclofenac and paracetamol, respectively, with recovery in the range 100.9–102.22%. The limits of detection and quantitation for ACF were 0.0369 and 0.1120 μg mL^?1, respectively; those for PCM were 0.0631 and 0.1911 μg mL^?1, respectively.     

Quantum Carpets: a Probe to Identify Wave-Packet Fractional Revivals

We explain quantum carpets in the position and momentum spaces woven by the self-interference of the de Broglie wave of an atom or an electron trapped in an infinitely deep potential well. The recurrence of self-similar structures in designs of these carpets mimics the phenomena of quantum revivals and fractional revivals. We identify fractional revivals of various order by means of these space–time and momentum–time interference patterns.     

Structural and Magnetic Properties of Chemically Synthesized Pd-Modified NiFe2O4 Nanoparticles

Magnetic nanoparticles of NiFe₂O₄-Pd composites have been synthesized using a simple, low cost, sol-gel auto-combustion method. As-prepared samples were sintered at 800 ℃ for 6 h in order to develop the crystalline phase. X-ray diffraction confirmed the spinel structure of the ferrite samples. Structural morphology and size of the nanoparticles were evaluated using a field emission scanning electron microscope. Magnetic hysteresis loops were obtained at 300 and 100 K using a physical properties measurement system. The value of saturation magnetization was observed to decrease at the temperatures with the increase of Pd contents up to 5% but then a sudden rise in saturation magnetization was observed for the addition of 10% Pd in NiFe₂O₄.