Ultrasound-assisted extraction of anthraquinones from roots of Morinda citrifolia

This study investigated the use of ultrasound-assisted extraction (UAE) to improve the extraction efficiency of the classical solvent extraction techniques such as maceration and soxhlet extraction to extract anti-oxidant activity compounds, anthraquinones, from the root of Morinda citrifolia. The effects of different extraction conditions were determined, i.e., temperature of (25, 45, 60 °C), ultrasonic power, solvent types, and compositions of ethanol in ethanol–water mixtures. The results show that the yield increases with increasing extraction times and extraction temperatures. The percent recovery of anthraquinones using ultrasound was found to be highly dependent on the type of solvents (acetone > acetonitrile > methanol > ethanol). Furthermore, the use of ethanol–water solution as extraction solvent increased the yield of anthraquinones due to the relative polarity, the swelling effect of plant tissue matrix by water, and increased sound absorption. To achieve the same recovery as that achieved by UAE, soxhlet extraction and maceration required much longer time.     

Flow-injection spectrophotometric determination of calcium using murexide as a color agent

FI spectrophotometric determination of calcium using murexide has been developed. The problem of the color of the dye fading and/or its complex in an alkaline medium in the batch method can be overcome by taking advantage of FIA. A calcium solution is injected into an ethylenediamine–ethylenediamine hydrochloride buffer (1 M, pH 11) which also serves as a masking agent, and is then merged with the aqueous murexide (0.005%, w/v) and continuously monitored. Simple FIA manifolds, including an LED colorimeter detector hooked up to a PC-based data acquisition and evaluation system are described. Optimization of FIA systems has been made. The proposed procedures have been validated by using reference materials and comparing the results with the standard methods, and then applied to ores and drug samples.     

Flow injection spectrophotometric determination of tetracycline in a pharmaceutical preparation by complexation with aluminium(III).

A rapid flow injection (FI) spectrophotometric procedure for tetracycline determination is described. It is based on the injection of a 100 microl sample solution containing tetracycline into merged streams of aluminium(III) chloride (0.01 mol 1(-1)) and Tris-buffer in the presence of KCl (0.06 mol l(-1)), pH 7.0, with the same optimum flow rate of 3.2 ml min(-1). A yellow Al(III)-tetracycline complex was monitored at 376 nm. The flow injection system and the experimental conditions were optimized by means of the univariate method. The procedure was applied to the determination of tetracycline in pharmaceutical preparations with a high sampling rate of at least 165 h(-1). A high precision with a relative standard deviation was obtained less than 0.72 and 0.30% of 5.0 and 10 microg ml(-1) (n=11), respectively. The detection limit (3sigma) and the quantification limit (10sigma) were 0.07 and 0.72 mg l(-1), respectively. There were no interference effects from traditional excipients in the dosage forms when the method was applied to pharmaceutical preparations. The matrix effect could be reduced by the standard addition method.     

Binding affinity of a small molecule to an amorphous polymer in a solvent. Part 1: free energy of binding to a binding site

Crystallization is commonly used in a separation and purification process in the production of a wide range of materials in various industries. In industry, crystallization usually starts with heterogeneous nucleation on a foreign surface. The complicated mechanism of heterogeneous nucleation is not well understood; however, we hypothesize that there might be a possible correlation between binding affinity to a surface and enhancement of nucleation. Recent studies show that amorphous polymers can be used to control crystallization, selectively produce pharmaceutical polymorphs, and discover novel pharmaceutical polymorphs. To investigate the possible correlation between the binding affinity of one molecule to key binding sites (local binding) and heterogeneous nucleation activity as well as the possibility of using this binding affinity to help guide the selection of polymers that promote heterogeneous nucleation, we computed the free energy of binding of aspirin to four nonporous cross-linked polymers in an ethanol-water 38 v% mixture. These cross-linked polymers are poly(4-acryloylmorpholine) (PAM), poly(2-carboxyethyl acrylate) (PCEA), poly(4-hydroxylbutyl acrylate) (PHBA), and polystyrene (PS); all of them were cross-linked with divinylbenzene (DVB). These systems were used because their heterogeneous nucleation activities are available in literature, and the ranking is PAM > PCEA > PHBA ≈ PS. We generated three independent surfaces for each polymer and computed the free energy of binding of aspirin to the best binding site that we found on each surface. The average free energies of binding to the best sites of PAM, PCEA, PHBA, and PS are -20.4 ± 1.0, -16.7 ± 1.0, -14.4 ± 1.1, and -13.6 ± 1.1 kcal/mol, respectively. We found that the trend of the magnitudes of the average free energies of binding to the best sites is PAM > PCEA > PHBA ≈ PS. This trend is very similar to that of heterogeneous nucleation activity. Our results suggest the importance of the free energy of binding to key sites (local binding) and the possibility of using this quantity to help guide the selection of polymers that promote heterogeneous nucleation.     

Free energy of binding of a small molecule to an amorphous polymer in a solvent

Crystallization is a commonly used purification process in industrial practice. It usually begins with heterogeneous nucleation on a foreign surface. The complicated mechanism of heterogeneous nucleation is not well understood, but we hypothesize that a possible correlation between binding affinity to a surface and nucleation enhancement might exist. Amorphous polymers have been used in controlling crystallization. However, to our knowledge, no attempt has been made to calculate the free energy of binding of a small molecule to an amorphous polymer in a solvent, and to characterize the binding sites/conformations of this system at a molecular level. We developed a two-step approach, first using Adsorption Locator to identify probable binding sites and molecular dynamics to screen for the best binding sites and then using the Blue-Moon Ensemble method to compute the free energy of binding. A system of ethylene glycol, polyvinyl alcohol (PVA), and heavy water (D(2)O) was used for validation, since experimental data exists on a related system. Looking at four independently constructed surfaces, we found that ethylene glycol binds to an indentation on the surface or in a hole beneath the surface. We focused on the indentation binding sites because they are easily accessible and do not have large free energy barriers. The closest system for which experimental data on binding energetics exists is ethylene glycol on PVA in aqueous solutions/gels, and the magnitudes of the free energy of binding to the three best indentation binding sites are close to the experimental value, 0.4-3.7 kcal/mol higher. Our approach offers a way to compute the free energy of binding and characterize the binding sites/conformations, and is general enough to apply to other small molecule/amorphous polymer/solvent systems.