Computational prediction of antibody binding sites on tetracycline antibiotics: electrostatic potentials and average local ionization energies on molecular surfaces.

Enzyme linked immunosorbent assay (ELISA) was used for the analysis of tetracycline, chlortetracycline, oxytetracycline, and their transformed compounds in environmental water samples. The antibodies employed in ELISA showed high relative affinity for tetracycline, epitetracycline, chlortetracycline, and epichlortetracycline as compared to anhydrotetracycline, epianhydrotetracycline, and anhydrochlortetracycline. The specificity and crossreactivity of these antibodies are discussed in relation to the electrostatic potentials and average local ionization energies computed on the molecular surfaces of tetracycline antibiotics and their transformed compounds with an objective of identifying common features as well as differences that may be related to the experimentally observed variation in cross-reactivity values. The computations were performed at both the HF/STO-3G and HF/6-31+G* levels using the Gaussian 98 program. The results in this study are based upon molecular electrostatic potentials and local ionization energies computed on isodensity molecular surfaces. The surface electrostatic potentials are characterized in terms of a group of statistically defined quantities, which include the average deviation, the positive, negative, and total variances, positive and negative surface extrema, and a parameter indicating the degree of electrostatic balance.

CHEMICAL AND MINERALOGICAL CHARACTERISTICS OF FRENCH GREEN CLAYS USED FOR HEALING.

The worldwide emergence of infectious diseases, together with the increasing incidence of antibiotic-resistant bacteria, elevate the need to properly detect, prevent, and effectively treat these infections. The overuse and misuse of common antibiotics in recent decades stimulates the need to identify new inhibitory agents. Therefore, natural products like clays, that display antibacterial properties, are of particular interest.The absorptive properties of clay minerals are well documented for healing skin and gastrointestinal ailments. However, the antibacterial properties of clays have received less scientific attention. French green clays have recently been shown to heal Buruli ulcer, a necrotic or 'flesh-eating' infection caused by Mycobacterium ulcerans. Assessing the antibacterial properties of these clays could provide an inexpensive treatment for Buruli ulcer and other skin infections.Antimicrobial testing of the two clays on a broad-spectrum of bacterial pathogens showed that one clay promotes bacterial growth (possibly provoking a response from the natural immune system), while another kills bacteria or significantly inhibits bacterial growth. This paper compares the mineralogy and chemical composition of the two French green clays used in the treatment of Buruli ulcer.Mineralogically, the two clays are dominated by 1Md illite and Fe-smectite. Comparing the chemistry of the clay minerals and exchangeable ions, we conclude that the chemistry of the clay, and the surface properties that affect pH and oxidation state, control the chemistry of the water used to moisten the clay poultices and contribute the critical antibacterial agent(s) that ultimately debilitate the bacteria.

An understanding of renal stone development in a mixed oxalate-phosphate system.

The in vivo formation of calcium oxalate concretions having calcium phosphate nidi is simulated in an in vitro (37 degrees C, pH 6.0) dual constant composition (DCC) system undersaturated (sigma DCPD = -0.330) with respect to brushite (DCPD, CaHPO 4 . 2H 2O) and slightly supersaturated (sigma COM = 0.328) with respect to calcium oxalate monohydrate (COM, CaC2O4 . H2O). The brushite dissolution provides calcium ions that raise the COM supersaturation, which is heterogeneously nucleated either on or near the surface of the dissolving calcium phosphate crystals. The COM crystallites may then aggregate, simulating kidney stone formation. Interestingly, two intermediate phases, anhydrous dicalcium phosphate (monetite, CaHPO4) and calcium oxalate trihydrate (COT), are also detected by X-ray diffraction during this brushite-COM transformation. In support of clinical observations, the results of these studies demonstrate the participation of calcium phosphate phases in COM crystallization providing a possible physical chemical mechanism for kidney stone formation.

Investigating the molecular interactions of oxytetracycline in clay and organic matter: insights on factors affecting its mobility in soil.

The interactions of oxytetracycline with model clay adsorbents were investigated as a function of suspension pH. The clay adsorbents used were native montmorillonite (SWy-2), Na-montmorillonite (Na-SWy-2), and hexadecyl trimethylammonium-montmorillonite (HDTMA-montmorillonite). The adsorption of oxytetracycline to the clay could be described by Freundlich-type adsorption isotherms. It was observed that the adsorption of oxytetracycline in the native and sodium forms of montmorillonite decreases with increasing pH in the order pH 1.5 > 5.0 > 8.7 > 11.0. This trend is consistent with cationic exchange interactions that are dominant at lower pH values when oxytetracycline has a net positive charge. On the other hand, hydrophobic interactions when oxytetracycline is zwitterionic (at pH 5.0) are predominant over other mechanisms, as evident from the FT-IR spectrum of the HDTMA-montmorillonite and humic acid-montmorillonite adsorbed with oxytetracycline. The presence of a large amount of dissolved organic matter (DOM) was also found to decrease the sorption of oxytetracycline to clay, suggesting that DOM may increase its mobility in the natural environment. Several mechanisms of interaction of oxytetracycline in clay are proposed based on the adsorption isotherms and the results from X-ray diffraction (XRD) and Fourier transform-infrared (FT-IR) analyses.