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Mechanism of the Odor-Adsorption Effect of Zinc Ricinoleate. A Molecular Dynamics Computer Simulation
H. Kuhna,*, F. Mllerb, J. Peggaub, and R. Zekornb
aUniversity of Essen, Department of Physical Chemistry, D-45141 Essen, Germany, and bGoldschmidt AG, D-45127 Essen, Germany
ABSTRACT: Zinc ricinoleate [Zn(Ri)2] is widely used in surfactant and detergent mixtures for the adsorption of odor-active compounds. The mechanism of this process is not known. In this initial study, we discuss the results of molecular dynamics computer simulations that were performed to get more information and detailed insights into the interaction mechanism between Zn(Ri)2 and odor-active substances. The calculations, based on simple molecular mechanics approximations, simulated the dynamic features of the molecular structures of Zn(Ri)2 in vacuum, in the oil phase, and in aqueous solution. We determined actual molecular conformations and simulated an adduct of ammonia with Zn(Ri)2. On close inspection, in the vacuum and oil phase structures, the Zn2+ ion is almost completely shielded by the oxygen ligands. Calculated structural transitions caused by the interaction of Zn(Ri)2 with water-solvent molecules resulted in a weakening of the electrostatic shield. Nucleophilic attack of odor-active compounds to the relatively unprotected Zn2+ atom
is easy to achieve in aqueous solution. Simulation of the addition product of Zn(Ri)2 with ammonia revealed an elementary structural change, resulting in an increase of the solubility and adsorption activity of Zn(Ri)2. Molecular dynamics simulations showed that the results coincide with experimental observations.
Paper no. S1130 in JSD 3, 335343 (July 2000).
KEY WORDS: Molecular dynamics simulation, molecular structure, odor-adsorption, zinc ricinoleate.
With comprehensive industrialization and production, foul-smelling wastes are increasing steadily in exhaust air and sewage. In the cosmetic area, decomposition products appear and often can be removed with odor-deleting deodorizing agents. Generally, the active substances that cause intensive odor are compounds with low odor threshold values. Inevitably, at a certain concentration, the compounds become nasal nuisances.
Through aerobic or anaerobic degradation processes, odor-active substances are released to the environment. Products of bacterial decomposition processes are present in human perspiration, in sour gasoline, in natural gas, in paper facilities, in the businesses of waste and sewage treatment, and in the agriculture and the food-processing
industry. Most of the odor-active materials include chemically reactive functional groups. Organic oxygen, sulfur, and nitrogen compounds are the...