IJPCBS 2014, 4(3), 802-806 Fatemeh Mostaghni et al. ISSN: 2249-9504 802 INTERNATIONAL JOURNAL OF PHARMACEUTICAL, CHEMICAL AND BIOLOGICAL SCIENCES Available online at www.ijpcbs.com CONFORMATIONAL ANALYSIS OF THETHREO AND ERYTHRO DIASTEREOMERIC FORMS OF A GUAIACYL β-O-4 DIMER USING MOLECULAR MECHANICS CALCULATIONS Seyed A Mirshokraei and Fatemeh Mostaghni* Department of Chemistry, Payame Noor University, I. R. of Iran, P.O. Box 19395-3697, Tehran, Iran. INTRODUCTION A major problem with paper manufactured from potential brightness reversion upon exposure to sunlight 1,2 . The low brightness stability, caused by high concentrations of chromophores, limits its utilization 3 . There is also a general agreement that the initial color reversion processes are associated with photochemical processes. In this regard, a number of researchers have attempted to elucidate the mechanism of photo degradation of wood 4 , pulp 5,6 , extracted lignin 7 and lignin model compounds 8-11 . Therefore structure of lignin is of great importance for optimizing the processes and understanding the reactions involved in its removal. Lignin remains a complex enigma, and structural details of the phenylpropanoid polymers in plants are still emerging. Applications of new and traditional methods continue to reveal a fascinating complexity. The number of monomers or monomer conjugates that undergo radical coupling reactions with typical monolignols to generate complex phenylpropanoid polymers continues to grow. Whether these are true lignins or not continues to be debated. However, components that act as monomers, coupling and cross-coupling with monolignols and oligolignols to become intimately incorporated into the structure are obviously important components of the plants architecture. These components will always analyze as lignin and for some industries such as the pulp and paper industry, will remain the troublesome polymeric phenolic components that must be removed during pulping or bleaching to produce high-end products such as white paper. Structural analysis of normal and perturbed plant systems reveals a lot about the phenylpropanoid component and interacting biochemical pathways, providing a basis for in- depth biochemical studies. Structural elucidation remains a key entry point into understanding these complex plant systems. Indeed, the -O-4 linkage represents the predominant interunit linkage in lignin and is an excellent model system for studying major conformational features of the lignin polymer such as H-bonding interactions and flexibility. For this reason, we chose to begin with the study of -O-4 model compounds 12 . The aryl glycerol -aryl ether substructures that arise from -O-4 coupling exist in two Research Article ABSTRACT The dynamical conformational behavior of a guaiacyl -O-4 lignin model compounds have been investigated by molecular calculation. Stereoisomerism can influence the shape of the lignin molecules. The stereochemistry and conformation of the lignin molecules are of interest in connection with the interpretation of NMR spectra of lignins. It is proposed that both structural differences and conformation are the main reasons for the broadness of the signals in NMR spectra of lignins. Here DFT is validated for preliminary conformational screening of β-O-4 structures. The results is shown that molecular calculation holds great potential for studying lignin and can provide valuable information. Keywords: DFT, lignin model compounds, lignin conformation, aryl glycerol β-guaiacyl ethers.