1936 † To whom correspondence should be addressed. E-mail: parkjk@knu.ac.kr Korean J. Chem. Eng., 28(9), 1936-1944 (2011) DOI: 10.1007/s11814-011-0043-3 INVITED REVIEW PAPER Highly improved adsorption selectivity of L-phenylalanine imprinted polymeric submicron/nanoscale beads prepared by modified suspension polymerization Nasrullah Shah, Jung Hwan Ha, Mazhar Ul-Islam, and Joong Kon Park † Department of Chemical Engineering, Kyungpook National University, Daegu 702-701, Korea (Received 27 January 2011 • accepted 10 March 2011) Abstract -Molecularly imprinted polymer (MIP) submicron/nanoscale beads selective for L-Phenylalanine (L-Phe) and D-Phe as well as non-imprinted beads were prepared by modified suspension polymerization involving agitation of the reaction mixture at high rotation speed under safe radical conditions. The effects of pH, template and concentration of racemate solution on the performance of the phenylalanine (Phe) imprinted polymeric submicron/nanoscale beads were studied. L-Phe-imprinted submicron/nanoscale beads prepared for the first time by modified suspension polymer- ization showed enhanced adsorption capacity and selectivity over those of D-Phe imprinted and non-imprinted beads. Maximum adsorption capacity, 0.35 mg/g, and selectivity, 1.62, of L-Phe imprinted submicron/nanoscale beads were higher than the adsorption capacities, 0.30 and 0.19 mg/g, and selectivities, 1.59 and 1.02, of D-Phe imprinted and non- imprinted submicron/nanoscale beads, respectively. FE-SEM analyses revealed that L- and D-Phe imprinted beads were larger (100 nm-1.5 μm) than non-imprinted nanobeads (100-800 nm). 13 C CP-MAS NMR spectroscopy helped in cor- relating the bead sizes and the extent of reaction during polymerization. Similarly, FT-IR study was used for evaluation of structural characteristics of the prepared Phe-imprinted and non-imprinted beads. The preparation of Phe-imprinted submicron/nanoscale beads with improved adsorption and separation properties and the study of effect of template on the size and performance of the prepared beads are suitable from both economical and research point of view in MIP field. Key words: Molecularly Imprinted Submicron/Nanoscale Beads, Modified Suspension Polymerization, FE-SEM, FT-IR, 13 C CP-MAS NMR INTRODUCTION Molecular imprinting has been used for synthesizing polymeric substances carrying specific binding sites having high affinity towards chiral compounds, drugs, peptides and proteins, etc. [1-7]. The syn- thesis of small MIPs is of great importance. The preparation of nano- scale MIPs is gaining importance due to small sizes and large num- ber of features per volume. Due to smaller sizes the binding sites are situated at or near the material’s surface, which minimizes the diffusion distances of molecules and results in high performance of the MIPs [8-13]. The dispersion of MIP nanomaterials in analyte solution and the removal of template are easy [7,14-16]. The nanos- cale MIPs are applicable in different fields such as in the construc- tion of biosensors, drug delivery systems or in the development of new material for separation and purification purposes. Large MIP particles may also be employed for such applications, but due to low mass transfer and low separation ability these are not suitable for obtaining rapid separations [14]. Considering the importance of small-sized MIPs, submicron and nanosized MIPs in different formats were tried by different research- ers [4,7-9,12,17,18]. However, most of these nanoscale MIP for- mats employ relatively long and complicated procedures [4,7,8,12] or suffer from lower uptake capacity [18] and some involve high agglomeration of the prepared MIP particles/beads [9]. For instance, nanosized MIPs were prepared using the surface modified alumina membrane. However, the modification of alumina and polymer- ization within the available pores made the process complicated and time consuming [4,7,8,12]. Zhu et al. [9] prepared submicron scaled particles selective for 17- β-estradiol by using precipitation polymerization and used in the HPLC column. However, the extent of agglomeration was very high. Nanosized S-propranolol imprinted nanoparticles were prepared using the mini-emulsion polymeriza- tion as was done by Priego-Capot et al. [18]. However, the uptake capacity of the imprinted nanoparticles was 10 times lower than that of the propranolol-imprinted microspheres prepared by precip- itation polymerization. Compared to these methods, suspension polymerization using simple agitation is convenient for the production of round MIP beads with suitable size distribution. According to our knowledge and litera- ture study, the modified suspension polymerization was not tried yet for the preparation of MIP submicron/nanoscale beads for the resolution of underivatized phenylalanine racemic mixture. In a previous study Khan and Park [16] attempted to reduce the size of the D-phenylalanine (D-Phe) imprinted polymeric beads and increase the adsorption capacity and selectivity. They prepared the D-Phe- imprinted beads with a minimum size of 2.38 μm [16]. The further decrease in beads size using the modified suspension polymeriza- tion was not successful because of the generation of unfavorable conditions for radical safety at high rotation speed. The basic reason was the entrapment of atmospheric oxygen at higher rotation speed, which acts as radical scavenger and reacts with free radicals and