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Molecular Specification of Homopolymer of Vinylbenzyl-Lactose-Amide in Aqueous Solution

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Molecular Specification of Homopolymer of Vinylbenzyl-Lactose-Amide in Aqueous Solution Polymer Journal, Vol. 31, No. 7, pp 590-594 (1999) Molecular Specification of Homopolymer of Vinylbenzyl-Lactose-Amide in Aqueous Solution Isao WATAOKA, Hiroshi URAKAWA, Kazukiyo KOBAYASHI,* Kohji OHNo,** Takeshi FUKUDA,** Toshihiro AKAIKE,*** and Kanji KAJIW ARA t Faculty of Engineering and Design, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606--8585, Japan *Graduate School of Engineering, Nagoya University, Chikusa-ku, Nagoya 464--8603, Japan **Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan ***Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, Midori-ku, Yokohama 227--8501, Japan (Received November 30, 1998) ABSTRACT: The lactose-carrying polystyrene derivative, PYLA, is known as the material suitable for the incubation of liver cells and for drug delivery systems. PYLA was dissolved in 0.1 M urea aqueous solution, and its structure was analyzed from the results of small-angle X-ray scattering and the molecular modeling. PYLA was found to have the shape of a molecular bottle brush in solution, composed of a large pseudo helix of polystyrene backbone. The amphiphilic nature of the backbone and side chains is thought to determine the backbone conformation. KEY WORDS Small-Angle X-Ray Scattering I Polymacromonomer I Glycopolymer I Lactose I Recent advance in the precise polymerization tech­ (or oligomers) with a vinyl end group, the radical nique has resulted in synthesizing many novel function­ polymerization results in polydisperse polymacromono­ al polymers, most of which mimic biopolymers. Those mers. The living radical polymerization is an alternative novel polymers are often found to be physiologically route to prepare polymacromonomers with less poly­ more active than the corresponding biopolymers. Thus dispersity, but the molecular weight cannot be expected in future, those novel materials are expected to compose so high as in the conventional radical polymerization. a major biomedical system including cell separation, Small-angle X-ray and light scattering revealed a cell culture, drug delivery agent, and artificial antigen. bottlebrush-like cylindrical shape representing the poly­ Hybrids of synthetic polymers and biopolymers are of a macromonomer composed of a polymethacrylate back­ particular interest, since the hybrid may enhance the bone with oligostyrene side chains in toluene solu­ characteristics of parent polymers. Carbohydrate is one tion. 3 •4 The polymethacrylate backbone seems to be of the most important candidates as a ligand or rec­ obliged to take an extended conformation in order to ognition signal, and a series of glycoconjugate poly­ accommodate overcrowded side chains. In fact, the main styrene derivatives have been synthesized with vary­ chain seems to assume an extended almost zigzag ing the types of a pendant oligosaccharides. Here a con­ conformation, and in consequence mesophase formation venient synthetic route1 was developed to construct was observed from highly concentrated solutions of the amphiphilic structure by arranging hydrophobic polymacromonomer. 5 At lower degrees of polymeriza­ polystyrene main chains and hydrophilic pendant oli­ tion, both the backbone and side chains seem to assume gosaccharides. Synthesized glycoconjugate polymers almost the same conformation as the linear homologues, were in fact found to function as a highly sensitive ligand. so that the conformational change of the backbone chain Highly concentrated multiantennary glyco signals along should take place when the degree of polymerization the hydrophobic main chains enhance the interaction exceeds a certain limiting value.6 with various types of carbohydrate-binding proteins. The In an earlier work, we have reported the structure of enhancement is also attributed to the presence of the glycopolymer composed of a polystyrene backbone with hydrophobic phenyl groups, although its active role is pentamaltose side chains in aqueous solution. 7 Here the not clearly understood. 2 small-angle X-ray scattering indicated the glycopolymer The glycoconjugate polystyrene derivative is a type as represented by a cylinder with one or two broken of comb-shaped polymers termed as polymacromono­ points, and its backbone was found to assume a large mers, where relatively long branches pendant from the cross-sectional pseudo-helix. Since the side chains are backbone chain with a regular interval. An extensive not long enough to fill the space along the extended research effort has been focused to prepare densely hydrophobic backbone, the backbone is thought to grafted polymacromonomers by radical polymerization. assume a large helical conformation in order to cover Although the monomer is a high molecular weight its surface with hydrophilic side chains. A similar meth­ precursor composed of almost monodisperse polymers od is applied for the structural characterization of lactose-carrying polystyrene in aqueous solution in the t To whom correspondence should be addressed. present work. Lactose-carrying polystyrene is known as 590 Molecular Specification of Homopolymer of VLA in Solution the material suitable for the incubation of liver cells and the drug delivery systems. 8 The physiological activity was found to depend on the type of the backbones, which determine the side chain conformation. That is, the side chain conformation with respect to the backbone is considered to play a key role in the physiological activi­ ty of glycoconjugate polymers. In this context, the present work focuses the conformational analysis of glycoconju­ gate polymers by combining the small-angle X-ray scattering and the molecular simulation. EXPERIMENTAL Lactose-Carrying Polystyrene Three lactose-carrying polystyrene samples are em­ ployed for the present work. PYLA was obtained by Figure 1. Chemical structure of PVLA. radical homopolymerization of the monomer with the initiator, so that the molecular weight distribution would tions) installed in the Silicon Graphics 0 2 series be rather broad. 1 The other two samples VLA29 and workstation. The universal force field 11 1.02 was used VLA92 were prepared by a living radical polymeriza­ for energy minimization and molecular dynamics. The tion,9 and the degree of polymerization were estimated molecular mechanics minimization was applied at first as 29 and 92, respectively, by GPC. The molecular weight to the molecular model constructed manually. The distribution Mw/Mn ofVLA29 and VLA92 are found to resulted model from the molecular mechanics minimiza­ be 1.12 and 1.22, respectively. The synthesis details will tion was annealed by affording a thermal disturbance, be found in the separate papers. 1.9 and then the energy-minimization was performed in the system containing solvent by the use of a conjugate Small-Angle X-Ray Scattering gradient12 algorithm, until the root mean square force Small-angle X-ray scattering (SAXS) was observed was less than 0.10 kcal mol A- 1 or the number of the from the 0.1 M urea solutions of lactose-carrying minimization step exceeded 3000 in the case of the initial polystyrenes. The measurement was performed with a minimization. The molecular dynamics simulation for SAXES10 (small-angle X-ray scattering equipment for annealing was conducted at a constant volume under the solutions) installed at the BLlOC of Photon Factory, conditions identical with those described for the energy Tsukuba, Japan. An incident X-ray from synchrotron minimization by the molecular mechanics. The tempera­ radiation was monochromatized to A= 1.488 A, and ture of the system was initially fixed at 300 K, increased then focused to the detector position. The scattered X-ray to 500 K and then cooled to 300 K with the temperature was detected by the one-dimensional position sensitive increment or decrement of 50 K per 50 steps. One cycle proportional counter (PSPC) of the effective length consists of 50 steps at each temperature from 300 K to 160 mm. The exact camera length was calibrated by using 500 K and then down to 350 K, and the elapsed time for the diffraction peaks of collagen fiber (the long 1 step corresponds to 0.0010 ps. Thus the total simulation period= 653 A at the 6th, 9th, and 11th orders). The time amounts 2.05 ps. SAXS intensities were accumulated to the total The particle scattering factor is calculated for lac­ measuring time of 30 min. The sample solutions were tose-carrying polystyrene from the atomic coordinates of prepared by weighing lactose-carrying polystyrene the simulated polymacromonomer molecule according directly in the sample bottle and adding solvent to adjust to the Debye formula. 13 The scattering profile is given by the concentration of the solutions. The solutions were n n-1 n sind.. q put into the flat cells (1 em x 0.5 em x 0.1 em) equipped I(q) = I gl</Jl(q) + 2 I I gigj</J;(q)</Jj(q) •J with a pair of thin quartz glass windows, which were i=1 i=1 j=i+1 dijq subjected to the SAXS measurements. The cells were (1) thermostated at 25°C by circulating water of a constant temperature through the cell holder. The scattered where q is the magnitude of scattering vector given by intensities were corrected with respect to the variation (4n/A) sine with e and A being a half of the scattering of the incident X-ray flux by monitoring the beam with angle and the wavelength of an incident X-ray, an ionizing chamber placed in front of the thermostated respectively. g; is an atomic scattering factor and dii is sample holder. The excess scattering intensities were the distance between ith andjth atoms. The form factor evaluated by subtracting the scattering intensities of for the ith atom </J;(q) is assumed to be given by the form solvent from those of lactose-carrying polystyrene factor of a sphere having a radius equivalent to a van solutions. 0.1 M urea was added to the aqueous solu­ der Waals radius of the ith atom as tions of lactose-carrying polystyrene in order to pre­ )= 3[sin(R;q)-(R;q)cos(R;q)] (2) vent aggregation by intermolecular hydrogen bonding.
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