Imaging of Poly(N-Isopropyl Acrylamide-Co-Acrylic Acid)–Amino Acid Conjugates with Scanning Tunnelling Microscopy

Imaging of poly(NIPA-co-MAH)–HIgG conjugate with scanning tunneling microscopy

Random copolymers of N-isopropylacrylamide (NIPA) and 2-methacryloylamidohistidine (MAH) with different MAH contents in the range of 0.125-0.725 mmol/g copolymer and with different molecular weights in the range of 62.0-77.5 kg/mol were synthesized by free radical copolymerization. Copolymers were interacted with human immunoglobulin-G (HIgG) in the aqueous medium with different concentrations. FT-IR and NMR data revealed both copolymer and copolymer-HIgG conjugates. The decrease in the lower critical solution temperature (LCST) of the copolymer observed was related with the increase in the HIgG content within the medium. The main goal of this study was imaging poly(NIPA-co-MAH)-HIgG conjugates using Scanning Tunneling Microscopy (STM), which is one of the widely used methods with the capability of atomic level imaging for biological molecules. STM images of the copolymer, HIgG and copolymer-HIgG conjugates were taken at room temperature at atmospheric pressure, using a 1-1.5 V sample bias and a tunneling current of 10-20 pA, which clearly demonstrated the formation of conjugates.

Molecularly designed water soluble, intelligent, nanosize polymeric carriers

Intelligent polymers, also referred as "stimuli-responsive polymers" undergo strong property changes (in shape, surface characteristics, solubility, etc.) when only small changes in their environment (changes in temperature, pH, ionic strength light, electrical and magnetic field, etc.). They have been used in several novel applications, drug delivery systems, tissue engineering scaffolds, bioseparation, biomimetic actuators, etc. The most popular member of these type of polymers is poly(N-isopropylacrylamide) (poly(NIPA)) which exhibits temperature-sensitive character, in which the polymer chains change from water-soluble coils to water-insoluble globules in aqueous solution as temperature increases above the lower critical solution temperature (LCST) of the polymer. Copolymerization of NIPA with acrylic acid (AAc) allows the synthesis of both pH and temperature-responsive copolymers. This paper summarizes some of our related studies in which NIPA and its copolymers were synthesized and used as intelligent carriers in diverse applications.