Seizo Masuda

Interaction Between Drugs and Water-Soluble Polymers. VII. Binding of Berberine with Bovine Serum Albumin

Abstract The interaction between berberine chloride (BC) and bovine serum albumin (BSA) was studied by equilibrium dialysis. Since the number (n) of binding sites per mole of BSA was large, the binding was nonspecific. Then the binding capacity (nK) was evaluated instead of the binding constant (K). According to the dependence of the NK value on ionic strength, the interaction was due to hydrophilic binding. Intermolecular interaction of BC was observed by the concentration (1–10 mmol/L) dependence of 1H-NMR parameters; that is, the respective signals shifted to a higher magnetic field, the spin-lattice relaxation time (T 1) decreased, and the spin-spin relaxation rate (T 2 −1) increased. The interaction of BC with BSA (1.45 × 10−4 mol/L) resulted in a decrease in T 1, an increase in T 2 −1, and little variation of the chemical shift. On the basis of the ratio of the spin-spin relaxation rate of bound BC to free BC (T 2b −1/T 2f −1). the binding position of BC to BSA was considered to be spread over the e...

Thermosensitive properties of a novel poly(methyl 2-acetamidoacrylate-co-methyl acrylate)

Abstract Copolymerizations of methyl 2-acetamidoacrylate (MAA) with methyl acrylate (MA) were carried out at 60 °C in chloroform. MAA-rich copolymers are soluble in water and MAA-poor copolymers insoluble. Among water-soluble copolymers obtained, only one (HP-77) which contains 77% of MAA units was thermosensitive. Thermal properties of HP-77 were investigated in the presence or absence of inorganic salts. The cloud point of aqueous HP-77 solution depended on polymer concentration: The cloud point decreased exponentially with an increasing concentration of the polymer. The cloud point of HP-77 was also affected significantly by the type and concentration of salts. The effectiveness of salts to reduce the cloud point is NaBr≈KBr 2 SO 4 ≈K 2 SO 4 . The salting-out coefficients were evaluated as 2.45 l/mol for sodium chloride and 14.56 l/mol for sodium sulfate, respectively, from the relationship (Setschenows equation) between logarithm of the solubility of HP-77 and salt concentration. The salting-out coefficient of sodium sulfate is larger than that of sodium chloride.

Binding position of phenylbutazone with bovine serum albumin determined by measuring nuclear magnetic resonance relaxation time

The binding of phenylbutazone (PB) to bovine serum albumin (BSA) was considered to be predominantly due to hydrophobic interaction based on the thermodynamic parameters obtained by an equilibrium dialysis method. Little variation of proton nuclear magnetic resonance (1H-NMR) chemical shift of PB was found with change in the concentration of PB (0.5-5 mM) or upon the addition of BSA (7.25 x 10(-5) M). The NMR spectrum of PB in 0.1 M phosphate buffer solution at pH 7 showed that PB existed as a mesomeric anion. The spin-lattice relaxation time (T1) of PB was almost concentration-independent, but decreased in the presence of BSA to 36-38% for the phenyl group and 48-100% for the butyl group. The spin-spin relaxation time (T2) of PB was also almost independent of concentration, but was remarkably decreased in the presence of BSA to ca. 2.5% for the phenyl group and ca. 6-9% for the butyl group. The ratios of the spin-spin relaxation rate (1/T2) of the free PB to that of the bound PB were ca. 5000-11000 for the butyl group and ca. 23000 for the phenyl group. The binding of PB to BSA was considered to involve primarily the phenyl group.

Metal complexes of poly(2-acetamidoacrylic acid)

Abstract Complexation constants of divalent and trivalent metal ions with 2-acetamidoacrylic acid (4A) and its polymer (P4A) were determined by the modified Bjerrum method. P4A has carboxyl and acetamido (acetyl) groups. Although an additive effect of two functional groups was expected in complexing with metal ions, the complexation constants of P4A were essentially the same as those for poly(acrylic acid), while P4A has greater complexing ability than 4A. The interactions of P4A and 4A with Cu(II) and Mn(II) ions were studied using 13 C n.m.r. The addition of Cu(II) ion to P4A and 4A solutions selectively broadens the α-carbon and carboxyl carbon signals, and the addition of Mn(II) ion broadens the acetyl and carboxyl carbonyl carbon signals. This finding suggests that Cu(II) and Mn(II) ions form five-membered and seven-membered chelate rings, respectively.

Spontaneous copolymerization of acrylic acid with 4-vinylpyridine and microscopic acid dissociation of the alternating copolymer

Abstract A large amount of heat was generated by mixing concentrated acrylic acid and concentrated 4-vinylpyridine, which led to carbonized products. When they were mixed within the limited concentration range, however, the polymerization took place spontaneously, and gave the alternating copolymer a relatively low molecular weight. The copolymerization was accelerated by a cationic catalyst, and inhibited by butylamine although it was not accelerated by a radical initiator and was not inhibited by a radical inhibitor. These findings suggest that the spontaneous copolymerization proceeds via cationic mechanism. However, copolymerization is accelerated by water, which is a typical inhibitor of ionic polymerization. Macroscopic and microscopic acid dissociation constants of the alternating copolymer were determined by pH-titration method. The relative concentrations of respective microscopic forms were calculated using the relation between micro-constants and hydrogen ion concentration. The fraction of the protonated form, which exists exclusively in the lower pH range, decreases with increasing pH value, and fully vanishes at pH≈6, while the deprotonated form begins to appear from about pH=9. The zwitterionic and neutral molecule forms coexist over a wide range of pH, and the latter form is predominant regardless of the pH value. Macro- and micro-constants were also measured for the system of monomer mixtures, and homopolymer mixtures as well.

Interaction between Drugs and Water-soluble Polymers. Part IV. Binding Position of Azathioprine with Bovine Serum Albumin Determined by Measuring Nuclear Magnetic Resonance Relaxation Time.

The interaction between azathioprine (AZ) and bovine serum albumin (BSA) is mainly due to hydrophobic binding according to the dependence of the binding constant on the ionic strength obtained by equilibrium dialysis. The binding constant and partition coefficient of AZ were smaller than those of warfarin, phenylbutazone and ibuprofen. Little variation in the proton chemical shift of AZ was observed whether there was an absence or presence of BSA (7.25 x 10(-5) M). The spin-lattice relaxation time (T1) of AZ decreased in the presence of BSA to 6-22%. The spin-spin relaxation rate (1/T2) of AZ increased 16-24 times for the methyl group and the imidazole ring and 8-13 times for the purine ring in the presence of BSA. The ratio of the spin-spin relaxation rate of the free AZ to the bound AZ ((1/T2)b/(1/T2)f) of the methyl group and the imidazole ring was 2-3 times larger than that of the purine ring. The binding of AZ to BSA was concluded to be mainly at the methyl group on the imidazole ring of AZ.

A Novel Thermosensitive Poly(methyl 2-acetamidoacrylate)

The thermosensitive properties of aqueous poly(methyl 2-acetamidoacrylate) (PMAA) solutions were investigated in the absence or presence of sodium sulfate. Poly(methyl 2-acetamidoacrylate) with a molecular weight of 23,000 (PMAA-1) exhibited the cloud point. On heating the PMAA-1 solution, the transmittance began to decrease from near 34 °C and increased again after the minimum value was shown at 36.0 °C. The minimum transmittance increased linearly with an increasing concentration of the polymer although the minimum-transmittance temperature did not depend on polymer concentration. The minimum transmittance was affected by the pH and the 1-butanol added. This finding suggests that the cloudiness is controlled by a delicate balance of hydrophilicity and hydrophobicity and by intra- and/or inter-molecular hydrogen bonding. Poly(methyl 2-acetamidoacrylate) with a molecular weight of 15,000 (PMAA-2) did not exhibit cloudiness in distilled water. However, the addition of sodium sulfate caused cloudiness to appear. The cloud point of a PMAA-2 solution depended on concentrations of polymer and salt added. It decreased with an increase in polymer and salt concentrations. The salting-out constants were determined from the relationship between the cloud point and concentrations of polymer and salt.

Polymerization and copolymerization of methyl α-acetylaminoacrylate

Methyl α-acetylaminoacrylate (1) is easily soluble in various organic solvents and water. Radical polymerization of 1 was kinetically investigated in acetonitrile and distilled water. In both solvents, 1 obeys a conventional model of radical polymerization. The application of the linear solvation energy relationship proposed by Taft et al. to the polymerization rates of 1 in various organic solvents revealed that the major factors governing the rates are polarity and polarizability of the solvent. The copolymerization of 1 with acrylic acid in water was not influenced very much by pH, although homopolymerization of acrylic acid was greatly dependent on pH. Parameters r 1 = 3.04, R 2 = 0058, Q 1 = 6.03, and e 1 = 0.52 were obtained in the copolymerization of 1 (M 1 ) and styrene (M 2 ) at 50°C in tetrahydrofuran with AIBN as the initiator. The obtained Q and e values suggest that the α-acetyl-amino group has no polarizing action and significant resonance effect.

Polymerization and complexation of methacryloylglycine

Radical polymerization of methacryloylglycine (MGly) was kinetically investigated in distilled water and dimethyl sulfoxide. In both solvents, the polymerization obeys a conventional radical equation (rule of square root). Monomer reactivity ratios r MGly = 0.64 and r St = 1.21 were obtained in the copolymerization of MGly and styrene (St) in DMSO. On the basis of the monomer reactivity ratios obtained, copolymerization parameters Q MGly and e MGly were calculated to be 0.55 and -0.29, respectively. Complexation constants of divalent metal ions with MGly and its polymer (PMGly) were determined by the modified Bjerrum method. The complexation constants of PMGly were larger than those of MGly. However, there is no difference between complexing abilities of PMGly and polyacrylic acid, although the additive effect of amide and carboxyl groups was expected on the complexation. The interactions of MGly and PMGly with Cu(II) and Mn(II) ions were studied using 13 C-NMR. The addition of copper(II) nitrate solution to MGly and PMGly solutions selectively broadens the methylene carbon and carboxyl carbon signals, and the addition of manganese(II) nitrate solution broadens the amide carbon and carboxyl carbon signals. These findings suggest that Cu(II) and Mn(II) ions form five- and seven-membered chelate rings, respectively.

Properties of polyacryloylacetone for adsorption of divalent metal ions

Abstract Polyacryloylacetone (PAA) was prepared by polymerizing acryloylacetone in a sealed tube, and examined as an adsorbent of divalent metal ions. The dissociation constant of PAA and overall binding constants of PAA-metal complexes were determined from experimental data on pH titration. The adsorptions of metal ions on PAA were in the order Hg( ii ) ⪢ Cu( ii ) > Ni( ii ) > Co( ii ) > Cd( ii ) , showing high selectivity for Hg( ii ). The adsorption depended significantly on the pH of the solution. The uses of a PAA column for separation and concentration of metal ions were also examined.