Amphiphilic block copolymers of vinyl ethers by living cationic polymerization. II. Synthesis and surface activity of macromolecular amphiphiles with pendant amino groups

Amphiphilic block polymers of vinyl ethers (VEs). $\rlap{--} [{\rm CH}_{\rm 2} {\rm CH}\left( {{\rm OCH}_{\rm 2} {\rm CH}_{\rm 2} {\rm NH}_{\rm 2} } \right)\rlap{--} ]_m \rlap{--} [{\rm CH}_{\rm 2} {\rm CH}\left( {{\rm OR}} \right)\rlap{--} ]_n \left( {{\rm R: }n{\rm - C}_{{\rm 16}} {\rm H}_{{\rm 33}} ,{\rm }n{\rm - C}_{\rm 4} {\rm H}_{\rm 9} ;m \simeq 40,{\rm n} = 1 - 10} \right)$ were prepared, each of which consists of a hydrophilic segment with pendant primary amino groups and a hydrophobic poly(alkyl VE) segment. Their precursors were obtained by the HI/I₂-initiated sequential living cationic polymerization of an alkyl VE and a VE with a phthalimide pendant (CH₂ = CHOCH₂CH₂Im; Im; phthalimide group), where the segment molecular weights and compositions (m/n ratio) could be controlled by regulating the feed ratio of two monomers and the concentration of hydrogen iodide. Hydrazinolysis of the imide functions gave the target polymers which were readily soluble in water under neutral conditions at room temperature. These amphiphilic block polymers lowered the surface tension of their aqueous solutions (0.1 wt%, 25°C) to a minimum ? 30 dyn/cm when the hydrophobic pendant R was n-C₄H₉ (n = 4–9). The polymers with n-C₄H₉ pendants in the hydrophobic segment exhibited a higher surface activity than those with n-C₁₆ H₃₃ pendants. The surface activity of the polymers also depended on the pH of the polymer solutions; the surface activity increased in more basic solutions where the ionization of the amino group (? NH₂)2? NH₃^⊕) is suppressed.     

Reactions of 1,2‐dihydro‐4H‐3,1‐benzothiazine‐2,4‐dithiones (trithioisatoic anhydrides) with N‐substituted benzylamines and trialkyl phosphites

Reactions of 1,2‐dihydro‐4H‐3,1‐benzothiazine‐2,4‐dithiones (trithioisatoic anhydrides) 3 with N‐substi‐tuted benzylamines 9 gave 1,2‐dihydroquinazoline‐4‐thiones 10 , o‐thioureidodithiobenzoic acid 11 , o‐aminothiobenzamides 12 , 2‐amino‐3,1‐benzothiazine‐4‐thiones 13 , or quinazoline‐2,4‐dithiones 14 , depending on the kinds of amine and the reaction solvent. On the other hand, reaction of 3 with trialkyl phosphites afforded dialkyl (1,2‐dihydro‐2‐thioxo‐4H‐3,1‐benzothiazin‐4‐yl)phosphonates 18 .     

Radical-initiated homopolymerization and copolymerization of ethyl α-hydroxymethylacrylate

Ethyl α-hydroxymethylacrylate (EHMA) was synthesized and homopolymerized in bulk and in solution. The poly(EHMA) is readily soluble in alcohol, acetone, tetrahydrofuran, and methylene chloride at room temperature. Intramolecular lactone formation occurred when poly(EHMA) was heated to 180–230°C. The kinetics of EHMA homopolymerization was investigated in ethyl acetate, using α,α′-azobisisobutylonitrile as an initiator. The rate of polymerization R_p was expressed by R_p = k[AIBN]^0.50[EHMA]^1.4 and the overall activation energy was calculated as 71.9 kJ/mol. Kinetic constants for EHMA polymerization were obtained as follows: k_p/k = 0.17L^0.9mol^?0.9s^?0.5; 2fk_d = 1.5 × 10^?5 s^?1. The relative reactivity ratios of EHMA(M₂) copolymerization with styrene (r₁ = 0.472, r₂ = 0.564) in ethyl acetate were obtained. Applying the Q-e scheme led to Q = 0.84 and e = 0.35 for EHMA.     

THE 'OPSIN SHIFT' IN BACTERIORHODOPSIN: STUDIES WITH ARTIFICIAL BACTERIORHODOPSINS

Abstract— The difference (in cm⁻¹) in absorption maxima between the protonated Schiff base of retinals and the pigment derived therefrom has been defined as the opsin shift. It represents the influence of the opsin binding site on the chromophore. The analysis of the opsin shifts of a series of dihydrobacteriorhodopsins has led to the external point-charge model, which in addition to a counter anion near the Schiff base ammonium, carries another negative charge in the vicinity of the β-ionone ring. This is in striking contrast to the external point-charge model proposed earlier for the bovine visual pigment. The absorption maxima of rhodopsins formed from bromo- and phenyl retinals support the two models. A retinal carrying a photoaffinity label has yielded a nonbleachable bacteriorhodopsin.     

Highly efficient recognition of native TpT by artificial ditopic hydrogen-bonding receptors possessing a conformationally well-defined linkage

Synthesis and binding affinity of rationally designed artificial ditopic nucleobase receptors are reported. The ditopic receptors were designed to recognize thymine-thymine dinucleotides by their two hydrogen-bonding moieties, which are connected to conformationally well-defined linkages such as ferrocene and biphenylene. The ditopic receptors exhibited a remarkably strong binding affinity for lipophilic TpT analogue in CDCl(3)/DMSO-d(6) (85:15, v/v). The binding affinity of the ditopic receptors for the dinucleotide was so high that even native TpT was extracted by them into CDCl(3). Detailed comparisons for the recognition abilities of the ditopic receptors were also conducted.     

Synthesis of pyrido[1′,2′:1,2]imidazo[4,5-b]quinoxalines

Synthesis of pyrido[1′,2′:1,2]imidazo[4,5-b]quinoxalines by the facile cyclizations of 2,3-dichloroquinoxalines with 2-aminopyridines and of 2-amino-3-chloroquinoxalines with various substituted pyridines is described.     

Small-angle neutron scattering study on microstructure of poly(N-isopropylacrylamide)-block-poly(ethylene glycol) in water

By employing small-angle neutron scattering (SANS), we investigated the microstructures of, poly(N-isopropylacrylamide) (PNIPA)-block-poly(ethylene glycol) (PEG) (NE) in deuterated water D₂O, as related to macroscopic behaviors of fluidity, turbidity and synerisis. SANS revealed following results: (i) microphase separation occurs at around above 17 °C in a temperature range of transparent sol below 30 °C. In the microdomain appeared in the transparent sol state, both block chains of PNIPA and PEG are swollen by water; (ii) for the NE solution of polymer concentration W_p > 3.5% (w/v), corresponding to opaque gel above 30 °C, a percolated structure, i.e., network-like domain is formed by NE as a result of macrophase separation due to dehydration of the PNIPA chains. As the temperature increases toward 40 °C, the network domain is squeezed along a direction parallel to the NE interface, which leads to increase of the interfacial thickness given by swollen PEG chains and to the macroscopic synerisis behavior.     

Nmr spectroscopic studies on the tautomerism in tenuazonic acid analogs

Nmr spectra of structural analogs of tenuazonic acid such as 3-acetyltetramic acid, 3-acetyltetronic acid, 3-acetylthiotetronic acid and others were investigated for elucidation of the tautomeric structures. These compounds have completely enolized β,β′-triketone systems, and the position of the nmr signals for the enolic proton shows that the strength of their intramolecular hydrogen-bonding is weaker than those of acyclic β,β′-triketones and six-membered cyclic triketones. The assignment was made for nmr signals split by the difference of the diamagnetic anisotropic effect in each tautomers. The percentages of each of the tautomers were calculated from the intensities of the corresponding nmr signals. The results were confirmed by means of ¹³C-nmr spectroscopy.