Rational syntheses of helical π-conjugated oligopyrrins with a bipyrrole linkage: geometry control of bis-copper(II) coordination

Rational syntheses of long-chain helical π-conjugated oligopyrrins and their bis-copper complexes afford systematically modulated optical and magnetic properties.</p

Thermal- and pH-Dependent Size Variable Radical Nanoparticles and Its Water Proton Relaxivity for Metal-free MRI Functional Contrast Agents

For development of the metal-free MRI contrast agents, we prepared the supra-molecular organic radical, TEMPO-UBD, carrying TEMPO radical, as well as the urea, alkyl group, and phenyl ring, which demonstrate self-assembly behaviors using noncovalent bonds in an aqueous solution. In addition, TEMPO-UBD has the tertiary amine and the oligoethyleneglycol chains (OEGs) for the function of pH and thermal responsiveness. By DLS and TEM imaging, the resulting self-assembly was seen to form the spherical nano-particles 10 – 150 nm in size. On heating, interestingly, the nano-particles showed a lower critical solution temperature (LCST) behavior having two-step variation. This double-LCST behavior is the first such example among the supra-molecules. To evaluate of the ability as MRI contrast agents, the values of proton (1H) longitudinal relaxivity (r1) were determined using MRI apparatus. In conditions below and above CAC at pH 7.0, the distinguishable r1 values were estimated to be 0.17 and 0.21 mM(-1)s(1), indicating the suppression of fast tumbling motion of TEMPO moiety in a nano-particle. Furthermore, r1 values became larger in the order of pH 7.0 > 9.0 > 5.0. Those thermal and pH dependencies indicated the possibility of metal-fee MRI functional contrast agents in the future

Effect of Hydrophobicity on the Self-Assembly Behavior of Urea Benzene Derivatives in Aqueous Solution

Urea benzene derivatives (UBD) with amphiphilic side chains showed self-assembly behavior in aqueous solution to form nanoparticles ~100 nm in size. Subsequent thermal treatment led to additional self-assembly of the nanoparticles due to dehydration of the amphiphilic side chains, producing microparticles. This self-assembly process was accompanied by a lower critical solution temperature (LCST) behavior, as revealed by the abrupt decrease in solution transmittance. In this study, three UBD (UBD-1&ndash;3) with different lengths of the alkyl segment in the amphiphilic side chain (namely, hexyl, heptyl, and octyl, respectively) were prepared to investigate the self-assembly behavior in aqueous solution. UBD-1&ndash;3 formed identical nanoparticles, with sizes in the 10~80 nm range but with different LCST values in the order 3 &lt; 2 &lt; 1. These results suggest a relationship between the hydrophobicity and the self-assembly behavior of UBD

Unexpectedly large water-proton relaxivity of TEMPO incorporated into micelle-oligonucleotides

Three lipid-oligonucleotides (ODN) carrying TEMPO were preparedand formed a micelle with a diameter of ca. 10 nm. Thedouble strand ODN, lipid-polyTinDS, incorporating TEMPO nearthe core of the micelle showed the largest water-proton relaxivity,r1, value of 2.4 (25 MHz, 0.59 T) and 6.8 mM21 s21 (42 MHz, 1.0 T)per TEMPO