13C NMR longitudinal relaxation time studies of a molecular tweezers derived from a calixarene-porphyrin conjugate.
Zn(II)porphyrin-substituted calix[4]arene 1 serves as molecular tweezers for 1,4-diazabicyclo[2.2.2] octane (DABCO) selectively, which led to the formation of Ensemble I. The molecular segments composing the calixarene cavity change upon inclusion of DABCO as Ensemble I were evaluated through (13)C NMR longitudinal relaxation times (T(1)) for the first time. As for Ensemble I, the 1:1 complex should be formed. The T(1) values for Ensemble I are generally smaller than those for 1: in CDCl(2)CDCl(2), DT1 = 5.03 s for C-1, 5.31 s for C-2, 0.13 s for C-3, 0.7 s for C-4, and 0.16 s for C-5. This substantiates that the rings of Ensemble I are firmly freezed because of the two-point coordination by DABCO. In 1, the T1 values for C-3 are always greater than those for C-4, and the difference between C-3 and C-4 is slight. As for Ensemble I, on the other hand, the difference between C-3 and C-4 is large. We can suggest two different motions for phenol units in 1 and Ensemble I: a rotational motion around a C-1 to C-4 axis (A) and a seesaw motion around a C-2 to C-2' axis (B). The data indicate that in Ensemble I motion (A) is predominant over motion (B). This indicates that motion (B) is specifically suppressed because of the two-point coordination interactions in Ensemble I.
Arimura
Takashi
T
Nanotechnology Research Institute, AIST, Tsukuba, Japan. takashi-arimura@aist.go.jp
Nishioka
Takuya
T
Suga
Yasuhiro
Y
Kumamoto
Satoshi
S
Tsuchiya
Youichi
Y
Yamaguchi
Tomohiko
T
Tachiya
Masanori
M
D047250:Calixarenes / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008665:Metalloporphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D015394:Molecular Structure; D015032:Zinc / Q000737:chemistry*
D008665:Metalloporphyrins; D047250:Calixarenes; D015032:Zinc