Self-assembled helical ribbon and tubes of alanine-based amphiphiles induced by two different formation mechanisms

Three long chain alanine-based amphiphiles (1-3) possessing either a saturated long alkyl chain group or unsaturated groups as the self-assembling unit of a highly organized molecular architecture were synthesized. Their self-assembling properties were investigated using EF-TEM, SEM, CD, XRD, and FTIR. The d-form (1) and the l-form (2) enantiomers showed the opposite CD signals. Furthermore, electron micrographs of the self-assembled 1 and 2 exhibited right- and left-handed helical structures, respectively. The helical structures of amphiphiles 1 and 2 were developed into tubular structures by slow cooling. On the other hand, in the helical ribbon growth process, the helical pitch and ribbon width were changed in fast cooling process. The findings strongly imply that the helical ribbon growth of alanine-based amphiphiles can be induced by two different pathways. This mechanism, quite different from that observed for sugar- and cholesterol-based tubes, is a rare example for a tube formation process.     

Microwave‐Assisted Synthesis of β‐Lactams and Cyclo‐β‐dipeptides

Different cyclo‐β‐dipeptides were prepared from corresponding N‐substituted β‐alanine derivatives under mild conditions using PhPOCl₂ as activating agent in benzene and Et₃N as base. To evaluate β³‐substituent influence, the amino acids 7 – 26 were synthesized, and a β‐lactam formation reaction was carried out instead of cyclo‐β‐dipeptide formation. The crystal structures of three derivatives of cyclo‐β‐peptides and one β‐lactam are presented.     

A color version of the Hinsberg test: permethylated cyclodextrin and crown-appended azophenol for highly selective sensing of amines

Azophenol dyes 1-5 having the permethylated cyclodextrin and/or crown moieties have been synthesized. Compounds 1 and 2 provide critical information for discrimination among 1°-3° amines by unique color changes. Addition of 1° and 2° amines to solutions of 1 or 2 in chloroform shifts the absorbance maximum of the initial solutions from 380 nm to ∼580 nm and ∼530 nm, respectively, but no change is observed with 3° amines. The high selectivity of 1 is mainly due to H-bonding between the ammonium H atoms of the amine and oxygen atoms of the crown-6. The selectivity of 1 possessing the β-cyclodextrin moiety toward amines was higher than that of 2 possessing the α-cyclodextrin moiety. On the other hand, chloroform solutions of 3 or 4, which lack the crown ether moiety, changed from yellow (380 nm) to pink (500 nm) with the addition of 1° and 2° amines, but with no selectivity. These results indicate that the crown unit in 1 or 2 plays an important role in discriminating among the types of amines.