A Supramolecular Chiroptical Switch Based on Chitosan and Anionic Porphyrin Complex Film

Abstract

ABSTRACT:A supramolecular chiroptical switch based on chitosan and tetrakis (4-sulfonatophenyl) porphine (TPPS) complex films was prepared. The reversible changes of the chirality of the complex films were studied by UV-vis and circular dichroism (CD) spectra. It was found that the chirality of the complex films can be wiped off by being exposed to NH 3 gas and subsequently recovered by being exposed to moist HCl gas. The complex film is stable and can stand at least 20 cycles of the switching to NH 3 and HCl gases. There is no change in the above properties after the complex films were store in the air at room temperature. Chirality is an attractive issue in chemistry, biology, material science etc. and has been studied extensively. [1][2][3][4] The chiral switch, which shows the reversible change in chirality with an external stimulation, is particularly attractive due to the potential applications in data storage and sensor systems.5-9 Many chiral optical switches have been proposed, which are based on photochemically induced interconversions, 10,11 photochemically induced changes in liquid crystals, 12,13 stereoisomers of chiral photoresponsive molecules and chiral supramolecular systems, 14,15 etc. The most attractive one in this filed is the chiral optical supramolecular switch because it is easily controlled. [16][17][18][19] Tetrakis(4-sulfonatophenyl)porphine (TPPS, Figure 1) is a well investigated dye. It has two negative charges and forms stable J-and H-aggregates depending on the pH and ionic strength in the system. The TPPS J-and H-aggregates shows the property of induced chirality in many systems, such as multilayer and Langmuir-Schaefer (L-S) films prepared from chiral and achiral molecules, 20-23 the solutions containing polylutamic acid, polylysine, cationic porphyrin etc., [24][25][26][27][28][29][30] and even by mechanical stirring in solutions. 31 However, there is no report about the reversible chirality of TPPS aggregates in film.Chitosan, a chiral biopolymer, is used widely in many fields, e.g. biomedical 32-34 and chemical materials, 35 textiles, 36 pharmaceutics, 37,38 etc. Chitosan is a cationic polyelectrolyte and can interact with the anionic TPPS. More recently, Synytsya et al.39 studied the interaction of TPPS with chitosan in aqueous solutions at different pH value. The results confirmed that the formation of optically active species of TPPS in the presence of chitosan and the J-and H-aggregates depended on pH value and chitosan concentration. However, no work had been reported on the interactions between TPPS and chitosan on chitosan film.In this paper, the reversible change in chirality of chitosan/TPPS complex films when they are alternatively exposed in moist HCl and NH 3 gases was studied. The morphology of the complex films and the interaction between chitosan and TPPS were discussed. EXPERIMENTALWater-soluble anionic porphyrin TPPS was purchased from Dojindo Laboratories. Chitosan (M n ¼ 100 Kda, the degree of deacetylation was 91 mol %) was received from Professor Yanming D...

Chiroptical Properties in Thin Films of π-Conjugated Systems

“…459 Very significant is the case of achiral 5,10,15,20tetrakis(4-N-methylpyridyl)porphine (TMPyP, 48, Figure 33), which generates induced ECD signals around 450 nm upon intercalation into DNA thin films; 460 in particular, the DNA/ 48 complex system was intensively studied as pH-sensitive reversible chiroptical switch by alternate exposure to HCl and NH 3 vapors. 461,462 Remarkable ECD signals were also found in thin films of several achiral porphyrins covalently or notcovalently incorporated to other biopolymers, including poly(L-glutamic acid), 463 chitosan, 464 and chitosan−methylcellulose. 465 As described above, the air/water interface is a 2D-confined space where the spontaneous breaking of symmetry of achiral molecules may happen through intermolecular interfacial interactions.…”

Induced Circular Dichroism of Anionic Porphyrin TPPS Aggregates in DNA Solutions

“…It can form stable J-aggregate or H-aggregate, which depends on the pH value and ionic strength in the system. TPPS aggregates can be easily induced to show chirality by many cationic chiral and achiral templates, such as L-(or D-) Trp film, 24 gemini-Type Amphiphiles, 25 polylutamic acid 26 and polylysine, 27 chitosan, 28 etc. Usually, these templates are just cationic, which can be directly interacted with the anionic TPPS.…”

Aggregation of an anionic porphyrin with chiral metal complexes and the competitive binding influences of a surfactant and a polyelectrolyte

“…[48][49][50][51][52][53] Various artificial photo-devices based on the chiral porphyrin supermolecules are anticipated to be potentially useful for the practical applications. [54][55][56][57] In our previously reported work, we found that the random symmetry breaking in the synthesis of a chiral octahedral cobalt complex (cis-[CoBr(NH 3 )(en) 2 ]Br 2 ) could be transferred in the supramolecular self-assembly process of anionic porphyrin derivatives. 58 What we are interested in is how did the chirality at the small molecular level transfer to the advanced supramolecular level.…”