360
8.3 A Brief History of Water-Insoluble
Cyclodextrin- Epichlorohydrin Polymers
for Environmental Applications
The idea of preparing ECP materials for analytical purposes, such as gel chromatography, inclusion chromatography, and target substance complexation, has been the
focus of attention of scientists worldwide for the past 60 years, but the most intensive studies on their use as adsorbents in wastewater treatment to remove toxic
contaminants have only begun in the past two decades.
In the mid-1960s, Professor Solms was the first to demonstrate that α-, β-, and
γ-cyclodextrin molecules have the ability to easily form cross-linked networks that
could have industrial applications in the field of separation sciences such as chromatography (Solms 1966, 1967, 1969; Solms and Egli 1964, 1965). He has shown that
cyclodextrin polymers exhibited strong adsorptive properties as inclusion resins for
the separation of various molecules such as aniline, nitrophenols, benzaldehyde,
pyridine, iodine, Congo red, and methylene blue and as chromatographic supports
for the separation of phenylalanine, tryptophan, vitamins, and perfumes. To demonstrate the fundamental role of cyclodextrin cavities in the performance of ECP
materials, Professor Solms compared the results with those obtained with a commercial cross-linking epichlorohydrin-dextran polymer, SEPHADEX
®
, which did
not have inclusion properties. The results were interpreted in terms of the formation
of inclusion complex or more simply complexation. Professor Solms also used the
concept of “molecular encapsulation,” introduced by Professor Cramer about
12 years earlier.
Professor Wiedenhof showed that α-cyclodextrin and β-cyclodextrin gels had a
chromatographic behavior comparable to that of SEPHADEX G-25 resin in terms
of swelling characteristics and heat resistance but with more interesting performances in terms of complexation. The results confirmed that ECP materials were
suitable chromatographic supports for gel inclusion chromatography. Different
separations using phenol, benzoic acid, aniline, chlorobenzoic acids, and tyrosine
were obtained, and again the results were mainly interpreted using the complexation
phenomenon. Professor Wiedenhof pointed out the fact that the ability of the
cyclodextrin- based resins to separate different molecules was due to the fact that
“each resin contained cyclodextrin voids which were able to form inclusion compounds.” He introduced the term “inclusion isotherm” instead of adsorption
isotherm.
Professor Wiedenhof was also the first to characterize ECP materials using infrared and NMR data (Wiedenhof 1969; Wiedenhof et al. 1969, 1971; Wiedenhof and
Trieling 1971). Figure 8.10 shows the infrared spectrum of an ECP material with the
following main bands: OH stretching, 3444 cm
−1
; CH stretching, 2928 cm
−1
; CH
stretching, 2865 cm
−1
; CH deformations, 1360 cm
−1
; OH bending (water),
1629 cm
−1
; OH bending, 1223 cm
−1
; bending of COH group/CO stretching glycosidic bond, 1070–1150 cm
−1
; CO/CC stretching, 1026 cm
−1
; anomeric CH
G. Crini
8.3 A Brief History of Water-Insoluble
Cyclodextrin- Epichlorohydrin Polymers
for Environmental Applications
The idea of preparing ECP materials for analytical purposes, such as gel chromatography, inclusion chromatography, and target substance complexation, has been the
focus of attention of scientists worldwide for the past 60 years, but the most intensive studies on their use as adsorbents in wastewater treatment to remove toxic
contaminants have only begun in the past two decades.
In the mid-1960s, Professor Solms was the first to demonstrate that α-, β-, and
γ-cyclodextrin molecules have the ability to easily form cross-linked networks that
could have industrial applications in the field of separation sciences such as chromatography (Solms 1966, 1967, 1969; Solms and Egli 1964, 1965). He has shown that
cyclodextrin polymers exhibited strong adsorptive properties as inclusion resins for
the separation of various molecules such as aniline, nitrophenols, benzaldehyde,
pyridine, iodine, Congo red, and methylene blue and as chromatographic supports
for the separation of phenylalanine, tryptophan, vitamins, and perfumes. To demonstrate the fundamental role of cyclodextrin cavities in the performance of ECP
materials, Professor Solms compared the results with those obtained with a commercial cross-linking epichlorohydrin-dextran polymer, SEPHADEX
®
, which did
not have inclusion properties. The results were interpreted in terms of the formation
of inclusion complex or more simply complexation. Professor Solms also used the
concept of “molecular encapsulation,” introduced by Professor Cramer about
12 years earlier.
Professor Wiedenhof showed that α-cyclodextrin and β-cyclodextrin gels had a
chromatographic behavior comparable to that of SEPHADEX G-25 resin in terms
of swelling characteristics and heat resistance but with more interesting performances in terms of complexation. The results confirmed that ECP materials were
suitable chromatographic supports for gel inclusion chromatography. Different
separations using phenol, benzoic acid, aniline, chlorobenzoic acids, and tyrosine
were obtained, and again the results were mainly interpreted using the complexation
phenomenon. Professor Wiedenhof pointed out the fact that the ability of the
cyclodextrin- based resins to separate different molecules was due to the fact that
“each resin contained cyclodextrin voids which were able to form inclusion compounds.” He introduced the term “inclusion isotherm” instead of adsorption
isotherm.
Professor Wiedenhof was also the first to characterize ECP materials using infrared and NMR data (Wiedenhof 1969; Wiedenhof et al. 1969, 1971; Wiedenhof and
Trieling 1971). Figure 8.10 shows the infrared spectrum of an ECP material with the
following main bands: OH stretching, 3444 cm
−1
; CH stretching, 2928 cm
−1
; CH
stretching, 2865 cm
−1
; CH deformations, 1360 cm
−1
; OH bending (water),
1629 cm
−1
; OH bending, 1223 cm
−1
; bending of COH group/CO stretching glycosidic bond, 1070–1150 cm
−1
; CO/CC stretching, 1026 cm
−1
; anomeric CH
G. Crini