106
P. W. KENT
gen bonding has been widely investigated. By X-rays and polarized
infrared spectroscopy, it was shown (97) that the C=0 and NH groups
of N-acetyl residues make significant contributions. Further, Clark and
Smith (62) in earlier findings gave a as 9.25, and Lotmar and Picken
(51) in 1950 reported b as 10.27 A. Comparable figures for fungal chitin
are a — 9.70, b = 10.4, and c — 4.6 A. In general, similar values are
obtained for anthropod and fungal chitins, and this type of structure has
been designated α-chitin. Similar X-ray patterns are also reported for
plant (98, 99), insect (51, 100), and Sarcophaga chitins (100).
A second form of the polymer, /3-chitin, was first reported by Lotmar
and Picken (51) on the basis of X-ray diffraction patterns, in the "pen"
of the common squid Loligo and in the chetae of Aphrodite. This form,
characterized by its cell dimensions, a — 9.32, b — 10.17, and c =
22.15 Α., is not derived merely by hydration of the «-form. In cephalopods, α-chitin occurs in beak, radula, and lining of the gut in contrast to
the ß-form in the "pen." It has been pointed out (96, 101) that a-chitin
can occur alone or in association with such proteins as arthropodin or,
possibly, resilin. After solution of ß-chitin in formic acid or in 45% nitric
acid, the reisolated material exhibits the α-chitin pattern. Acidic hydrolysis (102) of jS-chitin, like α-chitin, yields only D-glucosamine hydrochloride. The a- and ß-forms thus appear to differ at the macromolecular level.
Dweltz (103) has performed an X-ray crystallographic examination
of /?-chitin (a specimen from Loligo, deproteinized by 10% potassium hydroxide at 40° for 4 hours) and reported it to be monoclinic (space
group P 2 1 ) with a = 4.7, b = 10.5, and c (fiber repeat) = 10.3A. The
monoclinic angle was about 90 degrees, hence the unit cell had an
approximately rectangular cross section through which one polysaccharide chain passed. The unit cell was calculated to contain two Nacetylglucosamine residues. As in α-chitin, the NH and CO groups of
acetamido side chains are hydrogen bonded along the a axis, while in the
b axis, a hydroxyl group of one chain is bonded by one molecule of water
to a —CH 2 OH of an adjacent chain (Figs. 9a and 9b). Dweltz (103)
states that /?-chitin in the dry state can be regarded as a monohydrate
(CsHisOsN-HsO). Thus in the ß-iorm, chains are all parallel and, separated by the water molecule, readily take up more water in humid conditions. In the «-form half the chains are parallel and half antiparallel and
the side chains are believed to be directly linked. The X-ray data for
α-chitin has been reconsidered (104) in the light of Dweltz and Carlstrom's findings, and it is concluded that the findings of the latter author
give a somewhat better fit.
Most of these views relate to "purified" chitin, and it must be
P. W. KENT
gen bonding has been widely investigated. By X-rays and polarized
infrared spectroscopy, it was shown (97) that the C=0 and NH groups
of N-acetyl residues make significant contributions. Further, Clark and
Smith (62) in earlier findings gave a as 9.25, and Lotmar and Picken
(51) in 1950 reported b as 10.27 A. Comparable figures for fungal chitin
are a — 9.70, b = 10.4, and c — 4.6 A. In general, similar values are
obtained for anthropod and fungal chitins, and this type of structure has
been designated α-chitin. Similar X-ray patterns are also reported for
plant (98, 99), insect (51, 100), and Sarcophaga chitins (100).
A second form of the polymer, /3-chitin, was first reported by Lotmar
and Picken (51) on the basis of X-ray diffraction patterns, in the "pen"
of the common squid Loligo and in the chetae of Aphrodite. This form,
characterized by its cell dimensions, a — 9.32, b — 10.17, and c =
22.15 Α., is not derived merely by hydration of the «-form. In cephalopods, α-chitin occurs in beak, radula, and lining of the gut in contrast to
the ß-form in the "pen." It has been pointed out (96, 101) that a-chitin
can occur alone or in association with such proteins as arthropodin or,
possibly, resilin. After solution of ß-chitin in formic acid or in 45% nitric
acid, the reisolated material exhibits the α-chitin pattern. Acidic hydrolysis (102) of jS-chitin, like α-chitin, yields only D-glucosamine hydrochloride. The a- and ß-forms thus appear to differ at the macromolecular level.
Dweltz (103) has performed an X-ray crystallographic examination
of /?-chitin (a specimen from Loligo, deproteinized by 10% potassium hydroxide at 40° for 4 hours) and reported it to be monoclinic (space
group P 2 1 ) with a = 4.7, b = 10.5, and c (fiber repeat) = 10.3A. The
monoclinic angle was about 90 degrees, hence the unit cell had an
approximately rectangular cross section through which one polysaccharide chain passed. The unit cell was calculated to contain two Nacetylglucosamine residues. As in α-chitin, the NH and CO groups of
acetamido side chains are hydrogen bonded along the a axis, while in the
b axis, a hydroxyl group of one chain is bonded by one molecule of water
to a —CH 2 OH of an adjacent chain (Figs. 9a and 9b). Dweltz (103)
states that /?-chitin in the dry state can be regarded as a monohydrate
(CsHisOsN-HsO). Thus in the ß-iorm, chains are all parallel and, separated by the water molecule, readily take up more water in humid conditions. In the «-form half the chains are parallel and half antiparallel and
the side chains are believed to be directly linked. The X-ray data for
α-chitin has been reconsidered (104) in the light of Dweltz and Carlstrom's findings, and it is concluded that the findings of the latter author
give a somewhat better fit.
Most of these views relate to "purified" chitin, and it must be