TABLE 1.

Secondary structure assignments of insulin fibrils on the basis of FTIR spectra under representative conditions

Conditions	Major components	Wave number	Ratio	Structure assignment
		cm−1
pH 2.0, no alcohol	Native monomers α-helix	1682	0.02	High frequency β
		1667	0.3	Turn
		1650	0.4	α-Helix
		1644	0.08	Irregular
		1633	0.2	Antiparallel β
pH 2.0, no alcohol	Parallel β	1666	0.03	Turn
		1661	0.01	Turn
		1651	0.01	Helix
		1647	0.4	Irregular
		1627	0.48	Parallel β
		1618	0.07	Antiparallel β
pH 4.8, no alcohol	Amorphous aggregate irregular	1682	0.04	High frequency β
		1667	0.19	Turn
		1655	0.17	Turn/helix
		1644	0.31	Irregular
		1634	0.24	Antiparallel β
		1622	0.04	Antiparallel β
pH 2.0, 20% TFE	Antiparallel β	1669	0.14	Turn/high frequency β?
		1657	0.08	Turn/helix
		1648	0.06	Helix/irregular
		1637	0.26	Antiparallel β
		1630	0.23	Parallel β?
		1619	0.23	Antiparallel β
pH 4.8, 20% TFE	Antiparallel β	1678	0.04	High frequency β
		1664	0.12	Turn
		1650	0.09	Helix
		1644	0.17	Irregular
		1632	0.38	Antiparallel β
		1618	0.2	Antiparallel β
pH 2.0, 10% HFIP	Antiparallel β	1665	0.15	Turn/high frequency β
		1648	0.14	Helix/irregular
		1635	0.3	Antiparallel β
		1626	0.08	Parallel β
		1620	0.33	Antiparallel β
pH 4.8, 10% HFIP	Antiparallel β	1677	0.09	High frequency β
		1658	0.28	Turn
		1647	0.08	Irregular/helix
		1634	0.33	Antiparallel β
		1618	0.22	Antiparallel β