Raman microscopy of a small uniaxial crystal: Tetragonal aspartame

Abstract

A general method is presented for determining the shape and orientation of the Raman tensor of a molecule in a uniaxial crystal using a Raman microscope. First, equations are derived to connect the Raman tensor components (axx, a, , etc.) of a molecule to the Raman tensor components (aaa, a,,, etc.) of a crystal that is composed of molecules in a uniaxial arrangement, with an orientation specified by the two angles x and 9. Next, a method is presented to obtain a correct set of values of the intensity ratios Zac/Zaa and ZJZm from observed values of the intensity ratios measured with a Raman microscope. To augment the experimental data, the depolsrization ratio p (for a completely random molecular orientation) is plotted as a function of r l = axx/azz and rz = ay,,/azz, so that a possible set of r , and r z values can be found from an observed value of p. The method has been applied to an aspartame IIA crystal (P4,). A set of values of r,, r z , x and 9 has been determined for each of the following Raman fundamentals: 1741 cm-' (ester C -0 stretch), 1667 cm-' (amide I ) , 1275 cm-' (amide 111) and 1204 em-' (C-C,,,,,, stretch), excited at 488.0 nm.

Subunit Orientation in the Filamentous VirusFf(fd, f1, M13)

“…Relative magnitudes of Raman tensor components, a xx /a zz (0r 1 ) and a yy /a zz (0r 2 ), associated with a specific vibration can be (a) Here, the subunit a-helix is parallel to the fiber axis, Z (=c). Principal axes of the local amide I Raman tensor correspond to those of aspartame (Tsuboi et al, 1991), except that x and z axes are interchanged and the direction of x is reversed. The peptide group is in the xy plane with the carbonyl bond directed at an angle of 146°f rom x and 168°from c. Amide I Raman tensor quotients are r1 = 20 and r2 = 4.…”

Infrared and Raman microscopy of fowl feather barb

“…If this tensor is placed at every peptide group (see Fig. 4), the Raman scattering tensor a of an antiparallel-chain pleated sheet is given as 4 The principal axes of the synthetic Raman tensor a come out to be the X, Y, and Z axes shown in Fig. 4, as expected, and its tensor components are calculated to be Fig.…”

“…antiparallel-chain pleated sheet On the basis of the Raman spectroscopic measurement on a single crystal of a dipeptide (aspartame), whose molecule involves only one peptide group, Tsuboi et al (4) derived the shape and orientation of the amide I Raman tensor ( a t ) excited at 488.0 nm. The orientation of the principal axes, x, y, and z, of the tensor is reproduced in Fig.…”

“…Their barbs, in which the crystallite alignment looks better under a polarizing microscope, are too thin for conventional infrared and Raman spectroscopic measurements. Due to recent developments in infrared and Raman microscopy (3,4), however, even such a thin barb (10 pm in diameter, for example) can now be subjected to these vibrational spectroscopic examinations. If, in such spectroscopic examinations, a comparative study is possible of the infrared and Raman data for the same barb sample, it may yield additional benefits.…”

Raman scattering tensors of pseudouridine

“…The correction factor is 1.50 for the 50] objective, and it is nearly independent of wavelength in the wavenumber range in question. 16 On the basis of these Ðndings, the apparent (cb) spectrum was corrected by multiplying by this correction factor 1.50.…”