By measuring and quantitatively interpreting the IR polarized crystalline spec tra and the H/D isotopic efects in the spectra, we endeavored to answer the following questions: How strong are dynamical cooperative interactions involving hydrogen bonds in the lattice Which hydrogen bonds from an individual unit cell participate in the H/D isotopic self organization mechanism in the crystal Do the electrons of the substituent groups, namely of the phenyl and the acryl group, couple efectively with the hydrogen bonds in the crystal, and thereby afect the crystal spectral properties To what extent are the PAM crystal spectra similar to the relevant spectra of acetanilide and N methylacetamide crystals 2. EXPERIMENTAL SECTION PAM used for our studies was a commercial substance and was used without further purification.

The deuter ium bonded crystals were obtained by evaporation of D 2O solutions of the compound under reduced Pazopanib pressure at room temperature. The deuterium substitution rate for diferent stu died crystalline samples varied in a relatively wide range. The Raman spectra of polycrystalline samples of PAM were measured at room temperature with the use of the Raman Accessory for the Nicolet Magna 560 spectrometer. 2. 1. Crystal Structure of N Phenylacrylamide. The crystal structure of PAM was unknown at the moment of initiation of the studies, therefore, the spectral studies were preceded by the X ray studies. Crystals suitable for performing the crystal struc ture determination were obtained by crystallization from etha nol/acetone solution.

The X ray diffraction experiments were done at 100 K. It was estimated that crystals of PAM belong to the ortho 15 rhombic system, space symmetry group is Pbca _ D. The crystal 2h lattice Pazopanib constants are a _ 9. 6621 , b _ 9. 7317 , and c _ 16. 788 . There is one independent molecule in an asym metric unit cell. Each unit cell contains 8 molecules. The associated molecules form hydrogen bonded chains were found to elongate along the a axis. Other data concerning the difraction experiment and the geometry parameters of hydrogen bonds in the crystal were collected in Table 1. In the three crystalline lattices associating amide molecules, PAM, N methylacetamide, and acetanilide, form infinite hydro gen bonded chains. Moreover, the space symmetry groups of PAM and acetanilide crystals are identical.

In each diferent crystalline system the hydrogen bonds, belonging to two neigh boring chains from a unit cell, are related to one another by the inversion center operation. The diference between the two dife rent amide crystals is in the in uence of the molecular electronic properties on to the hydrogen bond Ponatinib IR spectral properties. 3. RESULTS AND DISCUSSION 3. 1. IR Spectra of the Hydrogen Bond in Amide Crystals: The State of the Art. Molecular structure of secondary amides like acetanilide and N methylacetamide as well as the amide group geometry is fairly similar to the corresponding geometry of polypeptides, therefore, studies of these molecular systems are interesting from the point of view of biochemistry and biophy sics.

O hydrogen bonded Single crystals of PAM, as well as its deuterium isotopomer, were obtained by crystallization from melted Ponatinib samples, occurring between two closely spaced CaF2 windows. In this way, thin enough crystals were prepared, characterized by their maximum absorbance close to 0. 5 at the N_H band frequency range. From the crystalline mosaic, suitable monocrystalline fragments were selected and then spatially oriented, using a polarization microscope. Next, these selected single crystals were exposed for the experiment by placing them on a metal plate diaphragm with a 1. 5 mm diameter hole. It was found that the PAM crystals most frequently developed the ab or ac plane of the lattice. The IR spectra of selected crystals were recorded with the FT IR Nicolet Magna 560 spectrometer by the transmission method with 2 cm resolution.

Measurements of the spectra were performed in the temperature range from 293 K to the tempera ture of liquid nitrogen for two diferent orientations of the electric field vector E. For crystals with the ac or ab face developed, the spectra were HSP recorded for the E vector parallel to the a axis of the lattice, and in the other case, for the one perpendicular to it, i. e., parallel to the c or b identity period. For each isotopomer case the measurements were repeated for ca. 10 diferent single crystals. 1 The Journal of Physical Chemistry A ARTICLE Figure 3. IR spectra of the polycrystalline samples of PAM, dispersed in the KBr pellets, measured at two diferent temperatures. To identify the C_H bands, the Raman spectra measured at room temperature are also drawn. 32_39 several monographs. The authors of these papers intro duced their own nomenclature for the two bands observed in the frequency range of the N_H bond stretching vibrations, propos ing their assignment as amide A and amide B.