It is the source of the invariability of the X_H and X_D band contours in IR spectra of isotopically diluted crystals, regardless of the H/D isotopic exchange rates According to our latest estimations based on the quantitative analysis of the IR spectra of the hydrogen bond in diverse isotopically diluted crystalline systems dynamical cooperative interactions involving hydrogen bonds seem to be common in nature. Dynamical co operative interactions result from dynamical couplings between the proton stretching motions and the electronic movement. They remain beyond the Born_Oppenheimer approximation. This term covers the nonadditive efects concerning the physicochemical constants characterizing hydrogen bonds.

This newly revealed mechanism substantially difers from the familiar mechanism of static cooperative interactions, which resulted from quantum chemical cal culations performed within p53 Signaling Pathway the limits of the Born_Oppenheimer approximation. The details of the theory of dynamical cooperative interactions in hydrogen bond dimeric systems have been described In the case of cyclic hydrogen bond dimers the H/D isotopic self organization always occurred. No system contradicting this rule was found. For crystals with chain systems of hydrogen bonded molecules a considerable diversity of the spectral proper ties attributed to the dynamical cooperative interactions was found. This remains in a relatively simple relation to the electronic properties of the associated molecules in crystals.

When the molecules contain easily polarizable electronic systems, directly linked to the hydrogen bond forming atoms, the strongest dynamical cooperative interactions involve the adja cent hydrogen bonds in a fragment of an individual hydrogen bond chain. This evokes the H/D isotopic self organization process in these domains, e. g., in pyrazole, imidazole, and 4 thiopyridone crystals. PARP Inhibitors This means that identical hydrogen isotope atoms are grouped together in fragments of the hydrogen bond chains. On the other hand, in the case of molecular systems that do not possess large electronic systems a random distribution of protons and deuterons in the hydrogen bond systems was deduced from the IR spectra of the and acetanilide and N methylthioacetamide ) exhibit an inter mediate behavior.

Although in these associated molecular crystals no large electronic systems exist, nevertheless some unique H/D isotopic self organization efects in the spectra of the isotopically diluted crystals were identified. Quantitative analysis of the spectra allowed us to prove that in this case the AMPK Signaling strongest dynamical cooperative interactions usually involved the closely spaced hydrogen bond pairs, in which each moiety belonged to a diferent chain of the associated molecules penetrating a unit cell of the lattice. Therefore, investigation of polarized IR spectra of crystals with chain arrangements of hydrogen bonds in their lattices may provide data facilitating the explanation of the mechanism of dynamical cooperative interactions. These studies may also help to elucidate the physical factors responsible for the observed diversity occurring during the H/D isotopic self organization processes in the isotopically diluted crystals.

Crystals of diverse secondary amides due to the mutual arrangement of the N_H and CdO RAF Signaling Pathway bonds in their molecules seem to be particularly promising systems for such investigations. These molecules are predestinated to form chain N_H 3 3 3 OdC bonded associates. Indeed, in the majority of amide crystals the associate amide molecules are linked together, thereby forming infinite chains. This type of hydrogen bonded associates is widespread in nature. The secondary amide crystals are suitable model systems for the interpretation of protein properties, since the N_H 3 3 3 OdC bond lengths in the crystals are very close to those found in proteins.

From our recent estimations it results that the electronic PARP structure of amide and thioamide molecules, additionally modified by diverse atomic substituent groups linked to the amide or thioamide fragment, undoubtedly afects the way in which the H/D isotopic self organization processes occur in diverse amide and thioamide crystals. However, our knowledge in this matter is still incomplete. Therefore, for our study of this problem a suitable molecular system should be chosen, i. e., one for which the efects of the substituent groups on to the electronic proper ties of the associating molecules appear to be extreme. We have chosen N phenylacrylamide, since in molecules of this compound two atomic groups with easily polarizable electrons on orbitals are linked to the two opposite sides of the amide fragments. Electrons of these groups are expected to couple efectively with the electronic and the proton stretching motions of the N_H 3 3 3 O hydrogen bonds in the crystal. In this paper we present the results of our studies on polarized IR spectra of the hydrogen bond in PAM crystals.