IR spectroscopy in studying

An additional example for the usefulness of IR spectroscopy in studying drug interactions with phospholipid vesicles is the quantitative determination of acyl chain conformation in gramicidin-DPPC mixtures [63]. The technique provides a quantitative measure of the extent to which membrane-spanning peptides induce disorder of phospholipid gel phases and order in liquid crystalline phases. 

Paukshtis E A and Yurchenko E N (1983), Use of IR-spectroscopy in studies of acid-basic properties of heterogeneous catalysts , Russ Chem Rev, 52, 242. 

So far we have exclusively discussed time-resolved absorption spectroscopy with visible femtosecond pulses. It has become recently feasible to perfomi time-resolved spectroscopy with femtosecond IR pulses. Flochstrasser and co-workers [M, 150. 151. 152. 153. 154. 155. 156 and 157] have worked out methods to employ IR pulses to monitor chemical reactions following electronic excitation by visible pump pulses these methods were applied in work on the light-initiated charge-transfer reactions that occur in the photosynthetic reaction centre [156. 157] and on the excited-state isomerization of tlie retinal pigment in bacteriorhodopsin [155]. Walker and co-workers [158] have recently used femtosecond IR spectroscopy to study vibrational dynamics associated with intramolecular charge transfer these studies are complementary to those perfomied by Barbara and co-workers [159. 160], in which ground-state RISRS wavepackets were monitored using a dynamic-absorption technique with visible pulses. 

The role of IR spectroscopy in the early penicillin structure studies has been described (B-49MI51103) and the results of more recent work have been summarized (B-72MI51101). The most noteworthy aspect of a penicillin IR spectrum is the stretching frequency of the /3-lactam carbonyl, which comes at approximately 1780 cm" This is in contrast to a linear tertiary amide which absorbs at approximately 1650 cm and a /3-lactam which is not fused to another ring (e.g. benzyldethiopenicillin), which absorbs at approximately 1740 cm (the exact absorption frequency will, of course, depend upon the specific compound and technique of spectrum determination). The /3-lactam carbonyl absorptions of penicillin sulfoxides and sulfones occur at approximately 1805 and 1810 cm respectively. The high absorption frequency of the penicillin /3-lactam carbonyl is interpreted in terms of the increased double bond character of that bond as a consequence of decreased amide resonance, as discussed in the X-ray crystallographic section. Other aspects of the penicillin IR spectrum, e.g. the side chain amide absorptions at approximately 1680 and 1510 cm and the carboxylate absorption at approximately 1610 cm are as expected. 

New IR techniques introduced for the study of prototropic tautomerism include IR dicroism for the photoinduced double proton transfer in por-phine 71 (Scheme 24) [89CPH(136)165], and IR spectroscopy in a supersonic jet (less than 50 K) for demonstrating the presence, in these conditions, of 2//-benzotriazole (57b) [96CPL(262)689]. 

Tire tautomerism and ionization of xanthosine (21), a 9-substituted xanthine, have been studied by IR spectroscopy in aqueous solution [83MI(2)231].Tlie diketo structure 21 was shown to exist below pH 5, and the 2-enolate anion 22 at neutral and slightly basic pH. 

Perfluoroallyl radical, C3F5, was obtained by vacuum pyrolysis (850-950°C, 10 Torr) of 1,5-perfluorohexadiene or of 3-iodopentafluoro-propylene (14) and was studied by pyrolytic mass spectrometry (Kagrama-nov et al., 1983b) and by IR spectroscopy in an argon matrix (Mal tsev et al., 1986). 

A matrix isolation IR study of cyclic siladienes was more successful (Khabashesku et al., 1992). At first, unstable l-silacyclopenta-2,4-diene [128] was generated by vacuum pyrolysis (800°C 10 -10 Torr) of 5-silaspiro[4.4]nona-2,7-diene [129] or pyrolysis and photolysis (A = 248 nm) of l,l-diazido-l-silacyclopenta-2,4-diene [130] it has been studied by UV and IR spectroscopy in an argon matrix at 12 K. The UV band at Amax = 278 nm and nine IR bands (including two sp Si-H stretching vibrations at 2175 and 2144 cm ) have been recorded in matrix spectra of [128]. Reversible photochemical interconversion of [128] with silacy-... 

The in vivo antitumor and trypanocidal effects of dimeric [Irn2(CH3COO)4(L)ra]° (L = classical organic antimalarial drugs, n= 1, 2) are reported.494 The dimeric complexes are characterized by IR spectroscopy. Further studies of monomeric Ir11 complexes, IrnL2, where L = alkyl or aryl dithiocarbamates and xanthates, reveal no clear relation between antitumor and antitrypanosomal actvities.495 Structure-activity data for the Ir11 complexes is presented. 

The extent of homogeneous mixing of pharmaceutical components such as active drug and excipients has been studied by near-IR spectroscopy. In an application note from NIRSystems, Inc. [47], principal component analysis and spectral matching techniques were used to develop a near-IR technique/algorithm for determination of an optimal mixture based upon spectral comparison with a standard mixture. One advantage of this technique is the use of second-derivative spectroscopy techniques to remove any slight baseline differences due to particle size variations. 

The applications of IR spectroscopy in catalysis are many. For example, IR can be used to directly characterize the catalysts themselves. This is often done in the study of zeolites, metal oxides, and heteropolyacids, among other catalysts [77,78], To exemplify this type of application, Figure 1.11 displays transmission IR spectra for a number of Co Mo O (0 < x < 1) mixed metal oxides with various compositions [79]. In this study, a clear distinction could be made between pure Mo03, with its characteristic IR peaks at 993, 863, 820, and 563 cm-1, and the Mo04 tetrahedral units in the CoMo04 solid solutions formed upon Co304 incorporation, with its new bands at 946 and 662 cm-1. These properties could be correlated with the activity of the catalysts toward carburization and hy-drodenitrogenation reactions. 

Further details of the theory and application of Raman spectroscopy in polymer studies can be found elsewhere (1. 9). However, vibrational frequencies of functional groups in polymers can be characterized from the spacing of the Raman lines and thus information complementary to IR absorption spectroscopy can be obtained. In addition, since visible radiation is used the technique can be applied to aqueous media in contrast to IR spectroscopy, allowing studies of synthetic polyelectrolytes and biopolymers to be undertaken. Conformation and crystallinity of polymers have also been shown to influence the Raman spectra Q.) while the possibility of studying scattering from small sample volumes in the focussed laser beam (-100 pm diameter) can provide information on localized changes in chemical structure. 

HadZi used IR spectroscopy to study some azophenols and azonaphthols (112). The phenylazophenols were found to be phenolic in the solid state. On the other hand the molecule of 4-phenylazo-l-naphthol is present in the crystal as the hydrazone tautomer. Had2i suggested that in l-phenylazo-2-naphthol and 2-phenylazo-1 -naphthol both tautomers are present. Similar suggestions have been made by others (113,114). 

No definitive studies on IR spectroscopy in this group have been found since the publication of Chapter 7.08 in <1996CHEC-II(7)283>. IR structural observations have only been used as supporting evidence for structure elucidation. For example, the IR spectra of 2-substituted-3-oxoisothiazolo[5,4- ]pyridines 43-58 have been reported (Table 9) <1998FES504>. The IR data for imidazo[4,5- ] and imidazo[4,5-. 

More recently, Koizumi et al. observed that Mn has an additional beneficial effect in unsupported Fe-based F-T catalysts. These authors studied the sulfur resistance of Mn-Fe catalysts and they observed superior catalysts stabilities, especially when the catalysts were pre-reduced in CO. This group also used IR spectroscopy in combination with CO as a probe molecule to compare Fe and Mn-Fe catalysts. It was found that the addition of Mn led to the appearance of several well-resolved bands upon CO adsorption. The appearance of the bands arising from bridged-bonded CO on Fe indicated that the size of the Fe particles were clearly larger than in the case of the unpromoted catalysts. They attributed the decreased reactivity towards H2S to the observed increase in Fe particle size. 

Although the estimates of range (more than five molecular distances) and cooperativity (three or four sites), which were developed in a semiquantitative treatment of long-range stress, must be considered highly approximate, the danger for simplistic interpretation of solid-state reaction mechanisms and the power of IR spectroscopy for studying such complications were clearly demonstrated [83]. 

Probing Ca++—Phosphate Binding. Although this question has been at the center of the current investigations, little experimentation was reported on direct evidence which could be furnished by IR spectroscopy. In a brief mention of IR absorption of DPL-uranyl nitrate in nujol paste, it was concluded that indeed Ca++ interacts with the lipid phosphate group (7). Subsequently, after thermodynamic analysis of calorimetric studies with DPL dispersions in aqueous electrolyte, the same laboratory suggested the absence of direct Ca++-phosphate interaction (8). Strangely, the authors of the second work (8) failed to provide explanations for the discrepancy between this and a previous report (7). The particular predicament implies that either one of the two experiments had to be... 

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