Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Amides infrared frequencies

The situation with 7V-acyloxy-/V-alkoxyureas and carbamates is similar although infrared data were mostly determined by liquid film or condensed phase (KBr/nujol mull).52,131 However, the limited data for V-acyloxy-TV-alkoxyureas (Table 2, entries 69-72) give amide carbonyl frequencies ca. 1730 cm-1 that are raised by some 37-40 cm-1 by acyloxylation. Values for carbamates (Table 2, entries 73-77) are higher (mostly 1780 cm-1) but are raised to a lesser extent (10-20 cm-1) relative to their parent carbamates. Clearly, carbonyl vibrational frequencies will be influenced strongly by the adjacent amino or alkoxyl group in both analogues. [Pg.56]

Doubts have been cast on these conclusions by Janssen (1961) and Cook (1964), who studied infrared spectra of the salts of dimethyl-acetamide. The strong C=0 band in the solid amide appears at 1639 cm-1. In the solid hydrochloride a band appears at 1693 cm-1, which was assigned to the C=N bond in the O-protonated cation (Janssen, 1961), but could equally be due to the C=0 vibration in the N-protonated cation. Raman spectra of dimethylacetamide (2 m ) in cone, hydrochloric acid show the same intense band at 1693 cm-1 (de Loze et al., 1972). In view of the high concentrations of both the amide and the acid, it is probable that the amide is present in these solutions largely as the O-protonated cation, so that the assignment of this band to the C=N frequency seems likely, especially for a tertiary amide. Infrared and Raman spectra are thus capable of interpretation in terms of both N- and O-protonation, depending to some extent on the amide (primary, secondary or tertiary),. and cannot provide unambiguous evidence for the site of protonation. [Pg.338]

The combination of infrared spectroscopy and hydrogen-deuterium exchange is a powerful technique for revealing small differences in protein secondary structure. Few proteins are composed solely of one type of structure, therefore several amide I and amide II frequencies may contribute to any amide I and II band. It is often difficult to resolve all of these frequencies in the difference spectrum, since some of the peaks have bandwidths which are smaller than the amide I or amide II bandwidth and are thus effectively hidden within the main peak. To resolve overlapping bands, second derivative spectra may be generated using a computer programme. The resultant spectrum is presented as absorbance/(wavenumber)2 versus wavenumber. [Pg.209]

As yet, however, infrared spectra cannot differentiate various helices that have been proposed (Donohue, 1953 Low and Edsall, 1956), nor is it clear that the random coil, which is in general the alternative conformation in solution, can be reliably distinguished from helices. Although the amide I frequency of helical poly-L-glutamic acid in DjO shifts from 1638 to 1644 cm upon forming the random coil (Klemperer and Doty, 1960) and similar shifts are observed in copolymers of glutamic acid and lysine upon loss of helical content (Blout and Idelson, 1958), this carbonyl frequency can be almost identical in the two forms (Elliott et al., 1957b, 1958). Additional techniques are therefore required to provide firm evidence for the a-helical conformation in solution. [Pg.429]

In addition, the infrared contributions of the side chains of the amino acids which constitute the protein must be considered. Amino acid side chains exhibit infrared modes that are often useful for investigating the local group in a protein. It is also important to be aware of the location of such modes as they may be confused with amide vibrations. Fortunately, these contributions have been found to be small in D2O when compared to the contributions made by the amide I band. The characteristic side-chain infrared frequencies of amino acids are summarised in Table 6.2b. [Pg.116]

Infrared spectroscopy has been used in a large number of studies of proteins over a range of different environments. Some examples of the proteins that have been analysed are listed in Table 6.2c, which details the deconvolved amide I frequencies and secondary structure assignments that have been made for a series of proteins in D2O. These assignments are based on the fact that the secondary structures of these globular proteins have been very well characterised by X-ray crystallography. [Pg.119]

Fraser and Suzuki (1970) have described a quantitative analysis of the infrared spectrum of / -keratin, using a method of interpreting the observed dichroism, which allowed all three infrared active components of amide I associated with the antiparallel chain pleated sheet to be detected and estimated. Fraser and Suzuki found the following amide I frequencies for -keratin V (0, t) = 1697 cm Vj (re, 0) = 1629cm and Vj (7t, 7t) = 1683cm". These frequencies were calculated from the following equations ... [Pg.195]

The combination of infrared reflection absorption spectroscopy and the Fourier transform technique has proven to be useful for structural studies of mono-molecular protein and amino acid films formed on metal surfaces. All protein films investigated exhibit a distinct blue shift of the Amide I frequency upon adsorption on metal surfaces, compared to the same band in aqueous solution. The magnitude of this blue shift seems to be larger for proteins with dominating )8-structure (32 cm" ) than for those with a large amount of a-helix or disordered structures (ca. 20 cm" ). It is concluded from reference spectra of... [Pg.74]

The whole concept of direct methylation has recently been critically reviewed and rejected by Gompper as a method to study tautomerism. The difference in the proportions of the two methyl derivatives produced w hen diazomethane is in excess, or the reverse, has now been ascribed to the relative importance of the Sn and Sn reactions of the tautomeric compound with diazomethane. The proportions of N- and 0-methyl derivatives formed by the reaction of cyclic amides with diazomethane has been related to the infrared vC—O frequencies. ... [Pg.324]

A criterion for the position of the extent of the mesomerism of type 9 is given by the bond order of the CO bond, a first approximation to W hich can be obtained from the infrared spectrum (v C=0). Unfortunately, relatively little is known of the infrared spectra of amide anions. How-ever, it can be assumed that the mesomeric relationships in the anions 9 can also be deduced from the infrared spectra of the free amides (4), although, of course, the absolute participation of the canonical forms a and b in structures 4 and 9 is different. If Table I is considered from this point of view, the intimate relationship betw-een the position of the amide band 1 (v C=0) and the orientation (0 or N) of methylation of lactams by diazomethane is unmistakeable. Thus the behavior of a lactam tow ard diazomethane can be deduced from the acidity (velocity of reaction) and the C=0 stretching frequency (orientation of methylation). Three major regions can be differentiated (1) 1620-1680 cm h 0-methylation (2) 1680-1720 cm i, O- and A -methylation, w ith kinetic dependence and (3) 1730-1800 em , A -methylation, The factual material in Table I is... [Pg.253]

Infrared radiation, electromagnetic spectrum and, 419, 422 energy of. 422 frequencies of, 422 wavelengths of, 422 Infrared spectroscopy, 422-431 acid anhydrides, 822-823 acid chlorides, 822-823 alcohols. 428, 632-633 aldehydes, 428. 730-731 alkanes, 426-427 alkenes, 427 alkynes, 427 amides. 822-823 amines, 428, 952 ammonium salts, 952-953 aromatic compound, 427-428, 534 bond stretching in, 422... [Pg.1301]

The UV-spectra of azolides have already been discussed in the context of hydrolysis kinetics in Chapter 1. Specific infrared absorptions of azolides were mentioned there as well increased reactivity of azolides in nucleophilic reactions involving the carbonyl group is paralleled by a marked shift in the infrared absorption of the corresponding carbonyl bond toward shorter wavelength. For example, for the highly reactive N-acetyl-tetrazole this absorption is found in a frequency range (1780 cm-1) that is very unusual for amides obviously the effect is due to electron attraction by the heterocyclic sys-tem.[40] As mentioned previously in the context of hydrolysis kinetics of both imidazo-... [Pg.35]

Figure 5.12 Dependence of peak frequencies in infrared spectrum of glucosamide bolaam-phiphiles NC( )GN-GLC (14) on methylene spacer length n. (a) The CH2 antisymmetric vas and symmetric vs stretching vibrations reveal gauche-included conformation for short chains and an all-trans conformation for longer chains, (b) Amide I and II frequencies show an even-odd effect for n > 10. Reprinted from Ref. 53 with permission of Wiley-VCH. Figure 5.12 Dependence of peak frequencies in infrared spectrum of glucosamide bolaam-phiphiles NC( )GN-GLC (14) on methylene spacer length n. (a) The CH2 antisymmetric vas and symmetric vs stretching vibrations reveal gauche-included conformation for short chains and an all-trans conformation for longer chains, (b) Amide I and II frequencies show an even-odd effect for n > 10. Reprinted from Ref. 53 with permission of Wiley-VCH.
Similar to the TGA experiments, in situ Infrared Spectroscopy has been used to follow the amide bond stretching frequencies while heating under various atmospheres. ° These experiments (see Fig. 7.2) suggest that dendrimer removal requires relatively forcing conditions to maximize CO adsorption on supported Pt catalysts prepared from A variety of activation conditions have been... [Pg.100]

The ambiguity of infrared criteria for the identification of protonation sites in imidazoles and 2-pyrazolines has been discussed by Elguero et al. (1967a), who have also provided new information on the infrared spectra of the hydrochloride of 3,5,5-trimethyl-2-pyrazoline in chloroform solution. There is a shift of the stretching vibration of the C=N bond from 1624 cm in the base to 1649 cm" in the hydrochloride salt in chloroform, i.e., in the N-1 protonated cation. This is analogous to similar shifts of the carbonyl frequency in some amide salts (see page 338). [Pg.327]

Piperazine-2,5-diones possess two cis amide bonds. In the infrared, the CO stretching bands occur at 1670-1690 cm 1 and the NH stretching frequency at 3180-3195 cm-1. More detailed analysis of IR and Raman spectra have been carried out [84SA(A)481, 84SA(A)503]. [Pg.200]

The wavelengths of IR absorption bands are characteristic of specific types of chemical bonds. In the past infrared had little application in protein analysis due to instrumentation and interpretation limitations. The development of Fourier transform infrared spectroscopy (FUR) makes it possible to characterize proteins using IR techniques (Surewicz et al. 1993). Several IR absorption regions are important for protein analysis. The amide I groups in proteins have a vibration absorption frequency of 1630-1670 cm. Secondary structures of proteins such as alpha(a)-helix and beta(P)-sheet have amide absorptions of 1645-1660 cm-1 and 1665-1680 cm, respectively. Random coil has absorptions in the range of 1660-1670 cm These characterization criteria come from studies of model polypeptides with known secondary structures. Thus, FTIR is useful in conformational analysis of peptides and proteins (Arrondo et al. 1993). [Pg.149]


See other pages where Amides infrared frequencies is mentioned: [Pg.473]    [Pg.338]    [Pg.63]    [Pg.111]    [Pg.379]    [Pg.219]    [Pg.227]    [Pg.44]    [Pg.8821]    [Pg.60]    [Pg.426]    [Pg.170]    [Pg.22]    [Pg.32]    [Pg.219]    [Pg.1138]    [Pg.17]    [Pg.136]    [Pg.721]    [Pg.56]    [Pg.57]    [Pg.318]    [Pg.338]    [Pg.339]    [Pg.348]    [Pg.448]    [Pg.350]    [Pg.153]    [Pg.715]    [Pg.738]    [Pg.1138]   
See also in sourсe #XX -- [ Pg.7 , Pg.52 ]

See also in sourсe #XX -- [ Pg.7 , Pg.52 ]




SEARCH



Amide frequency

Amides infrared absorption frequencies

Infrared frequencies

© 2024 chempedia.info