Pedagogia Crítica e Luta de Classes no Neoliberal Era do Terror
2. La Financiarización y la Mente Neoliberal
The most pronounced changes for the thermal unfold-ing of ribonuclease (RNase) A are observed from 4820 to 4940 cm–1. The strong N-H combination band found at 4867 cm–1 in the spectrum of native RNase A shifts to 4878 cm–1 upon thermal unfolding. The thermal unfolding of RNase A begins with some changes in β-sheet structure, followed by the loss of α-helical structures, and then end-ing with the unfoldend-ing of the remainend-ing β sheets.7 Fourier transform NIR (FT-NIR) spectra have been measured for Table 11.1 Band Assignments for Peptide Groups as
Delineated by Hecht and Wood
Reported Band Assignments Wavenumber Wavelength (nm) C-H stretch + CH deformation 3950–4400 2532–2270 2 X stretch C=O + peptide group mode 4590 2180
N-H stretch + peptide group mode 4850 2060
OH stretch + OH deformation of water 5135 1947
2 X CH stretch 5700–5850 1750–1710
2 X NH stretch 6500 1540
2 X OH stretch + deformation of water 6900 1450
3 X CH stretch 8100 1235
83 Amino Acids, Peptides, and Proteins
Table 11.2 Absorption Bands Associated with “Proteins” as Amides
Functional Grouping Nanometers Wavenumbers
N-H/C-N/N-H [Bonded NH stretching & Amide III (C-N stretching/N-H in-plane bending) combination] from
polyamide 11 2183 4586
N-H (3δ) 2180 4587
N-H/C-N/C=O [2x Amide I (2νSC=O stretching) & Amide III deformation (C-N stretching/N-H in-plane
bending) combination] for urea 2180 4687
N-H/C-N/C=O [2x Amide I (2νSC=O stretching) & Amide III deformation (C-N stretching/N-H in-plane
bending) combination] for secondary amides in proteins 2180 4590
N-H/C-N [νSN-H asymmetric & Amide III deformation (C-N stretching/N-H in-plane bending) combination]
for urea 2080 4808
N-H [νN-H & Amide II deformation (N-H in-plane bending) combination] for secondary amides in native
RNase A 2075 4820
N-H (3δ) & N-H stretching combination 2060 4854
N-H [ν N-H & Amide II deformation (N-H in-plane bending) combination] for secondary amides in proteins 2060 4850
CONH2 combination of amide A and amide II 2060 4855
N-H stretching & C=O stretching (Amide I) combination 2055 4866
N-H (ν N-H & δN-H combination) for Gamma-valerolactam 2055 4865
N-H combination band found in the spectrum of native RNase A (C=O amide I band) 2055 4867
CONH2 specifically due to peptide β-sheet structures. 2055 4865
N-H stretching & C=O stretching (Amide I) combination band in the spectrum of native RNase A 2055 4867 N-H from CONH2 as thermal unfolding of RNase A protein in aqueous solution (Assigned to an N-H
combination band) 2055–2050 4867–4878
N-H in-plane bend & C-N stretching & N-H in-plane bend combination 2050 4878
N-H native RNase A combination band at 4867cm–1 shifting due to thermal unfolding (C=O amide I band) 2050 4878 N-H stretching & C=O stretching (Amide I) combination band observed in the thermal unfolding
observed in native RNase A 2050 4878
N-H [ν N-H symmetric & Amide II deformation (N-H in-plane bending) combination] for primary amides 2040 4902
C=O (3ν), .C=ONH2 2030 4926
N-H [ν N-H asymmetric & Amide III deformation (C-N stretching/N-H in-plane bending) combination]
for primary amides 2030 4925
N-H/C=O [Bonded NH stretching & Amide I (2νSC=O stretching) combination] of native RNase A 2024 4940 N-H [ν N-H symmetric & Amide III deformation (C-N stretching/N-H in-plane bending) combination] for
primary amides 2010 4975
N-H [ν N-H asymmetric & Amide III deformation (C-N stretching/N-H in-plane bending) combination] for
primary amides 1990 5025
N-H stretching (asymmetric) & N-H in-plane bending combination 1980 5051
CONH2 specifically due to peptide β-sheet structures. 1691–1688 5915–5925
N-H (2ν), .CONHR 1490 6711
N-H (2ν), .CONH2 1483 6743
N-H (2ν), .CONHR 1471 6798
N-H (νN-H asymmetric & νN-H symmetric combination) for primary amides 1470 6805
Practical Guide and Spectral Atlas for Interpretive Near-Infrared Spectroscopy 84
various polypeptides and proteins with different secondary structures in order to identify an NIR marker band for the protein and polypeptide structures. Comparison between FT-NIR and FT-mid-IR spectra has shown a correlation between the frequency of a band near 4855 cm–1, assign-able to a combination of amide A and amide II, and that of a mid-IR band near 3300 cm–1 assigned to amide A (N-H stretch).8 The NIR spectra of various proteins (bovine serum albumin, lysozyme, ovalbumin, γ globulin, β lacto-globulin, myoglobin, cytochrome c) have been investigated for potential measurement of protein secondary structure.
The spectra of proteins in aqueous solutions and as freeze-dried solids indicated α-helix information present at 4090, 4365–4370, 4615, and 5755 cm–1; and β-sheet information at 4060, 4405, 4525–4540, 4865, and 5915–5925 cm–1.9
Ovalbumin (OVA) has been studied in acidified, aque-ous solutions using two-dimensional (2D) FT-NIR cor-relation spectroscopy. This technique demonstrates a significant change in bands when the molecule pH moves from 5.4 to 3.6. A band near 4265 cm–1 assigned
to a symmetric methylene (CH2) stretching mode and a CH2 bending mode of side chains observed at pH 5.4 dis appears completely in the synchronous spectrum at pH 3.6. A band near 4600 cm–1 assigned to a combination of amide B (a Fermi resonance band relating to the first overtone of the carbonyl and the N-H stretch) and amide II shifts downward with significant broadening between pH 3.0 and 2.4. A broad band at around 6950 cm–1 was assigned to free water and bound water with weak hydro-gen bonds becomes very weak in the synchronous spec-trum at pH 2.6, while broad auto peaks around 6450 cm–1 suddenly appear that are due to bound water with several hydrogen bonds and the first overtone of an NH stretch-ing mode of the amide groups of OVA.10 FT-NIR spectra have been measured for several globular proteins and a band near 4525 cm–1 seems to be highly associated with β-sheet structure. Low-wavenumber NIR bands from the 4500–4000 cm–1 region were considered to reflect the amino acid composition of proteins.11 Figure 11.1 shows a solid sample amino acid reflection spectrum.
Absorbance
10000 9500 9000 8500 8000 7500 7000 6500
1000 1053
3νN-H
2νN-H
CH3
1111 1176 1250 1333 1429 1538
L-Valine, 3-methyl-, 1,1-dimethylethyl ester, 99%
(a)
7000 cm–1
nm 1429
6500 6000 5500 5000 4500 4000
1538 1667 1818 2000 2222 2500
Absorbance
L-Valine, 3-methyl-, 1,1-dimethylethyl ester, 99%
(b)
FIGURE 11.1 (a) L-Valine, 3-methyl, 1,1-dimethylethyl ester (amino acid) spectrum (952–1587 nm). (b) L-Valine, 3-methyl, 1,1-dimethylethyl ester (amino acid) spectrum (1389–2632 nm). (Spectra used by permission from NIR Spectra of Organic Compounds, Wiley-VCH, ISBN 3-527-31630-2.)
85 Amino Acids, Peptides, and Proteins
References
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9. Izutsu, K.-I., Fujimaki, Y., Kuwabara, A., Hiyama, Y., Yomota, C., Aoyagi, N. Near-infrared analysis of protein secondary structure in aqueous solutions and freeze-dried solids. J. Pharmaceut. Sci. 2006, 95(4), 781–789.
10. Murayama, K., Ozaki, Y. Two-dimensional near-IR correla-tion spectroscopy study of molten globule-like state of oval-bumin in acidic pH region: Simultaneous changes in hydration and secondary structure. Biopolymers 2002, 67(6), 394–405.
11. Miyazawa, M., Sonoyama, M. Second derivative near infrared studies on the structural characterization of proteins. J. NIR Spectrosc. 1998, 6(1 –4), A253–A257.