Modern Polymer Spect..

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5.4 Poliyeptides 219 Table 5-11. Comparison of some modes of 3 ~~,-poly(cc-arninoisobutyri~ acid) and ccc-poly( L- alanine j . Mode" 3 !"-PA 1 B" XI-PLA Observed Calculated Calculated I II III Raman 1647 1531 1339 1313 1280 CN s, CNC' d 908 V NC"C d 594 C"CN d, CO ib 568 IR 1656 11 1665(A) 1661iE) 1545 i 1547(E) 1533(Aj 1346(E) 1312(A) 1280 )I 1287iA) 905 I/ 905(A) 694 1 701(E) 680 I1 676(A) 595 II 594(A) 557(A) 1657(A) 1655iEl) 1538( El) 15 19(A) 1345(El) 1287(E1) 1278( E2) 1262(A) 910(A) 660(E1) 608(E) 589(A) 522(E1) 537iA) a I, 11. 111, V: ainide modes in cm-l; s: stretch, d: deformation, ib: in-plane bend. From [110]. 11: parallel dichroism, I: perpendicular dichroism. From [106]. are well accounted for, and exhibit a quite different pattern from that of the MIhelix. This is undoubtedly due in part to the different involvement of side-chain structures in the two polypeptides. Since no such major difference is seen in the aniide V eigenvectors, the large frequency differences between the two helices must be due to differences in hydrogen-bonding geometry and/or main-chain conformation. (The disappearance of the 694 and 680 cm-l bands on N-deuteration [110] unambiguously confirms their assignments to ainide V.) The skeletal N CT d and CTN d, CO ib modes have reversed frequency order (and in one case changed species) in 3l"-PAIB, and again, this is probably partly due to the involvement of side-chain coordinates in the eigenvectors. Future studies of, for example, a 3 10- helix of PLA should help to establish the possible generality of these results. 5.4.2.4 Polyglycine I1 The PGII structure is the simplest one that is representative of polypeptide helices without intramolecular hydrogen bonding. In this case, the antiparallel chains of
280 5 Vibrational <strong>Spect</strong>roscopy of Polvpeytides essentially threefold helices [ 122, 1231 are completely intermolecularly N-H . .. O=C hydrogen bonded (Figure 5-8), with strong spectroscopic evidence [ 1231 for additional C"-H...O=C hydrogen bonds. The basis for this conclusion is of interest since it demonstrates the sensitivity of the spectroscopic technique to subtle features of the structure. The vibrational analysis [ 1231 was based on comparing the normal modes of a parallel-chain and an antiparallel-chain structure of PGII. In both structures all N-H... O=C hydrogen bonds can be made. However, whereas in the parallel-chain arrangement all CH2 groups participate equivalently in C"-H ... O=C hydrogen bonds (implying that all C=O groups have bifurcated hydrogen bonds), in the antiparallel-chain arrangement only every third CH2 group can be involved in such interactions, and only between like-directed chains. The result is that the chain no longer has strict threefold symmetry, and as a result the degeneracy of the E species modes is broken. This leads to the expected, and observed, presence of a larger number of bands than predicted by a strictly threefold-symmetric chain structure, and also of bands that occur in regions where no modes are predicted for the parallel-chain structure. Such symmetry-based conclusions are powerful constraints on structural possibilities. The antiparallel-chain structure (Figure 5-8) has only a screw axis of symmetry, and its modes are distributed as follows: A-62 modes, Raman, IR; B-61 modes, Raman, IR. As for PGI, extensive IR spectra on isotopic derivatives (NH, CD2; ND, CH?; and ND, CD2) were available [97] as well as Raman spectra on the N- deuterated molecule [98]. The PGI force field [96] was used as a starting point, and refinement required small adjustments in 10 of -70 intramolecular force constants [123]. Amide mode frequencies are given in Table 5-12; the overall rnis frequency error is 5.4 cm-'. The hydrogen bond in PGII is stronger than that in PGI (N...O=2.69 b, vs 2.91 A), so it is not surprising that the average amide I mode frequency is lower in PGII (the unperturbed modes are at 1651.0 f 1.7 cm-I). The very different splittings are due to the different TDC interactions for the two structures. The somewhat higher amide I1 modes are also consistent with stronger hydrogen bonds. The amide I11 modes with significant NH ib, CN s contributions are found near 1280 cm-', strongly mixed with CH2 tw, quite different from the situation in PGI. The isolated NH ib contribution is now found in the 1400-1300 cm-' region. The aniide V modes in PGII are divided between a higher frequency group near 750 cmP1 and a lower frequency group near 670 cm-'. This is a much larger separation than found for other helical structures, and may be a consequence of the interchain hydrogen bonding. 5.5 Summary The main message conveyed by the body of present vibrational spectroscopic studies of peptides and polypeptides is that detailed information on their structures
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Modern Polymer Spectroscopy Edited
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Modern Polymer Spectroscopy Edited
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Preface For unfortunate reasons the
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However, theory and calculations yi
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Contents 1 Two-Dimensional Infrared
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Con ten t~ xi Index 5.2 Force Field
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Contributors M. Del Zoppo Dipartime
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1 Two-Dimensional Infrared (2D IR)
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1.2 Brick~qrorrnrl 3 . Figure 1-3.
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1.0 , Figure 1-6. The in-phtrse and
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1.2 Bcrckgroinizd 7 where AA (i~) i
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1.2 Background 9 1.2.5 Two-Dimensio
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1.3 Bnsic Properties of 20 IR Corre
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2D IR spectrometer coupled with a d
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1.5 Applirtrtions 15 Unlike a dispe
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\ '\ Melliyleiie 1'7- -3000 Posiliv
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11 Amorphous Crystalline ,...." I F
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1.5 Applications 21 / I 1430 Figure
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1.5 Appliccitioiis 23 Methylene Fig
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1.5 Ajqdicrrtions 25 3024 Figure 1-
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1.5 Applicutions 27 Furthermore. th
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1.7 Coizclirsions 29 derived in a s
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1.9 References 31 [9] Colthup, N. B
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2 Segmental Mobility of Liquid Crys
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SRMPLE/DETECTOR e3 ‘retardation
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2.4 Srvuc me-Dependenr Alignment 37
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2.5 Electric Field-Innductid Orirnt
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2.5 Electric Field-nclticetl Orient
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a -@ COWER SRHPLE ._ 2.5 Elec tric
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2.5 Electric Field-Itzduced Orienta
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2.5 Electric Field-IwrElrced Orient
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2.5 Electric Field-Im/irced Orientu
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2.5 Electric Field-Induced Orientli
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2.5 Electric Field-Induced Orientat
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2.5 Electric Field-Induced Orienfat
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2.5 Elrc tric Field-Iiidircwl Orim
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2500 2008 I s00 WRVtNdMRtR CM-I Fig
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-3.6 Aligmient OJ' Side- Clinin Liy
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~ polyester 2.6 Alignnient qf Side-
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I." 0.9 0.8 Figure 2-34. FTlR 0.7 p
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induced alignment of the investigat
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2.7 Orientation oj Liquid Ci:i,stal
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2.7 Orieritation of Liquid Ciysttrl
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0 8 18 16 1 a W u z a m a 0 Ln m Q
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2.7 Orientation oj Liquid Crystals
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2.7 Orientation of Liquid Crjvtals
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2.7 Orientatioiz of Liquid Crystals
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2.8 Conclusions 81 strain. As A0 is
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3. I0 Refcreiice.r 83 [I 71 Hoffina
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2.10 References 85 [92] Wiesner, U.
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t Order/Disorder in Chain Molecules
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onds which hold atoms together thro
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3.2 The Dyriamical Case qf Simll ar
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3.2 The Dyrinniical Case of Sinnll
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3.4 S11or.f- and Loizg-Rcrizye Vibr
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3.4 Slzort- and Loiig-Range Vibrati
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eyularity), e.g., 2. During the pol
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3.5 Towards Lnrger Molecules: From
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3.5 TOIIYW~ Laiyer Molertiles: Fvoi
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3.5 Towmu" Larger Molecules: F~om O
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1700 - CIO --- ca c 22 _- c 12 l l
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3.6 From Dynamics to Vibrational Sp
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3.6 Froin Dynaiiiics to T’ihratio
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3.7 The Case of Isotactic Polypropy
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3.7 The Cuse of Isotactic Polypvop.
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3.8 Density of Vibrational States a
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3.8 Dtvz.sit,v of L’ihrntioizal S
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3.8 Driisity of Vibratioiid StLitrs
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3 9 Mouiiiq ToIvmds Rerrlitv: From
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3.9 Moving Towards Reality: From Or
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3.9 Moving Towards Reality: Froin O
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3.10 Wlmt Do We Learn from Cnlcailc
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+ 3.11 A Very Siriiple Ccrse: Latti
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3 I1 A Yey) Siiiiple Case: LLittice
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3.11 A Vq> Siiiiplc Crrw: Luttice D
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Figure 3-22. Sample eigenvectors in
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3.12 CIS-trans Opening @the Double
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3.13 Defect Modes cis Structtrr.al
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3.13 Defect Mo&s cis Structurcil Pr
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0 3.14 Case Studies N 0 d - Y N o m
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3.14 Case Studies 147 OC 60 58 57.
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3.14 Case Studies 149 GI A V E N U
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3.14 Case Studies 15 1 correspond t
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3.14 Case Studies 153 (I10 + 200) +
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3.14 Case Studies 155 1500 1480 146
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3.14 Case Studies 157 the molecular
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17E (ir 1, R): (iii) z = 4, t = 1,
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3.16 Stnictural Znlioi~zogeneity an
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3.1 7 Fermi Resonancrs 163 stants.
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3.1 7 Femi Resorinnces 165 2 L 1 29
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lowing. The CHl-bending mode 6 [cer
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3.17 Ferini Re.sonrriire.s 169 a Fi
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3. I7 Fernii Resoiiances 17 1 terin
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3.18 Band Broadening and Confonnati
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3.18 Bmd Brourleiziriy md Cmforrnat
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3.18 Band Bvoaderiing arid Conjonna
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3.18 Band Broadening and Confornmti
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3.19 A Worked E.utinple 181 pre-mel
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3.19 A Wovh-ecl E.uanzple 183
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3.19 A Worked Example 185 19 5°C 2
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3.19 A Workrd Example 187 Figure 3-
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3.19 A Worked E.rcnniplr 189 LAM I
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3.19 A Worked E.xuniple 191 Figure
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3.19 A Worked E.vnn~yle 193 Figure
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3.19 A Worked E.vnrqde 195 009.1 00
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3.19 A Worked Example 197 existence
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3.1 9 A Worked Example 199 The soli
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3.20 References 201 very important,
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3.20 References 203 [41] M. Gussoni
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3.20 Refeeveiicrs 205 [I 171 P. Jon
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4 Vibrational Spectroscopy of Intac
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4.3 Georrietvy oj Intuct Po1vniev.r
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1'45 4.4 Geometric Chunges I?zditce
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4.4 Geometric Chmges Iiid~lrcecl bj
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4 5 Mer1iodolog.v of Raiii~11 Studi
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4.7 Poly(p-pheiq.lene) 217 with an
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4.7 Pol)~(p-pheiz~~lene) 219 ENERGY
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is worthwhile pointing out that the
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~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ 801 Table 4-3
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4.7 Poly(y-phenylene) 225 Figure 4-
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Table 4-4. Observed Raman frequenci
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Page 254 and 255: 5 Vibrational Spectroscopy of Polyp
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Page 262 and 263: 5.2 Force Fields 247 ture with conf
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Page 266 and 267: 5.3 Ainide Modes 251 Table 5-1. Ami
Page 268 and 269: Table 5-2. Some amide modes of four
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Page 272 and 273: 5.4 Polypeptides 257 nonhydrogen-bo
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Page 276 and 277: I 5.4 Polypeptides 261 )I .- + $ 80
Page 278 and 279: 1226M 1222s (1 1165W 1167s (1 1120V
Page 280 and 281: 135s 9 1 Ms1i 122Wbr 147 NH ob(37)
Page 282 and 283: 5.4 Polypeptides 267 glycine residu
Page 284 and 285: 5.4 Polypeptides 269 Raman bands in
Page 286 and 287: 5.4 Polypeptides 271 Figure 5-7. St
Page 288 and 289: Frequency (cm-'1 100% b 700 500 300
Page 290 and 291: 5.4 Polypptidt~s 215 Table 5-9. Obs
Page 292 and 293: ~~ ~~ ~~~ ~ ~ ~~ 5.4 Polypeptides 2
Page 296 and 297: Table 5-12. Aniide mode frequencies
Page 298 and 299: 1351 Lifson, S., Stern, P. S., J. C
Page 300 and 301: 5.6 Refeverices 285 [130] Tiffany,
Page 302 and 303: Index Amide modes 249 Amorphous pol
Page 304 and 305: Step-scan FTIR spectroscopy 14,34 -
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