Excited‐state structural dynamics and vibronic coupling of 1,3‐dithiole‐2‐thione—resonance Raman spectroscopy and density functional theory calculation study

1,3‐Dithiole‐2‐thione (DTT) was synthesized and characterized using NMR, FT‐Raman, FT‐IR, UV spectroscopies. Resonance Raman spectra (RRs) were obtained with 341.5, 354.7 and 368.9 nm excitation wavelengths and density functional calculations were done to elucidate the electronic transitions and the RRs of DTT in cyclohexane solution. The RRs indicate that the Franck‐Condon region photodynamics is predominantly along the CS stretch+ H‐CC‐H scissor υ₄, accompanied by the H‐CC‐H scissor υ₃, S‐C‐S symmetric stretch υ₆, CC stretch υ₂, and overtone of the non‐totally symmetric SC‐S2 out‐of‐plane deformation 2υ₁₁. The excited‐state dynamics and the force constant of CS stretch calculated by the RRs were discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Resonance Raman spectroscopy and theoretical study on the photodissociation dynamics of formanilide in S3 state

Resonance Raman spectra were obtained for formanilide (FA) in acetonitrile solution with 239.5‐ and 245.9‐nm excitation wavelengths in resonance with the S₃ state, and density functional theory (DFT) was used to elucidate the electronic transitions and resonance Raman spectra of FA. The spectra indicate that, in the Franck–Condon region, photodissociation dynamics has a multidimensional character with the motions mainly along the CO stretching υ₈, the ring CC stretch υ₉, the NH wag and ring CCH in‐plane bend υ₁₁, the NH wag and ring CCH in‐plane bend υ₁₂, ring CC stretch and ring CCH in‐plane bend υ₁₆, the NH wag and ring CCH in‐plane bend υ₁₇, the ring CCH in‐plane bend υ₁₈, and the ring trigonal bend υ₂₄. The excited‐state dynamics of the S₃ state is discussed, and the results are compared with those previously reported for benzamide (BA) to examine the N‐ or C‐terminal‐substituted aromatic effect of the peptide bond. Copyright © 2010 John Wiley & Sons, Ltd.     

Resonance Raman intensity analysisof the excited‐state photochemical dynamicsof dimethyl 1,3‐dithiole‐2‐thione‐4,5‐dicarboxylate in the A‐band absorption

Dimethyl 1,3‐dithiole‐2‐thione‐4,5‐dicarboxylate (DDTD) was synthesized and characterized using NMR, Fourier transform (FT)‐Raman, Fourier transform‐infrared (FT‐IR) and UV spectroscopies. Resonance Raman spectra (RRs) were obtained with 341.5, 354.7 and 368.9 nm excitation wavelengths and density functional calculations were carried out to elucidate the π (S C S) →π* (S C S) electronic transitions and the RRs of DDTD in cyclohexane solution. The RRs indicate that the Franck–Condon region photo dynamics have a multidimensional character with motion predominantly along the CS stretch and the C S symmetric stretch modes in the five‐member heterocycle. A preliminary resonance Raman intensity analysis was carried out and the results for DDTD were compared with previously reported results for 1,3‐dithiole‐2‐thione (DTT). Differences and similarities of the spectra in terms of molecular symmetry and electron density are also discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman and surface‐enhanced Raman studies of α‐aminophosphinic inhibitors of metalloenzymes

Here, we report the nature of new di‐α‐amino (L¹–L³) and α‐amino‐α‐hydroxyphosphinic (L⁴–L⁶) acids, which are considered potential inhibitors of the aminopeptidase N, adsorbed on a colloidal silver surface by means of surface‐enhanced Raman scattering (SERS) spectroscopy. In order to reveal the adsorption mechanism of these species from their SERS spectra, Fourier‐transform Raman (FT‐RS) spectra of these nonadsorbed molecules were measured. By examining the enhancement, shift in wavenumbers, and changes in breadth of the SERS bands due to the adsorption process, we revealed that the tilted compounds interact with the colloidal silver substrate mainly through the benzene ring, amino group, and phosphinic moiety in the following way. The benzene ring of L² and L³ is ‘standing up’ on the colloidal silver surface, and the C N bond is almost vertical to it, while the tilt angle between the O PO bond and this surface is greater than 45°. On the other hand, for L¹, L⁴, and L⁵, the aromatic ring and C N bond are arranged more or less tilted, and the tilt angle between the O PO bond and the silver substrate is smaller than 45°. The elongation of the bond to the benzene ring, the L⁶ case, produces an almost horizontal orientation of the benzene ring and the O PO bond on the silver nanoparticles. For these ligands, the complement inhibition IC₅₀ tested in vitro using porcine kidney leucine aminopeptidase was correlated mainly with the behavior of the O PO and C CH N fragments on the silver surface. Copyright © 2009 John Wiley & Sons, Ltd.     

Crystal → nematic phase transition in the liquid crystalline system 1‐isothiocyanato‐4‐(trans‐4‐propylcyclohexyl) benzene (3CHBT) probed by temperature‐dependent micro‐Raman study and DFT calculations

Raman spectra of 3CHBT in unoriented form were recorded at 14 different temperature measurements in the range 25–55 °C, which covers the crystal → nematic (N) phase transition, and the Raman signatures of the phase transition were identified. The wavenumber shifts and linewidth changes of Raman marker bands with varying temperature were determined. The assignments of important vibrational modes of 3CHBT were also made using the experimentally observed Raman and infrared spectra, calculated wavenumbers, and potential energy distribution. The DFT calculations using the B3LYP method employing 6‐31G functional were performed for geometry optimization and vibrational spectra of monomer and dimer of 3CHBT. The analysis of the vibrational bands, especially the variation of their peak position as a function of temperature in two different spectral regions, 1150–1275 cm⁻¹ and 1950–2300 cm⁻¹, is discussed in detail. Both the linewidth and peak position of the ( C H ) in‐plane bending and ν(NCS) modes, which give Raman signatures of the crystal → N phase transition, are discussed in detail. The molecular dynamics of this transition has also been discussed. We propose the co‐existence of two types of dimers, one in parallel and the other in antiparallel arrangement, while going to the nematic phase. The structure of the nematic phase in bulk has also been proposed in terms of these dimers. The red shift of the ν(NCS) band and blue shift of almost all other ring modes show increased intermolecular interaction between the aromatic rings and decreased intermolecular interaction between two  NCS groups in the nematic phase. Copyright © 2009 John Wiley & Sons, Ltd.     

Short‐time photodecay dynamics of meso‐tetra(p‐hydroxyphenyl)porphine in the condensed phase explored via resonance Raman spectroscopy and density functional theory calculation

Resonance Raman (RR) spectra of free‐base meso‐tetra(p‐hydroxyphenyl)porphine(THPP) were obtained with 397.9, 416 and 514 nm excitation wavelengths, and density functional calculations were carried out to help the elucidation of the photorelaxation dynamics of Soret (B_x and B_y bands) electronic transitions and the RR spectra of THPP. The RR spectrum indicates that the Franck–Condon (FC) region photorelaxation dynamics for the S₀ → S₅ excited electronic state is predominantly along the totally symmetric C_m phC stretching and the C_βC_β stretchingand simultaneously along the asymmetric (C_mC_α)as stretching, ν(phC  C)asstretching, δ(NH)s and γ(C_βH) vibrational relaxation processes, while that for S₀ → S₄ electronic state is predominantly along the C_m phC stretching and pyrrole breathing. The excited‐state structural dynamics of THPP determined from the RR spectra shows that internal conversion (IC) B_y → B_x electronic relaxation occurs in tens of femtoseconds, and the short‐time dynamics is interpreted using the time‐dependent wave packet theory and Herzberg–Teller (vibronic coupling) contributions. Copyright © 2010 John Wiley & Sons, Ltd.     

Spectroscopic and computational studies on self‐assembly complexes of bis(pyrrol‐2‐ ylmethyleneamine) ligands linked by alkyl spacers with Cu(II)

Bis(pyrrol‐2‐ylmethyleneamine) ligands and their mononuclear monomeric and dinuclear dimeric self‐assembly complexes with Cu(II) were investigated by means of IR and Raman spectroscopies and density functional theory. The ground‐state geometries were calculated by using the Becke Lee Yang Parr composite exchange‐correlation functional (B3LYP) and a combined basis set (LanL2DZ for Cu; 6–31G(d) for C, H, N), and they were compared with the single‐crystal X‐ray diffraction (XRD) structures. The DFT‐calculated Cu N bond lengths are generally higher by 0.001–0.040 Å than those determined through XRD. The vibrational spectra were also calculated at the same level of theory for the optimized geometries. The calculated wavenumbers were scaled by a uniform scaling factor and compared with the experimental fundamentals. The predicted spectra are in good agreement with the experimental ones with the deviations generally less than 30 cm⁻¹. In comparison with the spectra of the ligands, the coordination effect shifts the υ(CN) wavenumber by about 50 cm⁻¹ toward a lower value. Because of the weak intermolecular C H···Cu hydrogen bond, the Cu N stretching mode is shifted toward a lower wavenumber. Copyright © 2006 John Wiley & Sons, Ltd.     

Structural dynamics of 4‐cyanobenzaldehyde in S2(ππ*) state

The excited state structural dynamics of 4‐cyanobenzaldehyde (p‐CNB) were studied by using the resonance Raman spectroscopy and the quantum mechanical calculations. The experimental A‐ and B‐band absorptions were, respectively, assigned to the major n_O → π₃* and π₂ → π₃* transitions according to the B3LYP‐TD/6‐31G(d) and CIS/6‐31G(d) computations, and the resonance Raman spectra. It was determined that the actual S₂(π₂π₃) state was in energy lower than S₃(π₁π₃), which was just opposite to the B3LYP‐TD/6‐31G(d) calculated order of the S₂(π₁π₃) and S₃(π₂π₃). The vibrational assignments were carried out for the A‐ and B‐band resonance Raman spectra. The B‐band resonance Raman intensities of p‐CNB were dominated by the C2–C3/C5–C6 symmetric stretch mode ν₈, the overtones nν₈ and their combination bands with the ring C–H bend mode ν₁₇, the C9–N10 stretch mode ν₆, the C7–O8 stretch mode ν₇ and the remaining modes. The conical intersection between S₁(n_Oπ₃) and S₂(π₂π₃) states of p‐CNB was determined at complete active space self‐consistent field (CASSCF)(8,7)/6‐311G(d,p) level of theory. The B‐band short‐time structural dynamics and the corresponding decay dynamics of p‐CNB were obtained by analysis of the resonance Raman intensity pattern and CASSCF computations. The resonance Raman spectra indicated that CI[S₁(n_Oπ₃)/S₂(π₁π₂π₃π₄)] located nearby the Franck–Condon region. The excited state decay dynamics evolving from the S_{2, FC}(π₂π₃) to the S₁(n_Oπ₃) state was proposed. Copyright © 2013 John Wiley & Sons, Ltd.     

NIR‐FT Raman,FT‐IR and surface‐enhanced Raman scattering spectra,with theoretical simulations on chloramphenicol

Chloramphenicol (CLM), originally derived from the bacterium Streptomyces venezuelae, is an inhibitor of bacterial ribosomal peptidyl transferase activity. The near infrared Fourier transform (NIR‐FT) Raman, surface‐enhanced Raman spectroscopy (SERS) and Fourier transform infrared (FT‐IR) spectral analyses of CLM, a potential antibacterial drug for the treatment of typhoid fever, were carried out along with density functional computations. The vibrational spectral analysis reveals that the CH₂ asymmetric and symmetric stretching modes are shifted to higher wavenumbers than the computed values, owing to the electronic effects resulting from induction of methylene group with the adjacent electronegative atom. The lowering of CO stretching wavenumber is due to the presence of the strong electronegative atom, nitrogen, attached to the carbonyl carbon, causing large degree of molecular π‐electron delocalization and redistribution of electrons, which weakens the CO bond. The absence of a C H stretching vibration and the observed C H out‐of‐plane bending modes suggest that the CLM molecule may be adsorbed in a flat orientation with respect to the silver surface. Copyright © 2008 John Wiley & Sons, Ltd.     

Structural dynamics of 4‐formaldehyde imidazole and imidazole in light absorbing S2(ππ*) state

The short‐time structural dynamics of 4‐formaldehyde imidazole and imidazole in light absorbing S₂(ππ*) state were studied by using resonance Raman spectroscopy and quantum mechanical calculations. The vibrational spectra and ultraviolet absorption spectra of 4‐formaldehyde imidazole were assigned. The resonance Raman spectra of imidazole and 4‐formaldehyde imidazole were obtained in methanol and acetonitrile with excitation wavelengths in resonance with the first intense absorption band to probe the short‐time structural dynamics. complete active space self‐consistent field calculations were carried out to determine the minimal singlet excitation energies and structures of S₁(nπ*), S₂(ππ*), and conical intersection point S₁(nπ*)/S₂(ππ*). The results show that the A‐band structural dynamics of imidazole is predominantly along the N₁H/C₄H/C₅H/C₂H in‐plane bending reaction coordinate, which suggests that excited state proton or hydrogen transfer reaction takes place somewhere nearby the Franck–Condon region. The significant difference in the short‐time structural dynamics between 4‐formaldehyde imidazole and imidazole is observed, and the underlying mechanism is interpreted in term of excited state charge redistribution. Copyright © 2015 John Wiley & Sons, Ltd.     

Experimental and computational studies on the solvation of lithium tetrafluorobrate in dimethyl sulfoxide

Solvation structures of the lithium cation and tetrafluorobrate anion in dimethyl sulfoxide (DMSO) were investigated by Raman spectroscopy and ab initio calculations at various salt concentrations. The SO and C S stretching bands were used to monitor the structural change of the solvation shell. It has been shown that the solvation number of Li⁺, calculated by the changes in intensities of the C S asymmetric and symmetric stretching bands, is consistent with the value predicted by ab initio calculations. The wavenumber shift of the C H stretching band is suggested to be the result of the anion solvation and the dissociation of the associated DMSO molecules. Copyright © 2007 John Wiley & Sons, Ltd.     

IR,Raman and SERS spectra of 5‐sulphosalicylic acid dihydrate

IR, Raman and surface‐enhanced Raman scattering (SERS) spectra of 5‐sulphosalicylic acid were recorded and analysed. The vibrational wavenumbers were computed by density functional theoretical (DFT) method using B3LYP/6–31G* basis. The bands due to the stretching modes CO, C S and SO₂ are intense in the SERS spectrum. The C H stretching mode also appears in the SERS spectrum. The molecule is found to adsorb through both the carboxyl and sulphonyl groups. A possible tilted orientation of the molecule is suggested. Copyright © 2006 John Wiley & Sons, Ltd.     

Resonance Raman spectroscopy and theoretical study on the photodissociation dynamics of diuron in S2 state

Resonance Raman spectra (RRs) and quantum chemical calculations were used to investigate the photodissociation dynamics of diuron in S₂ state. The RRs indicate that the photorelaxation dynamics for the S₀ → S₂ excited state is predominantly along nine motions: the ring C = C stretch vibration ν₁₂ (1593 cm⁻¹), Ph–N–H wag ν₁₄ (1517 cm⁻¹), CO–N(CH₃)₂ stretch ν₂₃ (1365 cm⁻¹)_, CCH wag in plane/ring C = C stretch ν₂₄ (1297 cm⁻¹)_, ring CH rock in plane/ring deformation ν₂₇ (1233 cm⁻¹), CCH wag in plane ν₂₉ (1151 cm⁻¹), Ph–Cl (para) stretch ν₃₅ (1028 cm⁻¹), Ph–N–H wag ν₃₇ (913 cm⁻¹) and ring breath ν₄₄ (685 cm⁻¹). Dissociation by Ph–Cl (para) cleavage at S₂ state directly or relaxation to T₂ state by internal conversion (S₂ → S₁) and intersystem crossing (S₁/T₂) is expected by ~250 nm irradiation based on the RRS, complete active space self‐consistent field, configuration interaction singles and time‐dependent density functional theory calculations. Copyright © 2012 John Wiley & Sons, Ltd.     

Vibrational spectroscopy and crystal structure analysis of two polymorphs of the di‐amino acid peptide cyclo(L‐Glu‐L‐Glu)

Cyclo(L ‐Glu‐L ‐Glu) has been crystallised in two different polymorphic forms. Both polymorphs are monoclinic, but form 1 is in space group P2₁ and form 2 is in space group C2. Raman scattering and FT‐IR spectroscopic studies have been conducted for the N,O‐protonated and deuterated derivatives. Raman spectra of orientated single crystals, solid‐state and aqueous solution samples have also been recorded. The different hydrogen‐bonding patterns for the two polymorphs have the greatest effect on vibrational modes with N H and CO stretching character. DFT (B3‐LYP/cc‐pVDZ) calculations of the isolated cyclo(L ‐Glu‐L ‐Glu) molecule predict that the minimum energy structure, assuming C₂ symmetry, has a boat conformation for the diketopiperazine ring with the two L ‐Glu side chains being folded above the ring. The calculated geometry is in good agreement with the X‐ray crystallographic structures for both polymorphs. Normal coordinate analysis has facilitated the band assignments for the experimental vibrational spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

Resonance Raman studies of the structures and vibrational assignments of photochromic S-alkyldithizones

The resonance Raman spectra of S-methyldithizone (MeHDz), S-ethyldithizone (EtHDz) and S-isopropyldithizone (iPrHDz) have been measured in the solid state and in solution. It is shown that the red and yellow isomers of these S-alkyldithizones adopt in solution the trans-syn-s-trans and trans-anti-s-trans configurations, respectively, with respect to the NN, CN and C N bonds of the formazan skeleton. It is also demonstrated that for EtHDz the red and yellow isomers can be isolated as different crystal forms. Vibrational assignments are given for both red and yellow isomers of MeHDz based on the frequency shifts of five kinds of isotopically substituted species.     

Spectroscopic and thermal studies on the inclusion of trans‐cinnamic acid and a number of its hydroxyl‐derivatives with α, β and γ‐cyclodextrins molecules

The inclusion compounds of α‐, β‐ and γ‐cyclodextrins (α‐CD, β‐CD and γ‐CD) with trans‐cinnamic acid (t‐CIA), 3‐hydroxy‐trans‐cinnamic acid (t‐3OHCIA), 4‐hydroxy‐trans‐cinnamic acid (t‐4OHCIA) and 3,4‐dihydroxy‐trans‐cinnamic acid (t‐3,4OHCIA) were prepared and characterized, in the solid state, by means of thermogravimetry and Raman spectroscopy. The effects of the inclusion process on the guest molecules and on the hydrogen bond interactions of the guest were studied by monitoring sensitive vibrational modes, such as CO, CC and ring C H stretching modes. By combining Raman and TG data with ab initio calculations and information from CSD database on similar compounds, inclusion geometries for the different compounds are proposed. The size of the host cavity and the maximization of host/guest hydrogen‐bonding contacts appear to be the main factors determining the inclusion geometries. Copyright © 2009 John Wiley & Sons, Ltd.     

Dynamics and mechanism of the Crystal II → smecticG phase transition in TB7A by a temperature‐dependent micro‐Raman study and DFT calculations

The solid to smecticG (SmG) phase transition in a Schiff base liquid crystalline compound, terepthal‐bis‐heptylaniline (TB7A), is monitored in situ by temperature‐dependent Raman microspectroscopy, using the band of a C H in‐plane bending mode as a marker. Contrary to the earlier report of a sudden wavenumber shift, the in situ measurement shows very clearly that a new Raman band at ∼1160 cm⁻¹ appears at the Crystal II → SmG transition. The dynamics of this phase transition is discussed in terms of a triple well potential below 210 K and a double well potential above 210 K. The phase transition essentially takes place as a result of intra‐molecular rotation about the long molecular axis. The optimization energy at various fixed dihedral angles, ( C C CN ) are calculated using density functional theory (DFT) at the B3LYP/6‐31G* level of theory. The relative energy at each dihedral angle is calculated relative to optimization energy obtained without any constraints and plotted as a function of dihedral angle (Φ) between the adjacent phenyl ring planes, which also shows a double well potential at room temperature. Copyright © 2009 John Wiley & Sons, Ltd.     

Effects of conformation and hydrogen bonding on the CC and NCN stretching Raman bands of N‐deuterated histidinium

Histidine is an important and versatile amino acid residue that plays a variety of structural and functional roles in proteins. Although the Raman bands of histidine are generally weak, histidine in the N‐deuterated cationic form with imidazole N_π D and N_τ D bonds (N‐deuterated histidinium) gives two strong Raman bands assignable to the C₄C₅ stretch (ν_CC) and the N_π C₂ N_τ symmetric stretch (ν_NCN) of the imidazole ring. We examined the Raman spectra of N‐deuterated histidinium in 12 crystals with known structures. The observed ν_CC and ν_NCN wavenumbers were analyzed to find empirical correlations with the conformation and hydrogen bonding. The effect of conformation on the vibrational wavenumber was expressed as a threefold cosine function of the C_α C_β C₄C₅ torsional angle. The effect of hydrogen bonding at N_π or N_τ was assumed to be proportional to the inverse sixth power of the distance between the hydrogen and acceptor atoms. Multiple linear regression analysis clearly shows that the conformational effect on the vibrational wavenumber is comparable for ν_CC and ν_NCN. The hydrogen bond at N_π weakly lowers the ν_CC wavenumber and substantially raises the ν_NCN wavenumber. On the other hand, the hydrogen bond at N_τ strongly raises the ν_CC wavenumber but does not affect the ν_NCN wavenumber. These empirical correlations may be useful in Raman spectral analysis of the conformation and hydrogen bonding states of histidine residues in proteins. Copyright © 2010 John Wiley & Sons, Ltd.     

Raman spectroscopic study of the mineral gerstleyite Na2(Sb,As)8S13·2H2O and comparison with some heavy‐metal sulfides

The mineral gerstleyite is described as a sulfosalt as opposed to a sulfide. This study focuses on the Raman spectrum of gerstleyite Na₂(Sb,As)₈S₁₃·2H₂O and makes a comparison with the Raman spectra of other common sulfides including stibnite, cinnabar and realgar. The intense Raman bands of gerstleyite at 286 and 308 cm⁻¹ are assigned to the SbS₃E antisymmetric and A₁ symmetric stretching modes of the SbS₃ units. The band at 251 cm⁻¹ is assigned to the bending mode of the SbS₃ units. The mineral stibnite also has basic structural units of Sb₂S₃ and SbS₃ pyramids with C_3v symmetry. Raman bands of stibnite Sb₂S₃ at 250, 296, 372 and 448 cm⁻¹ are assigned to Sb S stretching vibrations and the bands at 145 and 188 cm⁻¹ to S Sb S bending modes. The Raman band for cinnabar HgS at 253 cm⁻¹ fits well with the assignment of the band for gerstleyite at 251 cm⁻¹ to the S Sb S bending mode. Raman bands in similar positions are observed for realgar AsS and orpiment As₂S₃. Copyright © 2010 John Wiley & Sons, Ltd.     

Vibrational spectroscopic studies of the structure of di‐amino acid peptides. Part II: cyclo(L‐Asp‐L‐Asp) in the solid state and in aqueous solution

Solid‐state protonated and N,O‐deuterated Fourier transform infrared (IR) and Raman scattering spectra together with the protonated and deuterated Raman spectra in aqueous solution of the cyclic di‐amino acid peptide cyclo(L ‐Asp‐L ‐Asp) are reported. Vibrational band assignments have been made on the basis of comparisons with previously cited literature values for diketopiperazine (DKP) derivatives and normal coordinate analyses for both the protonated and deuterated species based upon DFT calculations at the B3‐LYP/cc‐pVDZ level of the isolated molecule in the gas phase. The calculated minimum energy structure for cyclo(L ‐Asp‐L ‐Asp), assuming C₂ symmetry, predicts a boat conformation for the DKP ring with both the two L ‐aspartyl side chains being folded slightly above the ring. The CO stretching vibrations have been assigned for the side‐chain carboxylic acid group (e.g. at 1693 and 1670 cm⁻¹ in the Raman spectrum) and the cis amide I bands (e.g. at 1660 cm⁻¹ in the Raman spectrum). The presence of two bands for the carboxylic acid CO stretching modes in the solid‐state Raman spectrum can be accounted for by factor group splitting of the two nonequivalent molecules in a crystallographic unit cell. The cis amide II band is observed at 1489 cm⁻¹ in the solid‐state Raman spectrum, which is in agreement with results for cyclic di‐amino acid peptide molecules examined previously in the solid state, where the DKP ring adopts a boat conformation. Additionally, it also appears that as the molecular mass of the substituent on the C^α atom is increased, the amide II band wavenumber decreases to below 1500 cm⁻¹; this may be a consequence of increased strain on the DKP ring. The cis amide II Raman band is characterized by its relatively small deuterium shift (29 cm⁻¹), which indicates that this band has a smaller N H bending contribution than the trans amide II vibrational band observed for linear peptides. Copyright © 2009 John Wiley & Sons, Ltd.