MP2(full)/aug-cc-pVDZ(-PP) computations predict that new triangular bonding complexes (where X? is a halide and H–C refers to a protic solvent molecule) consist of one halogen bond and two hydrogen bonds in the gas phase. Carbon tetrabromide acts as the donor in the halogen bond, while it acts as an acceptor in the hydrogen bond. The halide (which commonly acts as an acceptor) can interact with both carbon tetrabromide and solvent molecule (CH3CN, CH2Cl2, CHCl3) to form a halogen bond and a hydrogen bond, respectively. The strength of the halogen bond obeys the order CBr4???Cl? > CBr4???Br? > CBr4???I?. For the hydrogen bonds formed between various halides and the same solvent molecule, the strength of the hydrogen bond obeys the order C-H???Cl? > C-H???Br? > C-H???I?. For the hydrogen bonds formed between the same halide and various solvent molecules, the interaction strength is proportional to the acidity of the hydrogen in the solvent molecule. The diminutive effect is present between the hydrogen bonds and the halogen bond in chlorine and bromine triangular bonding complexes. Complexes containing iodide ion show weak cooperative effects.
Figure
The triangular bonding complexes consisting of halogen bond and hydrogen bonds were predict in the gas phase by computational quantum chemistry. 相似文献
Quantum chemical calculations have been performed for the complexes Li3OCCX–Y (X?=?Cl, Br, H; Y?=?NH3, H2O, H2S) and Li3OCN–X′Y′ (X′Y′?=?ClF, BrCl, BrF, HF) to study the role of superalkalis in hydrogen and halogen bonds. The results show that the presence of an Li3O cluster in a Lewis acid weakens its acidity, while its presence in a Lewis base enhances its basicity. Furthermore, the latter effect is more prominent than the former one, and the presence of an Na3O cluster causes an even greater effect than Li3O. The strengths of hydrogen and halogen bonds were analyzed using molecular electrostatic potentials. The contributions of superalkalis to the strength of hydrogen and halogen bonds were elucidated by analyzing differences in electron density. 相似文献
The character of the cooperativity between the HOX···OH/SH halogen bond (XB) and the Y―H···(H)OX hydrogen bond (HB) in OH/SH···HOX···HY (X = Cl, Br; Y = F, Cl, Br) complexes has been investigated by means of second-order Møller?Plesset perturbation theory (MP2) calculations and “quantum theory of atoms in molecules” (QTAIM) studies. The geometries of the complexes have been determined from the most negative electrostatic potentials (VS,min) and the most positive electrostatic potentials (VS,max) on the electron density contours of the individual species. The greater the VS,max values of HY, the larger the interaction energies of halogen-bonded HOX···OH/SH in the termolecular complexes, indicating that the ability of cooperative effect of hydrogen bond on halogen bond are determined by VS,max of HY. The interaction energies, binding distances, infrared vibrational frequencies, and electron densities ρ at the BCPs of the hydrogen bonds and halogen bonds prove that there is positive cooperativity between these bonds. The potentiation of hydrogen bonds on halogen bonds is greater than that of halogen bonds on hydrogen bonds. QTAIM studies have shown that the halogen bonds and hydrogen bonds are closed-shell noncovalent interactions, and both have greater electrostatic character in the termolecular species compared with the bimolecular species.
Figure
The character of the cooperativity between the X···O/S halogen bond (XB) and the Y―H···O hydrogen bond (HB) in OH/SH···HOX···HY (X=Cl, Br; Y=F, Cl, Br) complexes has been investigated by means of second-order Møller—Plesset perturbation theory (MP2) calculations and “quantum theory of atoms in molecules” (QTAIM) studies. 相似文献
A theoretical study of structural, electronic, topological and vibrational parameters of the ternary hydrogen-bonded complexes
C2H4O···2HF, C2H5N···2HF and C2H4S···2HF is presented here. Different from binary systems with a single proton donor, the tricomplexes have the property of
forming multiple hydrogen bonds, which are analyzed from a structural and vibrational point of view, but verified only by
means of the quantum theory of atoms in molecules (QTAIM). As traditionally done in the hydrogen bond theory, the charge transfer
between proton donors and acceptors was computed using the CHELPG calculations, which also revealed agreement with dipole
moment variation and a cooperative effect on the tricomplexes. Furthermore, redshift events on proton donor bonds were satisfactorily
identified, although, in this case, an absence of experimental data led to the use of a theoretical argument to interpret
these spectroscopic shifts. It was therefore the use of the QTAIM parameters that enabled all intermolecular vibrational modes
to be validated. The most stable tricomplex in terms of energy was identified via the strength of the hydrogen bonds, which
were modeled as directional and bifurcated. 相似文献
The capacity of SX2 (X = F, Cl, and Br) to engage in different kinds of noncovalent bonds was investigated by ab initio calculations. SCl2 (SBr2) has two σ-holes upon extension of Cl (Br)?S bonds, and two σ-holes upon extension of S?Cl (Br) bonds. SF2 contains only two σ-holes upon extension of the F?S bond. Consequently, SCl2 and SBr2 form chalcogen and halogen bonds with the electron donor H2CO while SF2 forms only a chalcogen bond, i.e., no F···O halogen bond was found in the SF2:H2CO complex. The S···O chalcogen bond between SF2 and H2CO is the strongest, while the strongest halogen bond is Br···O between SBr2 and H2CO. The nature of these two types of noncovalent interaction was probed by a variety of methods, including molecular electrostatic potentials, QTAIM, energy decomposition, and electron density shift maps. Termolecular complexes X2S···H2CO···SX′2 (X = F, Cl, Br, and X′ = Cl, Br) were constructed to study the interplay between chalcogen bonds and halogen bonds. All these complexes contained S···O and Cl (Br)···O bonds, with longer intermolecular distances, smaller values of electron density, and more positive three-body interaction energies, indicating negative cooperativity between the chalcogen bond and the halogen bond. In addition, for all complexes studied, interactions involving chalcogen bonds were more favorable than those involving halogen bonds.
The halogen bonding interactions between C6F5I and a series of transition metal monohalides trans-[M(X)(2-C5NF4)-(PR3)2] (M = Ni, Pd, Pt; X = F, Cl, Br; R = Me, Cy) have been studied with quantum chemical calculations. Optimized geometries of the halogen bonding complexes indicate that angles C1-I···X are basically linear (178–180°) and angles I···X-M mainly range from 90 to 150°. The strength of these metal-influenced halogen bonds alters with different metal centers, metal-bound halogen atoms and the substitutes on phosphine ligands. Electrostatic potential and natural bond orbital analysis show that both of the electrostatic and orbital interactions make a contribution to the formation of halogen bonds, while the electrostatic term plays a dominant role. AIM analysis suggests that, for trans-[M(F)(2-C5NF4)-(PR3)2] (M = Ni, Pd, Pt) monomers, the formed halogen bonding complexes are stabilized by local concentration of the charge of intermediate character, while for the metal monomers containing chlorine and bromine, a typical closed-shell interaction exist. These results prove that the structures and geometries of these halogen bonding complexes can be tuned by changing the halogen atoms and metal centers, which may provide useful information for the design and synthesis of new functional materials.
Figure
The properties and structural characteristics of a series of metal-influenced halogen-bonding complexes have been studied by using density functional theory (DFT) method. The calculation results indicate that metal centers and metal-bound halogen atoms have significant influence on the geometries and strength of halogen bonds 相似文献
Iron(III) porphinate complexes of phenolate that have NH?O hydrogen bonds on the coordinating oxygen, [FeIII(OEP){O-2,6-(RCONH)2C6H3}] (R = CF3 (1), CH3 (3)) and [FeIII(OEP)(O-2-RCONHC6H4)] (R = CF3 (2), CH3 (4)) (OEP = 2,3,7,8,12,13,17,18-octaethyl-21H, 23H-porphinato), were synthesized and characterized as models of heme catalase. The presence of NH?O hydrogen bonds was established by their crystal structures and IR shifts of the amide NH band. The crystal structure of 1 shows an extremely elongated Fe-O bond, 1.926(3) Å, compared to 1.887(2) Å in 2 or 1.848(4) Å in [FeIII(OEP)(OPh)]. The NH?O hydrogen bond decreases an electron donation from oxygen to iron, resulting in a long Fe-O bond and a positive redox potential. 相似文献
This theoretical study presents a comparative analysis of the molecular properties of heterocyclic (C2H4O⋯HF and C2H5N⋯HF) and homocyclic (C3H6⋯HF) hydrogen-bonded complexes. Initially, the equilibrium geometries of these complexes were analyzed in detail at the B3LYP/6–311++G(d,p)
level of theory. Subsequently, the interaction energies and polarizabilities were also evaluated, as well as the infrared
stretch frequencies and absorption intensities. In addition, by combining intermolecular criteria and charge density concepts,
calculations of Bader’s theory of atoms in molecules were used to determine the maxima and minima for electron density in
order to measure the strength of the n⋯H and pπ⋯H hydrogen bonds. Finally, the possibility of an F⋯Hα secondary interaction between the fluoride (F) of hydrogen fluoride and the axial hydrogen atoms (Hα) of the C2H4O and C2H5N heterocyclic rings was explored.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
Assemblies of 5-amino-2,4,6-triiodoisophthalic acid (H2ATIBDC) with Cd(II) and Zn(II) in the presence of N-donor auxiliary ligand, 1,4-bis(1,2,4-triazol-1-yl)butane (btb), at ambient conditions yield two new supramolecular complexes, [Cd(ATIBDC)(btb)(H2O)2]·3H2O (1), and [Zn(ATIBDC)(btb)]·2H2O (2). Generally, these two complexes display 1D ATIBDC2−-bridged coordination arrays. Distinct extended 3D network architectures are further constructed with the help of weak secondary interactions especially aromatic stacking, halogen bonding, and hydrogen bonding as supramolecular driving forces. It is worthy to mention that halogen bonds (C-I?π and C-I?N/O) play important roles in the supramolecular assembly. The pentameric cluster (H2O)5 in 1 assembles into highly ordered helical infinite chains. Complex 2 exhibits the fascinating single-walled tube-like chain structure. It loses crystallinity rapidly in the air and leads to the formation of [Zn(ATIBDC)(btb)]·H2O (2A). Thermal stabilities and solid state fluorescent properties of complexes 1 and 2A have been studied. 相似文献
The enthalpy of hydrogen-bond formation between guanine (G) and cytosine (C) in o-dichlorobenzene and in chloroform at 25°C has been determined by direct calorimetric measurement. We derivatized 2′-deoxyguanosine and 2′-deoxycytidine at the 5′- and 3′-hydroxyls with triisopropylsilyl groups; these groups increase the solubility of the nucleic acid bases in nonaqueous solvents. Such derivatization also prevents the ribose hydroxyls from forming hydrogen bonds. Consequently, hydrogen-bond formation in our system is primarily between the bases, and to a lesser extent, between base and solvent, and can be measured directly with calorimetry. To obtain the data on base-pair formation, we first took into account the contributions from self-association of each base, and where possible, have determined the ΔH of self-association. From isoperibolic titration calorimetry, our measured ΔH of C2 formation in chloroform is ?1.7 kcal/mol of C. Our measured ΔH of C:G base-pair formation in o-dichlorobenzene is ?6.65 ± 0.32 kcal/mol. Since o-dichlorobenzene does not form hydrogen bonds, the ΔH of C:G base-pair formation in this solvent represents the ΔH of the hydrogen-bonding interaction of C with G in a nonassociating solvent. In contrast, our measured ΔH of C:G base-pair formation in chloroform is ?5.77 ± 0.20 kcal/mol; thus, the absolute value of the enthalpy of hydrogen bonding in the C:G base pair is greater in o-dichlorobenzene than in chloroform. Since chloroform is a solvent known to form hydrogen bonds, the decrease in enthalpic contribution to C:G base pairing in chloroform is due to the formation of hydrogen bonds between the bases and the solvent. The ΔH of hydrogen bonding of G with C reported here differs from previous indirect estimates: Our measurements indicate the ΔH is 50% less in magnitude than the ΔH based on spectroscopic measurements of the extent of interaction. We have also observed that the enthalpy of hydrogen bonding of C with G in chloroform is greater when G is in excess than when C is in excess. This increased heat is due to the formation of C:Gn > 1 complexes that we have observed using 1H-nmr. Although C:G2 structures have previously been observed in triple-stranded polymeric nucleic acids, higher order structures have not been observed between C and G monomers in nonaqueous solvents until now. By using monomers as a model system to investigate hydrogen-bonding interactions in DNA and RNA, we have obtained the following results: A direct measurement of the ΔH of hydrogen bonding in the C:G complex in two nonaqueous solvents, and the first observation of C:Gn > 1 complexes between monomers. These results reinforce the importance of hydrogen bonding in the stabilization of various nucleic acid secondary and tertiary structures. 相似文献
Hydration of macromolecules and the structure of water of crystallization are not understood in detail because in these complex systems. H-atoms cannot be located and the hydrogen bonding schemes are not known. X-ray and neutron diffraction studies on a hydrated oligosaccharide, α-cyclodextrin 6H2O, ((C6H10O5)6·6H2O), crystals forms A and B, gave insight into the chain-like and circular arrangement of hydrogen bonds. In the circles, homodromic (unidirectional) and antidromic (counter-running) orientation of five to six hydrogen bounds is observed. PCILO calculations showed that homodromic circles and chains are approx. 8% per hydrogen bond more stable than antidromic circles, that the changes in electronic charges on H and O atoms are greater in homo than in antidromic systems and that the dipole moments are only approx. 3 D in the homodromic circles but 6–8 D in chain-like and antidromic arrangement. These results have been interpreted in terms of cooperative effect. Circular systems are considered as structural elements in hydration shells of macromolecules and in the assembly of ‘flickering’ water clusters. 相似文献
Abstract While it is well established that classical hydrogen bonds play an important role in enzyme structure, function and dynamics, the role of weaker, but ‘activated’ C-H donor hydrogen bonds is poorly understood. The most important such case involves histidine which often plays a direct role in enzyme catalysis and possesses the most acidic C-H donor group of the standard amino acids. In the present study, we obtained optimized geometries and hydrogen bond interaction energies for C-H…O hydrogen bonded complexes between methane, ethylene, benzene, acetylene, and imidazole with water at the MP2-FC/6-31++G(2d,2p) and MP2-FC/aug-cc-pVDZ//MP2-FC/6-31++G(2d,2p) levels of theory. A strong linear relationship is obtained between the stability of the various hydrogen bonded complexes and both separation distances for H…0 and C—O. In general, these calculations indicate that C-H…0 interactions can be classified as hydrogen bonding interactions, albeit significantly weaker than the classical hydrogen bonds, but significantly stronger than just van der Waals interactions. For instance, while the electronic energy of stabilization at the MP2-FC/aug-cc-pVDZ//MP2-FC/6-31++G(2d,2p) level of theory of a water C-H…O water hydrogen bond is 4.36 kcal/mol more stable than the methane C-H…O water interaction, the water-water hydrogen bond is only 2.06 kcal/mol more stable than the imidazole Ce?H…O water hydrogen bond. Neglecting this latter hydrogen bonding interaction is obviously unacceptable. We next compare the potential energy surfaces for the imidazole Ce?H…O water and imidazole Nd?H…O hydrogen bonded complexes computed at the MP2/6-31++G(2d,2p) level of theory with the potential energy surface computed using the AMBER molecular mechanics program and forcefields. While the Weiner et al and Cornell et al AMBER forcefields reasonably account for the imidazole N-H…O water interaction, these forcefields do not adequately account for the imidazole Ce?H…O water hydrogen bond. A forcefield modification is offered that results in excellent agreement between the ab initio and molecular mechanics geometry and energy for this C-H…O hydrogen bonded complex. 相似文献
Stairs of cyclic tellurane (1,3-dihydro-2λ4-benzotellurole-2,2-diyldicinnamate) [C8H8Te(OCOCHCHC6H5)2] 1 assisted by intermolecular Te-O secondary bonds, intramolecular Te-O secondary bonds and C-H-O hydrogen bonds have been obtained. 1 accounts for the rare example, in organotellurium chemistry, containing both intermolecular and intramolecular Te-O secondary bonds acting as crystal structure directors to yield stair type supramolecular association assisted by CH-O hydrogen bonds. 相似文献
Abstract (Pro-Pro-Gly)10 [(PPG10)], a collagen-like polypeptide, forms a triple-helical, polyproline-II structure in aqueous solution at temperatures somewhat lower than physiological, with a melting temperature of 24.5°C. In this article, we present circular dichroism spectra that demonstrate an increase of the melting temperature with the addition of increasing amounts of D2O to an H2O solution of (PPG)10, with the melting temperature reaching 40°C in pure D2O. A thermodynamic analysis of the data demonstrates that this result is due to an increasing enthalphy of unfolding in D2O vs. H2O. To provide a theoretical explanation for this result, we have used a model for hydration of (PPG)10 that we developed previously, in which inter-chain water bridges are formed between sterically crowded waters and peptide bond carbonyls. Energy minimizations were performed upon this model using hydrogen bond parameters for water, and altered hydrogen bond parameters that reproduced the differences in carbonyl oxygen-water oxygen distances found in small-molecule crystal structures containing oxygen-oxygen hydrogen bonds between organic molecules and H2O or D2O. It was found that using hydrogen bond parameters that reproduced the distance typical of hydrogen bonds to D2O resulted in a significant lowering of the potential energy of hydrated (PPG)10. This lowering of the energy involved energetic terms that were only indirectly related to the altered hydrogen bond parameters, and were therefore not artifactual; the intra-(PPG10) energy, plus the water-(PPG10) van der Waals energy (not including hydrogen bond interactions), were lowered enough to qualitatively account for the lower enthalpy of the triple-helical conformation, relative to the unfolded state, in D2O vs. H2O. This result indicates that the geometry of the carbonyl-D2O hydrogen bonds allows formation of good hydrogen bonds without making as much of an energetic sacrifice from other factors as in the case of hydration by H2O. 相似文献
Salts of 1,2,4,5-benzenetetracarboxylic acid with copper, aluminum, ammonium, cobalt(II), thallium(I), tin(II), uranyl ion, zinc, manganese, iron(II), nickel, potassium and sodium have been prepared and characterized by their IR spectra. The salts of aluminum, ammonium, thallium(I), tin(II), zinc, iron(II), nickel, potassium and sodium had not been reported before with adequate characterization. Raman spectra of selected compounds also aided structural interpretation. The IR spectra of Na2C10H4O8·2H2O, Fe(C10H5O8)2·12H2O, Zn(C10H5O8)2·12H2O, Ni(C10H5O8)2·12H2O, (NH4)3C10H3O8·H2O and CoC10H4O8·6H2O indicate very short, strong hydrogen bonds in these compounds. The IR and Raman spectra can be used to determine the mode of coordination (if any) of the carboxylate groups of 1,2,4,5- benzenetetracarboxylate to metal ions. 相似文献
The synthesis and spectroscopic characterization of 21 l,l′-disubstituted ferrocenoyl peptides of the general formula [Fe(C5H4-CO-Aal-OR) (C5H4-CO-Aa2-OR′)] is reported, with Aal and Aa2 being different amino acids. The one-pot synthesis from activated ferrocene-l,l′-dicarboxylic acid and two different amino acid esters gives the unsymmetrical ferrocenoyl peptides in yields between 27% and 42%, which can be easily separated from their symmetrical byproducts by column chromatography. All new compounds are comprehensively characterized by mass spectrometry (El and FAB, including high-resolution EI-MS), 1H and 13C NMR, and UV/Vis spectroscopy. CD spectroscopy in conjunction with 1H NMR is used to elucidate the solution structures. Using the achiral glycine (Gly) as Aal permits to determine qualitatively the structure-determining influence of the different amino acids Aa2. Helically chiral structures in ferrocene amino acids in this study are stabilized by hydrogen bonds. If one hydrogen bond partner is systematically moved away by the introduction of methylene groups, then indeed the strength of the hydrogen bond decreases as indicated by 1H NMR chemical shifts of the amide protons and the strength of characteristic CD bands. As proline (Pro) is the only naturally accuring secondary amino acid it cannot contribute any amide proton to intra-strand hydrogen bonding. DFT calculations on the compound [Fe(C5H4-CO-Gly-OMe)(C5H4-CO-Pro-OMe)] with one achiral and one secondary amino acid were therefore performed to quantify the more subtle influence of the relative orientations of the ferrocene carbonyl groups and the cis-/trans-conformation of both amide bonds. Not unexpectedly, the conformations with both amide bonds in cis orientation are highest in energy. Surprisingly, the calculations suggest the presence of a low-energy conformation with a non-classical hydrogen bond between the proline ester carbonyl oxygen and a glycine Hα atom. However, a second conformation with no apparent intra-strand contacts but optimal positioning of all relevant groups is similar in energy. Although two conformations were observed in solution for this compound, the experimental data did not permit to assign those two conformations. 相似文献
The unusual T-shaped X–H...π hydrogen bonds are found between the B=B double bond of the singlet state HB=BH and the acid
hydrogen of HF, HCl, HCN and H2C2 using MP2 and B3LYP methods at 6-311++G(2df,2p) and aug-cc-pVTZ levels. The binding energies follow the order of HB=BH...HF>HB=BH...HCl>HB=BH...HCN>HB=BH...H2C2. The hydrogen-bonded interactions in HB=BH...HX are found to be stronger than those in H2C=CH2...HX and OCB≡BCO...HX. The analyses of natural bond orbital (NBO) and the electron density shifts reveal that the nature
of the T-shaped X–H...π hydrogen-bonded interaction is that much of the lost density from the π-orbital of B=B bond is shifted
toward the hydrogen atom of the proton donor, leading to the electron density accumulation and the formation of the hydrogen
bond. The atoms in molecules (AIM) theory have also been applied to characterize bond critical points and confirm that the
B=B double bond can be a potential proton acceptor.
The unusual T-shaped X–H...π hydrogen bonds are found between the B=B double bond of the singlet state HB=BH and the acid
hydrogen of HF, HCl, HCN and H2C2相似文献
Different products have been observed in the reactions of C5H5Co+ and C5H5Ni+ ions with halogen-substituted pyridines (XPy) that have been studied by ion trap mass spectrometry (ITMS) techniques. In particular, an addition product C5H5M(XPy)+ and a product ion C5H4M(Py)+ corresponding to a loss of a HX molecule (X = F, Cl, Br) have been detected. The relative yield of these products is determined by the nature of the metal and by the nature and position of the halogen on the pyridine ring. A computational study at the DFT level on model-systems formed by 2-fluoro and 2-bromopyridine reacting either with the C5H5Ni+ or the C5H5Co+ ion has been carried out. This study shows the existence of a general mechanistic pattern. The rate-determining step of this mechanism is the migration of the halogen from the pyridine ring to the metal. A final hydrogen abstraction step carried out by the halogen leads to the expulsion of a HX molecule. The existence of avoided crossings between surfaces of different multiplicities (ground and first excited state) allows the system to follow lower energy reaction pathways. The barrier determined for the reactions involving 2-bromopyridine is significantly lower than that found for 2-fluoropyridine. This is mainly due to the poor migrating/leaving character and low polarizability of fluorine compared to that of bromine. 相似文献
The crystallization of 2,3-dihydro-thieno[3,4-b][1,4] dioxine-5,7-dicarboxylic acid (H2tddc) with divalent transitional metal (Co, Ni, Zn, Cd) or with tervalent lanthanide metal (Sm) and with mixed ligand 4,4′-bipyridine (4,4′-bipy) or 1,10-phenanthroline (1,10-phen) formed six new complexes: [Co(C8H4O6S) · 3H2O] (1), [Co(C8H4O6)(1,10-phen)(H2O)] · H2O (2), [Ni(C8H4O6S)(4,4′-bipy)(H2O)] · 3H2O (3) [Sm(C8H4O6S)(NO3)(H2O)4] · 2H2O (4), [Zn(C8H4O6S)(H2O)3] (5), and [Cd2(C8H4O6S)2(4,4′-bipy)2] (6). The structures of these six crystals have been characterized by single-crystal X-ray diffraction analyses, which revealed that complexes 1, 4, 5 are all one-dimensional chain structures and they self-assemble into three-dimensional super-molecules via the hydrogen bond interactions and π-π stacking interactions, 2 is also a one-dimensional chain structure but still self-assembles into one-dimensional double-chains, the complex 3 has two-dimensional undulating parallelogram grid structure extended along the bc-plane, the crystal of 6 is a 3D threefold interpenetration topology framework with 46638 nodes. The photoluminescent properties of the H2tddc ligand and the six compounds have been measured in the solid state at room temperature. Free ligand has no luminescence, while its complexes 1, 4, and 6 all exhibit intense photoluminescence which implies that these complexes may be excellent candidates for potential photoactive materials. 相似文献
Proton and 13C magnetic resonance studies are reported on the synthetic polypentapeptide of elastin, HCO-(Val(1)-Pro(2)-Gly(3)-Val(4)-Gly(5))n-Val-OMe, where n ∼- 18. Temperature and solvent dependence of peptide N chemical shift and solvent dependence of peptide carbonyl chemical shift were used to delineate these moieties preliminary to identification of secondary structure.Based on these studies it is proposed, for the organic solvents of dimethyl sulfoxide, methanol, and low-temperature trifluoroethanol, that dynamic hydrogen bonds form in order of decreasing frequency of occurrence between the Val(1)O and the Val(4) N (a β-turn), between the Gly(3) N and the Gly(5)O (an 11-atom, hydrogen-bonded ring), and a more limited interaction between the Gly(3)O and the Gly(5) N (a γ-turn).Arguments are presented that relate the conformational features proposed above to the coacervate, which is a filamentous state. 相似文献