Variable Temperature FTIR Research Articles

Organogelators from self-assembling peptide based dendrimers: structural and morphological features

Two peptide based dendrimers containing l-aspartic acid as the branching unit and succinic acid/terephthalic acid as the core unit were synthesized, characterized, and studied. These dendritic peptides form gels in various organic solvents including n-hexanol, benzene, toluene, chlorobenzene, 1,2-dichlorobenzene, o-xylene, tetralin, and nitrobenzene. Gels were characterized by freeze fracture transmission electron microscopic (FF-TEM), field emission scanning electron microscopic (SEM), transmission electron microscopic (TEM), wide angle X-ray powder diffraction (WAXPD), and variable temperature FTIR (VT-FTIR) studies. The VT-FTIR study indicates that amides and ester groups are involved in intermolecular hydrogen bonding in the gel state. Two transitions have been observed for both the dendrimer gels upon heating: the first one corresponds to the gel to sol transition and corresponds to the breaking of hydrogen bonds between esters and amides; the second one corresponds to the breaking of hydrogen bonds between amides. In the case of dendrimer 1 structural reorganization occurs in the sol state after the first transition, which is absent in the dendrimer 2 in the sol state. FF-TEM observations showed that both dendritic peptides form a platelet structure in gel state. SEM images of these dried gels indicate different geometry in different solvents in their self-assembled gel state.

New metallomesogens derived from unsymmetric 1,3,4-thiodiazoles: synthesis, single crystal structure, mesomorphism, and optical properties

A series of copper(II) complexes 1 derived from unsymmetric 1,3,4-thiadiazoles 2 exhibiting mesogenic properties are reported. All the precursors 2 and 3 exhibited smectic A or/and smectic C phases, whereas, copper complexes formed nematic, SmA or SmC phases. The mesophases formed by derivatives 2 and 3 were probably attributed to the H-bondings induced both intramolecularly or/and intermolecularly between amide (–NH) and phenolic (–OH) groups. The crystal and molecular structures of mesogenic 2-(5-(2-(hexyloxy)naphthalene-6-yl)-1,3,4-oxadiazole-2-yl)phenol ( 2; n=6, m=6) were determined by means of X-ray structural analysis. It crystallizes in the monoclinic space group P-1, with a=7.4255(18) Å, b=8.209(2) Å, c=17.315(5) Å, and Z=2. An intermolecular H-bond ( d=1.89 Å) between N2 and H1A atoms with an angle of 161.5° was observed. All molecules were packed as tilted layer arrangement and a π–π interaction (ca. 3.56 Å) was observed. Variable temperature FTIR and 1H NMR spectroscopies were also used to probe the possible H-bondings formed in compound 2 ( m=0, n=6). The fluorescent properties of these compounds 2 were examined. All λ max peaks of the absorption and photoluminescence spectra occurred at ca. 359–363 nm and 519–537 nm, respectively. Excited state intramolecular proton transfer (ESIPT) reaction in this type of ortho-hydroxy-1,3,4-thiadiazole was also observed.

Lanthanide/actinide ion-exchange and structural investigations of the layered phosphatoantimonic acid, H 3Sb 3P 2O 14· ZH 2O

The ion-exchange behaviour of the lamellar phosphatoantimonate phases, A 3Sb 3P 2O 14 · ZH 2O (A = H, K; Z = 5, 6) in acidic media has been explored for several trivalent lanthanides (La 3+, Eu 3+ and Pr 3+) and the actinide 241Am 3+. The protonated phase displayed high levels of uptake for each of these cations in mildly acidic media (<2 M HNO 3) and was also shown to be tolerant of moderate levels of potassium cations. The La 3+ ↔ 3H 3O + exchange has been further studied using thermogravimetric, variable temperature X-ray diffraction, FT-IR and 31P MAS NMR. Difficulties in drawing conclusions regarding the siting of La 3+ at one or both of the unique ion-exchange sites of the {Sb 3P 2O 14} ∞ framework were experienced due to complications arising from the presence of intercalated water. This study has demonstrated that the exchange of La 3+ leads to a proportion of the ion-exchange sites about some of the PO 4 tetrahedra being left vacant upon exchange. The utility of the phosphatoantimonate framework for removal of radiogenic lanthanide and americium from acidic media has been demonstrated.

Fabrication of functionally graded bulk materials of organic polymer blends by uniaxial thermal gradient

Compositionally graded bulk materials of organic polymer blends were prepared by using non-equilibrium self-organization processes with a uniaxial thermal gradient (Bridgman method). The Bridgman method was firstly applied to prepare two kinds of polymeric compositionally graded materials: a polymer/low molecular weight additive system (poly(e-caprolactone) (PCL)/4,4′-thiodiphenol (TDP)) and a polymer/polymer system (PCL/poly(ethylene oxide) (PEO)). In the PCL/TDP system, the content of TDP was decreased with respect to the solidification direction. From variable temperature FT-IR measurements, it was found that the amount of hydrogen bonding between PCL and TDP continuously increased with decreasing temperature, suggesting that the TDP molecules were captured by PCL with hydrogen bonding on the lower temperature side of thermal gradient. The crystallinity of PCL in the Bridgman sample increases in the solidification direction, indicating that more TDP molecules were trapped at an earlier stage of solidification. In the PCL/PEO system, the content of PEO decreased with respect to the solidification direction. The PCL molecules were excluded from the solidification surface to the liquid region, which is due to the higher crystallization temperature of PEO than that of PCL. This means that the PCL molecules can diffuse from the solidification interface to the liquid phase. The simple technique using a uniaxial thermal gradient provides a new way to fabricate polymeric functionally graded bulk materials.

Variable temperature FT-IR studies on hydrogen adsorption on the zeolite (Mg,Na)-Y

Variable-temperature infrared spectroscopy was used for the thermodynamic studies on the adsorption of hydrogen on the zeolite (Mg,Na)-Y. Adsorption renders the H H stretching mode infrared active, and simultaneous measurement of IR absorbance and hydrogen equilibrium pressure, over a range of temperature, allowed adsorption enthalpy and entropy to be determined. The standard adsorption enthalpy and entropy resulted to be Δ H° = −18.2(±0.8) kJ mol −1 and Δ S° = −136(±10) J mol −1 K −1, respectively. The adsorption enthalpy is substantially higher than the hydrogen liquefaction heat, which suggests that magnesium-containing porous materials are potential candidates in the search for suitable adsorbents for reversible hydrogen storage.

Variable temperature FTIR study on the surface acidity of variously treated sulfated zirconias

Abstract The acidity of three related sulfated zirconias has been compared by IR spectroscopy using CO and H 2 as probe molecules. The parent material (SZ) was obtained by calcination of a commercial sulfated zirconium hydroxide. The other two samples, SZ-WW and SZ-SO 3 , were obtained from SZ by water washing and by sulfation with gaseous SO 3 , respectively. The labile sulfate groups responsible for alkane activation and associated with an IR band at 1406 cm −1 are removed by water washing and increased by SO 3 -sulfation. No remarkable differences in the strength of either Lewis or Bronsted acid sites have been observed between SZ and SZ-SO 3 . Water washing strongly weakens Bronsted acidity but only slightly weakens Lewis acidity.

Influence of synthetic routes on the conformational order and mobility of C 18 and C 30 stationary phases

Silica gels modified with n-alkyl chains ( n = 18, 30) are prepared by two different synthetic routes and are examined by variable temperature FTIR and solid-state NMR spectroscopy. HPLC measurements of SRM 869, cis/trans ß-carotene isomers and xanthophylls isomers confirm the dependence of the separation mechanism on the alkyl chain length and the synthetic routes. The determination of the silane functionality and degree of cross-linking of silane ligands on the silica surface is achieved by 29Si CP/MAS NMR measurements. The structural order and mobility of the alkyl chains are investigated by means of variable temperature 13C CP/MAS NMR measurements. Variable temperature FTIR studies are performed where conformational order and flexibility of the alkyl chains in C 18 and C 30 phases are monitored through conformational sensitive CH 2 symmetric, anti-symmetric stretching and wagging modes. In addition, the chromatographic properties of the C 18 and C 30 phases are determined. The results derived from the FTIR, NMR and HPLC measurements are discussed in the context of the applied synthetic routes and alkyl chain lengths.

Influence of solvents on the conformational order of C 18 alkyl modified silica gels

The influence of solvents on the conformational order of C 18 alkyl modified silica gels is studied by means of variable temperature FTIR spectroscopy. Symmetric and anti-symmetric CH 2 stretching modes were utilized for getting qualitative information about the changes in alkyl chain conformational order as a function of both protonated and perdeuterated solvents. It was found that interaction between the C 18 alkyl modified silica gels and the mobile phase results in pronounced changes of the alkyl chain conformational order. Furthermore, it was observed that some perdeuterated solvents exhibit isotope effects, which again is reflected by a different alkyl chain conformational order as compared to the corresponding stationary phases with protonated solvents.

Hydrogen adsorption on magnesium-exchanged zeolites

By means of variable-temperature FTIR spectroscopy, the standard adsorption enthalpy of hydrogen on the zeolite (Mg,Na)-Y was found to be ΔH° = −17.5 kJ mol−1, which suggests that magnesium-containing porous materials are good candidates in the search for suitable adsorbents for reversible hydrogen storage.

Smectic A liquid crystals from dihydrazide derivatives with lateral intermolecular hydrogen bonding

Six dissymmetrical dihydrazide derivatives, N-(4-alkoxybenzoyl)- N′-(4′-nitrobenzoyl) hydrazine (C n–NO 2) and N-(4-alkoxybenzoyl)- N′-(4′-biphenyl carbonyl) hydrazine (C n–Ph), were synthesized and investigated by means of differential scanning calorimetry, polarized optical microscopy and wide angle X-ray diffraction. The compounds exhibit smectic A 1 phase. Based on the results of 1H NMR and variable temperature FT-IR spectroscopy, lateral intermolecular hydrogen bonding between –C O and –N–H groups was proposed and the effect of hydrogen bonding on the phase transitions was discussed. It was concluded that the combination of lateral intermolecular hydrogen bonding and microphase segregation stabilized the smectic A phase.

Conformational order of n-alkyl modified silica gels as evaluated by Fourier transform infrared spectroscopy

The conformational behaviour of non-deuterated and selectively deuterated alkyl modified silica gels in the dry state is examined by variable temperature FT IR spectroscopy. In the present study, three systems are considered, which are distinguished by the length of the tethered alkyl chains (C 9H 19 , C 18H 37 , C 22H 45 ). The desired information is obtained by the analysis of various conformational-sensitive IR bands, including CH 2 wagging, CD 2 stretching and CD 2 rocking bands. The analysis of the CH 2 wagging bands provides the relative amounts (i.e., integral numbers over the whole chain) of the kink/ gauche– trans– gauche, double- gauche and end- gauche conformers in the tethered alkyl chains. From the analysis of the CD 2 stretching and CD 2 rocking bands information about the conformational order at a specific deuterated methylene segment is available. Here, the CD 2 rocking band data are used to determine the amount of gauche conformers at the deuterated carbon positions C-4 and C-6, and C-12. It is found that the conformational order critically depends on the actual alkyl chain length, chain position and sample temperature. Particular emphasis is given to the impact of the external pressure during sample preparation on the alkyl chain conformations, about which so far no information is available. It is observed that the samples prepared as KBr pellets, which experienced a pressure of about 10 kbar, are characterised by a lower amount of gauche conformers. This substantial increase of conformational order is attributed to better alkyl chain packing along with a gain of intermolecular chain interactions.

One-dimensional oxalato-bridged Cu(II), Co(II), and Zn(II) complexes with purine and adenine as terminal ligands.

The reaction of nucleobases (adenine or purine) with a metallic salt in the presence of potassium oxalate in an aqueous solution yields one-dimensional complexes of formulas [M(mu-ox)(H(2)O)(pur)](n) (pur = purine, ox = oxalato ligand (2-); M = Cu(II) [1], Co(II) [2], and Zn(II) [3]), [Co(mu-ox)(H(2)O)(pur)(0.76)(ade)(0.24)](n)(4) and ([M(mu-ox)(H(2)O)(ade)].2(ade).(H(2)O))(n) (ade = adenine; M = Co(II) [5] and Zn(II) [6]). Their X-ray single-crystal structures, variable-temperature magnetic measurements, thermal behavior, and FT-IR spectroscopy are reported. The complexes 1-4 crystallize in the monoclinic space group P2(1)/a (No. 14) with similar crystallographic parameters. The compounds 5 and 6 are also isomorphous but crystallize in the triclinic space group P (No. 2). All compounds contain one-dimensional chains in which cis-[M(H(2)O)(L)](2+) units are bridged by bis-bidentate oxalato ligands with M(.)M intrachain distances in the range 5.23-5.57 A. In all cases, the metal atoms are six-coordinated by four oxalato oxygen atoms, one water molecule, and one nitrogen atom from a terminal nucleobase, building distorted octahedral MO(4)O(w)N surroundings. The purine ligand is bound to the metal atom through the most basic imidazole N9 atom in 1-4, whereas in 5 and 6 the minor groove site N3 of the adenine nucleobase is the donor atom. The crystal packing of compounds 5 and 6 shows the presence of uncoordinated adenine and water crystallization molecules. The cohesiveness of the supramolecular 3D structure of the compounds is achieved by means of an extensive network of noncovalent interactions (hydrogen bonds and pi-pi stacking interactions). Variable-temperature magnetic susceptibility measurements of the Cu(II) and Co(II) complexes in the range 2-300 K show the occurrence of antiferromagnetic intrachain interactions.

Directed metalation route to ferroelectric liquid crystals with a chiral fluorenol core: the effect of restricted rotation on polar order.

A new series of smectic C* (SmC*) mesogens containing a chiral (R)-2-octyloxy side chain and either a fluorenone (2a-e) or chiral fluorenol (3a-e) core were synthesized using a combined directed ortho metalation-directed remote metalation strategy. The SmC phase formed by the fluorenol mesogens is more stable and has a wider temperature range than that formed by the fluorenone mesogens, which may be ascribed to intermolecular hydrogen bonding according to variable-temperature FT-IR measurements. The C11 fluorenol mesogens (R,R)-3d and (S,R)-3d were obtained in diastereomerically pure form and gave reduced polarization (Po) values of +106 and +183 nC/cm2, respectively, at 10 K below the SmA*-SmC* phase transition temperature. The difference in Po values suggests that the chiral fluorenol core contributes to the spontaneous polarization of the SmC* phase. This is ascribed to the bent shape of the fluorenol core, which should restrict its rotation with respect to the side chains in the SmC* phase and favor one orientation of its transverse dipole moment along the polar axis, and to steric coupling of the core to the chiral 2-octyloxy side chain.

Short chain copper(II) n-alkanoate liquid crystals

Four short chain members of the copper(II) n-alkanoate series Cu(Cn)2, from propanoate to hexanoate, have been synthesized, purified and characterized by means of optical microscopy, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), FTIR and Raman spectroscopy. The TGA study shows that decomposition starts on heating above 420–470 K (depending on the sample) in a nitrogen atmosphere. In addition, thermal decomposition was investigated by DSC using special high pressure pans and endo- and exc-thermic processes were found which have not been reported previously. All but one of the compounds melt to a liquid crystal phase, which decomposes before the clearing point. The exception is the propanoate homologue, which decomposes directly from the solid state. Despite this problem of sample decomposition, the identification by optical microscopy of the tetragonal (butanoate) and hexagonal (pentanoate and hexanoate) discotic columnar phases was, for first time, possible by the addition of small amounts of the corresponding acid to the samples. These results are in agreement with the X-ray diffraction study performed using swelled mixtures of these salts with hydrocarbon solvents. Two solid–solid transitions, not previously reported in the literature, were found for the butanoate homologue at 395.9 and 422.9 K with ΔH=8.27 and 1.37 kJ mol−1, respectively. The solid and liquid crystalline phases were investigated using variable temperature FTIR spectroscopy.

Liquid crystalline amides: linear arrangement of rod-like molecules by lateral intermolecular hydrogen bonding and molecular shape effect

Bent- and straight-rod shaped liquid crystalline amides 1–3 were designed and synthesized, and their thermodynamic behaviors were investigated by polarized optical microscopy and differential scanning calorimetry, and their layer distances were measured by X-ray diffraction. Weak or strong hydrogen bonds were observed in variable-temperature FT-IR spectra for bent-rod shaped compounds 1 possessing a long alkoxy chain (OR2), straight-rod shaped compounds 2, and straight-rod shaped 3 in their smectic C, smectic Cx, and smectic A phases, respectively. Thus, these liquid crystalline amides could generate linear molecular aggregates in their smectic layers by the lateral intermolecular hydrogen bonds.

Variable temperature far and mid FT-IR as a valuable tool to determine the spin transition temperature of iron(II) spin-crossover coordination compounds

The thermally induced spin transition behaviour of selected iron(II) coordination compounds with substituted tetrazole ligands has been monitored using variable temperature FT-IR spectroscopy. The reliability of these results is discussed and compared with independent analytical techniques such as SQUID measurements and 57Fe Mössbauer spectroscopy proofing variable temperature IR spectroscopy to be a valuable tool in the determination of the spin transition temperature T 1/2.

The organization and assembly of a beta-sheet formed by a prion peptide in solution: an isotope-edited FTIR study.

Insight into the details of protein misfolding diseases requires a detailed understanding of the conformation and dynamics of multistrand beta-sheet aggregates. Here, we report an isotope-edited FTIR study of a model peptide directed at the elucidation of residue-level details of the structure and mechanism of a beta-sheet aggregate. A series of specifically isotope-labeled derivatives of a short peptide (H1) derived from residues 109 through 122 of the prion protein PrPC have been synthesized and characterized by FTIR. On the basis of the analysis of variable temperature FTIR spectra of these peptides in solution, the organization of strands within the beta-sheets has been determined; at equilibrium, the strands form a beta-sheet in which the hydrophobic core (112-122) participates in the sheet structure, resulting in the alignment of residue 117 in all of the strands. The peptides initially form a kinetically trapped intermediate beta-sheet, with a distribution of strand alignments, which can be rearranged into the stable equilibrium conformation by an annealing cycle. These observations are discussed in terms of the biological significance of residue 117 of the prion protein and the mechanism of beta-aggregate nucleation in prion proteins.

Chain Order in Lipid Bilayers: FTIR and Solid State NMR Studies on Bilayer Membranes from 1,2-Dimyristoyl-sn-glycero-3-phosphoglucose

Multilamellar dispersions from a new synthetic phospholipid, 1,2-dimyristoyl-sn-glycero-3-phosphoglucose (DMPGE), bearing a glucose ring in the polar headgroup, are studied by means of FTIR, 2H, and 31P NMR spectroscopy. The investigations are focused on the evaluation of the molecular ordering of the lipid molecules as a function of temperature and cholesterol content. Information about the conformational order of the acyl chains is obtained from variable temperature FTIR investigations. Analysis of the CH2 stretching and wagging modes of nondeuterated compounds provides the relative changes in conformational order in the vicinity of the main transition and integral values of distinct gauche conformers over the whole acyl chains, respectively. Likewise, CD2 rocking bands are used to derive the amount of gauche conformers at a specific chain segment in samples containing selectively deuterated acyl chains. The present work represents the first report where the orientational order parameter simultaneously ...

Liquid crystals with a 5-phenyltropone core

Liquid crystals with a 5-phenyltropone structure were prepared. 5-(4-Alkanoylaminophenyl)tropone derivatives (5 and 6) showed smectic A and C phases. From the layer spacing, compound 5q formed an interdigitated bilayer smectic A phase. The variable temperature FTIR spectra of 5q indicated the presence of intermolecular hydrogen bonding between the amide carbonyl group and the NH group on the phenyl ring of neighbouring molecules. The amide groups of the 2-alkanoylamino-5-phenyltropones controlled the occurrence of mesophases through not only inter- and intra-molecular hydrogen bonds, but also dipole-dipole interaction with the tropone carbonyl group of neighbouring molecules.

Conformation-Sensitive Infrared Bands and Conformational Characteristics of Stereoregular Poly(methyl methacrylate)s by Variable-Temperature FTIR Spectroscopy

Variable-temperature FTIR measurements were performed on amorphous films of isotactic and syndiotactic PMMA, followed by a detailed analysis of the temperature dependence of integrated band intensi...