The effect of pressure on the infrared spectrum of ammonium formate: HCO2NH4, DCO2NH4, HCO2ND4, DCO2ND4. An unusual intermolecular coupling of non-identical vibrations in phase II

1977 ◽  
Vol 30 (12) ◽  
pp. 2591 ◽  
Author(s):  
SD Hamann ◽  
E Spinner
Keyword(s):  
Hydrogen Bonds ◽  
Infrared Spectrum ◽  
Phase Change ◽  
Phase Ii ◽  
Pressure Range ◽  
Isotopic Substitution ◽  
Vibrational Coupling ◽  
Spectral Changes ◽  
Close Proximity ◽  
Frequency Changes

The infrared spectra of the title compounds have been measured over the pressure range 0-42 kbar at 25�C. The phase change at c. 12 kbar is accompanied by an increase in the NH stretching frequencies and other well-defined spectral changes. Vibrational coupling in phase II of HCO2NH4 between CH in-plane bending in HCO2- and a bending motion in NH4+, and its counterpart for DCO2ND4, account for some unusual frequency changes arising from isotopic substitution in the counter ion. The spectral changes suggest that during the phase change I → II the NH...O hydrogen bonds are weakened and the cations move to positions in close proximity beside the CH bonds.

Three-centre C—H...O hydrogen bonds in the DNA minor groove: analysis of oligonucleotide crystal structures

1999 ◽  
Vol 55 (12) ◽  
pp. 2005-2012 ◽  
Author(s):  
Anirban Ghosh ◽  
Manju Bansal
Keyword(s):  
Hydrogen Bonds ◽  
Crystal Structures ◽  
Base Pair ◽  
Minor Groove ◽  
Local Geometry ◽  
Data Sets ◽  
Base Pairs ◽  
Dna Minor Groove ◽  
Close Proximity ◽  
Using Data

AA·TT and GA·TC dinucleotide steps in B-DNA-type oligomeric crystal structures and in protein-bound DNA fragments (solved using data with resolution <2.6 Å) show very small variations in their local dinucleotide geometries. A detailed analysis of these crystal structures reveals that in AA·TT and GA·TC steps the electropositive C2—H2 group of adenine is in very close proximity to the keto O atoms of both the pyrimidine bases in the antiparallel strand of the duplex structure, suggesting the possibility of intra-base pair as well as cross-strand inter-base pair C—H...O hydrogen bonds in the DNA minor groove. The C2—H2...O2 hydrogen bonds in the A·T base pairs could be a natural consequence of Watson–Crick pairing. However, the cross-strand interactions between the bases at the 3′-end of the AA·TT and GA·TC steps obviously arise owing to specific local geometry of these steps, since a majority of the H2...O2 distances in both data sets are considerably shorter than their values in the uniform fibre model (3.3 Å) and many are even smaller than the sum of the van der Waals radii. The analysis suggests that in addition to already documented features such as the large propeller twist of A·T base pairs and the hydration of the minor groove, these C2—H2...O2 cross-strand interactions may also play a role in the narrowing of the minor groove in A-tract regions of DNA and help explain the high structural rigidity and stability observed for poly(dA)·poly(dT).

scholarly journals Investigation of solvation and solvent coordination effects in iron porphyrin nitrosyls by infrared spectroelectrochemistry and DFT calculations

2019 ◽  
Vol 23 (06) ◽  
pp. 639-644
Author(s):  
Md. Hafizur Rahman ◽  
Michael D. Ryan
Keyword(s):  
Infrared Spectrum ◽  
Dft Calculations ◽  
Methylene Chloride ◽  
Research Data ◽  
Iron Porphyrin ◽  
Spectral Changes ◽  
Nitrosyl Complexes ◽  
Chemistry Research ◽  
Visible Spectra

Visible and infrared spectroelectrochemistry of Fe(OEPone)(NO) (H2OEPone = octaethylporphinone) were examined in methylene chloride and THF. The visible spectra of Fe(OEPone)(NO) were similar in both solvents. Unlike other ferrous porphyrin nitrosyls, a six-coordinate complex was formed with THF as a ligand. This led to two nitrosyl bands in the infrared spectrum. The absorbance of these bands depended on the concentration of THF in the solution. Solvation and coordination effects on the carbonyl and nitrosyl bands were observed for both the nitrosyl and reduced-nitrosyl complexes. DFT calculations were carried out to interpret the spectral changes. Marquette University, Raynor Memorial Libraries, Chemistry Research Data: https://epublications.marquette.edu/chem_data/1/

scholarly journals Chromophore Assignment in C-Phycocyanin from Mastigocladus laminosus

1987 ◽  
Vol 42 (3) ◽  
pp. 258-262 ◽  
Author(s):  
S. Siebzehnrübl ◽  
R. Fischer ◽  
H. Scheer
Keyword(s):  
Circular Dichroism ◽  
Binding Sites ◽  
Specific Binding ◽  
Reactive Site ◽  
Spectral Changes ◽  
Mastigocladus Laminosus ◽  
Specific Binding Sites ◽  
Close Proximity ◽  
Circular Dichroïsm ◽  
Unambiguous Assignment

C-phycocyanin from the cyanobacterium, Mastigocladus laminosus, and its subunits have been treated with ρ-chloromercuribenzenesulfonate (PCMS). A single reactive site was found on the 13- subunit, and assigned to the single free cystein-β109. The concomitant spectral changes (absorp­tion, fluorescence, circular dichroism), together with the known close proximity of cys-β109 to chromophore β82, allowed an unambiguous assignment of the three spectrally, biochemically and functionally different chromophores to specific binding sites on the two peptide chains (α84: 616-618, β82: 622-624, β153: 598-600 nm).

scholarly journals Crystal structures oftrans-dichloridotetrakis[1-(2,6-diisopropylphenyl)-1H-imidazole-κN3]iron(II),trans-dibromidotetrakis[1-(2,6-diisopropylphenyl)-1H-imidazole-κN3]iron(II) andtrans-dibromidotetrakis[1-(2,6-diisopropylphenyl)-1H-imidazole-κN3]iron(II) diethyl ether disolvate

2014 ◽  
Vol 70 (8) ◽  
pp. 72-76
Author(s):  
Roger Mafua ◽  
Titus Jenny ◽  
Gael Labat ◽  
Antonia Neels ◽  
Helen Stoeckli-Evans
Keyword(s):  
Hydrogen Bonds ◽  
Diethyl Ether ◽  
Solvent Molecule ◽  
Dihedral Angles ◽  
Halide Ions ◽  
Π Interactions ◽  
Close Proximity ◽  
Coordination Spheres ◽  
Solvent Molecules ◽  
Compound Ii

The title compounds, [FeCl2(C15H20N2)4], (I), [FeBr2(C15H20N2)4], (II), and [FeBr2(C15H20N2)4]·2C4H10O, (IIb), respectively, all have triclinic symmetry, with (I) and (II) being isotypic. The FeIIatoms in each of the structures are located on an inversion center. They have octahedral FeX2N4(X= Cl and Br, respectively) coordination spheres with the FeIIatom coordinated by two halide ions in atransarrangement and by the tertiary N atom of four arylimidazole ligands [1-(2,6-diisopropylphenyl)-1H-imidazole] in the equatorial plane. In the two independent ligands, the benzene and imidazole rings are almost normal to one another, with dihedral angles of 88.19 (15) and 79.26 (14)° in (I), 87.0 (3) and 79.2 (3)° in (II), and 84.71 (11) and 80.58 (13)° in (IIb). The imidazole rings of the two independent ligand molecules are inclined to one another by 70.04 (15), 69.3 (3) and 61.55 (12)° in (I), (II) and (IIb), respectively, while the benzene rings are inclined to one another by 82.83 (13), 83.0 (2) and 88.16 (12)°, respectively. The various dihedral angles involving (IIb) differ slightly from those in (I) and (II), probably due to the close proximity of the diethyl ether solvent molecule. There are a number of C—H...halide hydrogen bonds in each molecule involving the CH groups of the imidazole units. In the structures of compounds (I) and (II), molecules are linkedviapairs of C—H...halogen hydrogen bonds, forming chains along theaaxis that encloseR22(12) ring motifs. The chains are linked by C—H...π interactions, forming sheets parallel to (001). In the structure of compound (IIb), molecules are linkedviapairs of C—H...halogen hydrogen bonds, forming chains along thebaxis, and the diethyl ether solvent molecules are attached to the chainsviaC—H...O hydrogen bonds. The chains are linked by C—H...π interactions, forming sheets parallel to (001). In (I) and (II), the methyl groups of an isopropyl group are disordered over two positions [occupancy ratio = 0.727 (13):0.273 (13) and 0.5:0.5, respectively]. In (IIb), one of the ethyl groups of the diethyl ether solvent molecule is disordered over two positions (occupancy ratio = 0.5:0.5).

Biomass Biodegradable Starch Material Cushioning Packaging Products and Plasticizing Properties of Compatibility

2014 ◽  
Vol 541-542 ◽  
pp. 343-348
Author(s):  
Xiu Jie Jia ◽  
Jian Feng Li ◽  
Fang Yi Li
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Infrared Spectrum ◽  
Ethylene Glycol ◽  
Environmental Protection ◽  
Spectrum Analysis ◽  
Packaging Material ◽  
Hydroxyl Group ◽  
Group Content ◽  
Electronegative Group

Biomass cushioning packaging material has been gaining attention in the properties of the materials because of biodegradable and green environmental protection, and the starch plastics play an important role. Urea, formamide, glycerol, ethylene glycol four material compounded with starch respectively, for the purpose to forming hydrogen bonds by the test in this paper, the ability to hydrogen bond with the starch has been observed by infrared spectrum analysis. The results showed that urea, formamide as strong electronegative group stronger binding, glycerol and ethylene glycol are more preferably to form hydrogen bonds with the starch because of more hydroxyl group content.

THE INTERACTION OF SILICON TETRAFLUORIDE WITH METHANOL

1963 ◽  
Vol 41 (6) ◽  
pp. 1477-1484 ◽  
Author(s):  
J. P. Guertin ◽  
M. Onyszchuk
Keyword(s):  
Hydrogen Bonding ◽  
Magnetic Resonance ◽  
Absorption Band ◽  
Hydrogen Bonds ◽  
Infrared Spectrum ◽  
Proton Magnetic Resonance ◽  
Methanol Solution ◽  
Silicon Tetrafluoride ◽  
Conductivity Measurements ◽  
Bond Stretching

Silicon tetrafluoride reacts with methanol in a 1:4 mole ratio, forming the complex SiF4.4CH3OH, which freezes to a glass at about −20° and is completely dissociated in the gaseous phase at 25°. Conductivity measurements show clearly that it is a very weak electrolyte in methanol solution. Its infrared spectrum does not contain an Si—O bond stretching absorption band. Proton magnetic resonance measurements provide strong evidence of hydrogen bonding between silicon tetrafluoride and methanol. These results indicate that the structure of the complex requires tetracovalent rather than hexacovalent silicon and strong hydrogen bonds between methanol and each of the four fluorine atoms.

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