scholarly journals Appendix: Structure and conformation of bilirubin. Opposing views that invoke tautomeric equilibria, hydrogen bonding and a betaine may be reconciled by a single resonance hybrid

1973 ◽  
Vol 133 (2) ◽  
pp. 364-368 ◽  
Author(s):  
C. C. Kuenzle ◽  
M. H. Weibel ◽  
R. R. Pelloni ◽  
P. Hemmerich
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Serum Albumin ◽  
Spectral Properties ◽  
Dimethyl Ester ◽  
Carboxyl Group ◽  
Conformational Structure ◽  
The Stability ◽  
Intramolecular Hydrogen ◽  
Resonance Hybrid

A novel conformational structure of bilirubin is presented which obtains maximum stabilization through a system of four intramolecular hydrogen bonds. Two hydrogen bonds link oxygen and nitrogen atoms of each end ring to the contralateral carboxyl group. The proposed structure can explain a variety of uncommon features of bilirubin, and reconciles many seemingly contradictory hypotheses by accommodating them in individual structures which are mesomeric forms of one resonance hybrid. In the light of this newly conceived structure the following characteristics of bilirubin are re-evaluated: the stability of the compound, its reaction with diazomethane, the conformational behaviour of its dimethyl ester, its spectral properties, the chirality of the compound when complexed to serum albumin, and the structure of its metal chelates.

scholarly journals The reaction of bilirubin with diazomethane

1973 ◽  
Vol 133 (2) ◽  
pp. 357-364 ◽  
Author(s):  
C. C. Kuenzle ◽  
M. H. Weibel ◽  
R. R. Pelloni
Keyword(s):  
Hydrogen Bonds ◽  
Dimethyl Ester ◽  
Equilibrium Mixture ◽  
Conformational Structure ◽  
Free Rotation ◽  
Polar Solvents ◽  
Methylene Bridge ◽  
Intramolecular Hydrogen Bonds ◽  
Conformational Isomers ◽  
Intramolecular Hydrogen

Dimethoxybilirubin dimethyl ester and monomethoxybilirubin dimethyl ester were prepared by treating bilirubin with diazomethane, and the correctness of the assigned structures was proved by elemental analysis as well as by i.r. and n.m.r. spectroscopy. The phenylazo compounds derived from monomethoxybilirubin dimethyl ester were also prepared and characterized spectroscopically. Dimethoxybilirubin dimethyl ester occurs in solution as a single molecular species, unlike bilirubin dimethyl ester, which in non-polar solvents exists as an equilibrium mixture of conformational isomers. This difference in the behaviour of the two compounds is explained by the absence of intramolecular hydrogen bonds in dimethoxybilirubin dimethyl ester, a situation that allows free rotation about the central methylene bridge, whereas in bilirubin dimethyl ester an internally hydrogen-bonded conformation can be distinguished by n.m.r. spectroscopy from a non-bonded family of rotamers. This finding is regarded as additional evidence for a newly conceived conformational structure of bilirubin and bilirubin dimethyl ester that is maximally stabilized by intramolecular hydrogen bonds. This is discussed in detail in the Appendix (Kuenzle et al., 1973), which also includes a description of the molecular mechanism pertaining to the reaction of bilirubin with diazomethane.

Hydrogen-bonding patterns in the cocrystal 2,4-diamino-6-phenyl-1,3,5-triazine–sorbic acid (1/1)

2007 ◽  
Vol 63 (11) ◽  
pp. o4450-o4451 ◽  
Author(s):  
Kaliyaperumal Thanigaimani ◽  
Packianathan Thomas Muthiah ◽  
Daniel E. Lynch
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Sorbic Acid ◽  
Carboxyl Group ◽  
Amino Group ◽  
Acid Molecule ◽  
Asymmetric Unit ◽  
Graph Set ◽  
Bonding Patterns

In the title cocrystal, C9H9N5·C6H8O2, the asymmetric unit contains one 2,4-diamino-6-phenyl-1,3,5-triazine molecule and a sorbic acid molecule. The triazine molecules are base-paired [with a graph set of R 2 2(8)] on either side via N—H...N hydrogen bonds, forming a supramolecular ribbon along the c axis. Each triazine molecule interacts with the carboxyl group of a sorbic acid molecule via N—H...O and O—H...N hydrogen bonds, generating R 2 2(8) motifs. The supramolecular ribbons are interlinked by N—H...O hydrogen bonds involving the 2-amino group of the triazine molecules and the carboxyl O atom of the sorbic acid molecule.

Effect of intramolecular hydrogen bonding on the relative acidities of substituted salicylic acids in benzene solution

1967 ◽  
Vol 45 (14) ◽  
pp. 1699-1706 ◽  
Author(s):  
G. E. Dunn ◽  
Thomas L. Penner
Keyword(s):  
Hydrogen Bonding ◽  
Electronic Effect ◽  
Benzene Solution ◽  
Intramolecular Hydrogen Bonding ◽  
Acid Strength ◽  
Carboxyl Group ◽  
Hammett Equation ◽  
Phenolic Group ◽  
Intramolecular Hydrogen ◽  
Salicylic Acids

The relative acidities of fifteen 4- and 5-substituted salicylic acids were determined in benzene solution by potentiometric titration. The potentials at half neutralization (h.n.p.) relative to that of salicylic acid were considered to measure the acidities of the substituted acids relative to the parent acid. These potentials, designated by Δhnp, gave a significantly better correlation with Hammett's sigma constants in an equation of the form proposed by Jaffe, Δhnp = ρ1σ1 + ρ2σ2, than in a simple Hammett equation, Δhnp = ρ1σ1. In these equations the subscripts 1 and 2 refer to the position of a substituent relative to the carboxyl group and to the phenolic group respectively. The value of ρ2/ρ1 was found to be 0.4, indicating that the electronic effect of a substituent on the acid strength via the phenolic hydrogen-bonded path is almost half as large as the direct effect through the carboxyl group. These results, together with the fact that in aqueous solution there is very little if any transmission via the phenolic group, are discussed in terms of intramolecular hydrogen bonding of salicylic acids in benzene and in water.

3-(4-Oxocyclohexyl)propionic acid monohydrate: hydrogen bonding in the hydrate of a ζ-keto acid

2007 ◽  
Vol 63 (3) ◽  
pp. o1173-o1175
Author(s):  
Stephanie M. Witko ◽  
Mark Davison ◽  
Hugh W. Thompson ◽  
Roger A. Lalancette
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Water Molecule ◽  
Carboxyl Group ◽  
Keto Acid ◽  
Carbonyl Groups ◽  
O 178 ◽  
Network Of Hydrogen Bonds

In the title crystal structure, C9H14O3·H2O, the water molecule accepts a hydrogen bond from the carboxyl group [O...O = 2.6004 (13) Å and O—H...O = 163°], while donating hydrogen bonds to the ketone [O...O = 2.8193 (14) Å and O—H...O = 178 (2)°] and the acid carbonyl groups [O...O = 2.8010 (14) Å and O—H...O = 174 (2)°]. This creates a network of hydrogen bonds confined within a continuous flat ribbon two molecules in width and extending in the [101] direction.

scholarly journals Hydrogen-bonding patterns in 2-amino-4,6-dimethoxypyrimidine–4-aminobenzoic acid (1/1)

2006 ◽  
Vol 62 (7) ◽  
pp. o2976-o2978 ◽  
Author(s):  
Kaliyaperumal Thanigaimani ◽  
Packianathan Thomas Muthiah ◽  
Daniel E. Lynch
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Carboxyl Group ◽  
Acid Molecule ◽  
Aminobenzoic Acid ◽  
Graph Set ◽  
Supramolecular Chain ◽  
Bonding Patterns ◽  
Hydrogen Bonded

In the title cocrystal, C6H9N3O2·C7H7NO2, the 2-amino-4,6-dimethoxypyrimidine molecule interacts with the carboxyl group of the 4-aminobenzoic acid molecule through N—H...O and O—H...N hydrogen bonds, forming a cyclic hydrogen-bonded motif [R 2 2(8)]. This motif further self-organizes through N—H...O hydrogen bonds to generate an array of six hydrogen bonds with the rings having the graph-set notation R 2 3(6), R 2 2(8), R 4 2(8), R 2 2(8) and R 2 3(6). The 4-aminobenzoic acid molecules self-assemble via N—H...O hydrogen bonds to form a supramolecular chain along the c axis.

Chlorobis[N′-ethoxycarbonyl-N-(4-methylphenyl)thiourea-κS]copper(I)

2003 ◽  
Vol 59 (11) ◽  
pp. m473-m474 ◽  
Author(s):  
You-Ming Zhang ◽  
Liang Xian ◽  
Tai-Bao Wei
Keyword(s):  
Hydrogen Bonds ◽  
Cupric Chloride ◽  
Title Complex ◽  
Thiourea Derivative ◽  
Coordination Environment ◽  
Intramolecular Hydrogen Bonds ◽  
The Stability ◽  
Intramolecular Hydrogen ◽  
Cl Atom

The title complex, chlorobis{ethyl N-[(4-methylanilino)thiocarbonyl]carbamate-κS}copper(I), [CuCl(C11H14N2O2S)2], was synthesized by the reaction of cupric chloride with the corresponding thiourea derivative. The complex has imposed crystallographic m symmetry and the CuI coordination environment is trigonal planar, formed by two S atoms and one Cl atom. The formation of intramolecular hydrogen bonds promotes the stability of the complex.

THEORETICAL STUDY OF THE HYDROGEN BOND CHARACTER BETWEEN THE FNO AND HO2 RADICAL

2010 ◽  
Vol 09 (05) ◽  
pp. 925-934 ◽  
Author(s):  
QIN HE ◽  
ZHI-FENG LI
Keyword(s):  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Theoretical Study ◽  
Basis Sets ◽  
Potential Density ◽  
Geometrical Characteristics ◽  
Intramolecular Hydrogen ◽  
Hydrogen Bonding Site ◽  
Ho2 Radical ◽  
Bond Character

The hydrogen-bonding characters between FNO and HO2 radical are studied systematically with the MPWB1K method and 6-311++G (d, p), aug-cc-PVDZ as well as aug-cc-PVTZ basis sets. The relevant geometrical characteristics, energy properties, and the characters of the intramolecular hydrogen bonds have been reported in this work. In addition, the changes of electrostatic potential density are presented for further understanding the nature of hydrogen bonds and the preference of F atom as the hydrogen-bonding site.

A DFT-D study on the stability and intramolecular interactions of the salts of 1,2,3- and 1,2,4-triazoles

2014 ◽  
Vol 92 (11) ◽  
pp. 1111-1117
Author(s):  
Xueli Zhang ◽  
Xuedong Gong
Keyword(s):  
Hydrogen Bonds ◽  
Density Functional ◽  
Energy Gap ◽  
Lattice Energy ◽  
Intramolecular Interactions ◽  
Dispersion Energy ◽  
Functional Theory ◽  
Formation Reaction ◽  
The Stability ◽  
Intramolecular Hydrogen

Nitrogen-rich 1,2,4-triazole (1) and 1,2,3-triazole (2) react as bases with the oxygen-rich acids HNO3 (a), HN(NO2)2 (b), and HClO4 (c) to produce energetic salts (1a, 1b, and 1c and 2a, 2b, and 2c, respectively) potentially applicable to composite explosives and propellants. In this study, these salts were studied with the dispersion-corrected density functional theory. For the isomers such as 1a and 2a, the more negative ΔrGm of the formation reaction leads to a higher thermally stable salt. The ability to form intramolecular hydrogen bonds predicted with the quantum theory of atoms in molecules has the order of 2 > 1. Different hydrogen bonds result in different second-order perturbation energies, redshifts in IR, and electron density differences. The charge transfer, binding energy, dispersion energy, lattice energy, and energy gap between frontier orbits in the salts of 1 are larger than those of 2, which is helpful for stabilizing the former, and 1 is more obviously stabilized than 2 by formation of salts. Different conformations of 1 and 2 hardly affect the frontier orbital distributions. Base 1 is a more preferred base than 2 to form salts.

scholarly journals Intra-molecular Interactions in Porous Covalent Organic Frameworks

2014 ◽  
Vol 70 (a1) ◽  
pp. C530-C530
Author(s):  
Rahul Banerjee
Keyword(s):  
Hydrogen Bonding ◽  
Schiff Base ◽  
Molecular Interactions ◽  
Chemical Stability ◽  
Intramolecular Hydrogen Bonding ◽  
Covalent Organic Frameworks ◽  
Covalent Organic Framework ◽  
New Strategy ◽  
The Stability ◽  
Intramolecular Hydrogen

A new strategy of intramolecular hydrogen bonding in 2D covalent organic framework as an extra stabilizing factor has been introduced, which helps to improve the crystallinity, porosity and chemical stability of the COF. Using this concept, highly stable porphyrin containing covalent organic frameworks have been synthesized using the Schiff base reaction. The stability of the COFs mainly arises due to the strong intramolecular O-H...N=C hydrogen bonding. Validation of this postulate was cross-checked by synthesizing methoxy (OCH3) substituted COF in which no hyrogen bonding exists. It was found that methoxy substituted COF have a low crystallinity, porosity and chemical stability as compared to hydrogen bonded COF.

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