Topic
Steric effects
About: Steric effects is a research topic. Over the lifetime, 16112 publications have been published within this topic receiving 319615 citations. The topic is also known as: steric hindrance.
Papers published on a yearly basis
Papers
More filters
TL;DR: It is found that the steric hindrance of ligand binding by the E11 residue and the polarity of the E7 residue in the β subunit are critical for fine-tuning ligand affinity.
Abstract: The geometries of the Fe–O2 and Fe–CO bonds in myoglobin and haemoglobin differ significantly from those in free porphyrin model compounds1–6. It has been suggested that steric hindrance by Val-Ell and His-E7 and a hydrogen bond between His-E7 and oxygen2,4,7 affect the geometry and electronic state of the Fe-ligand bond, and that these interactions may be important in controlling oxygen affinity8. We have produced mutant haemoglobins in E. coli9–11 having Val(67β)E11 replaced by Ala, Met, Leu or Ile and His(58β)E7 by Gin, Val or Gly. We have studied the effect of these mutations on the equilibrium and kinetics of ligand binding. The conformation of the new side chains and their effect on the protein structure have been examined by X-ray crystallography, and the vibrational properties of the Fe–CO bond observed by resonance Raman spectroscopy12. We found that the steric hindrance of ligand binding by the E11 residue and the polarity of the E7 residue in the β subunit are critical for fine-tuning ligand affinity.
155 citations
TL;DR: The chemistry of low coordinate germanium compounds has made important advances in recent years and a rather large number of these species have been isolated in a monomeric state owing to both electronic and/or steric effects as discussed by the authors.
154 citations
TL;DR: In this article, the role of Lewis and Bronsted sites in the dehydration of glycerol on niobium oxide and Na+-exchanged Niobium oxides was investigated using FTIR spectroscopy supported by DFT calculations.
Abstract: The role of Lewis and Bronsted sites in the dehydration of glycerol on niobium oxide and Na+-exchanged niobium oxide is investigated using FTIR spectroscopy supported by DFT calculations. Glycerol is impregnated on the catalysts at room temperature using an ex-situ method. Under high vacuum conditions, glycerol forms a stable multidentate alkoxy species through its primary hydroxyl groups with the Lewis sites. When coordinated this way, the primary C–O bonds are polarized, favoring dehydration in this position to form hydroxyacetone. In contrast, dehydration of the secondary alcohol group is kinetically favored over Bronsted acid sites in the absence of steric constraints. The primary product of this reaction, 1,3-propenediol, is further dehydrated to acrolein. When more than a monolayer of glycerol is impregnated on niobia, monoaromatic compounds are also formed on the surface upon heating.
153 citations
TL;DR: Hydrophobic, steric, and weak intermolecular C−H−π interactions are suggested to be responsible for the specific orientation of the olefin within a water-soluble, deep-cavity cavitand with eight carboxylic acid groups.
Abstract: Highly regioselective photooxidation of methyl cycloalkenes has been performed in an aqueous medium by selectively blocking two of the three allylic hydrogens through supramolecular steric effect. Hydrophobic, steric, and weak intermolecular C−H−π interactions are suggested to be responsible for the specific orientation of the olefin within a water-soluble, deep-cavity cavitand with eight carboxylic acid groups.
153 citations
TL;DR: This system possesses a high degree of chiroptical activity, which allows the differentiation of one of the smallest homologous elements of organic chemistry, that is, the methyl and ethyl groups attached to the asymmetric carbon, and additionally, which senses a remote chiral center at a position beta to the amine binding group.
Abstract: The achiral syn folded (face-to-face conformation) host molecule of the ethane-bridged bis(zinc porphyrin) transforms into the corresponding chiral extended anti bis-ligated species in the presence of enantiopure amine guests. The mechanism of the supramolecular chirogenesis is based upon the screw formation in bis(zinc porphyrin), arising from steric interactions between the largest substituent at the ligand's asymmetric carbon and peripheral alkyl groups of the neighboring porphyrin ring pointing toward the covalent bridge. The screw direction is determined by the guest's (amines) absolute configuration resulting in a positive chirality induced by (S)-enantiomers due to formation of the right-handed screw, and a negative chirality produced by the left-handed screw of (R)-enantiomers. The screw magnitude is strongly dependent upon the structure of the chiral guests. The amines with bulkier substituents result in stronger CD signals and larger 1H NMR resonance splittings of enantiotopic protons. This syst...
153 citations