Topic
Dihedral angle
About: Dihedral angle is a research topic. Over the lifetime, 15718 publications have been published within this topic receiving 174904 citations.
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TL;DR: In this article, the nonbonded interaction energy was computed for xylobiose and xylan as a function of the dihedral angles (ϕ,ψ), indicating that interactions higher than the second neighbor are negligible.
Abstract: The nonbonded interaction energy was computed for xylobiose and xylan as a function of the dihedral angles (ϕ,ψ). The energy maps indicate that interactions higher than the second neighbor are negligible. Of the four possibilities, the left-handed helical conformation with (ϕ,ψ) = (63°,25°) is of the lowest energy. The hydrogen bond search and the energy maps reveal that the xylan helix is stabilized mainly by van der Waals forces. The allowed region map shows that the freedom of rotation of the monomer units in cellulose is more restricted than that of the monomer units in xylan, because of the presence of the CH2OH group in the former. The intramolecular hydrogen bond of the O5 O3′ type is stronger in cellulose.
38 citations
TL;DR: The three-dimensional structure of acyl-coenzyme A binding protein as encoded by the recombinant gene in Escherichia coli has been determined using nuclear magnetic resonance (n.m.r.) spectroscopy using the program Pronto and the programs DIANA and X-PLOR.
38 citations
TL;DR: In this article, the monomeric two-coordinated complexes were characterized by multinuclear NMR spectroscopy and the structure of the complexes were determined by a single-crystal X-ray.
Abstract: The phosphine chalcogenides
Fe[η-C
5
H
4
P(E)Ph
2
]
2
(L)
[E = nothing (dppf), S (dptpf) or Se (dpspf)] reacted
readily with [Cu(MeCN)
4
]X (X = BF
4
,
PF
6
or ClO
4
) in CH
2
Cl
2
to
give quantitatively the monomeric two-co-ordinated complexes
[CuL]BF
4
(E = S 1 or Se 2) or
polynuclear three-co-ordinated derivatives analysing as
[CuL
1.5
]X (E = S 3 or Se 4),
depending on the ligand to copper molar ratio. The complexes have been
characterized by multinuclear NMR spectroscopy. Complexes 3 and
4 reversibly dissociate in solution, as was evident from the
concentration- and temperature-dependent NMR spectra. The
low-temperature 1
H, 31
P-{
1
H}
and 19
F NMR spectra are interpreted in terms of a
tetranuclear structure in which each copper atom is trigonally bonded by
bridging L ligands and one anion molecule is trapped inside the
tetrahedral Cu
I
4
cage. Single-crystal X-ray
structure determinations were performed for the two diphosphine
chalcogenides and complex 1. The structure of 1 shows
a slightly distorted linear two-co-ordination geometry around the copper
atom with an S(1)–Cu–S(2) angle of 171.5(2)°. The
Cu–S bond distances [2.144(5) and 2.140(5) A] and
the Cu–S–P angles [100.8(2) and 105.5(2)] point towards a
substantially sp
3
hybridization of the sulfur atoms. In the
ferrocene moiety the cyclopentadienyl rings are virtually parallel
(dihedral angle between the two planes 6.5°) and staggered by
16.1°.
38 citations
TL;DR: The X-ray structure of [Cu(dnpp)2]PF6, where dnpp denotes 2,9-dineopentyl-1,10-phenanthroline, reveals a flattened tetrahedral copper complex with a dihedral angle between the least-squares planes of the ligands of only 63.4° as discussed by the authors.
Abstract: The X-ray structure of [Cu(dnpp)2]PF6, where dnpp denotes 2,9-dineopentyl-1,10-phenanthroline, reveals a flattened tetrahedral copper complex with a dihedral angle between the least-squares planes of the ligands of only 63.4(1)°. Steric interactions involving γ methyl groups of the substituents have an important role in shaping the complex, but lattice forces are ultimately responsible for the flattened geometry. Crystal data: [Cu(C22H28N2)2]PF6, triclinic, P1, a = 10.2755(10) A, b = 13.9750(12) A, c = 16.4354(12) A, α = 79.376(7)°, β = 86.989(7)°, γ = 69.981(7)°, Z = 2. Spectral measurements involving four other Cu(NN)2+ systems, where NN denotes a 2,9-dialkyl-1,10-phenanthroline ligand, reveal that the room-temperature emission maxima fall at shorter wavelengths (20−50 nm) in the solid state as compared with fluid solution. The emission from Cu(dnpp)2+ is unique in that it maximizes at a slightly longer wavelength in the rigid solid (670 nm vs 665 nm in CH2Cl2). The spectral data support the following...
38 citations
TL;DR: In this paper, a notably higher diastereoselectivity is observed in the dimethyldioxirane epoxidation of chiral allylic alcohols when less polar solvent mixtures are employed.
38 citations