The crystal structure of the carotenoidal compound 1,14-bis-(2',6',6'-trimethylcyclohex-1'-enyl)-3,12-dimethyltetradeca-1,3,5,7,9,11,13-heptaene-6,9-dinitrile

Braun, P. B.; Hornstra, J.; Leenhouts, J. I.

doi:10.1107/s0567740871001742

Cited by 7 publications

(3 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These have s-cis conformations, with angles in the range 35°-80°. There are also two compounds (18,19) with a planar s-trans conformation; the existence of the latter suggests that the energy difference between distorted s-cis and planar s-trans ring conformations is sufficiently small for intermolecular crystal interactions to have a significant effect.…”

Section: Discussionmentioning

confidence: 99%

Ring Orientation in βIonone and Retinals

Honig

Hudson

Sykes

et al. 1971

Proc. Natl. Acad. Sci. U.S.A.

114

View full text Add to dashboard Cite

The ring orientation in i-ionone, alltrans retinal, and li-cis retinal, relative to that of the polyene chain, has been determined by means of semiempirical calculations and magnetic resonance measurements of the nuclear Overhauser effect and long-range coupling constants. The experimental results yield a distorted s-cis conformation about the C6-C7 "single bond", with the torsional angle in the range 300 to 700. This agrees well with the semi-empirical potential function, which has a broad, rather flat minimum for angles from 400 to 1200.The temperature dependence of the NMR results provide confirmation for the form of the torsional potential.The structure of retinal and related compounds is of considerable interest because of the importance of these compounds in living systems (1). Primary attention has been given to two aspects (2) of the retinal structure that might play a direct role in its function as the chromophore of the vertebrate visual pigment. One of these is the nature of the molecular distortion induced by the strong nonbonded repulsions present in the 1 1-cis isomer; the other is the orientation of the f3-ionone ring relative to the hydrocarbon chain. We determine the ring orientation in fl-ionone, all-trans retinal, and 1 1-cs retinal in this paper by means of semi-empirical calculations and nuclear magnetic resonance (NMR) measurements. In a subsequent paper we will report a similar NMR determination of the distortion in the polyene chain of 11-cis retinal (3).Earlier NMR studies of the retinals include the detailed analysis of the 220-MHz spectrum by Patel (4), as well as partial analyses of 60-MHz spectra by Barber (9) with the PCILO method. METHODThe semi-empirical approach for determining the ground-state energy is similar to that of others (10). The total energy, E, of the molecule relative to the energy of a standard geometry (e.g., the planar all-trans compound) is written in the form E = Et + Enb,where Et is the 7r-electron energy obtained from a Huckel calculation and Enb is the sum over the nonbonded interactions, which are expressed as pairwise terms dependent only on the distance between atoms or groups of atoms. Since there is considerable uncertainty about the value of both the Huckel and the nonbonded parameters, a number of sets were tried; it was found that the essential features of the potentialenergy surface are independent of the parameter values. To avoid the complication of having to minimize the energy as a function of all the bond lengths and angles for each ring orientation, we assumed that the only variable was the torsional angle j about the C6-C7 bond (see Fig.

show abstract

Section: Discussionmentioning

confidence: 99%

Ring Orientation in βIonone and Retinals

Honig

Hudson

Sykes

et al. 1971

Proc. Natl. Acad. Sci. U.S.A.

114

View full text Add to dashboard Cite

show abstract

“…Crystallographic evidence has been available for a long time indicating that a twisted s-cis conformation is preferred (15,33). Most carotenoids have angles in the range 35-80°, although two of them have a nearly planar s-trans ring-chain conformation (34,35). This indicates that the energy difference between the twisted s-cis and planar s-trans conformations is sufficiently small for intermolecular interactions in the crystal to have a significant effect.…”

mentioning

confidence: 99%

The Structure and Spectra of the Chromophore of the Visual Pigments

Honig¹,

Ebrey²

1974

Annu. Rev. Biophys. Bioeng.

139

View full text Add to dashboard Cite

Visual pigments consist of a chromophore, II-cis retinal (Figure ld) (or 3-dehydroretinal) covalently bound to a protein called an opsin. The pigments are situated in specialized membranes in vertebrate and invertebrate photoreceptors; the best studied, rhodopsin, is found in vertebrate rod outer segments. Light absorption by the visual pigments initiates a series of events that leads to the excitation of the photoreceptor cell. The mechanism of visual excitation is for the most part poorly understood although considerable progress has been made in understanding the structure and control of permeability of photoreceptor membranes (1, 2). The primary process in visual excitation elucidated by Wald, Hubbard and their colleagues (3) appears to be the photochemical isomerization of the chromophore to its all-trans conformation (Figure la). How this molecular event triggers the sequence of steps involved in visual excitation is unknown. To explain this will require understanding the properties of the isolated chromophore and its interactions with opsin as well as the structure of the pigment and the disk membrane in which it is located.This review is concerned with the conformational and spectroscopic properties of the chromophore, both when isolated in solution and when bound to an opsin to form a pigment. Due in part to advances in the underlying theory that have been stimulated by interest in the visual chromophore, the physical and theoretical chemistry of retinal isomers is now fairly well understood. The nature of the chromophore in the pigment is still uncertain although a number of recent experimental and theoretical studies have provided considerable insigh t as to possible modes of interaction.This article divides naturally into two parts. In the first section we discuss the ground and excited-state properties of the isolated retinal molecule; in the second we review the spectroscopic properties of the visual pigments and various theoretical models that have been proposed to explain the chromophore-opsin interaction. We 151 :-:9037 Annu. Rev. Biophys. Bioeng. 1974.3:151-177. Downloaded from www.annualreviews.org Access provided by New York University -Bobst Library on 07/24/15. For personal use only. Quick links to online content Further ANNUAL REVIEWS 152 HONIG & EBREY (a) (b) CH3 (e) (d) 0 (e) 0 (tl 0 016 (g) Figure I Conformations of retinal: (a) 6 s-cis, all-trans, (b) 6 s-trans, all-trans, (c) 6 s-cis,9-cis, (d) 12 s-trans, 11-cis, (e) 12 s-cis, ll-cis, (I) 12 s-trans, ll-cis, 14-methyl, (g) 12 s-cis, ll-trans; ¢6-7, ¢,0-1 1 ' ¢ 1 l-12 , and ¢,2-13 are the dihedral angles about bonds 6C-7C, lOC-llC, llC-12C, and l2C-13C respectively; 3,4 dehydroretinai has an extra double bond in the ring between 3C and 4C are concerned primarily with the chromophore and our discussion of the visual pigment is limited to phenomena in which we believe it is directly involved. A number of earlier reviews and collections of articles on visual pigments provide useful back ground material and cover many important topics not ...

show abstract

“…Substituting into equation (3), we get In practice, once a set of phases is given for the strongest reflexions, the right-hand side of equation (5) p-toluic acid (II; Takwale & Pant, 1971); 1,14-bis-(2', 6', 6'-t rimethylcyclohex -1' -enyl) -3,12 -dimethyl -tetradeca-1,3,5,7,9,11,13-heptaene-6,9-dinitrile (III; Braun, Hornstra & Leenhouts, 1971);(N,N'-dibenzyl-4,4'-bipyridylium) z + -(7,7, 8,8-tetracyano quinodimethane)l-(IV; Sundaresan & Wallwork, 1972), with 12,10, 19 and 45 independent non-hydrogen atoms respectively.…”

Section: ~-V3 ~ ~K ~L Ehekele-h-k-l"mentioning

confidence: 99%

A new figure of merit for multisolution methods of phase determination

Allegra¹,

Colombo²

1974

Acta Cryst Sect A

View full text Add to dashboard Cite

For a structure consisting of equal atoms, the point-atom densities of both the normal structure [O(r)] and the squared structure [02(r)] must be identical except for a scale factor. Starting from this consideration, similar to that which led Sayre [Acta Cryst. (1952). 5, 60-65] to his well-known equation, the volume integral of the squared difference between O(r)/I1 and .a2(r)/I2 must be zero,/1 and 12 being appropriate scale factors. Consequently a new figure of merit for a set of phases is derived; the method requires consideration of both triples and quadruples of reflexions with ~.Ht = 0. It proves to be effective in selecting the correct phase sets for four centrosymmetrical compounds whose structures are already known. An improved expression of the tangent formula is also derived from the new figure of merit.The choice of the correct set of phases from among the several sets having approximately the same degree of consistency in terms of the structure invariants related to the Sayre triples is frequently a time-consuming step. The criterion usually adopted consists essentially of the analysis of the different Fourier maps, searching for the one which gives the most acceptable image of the structure. The analysis may be speeded up by the adoption of suitable criteria. We believe it to be particularly worth mentioning the procedure suggested by Woolfson (1972), consisting of a fully automated search of the distances (and, possibly, of the angles) between the Fourier peaks, thus avoiding tedious manual analysis of the maps.In the present note we propose an alternative criterion, which consists of considering a single parameter, or figure of merit, for each phase set; as we shall see, its evaluation requires consideration of quadruples, in addition to triples, of reflexions. The underlying logic is as follows.The Fourier maps obtained with phase sets which, although incorrect, satisfy most of the triple products, are quite often characterized by exceedingly strong peaks. A well known example is offered by the trivial solution consisting of all plus signs for a PT space group, which leads to positive signs of all the structure invariants s(H). s(K). s(H + K) and is characterized by a very heavy peak at the origin. If we assume that all the atoms have the same weight then, as Sayre (1952) first pointed out, the squared structure must closely resemble the real structure. In fact, if we refer to the point-atom density 1 (r) = V ~ EH exp (-2zciH. r),-ff the real and the squared structures should be identical except for a scale factor. The simplest overall measure of the difference between the two structures is the in-

show abstract

The crystal structure of the carotenoidal compound 1,14-bis-(2',6',6'-trimethylcyclohex-1'-enyl)-3,12-dimethyltetradeca-1,3,5,7,9,11,13-heptaene-6,9-dinitrile

Cited by 7 publications

References 0 publications

Ring Orientation in βIonone and Retinals

Ring Orientation in βIonone and Retinals

The Structure and Spectra of the Chromophore of the Visual Pigments

A new figure of merit for multisolution methods of phase determination

Contact Info

Product

Resources

About