Alternative models for two crystal structures of bovine rhodopsin.
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ABSTRACT:
SUBMITTER: Stenkamp RE
PROVIDER: S-EPMC2483493 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Recently, progress in IR sources has led to the discovery that humans can detect infrared (IR) light. This is hypothesized to be due to the two-photon absorption (TPA) events promoting the retina dim-light rod photoreceptor rhodopsin to the same excited state populated via one-photon absorption (OPA). Here, we combine quantum mechanics/molecular mechanics and extended multiconfiguration quasi-degenerate perturbation theory calculations to simulate the TPA spectrum of bovine rhodopsin (Rh) as a model for the human photoreceptor. The results show that the TPA spectrum of Rh has an intense S0 ? S1 band but shows also S0 ? S2 and S0 ? S3 transitions whose intensities, relative to the S0 ? S1 band, are significantly increased when compared to the corresponding bands of the OPA spectrum. In conclusion, we show that IR light in the 950 nm region can be perceived by rod photoreceptors, thus supporting the two-photon origin of the IR perception. We also found that the same photoreceptor can perceive red (i.e., close to 680 nm) light provided that TPA induces population of S2.
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Project description:The title compounds, 5-(2H-1,3-benzodioxol-5-yl)-N-cyclo-hexyl-penta-2,4-dienamide, C18H21NO3 (I), and 5-(2H-1,3-benzodioxol-5-yl)-1-(pyrrolidin-1-yl)penta-2,4-dien-1-one C16H17NO3 (II), are derivatives of piperine, which is known as a pungent component of pepper. Their geometrical parameters are similar to those of the three polymorphs of piperine, which indicate conjugation of electrons over the length of the mol-ecules. The extended structure of (I) features N-H?O amide hydrogen bonds, which generate C(4) [010] chains. The crystal of (II) features aromatic ?-? stacking, as for two of three known piperine polymorphs.
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Project description:The title compounds consist of a bornane skeleton with attached acetamide, C12H21NO (±)-(1) {systematic name: (±)-N-[(1RS,2RS,4RS)-1,7,7-tri-methylbi-cyclo-[2.2.1]heptan-2-yl]acetamide}, and chloro-acetamide, C12H20ClNO (±)-(2) {systematic name: (±)-2-chloro-N-[(1RS,2RS,4RS)-1,7,7-tri-methylbi-cyclo-[2.2.1]heptan-2-yl]-acetamide}, functionalities to the 2-exo-position. The crystal structure of the first monoclinic polymorph of (±)-(1) has been reported previously [Ung et al. (2014 ?). Monatsh. Chem. 145, 983-992]. Compound (±)-(1) crystallizes in the space group P21/n with two independent mol-ecules in the asymmetric unit, in contrast to the above-mentioned polymorph which crystallized in the space group C2/c with one mol-ecule in the asymmetric unit. In the title compounds, the bicyclic bornane moieties have normal geometries. In the crystals of both compounds, mol-ecules are linked by N-H?O hydrogen bonds, reinforced by C-H?O contacts, forming trans-amide chains propagating along the a-axis direction. In the case of compound (±)-(1), neighbouring chains are linked by further C-H?O contacts, forming double-chain ribbons along [100].
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Project description:Two polymorphs, (I) and (II), of (S)-{2-[(8S,9S,10R,11S,13S,14S,17R)-11,17-dihy-droxy-10,13-dimethyl-3-oxo-2,6,7,8,9,11,12,14,15,16-deca-hydro-1H-cyclo-penta-[a]phenanthren-17-yl]-2-oxoeth-yl} 2,2-di-methyl-propane-thio-ate, C26H38O5S, have been identified. They are ortho-rhom-bic, non-centrosymmetric (P212121). The structures display layers of mol-ecules conected via O-H⋯O hydrogen bonds along the b-axis direction in polymorph (I) and along the c-axis direction in polymorph (II). The structure of (II) exhibits disorder of the main mol-ecule.
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