Ab initio (CASPT2) excited state calculations, including circular dichroism, of helically twisted cyanine dyes.

Ab initio calculations at the CASSCF/CASPT2 level were performed on helically twisted mono-, tri-, and pentamethine cyanine dyes in the all-Z-configurations. Excitation energies and oscillator and rotatory strengths were calculated for the five lowest energy singlet states. Both the long wavelength methine band and the cis-band could be identified unambiguously from their configurational parentage. The calculated state energies are within 0.09 eV of the experimental value for the methine band and within 0.16 eV for the cis-band. The calculated rotatory strengths of the methine band shows sign inversion as the length of the chromophore increases: negative for the short monomethine, strongly positive for the pentamethine. The trimethine presents a borderline case: the measured rotatory strength is almost nil, the calculated one depends on the geometry. There is good agreement between rotatory strengths calculated in the velocity and in the length formalism.

Inherent chirality of the retinal chromophore in rhodopsin-A nonempirical theoretical analysis of chiroptical data.

CASSCF and GAUSSIAN CIS calculations were performed on ground and excited states of different conformations of 11-cis-retinal protonated Schiff bases, the chromophore of rhodopsin, in order to study their chiroptical properties and attempt a correlation between absolute conformation and CD-spectral data. Geometries were taken from molecular models, from published rhodopsin models, and from retinal conformations obtained from molecular dynamics with geometry restraints. In all the cases studied we find that a positive sense of twist about the C12-C13 bond correlates with a calculated positive CD of the long wavelength absorption band; the twist of the C6-C7 bond modulates this primary contribution of the C12-C13 bond. The correlation of the beta-band with structural features is not straightforward. Calculations on bathorhodopsin lend support to the idea that this intermediate is a highly twisted all-trans-conformation.

Configurational ordering of cationic chiral dyes using a novel C(2)-symmetric hexacoordinated phosphate anion

C(2)-Symmetry hexacoordinated phosphorus BINPHAT anion-of configuration controlled by a BINOL ligand-can be prepared readily in a one-pot process and behaves as an efficient NMR chiral shift agent and chiral inducer onto monomethinium dyes (CD, (1)H NMR).

The chromophore induces a correct folding of the polypeptide chain of bacteriorhodopsin.

The pK values of the Schiff bases of several bacteriorhodopsin (BR) preparations have been determined by titration. While for the native protein a high pK of 13 has been reported [Druckmann et al. (1982) Biochemistry 21, 4953], we find that a BR reconstituted from retinal and the apoprotein obtained from the retinal-deficient strain JW5 exhibits a low pK value, 8.5. When the retinal chromophore is added to growing JW5 cells leading to in vivo BR formation, this BR shows a high Schiff base pK, >/=10.2. A value of 9.3 was determined when BR was reconstituted from retinal and BO, obtained from bleaching BR with hydroxylamine. A low pK value of 8.1 was found when 13-trifluoro(CF3)-retinal was used as chromophore for in vitro reconstitution [Sheves et al. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 3262], which is confirmed in this study. When we add CF3-retinal to growing JW5 cells, this low pK shifts to 9.1. Besides wild-type protein, the apoprotein from the mutant D96N (from the chromophore-deficient strain L-07) was also used for in vitro reconstitution with either chromophore, retinal or CF3-retinal. Irrespective of the chromophore used, both mutant BRs exhibit low pK values of their Schiff bases of 8.1. Flash photolysis with respect to the rise and decay of the M-photocycle intermediate of wild-type and D96N-mutated BR carrying retinal and CF3-retinal revealed that in both proteins the incorporation of the trifluororetinal leads to a faster rise of the M-intermediate and to a slower decay. Since the apoprotein from the chromophore-deficient JW5 strain of H. salinarium, despite its lower boyant density, is arranged into trimers (according to CD measurements), we propose that the high pK value of the BR Schiff base is induced by long-distance interactions between BR molecules in the purple membrane patches which control the pK of the chromophore.

[Biomechanics of human tendons: connection between stress relaxation and stress recovery (author's transl)]. / Zur Biomechanik menschlicher Sehnen: Zusammenhänge von Relaxation und Spannungsrückgewinn

108 tendons of the m. extensor hallucis longus were examined with a tensile testing machine within 36 h after death. The specimen were kept at a resting length of 20 mm. After the "steady state" was reached by cyclic loading, the tendons were stretched up to a maximum load of 18 kp, then deloaded to a certain level and after that the elongation was kept constant. At high loading level the tension of the tendon decreases with time (relaxation). At medium and low loading level the tension increases slightly (mechanical recovery). Between that two regions there is a certain load, where the tension will not change with time (isorheological point). The position of the isorheological point depends on the velocity of the elongation. At low velocity (2 mm/min) the isorheological point is situated at 70%, at high velocity (12 mm/min) at 60% of the maximum load. One will find the maximum relaxation, when no deloading occurs. The mechanical recovery, however, has its maximum at 5--25% of the maximum load. But when the tendon is totally deloaded, there seems to occur no recovery. The maximum relaxation is 5 to 6 times larger than the maximum recovery. Supposingly the relaxation- and recovery-processses will happen at the same time but with different intensity depending on the loading level. At least the relaxation-process consists of different relaxation components with different relaxation times. This will explain the phenomenon of a "secondary relaxation": After a long time of registration the recovery will turn into a slight relaxation.