Images of the assembly of surfactants and synthetic lipids on the surface of carbon nanotubes were obtained by transmission electron microscopy. Above the critical micellar concentration, sodium dodecyl sulfate (SDS) forms supramolecular structures made of rolled-up half-cylinders on the nanotube surface. Depending on the symmetry and the diameter of the carbon nanotube, we observed rings, helices, or double helices. Similar self-assemblies were also obtained with several synthetic single-chain lipids designed for the immobilization of histidine-tagged proteins. At the nanotube-water interface, permanent assemblies were produced from mixed micelles of SDS and different water-insoluble double-chain lipids after dialysis of the surfactant. Such arrangements could be further exploited for the development of new biosensors and bioelectronic nanomaterials.

Especially in the field of enantioselective synthesis, vicinal diamines (1,2-diamines) 1 and compounds easily prepared from them-such as 1,2-bisimines, 1,2-diamides, or imidazolidin-2-ones-are widely used by organic chemists. Various strategies have been developed to produce these compounds selectively. Many natural products and medicinal agents also contain a 1,2-diamino unit.

Two distinct proteins, streptavidin and HupR, bind and form regular helical arrays on the surface of multiwalled carbon nanotubes under appropriate conditions (see picture). The decoration of the outer surface of these nanostructures with biological macromolecules was investigated by electron microscopy.

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Light-induced QA-/QA FTIR difference spectra of the photoreduction of the primary quinone (QA) have been obtained for Rhodobacter sphaeroides reaction centers (RCs) reconstituted with ubiquinone (Q3) labeled selectively with 13C at the 1- or 4-position of the quinone ring, i.e., on either of the two carbonyls. The vibrational modes of the quinone in the QA site are compared to those in vitro. IR absorption spectra of films of the labeled quinones show that the two carbonyls contribute equally to the split C = O band at 1663-1650 cm-1. This splitting is assigned to the two different geometries of the methoxy group nearest to each carbonyl. The QA-/QA spectra of RCs reconstituted with either 13C1- or 13C4-labeled Q3 and with unlabeled Q3 as well as the double differences calculated from these spectra exhibit distinct isotopic shifts for the bands assigned to C = O and C = C vibrations of the neutral QA. For the unlabeled QA, these bands correspond to the bands at 1660, 1628, and 1601 cm-1 previously detected upon nonselective isotopic labeling [Breton, J., Burie, J.-R., Berthomieu, C., Berger, G., & Nabedryk, E. (1994) Biochemistry 33, 4953-4965]. The 1660-cm-1 band is unaffected upon selective labeling at C4 but shifts to approximately 1623 cm-1 upon 13C1 labeling, demonstrating that this band arises from the C1 carbonyl, proximal to the isoprenoid chain. The band at 1628 cm-1 shifts by 11 and 16 cm-1 upon 13C1 and 13C4 labeling, respectively, and is assigned to a C = C mode coupled to both carbonyls.(ABSTRACT TRUNCATED AT 250 WORDS)

The photoreduction of the secondary quinone acceptor QB in reaction centers (RCs) of the photosynthetic bacteria Rhodobacter sphaeroides and Rhodopseudomonas viridis has been investigated by light-induced FTIR difference spectroscopy of RCs reconstituted with several isotopically labeled ubiquinones. The labels used were 18O on both carbonyls and 13C either uniformly or selectively at the 1- or the 4-position, i.e., on either one of the two carbonyls. The QB-/QB spectra of RCs reconstituted with the isotopically labeled and unlabeled quinones as well as the double differences calculated from these spectra exhibit distinct isotopic shifts for a number of bands attributed to vibrations of QB and QB-. The vibrational modes of the quinone in the QB site are compared to those of ubiquinone in vitro, leading to band assignments for the C = O and C = C vibrations of the neutral QB and for the C***O and C***C of the semiquinone. The C = O frequency of each of the carbonyls of the unlabeled quinone is revealed at 1641 cm-1 for both species. This demonstrates symmetrical and weak hydrogen bonding of the two C = O groups to the protein at the QB site. In contrast, the C = C vibrations are not equivalent for selective labeling at C1 or at C4, although they both contribute to the approximately 1617-cm-1 band in the QB-/QB spectra of the two species. Compared to the vibrations of isolated ubiquinone, the C = C mode of QB does not involve displacement of the C4 carbon atom, while the motion of C1 is not hindered. Further analysis of the the spectra suggests that the protein at the binding site imposes a specific constraint on the methoxy and/or the methyl group proximal to the C4 carbonyl. The FTIR observations provide compelling evidence for almost identical conformation and identical interactions of the ubiquinone in the QB binding site of Rb. sphaeroides and Rp. viridis in contrast to the X-ray structures, which yield different descriptions for the hydrogen-bonding pattern of QB binding. In the semiquinone state, the bonding interactions of the C***O groups are also symmetrical and the C***C are inequivalent at C1 and C4. However, the interactions are almost the same in the RCs of both species.

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