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Abstract. Nitration of 2-tert-butyl-and 2,7-di-tert-butylpyrene affords molecules with severely hindered nitro groups. A nitro group ortho to a tert-butyl group is twisted at least 82" out of the plane of the aromatic nucleus. The lack of interaction between the hindered nitro group and the aromatic system is reflected in the chemical behaviour, as well as in the spectroscopic properties, of these nitro derivatives. Upon fragmentation in the mass spectrometer, the tert-butyl group is always replaced by a hydrogen atom. Nitro groups are only replaced by a hydrogen atom if they are ortho to a tert-butyl group.

Abstract.A simple technique for the preparation of anions of polycyclic aromatic hydrocarbons is described. 'H and I3C NMR spectra of dianions of pyrene and derivatives of pyrene are reported and discussed. The electron density is greatest at the carbon atoms in the perimeter of the dianions. The presence of an electron-donating substituent at position2 causes an increase in the charge at positions 1 and 3.

Nitration of 2-t-butylpyrene and 2,7-di-t-butylpyrene leads to nitro derivatives which show an extremely weak interaction between the nitro group and the aromatic r-system; the orientation of the nitro group prevents this group from conjugation with the n-system, leading to an unperturbed pyrene electronic spectrum.

The binding of the isomers fall-trans, tfcis, f f-c& and 94s) of ~~~~~t~~lr~t~~~ to ~~~t~~i~o~~~~ and the light-dark adaptation as well as the tight-driven proton pump action of the resulting bacteriorhodopsin analogue were studied. The (Sdemethyl)-bacteriorhodopsin is formed -3-times faster than unmodified bacteriorhodopsin and shows an efficient light-driven proton pump action. These findings show that upon binding of retinal to bacterioopsin the protein forces the chromophore to adopt a more planar ring-chain conformation than in free retinal.~~obacterium hatobium &r@e mernb~~e Proton pumpChromoproteins with a retinylidene chromophore such as bacteriorhodapsin, visual pigments and retinochrome, play an important role in photobiology [I]. Bacteriorhodopsin (hereafter bR), the light energy converting protein of the purple membrane of the halo~hili~ microorganism Iiutobucreriwn halobium, occurs in a light-(Amax = 570 nm) and in a dark-adapted form (hmBX = 560 nm) [2]* The chromophore of the lightadapted form is an all-irons retinylidene moiety. In the dark-adapted form a 1: 1 ~~~ibrium between 13-t& and all-Pans isomers exists [Z].retinal does not bind to bO [Ltf* In continuation of our study on the effect of the different methy groups in retinal upon the binding properties and the light-driven proton pump action of bR [7], we now report on the binding properties of 5-demethyiretinai ( fig. 1) (in its dl-trans, 13-c&, 1 I-& and 9-c& form) to bO. The light-dark adaptation together with the light-driven proton pump action of (%demethyl)-bR are also discussed. 2, MATERIALS AND METHODS The

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Abstract.Friedel-Crafts alkylation of pyrene with 2,5-dichloro-2,5-dimethylhexane and 2,4-dichloro-2,4-dimethylpentane in carbon disulfide yields 7,7,10,1O-tetramethyl-7,8,9,IO-tetrahydrobenzo[a]pyrene and 7,7,9,9-tetramethyl-8,9-dihydro-7H-cyclopenta[a]pyrene, respectively, both in 99 % yield. Alkylation with 1 ,4-dichlorobutane, followed by aromatization, yields benzo[a]pyrene in a facile two-step synthesis in 8% yield. A mechanism is proposed which rationalizes the fact that only one ring of pyrene undergoes substitution. The 'H-'H NMR coupling constants of the pyrene derivatives are discussed.

Abstract. The dianion of pyrene in THF reacts with 1 equivalent of a hard electrophile [H' or (CH,),SiCl] at posiiion 1 and with a second equivalent at position 9. 1-And 4-(trimethylsily1)pyrene and 1,9-bis(trimethylsilyl)pyrene have been thus prepared. In THF/NH, , the dianion of pyrene is converted into 1-hydropyrene monoanion by abstraction of a proton from ammonia. From 2-methoxypyrene and 2-tert-butylpyrene dianion, two different monoanions can be formed: protonation is possible at positions 1 and 6. The monoanions have been prepared and alkylated with sodium iodoacetate. Product analysis shows that the 2-tert-butyl-1-and -6-hydropyrene monoanions are formed in the ratio of 6/4, while the 2-methoxypyrene dianion is protonated exclusively at position 1. The results are in agreement with the charge distribution in the dianions of these 2-substituted pyrene derivatives.