Investigation of the spectral properties of the crowned retinals and bacteriorhodopsin analogs

Article abstract of DOI:10.1080/15421400590947243

The spectral properties of new crowned retinal analogs and their bacteriorhodopsin complexes are described.

Full text of DOI:10.1080/15421400590947243

Mol. Cryst. Liq. Cryst., Vol. 431, pp. 209=[509]–214=[514], 2005
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400590947243
Investigation of the Spectral Properties of the Crowned
Retinals and Bacteriorhodopsin Analogs
O. V. Demina
S. D. Varfolomeev
N.M. Emanuel Institute of Biochemical Physics RAS, Moscow,
Kosygina, Russia
A. Yu. Lukin
A. V. Laptev
V. I. Shvets
A. A. Khodonov
M.V. Lomonosov State Academy of Fine Chemical Technology,
Moscow, Vernadskogo, Russia
L. V. Khitrina
A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State
University, Vorob’evy Gory, Moscow, Russia
S. P. Gromov
A. I. Vedernikov
V. A. Barachevsky
Yu. P. Strokach
M. V. Alfimov
Photochemistry Center RAS, Moscow, Novatorov, Russia
J. Lugtenburg
Gorlaeus Lab., Leiden Institute of Chemistry, Leiden University,
Einsteinweg, The Netherlands
This work was partly supported by the RFBR (Projects No. 04-03-32746, No. 02-03-
32320, No. 03-04-49153); INTAS 2001-0267; ISTC No#2117; The Ministry of Science
and Education RF (No. PD02-1.3-64; No. 203.02.05.004) and Government of Moscow
grants.
Address correspondence to A. A. Khodonov, M.V. Lomonosov State Academy of Fine
Chemical Technology, 117571, Moscow, Vernadskogo 86, Russia. E-mail: khodretinal@
mtu-net.ru
209=[509]

210=[510]
O. V. Demina et al.
The spectral properties of new crowned retinal analogs and their bacteriorhodop-
sin complexes are described.
Keywords: benzocrown ethers and its dithiaderivatives; crowned bacteriorhodopsin
and retinal analogs; ionophore; spectral data
INTRODUCTION
Nowadays bacteriorhodopsin (BR) is a simple object, as compared with
other known photosynthetic systems, that performs the solar energy
transduction function. This natural biophotochrome was discovered
in 1971 in Halobacterium salinarum and functions as a light-driven
proton pump. Its polypeptide part (bacterioopsin) consists of a sole
peptide chain. The chromophoric group of BR is a protonated retinal
Schiff base (SB) with e-aminogroup Lys-216. Recently, we proposed a
number effective approaches for the synthesis of new crowned poly-
enes (1, 2, 4–6 a–d) and reference compounds (1, 2, 4–6 e), related
to the retinal, in order to study their spectral properties and ion-binding
capability and spectral behaviour of their complexes with bacterioop-
sin. Here, we described the spectral properties of the new retinal
analogs and their artificial bacteriorhodopsin (ABR) complexes.
EXPERIMENTAL
Polyene Synthesis
In the previous papers we designed and described effective synthetic
routes to unsaturated crowned compounds with variable length of
the conjugation chain (one or two C¼C bonds), crown-ether ring size
and nature of terminal polar group [1–4]. Below, we present a new
example of successful application of this synthetic strategy for the
preparation of retinal analogs. As ionophoric moieties, we selected
benzo-15-crown-5 (a) and benzo-18-crown-6 (b) fragments for alkali,
alkali-earth, and rare-earth metal ions and their dithiaderivatives
(c, d) for transition and heavy metal ions. Compounds (1, 2, 4–6 a–e)
were synthesized by the Horner-Emmons olefination of the correspond-
ing 40-formylbenzocrown ethers (3a–d) using the C5-phosphonate
reagents (7, 8), containing the ester or cyano terminal group (see
Scheme 1). Also, we synthesized the corresponding reference com-
pound (1 e), in which the crown-ether moiety was replaced by a related
structure of 3,4-dimethoxyphenyl residue. This fragment has similar
electron-donating properties but it lacks cation-binding ability. The

Spectral Data of the Crowned Retinals and BR’s
211=[511]
SCHEME 1
transformation of the ester group in the intermediate esters into the
hydroxymethyl function by LiAlH4 reduction followed by MnO2 oxi-
dation leads to the key aldehydes. For conversion of the nitrile group
into the aldehyde function we used a one-step procedure of DIBAL
reduction. The configuration of the new C¼C bond and the isomer ratio
1
in the products were determined using H-NMR spectroscopy by com-
paring the integral intensities of the proton signals for the polyene
chain (doublets with J 16.0 Hz and J 12.0 Hz for E- and Z-isomers,
respectively). It was found, that the Horner olefination follows prefer-
ably E-selectivity for the newly formed bond with moderate or high pro-
duct yields in all the series of compounds (a–e). The structure of all
compounds was confirmed unambiguously by IR; UV; 1H NMR-
spectroscopy and mass-spectrometry.
Finally, five series of compounds (1,2 a–e) containing monobenzo-
15-crown-5- and monobenzo-18-crown-6-ether; their dithiaderivatives
and compounds containing 3,4-dimethoxyphenyl fragment with differ-
ent length of the conjugation chain were prepared.
RESULTS AND DISCUSSION
Interaction of Retinal Analogs (1 a–e) with Bacterioopsin
The synthesized retinal analogs (1 a–e) and their short-cut derivatives
(2 a–e) were further tested in recombination with bacterioopsin (BO)

212=[512]
O. V. Demina et al.
TABLE 1 Spectral Properties of Retinal Analogs (1 a–e) and their ABR
Complexes
kmax
ABR
chromophore
code
of pigmentDA
with BO,
nm
kmax of aldehyde, nm,
Photocycle
effectiveness, %
MeCN (eꢂ10ꢃ4, Mꢃ1 cmꢃ1
)
9
381 (4.8)
400 (5.2)
400 (5.1)
396 (5.0)
396 (5.5)
402 (4.0)
558
495
495
497
497
500
100
23
22
n.d.ꢄ
n.d.ꢄ
35
1a
1b
1c
1d
1e
ꢄnot studied yet
from apomembranes H. salinarum (strain ET1001). It was found that
the formation of pigments takes place already within 1–2 hours. The
spectral parameters of these pigments (ABR-1 a–e) are presented in
the Table 1. It should be noted that kmax of ABR is located within
the wavelength range typical of pigments, in which trimethylcyclo-
hexene ring of the retinal is replaced by other aromatic rings (460–
530 nm) [2,5].
We have studied the photochemical properties of the crowned ABR
(ABR-1 a, b) and reference ABR (ABR-1 e) prepared from crowned
polyenal (1 a, b) and 3,4-dimethoxyphenylretinal (1 e), respectively.
The exposure of ABR samples to laser light flashes caused reversible
bleaching of the main absorption band of the pigments (absorption
changes induced by laser flash (k ¼ 532 nm, t1=2 ¼ 15 ns) in a suspen-
sion of membrane samples at 21ꢀC). The photocycle of the pigments
includes an M-like intermediate.
The quantum efficiency of the crowned ABR (ABR-1a, b)
photocycle was about 22–23% that found for the control BR. This
estimate was obtained from analysis of the photoinduced response
amplitude in the main absorption band as normalized to the
absorption value in this band: DDABR=DABR and DD570=D570 (control
BR). The measurements were done at equal protein concentration
or equal absorption level at the actinic light wavelength. According
to the relaxation kinetics of the M-like intermediate, the photo-
cycle rate of the crowned ABR was significantly lower than that
in the control BR. Also, we have demonstrated that for short-cut
polyenals (2 a–e), ABR formation with the kmax ꢁ 450–460 nm is
possible.

Spectral Data of the Crowned Retinals and BR’s
213=[513]
Investigation of the Spectral and Ion-binding Capability
We investigated the spectral properties and the ion-binding capability
of the crowned and reference compounds. The electronic spectra of all
compounds under study exhibit two groups of bands located in the
200–240 and 270–500 nm spectral regions. Comparison of the spectral
characteristics of the crowned polyenes with identical terminal groups
but different sizes and nature of the crown-ether fragment has demon-
strated almost complete coincidence of the spectral characteristics of
these compounds and the corresponding 3,4-dimethoxyphenyl analogs
containing no crown ether fragments (Table 1–3).
This means that the long-wavelength absorption of these com-
pounds is due to the same system of conjugated bonds. The position
of the long-wavelength absorption bands depends on the length of
the conjugated chain and the nature of the terminal group. An
increase in the chain length and the electron-withdrawing capability
of the terminal groups results in bathochromic shifts of the absorption
bands (see Tables 2, 3). Unlike the 3,4-dimethoxyphenyl analogs (1, 2,
4–6 e), in the case of crowned compounds, the introduction of metal
salts into their solutions in acetonitrile induces hypsochromic shifts
of the absorption bands – kmax (see Tables 2, 3). The observed spectral
changes are due to complex formation between the metal ions and the
crown-ether fragments. The hypsochromic shift depends on the nature
of the metal ion. The magnitude of the Dkmax for the 15-crown-5 deri-
vatives decreases in the sequence Ca2þ >Mg2þ > Ba2þ>La3þ >Naþ>
Liþ>Kþ, while for 18-crown-6, this sequence is different, namely,
TABLE 2 UV–Vis Spectral Data for E-Isomers of Compounds (1, 2, 5, 6 a–b,
1e) and their Complexes with Various Metal Cations
kmax of free
ligand,
k
max, nm (Dkmax ¼ kL ꢃ kML), in MeCN, cM=cL ¼ 1000
nm [e 10ꢃ4
No Mꢃ1 cmꢃ1
]
Liþ
Kþ Naþ Mg2 þ Ba2 þ Ca2 þ La3 þ
5a
2a
6a
1a
5b
2b
6b
1b
1e
340[3.3]
356[3.3]
383[4.5]
400[5.2]
342[3.4]
359[2.8]
387[4.4]
400[5.1]
402[4.0]
330(10) 338(2) 330(10) 320(20) 326(14) 319(21) 321(19)
347(9)
376(7)
393(7)
340(2)
356(3)
383(4)
398(2)
402(0)
353(3)
382(1)
396(4)
335(8)
346(9)
375(8)
391(9)
337(5)
335(21) 338(18) 333(23) 335(21)
369(14) 370(13) 368(15) 373(10)
381(19) 383(17) 382(18) 384(16)
339(3)
353(6)
383(4)
399(1)
402(0)
329(13) 329(13) 323(19)
342(17) 341(18) 336(23)
373(14) 372(15) 372(15)
388(12) 388(12) 386(14)
349(10) 350(9)
386(1)
395(5)
402(0)
382(5)
398(2)
402(0)
402(0)
402(0) 402(0)

214=[514]
O. V. Demina et al.
TABLE 3 UV-Vis Spectral Data for E-Isomers of Compounds (1, 2, 5, 6 c–d)
and their Complexes with Various Metal Cations
kmax, nm (Dkmax ¼ kL ꢃ kML), in MeCN, cM=cL ¼ 1000
kmax of free ligand,
No.
nm[e 10ꢃ4, Mꢃ1 cmꢃ1
]
Agþ
Hg2 þ
Pb2 þ
La3 þ
5c
2c
6c
1c
5d
2d
6d
1d
341[3.2]
354[2.7]
379[4.5]
396[5.0]
339[2.3]
359[2.9]
379[4.2]
396[5.5]
336(3)
349(5)
375(4)
389(7)
336(5)
352(7)
375(4)
393(3)
329(10)
341(13)
372(7)
388(8)
331(10)
346(13)
373(6)
388(8)
325(14)
338(16)
370(9)
384(12)
330(11)
342(17)
371(8)
340(1)
353(1)
379(0)
396(0)
341(0)
357(2)
379(1)
396(0)
386(10)
La3 þ> Ca2 þ> Ba2 þ> Kþ > Naþ > Mg2 þ > Liþ. This shift is due to
the decrease in the electron-donating ability of the oxygen atoms in
the macroheterocycle. Unlike oxygen-containing crowns series (a, b),
ionophores of the dithia-crowned series (c, d) don’t bind the alkali,
alkaline-earth, or rare-earth metal ions, but interact effectively with
heavy metal ions (Agþ , Hg2þ, Pb2þ) (see Table 3).
Thus, spectral data show that metal complex formation is observed
only for the crowned compounds. We hope that they could find an
application as ionophoric dye units for the development of optical
sensors, ion-selective electrodes and photocontrolled supramolecular
systems.
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