4th EucheMs chemistry congress

Poster Session 2
s1270
chem. Listy 106, s257–s1425 (2012)
Poster session 2 - organic chemistry
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wAter SoLuBLe n-heteroCyCLiC CArBene
GoLd CoMPLexeS
K. BeLGer 1 , n. KrAuSe 1
1 TU Dortmund, Chemistry, Dortmund, Germany
In 1991 Arduengo [1] isolated the first “free” N-heterocyclic
carbene. Since then the interest in NHC transition metal
complexes increased rapidly due to their σ-donating properties
and their broad variation range in steric features which allow an
excellent stabilization of the metal center and an enhancement of
[2, 3]
their catalytic activity.
In our investigations, water soluble NHC gold catalysts will
be synthesized. During the last two decades, water has gained
great interest as a solvent. Low costs as well as environmental and
safety aspects are the main advantages of water. Therefore,
water-based catalysts are required. [4] The introduction of a water
soluble residue at the NHC ligand like an ammonium salt or a
sulfonate group is a potential approach. These residues are already
known from phosphine ligands. [5] However, there are just a few
water soluble NHC complexes so far. [6-9]
references:
1. A.J. Arduengo III, R. L. Harlow, M. Kline, J. Am. Chem.
Soc. 1991, 113, 361.
2. S. Díez-González, N. Marion, S. P. Nolan, Chem. Rev.
2009, 109, 3612–3676.
3. S. P. Nolan, Acc. Chem. Res. 2011, 44, 91.
4. A. Azua, S. Sanz, E. Preis, Chem. Eur. J. 2011, 17,
3963–3967.
5. K. H. Shaughnessy, Chem. Rev. 2009, 109, 643-710.
6. W. Wang, J. Wu, C. Xia, F. Li, Green Chem. 2011, 13,
3440.
7. S. Roy, H. Plenio, Adv. Synth. Catal. 2010, 352,
1014–1022.
8. A. Azua, S. Sanz, E. Peris, Organometallics, 2010, 29,
3661–3664.
9. S. H. Hong, R. H. Grubbs, J. Am. Chem. Soc. 2006, 128,
3508–3509.
Keywords: Carbene ligands; Gold; Nitrogen heterocycles;
Ligand design; Water chemistry;
4 th EucheMs chemistry congress
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Proton trAnSfer in CALCiuM-reGuLAted
BioLuMineSCent reACtionS: PeCuLiAritieS of
fLuoreSCenCe SPeCtrA
n. BeLoGurovA 1 , n. KudryAShevA 1
1 Institute of Biophysics SB RAS, Photobiology, Krasnoyarsk,
Russia
Calcium-regulated bioluminescent reactions catalyzed by
photoproteins are responsible for bioluminescence of marine
coelenterates. Photoprotein is a stable enzyme-substrate complex
consisting of a single polypeptide chain and an oxygen “pre-activated”
substrate, 2-hydroperoxycoelenterazine which is tightly but
noncovalently bound within a hydrophobic cavity inside the protein.
Addition of calcium ions to photoprotein triggers a bioluminescent
reaction resulting in light emission with λ =485 nm. The product
max
of the bioluminescent reaction (enzyme-bound chromophore,
coelenteramide) is a fluorescent protein; It is called ‘discharged’
photoprotein. Obelin isolated from hydroid Obelia longissima is
one of the most studied among photoproteins. Obelin is stable and
nontoxic natural complex; its spectra, and hence, color of
luminescence, are variable. This is why it is considered as
perspective bioluminescent and fluorescent marker for biological
and medical investigations in vitro and in vivo. Therefore the
fluorescent peculiarities of obelin are of high interest.
Spectra of obelin bioluminescence and discharged obelin
photoluminescence are wide and complex. Photoluminescence
spectra depend on external physico-chemical conditions of obelin
solution (pH, calcium concentration, and temperature), but
bioluminescence spectra do not.
The spectra were deconvolved into spectral components
using Gauss distribution and method of second derivative.
Spectral components were attributed to protonated and several
deprotonated forms of coelenteramide with different acidity in its
fluorescent states. Effectiveness of proton-transfer process
depends on conformation of obelin active center - distance
between coelenteramide and proton-accepting group of amino
acid environment. We suggest that discharged obelin might form
several conformations depending on physico-chemical conditions.
For example, analysis of photoluminescent spectra of discharged
obelin under different calcium concentration revealed
considerable spectral changes at [Ca2+ ] ≈ 0.5 μM, this pointing to
enzymatic conformational transition in discharged obelin.
Meanwhile only one conformation of obelin is responsible for
bioluminescence under different conditions.
Keywords: Fluorescence spectroscopy; Proton transport;
Photoprotein;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc