Bioinspired model complexes for vanadium haloperoxidases [Elektronische Ressource] / von Simona Filofteia Nica

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• Publié par: friedrich-schiller-universitat_jena
• Publié le: 01 janvier 2005
• Nombre de lectures: 30
• Langue: English
• Poids de l'ouvrage: 5 Mo

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Bioinspired Model Complexes For
Vanadium Haloperoxidases
DISSERTATION
zur Erlangung des akademischen Grades doctor rerum naturalium
(Dr. rer. nat.)
vorgelegt dem Rat der Chemisch-Geowissenschaftlichen Fakult at
der Friedrich-Schiller-Universit at Jena
von M. Sc. Simona Filofteia Nica
geborem am 19.12.1976
in Curtea de Arges, RomaniaGutachter
1. Winfried Plass
2. Matthias Westerhausen
ndTag der o en tlichen Verteidigung: September 22 2005"Most zealously I’ve studied matters great and small;
Though I know much, I should like to know all." Goethe
Din s^ n ul vecinicului ieri
Tr aieste azi ce moare,
Un soare de s-ar stinge-n ceri
S-aprinde iarasi soare.
Mihai Eminescu
In memory of the most beloved father and to the memory of an extraordinary Professor,
Dr. Ovidiu Maior.Acknowledgements
I would like to thank my supervisor, Prof. Dr. Winfried Plass, for giving me the oppor-
tunity to work in this interesting eld and for support with new ideas and advises during
my research.
Special thanks to my partner, colleague and best friend, Adrian Ion, for moral sup-
port, patience and especially for helping me in having new ideas through our multitude
of scienti c conversations.
I also thank to my colleague, Dr. Axel Pohlmann, who helped a romanian student
lost in the german bureaucracy. Thanks also for bringing me from Siegen to Jena and
taking care of the new employment procedures. Without you, most likely, I would have
been deported three years ago. Of course, I thank to him, more importantly, for helping
me nd the way through the german world of computers and teaching me how to use
special programs.
Lots of thanks to Dr. Andrew Hall for nice friendship and for language support.
Only with your support my thesis reassembles now the English language. And because
we are here, I say millions of thanks to Dr. Ioana Pera, my best romanian friend. Thank
you very much for helping me to nd my house in Siegen, for accompanying me shopping
and for the very nice time spent together.
Thanks to Masroor, my Pakistani colleague for nice and enjoyable evenings spent
together and also for the nice talks about the structure of the enzyme and for correcting
my English in the manuscripts. I also thank to my colleague Arne Roth for his patience
Ain explaining me how the LT Xworks and especially for his help in the arrangement ofE
the thesis.
Many thanks to Ines Seidel for helping me with catalytic tests and some experiments
in the last months while writing my manuscripts and my thesis. Also, lots of thanks to mystudent, Bj orn Kusebauch for bringing me so many results during his "Forschungsprak-
tikum".
I would like to thank to Dr. Manfred Rudolph, who measured the cyclic voltam-
metry experiments of my complexes and also for helping me to interpret the spectropho-
tometric titration data.
I would like to thank to the NMR team, who measured my tons of samples and also
for trying to understand my very bad german language. Many thanks to Lotte Neupert
for the HPLC measurements.
Lots of thanks to a special person, Dr. Helmar G orls for measuring my X-ray
crystal structures and for his high sense of humor. He knew how to bring the smile on
my face even when the measured structures were the by-products. Thank you very much.
I also thank to my romanian friend, now Dr. Maria-Magadalena Titirici for her
help and understanding me.
Last but not least, I would like to thank to all my family for nancial and moral
support during all my studies. Thanks to my brother, Dr. Dorel-Daniel Nica for his
kindness and nancial support and also many thanks for the nice political and literature
talks. Thanks to my parents for understanding and supporting me in all my life deci-
sions. Unique thoughts of gratitude go to my wonderful father. I wish I would had the
opportunity to share all this achievements with you. I miss you and I wish you were still
here with me.Summary
Vanadium haloperoxidases represent a class of non-heme peroxidases with a high stabil-
ity to organic solvents and high temperatures. These enzymes proved also to be very
stable in presence of excess of their product (HOCl) which will readily inactivate the
heme-haloperoxidases. The active group of the enzymatic system consists in a vana-
date moiety, solely covalently bonded to a histidine residue and embedded in the protein
shell via a strong hydrogen bonding network. Structural similarities between the hydro-
gen bonding site of vanadium haloperoxidases and some acid phosphatases are evident.
An important role for the haloperoxidase activity has been attributed to the hydrogen
bonding interactions which besides the xation of the prosthetic group in the protein
environment are also activating the peroxide-intermediate.
The goal of this work was the synthesis of vanadium(v) complexes which model
the active site and the catalytic function of these enzymes. Vanadium in the highest
oxidation state proved to be a compulsory characteristic of model complexes, since the
reduced form of vanadium haloperoxidase showed no activity. Therefore, vanadium(v)
complexes with versatile N-salicylidene carbonic acid hydrazide were prepared. Both oxo
and dioxovanadium complexes will be described in Chapter 2 and Chapter 3, with both
types of vanadium coordination compounds regarded as model complexes for the natural
system. Besides the crystallographic description of these complexes, reactivity in solution
will be also discussed.
Starting from a non-substituted aliphatic side chain of the N-salicylidene hydrazide
ligand, new functionalities were introduced stepwise. This achievement had the role to
probe the importance of the amino acid residues which are in hydrogen bonding inter-
action with the equatorial oxygen atoms of the prosthetic group in vanadium containing
haloperoxidases. The modi cation of the aliphatic side chain will be discussed in sepa-
rate chapters, therefore additional groups such as hydroxyl, amine and guanidine a orded
vanadium(v) complexes with relevant functionalized side chain for the vanadium haloper-
oxidases, namely regarding the serine, lysine and arginine residues.
The mechanism of the catalytic reaction performed by vanadium haloperoxidases
was proposed to take place by addition rst of the hydrogen peroxide at the vanadate
1center to form a peroxo-intermediate which is subsequently able to oxidize the halides
in slightly acidic media. In Chapter 2, the characterization and reactivity of an oxo-
monoperoxovanadium(v) complex is presented. Further on, the cyclization on vanadium
coordination of a short amino-functionalized aliphatic side chain of N-salicylidene hy-
drazide ligand as well as the rst example of guanilation reaction of a vanadium coordi-
nation compound will be described in Chapter 4 and 5, respectively.
The cis-dioxovanadium(v) complexes obtained with N-salicylidene carbonic acid
hydrazides proved also to catalyze the biomimetic reaction. The bromide oxidation re-
action by hydrogen peroxide was monitored by bromination of 1,3,5-trimetoxybenezene
in acidi ed DMF solution. Apart from this speci c enzymatic reaction, the model com-
plexes were also able to catalyze the peroxide-mediated oxidation of phenyl methyl sul de
to the corresponding sulfoxide.
The replacement of vanadate from vanadium haloperoxidase with molybdate or
tungstate yielded an inactive enzyme. Therefore, cis-dioxomolybdenum(vi) complexes
based on N-salicylidene amino-functionalized aliphatic acid hydrazide were also obtained
in order to address the question whether a synthetic molybdenum complex can catalyze
the bromoperoxidase reaction. This was also based on the reported high bromoperoxidase
activity of the inorganic MoO (aq.) compound. But, however the cis-dioxomolybdenum3
complex based on N-salicylidene dihydropyrrole hydrazide showed no bromoperoxidase
activity, but instead the complex was capable of catalyzing e cien tly the oxidation of
sul de to sulfoxide.
In the last chapter, bis-N-salicylidene hydrazide ligands were prepared by the con-
densation of salicylaldehyde with bis-aliphatic hydrazides. The ligand H Ln may be con-4
sidered as two N-salicylidene hydrazide cavities linked via a methylene chain of variable
length. The ligand is able to bind two metal ions in a hexacoordinate fashion yielding bin-
uclear cis-dioxovanadium(v) and cis-dioxomolybdenum(vi) complexes. The complexes
showed a high e cien t capacity in catalyzing the oxidation of sul de when H O was used2 2
as oxidant. Moreover, a chiral binuclear cis-dioxomolybdenum(vi) complex was isolated
and used as catalyst of the sulfoxidation reaction. The complex proved to be an e cien t
catalyst of the reaction, but only 4% ee was obtained when the catalytic reaction was
performed in dichlormethane.
2Zusammenfassung
Vanadium-Haloperoxidasen stellen eine Klasse von nicht-H am-Peroxidasen mit hoher
Best andigkeitgegenub er organischen L osungsmitteln und hohen Temperaturen dar. Diese
Enzyme sind au erdem in Gegenwart von Uberschuss ihres Produktes (HOCl), was h am-
Haloperoxidasen leicht inaktivieren wurde, sehr stabil. Das aktive Zentrum des enzyma-
tischen Systems besteht aus einer Vanadatumgebung, welche kovalent an nur einen Histid-
inrest gebunden und im Proteinrumpf mittels eines starken Wassersto br uc kennetzwerks
verankert ist. Strukturelle Ahnlichkeiten zwischen der Wasse