The free radical, nitric oxide (√NO), is responsible for a myriad of physiological functions. The ability to verify and study √NO in vivo is required to provide insight into the events taking place ...upon its generation and in particular the flux of √NO at relevant cellular sites. With this in mind, several iron-chelates (Fe2+(L)2) have been developed, which have provided a useful tool for the study and identification of √NO through spin-trapping and electron paramagnetic resonance (EPR) spectroscopy. However, the effectiveness of √NO detection is dependent on the Fe2+(L)2 complex. The development of more efficient and stable Fe2+(L)2 chelates may help to better understand the role of √NO in vivo. In this paper, we present data comparing several proline derived iron-dithiocarbamate complexes with the more commonly used spin traps for √NO, Fe2+-di(N-methyl-D-glutamine-dithiocarbamate) (Fe2+(MGD)2) and Fe2+-di(N-(dithiocarboxy)sarcosine) (Fe2+(DTCS)2). We evaluate the apparent rate constant (kapp) for the reaction of √NO with these Fe2+(L)2 complexes and the stability of the corresponding Fe2+(NO)(L)2 in presence of NOS I.
Celotno besedilo
Dostopno za:
BFBNIB, DOBA, GIS, IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
From the reaction between Mo
2
(OCH
2
t
Bu)
6
and NaCp (Cp = C
5
H
5
) in THF the title complex was obtained as a crystalline product in the presence of DME (DME = dimethoxyethane). Crystal data for ...Mo
2
(OCH
2
t
Bu)
6
(Cp)Na(DME) at −167 °C: a = 11.885(2) Å, b = 19.240(1) Å, c = 11.562(2) Å, α = 102.73(1)°, β = 106.95(1)°, γ = 98.55(1)°, Z = 2 and space group of Formula: see text. In the solid state there is an unbridged Mo≡Mo bond of distance 2.276(1) Å. One Mo atom is bonded to four alkoxides, two of which are also bonded to Na
+
while the other is η
5
-bonded to the Cp ligand, with Mo—C distances ranging from 2.34 to 2.66 Å, and to two OR groups, one of which is bound to the Na
+
ion. In addition to the coordination to three OR groups the Na
+
ion binds one DME molecule via both of its ether oxygen atoms. The Mo—O distances fall in the range 1.91–2.01 Å with the longer distances being associated with those groups that are also bonded to the Na
+
ion. In polar solvents the title complex dissociates to give Mo
2
(OCH
2
t
Bu)
6
and Na
+
Cp
−
. Key words: molybdenum, alkoxide, cyclopentadienyl, metal–metal triple bonds.
W
2(OR)
6 compounds where R
t
Bu and CMe
2CF
3, both reversibly bind pyridine in hydrocarbon solvents to form adducts W
2(OR)
6L
2. Pyridine binds more strongly to the fluoroalkoxide but the ...structural parameters of the compounds W
2(OCMe
2CF
3)
6(C
6H
5N)
2 and W
2(O
t
Bu)
6(4-CH
3C
6H
4N)
2 reveal an essentially identical W
2O
6N
2 core with
W
W = 2.39(1)
A
̊
,,
W
O = 1.92–1.95
A
̊
and
W
N = 2.26(1)
A
̊
. Both compounds were crystallographically characterized in the space group
C2/
c and each molecule has rigorous
C
2 symmetry. Allene and 1,3-di-
p-tolycarbodiimide form 1:1 adducts with W
2(OCMe
2CF
3)
6 in which the substrate is bound parallel to the M-M axis, i.e.
μ-
η
2,
η
2-C
3H
4 and
μ-
η
2,
η
2-ArNCNAr-W
2(OCMe
2CF
3)
6. Also W
2(OCMe
2CF
3)
6 and W
2(OSi
t
BuMe
2)
6 bind two equivalents of xylylisocyanide to afford W
2(OR)
6(
η
1-CNAr)
2. For W
2(OCMe
2CF
3)
6(
η
1-CNAr)
2, the molecular structure has been determined by X-ray crystallography and shows a nearly eclipsed central W
2O
6C
2 skeleton with
W
W = 2.44(1)
A
̊
,
W
O = 1.94(1)
A
̊
(av.) and
W
C = 2.14(1)
A
̊
, whereas the WWO angles span the range of 105–114°, the WWC angles are 83(1)°. Similarly, W
2(OCMe(CF
3)
2)
4(NMe
2)
2 forms a
bis adduct upon reaction with the isocyanide. However, the molecular structure of W
2(OCMe(CF
3)
2)
4(NMe
2)
2(
η
1-CNAr)
2 shows a staggered arrangement of the two ligands about the ditungsten center where
W
W = 2.382(1)
A
̊
,
W
O = 2.00(1)
A
̊
(av.),
W
N = 1.93(1)
A
̊
(av.) and W
C = 2.14(1)
A
̊
(av.) with a CWWC dihedral angle of 41.9°. These reactions and their products are compared for W
2(OR)
6 compounds where
R
t
Bu,
t
BuMe
2
Si and Cme
2
CF
3
.
The compounds of W
2(NMe
2)
2(OCMe
2CF
3)
4,
1, W
2(NMe
2)
2(OCMe(CF
3)
2)
4,
2, and W
2(NMe
2)
2 (OC(CF
3)
3)
4,
3, have been obtained from reactions between W
2(NMe
2)
6 and the respective ...fluoroalcohol in hydrocarbon solvents. The compounds
2 and
3 appear inert to further reaction with their fluoroalcohol at room temperature while
1 reacts further to give W
2(OCMe
2CF
3)
6. In solution NMR data indicate that all three compounds exist in a mixture of
anti- and
gauche-rotamers with restricted rotations about both WN and WW bonds on the NMR time-scale. The solid-state molecular structure of
2 reveals a centrosymmetric NO
2WWO
2N core with
W
W = 2.3107(6)
A
̊
,
Wz.sbnd;
N = 1.914(4)
A
̊
,
W
O = 1.959(3)
aand 1.907(3) Å and angles WWO/N within the range 100 to 110°. The gas phase photoelectron spectra for
1, 2 and
3 were obtained and are compared with that for W
2(NMe
2)
6. The introduction of the fluoroalkoxide ligands has a pronounced effect in stabilizing the metal and nitrogen lone-pair based ionizations, and this effect is amplified by the successive replacement of each methyl group by a trifluoromethyl group. Also for the compounds
1, 2, and
3 the lowest ionization bands clearly reveal the removal of the degeneracy of the WW π MOs as expected for
anti and
gauche complexes.
