Ru-based
coordination compounds have important applications as
photosensitizers and catalysts. [RuII(bpy)2(bpyNO)]2+ (bpy = 2,2′-bipyridine and bpyNO = 2,2′-bipyridine-N-oxide) was reported to be extremely light-sensitive, but
its light-induced transformation pathways have not been analyzed.
Here, we elucidated a mechanism of the light-induced transformation
of [RuII(bpy)2(bpyNO)]2+ using UV–vis,
EPR, resonance Raman, and NMR spectroscopic techniques. The spectroscopic
analysis was augmented with the DFT calculations. We concluded that
upon 530–650 nm light excitation, 3[RuIII(bpyNO–•)(bpy)2]2+ is formed similarly to the 3[RuIII(bpy–•)(bpy)2]2+ light-induced
state of the well-known photosensitizer [RuII(bpy)3]2+. An electron localization on the bpyNO ligand
was confirmed by obtaining a unique EPR signal of reduced [RuII(bpy)2(bpyNO–•)]+ (g
xx
= 2.02, g
yy
= 1.99, and g
zz
= 1.87 and 14N hfs A
xx
= 12 G, A
yy
= 34 G, and A
zz
= 11 G). 3[RuIII(bpyNO–•)(bpy)2]2+ may evolve
via breaking of the Ru–O–N fragment at two different
positions resulting in [RuIVO(bpy)2(bpyout)]2+ for breakage at the O-|-N bond and [RuII(H2O)(bpy)2(bpyNOout)]2+ for breakage at the Ru-|-O bond. These pathways were found
to have comparable ΔG. A reduction of [RuIVO(bpy)2(bpyout)]2+ may result in water elimination and formation of [RuII(bpy)3]2+. The expected intermediates, [RuIII(bpy)2(bpyNO)]3+ and [RuIII(bpy)3]3+, were detected by EPR. In addition,
a new signal with g
xx
= 2.38, g
yy
= 2.10,
and g
zz
= 1.85 was observed
and tentatively assigned to a complex with the dissociated ligand,
such as [RuIII(H2O)(bpy)2(bpyNOout)]3+. The spectroscopic signatures of [RuIVO(bpy)2(bpyout)]2+ were not observed, although DFT analysis and [RuII(bpy)3]2+ formation suggest this intermediate. Thus,
[RuII(bpy)2(bpyNO)]2+ has potential
as a light-induced oxidizer.
Elevated levels of tumor necrosis factor alpha (TNF-alpha) have been reported to correlate with the development of transplant-related complications after bone marrow transplantation (BMT). In a recent phase I-II trial, oral administration of pentoxifylline (PTX), a xanthine derivative capable of downregulating TNF-alpha production in vitro, was reported to reduce morbidity and mortality in patients undergoing BMT. We conducted a prospective randomized trial of PTX therapy among 140 patients undergoing either allogeneic (n = 51) or autologous BMT (n = 89). Patients were randomized to receive (n = 70) or not receive (n = 70) oral PTX, 1,600 mg/d in four divided doses from day -8 until day + 100 post-BMT. The incidence of mucositis requiring morphine sulfate (MSO4) was similar in both groups (42.9%), with the mean number of days with MSO4 being 7.8 (SD = 3.4) in the PTX group versus 8.2 (SD = 3.4) in the control group (NS). The incidence of renal insufficiency was not affected by PTX administration (15.7% in the PTX group v 21.4% in the control group [NS]) and the highest serum creatinine value during the first 100 days post-BMT was 119 mumol/L (SD = 82.4) in the PTX group versus 103.9 mumol/L (SD = 57) in the control group (NS). The incidence of grade > or = 2 graft-versus-host disease was similar in each group (11/25 [44%] in the PTX group v 12/26 [46%] in the control group). No significant difference was observed in hematologic toxicity, transfusion requirements, duration of fever, and hepatic toxicity between the treatment groups. In conclusion, our study failed to show a prophylactic effect of PTX in transplant-related toxicities after BMT. On the basis of these findings, we cannot recommend that PTX be part of early mortality and morbidity prevention programs after BMT.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.