Corrole-silica hybrid particles: synthesis and effects on singlet oxygen generation

The present study describes the first example of hybrid particles composed of amorphous silica and corrole. The hybrid particles were obtained by covalent linking of the gallium(III)(pyridine) complex of 5,10,15-tris(pentafluorophenyl) corrole (GaPFC) at the surface of functionalized silica spheres. The functionalization step was achieved by a nucleophilic substitution reaction between corrole and 3-aminopropyltriethoxysilane previously grafted at the silica surfaces. The hybrids were morphologically and chemically characterized and the results have confirmed covalent linkages between corrole molecules and the silica particles. Preliminary studies on the capacity of corrole and hybrid particles to generate singlet oxygen was evaluated by a chemical method in which 1,3-diphenylisobenzofuran was used to trap singlet oxygen. The new corrole-silica hybrid particles have shown lower efficiency to generate singlet oxygen as compared to the pure corrole precursor. This effect was interpreted as a consequence of interparticle interactions mediated by the corrole molecules grafted at the silica surfaces that result in their clustering. Taken together, these findings demonstrate that despite lower efficiency in terms of singlet oxygen generation, the hybrid materials offer an alternative route to develop new platforms with potential for photodynamic therapy

Protective action of spermine and spermidine against photoinhibition of photosystem I in isolated thylakoid membranes

10.1371/journal.pone.0112893PLoS ONE911e11289

Protective Action of Spermine and Spermidine against Photoinhibition of Photosystem I in Isolated Thylakoid Membranes

<div><p>The photo-stability of photosystem I (PSI) is of high importance for the photosynthetic processes. For this reason, we studied the protective action of two biogenic polyamines (PAs) spermine (Spm) and spermidine (Spd) on PSI activity in isolated thylakoid membranes subjected to photoinhibition. Our results show that pre-loading thylakoid membranes with Spm and Spd reduced considerably the inhibition of O₂ uptake rates, P700 photooxidation and the accumulation of superoxide anions (O₂⁻) induced by light stress. Spm seems to be more effective than Spd in preserving PSI photo-stability. The correlation of the extent of PSI protection, photosystem II (PSII) inhibition and O₂⁻ generation with increasing Spm doses revealed that PSI photo-protection is assumed by two mechanisms depending on the PAs concentration. Given their antioxidant character, PAs scavenge directly the O₂⁻ generated in thylakoid membranes at physiological concentration (1 mM). However, for non-physiological concentration, the ability of PAs to protect PSI is due to their inhibitory effect on PSII electron transfer.</p></div

P700 photooxidation in thylakoid membranes after 30 min of photoinhibition.

<p>(A) Original traces of the Far-Red light-induced P700 photooxidation monitored as absorbance changes at 820 nm in the samples of thylakoid membranes either control (Ctrl) or photoinhibited for 30 min (PI) in the absence of PAs. PI+Spm and PI+Spd curves represent respectively, the absorbance changes at 820 nm in thylakoid membranes photoinhibited in presence of 1 mM Spm or Spd. The arrow indicates the switching on of Far-Red light (78 µmol m⁻²s⁻¹). Each trace is the average of six measurements. (B) Variation of the amount of photooxidizable P700 (ΔA 820 nm) in the thylakoid membranes either control (Ctrl) or photoinhibited for 30 min (PI+0) in the absence of PAs. PI+1, PI+2, PI+3, PI+5 and PI+7 represent the percentage of photooxidizable P700 in photoinhibited samples in presence of varying concentrations (1–7 mM) of Spm and Spd. Each value is the average of six measurements.</p

NBT photo-reduction in the absence or in presence of Spm and Spd.

<p>The changes in the optical density at 560 nm following NBT photo-reduction in thylakoid membranes preparation subjected to photoinhibition in the absence or presence of 1 mM Spm or Spd as a function of time.</p

Photo-protection of PSI activity by DCMU.

<p>The measurement of O₂ uptake rates in thylakoid membranes treated with 1 mM DCMU and exposed to photoinhibition for 180 minutes. The results are expressed as normalized values of O₂ uptake rates.</p

Changes in the O₂ uptake rates in thylakoid membranes during 30 min of photoinhibition (A) in the absence (Ctrl) or presence of 1 or 2 mM Spm.

<p>Inset: percentage of photoinhibition in presence of 1 and 2 mM of Spm in thylakoid membranes, from the experiment of Fig. 1A. (B) Comparison of the effect of increasing the Spm and Spd concentration on O₂ uptake rates in thylakoid membranes after 30 min of illumination. Control rate in the dark (Fig. 1A) was 525 µmol O₂ mg Chl⁻¹ h⁻¹, and the results are a mean of 9 assays.</p

Correlation of the PSI protection, PSII inhibition and NBT photo-reduction in presence of Spd.

<p>(A) Effect of increasing Spd doses on (i) inhibition of PSII in control thylakoid membranes (in dark) and (ii) protection of PSI activity after 30 min photoinhibition, expressed as percentage of P700 photooxidation and O₂ uptake obtained from the experiments of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112893#pone-0112893-g001" target="_blank">Fig. 1B</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112893#pone-0112893-g002" target="_blank">Fig. 2B</a>, and calculated using the following formula: Were PI+Spd is the photoinhibited sample in presence of Spd, PI is the photoinhibited samples and Ctrl is the control. (B) The variation of the initial rate of NBT photo-reduction in thylakoid membrane preparations subjected to photoinhibition in the absence or presence of increasing Spd doses. The rates were obtained as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112893#pone-0112893-g003" target="_blank">Fig. 3</a>.</p