Platinum-acetylide-based π-conjugated polymers and oligomers have attracted interest because their photophysics are dominated by long-lived and phosphorescent 3 π,π* excited states. 1,2 This characteristic leads to materials that may be used to fabricate highefficiency organic electroluminescent devices, 3 and for applications in laser protection. 4 Considerable insight concerning excited-state structure and delocalization in organic π-conjugated systems has been acquired through the study of monodisperse oligomers. 5 Comparatively less information is available concerning the effect of delocalization on 3 π,π* states in conjugated systems, because these states are spectroscopically "silent" due to the forbidden character of the S 0 T T 1 transitions.Herein we report the preparation and photophysical characterization of the series of linear Pt-acetylide oligomers (PAOs) shown in Scheme 1. PAOs with n > 2 luminesce from the 1 π,π* and 3 π,π* manifolds of the Pt-acetylide π-conjugated system, which allows us to probe in detail the effect of oligomer length on the spectroscopy, energetics, and dynamics of the long-lived excited states.PAOs are synthesized by an iterative-convergent approach that relies on the use of Pt-acetylide building blocks in which terminal acetylenes are protected using the trimethylsilyl protecting group. 5 Complete details of the synthesis and spectral characterization of the PAOs are available as Supporting Information.Absorption spectra of the PAOs (Figure 1a) exhibit three wellresolved bands. The spectra are dominated by an intense band (I) arising from the long-axis polarized π,π* transition. The maximum of band I red-shifts with increasing PAO length (Table 1), but the difference in λ max between Pt-5 and Pt-7 is small, indicating that the effective conjugation length as probed by the Franck-Condon absorption event is ∼6 repeat units. The width of band I also increases with PAO length, possibly signaling the existence of conformers that differ with respect to the relative orientations of the chromophoric units (i.e., the phenylene rings and the plane defined by the PtP 2 R 2 units) along the chain. Band broadening may occur because the number of different conformers increases with PAO length. Two other absorption bands (II and III) are resolved at shorter wavelengths. The intensity of these bands increases with PAO length, but their absorption maxima do not vary systematically. This observation is consistent with the notion that the high-energy bands arise from short-axis polarized transitions localized on the phenylene rings. Importantly, the spectra of the longer PAOs are very similar to the absorption of the analogous Pt-acetylide polymer, 1a,b which indicates that the oligomers are effective models for the excited-state properties of the corresponding polymer. Figure 1b illustrates the photoluminescence spectra of the series of PAOs Pt-2-Pt-7 obtained in degassed THF solutions. (At room temperature, Pt-1 is a nonemissive compound.) Each of the PAOs exhibits a very weak fluorescence b...
This study assessed the patterns of functional and structural connectivity abnormalities in patients with Parkinson's disease with freezing of gait (PD FOG+) compared with those without freezing (PD FOG-) and healthy controls (HCs). Resting state functional MRI (rs-fMRI) and diffusion tensor imaging (DTI) scans were obtained from 14 PD FOG+, 16 PD FOG- and 16HCs. Between-group difference in pedunculopontine nucleus (PPN) functional connectivity (FC) was performed to assess FC dysfunction. Tract-based spatial statistics (TBSS) was applied to compare white matter (WM) impairment across the whole brain between groups. PD FOG+ patients exhibited abnormal PPN FC, compared with HCs and with PD FOG-, mainly in the corticopontine-cerebellar pathways (in the bilateral cerebellum and in the pons), as well as the visual temporal areas (in the right middle temporal gyrus and in the right inferior temporal gyrus). Moreover, PD FOG+ patients, showed more pronounced WM abnormalities, relative to controls, including the interhemispheric connections of corpus callosum, the cortico-cortical WM tracts of the cingulum, the superior longitudinal fasciculus and inferior fronto-occipital fasciculus, the corticofugal tract (cerebral peduncles, internal capsule, corona radiata), as well as tracts connecting the thalamus (thalamic radiation). This study suggests that FOG in PD is associated with abnormal PPN FC network, mainly affecting the corticopontine-cerebellar pathways as well as visual temporal areas involved in visual processing, and with diffuse WM deficits extending to motor, sensory and cognitive regions. Combining rs-fMRI and DTI method, our study should advance the understanding of neural mechanisms underlying FOG in PD.
Astragaloside IV (AGS-IV), a new glycoside of cycloartane-type triterpene isolated from the root of Astragalus membranaceus (Fisch.) Bunge, has been used experimentally for its potent immune-stimulating, anti-inflammatory, and antioxidative actions. A recent study has shown AGS-IV to be an aldose-reductase inhibitor and a free-radical scavenger. This study examined the effects of AGS-IV on motor nerve conduction velocity (MNCV), tailflick threshold temperature, biochemical indexes, and the histology of the sural nerve after diabetes was induced in rats with 75 mg/kg streptozotocin (STZ). AGS-IV (3, 6, 12 mg/kg, twice a day) was administered by oral gavage for 12 weeks after diabetes was induced. Compared with control (nondiabetic) rats, obvious changes in physiological behaviors and a significant reduction in sciatic MNCV in diabetic rats were observed after 12 weeks of STZ administration. Morphological analysis showed that AGS-IV suppressed a decrease in myelinated fiber area, an increase in myelinated fiber density, and an increase in segmental demyelination in diabetic rats. The protective mechanism of AGS-IV involved a decrease in declining blood glucose concentration and HbA1C levels, and an increase in plasma insulin levels. AGS-IV increased the activity of glutathione peroxidase in nerves, depressed the activation of aldose reductase in erythrocytes, and decreased the accumulation of advanced glycation end products in both nerves and erythrocytes. Moreover, AGS-IV elevated Na+,K+-ATPase activity in both the nerves and erythrocytes of diabetic rats. These results indicate that AGS-IV exerts protective effects against the progression of peripheral neuropathy in STZ-induced diabetes in rats through several interrelated mechanisms.
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