Photocyclization reaction and related photodynamics in the photoproducts of a tetraphenylethylene derivative with bulky substituents: unexpected solvent viscosity effect.

Tetraphenylethylene (TPE) derivatives are ones of the most versatile building blocks showing aggregation-induced emission (AIE). However, their applications are limited by the photophysical and photochemical processes that occur in their excited state. Herein, we report a detailed study of the photochemical behaviour of a new TPE derivative with bulky terphenyl groups (TTECOOBu) in solvents of different viscosities and in a PMMA film. UV light irradiation shows an efficient photocyclization reaction, which produces a 9,10-diphenylphenanthrene (DPP) derivative photoproduct. The emission spectra of the irradiated samples show intermediate (∼420 nm) and final (∼380 nm) species. The photocyclization events are more efficient in environments of higher viscosities or rigidity. We show that in a photoirradiated PMMA film containing TTECOOBu, it is possible to etch a message for more than 1 year. The kinetics is dictated by the motions of the phenyl rings and is faster when their motions are precluded or inhibited. We also elucidated the femto- to millisecond photodynamics of the intermediate and final photoproducts and provide a full picture of their relaxation, with the latter in ∼1 ns at S1 and ∼1 µs at T1. We also demonstrate that the kinetics of the bulky TTECOOBu is much slower than that of the TPE core. Our results also show that both photoevents are not reversible contrary to the case of TPE kinetics. We believe that these results will shed more light on the photochemical behaviour of TPE derivatives and should help in the development of novel TPE-based materials with improved photostability and photo-properties.

Deciphering the ultrafast dynamics of a new tetraphenylethylene derivative in solutions: charge separation, phenyl ring rotation and CC bond twisting.

Tetraphenylethylene (TPE) derivatives are one of the fundamental units for developing aggregation induced emission (AIE) scaffolds. However, the underlying mechanisms implicated in the relaxation of the excited TPE remain a topic of ongoing discussion, while the effect of bulky substituents on its photobehaviour is still under scrutiny. Here, we report a detailed study of the photophysical properties of a new symmetrical and bulky TPE derivative with terphenyl groups (TTECOOBu) in solvents of different polarities and viscosities. Using femto- to nanosecond (fs-ns) time-resolved absorption and emission techniques, we elucidated the role of the phenyl group rotations and core ethylene bond twisting in its behaviour. We demonstrate that TTECOOBu in DCM solutions undergoes a 600 fs charge separation along the ethylene bond leading to a resonance structure with a lifetime of ∼1 ns. The latter relaxes via two consecutive events: a twisting of the ethylene bond (∼ 9 ps) and a rotation of the phenyl rings (∼ 30 ps) leading to conformationally-relaxed species with a largely Stokes-shifted emission (∼ 12 500 cm-1). The formation of the red-emitting species clearly depends on the solvent viscosity and rigidity of the medium. Contrary to the photobehavior in the highly viscous triacetin or rigid polymer matrix of PMMA, a reversible mechanism was observed in DCM and DMF solutions. These results provide new findings on the ultrafast mechanisms of excited TPE derivatives and should help in the development of new molecular rotors with interesting AIE properties for photonic applications.

Phenyltrimethylammonium Salts as Methylation Reagents in the Nickel-Catalyzed Methylation of C-H Bonds.

Methylation of C(sp(2))-H bonds was achieved through the Ni(II)-catalyzed reaction of benzamides with phenyltrimethylammonium bromide or iodide as the source of the methyl group. The reaction has a broad scope and shows high functional-group compatibility. The reaction is also applicable to the methylation of C(sp(3))-H bonds in aliphatic amides.

Evaluating middle cerebral artery atherosclerotic lesions in acute ischemic stroke using magnetic resonance T1-weighted 3-dimensional vessel wall imaging.

BACKGROUND: Atherosclerotic lesions in intracranial arteries are a leading cause of ischemic stroke. Magnetic resonance angiography (MRA) is often used to assess atherosclerotic changes by detecting luminal narrowing, whereas it cannot directly visualize atherosclerotic lesions. Here, we used a 3-dimensional vessel wall imaging (3D-VWI) technique to evaluate intracranial arterial wall changes in acute stroke. METHODS: Eighteen consecutive patients with acute noncardioembolic stroke in the middle cerebral artery (MCA) territory who were prospectively examined with a 1.5-T magnetic resonance scanner were studied. T1-weighted (T1-W) 3D-VWI was obtained using a flow-sensitized 3D fast-spin echo technique. Wall thickening of MCA that suggests atherosclerotic plaques was visually evaluated and the contrast ratio (CR) of signal intensity of the lesions to that of the corpus callosum was calculated and compared with stenotic changes by MRA. RESULTS: Wall thickenings of the MCA ipsilateral and contralateral to the lesion were observed in almost all patients on 3D-VWI (94.4% and 94.4%, respectively), whereas MRA showed stenotic changes of 50% only in 1 patient (5.9%; P < .001). The CR of the thickened wall in the ipsilateral MCA was significantly higher than that in the contralateral MCA (median, .53 and .45, respectively; P = .028), suggesting of unstable plaques consisting of hemorrhage or lipid. CONCLUSIONS: The T1-W 3D-VWI can provide direct visualization of atherosclerotic lesions of the intracranial arteries in stroke patients, and it can detect signal change suggestive of unstable plaque.

Amino acid residues of both the extracellular and transmembrane domains influence binding of the antiparasitic agent milbemycin to Haemonchus contortus AVR-14B glutamate-gated chloride channels.

Glutamate-gated chloride (GluCl) channels are pentameric receptors for the inhibitory neurotransmitter glutamate in invertebrates and are a major target for macrolide anthelmintics. Three amino acids in GluCl channels are reported to render macrolide resistance in nematodes and insects. To examine whether these three amino acids are involved in binding of the antiparasitic agent milbemycin (MLM) to the GluCl channels of the nematode parasite Haemonchus contortus, the equivalent amino acids (L256, P316, and G329) of the Hco-AVR-14B subunit were substituted with various amino acids. cDNAs encoding the wild type and mutants of this subunit were transfected into COS-1 cells for transient expression and analysis of GluCl channels. The abilities of these mutant channels to bind [(3)H]MLM A(4) were remarkably decreased when compared with the wild-type channel. In patch clamp analysis, L256F and P316S mutant channels were 37- and 100-fold less sensitive to MLM A(4) when compared with the wild-type channel, respectively. These findings indicate that amino acid changes in the ß10 strand, the M2-M3 linker, and the M3 region influence MLM A(4) binding to the channel. Homology modeling and ligand docking studies suggest the presence of two potential binding sites for MLM A(4).

Quantitative assessment of changes in carotid plaques during cilostazol administration using three-dimensional ultrasonography and non-gated magnetic resonance plaque imaging.

INTRODUCTION: Cilostazol, an antiplatelet agent, is reported to induce the regression of atherosclerotic changes. However, its effects on carotid plaques are unknown. Hence, we quantitatively investigated the changes that occur within carotid plaques during cilostazol administration using three-dimensional (3D) ultrasonography (US) and non-gated magnetic resonance (MR) plaque imaging. METHODS: We prospectively examined 16 consecutive patients with carotid stenosis. 3D-US and T1-weighted MR plaque imaging were performed at baseline and 6 months after initiating cilostazol therapy (200 mg/day). We measured the volume and grayscale median (GSM) of the plaques from 3D-US data. We also calculated the contrast ratio (CR) of the carotid plaque against the adjacent muscle and areas of the intraplaque components: fibrous tissue, lipid, and hemorrhage components. RESULTS: The plaque volume on US decreased significantly (median at baseline and 6 months, 0.23 and 0.21 cm(3), respectively; p = 0.03). In the group exhibiting a plaque volume reduction of more than 10%, GSM on US increased significantly (24.8 and 71.5, respectively; p = 0.04) and CR on MRI decreased significantly (1.13 and 1.04, respectively; p = 0.02). In this group, in addition, the percent area of the fibrous component on MRI increased significantly (68.6% and 79.4%, respectively; p = 0.02), while those of the lipid and hemorrhagic components decreased (24.9% and 20.5%, respectively; p = 0.12) (1.0% and 0.0%, respectively; p = 0.04). There were no substantial changes in intraplaque characteristics in either US or MRI in the other group. CONCLUSIONS: 3D-US and MR plaque imaging can quantitatively detect changes in the size and composition of carotid plaques during cilostazol therapy.

Carotid plaque signal differences among four kinds of T1-weighted magnetic resonance imaging techniques: a histopathological correlation study.

INTRODUCTION: Several magnetic resonance (MR) imaging techniques are used to examine atherosclerotic plaque of carotid arteries; however, the best technique for visualizing intraplaque characteristics has yet to be determined. Here, we directly compared four kinds of T1-weighted (T1W) imaging techniques with pathological findings in patients with carotid stenosis. METHODS: A total of 31 patients who were candidates for carotid endarterectomy were prospectively examined using a 1.5-T MRI scanner, which produced four kinds of T1W images, including non-gated spin echo (SE), cardiac-gated black-blood (BB) fast-SE (FSE), magnetization-prepared rapid acquisition with gradient echo (MPRAGE), and source image of three-dimensional time-of-flight MR angiography (SI-MRA). The signal intensity of the carotid plaque was manually measured, and the contrast ratio (CR) against the adjacent muscle was calculated. CRs from the four imaging techniques were compared to each other and correlated with histopathological specimens. RESULTS: CRs of the carotid plaques mainly containing fibrous tissue, lipid/necrosis, and hemorrhage were significantly different with little overlaps (range: 0.92-1.15, 1.22-1.52, and 1.55-2.30, respectively) on non-gated SE. However, BB-FSE showed remarkable overlaps among the three groups (0.89-1.10, 1.07-1.23, and 1.01-1.42, respectively). MPRAGE could discriminate fibrous plaques from hemorrhagic plaques but not from lipid/necrosis-rich plaques: (0.77-1.07, 1.45-2.43, and 0.85-1.42, respectively). SI-MRA showed the same tendencies (1.01-1.39, 1.45-2.57, and 1.12-1.39, respectively). CONCLUSION: Among T1W MR imaging techniques, non-gated SE images can more accurately characterize intraplaque components in patients who underwent CEA when compared with cardiac-gated BB-FSE, MPRAGE, and SI-MRA images.

Diffusion anisotropy color-coded map of cerebral white matter: quantitative comparison between orthogonal anisotropic diffusion-weighted imaging and diffusion tensor imaging.

BACKGROUND AND PURPOSE: Diffusion anisotropy color-coded maps of cerebral white matter can be generated from orthogonal anisotropic diffusion-weighted imaging (DWI) using the three-dimensional anisotropy contrast (3DAC) technique, but its precision has not been fully validated. Hence, we attempted to determine whether 3DAC is comparable to a diffusion tensor imaging (DTI) color map. METHODS: We examined 15 healthy individuals and generated color-coded maps using 3DAC as well as using primary eigenvector (e1) and fractional anisotropy (FA) from identical DTI datasets. The difference in the direction of the 3DAC vector from e1 (θ) in cerebral white matter was evaluated. Correlations between θ and FA or obliqueness of e1 were also examined. RESULTS: In cerebral white matter, θ had significantly negative and positive correlations with FA values and e1 obliqueness, respectively. Among white matter tracts, the pyramidal tract, cingulum, and corpus callosum, which had significantly high FA and/or low obliqueness, exhibited similar coloration and significantly smaller θ (4.4° ± 1.6°, 9.3° ± 2.8°, and 11.2° ± 1.1°, respectively) than the entire white matter (13.9° ± 1.1°). CONCLUSIONS: The 3DAC could visualize directional information of white matter tracts as precisely DTI-based color maps did, particularly when FA was large and/or e1 directions were orthogonal.

High-resolution diffusion tensor imaging for the detection of diffusion abnormalities in the trigeminal nerves of patients with trigeminal neuralgia caused by neurovascular compression.

PURPOSE: To detect diffusion abnormalities in the trigeminal nerves of patients with trigeminal neuralgia (TN) caused by neurovascular compression (NVC) by using a high-resolution diffusion tensor imaging (HR-DTI) technique. METHODS: Thirteen patients with TN and 14 healthy controls underwent HR-DTI scanning. After extracting the trigeminal nerve using a tractography technique, we measured the fractional anisotropy (FA) and apparent diffusion coefficient (ADC), and compared the contralateral ratios (CR) of these parameters between the patients and controls, and correlated these ratios with the cross-sectional areas of the nerves. RESULTS: The CRs of the FA values for the trigeminal nerves of the patients (1.00±0.15) had significantly higher variance than those of healthy controls (1.00±0.05) (P<.05) and showed a positive correlation with the cross-sectional area of the nerves (r=0.81). In contrast, the CRs of the ADC values were not significantly different between the two groups (1.02±0.10 and 1.01±0.08, respectively) and had no significant correlation with cross-sectional area. CONCLUSION: HR-DTI can detect an alteration in the relative FA values of affected trigeminal nerves and a correlation with atrophic changes in patients with NVC-induced TN.