A novel amphiphilic aggregation-induced emission (AIE) copolymer, that is, poly(NIPAM-co-TPE-SP), consisting of N-isopropylacrylamide (NIPAM) as a hydrophilic unit and a tetraphenylethylene-spiropyran monomer (TPE-SP) as a bifluorophoric unit is reported. Upon UV exposure, the close form of non-emissive spiropyran (SP) in poly(NIPAM-co-TPE-SP) can be photo-switched to the open form of emissive merocyanine (MC) in poly(NIPAM-co-TPE-MC) in an aqueous solution, leading to ratiometric fluorescence of AIEgens between green TPE and red MC emissions at 517 and 627 nm, respectively, via Förster resonance energy transfer (FRET). Distinct FRET processes of poly(NIPAM-co-TPE-MC) can be observed under various UV and visible light irradiations, acid-base conditions, thermal treatments, and cyanide ion interactions, which are also confirmed by theoretical studies. The subtle perturbations of environmental factors, such as UV exposure, pH value, temperature, and cyanide ion, can be detected in aqueous media by distinct ratiometric fluorescence changes of the FRET behavior in the amphiphilic poly(NIPAM-co-TPE-MC). Moreover, the first FRET sensor polymer poly(NIPAM-co-TPE-MC) based on dual AIEgens of TPE and MC units is developed to show a very high selectivity and sensitivity with a low detection limit (LOD = 0.26 μM) toward the cyanide ion in water, which only contain an approximately 1% molar ratio of the bifluorophoric content and can be utilized in cellular bioimaging applications for cyanide detections.
Several 2-substituted and 2,5-disubstituted piperazine-3,6-diones were synthesized starting from readily available alpha-amino acids. After activation of a lactam carbonyl via introduction of a methoxycarbonyl group onto nitrogen, this carbonyl was selectively reduced. Treatment of the resulting urethane with protic acid generated the corresponding N-acyliminium ion, which was trapped by a nucleophilic C2-side chain to provide 2,6-bridged piperazine-3-ones. Several aromatic, heteroaromatic, and nonaromatic side chains were used as pi-nucleophiles. In addition, the effect of the presence of a C5-methyl group on the stereochemical outcome of the cyclization was examined.
A series of novel photo-switchable [2]rotaxanes (i.e., Rot-A-SP and Rot-B-SP before and after shuttling controlled by acid–base, respectively) containing one spiropyran (SP) unit (as a photochromic stopper) on the axle and two tetraphenylethylene (TPE) units on the macrocycle were synthesized via click reaction. Upon UV/visible light exposure, both mono-fluorophoric rotaxanes Rot-A-SP and Rot-B-SP with the closed form (i.e., non-emissive SP unit) could be transformed into the open form (i.e., red-emissive merocyanine (MC) unit) to acquire their respective bi-fluorophoric Rot-A-MC and Rot-B-MC reversibly. The aggregation-induced emission (AIE) properties of bi-fluorophoric TPE combined with MC AIEgens of these designed rotaxanes and mixtures in semi-aqueous solutions induced interesting ratiometric photoluminescence (PL) and Förster resonance energy transfer (FRET) behaviors, which were further investigated and verified by dynamic light scattering (DLS), X-ray diffraction (XRD), and time-resolved photoluminescence (TRPL) measurements along with theoretical studies. Accordingly, in contrast to the model axle (Axle-MC) and the analogous mixture (Mixture-MC, containing the axle and macrocycle components in a 1:1 molar ratio), more efficient FRET behaviors and stronger red PL emissions were obtained from dual-AIEgens between a blue-emissive TPE donor (PL emission at 468 nm) and a red-emissive MC acceptor (PL emission at 668 nm) in both novel photo-switchable [2]rotaxanes Rot-A-MC and Rot-B-MC under various external modulations, including water content, UV/Vis irradiation, pH value, and temperature. Furthermore, the reversible fluorescent photo-patterning applications of Rot-A-SP in a powder form and a solid film with excellent photochromic and fluorescent behaviors are first investigated in this report.
We have synthesized 50 benzimidazole (BMZ) derivatives with 1,2‐phenylenediamines and aromatic aldehydes under mild oxidation conditions by using inexpensive, nontoxic inorganic salt sodium metabisulfite in a one‐pot condensation reaction and screened their ability to interfere with Zika virus (ZIKV) infection utilizing a cell‐based phenotypic assay. Seven BMZs inhibited an African ZIKV strain with a selectivity index (SI=CC50/EC50) of 9–37. Structure‐activity relationship analysis demonstrated that substitution at the C‐2, N‐1, and C‐5 positions of the BMZ ring were important for anti‐ZIKV activity. The hybrid structure of BMZ and naphthalene rings was a structural feature responsible for the high anti‐ZIKV activity. Importantly, BMZs inhibited ZIKV in human neural stem cells, a physiologically relevant system considering the severe congenital anomalies, like microcephaly, caused by ZIKV infection. Compound 39 displayed the highest antiviral efficacy against the African ZIKV strain in Huh‐7 (SI>37) and neural stem cells (SI=12). Compound 35 possessed the highest activity in Vero cells (SI=115). Together, our data indicate that BMZs derivatives have to be considered for the development of ZIKV therapeutic interventions.
A series of multistimuli-responsive [2]rotaxanes with a naphthalimide-functionalized macrocycle threaded through an axle containing a photochromic spiropyran (SP) or merocyanine (MC) stopper were fabricated and studied for their distinct photophysical properties in semiaqueous solutions. By different combinations of chemical and photochemical switchable stimuli, these [2]rotaxanes could be interconverted between multiple states, including monofluorophoric [2]rotaxanes with the close form of the SP unit, i.e., Rot-H-SP and Rot-SP before and after shuttling upon acid–base controls, respectively, along with their corresponding bifluorophoric [2]rotaxanes possessing the open form of the MC unit, i.e., Rot-H-MC and Rot-MC after UV exposure. Interestingly, the photoinduced electron-transfer (PET) effects appeared between nonemissive SP and aggregation-caused quenching (ACQ) naphthalimide units in [2]rotaxanes Rot-H-SP and Rot-SP, whereas the Förster resonance energy transfer (FRET)/Dexter energy transfer occurred in [2]rotaxanes Rot-H-MC and Rot-MC between green-emissive naphthalimide donor (λem = 528 nm) and red-emissive MC acceptor (λem = 648 nm) moieties after UV exposure. Moreover, the PET as well as FRET/Dexter energy-transfer processes and the speculated molecular arrangements (with/without macrocyclic tilting) of all [2]rotaxanes and related derivatives were verified by time-resolved photoluminescence (TRPL) measurements and theoretical studies. Among all [2]rotaxanes and derivatives, Rot-MC in tetrahydrofuran (THF)/H2O (2:8, v/v) revealed the strongest red MC emission with the most effective FRET process that possessed attractive ratiometric photoluminescence (PL) due to the ideal shortest donor–acceptor distance. Regardless of pH and temperature effects, the highest red MC emissions with the optimum FRET processes of all compounds were maintained at room temperature in near-neutral conditions (i.e., pH = 5–9). Importantly, the red-emissive [2]rotaxane Rot-MC showed high selectivity and sensitivity toward sulfite-ion sensing to recover green donor emission via FRET-OFF behavior owing to the Michael reaction of the MC moiety with the sulfite ion, which had an excellent limit of detection (LOD) value of 0.76 μM to be further utilized for the cellular imaging of sulfite detection in living cells. Accordingly, the novel ratiometric sensor approaches of bifluorophoric [2]rotaxane systems have been well developed in this study as the first rotaxane application of FRET processes toward sulfite detection with higher sensitivities than those of their monofluorophoric analogues. Various LOD values could be evaluated to realize the sulfite-sensing mechanisms of well-designed [2]rotaxane systems by the shuttling of macrocyclic fluorophores along with photoswitchable FRET behaviors via alternative UV–vis exposures.
10The present work investigates the properties and oxidation stabilities of biodiesel derived from catfish oil 11 (B100 CFO) generated by the fish processing plants in Vietnam. The composition and physicochemical 12properties of the B100 CFO were measured, including oxygen content (~11 wt%), viscosity (4.5306 mm 2 13 s -1 ), density (0.8772 g cm -3 ), peroxide value (28.13 mg kg -1 ), heat of combustion (39.18 MJ kg -1 ), and acid 14 number (0.12 mg KOH g -1 ). Methyl oleate (46.44 wt%) was the dominant fatty acid methyl ester. B100 15 CFO was found to have poorer low-temperature quality than most vegetable oil derived biodiesels as 16 determined by its fusion and crystallization properties. Novel modified ASTM D5304 and D2274 tests 17 were employed to study the oxidation process of B100 CFO and the impact of oxidation time on its 18 stability. Under ASTM 5304 test conditions, rapid O 2 consumption by B100 CFO occurred after 8 hours, 19 behavior similar to commercial biodiesel stabilized with antioxidant additives. The influence of oxidation 20 condition and time on the B100 CFO physicochemical properties and low-temperature qualities was also 21 investigated according to ASTM methods. Three oxidation stages were identified in B100 CFO based on 22 the peroxide value change during the modified ASTM D5304 and D2274 tests. B100 CFO was also found 23 have superior oxidation stability in comparison with B100 derived from waste cooking oil. This is the 24 first report on oxidation stability of B100 derived from catfish oil. 25Keywords: biodiesel; fuel oxidative stability; distillate physicochemical properties; catfish oil. 26 27
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