Modification-Free Fabricating Ratiometric Nanoprobe Based on Dual-Emissive Carbon Dots for Nitrite Determination in Food Samples

Great challenges still exist for facilely fabricating ratiometric fluorescent nanoprobes. Fortunately, the appearance of dual-emissive carbon dots (CDs) offers a glimmer of hope for the fabrication of modification-free ratiometric nanoprobe. The chemical and electronic structure characteristics of the dual-emissive CDs might be modulated by conjugated structures of carbon sources and the doped nitrogen and sulfur atoms, and the surface state also contributed to the fluorescence properties via surface functional groups. Herein, we report a one-pot strategy for simultaneous preparation of two kinds of CDs named RYDE CDs and RODE CDs, showing dual-emissive fluorescent peaks with long wavelength by 2,3-diaminobenzoic acid hydrochloride for the first time. Notably, trace nitrite determination with high sensitivity and selectivity was realized for the first time based on the modification-free ratiometric fluorescent nanoprobe fabricated rapidly and directly by the as-prepared RYDE CDs at constant room temperature (20 °C). Under the optimal conditions, the limit of detection for nitrite was 31.61 nM, with a wide concentration linear range of 0.1-100 μM. Furthermore, this ratiometric nanoprobe was successfully applied for nitrite analysis in bacon, sausage, pickle, and milk samples. Additionally, the nanoprobe was also capable of visually monitoring temperature fluctuations and cell imaging.

Gelation behaviour of a bent-core dihydrazide derivative: effect of incubation temperature in chloroform and toluene

In this work, a new kind of gelator, 1,3-bis[(3,4-dioctyloxy phenyl) hydrazide]phenylene (BP8-C), containing two dihydrazide units as the rigid bent-core, has been synthesized and investigated. It was demonstrated that BP8-C is an efficient gelator which can gel various organic solvents, such as ethanol, benzene, toluene, chloroform, etc. Both an opaque gel (O-gel) and a transparent gel (T-gel), which is more stable, were obtained with BP8-C in chloroform at different incubation temperatures. Kinetic data based on fluorescence spectra revealed that the T-gels showed a larger Avrami parameter (n = 1.44 at 20 °C) than that of the O-gels (n = 1.21 for gelation at temperatures below 0 °C). While BP8-C did form the opaque gel in toluene, gelation took longer at lower incubation temperatures and even precipitated out below 0 °C. The kinetic Avrami analysis on sols of BP8-C with different concentrations shows a two-phrase mechanism, i.e. the n values are between 0.88 and 1.74 followed by 1.69 and 3.01 throughout the temperature range of 5 °C and 35 °C for 5.34 mg mL(-1) BP8-C in toluene, indicating that the fibers formed first and then bundled to produce compact networks. We propose that supersaturation governs the formation of gel in chloroform and that the diffusion process denominates gelation in toluene. XRD and FT-IR measurements confirmed that the xerogels prepared at different temperatures in different solvents exhibited a Col(h) structure and that there are three molecules in one columnar slice. Our results indicate that the gelation process, morphology of the gels and thus the final properties of the gels depend strongly on the preparation conditions such as temperature, solvent, concentration, etc.

Controlled self-assembly of helical nano-ribbons formed by achiral amphiphiles

Helical nano-ribbons with a large aspect ratio were obtained through the self-assembly of an achiral amphiphile. The symmetry breaking is attributed to the orderly but twisted stacking of terpyridine groups. In addition, the morphology of the assemblies can be tuned by the coordination between terpyridine and Zn(2+) ion.

Photoresponsive structure transformation and emission enhancement based on a tapered azobenzene gelator

Due to trans-to-cis photoisomerization of azobenzene unit, an enhanced fluorescence via J-aggregate molecular arrangement can be observed.

Ultrasound-induced controllable morphology and growth dimension in a dihydrazide-based self-assembly system

We have demonstrated ultrasound-induced organogels based on twin-tapered dihydrazide derivatives, oxalyl acid N,N-di(3,4,5-trialkoxybenzoyl)hydrazide (FH-Tn). Ultrasound irradiation has been proved to influence gel properties at micro-levels. Different self-assembled structures from entangled fibers to tube-like structures and nanoparticles can be easily manipulated by tuning irradiation time and water bath temperature. FT-IR spectra exhibit weakened hydrogen bonding interactions, and XRD studies showed different packing modes before and after sonication. In addition, ultrasound can have effects on gel properties at macro-levels. Gels obtained from ultrasound treatment possess different wetting properties, relatively worse rheological properties and thermo-stability. Kinetic studies based on dynamic fluorescence spectra, rheological studies and theoretical calculations suggest that molecular aggregation mode differed from one-dimension to two-dimension for the gel after sonication.

Solvent-induced helix superstructure in achiral dumbbell-shaped hydrazine derivatives

We studied hydrogen-bonding assemblies in a series of dumbbell-shaped hydrazine derivatives, namely oxalyl N',N'-bis(3,4-dialkoxybenzoyl)-hydrazide (BFH-n, n = 4, 6, 8, 10) and oxalyl N',N'-dibenzoyl-hydrazide (FH-0). It has been demonstrated that NH-1 protons of BFH-n precipitated from tetrahydrofuran (THF) or dimethylformamide (DMF) were involved in intramolecular H-bonding to form 6-membered rings. Meanwhile, NH-2 protons of BFH-n precipitated from THF formed intermolecular hydrogen bonds with C═O groups of neighboring molecules, while NH-2 protons of BFH-n precipitated from DMF formed intermolecular hydrogen bonds with C═O group of neighboring DMF molecules. C═O, -CH(3), and -CH groups of DMF molecules participated in multiple intermolecular hydrogen bonds with the -N-H and -C═O groups of FH-0 molecules in single-crystals formed in DMF, leading to a double helix morphology with a pitch of 24.2 Å along the c direction. Both left- and right-handed helical micrometer-length ribbons with nonuniform helical pitches were observed in an achiral BFH-10 xerogel precipitated from DMF.

Fluorescence-enhanced organogels and mesomorphic superstructure based on hydrazine derivatives

New low-molecular-mass organic gelators (LMOGs) bearing hydrazine linkage and end-capped by phenyl, namely 1,4-bis[(3,4-bisalkoxyphenyl)hydrozide]phenylene (BPH-n, n = 4, 6, 8, 10), were designed and synthesized. These organogelators have shown great ability to gel a variety of organic solvents to form stable organogels with the critical gelation concentration as low as 8.7 x 10(-4) mol L(-1) (0.06 wt %). The formed gel has a high gel-sol transition temperature (T(gel)) at low gelation concentration. Aggregation-induced emission (AIE) has been observed after gelation though conventional chromophore units not incorporated in BPH-n. The fluorescence quantum yields of xerogel are 2 orders higher than that of dilute solution. In addition, the BPH-n (n = 6, 8, 10) exhibited thermotropic hexagonal column (Col(h)) mesophase, which are stable at room temperature as revealed by differential scanning calorimetry (DSC), polarized optical microscopy (POM), and X-ray diffraction (XRD) studies.