Synthesis and Investigation of Derivatives of 1,8-Naphthalimide with a Red Emission via an Aromatic Nucleophilic Substitution Reaction

1,8-Napthalimides (NIs) have been widely used as fluorescent molecules in biological, chemical, and medical fields because NIs shows high stability and various fluorescence properties under different conditions. However, NIs typically display a fluorescence emission wavelength in the range of 350 – 550 nm which can be notably interfered with by autofluorescence in living cells, significantly limiting their bio-applications. Moreover, low solubility in aqueous media is another major limitation for NIs. In this project, four derivatives of NIs (1–4) have been synthesized via an aromatic nucleophilic substitution reaction and their photophysical properties have been investigated in various media (water, MeOH, MeCN, DMSO, EtOAc, and THF). All of these derivatives (1–4) show a long emission wavelength around 600 nm and high solubility in polar solvents. Particularly molecules (1–4) show the longest emission (624–629 nm) in water and the fluorescence intensity is not significantly varied in the range of pH 4–11. These unique features, long emission wavelength, high solubility, and high stability in difference pH media, will allow these derivative (1–4) to be used as excellent labeling reagents in the biological system.

     

Substituent effects on monoboronic acid sensors for saccharides based on N-phenyl-1,8-naphthalenedicarboximides

In the course of our investigations on new monoboronic acid saccharide sensors with C(0) spacers, a series of probes 1-6 based on 1,8-naphthalenedicarboximide were synthesized. Sensor 1 displays features typical of PET monoboronic acid sensors and shows high selectivity to fructose. Sensor 2 exhibits a novel dual emission and remarkable sensitivity for glucose relative to fructose and galactose through subtle changes in pH. Sensor 3 displays significantly enhanced fluorescence in the presence of galactose at low pH. Although probes 4-6 exhibit unique properties such as high quantum yield (Phi(F) = 0.407) and excellent solubility in water, they did not show significant change in fluorescence intensity in the presence of monosaccharides. The effects of substituent on all six probes lend support to the proposed photoelectrochemical model.     

CrAsH: a biarsenical multi-use affinity probe with low non-specific fluorescence

CrAsH is a tetracysteine-binding probe which has improved properties in terms of signal-to-noise ratio and pH dependence of fluorescence compared to the parent compound.     

Matrix screening of substituted N-aryl-1,8-naphthalimides reveals new dual fluorescent dyes and unusually bright pyridine derivatives

A 3 x 14 matrix of substituted N-aryl-1,8-naphthalimides was synthesized for the evaluation and discovery of dual fluorescence. Because of their unique photophysical properties, these dual fluorescent systems represent an exception to the widely studied TICT (Twisted Internal Charge Transfer) fluorescent dyes or tautomeric benzofluorescein class of two-color dyes. The matrix library was designed to investigate the effects of heterocycles, particularly pi-excessive and pi-deficient systems. Of the 42 compounds surveyed, five displayed well-resolved two-color emission in solvents as nonpolar as hexane. Based on the observed trends in fluorescence lambda(max) and quantum yield, a new model is proposed that predicts LW and SW emission for these systems. In addition, this model provides potential design features for the synthesis of new dual fluorescent species.     

Network images of drainage channels in sea spray icing by MR microscopy

An MR imaging system was developed to visualize brine drainage channels in sea spray icing. Brine pockets trapped in spray-ice matrices during ice growth are structural features of sea spray icing. Brine in the spray ice sample had drained out; therefore, using a suction pump, we filled the air gaps in the drainage channels with dodecane. In the experiments, 0.5-1.0 h was necessary to accumulate signals sufficient to obtain a 3-D micro-image; the image matrix comprised 128(3) voxels (each voxel was 200 microm per side). The MIP view showed that sea spray icing has a developed drainage-channel network structure.     

Thawing of frozen vegetables observed by a small dedicated MRI for food research

The thawing process for boiled and frozen edible vegetables was traced by a dedicated MRI for food research. The MRI system is small, with a 1.0-T static magnetic field, and can be placed in an ordinary research room with a light air conditioner. Images of green soybeans, broad beans, okra, asparagus and taro were measured by the spin-echo method (echo time=7 ms) with 0.1 or 0.2 s and 1 s repetition times. The images appeared along with the thawing time, and signals uniformly covered the sliced plane of the samples in the thawed condition. Information about the thawing process and tissue structures of the materials was obtained during transit thawing conditions. The thawing kinetics were examined with increased signal intensity, which were divided into two types. The signal increased linearly and saturated for okra and asparagus but exhibited convex curves for soybeans, broad beans and taro. The small MRI was stable, its handling was simple, and the internal structures of food materials could be accurately identified, although the grey-scale of the images was insufficient for determining precise textural fluctuations of tissue organization. We conclude that the devised MRI is useful for examining the quality of frozen foods and for developmental research into frozen foods.     

A new N-imidazolyl-1,8-naphthalimide based fluorescence sensor for fluoride detection

A chemosensor is reported with high sensitivity and selectivity for detection of fluoride anion. The recognition mechanism is attributed to a fluoride-triggered disruption of the hydrogen bond between imidazole and naphthalimide moieties, resulting in a noncoplanar geometry with low fluorescence.     

Development of a 1.0 T MR microscope using a Nd-Fe-B permanent magnet

A compact 1.0 T MR microscope was developed using a permanent magnet made of high performance Nd-Fe-B magnetic material and a compact MRI console (54 cm (W) x 77 cm (H) x 60 cm (D), 80 kg weight). Since the magnetic field of the permanent magnet had a large temperature coefficient (-1200 ppm/deg), an internal NMR locking technique was developed for the imaging sequences. The performance of the system was evaluated using several biological specimens. As a result, good SNR 3D images at (50 microm)(3)-(200 microm)(3) voxel dimensions were obtained in practical imaging times (0.5-7.5 hours). Thus we have concluded that the permanent-magnet compact MR microscope has great promise as a research or analytical tool.     

Monoboronic acid sensor that displays anomalous fluorescence sensitivity to glucose

[reaction: see text]. A monoboronic acid fluorescent sensor was conveniently synthesized from 3-nitronaphthalic anhydride and 3-aminophenylboronic acid. This novel saccharide probe exhibits dual emission suitable for ratiometric sensing and displays a remarkable sensitivity for glucose relative to fructose and galactose.