C. Geng, J. Zhan, X. Hao et al.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 264 (2022) 120271
activities. The disorder of mitochondrial function will lead to the
change of mitochondrial matrix composition, resulting to the
change of its viscosity [10–15]. Therefore, it is crucial to develop
an effective strategy for monitoring the mitochondrial viscosity
to better understand various physiological activities and functions
in cells.
2.2. Synthesis of the trans-form of HVM and IVM
HVM ((E)-4-(4-(dimethylamino)styryl)-1-ethylquinolin-1-ium
iodide) and IVM ((E)-4-(4-(diphenylamino)styryl)-1-ethylquino
lin-1-ium iodide) were synthesized according to the methods used
in previous studies [37,38]. Compounds 1 (296 mg, 1 mmol), 4-
The current intracellular viscosity senser is still a hot point in
academic student, particularly in biochemical field. Several tradi-
tional analytical methods are developed to detect viscosity, such
as chemiluminescence, capillary electrophoresis, spectrophotome-
try, and electrochemical. However, the above methods cannot be
applied for viscosity measurement of biological systems in situ
although they have wally universality for macro fluid detection.
Till now, small-molecule fluorescent probes transmute the main-
stream tool for detecting the viscosity in biological and pathology
due to their high sensitivity, nondestructive detection, real-time
imaging, and so on [16–21]. Additionally, near-infrared (NIR) fluo-
rescent dyes are becoming effective means to monitor the level of
biological indicators in cells and organisms due to its low back-
ground, high penetration depth and other advantages [22–27].
Recently, several fluorescent probes for monitoring endocellular
viscosity changes have been reported (Table S3, ESI) [28–34].
Undeniably, most of them have excellent optical and biological
properties but complex structure and difficult to be synthesized
[35,36]. Therefore, a new simple and easy-to-do design idea of
red emitting fluorescent probe is proposed in this paper, which
seems to be a decent point.
We herein synthesized a new near-infrared fluorescent probe
(HVM) by using 4-Dimethylaminobenzaldehyde and modified
quinoline as a donor and an acceptor respectively, to distinguish
normal and inflammatory models by viscosity variation with min-
imal background fluorescence and immense response multiples
(Scheme 1). HVM hold an emission maximum at 670 nm and large
stokes shift (160 nm). In addition, the biological imaging experi-
ments result confirmed the ability of HVM was not only possesses
mitochondrial targeting capability, but also has excellent mem-
brane permeability, and can high-speed enter mitochondria in a
short space of time. Thus, by way of the probe HVM, detected vis-
cosity anomalous in living cells, zebrafish and mice, based on the
low background fluorescence, good biocompatibility and high sen-
sitivity of the probe. Besides, the probe HVM constructed in this
work was potential to portray the curve of micro viscosity config-
uration in vivo.
Dimethylaminobenzaldehyde (149 mg, 1 mmol) or 4-(N, N-
Diphenylamino) benzaldehyde (273 mg, 1 mmol) were dissolved
in 8 mL alcohol with two drops of piperidine. The mixture was kept
stirring vigorously for 12 h at ambient temperature, and then the
solvent of the reaction mixture was removed under pressure. The
crude product was purified by silica column chromatography to
obtain the desired product.
HVM (258 mg, yield 60%). 1H NMR (500 MHz, DMSO d6) d 9.17
(d, J = 5.9 Hz, 1H), 9.02 (d, J = 8.1 Hz, 1H), 8.43(d, J = 8.5 Hz, 1H),8.36
(d, J = 5.9 Hz, 2H), 8.20–8.16 (m, 2H), 8.04–7.92 (m, 2H), 7.86(d,
J = 7.9 Hz, 2H), 6.80 (d, J = 7.9 Hz, 2H), 4.92 (d, J = 6.5 Hz, 3H),
3.06(s, 6H), 13C NMR (126 MHz, DMSO d6) d 153.69, 146.26,
145.32, 138.10, 135.20, 131.86, 129.00, 127.20, 126.55, 123.5,
119.17, 114.76, 113.57, 112.33, 51.86, 40.57, 40.54, 40.37, 40.20,
40.03. HRMS(m/z): [M]+ calcd for C21H23N+2:303.1861; found,
303.1857.
IVM (221 mg, yield 40%). 1H NMR (500 MHz, DMSO d6) d 9.32(d,
J = 6.6 Hz, 1H), 9.06–8.98 (m, 1H), 8.52 (d, J = 8.9 Hz, 1H), 8.47 (d,
J = 6.7 Hz, 1H), 8.26–8.21 (m, 1H), 8.16 (d, J = 3.3 Hz), 8.03–7.99 (m,
1H), 7.90(d, J = 8.8 Hz, 2H), 7.44–7.37 (m, 4H), 7.21–7.12 (m, 6H),
6.97 (d, J = 8.8 Hz, 2H), 3.34 (s, 3H). 13C NMR (126 MHz, DMSO d6)
d 153.35, 150.29, 147.20, 146.56, 143.54, 138.13, 135.48, 131.07,
130.34, 129.39, 128.88, 127.20, 126.97, 125.96, 125.13, 120.90,
119.44, 117.35, 116.17, 40.71, 40.01, 39.78, 39.61, 39.51. HRMS
(m/z): [M]+ calcd for C31H27N+2:427.2174; found, 427.2160.
3. Results and discussion
3.1. Design and synthesis of HVM and IVM
The excogitation of viscosity probes is usually including two key
factors: molecular rotor and push–pull electronic structure. Quino-
line derivatives are attracted much attention in recent years
because of their wide range of biological activities, excellent pho-
tophysical properties, and significant effect in organic synthesis
and therapeutic chemistry [39,40]. Thus, Quinoline derivatives
with the ability to target mitochondria were selected as receptor
of probe. Besides, we presumed that increasing the molecular rotor
might change the fluorescence properties of the fluorophores.
Based on this idea, we utilized two similar structure moieties, 4-
(Dimethylamino) benzaldehyde and 4-(N, N-Diphenylamino) ben-
zaldehyde (Scheme 2), to structure different viscosity probes HVM
and IVM, and discuss the trend of its fluorescence intensity with
the quantity of molecular rotors. When the probe was in non-
viscosity or low viscosity environment, the molecular rotates
rotors freely around the single bond, resulting the probe inter-
molecular energy nonradiative (Scheme 1). With the increase of
viscosity, the rotation of molecules was limited, which turned on
2. Experimental section
2.1. Apparatus and chemicals
Unless otherwise mentioned, the reagents and drugs used in
this paper are purchased. In addition, details of the instruments
used were reviewed in the supporting literature.
Scheme 1. The design strategy of HVM response to viscosity.
2