Highly Hydrophilic, Two-photon Fluorescent Terpyridine Derivatives Containing Quaternary Ammonium for Specific Recognizing Ribosome RNA in Living Cells

Computational Comparative Study of the Binding of Americium with N-Donor Ligands

The accessibility of multiple valence states of americium (Am) inspired redox-based protocols aimed at efficient separation of trivalent Am (Am3+) from trivalent lanthanides (Ln3+) alternative to the traditional liquid-liquid extraction. This requires an extensive understanding of the coordination chemistry of Am in its various accessible valence states in the aqueous phase. In this work, by means of DFT calculations, the coordination of AmIII-VI with five typical N-donor ligands, i.e., terpyridine (tpy), bispyrazinylpyridine (dpp), bistriazinylpyridine (BTP), bistriazinyl bipyridine (BTBP), and bistrazinyl phenanthroline (BTPhen), was studied in terms of energy and topological analysis. The results show that the exchange of aqua ligands of hydrated ions by N-donor ligands is an entropy-driven process and enthalpically unfavorable. Topological analysis suggests a distinct mechanism of BTP to modulate the redox potential of Am(III) in that BTP can assist the relay of the leaving electron of AmIII, while the other N-donor ligands can detain the oxidation of Am by offering their electron instead. This comparative study enriches our understanding of the coordination chemistry of high-valent Am with N-donor ligands and recommends the ligand design toward the modulation of redox potentials of hydrated Am(III) ions.

Revealing the amyloid β-protein with zinc finger protein of micronucleus during Alzheimer's disease progress by a quaternary ammonium terpyridine probe

Micronucleus (MN) is regarded as an abnormal structure in eukaryotic cells which can be used as a biomarker for genetic instability. However, direct observation of MN in living cells is rarely achieved due to the lack of probes that are capable of distinguishing nuclear- and MN-DNA. Herein, a water-soluble terpyridine organic small molecule (ABT) was designed and employed to recognize Zinc-finger protein (ZF) for imaging intracellular MN. The in vitro experiments suggested ABT has a high affinity towards ZF. Further live cell staining showed that ABT could selectively target MN in HeLa and NSC34 cells when combined with ZF. Importantly, we use ABT to uncover the correlation between neurotoxic amyloid β-protein (Aβ) and MN during Alzheimer's disease (AD) progression. Thus, this study provides profound insight into the relationship between Aβ and genomic disorders, offering a deeper understanding for the diagnosis and treatment of AD.

Real-time imaging of RNA polymerase I activity in living human cells

RNA polymerase I (Pol I) synthesizes about 60% of cellular RNA by transcribing multiple copies of the ribosomal RNA gene (rDNA). The transcriptional activity of Pol I controls the level of ribosome biogenesis and cell growth. However, there is currently a lack of methods for monitoring Pol I activity in real time. Here, we develop LiveArt (live imaging-based analysis of rDNA transcription) to visualize and quantify the spatiotemporal dynamics of endogenous ribosomal RNA (rRNA) synthesis. LiveArt reveals mitotic silencing and reactivation of rDNA transcription, as well as the transcriptional kinetics of interphase rDNA. Using LiveArt, we identify SRFBP1 as a potential regulator of rRNA synthesis. We show that rDNA transcription occurs in bursts and can be altered by modulating burst duration and amplitude. Importantly, LiveArt is highly effective in the screening application for anticancer drugs targeting Pol I transcription. These approaches pave the way for a deeper understanding of the mechanisms underlying nucleolar functions.

Bright and Light-Up Sensing of Benzo[c,d]indole-oxazolopyridine Cyanine Dye for RNA and Its Application to Highly Sensitive Imaging of Nucleolar RNA in Living Cells

Small molecular weight probes that can show a fluorescence signaling response upon binding to RNAs are promising for RNA imaging in living cells. Live-cell RNA imaging probes that can achieve a large light-up ability (>100-fold) and high Φ_bound value for RNA (>0.50) have been rarely reported to date. Here, benzo[c,d]indole-oxazolopyridine (BIOP), an unsymmetrical monomethine cyanine analogue, was newly developed as a bright and large light-up probe for imaging of nucleolar RNA in living cells. BIOP served as a yellow-emissive probe (λ_em = 570 nm) and exhibited a significant light-up response upon RNA binding (770-fold) with a high Φ_bound value (0.52). We demonstrated the advantages of BIOP over a commercially available RNA-staining probe, SYTO RNA select, for robust and sensitive RNA sensing by a systematic comparison of fluorescent properties for RNA. In addition, BIOP was found to possess high membrane permeability and low cytotoxicity in living cells. The examination of live-cell imaging revealed that BIOP exhibited emission in the nucleolus upon binding to nucleolar RNA much stronger than that of SYTO RNA select. Furthermore, BIOP facilitated the highly sensitive imaging of nucleolar RNA, in which 50 nM BIOP can stain nucleolar RNA in living cells with a 20 min incubation.

Organosulfur/selenium-based Highly Fluorogenic Molecular Probes for Live-Cell Nucleolus Imaging

We present rationally designed cationic organochalcogens highly selective to RNA. We have demonstrated that the conformational dynamics and subsequently the optical properties of these dyes can be controlled to facilitate efficient bioimaging. We report organoselenium and organosulfur-based cell-permeable red-emissive probes bearing favorable cyclic sidearm with potential for selective and high contrast imaging of cell nucleoli. The probes exhibit high quantum yield upon interaction with RNA in an aqueous solution. An in-depth multiscale simulation study reveals that the prominent rotational freezing of the electron-donating sidearm of the probes in the microenvironment of RNA helps in attaining more planar conformation when compared to DNA. It exerts a greater extent of intramolecular charge transfer and hence leads to enhanced fluorescence emission. A systematic structure-interaction relationship study highlighted the impact of heavy-chalcogens toward the improved emissive properties of the probes.

Switching the Conformation of 3,2':6',3″-tpy Domains in 4'-(4-n-Alkyloxyphenyl)-3,2':6',3″-Terpyridines

The preparation and characterization of 4'-(4-n-octyloxyphenyl)-3,2':6',3″-terpyridine (8) and 4'-(4-n-nonyloxyphenyl)-3,2':6',3″-terpyridine (9) are reported. The single crystal structures of 4'-(4-n-hexyloxyphenyl)-3,2':6',3″-terpyridine (6), 4'-(4-n-heptyloxyphenyl)-3,2':6',3″-terpyridine (7), and compounds 8 and 9 have been determined. The conformation of the 3,2':6',3″-tpy unit is trans,trans in 6 and 7, but switches to cis,trans in 8 and 9. This is associated with significant changes in the packing interactions with a more dominant role for van der Waals interactions between adjacent n-alkyloxy chains and C-Hmethylene... π interactions in 8 and 9. The solid-state structures of 6 and 7 with the n-hexyloxy and n-heptyloxy chains feature interwoven sheets of supramolecular assemblies of molecules, with pairs of n-alkyloxy chains threaded through cavities in an adjacent sheet.

Modification of side chain of conjugated molecule for enhanced charge transfer and two-photon activity

Amounts of strategies implemented to obtain improved two-photon absorption responses but remains challenging. Herein, a serials zwitterionic chromophores, TSEO1-3, with D-π-A configuration were rational designed and synthesized. Notably, by minor modification of the side chain, the obtained TSEO3 exhibited enhanced two-photon activity and considerable two-photon imaging in vitro and in vivo. It manifested that appropriate modifications of side chains that are linked to conjugated frameworks can improve the intermolecular packing order and boost charge transfer favoring two-photon activity.

A turn-off fluorescence probe based on terpyridine for pH monitoring

A new pH-dependent fluorescence probe 2,8-bis((E)-4-([2,2':6',2″-terpyridin]-4'-yl)styryl)-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine (TBPTP) based on Tröger's base (TB) bound to terpyridine was designed and synthesized. Photophysical properties and titration experiments of TBPTP were investigated by absorption and fluorescence spectroscopy. TBPTP exhibited high sensitivity in an acidic environment with the working pH range 7.2-2.5, especially having a good liner response to pH changes in the range 2.5-4.3, which suggested that TBPTP is a good candidate for pH monitoring.

N,N,N-Trimethyl-1-[4-(pyridin-2-yl)phenyl]methanaminium hexafluoridophosphate

In the cation of the title molecular salt, C15H19N2 +·PF6 −, the dihedral angle between the benzene and pyridine rings is 38.21 (10)°. In the crystal, weak C—H...F interactions arising from methyl and methylene groups adjacent to the quaternary N atom generate (001) sheets.

Ribosomal RNA-Selective Light-Up Fluorescent Probe for Rapidly Imaging the Nucleolus in Live Cells

RNA-based fluorescent probes are currently limited by their low selectivity toward RNA versus DNA, and low specificity to different RNA structures. Poor membrane permeability is another defect of existing fluorogenic RNA probes for intracellular imaging. In this work, a naphthalimide derivative, probe 1, was developed for the rapid and selective detection of intracellular rRNA (rRNA). Probe 1 exhibited a 32-fold fluorescent enhancement in response to rRNA binding and showed desirable selectivity for rRNA versus DNA and other nucleic acids in phosphate buffer at pH 7.2. Importantly, probe 1 displayed excellent permeability of the nucleolus, could be taken up in 1 min by four different cell lines, and may be the fastest nucleolus dye. The excellent selectivity of probe 1 toward rRNA is attributed to the specific interaction between the complicated 3D structures of rRNA, which was confirmed by quantum calculations using molecular docking simulations. An appropriate lipophilic balance in 1 with the hydrophilic amine group and hydrophobic naphthalimide, as well as its high water solubility, guarantees the high permeability of 1 in cell membranes and nucleolus pores, compared to other analogues (e.g., probes 2-8 in this work). Furthermore, enlarged confocal laser micro images of nucleoli and RNase digestion tests revealed that 1 remained highly selective toward rRNA, even for intracellular imaging. As a live cell probe, 1 also exhibited better photostability than the commercial RNA dye, SYTO RNA select.

Amphiphilic Gemini Iridium(III) Complex as a Mitochondria-Targeted Theranostic Agent for Tumor Imaging and Photodynamic Therapy

Clinical diagnostics and therapeutics of tumors are significantly benefitted by the development of multifunctional theranostic agents, which integrate tumor targeting, imaging, and therapeutics. However, the integration of imaging and therapy functionalities to a unimolecular framework remains a great challenge. Herein, a family of amphiphilic gemini iridium(III) complexes (GIC), Ir1-Ir6, are synthesized and characterized. The presence of quaternary ammonium (QA) groups endows GIC with adjustable water solubility and excellent self-assembly properties. Spectroscopic and computational results reveal that introducing QA groups into cyclometalating ligands (ĈN ligands) can overcome the drawback of aggregation-caused emission quenching and ensure Ir1-Ir3 with high emission intensity and excellent singlet oxygen (¹O₂) generation ability in aqueous media. Cell-based assays indicate that Ir3 shows higher cellular uptake efficiency and localizes specifically in the mitochondria, as well as exhibits outstanding photostability and an impressive phototoxicity index with satisfactory performance in mitochondria-targeted imaging and photodynamic therapy (PDT) of tumor cells. Furthermore, in vivo studies further prove that Ir3 possesses excellent antitumor activity and remarkably inhibits the growth of the HepG2 cells under PDT treatment. Consequently, this study presents a promising strategy for designing clinical application potential multifunctional iridium complex theranostic agents for mitochondria-targeted imaging and PDT in a single molecular framework.

Endoplasmic reticulum-targeted phototherapy using one-step synthesized trace metal-doped carbon-dominated nanoparticles: Laser-triggered nucleolar delivery and increased tumor accumulation

Lysosomal entrapment and liver accumulation are the two main obstacles faced by many anticancer drugs for achieving satisfactory therapeutic outcomes. Here, we develop a facile one-step hydrothermal synthetic route to prepare trace metal (M)-, N-, and O-doped carbon-dominated nanoparticles (termed as MNOCNPs, M = Ni, Pd, or Cu, metal content: <0.1 mol%) with exceptional photothermal properties (e.g., the ultrahigh extinction coefficient of 32.7 L g^-1 cm^-1), which can simultaneously realize preferable endoplasmic reticulum (ER) targeting and specific tumor enrichment without noticeable liver accumulation after poly(ethylene glycol) (PEG) conjugation. More interestingly, the PEG-modified MNOCNPs with nanoscale lengths exhibit considerable nucleolar delivery and increased tumor accumulation upon laser irradiation. After fluorescence labeling, these PEG-modified MNOCNPs are suitable for fluorescence/photoacoustic/thermal triple-modal imaging-guided photothermal cancer treatment. Additionally, the ultralow metal content ensures the exceptional biosafety of the nanoagents. The present work provides a novel, facile, and general synthetic method of carbon-dominated nanoparticles with superior photothermal properties for highly efficient tumor ablation, and the large-organelle (ER and nucleus)-targeted cancer therapeutic strategy may represent an alternative solution for optimizing the anticancer efficacy of nanomaterials. STATEMENT OF SIGNIFICANCE: Limited wire-like nanomaterials have been used for biomedical applications due to their lack of intrinsic photothermal properties, poor cellular uptake and tumor accumulation, and potential biotoxicity arising from their micrometer lengths and/or massive heavy metal doping. Besides, the clinical applications of many nanoagents are hindered by their tendency to accumulate in liver, which may cause severe liver toxicity. Herein, we develop for the first time a one-step hydrothermal method to prepare wire-like trace metal-, N-, and O-doped carbon-dominated nanoparticles with excellent photothermal properties, massive cellular uptake, preferable ER localization, selective tumor targeting with negligible liver deposition, laser irradiation-enhanced nucleolar delivery and tumor accumulation, and multimodal imaging-guided cancer therapy. This work opens a new window for simultaneously overcoming lysosomal entrapment and liver accumulation in cancer therapy.

Aggregation-induced emission (AIE)-active molecules bearing singlet oxygen generation activities: the tunable singlet–triplet energy gap matters

Two-photon active photosensitizers showed relatively strong intersystem crossing facilitating ¹O₂ generation and cell apoptosis with near-infrared excitation.

Dual-channel fluorescent probe bearing two-photon activity for cell viability monitoring

We developed a dual-channel two-photon fluorescence probe to monitor cell viability.

A ratiometric fluorescent composite nanomaterial for RNA detection based on graphene quantum dots and molecular probes

RNA plays a central role in controlling cellular functions. Research of the content and distribution of RNA in living cells is of great significance to both biochemistry and biomedicine. However, ratiometric fluorescent probes for the detection of RNA in the cytoplasm and nucleoli are still rarely reported. We herein present the first example of a novel ratiometric fluorescent composite nanomaterial by using graphene quantum dots (GQDs) and a fluorescent probe molecule for the sensitive and selective detection of RNA. HVC-6 was selected as the detection group. The fluorescence was excited at 365 nm and the fluorescence emission at 470 and 610 nm increased gradually with the addition of RNA. The fluorescence intensity ratio of I₆₁₀/I₄₇₀ displayed a linear response to RNA. Furthermore, the developed nanomaterial HVC-6@GQDs showed potential for utilization as a fluorescent RNA probe in living cells.

Real-time noninvasive monitoring of cell mortality using a two-photon emissive probe based on quaternary ammonium

We report that a dicyanyl derivative QN2 containing quaternary ammonium was capable of identifying apoptotic cells by targeting nucleic acid (DNA and RNA).

A molecular probe based on pyrimidine imidazole derivatives for stable super-resolution endoplasmic reticulum imaging in living cells

Multi-functional florescent dyes capable of acting as molecular probes in living systems under two-photon microscopy, as well as super-resolution nanoscopy, are of great interest.

Far-red fluorescent probes for canonical and non-canonical nucleic acid structures: current progress and future implications

Our review presents the recent progress on far-red fluorescent probes of canonical and non-canonical nucleic acid (NA) structures, critically discusses the design principles, applications, limitations and outline the future prospects of developing newer probes with target-specificity for different NA structures.