A switch-on near-infrared fluorescence-ready probe for Cu(I): live cell imaging

A reaction-based strategy exploiting metal ion mediated oxidative C–O bond cleavage affords selective ‘switch-on’ near-infrared (NIR) emitting cyanine probe for Cu⁺ in aqueous media and live cells. Near-infrared fluorescence-ready probe TPACy readily reacts with Cu⁺ to release the quinone embedded heptamethine cyanine (Cy-quinone) with extended π-electron conjugation responsible for the switch-on NIR fluorescence in aqueous buffer solution (50 mM HEPES, pH 7.2). This probe can be conveniently used for monitoring Cu⁺ without the interference from pH dependent effects of physiological media. Utility of the probe has been demonstrated by its application in the detection of unbound copper species (Cu⁺) in live cells.     

Rational Molecular Design and Synthesis of Highly Thermo‐ and Photostable Near‐Infrared‐Absorbing Heptamethine Cyanine Dyes with the Use of Fluorine Atoms

Highly thermo‐ and photostable, near‐infrared‐absorbing heptamethine cyanine dyes were achieved with the use of fluorine‐containing components. In particular, one prepared heptamethine cyanine dye, bearing a tetrakis(pentafluorophenyl)borate as a counter anion and an N‐ethyl‐2,2,2‐trifluoroacetamido group at the meso position, showed not only a high decomposition temperature (T_dt), but also very high photostability toward white LED irradiation.     

Sterically Shielded Heptamethine Cyanine Dyes for Bioconjugation and High Performance Near‐Infrared Fluorescence Imaging

The near‐infrared window of fluorescent heptamethine cyanine dyes greatly facilitates biological imaging because there is deep penetration of the light and negligible background fluorescence. However, dye instability, aggregation, and poor pharmacokinetics are current drawbacks that limit performance and the scope of possible applications. All these limitations are simultaneously overcome with a new molecular design strategy that produces a charge balanced and sterically shielded fluorochrome. The key design feature is a meso‐aryl group that simultaneously projects two shielding arms directly over each face of a linear heptamethine polyene. Cell and mouse imaging experiments compared a shielded heptamethine cyanine dye (and several peptide and antibody bioconjugates) to benchmark heptamethine dyes and found that the shielded systems possess an unsurpassed combination of photophysical, physiochemical, and biodistribution properties that greatly enhance bioimaging performance.     

Orthogonal Activation of RNA‐Cleaving DNAzymes in Live Cells by Reactive Oxygen Species

RNA‐cleaving DNAzymes are useful tools for intracellular metal‐ion sensing and gene regulation. Incorporating stimuli‐responsive modifications into these DNAzymes enables their activities to be spatiotemporally and chemically controlled for more precise applications. Despite the successful development of many caged DNAzymes for light‐induced activation, DNAzymes that can be intracellularly activated by chemical inputs of biological importance, such as reactive oxygen species (ROS), are still scarce. ROS like hydrogen peroxide (H₂O₂) and hypochlorite (HClO) are critical mediators of oxidative stress‐related cell signaling and dysregulation including activation of immune system as well as progression of diseases and aging. Herein, we report ROS‐activable DNAzymes by introducing phenylboronate and phosphorothioate modifications to the Zn²⁺‐dependent 8–17 DNAzyme. These ROS‐activable DNAzymes were orthogonally activated by H₂O₂ and HClO inside live human and mouse cells.     

Copper‐Catalyzed Oxidative Reaction of β‐Keto Sulfones with Alcohols via C−S Bond Cleavage: Reaction Development and Mechanism Study

A Cu‐catalyzed cascade oxidative radical process of β‐keto sulfones with alcohols has been achieved by using oxygen as an oxidant. In this reaction, β‐keto sulfones were converted into sulfinate esters under the oxidative conditions via cleavage of C?S bond. Experimental and computational studies demonstrate that a new pathway is involved in this reaction, which proceeds through the formation of the key four‐coordinated Cu^II intermediate, O?O bond homolysis induced C?S bond cleavage and Cu‐catalyzed esterification to form the final products. This reaction provides a new strategy to sulfonate esters and enriches the research content of C?S bond cleavage and transformations.     

Pulsed Corona Discharge-Induced Reactions of Acetophenone in Water

The reactions of acetophenone in water by pulsed corona discharges have been investigated to provide fundamental information concerning the reactions of acetophenone in water. Experimental results indicated that photolysis of acetophenone did not involve a hydroxyl radical mechanism and the majority flux of hydroxyl radicals originated from the dissociation of gas-phase oxygen in the plasma channels. The rate constants for photolysis and pyrolysis were determined to be 1.5×10^–7 M-s^–1, 2.2×10^–4 s^–1, respectively. The rate constant for the oxidative reactions was measured as 1.2×10^–7 M-s^–1. Results from this study support the proposal that acetophenone degradation reaction proceed through the oxidative reaction pathway, where molecular oxygen accelerates acetophenone degradation, photolysis, and pyrolysis pathways.     

Pyrazole‐substituted Near‐infrared Cyanine Dyes Exhibit pH‐dependent Fluorescence Lifetime Properties

Near‐infrared heptamethine cyanine dye is functionalized with pyrazole derivatives at the meso‐position to induce pH‐dependent photophysical properties. The presence of pyrazole unsubstituted at ¹N‐position is essential to induce pH‐dependent fluorescence intensity and lifetime changes in these dyes. Replacement of meso‐chloro group of cyanine dye IR820 with ¹N‐unsubstituted pyrazole resulted in the pH‐dependent fluorescence lifetime changes from 0.93 ns in neutral media to 1.27 ns in acidic media in DMSO. Time‐resolved emission spectra (TRES) revealed that at lower pH, the pyrazole consists of fluorophores with two distinct lifetimes, which cor‐responds to pH‐sensitive and non‐pH‐sensitive species. In contrast, ¹N‐substituted pyrazoles do not exhibit pH response, suggesting excited state electron transfer as the mechanism of pH‐dependent fluorescence lifetime sensitivity for this class of compounds.     

Sterically Shielded Heptamethine Cyanine Dyes for Bioconjugation and High Performance Near-Infrared Fluorescence Imaging

The near-infrared window of fluorescent heptamethine cyanine dyes greatly facilitates biological imaging because there is deep penetration of the light and negligible background fluorescence. However, dye instability, aggregation, and poor pharmacokinetics are current drawbacks that limit performance and the scope of possible applications. All these limitations are simultaneously overcome with a new molecular design strategy that produces a charge balanced and sterically shielded fluorochrome. The key design feature is a meso-aryl group that simultaneously projects two shielding arms directly over each face of a linear heptamethine polyene. Cell and mouse imaging experiments compared a shielded heptamethine cyanine dye (and several peptide and antibody bioconjugates) to benchmark heptamethine dyes and found that the shielded systems possess an unsurpassed combination of photophysical, physiochemical, and biodistribution properties that greatly enhance bioimaging performance.     

Electron spin resonance studies of the anaerobic and aerobic photolysis of alkylcobaloximes

Aerobic and anaerobic photolysis of methyl(pyridine)cobaloxime, benzyl(pyridine)cobaloxime and analogous compounds in CHCl₃ results only in an electron transfer reaction from an equatorial ligand producing photo-reduction of Co^III to Co^II, the complex retaining its axial ligands.If after the anaerobic photolysis of benzyl(pyridine)cobaloxime the oxygen is introduced without any further photolysis we obtain an ESR spectrum of nitroxide, arising from the attack of a benzyl radical on the dimethylglyoxime equatorial ligand.For the other complexes, homolytic cleavage of the CoC bond occurs and in the presence of oxygen gives rise to the superoxide cobalt complex adduct Py(Co^IIIO₂^?.During photolysis of methyl(pyridine)cobaloxime in isopropanol homolytic cleavage of the CoC bond occurs in preference to electron transfer reaction from the equatorial ligands.The anaerobic photolysis of benzyl(pyridine)cobaloxime in isopropanol or in water at 113–133 K results in an electron transfer reaction. However, at 170 K we observe the formation of the Co^II complex arising from CoC bond cleavage.A mechanism for photo-induced insertion of oxygen in the CoC bond is proposed.     

血红蛋白/光敏剂复合药物体系用于光动力治疗

通过等电点法实现了血红蛋白(Hb)与光敏剂药物七甲川花菁类小分子:11-氯-1,1'-二正丙基-3,3,3',3'-四甲基-10,12-三亚甲基吲哚三碳花青碘盐(IR780)的共担载,并研究了Hb供氧治疗与光动力治疗的联合治疗效果。 通过透射电子显微镜和动态光散射研究了Hb/IR780复合药物载体的形貌与稳定性,证明了药物载体在生理条件下能够稳定存在。 通过对药物在体外溶液和细胞水平的活性氧(ROS)检测,验证了Hb供氧能够有效地促进光敏剂ROS的产生,并且细胞毒性实验也证实了Hb/IR780复合药物载体拥有比单组份IR780药物更明显的肿瘤细胞杀伤效果。     

Nanotechnology for Electroanalytical Biosensors of Reactive Oxygen and Nitrogen Species

Over the past several decades, nanotechnology has contributed to the progress of biomedicine, biomarker discovery, and the development of highly sensitive electroanalytical / electrochemical biosensors for in vitro and in vivo monitoring, and quantification of oxidative and nitrosative stress markers like reactive oxygen species (ROS) and reactive nitrogen species (RNS). A major source of ROS and RNS is oxidative stress in cells, which can cause many human diseases, including cancer. Therefore, the detection of local concentrations of ROS (e. g. superoxide anion radical; O₂^•−) and RNS (e. g. nitric oxide radical; NO^• and its metabolites) released from biological systems is increasingly important and needs a sophisticated detection strategy to monitor ROS and RNS in vitro and in vivo. In this review, we discuss the nanomaterials‐based ROS and RNS biosensors utilizing electrochemical techniques with emphasis on their biomedical applications.     

Metal-Free,Visible-Light-Induced Selective C−C Bond Cleavage of Cycloalkanones with Molecular Oxygen

A metal-free, visible-light-induced oxidative C−C bond cleavage of cycloketones with molecular oxygen is described. Cooperative Brønsted-acid catalysis and photocatalysis enabled selective C−C bond cleavage of cycloketones to generate an array of γ-, δ- and ϵ-keto esters under very mild conditions. Mechanistic studies indicate that singlet molecular oxygen (¹O₂) is responsible for this transformation.     

Oxidation of an Oligonucleotide‐Bound CeIII/Multiphosphonate Complex for Site‐Selective DNA Scission

Oligodeoxyribonucleotide conjugates of ethylenediamine‐N,N,N′,N′‐tetrakis(methylenephosphonic acid) (EDTP) have been used to place a Ce^III/EDTP complex in close proximity to predetermined phosphodiester linkages of a complementary target oligonucleotide. In the presence of atmospheric oxygen, the Ce^III is oxidized into Ce^IV which, in turn, efficiently cleaves the target phosphodiester linkage. No cleavage occurs at the other single‐stranded regions, which suggests that the catalytic Ce species is strictly localized next to the target phosphodiester linkage. No decrease in the reaction rate is observed upon introduction of scavengers for hydroxyl radicals (such as DMSO or MeOH) or singlet oxygen (such as NaN₃) to the system; this indicates that the reaction proceeds via a hydrolytic pathway. Any significant contribution by an oxidative pathway is further ruled out by the observation that nucleosides remain intact after incubation with Ce^IV/EDTP complex for extended periods.     

Mechanistic Insights into the Ni‐Catalyzed Reductive Carboxylation of C−O Bonds in Aromatic Esters with CO2: Understanding Remarkable Ligand and Traceless‐Directing‐Group Effects

The mechanism of the Ni⁰‐catalyzed reductive carboxylation reaction of C(sp²)?O and C(sp³)?O bonds in aromatic esters with CO₂ to access valuable carboxylic acids was comprehensively studied by using DFT calculations. Computational results revealed that this transformation was composed of several key steps: C?O bond cleavage, reductive elimination, and/or CO₂ insertion. Of these steps, C?O bond cleavage was found to be rate‐determining, and it occurred through either oxidative addition to form a Ni^II intermediate, or a radical pathway that involved a bimetallic species to generate two Ni^I species through homolytic dissociation of the C?O bond. DFT calculations revealed that the oxidative addition step was preferred in the reductive carboxylation reactions of C(sp²)?O and C(sp³)?O bonds in substrates with extended π systems. In contrast, oxidative addition was highly disfavored when traceless directing groups were involved in the reductive coupling of substrates without extended π systems. In such cases, the presence of traceless directing groups allowed for docking of a second Ni⁰ catalyst, and the reactions proceed through a bimetallic radical pathway, rather than through concerted oxidative addition, to afford two Ni^I species both kinetically and thermodynamically. These theoretical mechanistic insights into the reductive carboxylation reactions of C?O bonds were also employed to investigate several experimentally observed phenomena, including ligand‐dependent reactivity and site‐selectivity.     

Photochemical and Photophysical Studies of 3-Amino-6-lodoacridine and the Inactivation of λ Phage

Abstract— The photochemistry and photophysics of 3-amino-6-io-doacridine (Acr-I) was studied. Photolysis (350 nm) of Acr-I (free base) generates products consistent with a free radical intermediate in methanol, benzene and carbon tetrachloride. The Acr-I hydrochloride is shown to bind to calf thymus DNA and to the self-complementary dinucleotide cytidylyl-(3′-5′)-guanosine (CpG) minidu-plex in a manner similar to that of proflavine (Acr-NH₂), a known DNA intercalator. The Acr-I is shown to more efficiently nick supercoiled plasmid DNA pBR322 upon 350 nm or 420 nm photolysis than Acr-NH₂. The efficiency of Acr-I-sensitized DNA nicking is not oxygen dependent. Photolysis of the Acr-I/(CpG)₂ complex leads to cleavage of the dinucleotide and to cytidine base release by selective damage to a specific ribose moiety. Dinucleotide cleavage occurs equally well in the presence or absence of oxygen, thereby eliminating a singlet oxygen- or peroxyl radical-mediated process. Photolysis of Acr-I in the presence of a mononucleotide (GMP) or a non-self-complementary dinucleotide (uridylyl-[3′-5′]-cytidine– UpC) does not lead to fragmentation and base release. Similarly, photolysis of the Acr-NH₂/(CpG)₂ complex does not lead to fragmentation and base release. The data indicate that photolysis of an iodinated intercalator bound to CpG or plasmid DNA generates an intercalated aryl radical and that the reactive intermediate initiates a sequence of reactions that efficiently nick nucleic acids. The inactivation of Λ phage sensitized by Acr-I with UV (350 nm) light is oxygen independent but with visible (420 nm) light is strongly oxygen dependent. The Acr-I fluoresces more intensely when excited at 446 than at 376 nm. Thus, UV photolysis may lead to C-I bond homolysis and free radical formation, a process that is not energetically feasible with visible light. The results demonstrate the difficulty of extrapolating model studies involving simple molecules and DNA to understanding the mechanism of viral inactivation with a particular sensitizer.     

Addition of aluminium,zinc and magnesium hydrides to rhodium(iii)

We report the addition of M–H bonds (M = Al, Zn, Mg) to a Rh(iii) intermediate generated from the reductive elimination of triethylsilane from [Cp*Rh(H)₂(SiEt₃)₂]. A series of new heterobimetallic complexes possessing Rh–M bonds have been isolated and characterised by a number of spectroscopic (¹H, ²⁹Si, ¹³C, ¹⁰³Rh NMR, infrared, and X-ray diffraction) and computational techniques (NBO and QTAIM analysis). Experimental and computational data are consistent with cleavage of the M–H bond upon addition to rhodium with formation of new Rh–M and Rh–H bonds. Upon photolysis the Al analogue of this series undergoes a further elimination reaction producing triethylsilane and a highly unusual Rh₂Al₂H₄ containing cluster proposed to contain an Al(i) bridging ligand.     

J-Aggregates Formed by NaCl Treatment of Aza-Coating Heptamethine Cyanines and Their Application to Monitoring Salt Stress of Plants and Promoting Photothermal Therapy of Tumors

The cationic nature of heptamethine cyanines gives them the capacity to form aggregates with salts by electrostatic interactions. In this work, NaCl promoted J-aggregate formation of aza-coating heptamethine cyanines is explored. NaCl can induce the N-benzyloxycarbonyl Cy-CO₂Bz to assemble into a J-aggregate having an absorption at 890 nm. Its excellent fluorescence response to NaCl implies that it has great potential for use as a probe for tracing salt stress in plants. Moreover, NaCl also promotes formation of J-aggregates from the N-ethyloxycarbonyl Cy-CO₂Et . The aggregate shows an intense absorption at 910 nm compared to the monomer which absorbs at 766 nm. Its J-aggregated form can serve as a photothermal agent. And the photothermal conversion efficiency is increased from 29.37 % to 57.59 %. This effort leads to the development of two applications of new cyanine J-aggregates including one for tracing salt stress of plants and the other for promoting photothermal therapy of tumors.     

Synthesis and photophysical properties of heptamethine cyanine–fullerene C60 dyads with non-quenched fluorescence

Two new heptamethine cyanine dye–fullerene C₆₀ covalently- linked dyads, which absorb in far-red and NIR spectral regions, have been synthesized by esterification click reaction and characterized by physicochemical methods. No significant fluorescence quenching was found due to weak electronic coupling between heptamethine moiety and fullerene core, which was confirmed by photophysical and electrochemical methods. Such dyads can be useful for cell imaging and fluorescence diagnostics of various fullerene derivatives.     

Apoptosis induced by NaYF<Subscript>4</Subscript>:Eu<Superscript>3+</Superscript> nanoparticles in liver cells via mitochondria damage dependent pathway

As lanthanide-doped sodium yttrium flouride (NaYF₄) nanoparticles have great potential in biomedical applications, their biosafety is important and has attracted significant attention. In the present work, three different sized NaYF₄:Eu³⁺ nanoparticles have been prepared. Liver BRL 3A cell was used as a cell model to evaluate their biological effects. Cell viability and apoptosis assays were used to confirm the cytotoxicity induced by NaYF₄:Eu³⁺ NPs. Apart from the elevated malondialdehyde (MDA), the decrease of superoxide dismutase (SOD), glutathione peroxidase (GSH-PX) and catalase (CAT) activity indicated reactive oxygen species (ROS) generation, which were associated with oxidative damage. The decrease of mitochondrial membrane potential (MMP) value demonstrated the occurrence of mitochondria damage. Then, release of cytochrome c from mitochondria and activation of caspase-3 confirmed that NaYF₄:Eu³⁺ NPs induced apoptosis was mitochondria damage-dependent.     

Alleviating Cellular Oxidative Stress through Treatment with Superoxide‐Triggered Persulfide Prodrugs

Overproduction of superoxide anion (O₂^.?), the primary cellular reactive oxygen species (ROS), is implicated in various human diseases. To reduce cellular oxidative stress caused by overproduction of superoxide, we developed a compound that reacts with O₂^.? to release a persulfide (RSSH), a type of reactive sulfur species related to the gasotransmitter hydrogen sulfide (H₂S). Termed SOPD‐NAC , this persulfide donor reacts specifically with O₂^.?, decomposing to generate N‐acetyl cysteine (NAC) persulfide. To enhance persulfide delivery to cells, we conjugated the SOPD motif to a short, self‐assembling peptide (Bz‐CFFE‐NH₂) to make a superoxide‐responsive, persulfide‐donating peptide ( SOPD‐Pep ). Both SOPD‐NAC and SOPD‐Pep delivered persulfides/H₂S to H9C2 cardiomyocytes and lowered ROS levels as confirmed by quantitative in vitro fluorescence imaging studies. Additional in vitro studies on RAW 264.7 macrophages showed that SOPD‐Pep mitigated toxicity induced by phorbol 12‐myristate 13‐acetate (PMA) more effectively than SOPD‐NAC and several control compounds, including common H₂S donors.