Identifying Key Metabolites Associated with Glucosinolate Biosynthesis in Response to Nitrogen Management Strategies in Two Rapeseed (Brassica napus) Varieties

A high glucosinolate (GSL) concentration, an undesirable substance, has severely restricted rapeseed (Brassica species) development. We performed widely targeted metabolomics analysis based on the ultra-high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry (UPLC–ESI–MS/MS) technology to analyze the metabolic profiles and identify the differential metabolites and GSL components in response to different nitrogen (N) levels in two rapeseed varieties. A total of 341 metabolites and 38 GSL components were detected in the seeds. A total of 188 differential metabolites, including 34 GSL components, were identified in response to different treatments, which were mapped into 2-oxocarboxylic acid metabolism, tryptophan metabolism, and GSL biosynthesis. Key indicators of GSL components highly responsible for different N levels under two contrasting varieties were recognized, i.e., 1-methylpropyl GSL and 4-methylthiobutyl GSL. This study suggests that the efficient N management and variety selection are important strategies for developing rapeseed with low GSLs

Identifying Key Metabolites Associated with Glucosinolate Biosynthesis in Response to Nitrogen Management Strategies in Two Rapeseed (Brassica napus) Varieties

A high glucosinolate (GSL) concentration, an undesirable substance, has severely restricted rapeseed (Brassica species) development. We performed widely targeted metabolomics analysis based on the ultra-high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry (UPLC–ESI–MS/MS) technology to analyze the metabolic profiles and identify the differential metabolites and GSL components in response to different nitrogen (N) levels in two rapeseed varieties. A total of 341 metabolites and 38 GSL components were detected in the seeds. A total of 188 differential metabolites, including 34 GSL components, were identified in response to different treatments, which were mapped into 2-oxocarboxylic acid metabolism, tryptophan metabolism, and GSL biosynthesis. Key indicators of GSL components highly responsible for different N levels under two contrasting varieties were recognized, i.e., 1-methylpropyl GSL and 4-methylthiobutyl GSL. This study suggests that the efficient N management and variety selection are important strategies for developing rapeseed with low GSLs

Identifying Key Metabolites Associated with Glucosinolate Biosynthesis in Response to Nitrogen Management Strategies in Two Rapeseed (Brassica napus) Varieties

A high glucosinolate (GSL) concentration, an undesirable substance, has severely restricted rapeseed (Brassica species) development. We performed widely targeted metabolomics analysis based on the ultra-high-performance liquid chromatography–electrospray ionization–tandem mass spectrometry (UPLC–ESI–MS/MS) technology to analyze the metabolic profiles and identify the differential metabolites and GSL components in response to different nitrogen (N) levels in two rapeseed varieties. A total of 341 metabolites and 38 GSL components were detected in the seeds. A total of 188 differential metabolites, including 34 GSL components, were identified in response to different treatments, which were mapped into 2-oxocarboxylic acid metabolism, tryptophan metabolism, and GSL biosynthesis. Key indicators of GSL components highly responsible for different N levels under two contrasting varieties were recognized, i.e., 1-methylpropyl GSL and 4-methylthiobutyl GSL. This study suggests that the efficient N management and variety selection are important strategies for developing rapeseed with low GSLs

Structural, UV−Visible, and Electrochemical Studies on 2,3-Dicyano-5,6-di-2-pyridylpyrazine, [(CN)₂Py₂Pyz], Related Species and Its Complexes [(CN)₂Py₂PyzMCl₂] (M = Pt^II, Pd^II)

2,3-Dicyano-5,6-di-2-pyridylpyrazine, [(CN)2Py2Pyz], which autocyclotetramerizes to give the macrocycle tetrakis[5,6-di(2-pyridyl)-2,3-pyrazino]porphyrazine, [Py8TPyzPzH2], bearing externally four dipyridinopyrazine fragments, reacts with bis(benzonitrile)dichloroplatinum(II), [(C6H5CN)2PtCl2], in CH3CN, affording the monometalated species [(CN)2Py2PyzPtCl2]. Single-crystal X-ray work on this compound shows that PtII is bound to [(CN)2Py2Pyz] through the two pyridine N atoms (“py−py” coordination) in a way similar to that found for its monopalladium analogue, [(CN)2Py2PyzPdCl2]. Cyclic voltammetry of [(CN)2Py2PyzPtCl2] and [(CN)2Py2PyzPdCl2] in nonaqueous media (pyridine, DMSO, and DMF) indicates that the electron-withdrawing effect of the coordinated PtCl2 and PdCl2 units results in an initial one-electron reduction (E1/2 = −0.60 and −0.54 V vs SCE in DMSO, respectively), which is easier by 0.25−0.30 V than the unmetalated [(CN)2Py2Pyz] (first reduction: E1/2 = −0.87 V vs SCE). These electrochemical data are analyzed along with new results for a selected number of related pyrazine and 2,3-dicyanopyrazine molecules as well as earlier reported data on the mono- and bis-N-methylated derivatives [(CN)2Py(2-Mepy)Pyz]+ and [(CN)2(2-Mepy)2Pyz]2+, with these latter species being formed by reaction of the precursor [(CN)2Py2Pyz] with methyl iodide or p-toluensulfonate. The data in this study are also compared to electrochemical data previously reported for a triad of palladium(II) porphyrazine macrocycles obtained from the precursor [(CN)2Py2Pyz], i.e., [Py8TPyzPzPd], the corresponding pentanuclear complex [(PdCl2)4Py8TPyzPzPd] (presenting “py−py” coordination at the dipyridinopyrazine fragments), and the octacation [(2-Mepy)8TPyzPzPd]8+ (N-methylated at the pyridine rings). Thin-layer UV−visible spectra of singly reduced [(CN)2Py2Pyz]− and its metalated analogues, [(CN)2Py2PyzPtCl2]− and [(CN)2Py2PyzPdCl2]−, were measured in pyridine, DMF, and DMSO and show π−π* transitions, as well as unusually intense absorptions in the near-IR region (500−900 nm) of the spectrum

Tetrakis(thiadiazole)porphyrazines. 6. Spectroelectrochemical and Density Functional Theory Studies of the Anions [TTDPzM]^<i>n</i>− (<i>n</i> = 1−4; M = Zn^II, Mg^II(H₂O), Cu^II, 2H^I)

Following previous cyclic voltammetric studies of tetrakis(thiadiazole)porphyrazines [TTDPzM] where M = ZnII, MgII(H2O), CuII, or 2HI in nonaqueous media, a thin-layer spectroelectrochemical investigation was carried out in pyridine to characterize each stepwise one-electron reduction of the electrogenerated [TTDPzM]n− complexes where n = 1−4. A similar UV−visible spectrum was observed for each form of the anion, independent of the central metal ion and detailed theoretical calculations by density functional theory (DFT) and time-dependent DFT (TDDFT) methods were applied to interpret the spectral features of [TTDPzZn]n− (n = 1−4) which was selected as representative for describing the ground and excited-state electronic structures of the entire [TTDPzM]n− series. The use of two exchange-correlation functionals, the pure, asymptotically correct statistical average of orbital potentials (SAOP) and the hybrid B3LYP functionals, proved to be essential for attaining a correct assignment of the key spectral features. The nature and intensity of the main spectral features are highlighted and interpreted on the basis of the ground-state electronic structure of the complexes

Tetra-2,3-pyrazinoporphyrazines with Externally Appended Pyridine Rings. 8. Central (Zn^II, Cu^II, Mg^II(H₂O), Cd^II) and Exocyclic (Pd^II) Metal Ion Binding in Heteropentametallic Complexes from Tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine

A series of heteropentametallic porphyrazine macrocycles, represented as [(PdCl2)4LM], where L = dianion of tetrakis-2,3-[5,6-di(2-pyridyl)pyrazino]porphyrazine and M = ZnII, CuII MgII(H2O) or CdII, were prepared by reaction of the corresponding mononuclear [LM] species, and their behavior was examined by UV−visible and NMR spectroscopy, electrochemistry, and thin layer spectroelectrochemistry in nonaqueous media. The PdCl2 units in [(PdCl2)4LM] are coordinated at the pyridine N atoms of the external dipyridinopyrazine fragments (“py-py” coordination) and are displaced out of the plane of the central pyrazinoporphyrazine macrocycle as verified by 1H and 13C NMR data on [(PdCl2)4LZn]. The same arrangement is also strongly suggested by similar NMR data on the MgII and CdII analogues. The predominant component in the synthesized materials among the four predictable macrocyclic isomers has the four exocyclic N2(py)PdCl2 square planar coordination sites on the same side of the central macrocyclic framework (4:0 isomer, C4v symmetry), and this is accompanied by a minor isomeric component (2:2 cis or trans), in line with previous findings on the pentapalladated species [(PdCl2)4LPd]. IR, UV−visible, and NMR spectral data also provide evidence for transmetalation reactions of the type [(PdCl2)4LMg(H2O)] → [(PdCl2)4LPd] and [(PdCl2)4LCd] → [(PdCl2)4LPd], with the amount of [(PdCl2)4LPd] formed varying from batch to batch. Dissociation of the four exocyclic PdCl2 units from [(PdCl2)4LM] occurs in pyridine, but the compounds are stable in N,N-dimethylformamide (DMF) or dimethylsulfoxide (DMSO) and can be stepwise reduced via two one-electron reversible or quasi-reversible processes, prior to an irreversible electroreduction of the bound PdCl2 group at more negative potentials. This metal-centered reduction leads to a [LM]2− product which is then further reduced to [LM]3− and [LM]4− at the electrode surface. The first two reductions of the heteropentametallic compounds are easier than those of the monometallic [LM] species but generally more difficult than reduction of the related octacationic [L′M]8+ derivatives (L′ = the octamethylated free-base dianion) whose redox properties were previously reported. The CdII octacation [L′Cd]8+, isolated as an iodide salt, was also synthesized for the first time in the current study, and its spectroscopic and electrochemical properties are compared to that of the previously examined analogues

Structural, UV−Visible, and Electrochemical Studies on 2,3-Dicyano-5,6-di-2-pyridylpyrazine, [(CN)₂Py₂Pyz], Related Species and Its Complexes [(CN)₂Py₂PyzMCl₂] (M = Pt^II, Pd^II)

2,3-Dicyano-5,6-di-2-pyridylpyrazine, [(CN)2Py2Pyz], which autocyclotetramerizes to give the macrocycle tetrakis[5,6-di(2-pyridyl)-2,3-pyrazino]porphyrazine, [Py8TPyzPzH2], bearing externally four dipyridinopyrazine fragments, reacts with bis(benzonitrile)dichloroplatinum(II), [(C6H5CN)2PtCl2], in CH3CN, affording the monometalated species [(CN)2Py2PyzPtCl2]. Single-crystal X-ray work on this compound shows that PtII is bound to [(CN)2Py2Pyz] through the two pyridine N atoms (“py−py” coordination) in a way similar to that found for its monopalladium analogue, [(CN)2Py2PyzPdCl2]. Cyclic voltammetry of [(CN)2Py2PyzPtCl2] and [(CN)2Py2PyzPdCl2] in nonaqueous media (pyridine, DMSO, and DMF) indicates that the electron-withdrawing effect of the coordinated PtCl2 and PdCl2 units results in an initial one-electron reduction (E1/2 = −0.60 and −0.54 V vs SCE in DMSO, respectively), which is easier by 0.25−0.30 V than the unmetalated [(CN)2Py2Pyz] (first reduction: E1/2 = −0.87 V vs SCE). These electrochemical data are analyzed along with new results for a selected number of related pyrazine and 2,3-dicyanopyrazine molecules as well as earlier reported data on the mono- and bis-N-methylated derivatives [(CN)2Py(2-Mepy)Pyz]+ and [(CN)2(2-Mepy)2Pyz]2+, with these latter species being formed by reaction of the precursor [(CN)2Py2Pyz] with methyl iodide or p-toluensulfonate. The data in this study are also compared to electrochemical data previously reported for a triad of palladium(II) porphyrazine macrocycles obtained from the precursor [(CN)2Py2Pyz], i.e., [Py8TPyzPzPd], the corresponding pentanuclear complex [(PdCl2)4Py8TPyzPzPd] (presenting “py−py” coordination at the dipyridinopyrazine fragments), and the octacation [(2-Mepy)8TPyzPzPd]8+ (N-methylated at the pyridine rings). Thin-layer UV−visible spectra of singly reduced [(CN)2Py2Pyz]− and its metalated analogues, [(CN)2Py2PyzPtCl2]− and [(CN)2Py2PyzPdCl2]−, were measured in pyridine, DMF, and DMSO and show π−π* transitions, as well as unusually intense absorptions in the near-IR region (500−900 nm) of the spectrum

Tetra-2,3-pyrazinoporphyrazines with Externally Appended Thienyl Rings: Synthesis, UV–Visible Spectra, Electrochemical Behavior, and Photoactivity for the Generation of Singlet Oxygen

A series of pyrazinoporphyrazine macrocycles carrying externally appended 2-thienyl rings, represented as [Th8TPyzPzM], where Th8TPyzPz = tetrakis-2,3-[5,6-di(2-thienyl)pyrazino]porphyrazinato anion and M = MgII(H2O), ZnII, CoII, CuII, or 2H1, were prepared and isolated as solid air-stable hydrated species. All of the compounds, completely insoluble in water, were characterized by their UV–visible spectra and electrochemical behavior in solutions of dimethylformamide (DMF), dimethyl sulfoxide, and pyridine. Molecular aggregation occurs at concentrations of ca. 10–4 M, but monomers are formed in more dilute solutions of 10–5 M or less. The examined octathienyl compounds [Th8TPyzPzM] behave as electron-deficient macrocycles, and UV–visible spectral measurements provide useful information about how the peripheral thienyl rings influence the electronic distribution over the entire macrocyclic framework. Cyclic voltammetric and spectroelectrochemical data confirm the easier reducibility of the compounds as compared to the related phthalocyanine analogues, and the overall redox behavior and thermodynamic potentials for the four stepwise one-electron reductions of the compounds are similar to those of the earlier examined octapyridinated analogues [Py8TPyzPzM]. Quantum yields (ΦΔ) for the generation of singlet oxygen, 1O2, the cytotoxic agent active in photodynamic therapy (PDT), and fluorescence quantum yields (ΦF) were measured for the ZnII and MgII complexes, [Th8TPyzPzZn] and [Th8TPyzPzMg(H2O)], and the data were compared to those of corresponding octapyridino macrocycles [Py8TPyzPzZn] and [Py8TPyzPzMg(H2O)] and their related octacations [(2-Mepy)8TPyzPzZn]8+ and [(2-Mepy)8TPyzPzMg(H2O)]8+. These measurements were carried out in DMF and in DMF preacidified with HCl (ca. 10–4 M). All of the examined ZnII compounds behave as excellent photosensitizers (ΦΔ = 0.4–0.6) both in DMF and DMF/HCl solutions, whereas noticeable fluorescence activity (ΦF = 0.36–0.43) in DMF/HCl solutions is shown by the MgII derivatives; these data might provide perspectives for applications in PDT (ZnII) and imaging response and diagnosis (MgII)

Hypoxia-Responsive Stereocomplex Polymeric Micelles with Improved Drug Loading Inhibit Breast Cancer Metastasis in an Orthotopic Murine Model

Tumor metastasis is a leading cause of breast cancer-related death. Taxane-loaded polymeric formulations, such as Genexol PM and Nanoxel M using poly­(ethylene glycol)-poly­(d,l-lactide) (PEG-PLA) micelles as drug carriers, have been approved for the treatment of metastatic breast cancer. Unfortunately, the physical instability of PEG-PLA micelles, leading to poor drug loading, premature drug leakage, and consequently limited drug delivery to tumors, largely hinders their therapeutic outcome. Inspired by the enantiomeric nature of PLA, this work developed stereocomplex PEG-PLA micelles through stereoselective interactions of enantiomeric PLA, which are further incorporated with a hypoxia-responsive moiety used as a hypoxia-cleavable linker of PEG and PLA, to maximize therapeutic outcomes. The results showed that the obtained micelles had high structural stability, showing improved drug loading for effective drug delivery to tumors as well as other tissues. Especially, they were capable of sensitively responding to the hypoxic tumor environment for drug release, reversing hypoxia-induced drug resistance and hypoxia-promoted cell migration for enhanced bioavailability under hypoxia. In vivo results further showed that the micelles, especially at a high dose, inhibited the growth of the primary tumor and improved tumor pathological conditions, consequently remarkably inhibiting its metastasis to the lungs and liver, while not causing any systemic toxicity. Hypoxia-responsive stereocomplex micelles thus emerge as a reliable drug delivery system to treat breast cancer metastasis