Category: pyridine-derivatives

Pyridine is colorless, but older or impure samples can appear yellow. 766-11-0, formula is C5H3BrFN, Name is 5-Bromo-2-fluoropyridine. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. Formula: C5H3BrFN.

Tang, Yu;Miller, Scott J. research published 《 Catalytic Enantioselective Synthesis of Pyridyl Sulfoximines》, the research content is summarized as follows. The synthesis of chiral sulfoximines, e.g., I, through the desymmetrizing N-oxidation of pyridyl sulfoximines, e.g., II, using an aspartic-acid-containing peptide catalyst III (R = Ts, Boc) was reported. Various mono- and bis-pyridyl sulfoximine oxides, e.g., I and IV, are obtained with up to 99:1 er. The directing group introduced on the substrate highly enhances the enantioinduction and could be easily removed to give the free N-H sulfoximines V. Addnl., peptides with Me ester and the Me amide C-terminal protecting group give the opposite enantiomers of the product. A binding model is proposed to explain this phenomenon.

766-11-0, 5-Bromo-2-fluoropyridine is a useful research compound. Its molecular formula is C5H3BrFN and its molecular weight is 175.99 g/mol. The purity is usually 95%.
5-Bromo-2-fluoropyridine is a boronic acid that has been shown to react with iodides and form 5-bromo-2-fluoroiodobenzene. The reaction of 5-bromo-2-fluoropyridine with benzene gives the same product as the reaction with 1,3,5-trioxane. The UV absorption of 5-bromo-2-fluoropyridine is found at 230 nm and 260 nm. It also has an absorption band in the infrared region at 1625 cm−1. Vibrational progressions have been observed for this molecule, which are due to dipole moments and electron density distributions in the molecule.
5-bromo-2-fluoropyridine is used in the synthesis of heteroaromatic and aniline derivatives of piperidines as potent ligands used for vesicular acetylcholine transport. , Formula: C5H3BrFN

Referemce:
Pyridine – Wikipedia,
Pyridine | C5H5N – PubChem

Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one methine group (=CH−) replaced by a nitrogen atom. 766-11-0, formula is C5H3BrFN, Name is 5-Bromo-2-fluoropyridine. It is a highly flammable, weakly alkaline, water-miscible liquid with a distinctive, unpleasant fish-like smell. Category: pyridine-derivatives.

Tao, Sheng;Ji, Enhui;Shi, Lei;Liu, Ning;Xu, Liang;Dai, Bin research published 《 Copper-Catalyzed C-N Bond Exchange of N-Heterocyclic Substituents around Pyridine and Pyrimidine Cores》, the research content is summarized as follows. A copper-catalyzed transfer N-heteroarylation strategy using a C-N bond exchange reaction is described. This reaction accommodates a wide range of pyridine and pyrimidine rings bearing halogen atoms, which have wide utility for subsequent transformations. This method provides a direct and operationally simple approach for modifying complex mols. by the exchange of N-heterocyclic substituents.

Category: pyridine-derivatives, 5-Bromo-2-fluoropyridine is a useful research compound. Its molecular formula is C5H3BrFN and its molecular weight is 175.99 g/mol. The purity is usually 95%.
5-Bromo-2-fluoropyridine is a boronic acid that has been shown to react with iodides and form 5-bromo-2-fluoroiodobenzene. The reaction of 5-bromo-2-fluoropyridine with benzene gives the same product as the reaction with 1,3,5-trioxane. The UV absorption of 5-bromo-2-fluoropyridine is found at 230 nm and 260 nm. It also has an absorption band in the infrared region at 1625 cm−1. Vibrational progressions have been observed for this molecule, which are due to dipole moments and electron density distributions in the molecule.
5-bromo-2-fluoropyridine is used in the synthesis of heteroaromatic and aniline derivatives of piperidines as potent ligands used for vesicular acetylcholine transport. , 766-11-0.

Referemce:
Pyridine – Wikipedia,
Pyridine | C5H5N – PubChem

Pyridine is colorless, but older or impure samples can appear yellow. 31181-90-5, formula is C6H4BrNO, Name is 5-Bromopicolinaldehyde. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. Recommanded Product: 5-Bromopicolinaldehyde.

Taylor, Lauren L. K.;Vitorica-Yrezabal, Inigo J.;Borilovic, Ivana;Tuna, Floriana;Riddell, Imogen A. research published 《 Self-assembly of a trigonal bipyramidal architecture with stabilisation of iron in three spin states》, the research content is summarized as follows. Self-assembly and characterization of a supramol. trigonal bipyramidal iron cage containing an [Fe^III(μ₂-F)₆(Fe^II)₃]³⁺ star motif at its core is reported. The complex can be formed in a one step reaction using an heterotopic ligand that supports site-specific incorporation of iron in three distinct electronic configurations: low-spin Fe^II, high-spin Fe^II and high-spin Fe^III, with iron(II) tetrafluoroborate as the source of the bridging fluorides. Formation of a μ₂-F bridged mixed-valence Fe^II-Fe^III star is unprecedented. The peripheral high-spin Fe^II centers of the mixed-valence tetranuclear star incorporated in the iron cage are highly anisotropic and engage in F-mediated antiferromagnetic exchange with the central Fe^III ion.

Recommanded Product: 5-Bromopicolinaldehyde, 5-Bromopyridine-2-carbaldehyde is a useful research compound. Its molecular formula is C6H4BrNO and its molecular weight is 186.01 g/mol. The purity is usually 95%.

5-Bromopyridine-2-carbaldehyde is a water soluble organic molecule that has been shown to inhibit the mitochondrial respiratory chain. It is a structural analog of the natural substrate for mitochondrial cytochrome c oxidase, 5-aminolevulinic acid. This compound has been shown to be selective against cancer cells and has anti-viral properties. The photophysical properties of 5-bromopyridine-2-carbaldehyde have been studied extensively. The fluorescence quantum yield of this molecule in aqueous solution is 0.06%., 31181-90-5.

Referemce:
Pyridine – Wikipedia,
Pyridine | C5H5N – PubChem

Pyridine is diamagnetic and has a diamagnetic susceptibility of −48.7 × 10−6 cm3·mol−1.The molecular electric dipole moment is 2.2 debyes. 31181-90-5, formula is C6H4BrNO, Name is 5-Bromopicolinaldehyde. TThe standard enthalpy of formation is 100.2 kJ·mol−1 in the liquid phase and 140.4 kJ·mol−1 in the gas phase. Name: 5-Bromopicolinaldehyde.

Teng, Teng;Li, Kai;Cheng, Gang;Wang, Yuan;Wang, Jian;Li, Jiafang;Zhou, Changjiang;Liu, He;Zou, Taotao;Xiong, Jinfan;Wu, Chao;Zhang, Hong-Xing;Che, Chi-Ming;Yang, Chuluo research published 《 Lighting Silver(I) Complexes for Solution-Processed Organic Light-Emitting Diodes and Biological Applications via Thermally Activated Delayed Fluorescence》, the research content is summarized as follows. Luminescent coinage metal complexes have shown promising applications as electroluminescent emitters, photocatalysts/photosensitizers, and bioimaging/theranostic agents, rendering them attractive alternatives to transition metal complexes based on iridium, ruthenium, and platinum that have extremely low earth abundance. In comparison to the widely studied Au(I) and Cu(I) complexes, Ag(I) complexes have seldom been explored in this field because of their inferior emission properties. Herein, we report a novel series of [Ag(N^N)(P^P)]PF₆ complexes exhibiting highly efficient thermally activated delayed fluorescence by using easily accessible neutral diamine ligands and com. available ancillary diphosphine chelates. The photoluminescence quantum yields (PLQYs) of the Ag(I) emitters are ≤0.62 in doped films. The high PLQY with a large delayed fluorescence ratio enabled the fabrication of solution-processed organic light-emitting diodes (OLEDs) with a high maximum external quantum efficiency of 8.76%, among the highest values for Ag(I) emitter-based OLEDs. With superior emission properties and an excited state lifetime in the microsecond regime, together with its potent cytotoxicity, the selected Ag(I) complex has been used for simultaneous cell imaging and anticancer treatment in human liver carcinoma HepG2 cells, revealing the potential of luminescent Ag(I) complexes for biol. applications such as theranostics. Four silver(I) complexes containing a diphosphoine ligand and an easily synthesized donor-acceptor type diimine ligand were prepared Spectroscopic and theor. studies revealed their efficient photoluminescence via the thermally activated delayed fluorescence mechanism. The selected silver complex afforded good performance in a solution-processed electroluminescent device. The silver complex also demonstrated promising in vitro anticancer activity in human liver carcinoma HepG2 cells, and its location in the cytoplasm instead of the nucleus was visualized by confocal fluorescence imaging.

Name: 5-Bromopicolinaldehyde, 5-Bromopyridine-2-carbaldehyde is a useful research compound. Its molecular formula is C6H4BrNO and its molecular weight is 186.01 g/mol. The purity is usually 95%.

5-Bromopyridine-2-carbaldehyde is a water soluble organic molecule that has been shown to inhibit the mitochondrial respiratory chain. It is a structural analog of the natural substrate for mitochondrial cytochrome c oxidase, 5-aminolevulinic acid. This compound has been shown to be selective against cancer cells and has anti-viral properties. The photophysical properties of 5-bromopyridine-2-carbaldehyde have been studied extensively. The fluorescence quantum yield of this molecule in aqueous solution is 0.06%., 31181-90-5.

Referemce:
Pyridine – Wikipedia,
Pyridine | C5H5N – PubChem

Pyridine is colorless, but older or impure samples can appear yellow. 5315-25-3, formula is C6H6BrN, Name is 2-Bromo-6-methylpyridine. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. Computed Properties of 5315-25-3.

Tesch, Roberta;Rak, Marcel;Raab, Monika;Berger, Lena M.;Kronenberger, Thales;Joerger, Andreas C.;Berger, Benedict-Tilman;Abdi, Ismahan;Hanke, Thomas;Poso, Antti;Strebhardt, Klaus;Sanhaji, Mourad;Knapp, Stefan research published 《 Structure-Based Design of Selective Salt-Inducible Kinase Inhibitors》, the research content is summarized as follows. Salt-inducible kinases (SIKs) are key metabolic regulators. The imbalance in SIK function is associated with the development of diverse cancers, including breast, gastric, and ovarian cancers. Chem. tools to clarify the roles of SIK in different diseases are, however, sparse and are generally characterized by poor kinome-wide selectivity. Here, we have adapted the pyrido[2,3-d]pyrimidin-7-one-based p21-activated kinase (PAK) inhibitor G-5555 for the targeting of SIK, by exploiting differences in the back-pocket region of these kinases. Optimization was supported by high-resolution crystal structures of G-5555 bound to the known off-targets, MST3 and MST4, leading to a chem. probe, MRIA9, with dual SIK/PAK activity and excellent selectivity over other kinases. Furthermore, we show that MRIA9 sensitizes ovarian cancer cells to treatment with the mitotic agent paclitaxel, confirming earlier data from genetic knockdown studies and suggesting a combination therapy with SIK inhibitors and paclitaxel for the treatment of paclitaxel-resistant ovarian cancer.

5315-25-3, 2-Bromo-6-methylpyridine (2BMPy) is a bromopyridine derivative. It is formed when 2-chloro-6-methylpyridine is heated with bromotrimethylsilane. Its synthesis from various methods have been reported.
2-Bromo-6-methylpyridine is a building block in the preparation of nitrogen containing heterocyclic compounds.
2-Bromo-6-methylpyridine is an organic compound that belongs to the group of pyridinium halides. It is soluble in common solvents such as water, ethanol, and acetone. 2BMPy has been shown to act as a glutamate receptor antagonist and has been used in the study of glutamate receptors, including their subtypes. This chemical has also been shown to have antioxidant properties and can be used in the prevention of atherosclerosis., Computed Properties of 5315-25-3

Referemce:
Pyridine – Wikipedia,
Pyridine | C5H5N – PubChem

The critical parameters of pyridine are pressure 6.70 MPa, temperature 620 K and volume 229 cm3·mol−1. 31181-90-5, formula is C6H4BrNO, Name is 5-Bromopicolinaldehyde. In the temperature range 340–426 °C its vapor pressure p can be described with the Antoine equation.. Electric Literature of 31181-90-5.

Singh, Dharmender;Sharma, Shubham;Kumar, Mukesh;Kaur, Inderpreet;Shankar, Ravi;Pandey, Satyendra Kumar;Singh, Virender research published 《 An AcOH-mediated metal free approach towards the synthesis of bis-carbolines and imidazopyridoindole derivatives and assessment of their photophysical properties》, the research content is summarized as follows. An AcOH-mediated concise, atom-economical and environmentally sustainable tandem strategy was formulated to access highly fluorescent (φ_F up to 40%) bis-carbolines I [R¹ = Me, Et, allyl, Bn, etc.; R² = H, CO₂Me, CO₂Et, CO₂i-Pr], imidazopyrido[3,4-b]indoles II [R³ = H, Me, 2-HOC₆H₄, etc.] and imidazo[1,5-a]pyridines III [R⁴ = H, n-Pr, 2-pyridyl, etc.; R⁵ = H, 5-Br, 6-Br, 7-Cl] via the formation of three C-N bonds in a single operation. The multicomponent character of the reaction, easy to execute reaction conditions, simple purification procedure and excellent light emitting properties of the product afforded thereof provide a huge scope.

Electric Literature of 31181-90-5, 5-Bromopyridine-2-carbaldehyde is a useful research compound. Its molecular formula is C6H4BrNO and its molecular weight is 186.01 g/mol. The purity is usually 95%.

5-Bromopyridine-2-carbaldehyde is a water soluble organic molecule that has been shown to inhibit the mitochondrial respiratory chain. It is a structural analog of the natural substrate for mitochondrial cytochrome c oxidase, 5-aminolevulinic acid. This compound has been shown to be selective against cancer cells and has anti-viral properties. The photophysical properties of 5-bromopyridine-2-carbaldehyde have been studied extensively. The fluorescence quantum yield of this molecule in aqueous solution is 0.06%., 31181-90-5.

Referemce:
Pyridine – Wikipedia,
Pyridine | C5H5N – PubChem

Pyridine has a conjugated system of six π electrons that are delocalized over the ring. 5315-25-3, formula is C6H6BrN, Name is 2-Bromo-6-methylpyridine. The molecule is planar and, thus, follows the Hückel criteria for aromatic systems. Reference of 5315-25-3.

Singh, Reena;Ganguly, Gaurab;Malinkin, Sergey O.;Demeshko, Serhiy;Meyer, Franc;Nordlander, Ebbe;Paine, Tapan Kanti research published 《 A Mononuclear Nonheme Iron(IV)-Oxo Complex of a Substituted N4Py Ligand: Effect of Ligand Field on Oxygen Atom Transfer and C-H Bond Cleavage Reactivity》, the research content is summarized as follows. A mononuclear iron(II) complex [Fe^II(N4Py^Me2)(OTf)](OTf) (1), supported by a new pentadentate ligand, bis(6-methylpyridin-2-yl)-N,N-bis((pyridin-2-yl)methyl)methanamine (N4Py^Me2), has been isolated and characterized. Introduction of Me groups in the 6-position of two pyridine rings makes the N4Py^Me2 a weaker field ligand compared to the parent N4Py ligand. Complex 1 is high-spin in the solid state and converts to [Fe^II(N4Py^Me2)(CH₃CN)](OTf)₂ (1a) in acetonitrile solution The iron(II) complex in acetonitrile displays temperature-dependent spin-crossover behavior over a wide range of temperature In its reaction with m-CPBA or oxone in acetonitrile at -10°, the iron(II) complex converts to an iron(IV)-oxo species, [Fe^IV(O)(N4Py^Me2)]²⁺ (2). Complex 2 exhibits the Moessbauer parameters δ = 0.05 mm/s and ΔE_q = 0.62 mm/s, typical of N-ligated S = 1 iron(IV)-oxo species. The iron(IV)-oxo complex has a half-life of only 14 min at 25° and is reactive toward oxygen-atom-transfer and hydrogen-atom-transfer (HAT) reactions. Compared to the parent complex [Fe^IV(O)(N4Py)]²⁺, 2 is more reactive in oxidizing thioanisole and oxygenates the C-H bonds of aliphatic substrates including that of cyclohexane. The enhanced reactivity of 2 toward cyclohexane results from the involvement of the S = 2 transition state in the HAT pathway and a lower triplet-quintet splitting compared to [Fe^IV(O)(N4Py)]²⁺, as supported by DFT calculations The second-order rate constants for HAT by 2 is well correlated with the C-H bond dissociation energies of aliphatic substrates. Surprisingly, the slope of this correlation is different from that of [Fe^IV(O)(N4Py)]²⁺, and 2 is more reactive only in the case of strong C-H bonds (>86 kcal/mol), but less reactive in the case of weaker C-H bonds. Using oxone as the oxidant, the iron(II) complex displays catalytic oxidations of substrates with low activity but with good selectivity.

Reference of 5315-25-3, 2-Bromo-6-methylpyridine (2BMPy) is a bromopyridine derivative. It is formed when 2-chloro-6-methylpyridine is heated with bromotrimethylsilane. Its synthesis from various methods have been reported.
2-Bromo-6-methylpyridine is a building block in the preparation of nitrogen containing heterocyclic compounds.
2-Bromo-6-methylpyridine is an organic compound that belongs to the group of pyridinium halides. It is soluble in common solvents such as water, ethanol, and acetone. 2BMPy has been shown to act as a glutamate receptor antagonist and has been used in the study of glutamate receptors, including their subtypes. This chemical has also been shown to have antioxidant properties and can be used in the prevention of atherosclerosis., 5315-25-3.

Referemce:
Pyridine – Wikipedia,
Pyridine | C5H5N – PubChem

Pyridine is colorless, but older or impure samples can appear yellow. 766-11-0, formula is C5H3BrFN, Name is 5-Bromo-2-fluoropyridine. The pyridine ring occurs in many important compounds, including agrochemicals, pharmaceuticals, and vitamins. Historically, pyridine was produced from coal tar. Quality Control of 766-11-0.

Smolinski, Michael P.;Bu, Yahao;Clements, James;Gelman, Irwin H.;Hegab, Taher;Cutler, David L.;Fang, Jane W. S.;Fetterly, Gerald;Kwan, Rudolf;Barnett, Allen;Lau, Johnson Y. N.;Hangauer, David G. research published 《 Discovery of Novel Dual Mechanism of Action Src Signaling and Tubulin Polymerization Inhibitors (KX2-391 and KX2-361)》, the research content is summarized as follows. The discovery of potent, peptide site directed, tyrosine kinase inhibitors has remained an elusive goal. Herein we describe the discovery of two such clin. candidates that inhibit the tyrosine kinase Src. Compound 1 is a phase 3 clin. trial candidate that is likely to provide a first in class topical treatment for actinic keratosis (AK) with good efficacy and dramatically less toxicity compared to existing standard therapy. Compound 2 is a phase 1 clin. trial candidate that is likely to provide a first in class treatment of malignant glioblastoma and induces 30% long-term complete tumor remission in animal models. The discovery strategy for these compounds iteratively utilized mol. modeling, along with the synthesis and testing of increasingly elaborated proof of concept compounds, until the final clin. candidates were arrived at. This was followed with mechanism of action (MOA) studies that revealed tubulin polymerization inhibition as the second MOA.

Quality Control of 766-11-0, 5-Bromo-2-fluoropyridine is a useful research compound. Its molecular formula is C5H3BrFN and its molecular weight is 175.99 g/mol. The purity is usually 95%.
5-Bromo-2-fluoropyridine is a boronic acid that has been shown to react with iodides and form 5-bromo-2-fluoroiodobenzene. The reaction of 5-bromo-2-fluoropyridine with benzene gives the same product as the reaction with 1,3,5-trioxane. The UV absorption of 5-bromo-2-fluoropyridine is found at 230 nm and 260 nm. It also has an absorption band in the infrared region at 1625 cm−1. Vibrational progressions have been observed for this molecule, which are due to dipole moments and electron density distributions in the molecule.
5-bromo-2-fluoropyridine is used in the synthesis of heteroaromatic and aniline derivatives of piperidines as potent ligands used for vesicular acetylcholine transport. , 766-11-0.

Referemce:
Pyridine – Wikipedia,
Pyridine | C5H5N – PubChem

Pyridine is diamagnetic and has a diamagnetic susceptibility of −48.7 × 10−6 cm3·mol−1.The molecular electric dipole moment is 2.2 debyes. 31181-90-5, formula is C6H4BrNO, Name is 5-Bromopicolinaldehyde. TThe standard enthalpy of formation is 100.2 kJ·mol−1 in the liquid phase and 140.4 kJ·mol−1 in the gas phase. Quality Control of 31181-90-5.

So, Haeri;Lee, Hangyul;Kim, Cheal research published 《 A heterocyclic-based bifunctional sensor for detecting cobalt and zinc ion》, the research content is summarized as follows. A new bifunctional chemosensor HBP ((E)-2-(2-((5-bromopyridin-2-yl)methylene)hydrazinyl) quinoline) based on heterocyclic compounds was designed and studied. The HBP showed successful detecting ability toward cobalt ion with a UV-visible red-shift and a color change of colorless to pink. Moreover, toward zinc ion, the HBP showed an obvious fluorescence turn-on response. The binding ratio of the HBP to cobalt and zinc was a 2 to 1 for both ions. The detection limits were found to be 10 nM for Co²⁺ and 18 nM for Zn²⁺. Based on UV-vis and fluorescent spectral variations, Job plots, ESI-MS, FT-IR and calculations, the binding mechanisms of the HBP toward cobalt and zinc ions were proposed.

Quality Control of 31181-90-5, 5-Bromopyridine-2-carbaldehyde is a useful research compound. Its molecular formula is C6H4BrNO and its molecular weight is 186.01 g/mol. The purity is usually 95%.

5-Bromopyridine-2-carbaldehyde is a water soluble organic molecule that has been shown to inhibit the mitochondrial respiratory chain. It is a structural analog of the natural substrate for mitochondrial cytochrome c oxidase, 5-aminolevulinic acid. This compound has been shown to be selective against cancer cells and has anti-viral properties. The photophysical properties of 5-bromopyridine-2-carbaldehyde have been studied extensively. The fluorescence quantum yield of this molecule in aqueous solution is 0.06%., 31181-90-5.

Referemce:
Pyridine – Wikipedia,
Pyridine | C5H5N – PubChem

In contrast to benzene, Pyridine’s electron density is not evenly distributed over the ring, reflecting the negative inductive effect of the nitrogen atom. 31181-90-5, formula is C6H4BrNO, Name is 5-Bromopicolinaldehyde. For this reason, pyridine has a dipole moment and a weaker resonant stabilization than benzene (resonance energy 117 kJ·mol−1 in pyridine vs. 150 kJ·mol−1 in benzene). Application of C6H4BrNO.

So, Haeri;Lee, Minji;Kim, Cheal research published 《 A Unique Thiosemicarbazide-Based Colorimetric Chemosensor for Fe²⁺ in Pure Aqueous Solution with the Lowest Detection Limit》, the research content is summarized as follows. A unique colorimetric chemosensor Hy-bp based on thiosemicarbazide was prepared Hy-bp showed an obvious red-shifted spectrum and unique color change from colorless to deep green only for Fe2+. Detection limit for Fe2+ was 0.34 μM, which is the lowest among those of colorimetric chemosensors previously reported for Fe2+ in pure aqueous solution Hy-bp can be utilized in paper strips and water samples as a colorimetric sensor for detecting Fe2+. The sensing mechanism of Hy-bp for Fe2+ was demonstrated by UV-vis spectroscopy, Job plot, FT-IR and 1H NMR titrations

31181-90-5, 5-Bromopyridine-2-carbaldehyde is a useful research compound. Its molecular formula is C6H4BrNO and its molecular weight is 186.01 g/mol. The purity is usually 95%.

5-Bromopyridine-2-carbaldehyde is a water soluble organic molecule that has been shown to inhibit the mitochondrial respiratory chain. It is a structural analog of the natural substrate for mitochondrial cytochrome c oxidase, 5-aminolevulinic acid. This compound has been shown to be selective against cancer cells and has anti-viral properties. The photophysical properties of 5-bromopyridine-2-carbaldehyde have been studied extensively. The fluorescence quantum yield of this molecule in aqueous solution is 0.06%., Application of C6H4BrNO

Referemce:
Pyridine – Wikipedia,
Pyridine | C5H5N – PubChem