Trichlorfon (T3D3938)

IdentificationTaxonomyBiological PropertiesPhysical PropertiesToxicity ProfileSpectraConcentrationsLinksReferencesGene RegulationTargets (6)XML
Targets (6)
Record Information
Version2.0
Creation Date2013-04-25 07:56:55 UTC
Update Date2014-12-24 20:26:34 UTC
Accession NumberT3D3938
Identification
Common NameTrichlorfon
ClassSmall Molecule
DescriptionTrichlorfon is an organophosphate insecticide used to control cockroaches, crickets, silverfish, bedbugs, fleas, cattle grubs, flies, ticks, leafminers and leaf-hoppers. It is applied to vegetable, fruit and field crops; livestock; ornamental and forestry plantings; in agricultural premises and domestic settings; in greenhouses, and for control of parasites of fish in designated aquatic environments. It is also used for treating domestic animals for control of internal parasites. Trichlorfon is a selective insecticide, meaning that it kills selected insects, but spares many or most other organisms. Trichlorfon is toxic to target insects through direct applications and by ingestion. In other words, it works both by contact and stomach poison action. Trichlorfon acts by interfering with an essential nervous system enzyme, cholinesterase.
Compound Type
  • Ester
  • Household Toxin
  • Insecticide
  • Organic Compound
  • Organochloride
  • Pesticide
  • Synthetic Compound
Chemical Structure
Thumb
MOLSDFPDBSMILESInChI
Synonyms
Synonym
(+-)-Trichlorfon
1-Hydroxy-2,2,2-trichloroethylphosphonic acid dimethyl ester
Chlorophos
Methyl chlorophos
Metrifonate
Metrifonato
Metrifonatum
Chemical FormulaC4H8Cl3O4P
Average Molecular Mass257.437 g/mol
Monoisotopic Mass255.923 g/mol
CAS Registry Number52-68-6
IUPAC Namedimethyl (2,2,2-trichloro-1-hydroxyethyl)phosphonate
Traditional Namebriten
SMILESCOP(=O)(OC)C(O)C(Cl)(Cl)Cl
InChI IdentifierInChI=1S/C4H8Cl3O4P/c1-10-12(9,11-2)3(8)4(5,6)7/h3,8H,1-2H3
InChI KeyInChIKey=NFACJZMKEDPNKN-UHFFFAOYSA-N
Chemical Taxonomy
Description belongs to the class of organic compounds known as dialkyl alkylphosphonates. Dialkyl alkylphosphonates are compounds containing a phosphonic acid that is diesterified with alkyl groups, and the phosphorus atom is also directly attached to an alkyl group.
KingdomOrganic compounds
Super ClassOrganic acids and derivatives
ClassOrganic phosphonic acids and derivatives
Sub ClassPhosphonic acid diesters
Direct ParentDialkyl alkylphosphonates
Alternative Parents
Substituents
  • Dialkyl alkylphosphonate
  • Phosphonic acid ester
  • Halohydrin
  • Chlorohydrin
  • Organic oxygen compound
  • Organopnictogen compound
  • Organic oxide
  • Hydrocarbon derivative
  • Organophosphorus compound
  • Organooxygen compound
  • Organochloride
  • Organohalogen compound
  • Alkyl halide
  • Alkyl chloride
  • Aliphatic acyclic compound
Molecular FrameworkAliphatic acyclic compounds
External Descriptors
Biological Properties
StatusDetected and Not Quantified
OriginExogenous
Cellular Locations
  • Cytoplasm
  • Extracellular
Biofluid LocationsNot Available
Tissue LocationsNot Available
PathwaysNot Available
Applications
Biological Roles
Chemical Roles
Physical Properties
StateSolid
AppearanceWhite powder.
Experimental Properties
PropertyValue
Melting PointNot Available
Boiling PointNot Available
SolubilityNot Available
LogPNot Available
Predicted Properties
PropertyValueSource
Water Solubility7.17 g/LALOGPS
logP0.81ALOGPS
logP1.14ChemAxon
logS-1.6ALOGPS
pKa (Strongest Acidic)10.12ChemAxon
pKa (Strongest Basic)-4.9ChemAxon
Physiological Charge0ChemAxon
Hydrogen Acceptor Count2ChemAxon
Hydrogen Donor Count1ChemAxon
Polar Surface Area55.76 ŲChemAxon
Rotatable Bond Count4ChemAxon
Refractivity47.59 m³·mol⁻¹ChemAxon
Polarizability19.33 ųChemAxon
Number of Rings0ChemAxon
Bioavailability1ChemAxon
Rule of FiveYesChemAxon
Ghose FilterYesChemAxon
Veber's RuleYesChemAxon
MDDR-like RuleYesChemAxon
Spectra
Spectra
Spectrum TypeDescriptionSplash KeyDeposition DateView
GC-MSGC-MS Spectrum - EI-B (Non-derivatized)splash10-0bvi-6900000000-bc340a4a5dc69af91e1c2017-09-12View Spectrum
Predicted GC-MSPredicted GC-MS Spectrum - GC-MS (Non-derivatized) - 70eV, Positivesplash10-08fv-4910000000-377b26693efe1dfbe4cf2021-09-23View Spectrum
Predicted GC-MSPredicted GC-MS Spectrum - GC-MS (Non-derivatized) - 70eV, PositiveNot Available2021-10-12View Spectrum
Predicted GC-MSPredicted GC-MS Spectrum - GC-MS (TMS_1_1) - 70eV, PositiveNot Available2021-11-04View Spectrum
Predicted GC-MSPredicted GC-MS Spectrum - GC-MS (TBDMS_1_1) - 70eV, PositiveNot Available2021-11-04View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 10V, Positivesplash10-0a4i-0090000000-aa5fd250bfa9fee850d52016-08-02View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 20V, Positivesplash10-0006-6970000000-dc597af04c29ce444a942016-08-02View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 40V, Positivesplash10-0006-9210000000-3d224da1d1c959e0c2832016-08-02View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 10V, Negativesplash10-0pb9-1980000000-7d2bf4a5fb9e32654d662016-08-03View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 20V, Negativesplash10-0abc-3690000000-64d4c35a35ea5e4d7c9d2016-08-03View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 40V, Negativesplash10-00dr-3980000000-25b9c552029e0cd0cb752016-08-03View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 10V, Positivesplash10-0a4i-0920000000-dff60238bdc7e3921d702021-10-12View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 20V, Positivesplash10-0a4i-1900000000-dd9d9e4a8e56529eb0b92021-10-12View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 40V, Positivesplash10-0a6r-6900000000-734aca239b9fbf171be22021-10-12View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 10V, Negativesplash10-0udi-0090000000-6884dc582fd40332e5702021-10-12View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 20V, Negativesplash10-0006-9350000000-4bb48a2037b65de50d322021-10-12View Spectrum
Predicted LC-MS/MSPredicted LC-MS/MS Spectrum - 40V, Negativesplash10-05fu-3490000000-c91d932fa28ad35e2f6a2021-10-12View Spectrum
MSMass Spectrum (Electron Ionization)splash10-0bvj-8900000000-7ca1c4413fd81f66277d2014-10-20View Spectrum
1D NMR1H NMR Spectrum (1D, 400 MHz, CDCl3, experimental)Not Available2014-10-20View Spectrum
1D NMR13C NMR Spectrum (1D, 50.18 MHz, CDCl3, experimental)Not Available2014-10-20View Spectrum
1D NMR1H NMR Spectrum (1D, 100 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR13C NMR Spectrum (1D, 100 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR13C NMR Spectrum (1D, 1000 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR1H NMR Spectrum (1D, 1000 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR13C NMR Spectrum (1D, 200 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR1H NMR Spectrum (1D, 200 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR1H NMR Spectrum (1D, 300 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR13C NMR Spectrum (1D, 300 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR1H NMR Spectrum (1D, 400 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR13C NMR Spectrum (1D, 400 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR1H NMR Spectrum (1D, 500 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR13C NMR Spectrum (1D, 500 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR1H NMR Spectrum (1D, 600 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR13C NMR Spectrum (1D, 600 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR1H NMR Spectrum (1D, 700 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR13C NMR Spectrum (1D, 700 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR13C NMR Spectrum (1D, 800 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR1H NMR Spectrum (1D, 800 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR1H NMR Spectrum (1D, 900 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
1D NMR13C NMR Spectrum (1D, 900 MHz, D2O, predicted)Not Available2021-10-25View Spectrum
Toxicity Profile
Route of ExposureNot Available
Mechanism of ToxicityTrichlorfon is a cholinesterase or acetylcholinesterase (AChE) inhibitor. A cholinesterase inhibitor (or 'anticholinesterase') suppresses the action of acetylcholinesterase. Because of its essential function, chemicals that interfere with the action of acetylcholinesterase are potent neurotoxins, causing excessive salivation and eye-watering in low doses, followed by muscle spasms and ultimately death. Nerve gases and many substances used in insecticides have been shown to act by binding a serine in the active site of acetylcholine esterase, inhibiting the enzyme completely. Acetylcholine esterase breaks down the neurotransmitter acetylcholine, which is released at nerve and muscle junctions, in order to allow the muscle or organ to relax. The result of acetylcholine esterase inhibition is that acetylcholine builds up and continues to act so that any nerve impulses are continually transmitted and muscle contractions do not stop. Among the most common acetylcholinesterase inhibitors are phosphorus-based compounds, which are designed to bind to the active site of the enzyme. The structural requirements are a phosphorus atom bearing two lipophilic groups, a leaving group (such as a halide or thiocyanate), and a terminal oxygen.
MetabolismMetabolism of organophosphates occurs principally by oxidation, by hydrolysis via esterases and by reaction with glutathione. Demethylation and glucuronidation may also occur. Oxidation of organophosphorus pesticides may result in moderately toxic products. In general, phosphorothioates are not directly toxic but require oxidative metabolism to the proximal toxin. The glutathione transferase reactions produce products that are, in most cases, of low toxicity. Paraoxonase (PON1) is a key enzyme in the metabolism of organophosphates. PON1 can inactivate some organophosphates through hydrolysis. PON1 hydrolyzes the active metabolites in several organophosphates insecticides as well as, nerve agents such as soman, sarin, and VX. The presence of PON1 polymorphisms causes there to be different enzyme levels and catalytic efficiency of this esterase, which in turn suggests that different individuals may be more susceptible to the toxic effect of organophosphate exposure.
Toxicity ValuesNot Available
Lethal DoseNot Available
Carcinogenicity (IARC Classification)3, not classifiable as to its carcinogenicity to humans. (1)
Uses/SourcesThis is a man-made compound that is used as a pesticide.
Minimum Risk LevelNot Available
Health EffectsAcute exposure to cholinesterase inhibitors can cause a cholinergic crisis characterized by severe nausea/vomiting, salivation, sweating, bradycardia, hypotension, collapse, and convulsions. Increasing muscle weakness is a possibility and may result in death if respiratory muscles are involved. Accumulation of ACh at motor nerves causes overstimulation of nicotinic expression at the neuromuscular junction. When this occurs symptoms such as muscle weakness, fatigue, muscle cramps, fasciculation, and paralysis can be seen. When there is an accumulation of ACh at autonomic ganglia this causes overstimulation of nicotinic expression in the sympathetic system. Symptoms associated with this are hypertension, and hypoglycemia. Overstimulation of nicotinic acetylcholine receptors in the central nervous system, due to accumulation of ACh, results in anxiety, headache, convulsions, ataxia, depression of respiration and circulation, tremor, general weakness, and potentially coma. When there is expression of muscarinic overstimulation due to excess acetylcholine at muscarinic acetylcholine receptors symptoms of visual disturbances, tightness in chest, wheezing due to bronchoconstriction, increased bronchial secretions, increased salivation, lacrimation, sweating, peristalsis, and urination can occur. Certain reproductive effects in fertility, growth, and development for males and females have been linked specifically to organophosphate pesticide exposure. Most of the research on reproductive effects has been conducted on farmers working with pesticides and insecticdes in rural areas. In females menstrual cycle disturbances, longer pregnancies, spontaneous abortions, stillbirths, and some developmental effects in offspring have been linked to organophosphate pesticide exposure. Prenatal exposure has been linked to impaired fetal growth and development. Neurotoxic effects have also been linked to poisoning with OP pesticides causing four neurotoxic effects in humans: cholinergic syndrome, intermediate syndrome, organophosphate-induced delayed polyneuropathy (OPIDP), and chronic organophosphate-induced neuropsychiatric disorder (COPIND). These syndromes result after acute and chronic exposure to OP pesticides.
SymptomsSymptoms of low dose exposure include excessive salivation and eye-watering. Acute dose symptoms include severe nausea/vomiting, salivation, sweating, bradycardia, hypotension, collapse, and convulsions. Increasing muscle weakness is a possibility and may result in death if respiratory muscles are involved. Hypertension, hypoglycemia, anxiety, headache, tremor and ataxia may also result.
TreatmentIf the compound has been ingested, rapid gastric lavage should be performed using 5% sodium bicarbonate. For skin contact, the skin should be washed with soap and water. If the compound has entered the eyes, they should be washed with large quantities of isotonic saline or water. In serious cases, atropine and/or pralidoxime should be administered. Anti-cholinergic drugs work to counteract the effects of excess acetylcholine and reactivate AChE. Atropine can be used as an antidote in conjunction with pralidoxime or other pyridinium oximes (such as trimedoxime or obidoxime), though the use of '-oximes' has been found to be of no benefit, or possibly harmful, in at least two meta-analyses. Atropine is a muscarinic antagonist, and thus blocks the action of acetylcholine peripherally.
Normal Concentrations
Not Available
Abnormal Concentrations
Not Available
DrugBank IDNot Available
HMDB IDNot Available
PubChem Compound ID5853
ChEMBL IDCHEMBL167150
ChemSpider ID5644
KEGG IDC07971
UniProt IDNot Available
OMIM ID
ChEBI ID6908
BioCyc IDNot Available
CTD IDNot Available
Stitch IDNot Available
PDB IDNot Available
ACToR IDNot Available
Wikipedia LinkNot Available
References
Synthesis ReferenceNot Available
MSDST3D3938.pdf
General References
  1. International Agency for Research on Cancer (2014). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans. [Link]
Gene Regulation
Up-Regulated GenesNot Available
Down-Regulated Genes
GeneGene SymbolGene IDInteractionChromosomeDetails

Targets

Target Details
1. Collagen alpha-1(III) chain
General Function:
Platelet-derived growth factor binding
Specific Function:
Collagen type III occurs in most soft connective tissues along with type I collagen. Involved in regulation of cortical development. Is the major ligand of GPR56 in the developing brain and binding to GPR56 inhibits neuronal migration and activates the RhoA pathway by coupling GPR56 to GNA13 and possibly GNA12.
Gene Name:
COL3A1
Uniprot ID:
P02461
Molecular Weight:
138564.005 Da
Binding/Activity Constants
TypeValueAssay TypeAssay Source
AC501.48 uMBSK_hDFCGF_CollagenIII_downBioSeek
References
  1. Sipes NS, Martin MT, Kothiya P, Reif DM, Judson RS, Richard AM, Houck KA, Dix DJ, Kavlock RJ, Knudsen TB: Profiling 976 ToxCast chemicals across 331 enzymatic and receptor signaling assays. Chem Res Toxicol. 2013 Jun 17;26(6):878-95. doi: 10.1021/tx400021f. Epub 2013 May 16. [23611293 ]
Target Details
2. Urokinase plasminogen activator surface receptor
General Function:
Urokinase plasminogen activator receptor activity
Specific Function:
Acts as a receptor for urokinase plasminogen activator. Plays a role in localizing and promoting plasmin formation. Mediates the proteolysis-independent signal transduction activation effects of U-PA. It is subject to negative-feedback regulation by U-PA which cleaves it into an inactive form.
Gene Name:
PLAUR
Uniprot ID:
Q03405
Molecular Weight:
36977.62 Da
Binding/Activity Constants
TypeValueAssay TypeAssay Source
AC501.48 uMBSK_BE3C_uPAR_upBioSeek
References
  1. Sipes NS, Martin MT, Kothiya P, Reif DM, Judson RS, Richard AM, Houck KA, Dix DJ, Kavlock RJ, Knudsen TB: Profiling 976 ToxCast chemicals across 331 enzymatic and receptor signaling assays. Chem Res Toxicol. 2013 Jun 17;26(6):878-95. doi: 10.1021/tx400021f. Epub 2013 May 16. [23611293 ]
Target Details
3. Nuclear receptor subfamily 1 group I member 2
General Function:
Zinc ion binding
Specific Function:
Nuclear receptor that binds and is activated by variety of endogenous and xenobiotic compounds. Transcription factor that activates the transcription of multiple genes involved in the metabolism and secretion of potentially harmful xenobiotics, drugs and endogenous compounds. Activated by the antibiotic rifampicin and various plant metabolites, such as hyperforin, guggulipid, colupulone, and isoflavones. Response to specific ligands is species-specific. Activated by naturally occurring steroids, such as pregnenolone and progesterone. Binds to a response element in the promoters of the CYP3A4 and ABCB1/MDR1 genes.
Gene Name:
NR1I2
Uniprot ID:
O75469
Molecular Weight:
49761.245 Da
Binding/Activity Constants
TypeValueAssay TypeAssay Source
AC502.60 uMNVS_NR_hPXRNovascreen
References
  1. Sipes NS, Martin MT, Kothiya P, Reif DM, Judson RS, Richard AM, Houck KA, Dix DJ, Kavlock RJ, Knudsen TB: Profiling 976 ToxCast chemicals across 331 enzymatic and receptor signaling assays. Chem Res Toxicol. 2013 Jun 17;26(6):878-95. doi: 10.1021/tx400021f. Epub 2013 May 16. [23611293 ]
Target Details
4. HLA class II histocompatibility antigen, DR alpha chain
General Function:
Peptide antigen binding
Specific Function:
Binds peptides derived from antigens that access the endocytic route of antigen presenting cells (APC) and presents them on the cell surface for recognition by the CD4 T-cells. The peptide binding cleft accommodates peptides of 10-30 residues. The peptides presented by MHC class II molecules are generated mostly by degradation of proteins that access the endocytic route, where they are processed by lysosomal proteases and other hydrolases. Exogenous antigens that have been endocytosed by the APC are thus readily available for presentation via MHC II molecules, and for this reason this antigen presentation pathway is usually referred to as exogenous. As membrane proteins on their way to degradation in lysosomes as part of their normal turn-over are also contained in the endosomal/lysosomal compartments, exogenous antigens must compete with those derived from endogenous components. Autophagy is also a source of endogenous peptides, autophagosomes constitutively fuse with MHC class II loading compartments. In addition to APCs, other cells of the gastrointestinal tract, such as epithelial cells, express MHC class II molecules and CD74 and act as APCs, which is an unusual trait of the GI tract. To produce a MHC class II molecule that presents an antigen, three MHC class II molecules (heterodimers of an alpha and a beta chain) associate with a CD74 trimer in the ER to form a heterononamer. Soon after the entry of this complex into the endosomal/lysosomal system where antigen processing occurs, CD74 undergoes a sequential degradation by various proteases, including CTSS and CTSL, leaving a small fragment termed CLIP (class-II-associated invariant chain peptide). The removal of CLIP is facilitated by HLA-DM via direct binding to the alpha-beta-CLIP complex so that CLIP is released. HLA-DM stabilizes MHC class II molecules until primary high affinity antigenic peptides are bound. The MHC II molecule bound to a peptide is then transported to the cell membrane surface. In B-cells, the interaction between HLA-DM and MHC class II molecules is regulated by HLA-DO. Primary dendritic cells (DCs) also to express HLA-DO. Lysosomal microenvironment has been implicated in the regulation of antigen loading into MHC II molecules, increased acidification produces increased proteolysis and efficient peptide loading.
Gene Name:
HLA-DRA
Uniprot ID:
P01903
Molecular Weight:
28606.685 Da
Binding/Activity Constants
TypeValueAssay TypeAssay Source
AC504.44 uMBSK_BE3C_hLADR_upBioSeek
References
  1. Sipes NS, Martin MT, Kothiya P, Reif DM, Judson RS, Richard AM, Houck KA, Dix DJ, Kavlock RJ, Knudsen TB: Profiling 976 ToxCast chemicals across 331 enzymatic and receptor signaling assays. Chem Res Toxicol. 2013 Jun 17;26(6):878-95. doi: 10.1021/tx400021f. Epub 2013 May 16. [23611293 ]
Target Details
5. Interleukin-1 alpha
General Function:
Cytokine activity
Specific Function:
Produced by activated macrophages, IL-1 stimulates thymocyte proliferation by inducing IL-2 release, B-cell maturation and proliferation, and fibroblast growth factor activity. IL-1 proteins are involved in the inflammatory response, being identified as endogenous pyrogens, and are reported to stimulate the release of prostaglandin and collagenase from synovial cells.
Gene Name:
IL1A
Uniprot ID:
P01583
Molecular Weight:
30606.29 Da
Binding/Activity Constants
TypeValueAssay TypeAssay Source
AC504.44 uMBSK_BE3C_IL1a_upBioSeek
References
  1. Sipes NS, Martin MT, Kothiya P, Reif DM, Judson RS, Richard AM, Houck KA, Dix DJ, Kavlock RJ, Knudsen TB: Profiling 976 ToxCast chemicals across 331 enzymatic and receptor signaling assays. Chem Res Toxicol. 2013 Jun 17;26(6):878-95. doi: 10.1021/tx400021f. Epub 2013 May 16. [23611293 ]
Target Details
6. Tissue-type plasminogen activator
General Function:
Serine-type endopeptidase activity
Specific Function:
Converts the abundant, but inactive, zymogen plasminogen to plasmin by hydrolyzing a single Arg-Val bond in plasminogen. By controlling plasmin-mediated proteolysis, it plays an important role in tissue remodeling and degradation, in cell migration and many other physiopathological events. Plays a direct role in facilitating neuronal migration.
Gene Name:
PLAT
Uniprot ID:
P00750
Molecular Weight:
62916.495 Da
Binding/Activity Constants
TypeValueAssay TypeAssay Source
AC504.44 uMBSK_BE3C_tPA_upBioSeek
References
  1. Sipes NS, Martin MT, Kothiya P, Reif DM, Judson RS, Richard AM, Houck KA, Dix DJ, Kavlock RJ, Knudsen TB: Profiling 976 ToxCast chemicals across 331 enzymatic and receptor signaling assays. Chem Res Toxicol. 2013 Jun 17;26(6):878-95. doi: 10.1021/tx400021f. Epub 2013 May 16. [23611293 ]