Category: pyridine-derivatives

Authors Diez-Simon, C; Eichelsheim, C; Jacobs, DM; Mumm, R; Hall, RD in ELSEVIER published article about VOLATILE COMPOUNDS; FERMENTATION; COMPONENTS; PROFILES; SAMPLE; ACID; TOOL in [Diez-Simon, Carmen; Eichelsheim, Charlotte; Hall, Robert D.] Wageningen Univ & Res, Lab Plant Physiol, Droevendaalsesteeg 1, NL-6708 PB Wageningen, Netherlands; [Diez-Simon, Carmen; Mumm, Roland; Hall, Robert D.] Netherlands Metabol Ctr, Einsteinweg 55, NL-2333 CC Leiden, Netherlands; [Mumm, Roland; Hall, Robert D.] Wageningen Univ & Res, Wageningen Plant Res Biosci, Droevendaalsesteeg 1, NL-6708 PB Wageningen, Netherlands; [Eichelsheim, Charlotte] Wageningen Univ & Res, Food Chem Lab, Bornse Weilanden 9, NL-6708 WG Wageningen, Netherlands; [Jacobs, Doris M.] Unilever Foods Innovat Ctr, Bronland 14, NL-6708 WH Wageningen, Netherlands in 2021, Cited 36. Quality Control of Ethyl nicotinate. The Name is Ethyl nicotinate. Through research, I have a further understanding and discovery of 614-18-6

Fermented soy sauce is used worldwide to enhance the flavour of many dishes. Many types of soy sauce are on the market, and their differences are mostly related to the country of origin, the production process applied and the ratio of ingredients used. Consequently, several aromas, tastes, colours, and textures are obtained. Nowadays, soy sauce can also be produced without microorganisms making the process shorter and cheaper. However, flavour may be lost. We have carried out a comprehensive metabolomics analysis of volatile compounds using stir bar sorptive extraction (SBSE)-GC-MS to relate differences in volatile content to production history and origin. The results revealed major differences between fermented and non-fermented soy sauces, and a list of volatile compounds is reported as being characteristic of each type. This study was able to relate volatiles to the production process using SBSE-GC-MS and to aroma characteristics using GC-O-MS.

Quality Control of Ethyl nicotinate. Bye, fridends, I hope you can learn more about C8H9NO2, If you have any questions, you can browse other blog as well. See you lster.

Reference:
Pyridine – Wikipedia,
,Pyridine | C5H5N – PubChem

An article Highly selective electrocatalytic oxidation of benzyl C-H using water as safe and sustainable oxygen source WOS:000583614600028 published article about AEROBIC OXIDATION; ANODIC-OXIDATION; ORGANIC ELECTROSYNTHESIS; N-HYDROXYPHTHALIMIDE; ELECTRON-TRANSFER; PRIMARY ALCOHOLS; REDOX CATALYSTS; P-XYLENE; EFFICIENT; HYDROCARBONS in [Sun, Yuxia; Li, Xiaoshan; Yang, Miao; Ding, Mengning] Nanjing Univ, Sch Chem & Chem Engn, Key Lab Mesoscop Chem, Nanjing 210023, Peoples R China; [Xu, Wentao; Xie, Jin] Nanjing Univ, Sch Chem & Chem Engn, State Key Lab Coordinat Chem, Jiangsu Key Lab Adv Organ Mat, Nanjing 210023, Peoples R China in 2020, Cited 78. The Name is Phenyl(pyridin-2-yl)methanone. Through research, I have a further understanding and discovery of 91-02-1. SDS of cas: 91-02-1

The selective oxidation of C-H bond is critical for feedstock manufacturing in chemical industry. Current strategies typically involve the use of oxygen or peroxide as the oxidation reagent under high temperature, which sets severe challenges in production sustainability and industrial safety. Herein, we demonstrate an environmental-friendly and safe electrocatalytic strategy for the selective oxidation of benzyl group to ketones at ambient conditions, while using water as the sole oxygen source. Water addition reduces the onset potential of anodic C-H oxidation, and produces 1-tetralone with satisfying conversion and excellent ketone to alcohol ratio. Layered MnO2 catalysts (with rich oxygen vacancies) further adjust the water affinity and facilitate the oxidation, leading to a significantly improved faradaic efficiency.

Welcome to talk about 91-02-1, If you have any questions, you can contact Sun, YX; Li, XS; Yang, M; Xu, WT; Xie, J; Ding, MN or send Email.. SDS of cas: 91-02-1

Reference:
Pyridine – Wikipedia,
,Pyridine | C5H5N – PubChem

Recommanded Product: Phenyl(pyridin-2-yl)methanone. Mathews, NA; Jose, A; Kurup, MRP in [Mathews, Nimya Ann; Kurup, M. R. Prathapachandra] Cochin Univ Sci & Technol, Dept Appl Chem, Kochi 682022, Kerala, India; [Jose, Anitha] Marthoma Coll, Dept Bot, Tiruvalla 689103, Kerala, India; [Kurup, M. R. Prathapachandra] Cent Univ Kerala, Sch Phys Sci, Dept Chem, Tejaswini Hills, Periye 671316, Kasaragod, India published Synthesis and characterization of a new aroylhydrazone ligand and its cobalt(III) complexes: X-ray crystallography and in vitro evaluation of antibacterial and antifungal activities in 2019.0, Cited 40.0. The Name is Phenyl(pyridin-2-yl)methanone. Through research, I have a further understanding and discovery of 91-02-1.

A new aroylhydrazone ligand, 2-benzoylpyridine-4-methoxybenzhydrazone (BPMBH). and its two cobalt(III) complexes, [Co(BPMB)(2)]NO3 center dot 1.5H(2)O (1) and [Co(BPMB)(2)]Cl center dot 2H(2)O (2) have been synthesized and structurally characterized. The synthesized compounds are physico-chemically characterized by CHN analysis, molar conductivity, magnetic susceptibility measurements and spectroscopic techniques like MS, IR, UV and NMR. The high molar conductivity values of the complexes confirmed the presence of counter ions in the lattice of the cationic complexes. The molecular structure of the aroylhydrazone and its complexes have been resolved using single crystal XRD studies. In the solid state, the aroylhydrazone exists in the amido form as evident from the IR and XRD studies. The tridentate nature of the NNO donor aroylhydrazone was also confirmed from the IR spectral studies. XRD studies reveal that in all complexes, the tridentate aroylhydrazone coordinates to the Co(III) center via pyridine nitrogen, azomethine nitrogen and iminolate oxygen and found to possess distorted octahedral geometry. The complexes are bis-ligated cationic complexes in which chloride and nitrate ions act as counter ions. The antibacterial and antifungal activities of the aroylhydrazone and its Co(III) complexes have been screened against bacterial species Staphylococcus aureus, Enterobacter aerogenes, Bacillus subtilis, Streptococcus pyogenes, Klebsiella pneumonia, Salmonella typhi and Escherichia coli. The antifungal activity was also checked using fungi Aspergillus niger, Penicillium chrysogenum and Rhizopus oryzae. From the activity data we can infer that the metal complexes have better biological activity than the metal free ligand against the bacterial and fungal species which were tested. (C) 2018 Elsevier B.V. All rights reserved.

Recommanded Product: Phenyl(pyridin-2-yl)methanone. Welcome to talk about 91-02-1, If you have any questions, you can contact Mathews, NA; Jose, A; Kurup, MRP or send Email.

Reference:
Pyridine – Wikipedia,
,Pyridine | C5H5N – PubChem

Recommanded Product: 65-22-5. I found the field of Chemistry very interesting. Saw the article A 1,8-naphthalimide-pyridoxal conjugate as a supramolecular gelator for colorimetric read out of F- ions in solution, gel and solid states published in 2019.0, Reprint Addresses Ghosh, K (corresponding author), Univ Kalyani, Dept Chem, Kalyani 741235, W Bengal, India.. The CAS is 65-22-5. Through research, I have a further understanding and discovery of 3-Hydroxy-5-(hydroxymethyl)-2-methylisonicotinaldehyde hydrochloride.

A naphthalimide-pyridoxal conjugate 1 has been designed and synthesized. Compound 1 forms a stable greenish yellow colored gel in DMSO:H2O (8:1 v/v). Rheological study reveals that the gel is mechanically strong (G> G) over a wide range of applied strains. The morphology of the gel as determined by FESEM shows a highly cross-linked fibrous network. The gel is anion-responsive and is selectively transformed into a sol with a color change from greenish yellow to deep blue only in the presence of F- among other anions. In CH3CN, compound 1 was also sensitive to basic anions such as F- and AcO- ions. In solution, F- was differentiated from AcO- through a color change. While the yellow colored solution of 1 in acetonitrile was changed into deep blue in the presence of F-, AcO- ions gave a faint blue coloration. A similar colorimetric differentiation of F- from AcO- has been possible in CH3CN by a reusable Schiff base-linked Merrifield resin 1a or 1b.

Welcome to talk about 65-22-5, If you have any questions, you can contact Pati, C; Ghosh, K or send Email.. Recommanded Product: 65-22-5

Reference:
Pyridine – Wikipedia,
,Pyridine | C5H5N – PubChem

An article Design, synthesis, antiviral bioactivities and interaction mechanisms of penta-1,4-diene-3-one oxime ether derivatives containing a quinazolin-4(3H)-one scaffold WOS:000462706900001 published article about BIOLOGICAL EVALUATION; 1,4-PENTADIEN-3-ONE DERIVATIVES; VIRUS; CURCUMIN; BEARING; 3D-QSAR in [Chen, Lijuan; Wang, Xiaobin; Tang, Xu; Xia, Rongjiao; Guo, Tao; Zhang, Cheng; Li, Xiangyang; Xue, Wei] Guizhou Univ, Minist Educ, Key Lab Green Pesticide & Agr Bioengn, State Key Lab Breeding Base Green Pesticide & Agr, Guiyang 550025, Guizhou, Peoples R China; [Wang, Xiaobin] Nanjing Agr Univ, Coll Sci, Nanjing 210095, Jiangsu, Peoples R China in 2019.0, Cited 39.0. The Name is 3-Pyridinecarboxaldehyde. Through research, I have a further understanding and discovery of 500-22-1. Application In Synthesis of 3-Pyridinecarboxaldehyde

Background: penta-1,4-diene-3-one oxime ether and quinazolin-4(3H)-one derivatives possess favorable agricultural activities. Aiming to discover novel molecules with highly-efficient agricultural activities, a series of penta-1,4-diene-3-one oxime ether derivatives containing a quinazolin-4(3H)-one scaffold were synthesized and evaluated for their antiviral activities. Result: Antiviral bioassays indicated that some title compounds exhibited significant antiviral activity against tobacco mosaic virus (TMV). In particular, compounds 8c, 8j and 8k possessed appreciable curative activities against TMV in vivo, with half-maximal effective concentration (EC50) values of 138.5, 132.9 and 125.6 mu g/mL, respectively, which are better than that of ningnanmycin (207.3 mu g/mL). Furthermore, the microscale thermophoresis experiments (MST) on the interaction of compound 8k with TMV coat protein (TMV CP) showed 8k bound to TMV CP with a dissociation constant of 0.97 mmol/L. Docking studies provided further insights into the interaction of 8k with the Arg90 of TMV CP. Conclusions: Sixteen penta-1,4-diene-3-one oxime ether derivatives containing a quinazolin-4(3H)-one scaffold were designed, synthesized, and their antiviral activities against TMV were evaluated. Antiviral bioassays indicated that some target compounds exhibited remarkable antiviral activities against TMV. Furthermore, through the MST and docking studies, we can speculate that 8k inhibited the virulence of TMV by binding Arg90 in TMV CP. These results indicated that this kind of penta-1,4-diene-3-one oxime ether derivatives containing a quinazolin-4(3H)-one scaffold could be further studied as potential alternative templates in the search for novel antiviral agents.

Welcome to talk about 500-22-1, If you have any questions, you can contact Chen, LJ; Wang, XB; Tang, X; Xia, RJ; Guo, T; Zhang, C; Li, XY; Xue, W or send Email.. Application In Synthesis of 3-Pyridinecarboxaldehyde

Reference:
Pyridine – Wikipedia,
,Pyridine | C5H5N – PubChem

An article Diverse reactivity to hypochlorite and copper ions based on a novel Schiff base derived from vitamin B6 cofactor WOS:000583948500064 published article about FLUORESCENT-PROBE; MITOCHONDRIA; BIOMARKER; SENSORS in [Li, Xiangqian; Wen, Qin; Gu, Jiapei; Wang, Qianming; Zheng, Yuhui] South China Normal Univ, Sch Chem, Guangzhou 510006, Peoples R China; [Liu, Wanqiang] Hunan Univ Sci & Technol, Sch Chem & Chem Engn, Xiangtan 411201, Peoples R China; [Wang, Qianming; Zhou, Guofu; Gao, Jinwei] South China Normal Univ, South China Acad Adv Optoelect, Inst Adv Mat, Guangzhou 510006, Peoples R China; [Wang, Qianming; Zhou, Guofu; Gao, Jinwei] South China Normal Univ, Guangdong Prov Key Lab Opt Informat Mat & Technol, Guangzhou 510006, Peoples R China in 2020.0, Cited 50.0. The Name is 3-Hydroxy-5-(hydroxymethyl)-2-methylisonicotinaldehyde hydrochloride. Through research, I have a further understanding and discovery of 65-22-5. Quality Control of 3-Hydroxy-5-(hydroxymethyl)-2-methylisonicotinaldehyde hydrochloride

A new Schiff base receptor (2-amino-3-(((3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl)methylene) amino)maleonitrile (GAL)) has been synthesized and such diaminomaleonitrile-based molecular framework is observed to be water soluble. GAL possesses both colorimetric and off-on fluorescent response in the presence of ClO-. The response time has been controlled within 6 min. The limit of detection (LOD) has been calculated to be 47.5 nM. The addition of Cu2+ can only induce clear color evolution from pale to deep yellow (LOD: 0.22 mu M) and no fluorescence changes are found. Moreover, its reliability and practicality are verified via the determination of ClO- in spiked samples of tap water and pond water. The exploration of bioactive vitamin B6 cofactor as a sensing platform will open a new way for multiple target recognition in competitive mediums. (C) 2020 Elsevier B.V. All rights reserved.

Welcome to talk about 65-22-5, If you have any questions, you can contact Li, XQ; Wen, Q; Gu, JP; Liu, WQ; Wang, QM; Zhou, GF; Gao, JW; Zheng, YH or send Email.. Quality Control of 3-Hydroxy-5-(hydroxymethyl)-2-methylisonicotinaldehyde hydrochloride

Reference:
Pyridine – Wikipedia,
,Pyridine | C5H5N – PubChem

An article A novel diarylethene probe with high selective recognition of CN- and Mg2+ and its application WOS:000573273600005 published article about DUAL-CHANNEL RECOGNITION; MOLECULAR LOGIC GATES; TURN-ON SENSOR; FLUORESCENT SENSOR; AQUEOUS-MEDIA; COLORIMETRIC SENSOR; SCHIFF-BASE; CYANIDE; CHEMOSENSOR; MAGNESIUM in [Yuwen, Zhiyang; Li, Hui; Pu, Shouzhi] Jiangxi Sci & Technol Normal Univ, Jiangxi Key Lab Organ Chem, Nanchang 330013, Jiangxi, Peoples R China; [Mei, Hongxin] Nanchang Normal Univ, Dept Chem, Nanchang 330013, Jiangxi, Peoples R China in 2020.0, Cited 70.0. Application In Synthesis of 3-Hydroxy-5-(hydroxymethyl)-2-methylisonicotinaldehyde hydrochloride. The Name is 3-Hydroxy-5-(hydroxymethyl)-2-methylisonicotinaldehyde hydrochloride. Through research, I have a further understanding and discovery of 65-22-5

A chemical sensor composed of pyridoxal hydrochloride schiff base based on diarylethene (1O) was synthesized. Its photochemical properties and selectivity to ions were further studied. The chemosensor could detect cyanide effectively and is almost undisturbed by other ions. When titrating CN-, the reaction aroused a distinct change in the absorption spectrum with the color change from transparent to yellow, and the fluorescence intensity centered at 562 nm was increased 68 folds. It also exhibited a good fluorescence sensing of Mg(2+ )with high selectivity and sensitivity. Upon addition of Mg2+, its emission intensity enhanced 110 folds, with the color change from dark to bright blue. Its good spectral response could be applied to molecular logic circuit. Moreover, the chemosensor could be made into test paper strips for the qualitative and quantitative detection of CN- and Mg2+.

Welcome to talk about 65-22-5, If you have any questions, you can contact Yuwen, ZY; Mei, HX; Li, H; Pu, SZ or send Email.. Application In Synthesis of 3-Hydroxy-5-(hydroxymethyl)-2-methylisonicotinaldehyde hydrochloride

Reference:
Pyridine – Wikipedia,
,Pyridine | C5H5N – PubChem

An article Non-covalent interactions governing the supramolecular assembly of copper(II) complexes with hydrazone-type ligand: Experimental and quantum chemical study WOS:000640386000003 published article about SUPEROXIDE-DISMUTASE ACTIVITY; PARAMAGNETIC-RESONANCE SPECTRA; DENSITY-FUNCTIONAL THEORY; AB-INITIO HF; CRYSTAL-STRUCTURES; X-RAY; ACTIVE-SITE; SPECTROSCOPIC CHARACTERIZATION; INTERMOLECULAR INTERACTIONS; NICKEL(II) COMPLEXES in [Singh, Y.; Patel, Ram N.; Patel, Satish K.] APS Univ, Dept Chem, Rewa 486003, MP, India; [Jadeja, R. N.; Patel, Abhay K.; Patel, Neetu] Maharaja Sayajirao Univ Baroda, Fac Sci, Dept Chem, Vadodara 390002, India; [Roy, H.] Maharaja Sayajirao Univ Baroda, Fac Sci, Dept Zool, Vadodara 390002, India; [Kumar, P.] VBS Purvanchal Univ, Rajju Bhaiya Inst Phys Sci Study & Res, Dept Chem, Jaunpur 222203, UP, India; [Butcher, R. J.] Howard Univ, Dept Inorgan & Struct Chem, Washington, DC 22031 USA; [Jasinski, Jerry P.] Keene State Coll, Dept Chem, 229 Main St, Keene, NH 03435 USA; [Cortijo, M.; Herrero, S.] Univ Complutense Madrid, Fac Ciencias Quim, Dept Quim Inorgan, Madrid 28040, Spain in 2021.0, Cited 133.0. SDS of cas: 91-02-1. The Name is Phenyl(pyridin-2-yl)methanone. Through research, I have a further understanding and discovery of 91-02-1

A series of two new mono- and one binuclear m-nitrato bridged copper(II) complexes [Cu(L)(HL)]ClO4 (1), [Cu(HL)(NO3)(H2O)](2)NO3 center dot H2O (2) and [Cu-2(L-2)(mu-NO3)(2)] (3), with an unsymmetrical NNO donor Schiff base (HL) have been synthesized and characterized by elemental analysis, FTIR, CV, UV-vis and EPR spectroscopy. Their molecular structures were also determined by single crystal X-ray crystallography. In the binuclear complex 3, the Cu center dot center dot center dot Cu distance is 3.494 angstrom. In 1, 2 and 3, the Cu(II) centers have distorted square pyramidal geometry (tau(5) = 0.05-0.17). Evidence of weak pi center dot center dot center dot pi stacking intermolecular interactions along with other non-covalent interactions (hydrogen bonding) was observed by analyzing the respective crystal structures of the complexes. Thus, these hydrogen bonds, pi center dot center dot center dot pi stacking interactions and other weak intermolecular interactions establish in the form of supramolecular architectures a crystalline network environment. The non-covalent interactions were also investigated by employing Hirshfeld Analysis. The room temperature magnetic moments of the mononuclear complexes are less than the spin only values which are indicative of small interactions. Also, significant magnetic interactions were not exhibited by binuclear copper(II) complex 3 in the variable temperature magnetic measurements. The X-band EPR spectra of all three complexes exhibit copper(II) hyperfine structures as well as zero-field splitting which are appropriate for the triplet states of dimers. In complexes 1 and 2, the presence of pseudo dipolar interactions is proposed. Quantum chemical calculations (DFT) were carried out on complexes 1-3 to explore the electronic and spectral properties of these newly synthesized complexes. These complexes show significant antiproliferative and SOD activity. The SOD activity measured in terms of kMcCF is in the range 4.94-12.31 (mol L)(-1)s(-1))x 10(4). (C) 2021 Elsevier Ltd. All rights reserved.

SDS of cas: 91-02-1. About Phenyl(pyridin-2-yl)methanone, If you have any questions, you can contact Singh, Y; Patel, RN; Patel, SK; Jadeja, RN; Patel, AK; Patel, N; Roy, H; Kumar, P; Butcher, RJ; Jasinski, JP; Cortijo, M; Herrero, S or concate me.

Reference:
Pyridine – Wikipedia,
,Pyridine | C5H5N – PubChem

SDS of cas: 91-02-1. In 2020.0 SYNTHESIS-STUTTGART published article about STEREOSELECTIVE ADDITION; DIMETHYLPHOSPHINE OXIDE; SYNERGISTIC EXTRACTION; CARBONYL-COMPOUNDS; PHOSPHORUS; ALKENES; CHALCOGENIDES; METHODOLOGY; ABSORPTION; COMPLEXES in [Gusarova, Nina K.; Ivanova, Nina I.; Khrapova, Kseniya O.; Volkov, Pavel A.; Telezhkin, Anton A.; Larina, Lyudmila I.; Afonin, Andrei V.; Pavlov, Dmitry V.; Trofimov, Boris A.] Russian Acad Sci, Siberian Branch, AE Favorsky Irkutsk Inst Chem, 1 Favorsky Str, Irkutsk 664033, Russia in 2020.0, Cited 69.0. The Name is Phenyl(pyridin-2-yl)methanone. Through research, I have a further understanding and discovery of 91-02-1.

Tertiary alpha-hydroxyphosphine oxides have been synthesized via the catalyst- and solvent-free reaction between available secondary phosphine oxides and aliphatic, aromatic and heteroaromatic ketones at 20-62 degrees C in near to 96-98% yield. The developed method meets the requirements of green chemistry and the PASE (pot, atom, step economy) paradigm. According to quantum-chemical calculations at the B3LYP/6-311++G(d,p) level, the synthesized hydroxyphosphine oxides feature a weak (approximate to 3 kcal center dot mol(-1)) O-H center dot center dot center dot O=P intramolecular hydrogen bond.

SDS of cas: 91-02-1. Welcome to talk about 91-02-1, If you have any questions, you can contact Gusarova, NK; Ivanova, NI; Khrapova, KO; Volkov, PA; Telezhkin, AA; Larina, LI; Afonin, AV; Pavlov, DV; Trofimov, BA or send Email.

Reference:
Pyridine – Wikipedia,
,Pyridine | C5H5N – PubChem

SDS of cas: 500-22-1. Riaz, S; Iqbal, M; Ullah, R; Zahra, R; Chotana, GA; Faisal, A; Saleem, RSZ in [Riaz, Sharon; Chotana, Ghayoor Abbas; Saleem, Rahman Shah Zaib] Lahore Univ Management Sci, Syed Babar Ali Sch Sci & Engn, Dept Chem & Chem Engn, Lahore 54792, Pakistan; [Iqbal, Maheen; Ullah, Rahim; Zahra, Rida; Faisal, Amir] Lahore Univ Management Sci, Syed Babar Ali Sch Sci & Engn, Dept Biol, Lahore 54792, Pakistan published Synthesis and evaluation of novel alpha-substituted chalcones with potent anti-cancer activities and ability to overcome multidrug resistance in 2019.0, Cited 45.0. The Name is 3-Pyridinecarboxaldehyde. Through research, I have a further understanding and discovery of 500-22-1.

A series of forty a-substituted chalcones were synthesized and screened for their antiproliferative activities against HCT116 (colorectal) and HCC1954 (breast) cancer cell lines. Compounds 5a and 5e were found to be the most potent compounds with GI(50) values of 0.63 mu M and 0.725 mu M in HCC1954 cell line and 0.69 mu M and 1.59 mu M in HCT116 cell line, respectively. Both compounds induced a G2/M cell cycle arrest and caused apoptotic cell death in HCT116 cells as shown by the induction of PARP cleavage. The compounds also stabilized p53 in a dose-dependent manner in HCT116 cells following 24-hour treatment. Furthermore, both 5a and 5e were able to overcome multidrug resistance in two MDR-1 overexpressing multidrug resistant cell lines.

SDS of cas: 500-22-1. Welcome to talk about 500-22-1, If you have any questions, you can contact Riaz, S; Iqbal, M; Ullah, R; Zahra, R; Chotana, GA; Faisal, A; Saleem, RSZ or send Email.

Reference:
Pyridine – Wikipedia,
,Pyridine | C5H5N – PubChem