Loss Of Ethylene Research Articles

Single-Step Synthesis of Cell-Permeable Protein Dimerizers That Activate Signal Transduction and Gene Expression

The one-step “dimerization” (with loss of ethylene) of the immunosuppressant FK506 by olefin metathesis has been used to create new chemical inducers of dimerization (CIDs). These small-molecule protein dimerizers are shown to activate signal transduction pathways and gene transcription at low concentrations in mammalian cells. Their ease of synthesis provides ready access to reagents of widespread utility in studies of the cellular functions of proteins.

A tandem mass spectrometry and Fourier transform-ion cyclotron resonance study of ionized ethylated acetone and deuterated analogs

The unimolecular dissociation of (CH3)2C+OC2H5 ions (I) and their deuterated analogs, generated by ion-molecule reactions (IMR) in acetone-ethyl iodide mixtures was studied by tandem mass Spectrometry methods. Two significant processes that yielded I ions were identified. The Fourier transform ion cyclotron resonance study showed that the reaction between ionized ethyl iodide and neutral acetone was the principal source of I. This process involved the formation of the stable mixed ionized dimer, [C2H5I·O=C(CH3)2]+· (II), which dissociated by the loss of an I atom. Other important fragmentation pathways of II were the formation of C2H5I+·, (CH3)2CO+·; and (CH3)2COI+ and the loss of CH3CHI·. The major dissociation of I was the loss of C2H4. The activation energy for this reaction was determined by metastable ion appearance energy measurements to be ∼55 kJ mol−1 above the thermochemical minimum. The analysis of the metastable and collision-induced dissociation of D-labeled I showed an unusual time-energy effect on the degree of H/D mixing, with the highest selectivity for the ethene loss [β-H(D)-atom shift] being observed for ions with the lowest internal energies. Collisional excitation could not produce significant H/D mixing among dissociating ions. The results were rationalized by the existence of two species— the classical (2-ethoxypropyl) and nonclassical (proton-bound acetone-ethene pair) isomers of I. The classical structure was originally formed by IMR or from II. The energy barrier for the classical to nonclassical isomerization lay well above the thermochemical threshold for C2H4 loss, providing only limited H-atom mixing in nonclassical ions that were always formed in their dissociative state. The effect of the proton affinity of the carbonyl compound on the H/D mixing in RR′C+OC2H5 ions was studied. It was shown that the selectivity for the ethene loss (β-H-atom shift) generally increased with the increase of the proton affinity of RR′CO. Neutralization-reionization mass spectrometry was applied to a study of (CH3)2C+OR ions, where R = H, I, C2H5. The observation of a recovery signal for the ion I was attributed to the formation of the 2-ethoxypropyl radical. Neutral counterparts of (CH3)2COI+ ions were also generated, being the first example of IO-substituted alkyl radicals.

Novel [3 + 2] 1,3-Cycloaddition of the Ionized Carbonyl Ylide +CH2OCH2• with Carbonyl Compounds in the Gas Phase

For the first time [3 + 2] 1,3-cycloaddition of an ionized carbonyl ylide has been observed in gas phase ion−molecule reactions of +CH2OCH2• (1) with several carbonyl compounds. The reaction, which competes with electrophilic addition that leads to net CH2•+ transfer, occurs across the CO double bond of acetaldehyde and several acyclic ketones yielding ionized 4,4-dialkyl-1,3-dioxolanes as unstable cycloadducts. Rapid dissociation of the nascent cycloadducts by loss of a 4-alkyl substituent as a radical leads to the observed products, that is cyclic 4-alkyl-1,3-dioxolanylium ions. Cycloaddition of 1 with cyclic ketones yields bicyclic spiro adducts, which also undergo rapid dissociation. Cyclobutanone yields ionized 1,3-dioxaspiro[4,3]octane, which dissociates exclusively by neutral ethene loss to ionized 4-methylene-1,3-dioxolane. Ionized 1,3-dioxaspiro[4,4]nonane is formed in reactions with cyclopentanone, and its rapid dissociation by loss of C3H6 and C2H5• yields the ionized 4-methylene-1,3-dioxolanylium and the 4-ethenyl-1,3-dioxolanylium product ions, respectively. A systematic study of this novel reaction and characterization of the product ions carried out via pentaquadrupole (QqQqQ) multiple stage (MS2 and MS3) mass spectrometric experiments provide experimental evidence for the cycloaddition mechanism. The dissociation chemistry observed for the cycloaddition products correlate well with their proposed structures and was compared to that of both isomeric and reference ions. Ab initio MP2/6-31G(d,p)//HF/6-31G(d,p) + ZPE potential energy surface diagrams for the reactions of 1 with acetone, fluoroacetone, and 1,1,1-trifluoroacetone support the operation of the two competitive reaction pathways, that is CH2•+ transfer and [3 + 2] 1,3-cycloaddition/dissociation, and show that the cycloaddition process is favored by electron-withdrawing substituents.

Ethylene elimination upon addition of acids to the μ-ethenyl complex [Fe2(CO)4(μ-η2-HC=CH2)(μ-PCy2)(μ-dppm)]: Synthesis of halide- and carboxylate-bridged diiron carbonyl complexes

Addition of acids to the μ-ethenyl complex [Fe2(CO)4(μ-η2-HC=CH2)(μ-PCy2)(μ-dppm)] 1 results in selective proton transfer to the α-carbon and loss of ethylene. When the anion is coordinating, subsequent attack at the diiron centre provides a convenient synthesis of halide- and carboxylate-bridged diiron complexes [Fe2(CO)4(μ-X)(μ-PCy2)(μ-dppm)] 2a–c (X = F, Cl, Br) and [Fe2(CO)4(μ-η2O2CY)(μ-PCy2)(μ-dppm)] 3a–e (Y = H, CF3, CCl3, CBr3, CO2H) respectively. When it is poorly coordinating, scavenging of two carbonyls affords the hexacarbonyl complexes [Fe2(CO)6(μ-PCy2)(μ-dppm)] [Z]4 (Z = F, BF4, PF6, 0.5SO4), the yield of which is increased under a carbon-monoxide atmosphere. In order to elucidate mechanistic details the reactions have been monitored by IR, 1H and 31P NMR spectroscopies. These reveal the formation of an intermediate, spectroscopically characterised as the vinyl-hydride [HFe2(CO)4(μ-η2-HC=CH2)(μ-PCy2)(μ-dppm)][BF4] 5, which is stable in the presence of ethylene and propene. Crystallographic studies have been carried out on [Fe2(CO)4(μ-Cl)(μ-PCy2)(μ-dppm)] 2b, [Fe2(CO)4(μ-Br)(μ-PCy2)(μ-dppm)] 2c and [Fe2(CO)4)(μ-η2-O2CH)(μ-PCy2)(μ-dppm)] 3a. All contain a short iron—iron vector bridged symmetrically by diphosphine and phosphido moieties with a relative trans orientation, and the halide or carboxylate anion which lies cis to both the latter.

Computational View of the Mechanism of Vinylphosphirane Pyrolysis and a New Route to Phosphaalkynes

Results obtained with semiempirical MO methods support a mechanism for the pyrolysis of vinylphosphirane yielding phosphapropyne in which extrusion of ethylene leads to a vinylphosphinidene intermediate. A pathway from vinylphosphinidene to phosphapropyne involving 2H-phosphirene and 2-phosphapropenylidene intermediates is predicted from high level ab initio results to have a higher energy barrier than that for direct rearrangement. A higher energy pathway from vinylphosphirane is the migration of a hydrogen atom forming methyl(1-phosphiranyl)methylene, followed by loss of ethylene to yield the phosphaalkyne product. However, since fragmentation of 1-phosphiranylmethylene, once formed, has a low predicted barrier, its generation emerged as a new route to phosphaalkynes. (Trimethylsilyl)(1-phosphiranyl)diazomethane was synthesized, and its pyrolysis yields Me3SiC⋮P.

Gas phase studies of silacyclobutanes: recent developments employing triple quadrupole detection

Four silacyclobutyl anions have been prepared and studied by gas phase ion-molecule chemistry using newly modified tandem flowing afterglow instrumentation. These silacyclobutyl anions, which include a pentacoordinate adduct of 1,1-dimethylsilacyclobutane and fluoride and an α-silylcarbanion, siloxide, and mercaptide corresponding to 1,1-dimethylsilacyclobutane, have been characterized by their chemical reactivity and collision-induced loss of ethylene under a variety of conditions. The CH, OH, and SH gas phase acidities of 1,1-dimethylsilacyclobutane. 1-hydroxy-1-methylsilacyclobutane, and 1-mercapto-1-methylsilacyclobutane have been measured and show no effect of the silacyclobutyl attachment. The full capabilities of the newly modified instrumentation include the mass selection of ions, their chemical characterization, collision-induced dissociation of both mass selected ions and those prepared by chemical reactions, and triple quadrupole detection.

Gas-Phase Chemistry of Protonated Ethylamine: A Mass Spectrometric and Molecular Orbital Study

The unimolecular dissociation of protonated ethylamine, [CH3CH2NH3]+, 1, has been examined by both mass spectrometric techniques and molecular orbital calculations. Metastable dissociations of various deuterated species demonstrate that the loss of ethene from 1 involves specifically a transfer of a hydrogen atom from the methyl to the NH2 group. A very limited scrambling (4%) of the hydrogen atoms of the ethyl moiety is observed. Ab initio molecular orbital calculations have been performed at the MP4SDTQ/6-311G**//MP2/6-31G*+ZPE level of theory to examine the mechanism of the unimolecular dissociation of ions 1. It appears that 1 loses a molecule of ethene after a rate-determining isomerization into a proton-bound complex: [C2H4···NH4]+, 2. The marginal hydrogen scrambling is accounted for by 1,2-H shifts on the ethyl group inside a second, loosely bonded, complex involving an ethyl cation and a molecule of ammonia: [C2H5···NH3]+, 3.

Examination of Sputtered Ion Mechanisms Leading to the Formation of C7H7+ during Surface Induced Dissociation (SID) Tandem Mass Spectrometry (MS/MS) of Benzene Molecular Cations

Recent work reported in the literature has shown new evidence of a sputtered ion mechanism for associative ion surface reactions occurring during surface induced dissociation (SID) tandem mass spectrometry (MS/MS). In the context of a sputtered ion mechanism, we have studied selected routes to the formation of C7H7+ during the low-energy collision (ca. 30 eV) of benzene molecular ions with surfaces covered with a hydrocarbon overlayer. A key approach utilized in this work is the use of gas phase ion molecule chemistry to model reactive ion surface collisions. Benzene, 2H6-labeled benzene, and 13C6-labeled benzene have been examined by SID and collision activated dissociation (CAD). The CAD experiments have been used to investigate the fragmentation of hydrocarbon adducts of benzene and labeled benzene formed by methane and isobutane chemical ionization (CI) as models of those ions which may be formed via a sputtered ion mechanism during SID. In addition, the thermodynamics of many of the possible sputtered ion routes to the formation of C7H7+ have been compared using experimental heats of formation as well as total energies and zero-point vibrational energies (ZPVE) obtained by ab initio (MP2 6-31G*//HF 6-31G*) calculations. While there are several seemingly viable sputtered ion routes to the formation of C7H7+ during SID of benzene molecular ions, the combination of thermodynamic considerations and experimental results suggest that a likely sputtered ion route involves the reaction of neutralized benzene ions with C3H5+ ions (sputtered from the hydrocarbon overlayer) followed by the loss of ethene.

Fragmentation of Organosulfur Compounds upon Electron Impact. II. Metastable Decomposition of Methyl and Ethyl Thiolactates.

The unimolecular decomposition of the molecular ions of methyl thiolactate (1) and ethyl thiolactate (2) upon electron impact was investigated. The metastable fragmentation of 1+· is dominated by the loss of methanol. The molecular ions 2+· decompose in a variety of ways: the loss of water, the loss of ethylene, as well as the loss of ethanol are prominent. Both methyl and ethyl thiolactates do not show the fragmentation with double hydrogen transfer, which is observed in methyl lactate (3) and ethyl lactate (4).

Origin and fine tuning of the stability of five-coordinated platinum(II) and palladium(II) species. A quantum-mechanical study

Ab initio computations have been performed to characterize the ground state geometries of a number of platinum and palladium complexes [M(N-N) (C 2H 4)XY] N-N = bidentate N-donor ligand; X,Y = monodentate ligands) and their stability toward the loss of ethylene. The results have been interpreted by an energy component analysis. The computations point out the respective roles of electron donation from ethylene and of back-donation from the metal in determining the relative stabilities of different five-coordinated complexes with respect to their four-coordinated counterparts. Experimental trends are correctly reproduced and interpreted in terms of these two effects. Modifications induced by the deformation energy connected to the addition of a fifth ligand are probably overestimated by our computational model.

Ethylene oxidation in a well‐stirred reactor

AbstractThe detailed ethylene oxidation data set of Thornton [1], obtained for a well‐stirred reactor operated fuel‐lean at atmospheric pressure and for temperatures of 1003 K to 1253 K, is used as a basis for the comparison of chemical kinetic mechanisms reported in the literature and for the development of a new ethylene oxidation mechanism. The mechanisms examined are those of Westbrook and Pitz [2] and Dagaut et al. [3]. These mechanisms indicated that unusually large rates for the vinyl decomposition reaction are required to obtain agreement with the Thornton data set.A new ethylene oxidation mechanism is developed in order to overcome some of the drawbacks of the previous mechanisms. The new mechanism closely simulates the overall rate of loss of ethylene, and the concentration of CO, CO2, H2, CH2O, C2H2, CH3OH, CH4, and C2H6 measured for the stirred reactor. Predictions by this mechanism are dependent on a new high temperature vinyl oxidation route, with akC2H3+O2CH2CHO+C/kC2H3+O2CH2O+HCO branching ratio of 1.4 at 1053 K to 2.05 at 1253 K. The branching ratio values were dependent upon the extent of fall‐off for the C2H3 + O2 = CH2O + HCO reaction. © 1995 John Wiley & Sons, Inc.

ANALYSIS OF ETHANOL AND ACETALDEHYDE RECOVERY FROM PERCHLORIC ACID-TREATED BLOOD

Recovery of acetaldehyde (0-20 microM) or ethanol (0-50 mM) added to blood and subsequently treated with perchloric acid (PCA) was evaluated using head-space gas chromatography and compared with controls. Using blood from five dogs, < 100% of acetaldehyde and ethanol was recovered from PCA-treated samples. Mathematical models of putative binding mechanisms indicated acetaldehyde partitioned simply between supernatant and PCA-induced precipitate and occupied < 1% of acetaldehyde binding sites on precipitate; ethanol partitioned simply between supernatant and precipitate and occupied > 62% of ethanol binding sites. The mathematical model also indicated acetaldehyde binding is 2500-fold stronger than ethanol binding. These results indicate as much as 46.4% of acetaldehyde may be bound to PCA-induced precipitate formed in whole blood. This loss of acetaldehyde is 3- to 4-fold greater than acetaldehyde loss caused by evaporation from PCA-treated blood.

Ion–neutral complex formation and hydrogen‐shifts in the alkene loss from ionized alkyl phenyl thioethers in the gas phase

AbstractThe mechanistic aspects of alkene loss from ionized ethyl‐and n‐propyl phenyl thioethers have been studied by use of deuterium labelling and tandem mass spectrometry. Loss of ethene from the molecular ion of ethyl phenyl thioether proceeds predominantly by a specific H‐shift from the β‐position of the ethyl group to the remaining part of the ion. In contrast, deuterium labelling reveals that elimination of propene from the molecular ions of the n‐propyl phenyl and n‐propyl 2,6‐dimethylphenyl thioethers involves three competing reactions: (i) a 1,2‐hydride shift assisted cleavage of the bond between the propyl group and the sulfur atom yielding an ion–neutral complex of a thiophenyoxy radical and a secondary propyl carbenium ion, which reacts further by proton transfer prior to dissociation; (ii) a partially reversible 1,5‐H shift from the β‐position to the 2‐ or 6‐position of the ring; and (iii) a 1,3‐H shift from the β‐position to the sulfur atom. The preference for transfer of a hydrogen atom from the β‐position is particularly pronounce for the reactions of the metastable molecular ions of the n‐propyl phenyl and n‐propyl 2,6‐dimethylphenyl thioethers. This indicates that the critical energies of the processes involving H‐shifts are lower than the critical energy for propene loss with intermediate formation of an ion–neutral complex. In addition to ethene elimination, ionized ethyl phenyl thioether expels a HS+· radical. This reaction is preceded by an interchange between the hydrogen atoms at the α‐methylene group and the hydrogen atoms at the 2‐ and 6‐positions of the ring as observed also for ionized methyl phenyl thioether.

Comparison of the mass spectrometric behaviour of fluorinated ethers and sulphides

AbstractThe mass spectrometric behaviour of two pairs of fluorinated vinyl‐ and allyl‐ethers and thioethers has been studied in detail with the aid of metastable ion data and accurate mass measurements. Clear differences have been observed between the two sets of compounds; while for the ethers the McLafferty rearrangement with ethylene loss represents a highly favoured decomposition route, for the thioethers the loss of the ethyl radical is preferred. Some decomposition routes, common to all the compounds examined, suggest the presence of hydrogen atom bridging between carbon and fluorine atoms. Theoretical calculations have shown that such a quasi CHF structure is already present in the neutral molecule in its ground state.

A tandem mass spectrometric study of C2H5I+CH3 ions: A search for the non‐classical ethyl cation stabilized by methyl iodide

AbstractThe results of this study have shown that the C2H5I+CH3 ion containing classical and non‐classical forms of the ethyl group can be generated by gas‐phase ion—molecule reactions. The classical ions fragment by CH4 and CH3⋅ losses, the latter without loss of positional identity of H atoms in the ethyl group. Hydrogen scrambling, however, precedes ethene loss, taking place in an ion of non‐classical form. The latter is produced directly from ion—molecule reactions and from energy‐rich classical ions. The relative energies of the classical and non‐classical ions could not be determined, although the former was proposed to be the global minimum. Finally, the classical ion serves as a source for the ylid ion CH3ICH2+., which previously had eluded preparation.

Effect of ring strain on the formation and pyrolysis of some Diels–Alder adducts of 2-sulfolene (2,3-dihydrothiophene 1,1-dioxide) and maleic anhydride with 1,3-dienes and products derived therefrom

7-Thiabicyclo[4.3.0]non-3-ene 7,7-dioxide 3 and the 2,5-bridged analogues 4–6 formed by Diels–Alder reaction of 2,3-dihydrothiophene 1,1-dioxide (2-sulfolene)2 with butadiene and cyclic 1,3-dienes are found, upon flash vacuum pyrolysis, either to lose SO2 and ethene, or to undergo a retro-Diels–Alder reaction, depending on the degree of ring strain present. The epoxides 10, 13 and 17 of these compounds decompose exclusively by loss of SO2 and ethene to give the mono-epoxides of cyclic 1,4-dienes which undergo further reactions under the pyrolysis conditions. The same final products can also be obtained by extrusion of CO and CO2 from the epoxides 12, 16 and 19 of the corresponding diene–maleic anhydride adducts. In the case of the furan–maleic anhydride adduct, its epoxide 20 fragments by a retro-Diels–Alder reaction to give 1,4-dioxine, which, at high temperatures, is transformed into acrylaldehyde. Pyrolysis of the aziridines 22–24, formed by photochemical reaction of the diene–maleic anhydride adducts with ethyl azidoformate, generally gives complex decomposition products, although for the methylene-bridged compound 22 there is good evidence for the generation of a 1,4-dihydropyridine via a retro-Diels–Alder reaction.

Flash vacuum pyrolysis of stabilised phosphorus ylides. Part 1. Preparation of aliphatic and terminal alkynes

Thermal extrusion of Ph3PO from β-oxoalkylidenetriphenylphosphoranes 4 to give the alkynes 5, which under conventional pyrolysis conditions is restricted to cases in which R1 is an electron withdrawing group, has been successfully achieved for R1= H or alkyl by using FVP. The method allows convenient construction of multigram quantities of the alkynes 5 from alkyl halides 1 and acid chlorides 3 in three steps with good overall yields. Under the conditions used the ylides with R2= cyclobutyl also undergo loss of ethene to provide convenient access to the vinylalkynes 6.

Formation of· CH2CH2CO + and C2H6+· in the metastable decompositions of ionized ethyl formate

AbstractThe products of the metastable decompositions of ionized ethyl formate (a) are characterized. The loss of water from a produces ·CH2CH2CO+, a rarely reported product. Loss of H appears to produce CH2=CHC(OH). The third decomposition is an unusual formation of C2H. This work demonstrates that a previous supposition that isomerization to different intermediates is involved in the losses of ethene and of water from a is correct.

Gas phase reactions of the methylsulfinyl and methyl disulfide anions

The collision induced loss of ethene from deprotonated ethyl methyl sulfoxide yields the methylsulfinyl anion (CH 3SO −) as the major ionic product. This species is a weak base (Δ G° acid (CH 3SOH) = 352 ± 3 kcal mol −1) and a weak oxidising agent. For example it reacts with CS 2 and SO 2 in slow reactions to form OCS − 2 and SO − 3 respectively. The major ionic product of the reaction between CH 3SO − and CS 2 is the methyl disulfide ion CH 3SS −. This species is quite unreactive, consonant with its low basicity (Δ G° acid (CH 3SSH = 345 ± 3 kcal mol −1). It reacts with SO 2 by (i) a fast electron transfer reaction to form SO − 2 and (ii) a slow S/O exchange to form CH 3SO −.

Photoinduced decomposition of fusaric acid with the loss of ethylene

Photoinduced decomposition of fusaric acid with the loss of ethylene