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PubMed2005

A facile synthesis of [(11)C]acetylene.

Acetylene is a versatile synthon organic chemistry. The complexity and difficulty of synthesis of [(11)C]acetylene has limited its use as a labeling intermediate for PET radiotracers. A new method for production of [(11)C]acetylene has been developed in our laboratory that simplifies the synthesis procedure allowing for easy automation and implementation. The technique is a modification of Madsen et al. (1981, Phys. Med. Biol. 26(5), 875) that utilized carbon dioxide ((11)C) and barium. First [(11/12)C]CO(2) was trapped at room temperature on barium within a quartz reaction tube, then heated to 900 degrees C under hydrogen flow to release [(11)C]acetylene. Hydrogen gas is apparently oxidized to form water vapor which reacts immediately with the formed carbide to liberate acetylene. Radiochemical yields of 31.4--75.4% and specific activities of 0.11-- 161 mCi/micromol have been obtained with radiochemical purities greater than 99%. This technique provides a new, efficient and very practical synthesis of [(11)C]acetylene that can be utilized as synthon for novel PET radiopharmaceuticals.

Acetylene↗
PubMed2000

Trimethyl phosphate-acetylene interaction: a matrix-isolation infrared and ab initio study.

Trimethyl phosphate (TMP) and acetylene were codeposited in nitrogen and argon matrices and adducts of these species were identified using infrared spectroscopy. Formation of the adducts was evidenced by shifts in the vibrational frequencies of the modes involving the TMP and acetylene submolecules. The structures of these adducts, energies and the vibrational frequencies were computed at the HF/6-31G** level. Both the experimental and computational studies indicated that two types of TMP-acetylene complexes were formed; one in which the hydrogen in acetylene was bonded to the phosphoryl oxygen and another in which the bonding was at the alkoxy oxygen of the phosphate. In addition to the primary hydrogen bonded interaction at the phosphoryl oxygen, this complex, also appeared to be stablilized by a secondary and weaker interaction involving a methyl hydrogen in TMP and the pi cloud in acetylene--a case of a H...pi interaction. The computed vibrational frequencies in the adducts agreed well with the observed frequencies for the modes involving the TMP submolecule, while the agreement was relatively poor for the modes involving the acetylene submolecule. The stabilization energies of these adducts, corrected for both zero-point energies and basis set superposition errors, were approximately 3 kcal/mol for the phosphoryl complex and, approximately 1 kcal/mol for the alkoxy complex.

Acetylene↗
PubMed1978

Metabolic activation of acetylenic substituents to derivatives in the rat causing the loss of hepatic cytochrome P-450 and haem.

1. A number of acetylenic-substituted steroidal and non-steroidal compounds, including 2,2-dipropargylacetamide, pregna-2,4-dien-20-yno[2,3-d]isoxazol-17-ol (Danazol) and acetylene gas, when administered to rats in vivo brought about a decrease in the concentrations of hepatic microsomal cytochrome P-450 and haem. Abnormal haem-breakdown products, ;green pigments', and porphyrins accumulated in the livers of these animals. 2. For loss of microsomal cytochrome P-450 to occur in vitro, metabolic activation of the acetylenic substituent was necessary. The enzyme system responsible required NADPH and air, and was induced by pretreatment of rats with phenobarbitone; these are characteristics typical of the microsomal mixed-function oxidases. 3. When rats were dosed with 17alpha-ethynyl-17beta-hydroxyandrost-4-en-3-one (ethynyltestosterone, 1mmol/kg) the pattern of green pigments extracted from the liver 4h after dosing and separated by t.l.c. was quite different from that in rats given 17beta-hydroxy-17alpha-vinylandrost-4-en-3-one (vinyltestosterone), suggesting that reduction of the unsaturated triple bond to a double bond is not normally part of the metabolic activation pathway of the acetylenic substituent. 4. The green pigments extracted from the livers of rats 4h after the administration of the acetylenic-substituted compounds (1mmol/kg) when separated by silica-gel t.l.c. had variable R(F) values. The number and distribution of green pigments was characteristic for each compound examined. There was little correlation between the total loss of hepatic microsomal haem and the apparent intensity of the green pigments seen on the thin-layer chromatograms. 5. After incubation of [(14)C]acetylene in vitro with microsomal preparations from phenobarbitone-pretreated rats and a NADPH-generating system, no significant covalent binding to microsomal protein was detected over a 30min incubation period, although under similar conditions there was a significant loss of cytochrome P-450.

Acetamides↗
PubMed1986

Evaluation of a modified acetylene rebreathing method for the determination of cardiac output.

In order to evaluate a computerized modified acetylene rebreathing method for the determination of cardiac output, 15 healthy subjects were studied at different levels of their maximal oxygen uptake (VO2max). Submaximal exercise was performed on a cycle ergometer and maximal exercise on a treadmill. Oxygen uptake, heart rate, and cardiac output (acetylene method) were determined in all test situations. In seven subjects simultaneous determinations of cardiac output were made by a modified acetylene rebreathing method (QA) and a dye dilution method (QD). Furthermore, a new resting rebreathing technique was used. The methodological error for QA (means of double samples) was 0.37 litre min-1 (2.8%) in the same individual at 150 W. The corresponding values between individuals were 0.71 (rest), 0.41 (50 W), 0.69 (150 W), and 0.40 litre min-1 (VO2max). Thus the methodological error of the modified acetylene method was very low. There was a significant difference (P less than 0.01), however, between the acetylene method and the dye dilution method, which showed a lower value for QA at all levels. This was probably due to the long response time of the mass spectrometer combined with anatomical and physiological arteriovenous shunt effects in the lungs during exercise. When these factors were considered the correcting formula was: QAc = QA + 0.005 X Q2A. There was no significant difference between the corrected cardiac output values (QAc), and the corresponding QD values. In conclusion, this modified acetylene rebreathing method is a very useful non-invasive method for measuring cardiac output at rest as well as during heavy exercise.

Acetylene↗
PubMed1979

Growth of Nocardia rhodochrous on acetylene gas.

Soil sediment enrichment cultures yielded a coryneform bacterium capable of growing in a mineral salts solution with acetylene gas as its only source of carbon and energy. Based on morphological and physiological traits as well as on cell wall analysis, the bacterium was characterized as a strain of Nocardia rhodochrous. Maximal growth rates (generation time 2.7 to 3.0 h) on acetylene were obtained at 5 to 20% acetylene, 25 to 40% oxygen, pH 7.0 and 26 to 28 degrees C. Yields (grams of dry cells produced per gram of acetylene consumed) ranged between 90 and 110%. N. rhodochrous exhibits a growth factor requirement for the pyrimidine moiety of thiamine. Acetylene utilization is not an obligate trait, and a wide range of alternate carbon sources is utilized. Ethylene is neither produced nor consumed. The only previous report on acetylene utilization appeared in 1932. The Mycobacterium lacticola strain described in that report strongly resembles N. rhodochrous.

Acetylene↗
PubMed1982

Metabolism of acetylene by Nocardia rhodochrous.

A Nocardia rhodochrous strain capable of utilizing acetylene as its sole source of carbon and energy exhibited slow growth on low concentrations of acetaldehyde. Resting cells incubated with acetylene formed a product identified as acetaldehyde, but attempts to demonstrate acetylene hydrase activity in cell-free extracts were unsuccessful. Acetaldehyde dehydrogenase in N. rhodochrous was found to be NAD+ linked and nonacylating, converting acetaldehyde to acetate. Specific activities of acetaldehyde dehydrogenase, acetothiokinase, and isocitrate lyase were enhanced in cells grown on acetylene and ethanol as compared with cells grown on alternate substrates. These results suggest that acetylene is catabolized via acetaldehyde to acetate and eventually to acetyl coenzyme A. Acetylene oxidation in N. rhodochrous appears to be constitutive and is not inhibited in the presence of either ethylene, nitrous oxide, or methane.

Acetaldehyde↗
PubMedDate not supplied

[Study of the inhibitory effect of acetylene on the biological methane formation in a paddy soil (author's transl)].

A 0.05 atm partial pressure of acetylene stopped all the CH4 evolution during anaerobic paddy soil incubations when different carbon substances were added. It was shown proof that acetylene did not disturbe the volatil fatty acids yielding but prohibited the methane forming bacteria from doing future use of those. Acetylene does inhibit methane forming bacteria. Besides, the growth of a Methanosarcina strain was stopped by a 0.01 atm partial pressure of acetylene, and resting cells lost 98 per cent of their activity when the acetylene concentration was 0.5 x 10-3 M in the liquid. This acetylene inhibition can be used for studying the metabolism of methane forming bacteria.

Acetates↗
PubMed1977

Quantitative effects of unsaturated fatty acids in microbial mutants. VII. Influence of the acetylenic bond location on the effectiveness of acyl chains.

The ability of a series of 18 carbon acetylenic fatty acids to fulfill the unsaturated fatty acid requirements of Escherichia coli and Saccharomyces cerevisiae was investigated. Despite their high melting points (greater than 40 degrees C), several isomers of the acetylenic fatty acids were as efficient or more efficient in supporting growth than the analogous fatty acid having a cis-double bond. The efficiencies of the different positional isomers in supporting cell proliferation varied from essentially 0 cells per fmol for the 2-5 and 13-17 isomers to high values when the acetylenic bond was near the center of the chain: e.g. 45 E. coli and 5.5 S. cerevisiae cells/fmol for the 10 isomer. A striking ineffectiveness of the 9 isomer was observed with E. coli. The 7, 8 and 10 isomers were at least 10-fold more efficient than any of the other positional isomers in supporting the growth of E. coli. In contrast, the 9 isomer was among the most effective acetylenic fatty acids tested with the yeast mutant. Chromatographic analysis of the extracted lipids indicated that each of the acetylenic isomers tested (except delta2 and delta3) could be esterified by the prokaryotic and eukaryotic microorganisms. The content of unsaturated plus cyclopropane acids observed when growth ceased in E. coli cultures supplemented with growth-limiting concentrations of the acetylenic fatty acids ranged from approx. 15 mol% for the 8 isomer to approx. 35 mol% for the 14 and 17 isomers. The 8-11 isomers were observed to be esterified predominantly at the two position in phosphatidylethanolamine of E. coli and in phosphatidylcholine of S. cerevisiae.

Cell Division↗
PubMed1985

Effects of acetylenic and olefinic pyrenes upon cytochrome P-450 dependent benzo[a]pyrene hydroxylase activity in liver microsomes.

1-Ethynylpyrene, trans-, & cis-1-(2-bromovinyl)pyrene, methyl 1-pyrenyl acetylene, and phenyl 1-pyrenyl acetylene are substrates for cytochrome P-450 dependent monooxygenases and also inhibitors of cytochrome P-450 dependent benzo[a]pyrene hydroxylase activities in liver microsomes from 5,6-benzoflavone or phenobarbital pretreated rats. 1-Ethynylpyrene, trans-1-(2-bromovinyl)pyrene, and methyl 1-pyrenyl acetylene cause a mechanism based inhibition (suicide inhibition) of the benzo[a]pyrene hydroxylase activities in microsomes from 5,6-benzoflavone or phenobarbital pretreated rats, while cis-1-(2-bromovinyl)pyrene only causes suicide inhibition of the hydroxylse activities in the 5,6-benzoflavone induced microsomes and phenyl 1-pyrenyl acetylene does not cause a detectable suicide inhibition of these activities in either type of microsome. Incubation with NADPH and 1-ethynylpyrene, trans-, or cis-1-(2-bromovinyl)pyrene causes a loss of the P-450 content in the microsomes from 5,6-benzoflavone or phenobarbital pretreated rats, but incubations with methyl 1-pyrenyl acetylene or phenyl 1-pyrenyl acetylene did not cause a loss of the P-450 content of either microsomal preparation.

Animals↗
PubMed1999

Acetylene hydratase of Pelobacter acetylenicus. Molecular and spectroscopic properties of the tungsten iron-sulfur enzyme.

Acetylene hydratase of Pelobacter acetylenicus is a tungsten iron-sulfur protein involved in the fermentation of acetylene to ethanol and acetate. Expression of the enzyme was increased 10-fold by feeding a 50-L batch culture continuously with 104 Pa acetylene at pH 6.8-7.0. Acetylene hydratase was purified to homogeneity by a three-step procedure in either the absence or presence of dioxygen. The enzyme was a monomer with a molecular mass of 73 kDa (SDS/PAGE) or 83 kDa (matrix-assisted laser-desorption ionization MS) and contained 0.5 +/- 0.1 W (inductively coupled plasma/MS) and 1.3 +/- 0.1 molybdopterin-guanine dinucleotide per mol. Selenium was absent. EPR spectra (enzyme as isolated, under air) showed a signal typical of a [3Fe-4S] cluster with gav = 2.01, at 10 K. In enzyme prepared under N2/H2, this signal was absent and reaction with dithionite led to a rhombic signal with gz = 2.048, gy = 1.939 and gx = 1.920 indicative of a low-potential ferredoxin-type [4Fe-4S] cluster. Upon oxidation with hexacyanoferrate(III), a new signal appeared with gx = 2.007, gy = 2.019 and gz = 2.048 (gav = 2.022), which disappeared after further oxidation. The signal was still visible at 150 K and was tentatively assigned to a W(V) center. The iron-sulfur center of acetylene hydratase (prepared under N2/H2) gave a midpoint redox potential of -410 +/- 20 mV in a spectrophotometric titration with dithionite. Enzyme activity depended on the redox potential of the solution, with 50% of maximum activity at -340 +/- 20 mV. The presence of a pterin-guanine dinucleotide cofactor differentiates acetylene hydratase from the aldehyde ferredoxin oxidoreductase-type enzymes which have a pterin mononucleotide cofactor.

Bacteria, Anaerobic↗
PubMed2006

Rotational spectroscopy and molecular structure of the 1,1-difluoroethylene-acetylene complex.

Fourier transform microwave, rotational spectra in the 6-21 GHz region are obtained for the complex formed between 1,1-difluoroethylene and acetylene, including the normal isotopomer and each singly substituted (13)C species along with complexes derived from commercially available isotopic varieties of acetylene (HCCD, DCCD, and H(13)C(13)CH). Although two possible planar structures are consistent with the rotational constants derived from analysis of the spectra, ab initio calculations, as well as chemical intuition, support only one of the two as the structure of the complex. Nuclear quadrupole coupling constants for D-containing species show no evidence of electric field gradient perturbation and are consistent with the structures obtained from inertial data. The primary interaction between the two molecules is a 2.646(11) A hydrogen bond with acetylene as the donor and a 1,1-difluoroethylene fluorine as the acceptor that forms a 122.41(79) degrees C-Fcdots, three dots, centeredH angle. A secondary interaction between the acetylenic bond and the difluoroethylene hydrogen atom cis to the acceptor fluorine atom causes the hydrogen bond to deviate 53.25(24) degrees from linearity. Structural comparisons with the related complex, 1,1-difluoroethylene-hydrogen chloride [Z. Kisiel et al., J. Chem. Soc., Faraday Trans. 88, 3385 (1992)], suggest that the hydrogen bond in the acetylene complex is weaker, whereas comparisons with vinyl fluoride-acetylene [G. C. Cole and A. C. Legon, Chem. Phys. Lett. 369, 31 (2003)] indicate that the fluorine atoms in 1,1-difluoroethylene are less basic than the one in vinyl fluoride.

Journal Article↗
PubMed1979

Immediate acetylene reduction by excised grass roots not previously preincubated at low oxygen tensions.

Excised roots of Spartina alterniflora Loisel. and corn reduced acetylene in air without the previously reported period of zero activity lasting 8 to 18 hours. The profiles of acetylene-dependent ethylene accumulation by excised roots and intact plants of S. alterniflora were similar. No significant change in the number of bacteria associated with the roots was detectable during the assay. Most of the nitrogenase activity was detected in the roots and rhizomes of the plants. The salt marsh sediment also was capable of reducing acetylene. Additional damage to roots by washing and cutting increased the rate of acetylene reduction with samples incubated in air. Low concentrations of nitrate significantly inhibited the nitrogenase activity associated with the sediment and excised roots, but not with intact plants. Rates of acetylene reduction by excised corn roots were low. Oxidation and endogenous production of ethylene in the absence of acetylene were negligible. Measurements made with excised grass roots as described probably reflect the occurrence and magnitude of nitrogenase activity associated with the plants in the field.

Journal Article↗
PubMed1984

Diffusion of Gases through Plant Tissues : Entry of Acetylene into Legume Nodules.

I have measured acetylene diffusion through plant tissues including nodules from several species of legume-vetch, peas, soybeans, and Sesbania rostrata. The observed half-time for reequilibration of internal and external concentration is less than 1 minute for typical nodules. Inward diffusion of acetylene in air is rapid relative to the use of acetylene by nitrogenase so that diffusion of acetylene would not be a significant limiting factor for nitrogenase activity in air. However, under an atmosphere of Ar:O(2) where there is no N(2) reduction, the inward diffusion rate of acetylene into larger nodules could produce a measurable limitation of observed nitrogenase activity at low acetylene concentrations.

Journal Article↗
PubMed1982

Influence of acetylene on growth of sulfate-respiring bacteria.

At a concentration of 20% of the atmosphere of the culture flasks, acetylene inhibited growth and carbon dioxide production by Desulfovibrio desulfuricans and Desulfovibrio gigas. The bacteria did not reduce acetylene to ethylene, and neither acetylene dicarboxylic acid nor ethylene was inhibitory. At 10%, acetylene was partially inhibitory for the desulfovibrios. At 5%, acetylene impeded the rate but did not limit the extent of growth and catabolism of the desulfovibrios. Desulfotomaculum ruminis was affected only negligibly, if at all, by acetylene and ethylene at any of these concentrations.

Journal Article↗
PubMed1989

Prostaglandin and fatty acid omega- and (omega-1)-oxidation in rabbit lung. Acetylenic fatty acid mechanism-based inactivators as specific inhibitors.

Terminal acetylenic fatty acid mechanism-based inhibitors (Ortiz de Montellano, P. R., and Reich, N. O. (1984) J. Biol. Chem. 259, 4136-4141) were used as probes in determining the substrate specificity of rabbit lung cytochrome P-450 isozymes of pregnant animals in both microsomes and reconstituted systems. Lung microsomal and reconstituted P-450 form 5-catalyzed lauric acid omega- and (omega-1)-hydroxylase activities were inhibited by a 12-carbon terminal acetylenic fatty acid, 11-dodecynoic acid (11-DDYA), and an 18-carbon terminal acetylenic fatty acid, 17-octadecynoic acid (17-ODYA). Rabbit lung microsomal lauric acid omega-hydroxylase activity was more sensitive to inhibition by 11-DDYA than was (omega-1)-hydroxylase activity. In reconstituted systems containing purified P-450 form 5, both omega- and (omega-1)-hydroxylation of lauric acid were inhibited in parallel when either 11-DDYA or 17-ODYA was used. These data suggest the presence of at least two P-450 isozymes in rabbit lung microsomes capable of lauric acid omega-hydroxylation. This is the first report indicating the multiplicity of lauric acid hydroxylases in lung microsomes. Lung microsomal prostaglandin omega-hydroxylation, mediated by the pregnancy-inducible P-450PG-omega (Williams, D. E., Hale, S. E., Okita, R. T., and Masters, B. S. S. (1984) J. Biol. Chem. 259, 14600-14608) was subject to inhibition by 17-ODYA only, whereas 11-DDYA acid was not an effective inhibitor of this hydroxylase. We have recently developed a new terminal acetylenic fatty acid, 12-hydroxy-16-heptadecynoic acid (12-HHDYA), that contains a hydroxyl group at the omega-6 position. We show that 12-HHDYA possesses a high degree of selectivity for the inactivation of rabbit lung microsomal prostaglandin omega-hydroxylase activity which cannot be obtained with the long chain acetylenic inhibitor, 17-ODYA. In addition, 12-HHDYA has no effect on lauric acid omega- or omega-1-hydroxylation or on benzphetamine N-demethylation. The development of this new terminal acetylenic fatty acid inhibitor provides us with a useful tool with which to study the physiological role of prostaglandin omega-hydroxylation in the rabbit lung during pregnancy.

Animals↗
PubMed1982

Modulation of leukotriene formation by various acetylenic acids.

A series of acetylenic acids varying in chain length as well as in number and position of triple bonds were tested for their effect on arachidonic acid metabolism via cyclo-oxygenase and 5-lipoxygenase in homogenates of RBL-l cells. A number of trends which differentiate 5-lipoxygenase from cyclo-oxygenase were observed: (a) In general, the potency of the acetylenic acids to inhibit 5-lipoxygenase increased with the carbon chain length up to carbons. (b) A minimum of three triple bonds is necessary for the inhibitory action. (c) With the 20-carbon delta 8 and delta 6 acetylenic acids, activity decreased when the number of triple bonds increased from three to four. These structure activity relationships were not observed with cyclo-oxygenase. The delta 4 acetylenic acids proved to be an interesting group of compounds. They did not inhibit cyclo-oxygenase or 5-lipoxygenase but were good inhibitors of SRS synthesis. The potency of the delta 4 acetylenic acids increased with chain length, and 21:4 (4a, 7a, 10a, 13a) was the most potent compound inhibiting SRS formation. The delta 4 acetylenic acids are therefore useful tools for investigating the function and action of LTC4 and LTD4.

Animals↗
PubMed1997

Analysis of the seed oil of Heisteria silvanii (Olacaceae)--a rich source of a novel C18 acetylenic fatty acid.

Besides some usual fatty acids (FA), two conjugated ene-yne acetylenic FA [trans-10-heptadecen-8-ynoic acid (pyrulic acid) (7.4%), and trans-11-octadecen-9-ynoic acid (ximenynic acid) (3.5%)], a novel ene-yne-ene acetylenic FA [cis-7, trans-11-octadecadiene-9-ynoic acid (heisteric acid) (22.6%)], and 9,10-epoxystearic acid (0.6%) could be identified in the seed oil of Heisteria silvanii (Olacaceae). Two further conjugated acetylenic FA [9,11-octadecadiynoic acid (0.1%) and 13-octadecene-9,11-diynoic acid (0.4%)] were identified tentatively by their mass spectra. The FA mixture has been analyzed by gas chromatography/mass spectrometry (GC/MS) of their methyl ester and 4,4-dimethyloxazoline derivatives. The structure of heisteric acid was elucidated after isolation via preparative silver ion thin-layer chromatography and by various spectroscopic methods [ultraviolet; infrared; 1H, 13C nuclear magnetic resonance (NMR); 1H-1H and 1H-13C correlation spectroscopy]. To determine the position of the conjugated ene-yne-ene system, the NMR spectra were also measured after addition of the lanthanide shift reagent Resolve-Al EuFOD. Furthermore, the triyglyceride mixture was analyzed by high-temperature GC and high-temperature GC coupled with negative chemical ionization MS. A glass capillary column coated with a methoxy-terminated 50%-diphenyl-50%-dimethylpolysiloxane was used for the separation of the triacylglycerol (TAG) species. No evidence of decomposition of the TAG species containing conjugated ene-yne-ene FA was observed. Twenty-six species of the separated TAG were identified by means of their abundant quasi molecular ion [M - H]- and their corresponding carboxylate anions [RCOO]- of the fatty acids, respectively. The major molecular species of the TAG were found to be 16:0/18:1/18:1, 16:0/18:1/18:3 (heisteric acid), 17:2 (pyrulic acid)/18:1/18:1, 18:1/18:1/18:3 (heisteric acid). The TAG containing acetylenic FA showed an unexpected increase of the retention time in comparison to the TAG containing usual FA, thus making the prediction of the elution order of lipid samples containing acetylenic FA difficult.

Acetylene↗
PubMed2005

Low-temperature synthesis of amorphous carbon nanocoils via acetylene coupling on copper nanocrystal surfaces at 468 K: a reaction mechanism analysis.

A new type of amorphous helical carbon nanofibers has been synthesized using copper nanocatalysts and an acetylene gas source at atmospheric pressure. The nanofibers are grown at 468 K, which is the lowest temperature by ordinary metal-catalyzed thermal chemical vapor deposition of hydrocarbon, and exhibit a symmetric growth mode in the form of twin helices. IR, XRD, Raman, and C/H molar ratio analyses reveal a polymer-like structure with a weak trans-polyacetylene feature. The nanofibers are a mixture of solid polymers and a small amount of carbon. A reaction mechanism has been proposed on the basis of the previous studies of acetylene adsorption, desorption properties, and surface reactions on copper (111), (110), and (001) planes under ultrahigh-vacuum (UHV) conditions as well as the results obtained in our study. The reaction mechanism of acetylene on copper single-crystal surfaces under UHV conditions indeed reflects the reaction mechanism under practical catalytic conditions at atmospheric pressure. The nanofibers grow mainly via acetylene coupling to solid polymers on copper nanocrystal surfaces. Acetylene also couples to yield small amounts of liquid oligomers and gaseous products, and undergoes slight carbon deposition during the fiber growth.

Acetylene↗