Hydrogen Isotope Exchange Reactions in an Electrical Discharge

Hydrogen isotope exchange reactions occurring in (H₂O, D₂)or (D₂O, H₂) reacting system under a DC electricaldischarge were investigated using spectroscopic methods such asFourier-transform infrared (FTIR) and plasma emission spectroscopy(PES). The progress of the reactions was determined by real-time measurementof the IR absorbance of HDO molecule, a major product of the reaction. Theprogress of the reaction was studied as a function of the temperature, thecurrent density, and the composition of the reactants, while the pressure ofthe system was maintained at approximately 67 mbar. The results revealedthat the discharge method was far more effective in facilating the exchangereaction than was the conventional catalytic method. The (H₂O, D₂)system also generated a significant amount of D₂O besides HDO andHD as the ratio of D₂ to H₂O was increased. Thetransient species of the system, such as H or D atoms, were monitored duringthe discharge using emission spectroscopy. The analysis of the final products by mass spectroscopy confirmed that neither H₂ nor O₂was among the major products of the system in the discharge.     

Directed Iridium-Catalyzed Hydrogen Isotope Exchange Reactions of Phenylacetic Acid Esters and Amides

For the first time, a catalytic protocol for a highly selective hydrogen isotope exchange (HIE) of phenylacetic acid esters and amides under very mild reaction conditions is reported. Using a homogeneous iridium catalyst supported by a bidentate phosphine-imidazolin-2-imine P,N ligand, the HIE reaction on a series of phenylacetic acid derivatives proceeds with high yields, high selectivity, and with deuterium incorporation up to 99 %. The method is fully adaptable to the specific requirements of tritium chemistry, and its effectiveness was demonstrated by direct tritium labeling of the fungicide benalaxyl and the drug camylofine. Further insights into the mechanism of the HIE reaction with catalyst 1 have been provided utilizing DFT calculations, NMR studies, and X-ray diffraction analysis.     

Comparison of Iridium(I) Catalysts in Temperature Mediated Hydrogen Isotope Exchange Reactions

The reactivity and selectivity of iridium(I) catalysed hydrogen isotope exchange (HIE) reactions can be varied by using wide range of reaction temperatures. Herein, we have done a detailed comparison study with common iridium(I) catalysts ( 1 – 6 ) which will help us to understand and optimize the approaches of either high selectivity or maximum deuterium incorporation. We have demonstrated that the temperature window for these studied iridium(I) catalysts is surprisingly very broad. This principle was further proven in some HIE reactions on complex drug molecules.     

Photoredox-Mediated Hydrogen Isotope Exchange Reactions of Amino-Acids,Peptides, and Peptide-Derived Drugs

Hydrogen isotopically labelled compounds are essential diagnostic tools in drug research and development, as they provide vital information about the biological metabolism of drug candidates and their metabolites. Herein we report a photoredox-initiated hydrogen atom transfer (HAT) protocol which efficiently and selectively introduces deuterium or tritium at C(sp³)−H bonds, utilizing heavy water (D₂O or T₂O) as the hydrogen isotope source, and a guanidine base. This protocol has been successfully applied to the incorporation of deuterium in several amino acids (lysine, glycine and proline) and small peptides. Finally, the method has been applied to tritium, because tritium-labelled peptides are essential for application in biological experiments, such as ligand-binding assays, or absorption, distribution, metabolism, and excretion (ADME) studies.     

NHC‐Stabilized Iridium Nanoparticles as Catalysts in Hydrogen Isotope Exchange Reactions of Anilines

The preparation of N‐heterocyclic carbene‐stabilized iridium nanoparticles and their application in hydrogen isotope exchange reactions is reported. These air‐stable and easy‐to‐handle iridium nanoparticles showed a unique catalytic activity, allowing selective and efficient hydrogen isotope incorporation on anilines using D₂ or T₂ as isotopic source. The usefulness of this transformation has been demonstrated by the deuterium and tritium labeling of diverse complex pharmaceuticals.     

Silane-Based Coatings on Polypropylene,Deposited by Atmospheric Pressure Glow Discharge Plasmas

The aim of this paper is to show the possibility to synthesize silicon-based deposits on a polypropylene substrate, using a glow dielectric barrier discharge at atmospheric pressure, and to correlate the gas phase behavior with the properties of the thin film deposits. The discharge is generated in a mixture of nitrous oxide and silane, diluted in nitrogen. The influence of the [N₂O]/[SiH₄] ratio on the layer characteristics is mainly studied. Deposits are analyzed by XPS, SSIMS, AFM and wetting angle measurements. The discharges are also characterized by their optical emission spectra. Measurements are made as a function of the distance from the gas inlet, and they allow one to correlate these spectra with the film thickness and its chemical composition. Finally, chemical kinetics of the reactive gas decomposition reactions are proposed.     

Highly Selective Directed Iridium‐Catalyzed Hydrogen Isotope Exchange Reactions of Aliphatic Amides

For the first time, we describe highly selective homogeneous iridium‐catalyzed hydrogen isotope exchange (HIE) of unactivated C(sp³) centers in aliphatic amides. When using the commercially available Kerr catalyst, the HIE with a series of common antibody–drug conjugate (ADC) linker side chains proceeds with high yields, high regioselectivity, and with deuterium incorporation up to 99 %. The method is fully translatable to the specific requirements of tritium chemistry and its effectiveness was demonstrated by direct tritium labelling of a maytansinoid. The scope of the method can be extended to simple amino acids, with high HIE activity observed for glycine and alanine. In di‐ and tripeptides, a very interesting protecting‐group‐dependent tunable selectivity was observed. DFT calculations gave insight into the energies of the transition states, thereby explaining the observed selectivity and the influence of the amino acid protecting groups.     

C−H Functionalization—Prediction of Selectivity in Iridium(I)‐Catalyzed Hydrogen Isotope Exchange Competition Reactions

An assessment of the C?H activation catalyst [(COD)Ir(IMes)(PPh₃)]PF₆ (COD=1,5‐cyclooctadiene, IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene) in the deuteration of phenyl rings containing different functional directing groups is divulged. Competition experiments have revealed a clear order of the directing groups in the hydrogen isotope exchange (HIE) with an iridium (I) catalyst. Through DFT calculations the iridium–substrate coordination complex has been identified to be the main trigger for reactivity and selectivity in the competition situation with two or more directing groups. We postulate that the competition concept found in this HIE reaction can be used to explain regioselectivities in other transition‐metal‐catalyzed functionalization reactions of complex drug‐type molecules as long as a C?H activation mechanism is involved.     

Reactions in a Mixture of CH4 and CO2 under the Action of Microwave Discharge at Atmospheric Pressure

Reactions between CH4 and CO2 under the action of continuous microwave discharge atatmospheric pressure were studied in a special homemade reactor. The main products were CO and H2,while acetylene and ethylene were also found in the products. Experimental results show that conversionsof CH4 and CO2 could be higher than 90% without the presence of any catalyst. Effects of CO2/CH4molar ratio and total flow rate of the feed gas on the reaction were also investigated.     

Reactions in a Mixture of CH_4 and CO_2 under the Action of Microwave Discharge at Atmospheric Pressure

Reactions between CH_4 and CO_2 under the action of continuous microwave discharge at atmospheric pressure were studied in a special homemade reactor. The main products were CO and H2, while acetylene and ethylene were also found in the products. Experimental results show that conversions of CH4 and CO2 could be higher than 90% without the presence of any catalyst. Effects of CO2/CH4 molar ratio and total flow rate of the feed gas on the reaction were also investigated.     

In situ Generated Iridium Nanoparticles as Hydride Donors in Photoredox-Catalyzed Hydrogen Isotope Exchange Reactions with Deuterium and Tritium Gas

We have studied the photoredox-catalyzed hydrogen isotope exchange (HIE) reaction with deuterium or tritium gas as isotope sources and in situ formed transition metal nanoparticles as hydrogen atom transfer pre-catalysts. By this means we have found synergistic reactivities applying two different HIE mechanisms, namely photoredox-catalyzed and CH-functionalization HIE leading to the synthesis of highly deuterated complex molecules. Finally, we adopted these findings successfully to tritium chemistry.     

Diagnosis of OH Radical by Optical Emission Spectroscopy in Atmospheric Pressure Unsaturated Humid Air Corona Discharge and its Implication to Desulphurization of Flue Gas

OH radical in the corona discharge with pipe–nozzle–plate electrode has been diagnosed by optical emission spectroscopy. Spatial variations of OH radical emission in discharge gap have been measured. Relative intensity of OH radical emission spectroscopy increases with increasing water vapor flux injected into the reactor or intensity of electric field supported. In positive pulsed corona discharge, relative intensity is higher than that in positive DC corona discharge and lower than that in negative DC corona discharge. Strongest intensity of OH radical spectrum appears within the range of 5 mm near the discharge nozzle- electrode. In addition, it is proved that the efficiency of desulphurization from flue gas by pulsed corona discharge plasma processes can be improved when OH radical is produced in the reactor.     

Studies on Gas Purification by a Pulsed Microwave Discharge at 2.46 GHz in Mixtures of N2/NO/O2 at Atmospheric Pressure

Pulsed microwave discharges operated at atmospheric pressure in gas mixtures containing N₂, O₂, and NO are investigated experimentally and theoretically for various gas mixture constituents and operating conditions with respect to the ability of exhaust gas purification. The rotational gas temperature and the vibrational temperature of N₂ are derived from CARS measurements. The composition of the exhaust gas after treatment is monitored using FTIR spectroscopy. The processes of the chemical, electronic, and vibrational kinetics are described by a model that has been developed to calculate the species densities. The results obtained show that in N₂/NO gas mixtures an overall reduction of NO_x takes place. In the case of N₂/O₂/NO gas mixtures, no net reduction of NO_x is achieved for a pulsed microwave power below 3600 W, a pulse length of 50 s, and a typical repetition frequency of 2 kHz.