Glass Electrode Measurements in Deuterium Oxide

Abstract

When hydrogen selective glass electrodes are transferred between acid solutions in ordinary water and deuterium oxide their potentials drift systematically by 1–2 mV over several hours, and hence electrodes standardised in H₂O cannot be readily used for the precise measurement of deuterium ion activity a_D+ in D₂O.     

Hydrogenation of arenes by the RhCl3-aliquat® 336 catalyst: Part 3. Selective reduction of polycyclic compounds

Acenaphthylene, fluorene, anthracene, phenanthrene, benz[a]anthracene, pyrene, fluoranthene, benzo[c] phenanthrene and some of their derivatives were shown to undergo partial hydrogenation in the presence of the RhCl₃-Aliquat^® 336 catalyst in a highly selective manner. Olefinic double bonds were found to be hydrogenated prior to aromatic moieties. In linear aromatic molecules, only the terminal rings are reduced. In phenanthrene the C₉-C₁₀ bond and in pyrene the C₄-C₅ linkage are the only ones to be affected. Benz [a] anthracene is converted exclusively into 7,8,9,10-tetrahydrobenz[a]anthracene. Benzo[c] phenanthrene is hydrogenated to give primarily the 5,6-dihydro derivative. Chlorine and bromine substituents were found to undergo hydrogenolysis when attached to the reacting moieties, but usually remain unaffected when located on non-reacting aromatic rings.     

Monitoring allostery in D2O: a necessary control in studies using hydrogen/deuterium exchange to characterize allosteric regulation

There is currently a renewed focus aimed at understanding allosteric mechanisms at atomic resolution. This current interest seeks to understand how both changes in protein conformations and changes in protein dynamics contribute to relaying an allosteric signal between two ligand binding sites on a protein (e.g., active and allosteric sites). Both nuclear magnetic resonance (NMR), by monitoring protein dynamics directly, and hydrogen/deuterium exchange, by monitoring solvent accessibility of backbone amides, offer insights into protein dynamics. Unfortunately, many allosteric proteins exceed the size limitations of standard NMR techniques. Although hydrogen/deuterium exchange as detected by mass spectrometry (H/DX-MS) offers an alternative evaluation method, any application of hydrogen/deuterium exchange requires that the property being measured functions in both H₂O and D₂O. Due to the promising future H/DX-MS has in the evaluation of allosteric mechanisms in large proteins, we demonstrate an evaluation of allosteric regulation in D₂O. Exemplified using phenylalanine inhibition of rabbit muscle pyruvate kinase, we find that binding of the inhibitor is greatly reduced in D₂O, but the effector continues to elicit an allosteric response.     

The bimolecular hydrogen-deuterium exchange behavior of protonated alkyl dipeptides in the gas phase

As part of an ongoing characterization of the intrinsic chemical properties of peptides, thermal hydrogen-deuterium exchange has been studied for a series of fast-atom-bombardment-generated protonated alkyldipeptides and related model compounds in the reaction with D₂O, CH₃OD, and ND₃ in a Fourier transform ion cyclotron resonance mass spectrometer. Despite the very large basicity difference between the dipeptides and the D₂O and CH₃OD exchange reagents, efficient exchange of all active hydrogen atoms occurs. From the kinetic data it appears that exchange of the amino, amide, and hydroxyl hydrogens proceeds with different efficiencies, which implies that the proton in thermal protonated dipeptides is immobile. The selectivity of the exchange at the different basic sites is governed by the nature of both the dipeptide and the exchange reagent. The results indicate that reversible proton transfer in the reaction complexes, which effectuates the deuterium incorporation, is assisted by formation of multiple hydrogen bonds between the reagents. Exchange is considered to proceed via the intermediacy of different competing intermediate complexes, each of which specifically leads to deuterium incorporation at different basic sites. The relative stabilization of the competing intermediate complexes can be related to the relative efficiencies of deuterium incorporation at different basic sites in the dipeptide. For all protonated dipeptides studied, the exchange in the reaction with ND₃ proceeds with unit efficiency, whereas all active hydrogen atoms are exchanged equally efficiently. Evidently specific multiple hydrogen bond formations are far less important in the reversible proton transfers with the relatively basic ammonia, which allows effective randomization of all active hydrogen atoms in the reaction complexes.     

Intermolecular interactions in N‐(ferrocenyl­methyl)­anthracene‐9‐carbox­amide

The title compound, [Fe(C₅H₅)(C₂₁H₁₆NO)], was synthesized from the coupling reaction of anthracene‐9‐carboxyl­ic acid and ferrocenyl­methyl­amine. The ferrocenyl (Fc) group and the anthracene ring system both lie approximately orthogonal to the amide moiety. An amide–amide interaction (along the a axis) is the principal interaction [N⋯O = 2.910 (2) Å]. A C—H⋯π(arene) interaction [C⋯centroid = 3.573 (2) Å] and a C—H⋯O interaction [C⋯O = 3.275 (3) Å] complete the hydrogen bonding; two short (Fc)C⋯C(anthracene) contacts are also present.     

The mass spectrometric [M ? C2H4O]+ process in cyclic ketones. I—the nature of the C2H4O losss in bicyclo[3.3.1]nonan-2-one and 3-one

Although the loss of a C₂H₄O molecule from the molecular ions of the isomeric bicyclo[3.3.1]nonan-2- and 3-ones gives rise to the base peak at m/e 94 in both spectra, deuterium labelling results show that the processes leading to this ion are markedly different in the two cases. While the 2-one follows essentially (>80%) the same [M ? C₂H₄O]+ fragmentation pathway described for other 2-alkylcyclohexanones, the 3-one exhibits a more complex decomposition pathway in which one α-hydrogen is transferred away from the departing C₂ unit and three hydrogen atoms are subsequently rearranged to the eliminated C₂H₄O molecule. Similar competing fragmentation schemes have been invoked to explain deuterium labelling results in cycloheptanone, 2-methylcycloheptanone and cyclooctanone.     

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.     

A Single‐Molecule Perspective on the Role of Solvent Hydrogen Bonds in Protein Folding and Chemical Reactions

We present an array of force spectroscopy experiments that aim to identify the role of solvent hydrogen bonds in protein folding and chemical reactions at the single‐molecule level. In our experiments we control the strength of hydrogen bonds in the solvent environment by substituting water (H₂O) with deuterium oxide (D₂O). Using a combination of force protocols, we demonstrate that protein unfolding, protein collapse, protein folding and a chemical reaction are affected in different ways by substituting H₂O with D₂O. We find that D₂O molecules form an integral part of the unfolding transition structure of the immunoglobulin module of human cardiac titin, I27. Strikingly, we find that D₂O is a worse solvent than H₂O for the protein I27, in direct contrast with the behaviour of simple hydrocarbons. We measure the effect of substituting H₂O with D₂O on the force dependent rate of reduction of a disulphide bond engineered within a single protein. Altogether, these experiments provide new information on the nature of the underlying interactions in protein folding and chemical reactions and demonstrate the power of single‐molecule techniques to identify the changes induced by a small change in hydrogen bond strength.     

Methyl guanine isomer distinction by hydrogen / deuterium exchange using a fourier transform mass spectrometer

Analytical Chemistry Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA Differentiation of the seven isomers of methyl guanine has been accomplished by monitoring gas-phase hydrogen/deuterium (H/D) exchange reactions of the protonated molecular ions with deuterium oxide (D₂O) in a Fourier transform mass spectrometer. In each case a distinctive reaction rate for the first H/D exchange was observed, and exchanges of up to three deuterium atoms occurred with characteristic ion abundances that could be used to differentiate the isomers. O⁶-Methyl guanine, for example, showed only one slow H/D exchange with D₂O, whereas l-methyl guanine exchanged two hydrogen atoms at a significantly faster rate. On comparison of the possible resonance structures of each protonated isomer with the experimental information about the number and rate of H/D exchanges observed, a reaction mechanism involving a concerted proton abstraction-deuterium cation donation was proposed.     

Two-dimensional vibrational analysis of the Lippincott-Schröder potential for OHO,NHO and NHN hydrogen bonds and the deuterium isotope effect

Two-dimensional vibrational analyses [i.e. crude adiabatic approximation, SCF approximation and variational method (crude adiabatic basis function)] are performed on the hydrogen bond systems consisting of the Lippincott-Schröder potentials for the OHO, NHO and NHN bonds. The OHO and NHN systems are supposed to be linear and the bent structure is considered for the NHO system. The frequency shift for the hydrogen bond length variation and its deuterium substitution effects are in good agreement with experiment. The anomalies in the frequency ratio ν_OH/ν_OD at an O—O distance of 2.5 Å, and in the interminimum distance shift on deuteration at 2.5 Å are well explained as the difference of double minimum behavior between the vibrational states of proton and deuterium. It is also shown that the Lippincott-Schröder model for the OHO system supplies the general features for proton tunneling, proton delocalization beyond the barrier and other type processes in hydrogen bonds.     

Hydrogen–Deuterium Exchange Reactions of Aromatic Compounds and Heterocycles by NaBD4‐Activated Rhodium,Platinum and Palladium Catalysts

Conventional thermal and microwave conditions were compared for hydrogen–deuterium (H/D) exchange reactions of aminobenzoic acids catalysed by NaBD₄‐activated Pd/C or RhCl₃ with D₂O as the deuterium source. We also investigated different NaBD₄‐activated metal catalysts (including Pd/C, RhCl₃ and Pt/C) under microwave conditions for an efficient H/D exchange of aromatic and heterocyclic compounds. Even higher deuterium incorporations were obtained for Pd/C and Pt/C catalyst mixtures due to the previously observed synergistic effect. Finally, we have applied these optimised conditions for one‐step syntheses of the MS standards of several pharmaceutically active compounds.     

The mass spectrum of 2,4-dihydroxybenzophenone oxime

2,4-Dihydroxybenzophenone Oxime is found to undergo loss of OH·, H₂O, NHOH·; and PhCNO when subjected to electron impact, revealing novel hydrogen and skeletal migrations. The fragmentation mechanisms are found to differ considerably from those of benzophenone oxime and we confirmed these cleavages by exact mass measurements and deuterium labelling.     

Localization of hydrogen in the layer oxide HTiNbO5

The structure of HTiNbO₅ at 10 and 300 K and of DTiNbO₅ at 300 K has been investigated by neutron powder diffraction. The TiNbO₅ framework and the octahedral distortions previously found for the alkalititanoniobates by X-ray diffraction are confirmed. The position of hydrogen (or deuterium) has been determined: very strong OH … O hydrogen bonds with O … O distances ranging from 2.51 to 2.63 Å are observed. The similarity of these compounds with acids is shown, explaining their ion exchange properties. The absence of protonic conductivity can be explained from structural arguments. The open character of this structure, which can play a part in intercalation and deintercalation reactions is also discussed.     

Overall kinetics of photosystem II: pH Dependence and deuterium isotope effect

The overall kinetics of photosystem II was scanned by means of a double flash technique. Oxygen evolution by pea thylakoids provided with an artificial electron acceptor was measured under a regime of double flashes of variant intervals. The pH optimum in H₂O lies near p¹H 7.2 (p¹H meaning the pH in H₂O), with a first-order rate constant of 800 s⁻¹ at 20°C. In deuterium oxide (D₂O), a plateau of maximum reaction rate was found between p²H 6.6 and 7.8 (p²H meaning the “pH” in D₂O), the highest rate constant being 550 s⁻¹. The apparent kinetic deuterium isotope effect is therefore 1.45. Outside this plateau region, there seems to exist another isotope effect of 1.2 to 1.3. These effects are small but may nevertheless reflect the fact that more than one step of the photosystem II reaction sequence is involved in the splitting of a bond to hydrogen. However, the effects may also be solvent effects or located on the acceptor side of the photosystem.     

Crystalline inclusion compounds of a new diol host featuring a combination of anthracene and 9-fluorenol units

The diol host compound 2 has been synthesised and its behaviour to form crystalline inclusion compounds is discussed in comparison with an analogous ethynylene spaced host compound 1. The rotation around the fluorenol–anthracene bonds in 2 is highly restricted as indicated by solution NMR spectroscopy, molecular mechanics and semi-empirical calculations. Single-crystal X-ray structures of the inclusion complexes of 2 with 1-BuOH (2a), morpholine/H₂O (2b) and DMSO (2c) are in agreement with the bent geometry of the anthracene ring system suggested by the calculations. The structures exhibit specific modes of hydrogen bond interactions.     

Mechanistic study of hydrogen/deuterium exchange between [M - 1]− ions of chlorinated benzenes and D2O or ND3

Low-energy collisions between [M - 1]^? ions derived from the three isomers of dichlorobenzene and deuterated water and ammonia are found to produce distinctive hydrogen/ deuterium (H/D) exchange reaction product patterns. The predominant products observed for p-, m-, and o-dichlorobenzene are 1, 2, and 3 sequential deuterium exchanges, respectively. The reactivity is substantially higher for D₂O than ND₃ We postulate a mechanism that involves the formation of a five-membered-ring intermediate. The intermediate is thought to be initiated by the attack of ND₃ or D₂O at the localized negative charge site on the aromatic ring. A successful exchange is followed by the relocation of the charge site to the adjacent carbon. Ion products with higher degrees of deuterium substitution than the expected predominant products of their corresponding isomers are believed to be the results of isomerization of the reactant ions occurring in the ion source. The proposed mechanism fuily explains the observed product spectra derived from al1 the isomers of chlorinated benzenes. The trends for the formation of various H/D exchange products represented by the sweated product-time plots based on the proposed mechanism compare well with the similar trends obtained from the experimental product-pressure plots. The reaction is useful for the mass spectrometric differentiation of chlorobenzene isomers.     

Decompositions of metastable [C6H12O]+ ions with the oxygen on the third carbon: Ring-size preferences in [CnH2nO]+˙ ions

The isomerizations preceding the metastable decompositions in the mass spectrometer of a number of [C₆H₁₂O]⁺˙ ions with the oxygen on the third carbon are characterized utilizing deuterium labeling. Hydrogens are transferred in these ions by three-, five- and six-membered ring rearrangements, with propensities determined by features of the individual reactions. Three-membered ring hydrogen transfers between α and β-carbons are preferred to all five-membered ring hydrogen transfers. However, six-membered ring hydrogen transfers take place to the apparent exclusion of three-membered ring hydrogen transfers to enol carbons when the products are of comparable stability. The low-energy [C₆H₁₂O]⁺˙ isomerizations characterized are predictable from the behavior of their lower homologs. It is concluded that the determinants of these reactions are the same as those of other highly reactive organic intermediates.     

Cadmium(II) Complexes with a Bulky Anthracene‐based Carboxylate Ligand: Syntheses,Crystal Structures,and Luminescent Properties

To explore the coordination possibilities of anthracene‐based ligands, three cadmium(ιι) complexes with anthracene‐9‐carboxylate ( L ) and relevant auxiliary chelating or bridging ligands were synthesized and characterized: Cd₂( L )₄(2bpy)₂(μ‐H₂O) ( 1 ), Cd₂( L )₄(phen)₂(μ‐H₂O) ( 2 ), and {[Cd₃( L )₆(4bpy)]}_∞ ( 3 ) (2bpy = 2,2′‐bipyridine, phen = 1,10‐phenanthroline, and 4bpy = 4,4′‐bipyridine). Structural analyses show that complexes 1 and 2 both take dinuclear structures by incorporating the chelating 2bpy or phen ligand, which are further interlinked by intermolecular hydrogen‐bonding, π ··· π stacking, and/or C–H ··· π supramolecular interactions to generate higher‐dimensional supramolecular frameworks. Complex 3 has a one‐dimensional (1D) ribbon‐like structure, which is further assembled into a two‐dimensional (2D) layer, and a three‐dimensional (3D) framework by the co‐effects of interchain C–H ··· O hydrogen‐bonding and C–H ··· π supramolecular interactions. Moreover, the luminescent properties of these complexes were further investigated in detail.     

The synthesis of diene and of vinyl copolymers containing predetermined quantities of polynuclear hydrocarbon or heterocyclic adducts-III. Copolymers formed from polynuclear hydrocarbons and alkyldihalides

The reaction in tetrahydrofuran between the disodium salt of anthracene (A) and alkyl dihalides (RX₂) results in oligomeric products with a repeat unit -[A-R]-. The same reaction with the dilithium derivative is complicated by the high reactivity of this species toward solvent; oligomers with -(CH₂)₄OH end groups are isolated. The xylylene dihalides undergo metallation and Wurtz coupling, and they produce low yields of oligomers rich in xylylene units.The reaction with dilithium acenaphthylene and alkyl dihalides gives a high yield of copolymer but there is evidence of crosslinking. Although addition occurs principally across the 1.2 position, some 1,5 addition is believed to cause this crosslinking. With dilithium phenanthrene the reaction is mainly one of electron transfer; the oligomers produced in low yield are low in phenanthrene adducts.     

Volumetric and transport properties of aerosol-OT reversed micelles containing light and heavy water

Densities and viscosities of sodium bis(2-ethylhexyl) sulfosuccinate (AOT in-heptane system containing light and heavy water, as a function of the molar ratio R (R=[H₂O or D₂O]/[AOT]) were measured at 0, 5, 25 and 40°C. At low R values, the apparent molar volume of deuterium oxide is smaller than that of light water. The difference is related to the strength of the hydrogen bonding H₂O and D₂O. The viscosities of both H₂O-AOT-n-heptane and D₂O-AOT-n-heptane systems were explained in terms of intermicellar interactions mainly governed by hydration of the head groups of AOT.