Deuterium effects on radiationless electronic transitions of xanthene dyes in aqueous and alcoholic solutions

Solvent deuteration effects on internal conversion (S₁ ～→ S₀) and intersystem crossing (S₁ ～→ T₁) in 6-hydroxy-9-phenylfluoron and fluorescein were determined from fluorescence and triplet quantum yield measurements in alkaline solutions of H₂O, D₂O, CH₃OH, CH₃OD, C₂H₅OH, and C₂D₅OD. Deuterium substitution of the oxygen-bonded hydrogens of these solvenis reduces both the internal conversion (by approximately 1.6) and the intersystem crossing (by approximately 1.2) rate constants; the additional deuteration of the alkyl groups of the alcohols does not produce any further effect. The effect of solvent deuteration was negligible for fluorescein. Deuteration of the xanthene groups of the dyes does not influence the radiationless transition probabilities to any significant extent.     

Reversible PtII–CH3 deuteration without methane loss: metal–ligand cooperation vs. ligand-assisted PtII-protonation

Di(2-pyridyl)ketone dimethylplatinum(ii), (dpk)Pt^II(CH₃)₂, reacts with CD₃OD at 25 °C to undergo complete deuteration of Pt–CH₃ fragments in ∼5 h without loss of methane to form (dpk)Pt^II(CD₃)₂ in virtually quantitative yield. The deuteration can be reversed by dissolution in CH₃OH or CD₃OH. Kinetic analysis and isotope effects, together with support from density functional theory calculations indicate a metal–ligand cooperative mechanism wherein DPK enables Pt–CH₃ deuteration by allowing non-rate-limiting protonation of Pt^II by CD₃OD. In contrast, other model di(2-pyridyl) ligands enable rate-limiting protonation of Pt^II, resulting in non-rate-limiting C–H(D) reductive coupling. Owing to its electron-poor nature, following complete deuteration, DPK can be dissociated from the Pt^II-centre, furnishing [(CD₃)₂Pt^II(μ-SMe₂)]₂ as the perdeutero analogue of [(CH₃)₂Pt^II(μ-SMe₂)]₂, a commonly used Pt^II-precursor.

Di(2-pyridyl)ketone dimethylplatinum(ii), (dpk)Pt^II(CH₃)₂, reacts with CD₃OD at 25 °C to undergo complete deuteration of Pt–CH₃ fragments in ∼5 h without loss of methane to form (dpk)Pt^II(CD₃)₂ in virtually quantitative yield.     

Isotopic splitting patterns in the 13C NMR spectra of some partially deuterated 1‐aryl‐2‐(phenyldiazenyl)butane‐1,3‐dione and 4‐hydroxy‐3‐(phenyldiazenyl)‐2H‐chromen‐2‐one: evidence for elucidation of tautomeric forms

Nuclear magnetic resonance spectra of synthesized azo dyes derived from aniline derivatives in reaction with benzoylacetone and 4‐hydroxycoumarin were studied in both CDCl₃ and (CD₃)₂SO (two drops of D₂O were added into solutions of dyes). All dyes showed intramolecular hydrogen bonding. Dyes derived from o‐nitro aniline in the reaction with benzoylacetone, and 4‐hydroxycoumarin showed bifurcated intramolecular hydrogen bonds. The solvent‐substrate proton exchange of dyes derived from benzoylacetone and 4‐hydroxycoumarin was examined in the presence of two drops of D₂O. Among ten dye samples, two dyes derived from benzoylacetone did not show deuteration, three dyes showed partial deuteration and five dyes showed full deuteration under similar conditions. For the partially deuterated dyes the β‐isotope effect in ¹³C splitting was investigated and was used for the determination of the predominant tautomeric form. Copyright © 2016 John Wiley & Sons, Ltd.     

Asymmetric synthesis of l-proline regio- and stereoselectively labelled with deuterium

A synthesis of l-proline where all of the ring methylenes are stereoselectively labelled with deuterium is described. A catalytic deuteration of protected 3,4-dehydro-l-proline using transition metal catalyst followed by RuO₄-oxidation gave a [3,4-D₂]pyroglutamic acid derivative. A syn-selective deuteration of the aminal derived from the pyroglutamate with Et₃SiD–BF₃·OEt₂ furnished (2S,3S,4R,5S)-[3,4,5-D₃]proline. The present procedure is also applied to the synthesis of the corresponding (2S,3S,4R,5R)-isomer.     

The rate of increase in fluorescence intensity caused by deuteration of tryptophan

Tryptophan was rapidly transferred from ¹H₂O into a ²H₂O medium by a stopped-flow device, and a time-dependent fluorescence increase was traced. It has been shown that this fluorescence change is caused by the deuteration of the α-ammonium (—NH⁺₃) group.     

Infrared spectra of some isotopomers of isopropylamine: A theoretical study

The normal‐mode frequencies and the corresponding vibrational assignments of some isotopomers of isopropylamine are examined theoretically using the Gaussian 94 set of quantum chemistry codes at the MP2 level of theory using a 6‐311g** basis set. In particular deuteration of the NH₂ hydrogen atoms as well as the deuteration of the CH₃ hydrogen atoms, the α‐CH hydrogen atom, and various combinations of deuteration of isopropylamine are examined. Correction factors for predominant vibrational motions are reported and compared for a number of isotopomers of s‐trans‐ and gauche‐isopropylamine. Comparison of theoretically predicted infrared spectra with experimental spectra is made for isotopomers for which experimental data exist. Enthalpy, entropy, and Gibbs free energy changes are considered for the trans→gauche transformation. An amino torsional potential is deduced and barrier heights are calculated for the trans→gauche, gauche→trans, and gauche→gauche transformations. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 109–126, 1999     

Assignment of 13C Cpmas Nmr Spectra of Crystalline Methyl β-D-Glucopyranoside and Sucrose using Deuterium Labelling and Interrupted Proton Decoupling

ABSTRACT

The solid state ¹³C cross polarization magic angle spinning (CPMAS) NMR spectra of partially deuterated samples of methyl β-D-glucopyranoside (1) and sucrose (2) were assigned using the spectral editing technique of interrupted proton decoupling (IPD). With the exception of the deuterium substituted CH₂OH each carbon resonance area of the IPD spectra, (after allowing for differences in magnetization) corresponded closely with the established level of deuteration at each site. A direct relationship between the level of deuteration and observed ¹³C resonance intensity facilitated a number of ¹³C CPMAS isotropic shift assignments without resorting to expensive and complex ¹³C labelling. In general, the procedure is excellent for assigning deuterium exchangeable methine carbon resonances in solid state carbohydrate spectra, however, the methodology is problematic when applied to the identification of CH₂ and CH₃ resonances, which are not readily recognizable from the characteristic position of their chemical shifts.     

Halogen-deuterium exchange reaction mediated by tributyltin hydride using THF-d8 as the deuterium source

A regioselective deuteration method for a wide variety of aromatic compounds using the halogen-deuterium exchange reaction initiated by Bu₃SnH using THF-d₈ as the deuterium source was developed.     

The structure and phase transitions in oxyfluoride (ND4)2MoO2F4

Single crystals of (ND₄)₂MoO₂F₄ containing 95% deuterium were produced by repeated recrystallization of (NH₄)₂MoO₂F₄ in heavy water. The effect of deuteration on the parameters of successive phase transitions was investigated by differential scanning microcalorimetry and polarization optics. X-ray analysis of the original and distorted phases was performed. It was found that deuteration does not change the sequence of crystal phases typical for (NH₄)₂MoO₂F₄, but leads to a shift in the phase transition Cmcm → Pnma towards the tricritical point. The mechanism of phase transitions in (ND₄)₂MoO₂F₄ was associated with both the ordering and the displacement of atoms.     

Photocatalytic Deuterium Atom Transfer Deuteration of Electron-Deficient Alkenes with High Functional Group Tolerance

Due to its mild reaction conditions and unique chemoselectivity, hydrogen atom transfer (HAT) hydrogenation represents an indispensable method for the synthesis of complex molecules. Its analog using deuterium, deuterium atom transfer (DAT) deuteration, is expected to enable access to complex deuterium-labeled compounds. However, DAT deuteration has been scarcely studied for synthetic purposes, and a method that possesses the favorable characteristics of HAT hydrogenations has remained elusive. Herein, we report a protocol for the photocatalytic DAT deuteration of electron-deficient alkenes. In contrast to the previous DAT deuteration, this method tolerates a variety of synthetically useful functional groups including haloarenes. The late-stage deuteration also allows access to deuterated amino acids as well as donepezil-d₂. Thus, this work demonstrates the potential of DAT chemistry to become the alternative method of choice for preparing deuterium-containing molecules.     

1H,2H,19F and 31P NMR and ESR investigations of aryl-t-butyl nitroxides

Aspects of translocation of spin to fluorine and phosphorus are discussed. (2p–3d)_π overlap in phosphorus is insignificant. Spin polarization and (2p–3p)_π overlap are opposing spin transfer mechanisms for phosphorus. The³¹P NMR spectrum of the nitroxide from 7a shows some features which are not fully understood. Some gain in resolution of the NMR spectra can be achieved by deuteration, but it is considerably lower than predicted.     

Vibrational spectra of WO3·nH2O and WO3 polymorphs

Vibrational spectra of polycrystalline WO₃ hydrates and polymorphs were measured and analyzed. The effect of sampling techniques on IR spectra has been demonstrated. The phase transition into triclinic polymorph (C⁵_2 h → C¹_i) has been revealed for the sample of monoclinic WO₃ prepared as KBr pellet. Using the deuteration method in situ has shown that cubic WO₃ is non-stoichiometric oxide stabilized by residual OH groups of WO₃·H₂O precursor.     

Kinetics and Mechanisms of Racemization: 5-Substituted Hydantoins (= Imidazolidine-2,4-diones) as Models of Chiral Drugs

A chiral center in a drug molecule increases the complexity of synthetic, metabolic, pharmacological, and clinical studies, an additional problem being a possible lack of configurational stability. Here, we report detailed kinetic and mechanistic studies on the deuteration and racemization of seven 5-monosubstituted hydantions (= imidazolidine-2,4-diones) used as model compounds. Using ¹H-NMR and chiral RP-HPLC, rates of reaction and thermodynamic parameters of activation were determined for the reactions of deuteration and racemization. Energies of deprotonation were obtained by molecular-orbital calculations performed at the AM1 level. It is demonstrated that the deuteration and racemization of 5-monosubstituted hydantoins follow general-base catalysis. The identical (within experimental errors) activation energies of deuteration and racemization indicate that the two reactions share a common reaction mechanism. The fact that the pseudo-first-order rate constants of deuteration are about half of those of racemization suggests that deuteration occurs with inversion of configuration. Very large differences in reaction rates were observed between the seven compounds, indicating the marked influence of substituents on chiral stability. These results, together with the small isotope effects observed, and the comparison between experimental activation energies and calculated energies of deprotonation, suggest a S_E2 push-pull mechanism for the racemization of 5-monosubstituted hydantoins.     

On spectroscopic properties and isotope effects of vibrationally stabilized molecules

Results of quantum and semiclassical calculations obtained for two different potential-energy surfaces are used to discuss spectroscopic properties and isotope effects of the linear IHI and IDI molecules. The potentials are a purely repulsive LEPS surface and a DIM-3C potential with two van der Waals type minima for equivalent IH ··· I and I ··· HI configurations. Both systems are dominated by the effect of vibrational bonding giving rise to some very unusual spectroscopic phenomena, which are discussed in detail. The different vibrational frequencies and rotational constants are roughly estimated as ν₁ = 120 (100) cm^?1, ν₂ = 280 (210) cm^?1, ν₃ = 360 (160) cm^?1 and B = 0.0194 (0.0196) cm^?1 for IHI (IDI). A detailed discussion of the dependence of ν₁, ν₂ and B on ν₃, their sensitivity to variations of the potential-energy surface, and a comparison with the vibrational frequencies of I₂ and HI (ID) is given. It is predicted that there exists only one excited level of the antisymmetric stretching mode. The numbers of symmetrical stretching and bending levels are fairly constant or may even decrease upon deuteration. Simultaneously deuteration destabilizes the molecule. These unusual phenomena are rationalized by our calculations. A set of criteria for observing infrared and Raman bound-to-bound and bound-to-resonance state transitions are presented for the IHI and IDI molecule.     

Silicon-29 and carbon-13 n.m.r. studies of organosilicon chemistry. VIII—Assignment of the 29Si and related 1H resonances of trimethylsilylated sugars by deuteration and shift reagent studies

Two techniques were investigated for assigning the ²⁹Si n.m.r. spectra of trimethylsilylated sugars. Specific deuteration, together with selective proton decoupling experiments, has allowed the complete assignment for methyl 2,3,4,6-tetra-O-trimethylsilyl-α-D-glucopyranoside. Double resonance spectra obtained in the presence of a lanthanide shift reagent, Pr(dpm)₃, have enabled the ²⁹Si and ¹H signals for the -SiMe₃, groups of methyl 2,3,4-tri-O-trimethylsilyl-α-D-glucopyranoside, to be linked. A complete and unambiguous assignment of the ²⁹Si spectrum for this molecule was obtained by selective deuteration, thus giving an unequivocal assignment of the –SiMe₃ proton resonances also. Definitive data regarding the effects of Pr(dpm)₃ on the ²⁹Si and ¹H resonances of the various –SiMe₃ groups of methyl 2,3,4-tri-O-trimethylsilyl-α-D-glucopyranoside are therefore available.     

Hydride‐Rhodium(III)‐N‐Heterocyclic Carbene Catalysts for Vinyl‐Selective H/D Exchange: A Structure–Activity Study

A series of neutral and cationic Rh^III‐hydride and Rh^III‐ethyl complexes bearing a NHC ligand has been synthesized and evaluated as catalyst precursors for H/D exchange of styrene using CD₃OD as a deuterium source. Various ligands have been examined in order to understand how the stereoelectronic properties can modulate the catalytic activity. Most of these complexes proved to be very active and selective in the vinylic H/D exchange, without deuteration at the aromatic positions, displaying very high selectivity toward the β‐positions. In particular, the cationic complex [RhClH(CH₃CN)₃(IPr)]CF₃SO₃ showed excellent catalytic activity, reaching the maximum attainable degree of β‐vinylic deuteration in only 20 min. By modulation of the catalyst structure, we obtained improved α/β selectivity. Thus, the catalyst [RhClH(κ²‐O,N‐C₉H₆NO)(SIPr)], bearing an 8‐quinolinolate ligand and a bulky and strongly electron‐donating SIPr as the NHC, showed total selectivity for the β‐vinylic positions. This systematic study has shown that increased electron density and steric demand at the metal center can improve both the catalytic activity and selectivity. Complexes bearing ligands with very high steric hindrance, however, proved to be inactive.     

1H-NMR-untersuchungen an sialinsäuren markierung von N-acetyl-D-neuraminsäure mit deuterium

An efficient method for the deuteration of N-acetyl-D-neuraminic-acid (NeuAc) at C-3 is described. In alkaline D₂O solution both protons of NeuAc (H_3a and H_3e) will be substituted by deuterium, whereby the substitution effect was found to be faster for H_3a than for H_3e. The rate of this exchange depends strongly on the pD value: the rate increases with increasing pD value. In acidic solution no effect could be observed. The process of H-D-exchange is reversible.     

Deoxygenative Deuteration of Carboxylic Acids with D2O

We report a general, practical, and scalable means of preparing deuterated aldehydes from aromatic and aliphatic carboxylic acids with D₂O as an inexpensive deuterium source. The use of Ph₃P as an O‐atom transfer reagent can facilitate the deoxygenation of aromatic acids, while Ph₂POEt is a better O‐atom transfer reagent for aliphatic acids. The highly precise deoxygenation of complex carboxylic acids makes this protocol promising for late‐stage deoxygenative deuteration of natural product derivatives and pharmaceutical compounds.     

Formyl-selective deuteration of aldehydes with D2O via synergistic organic and photoredox catalysis

Formyl-selective deuteration of aldehydes is of high interest for labeling purposes and for optimizing properties of drug candidates. Herein, we report a mild general method for formyl-selective deuterium labeling of aldehydes with D₂O, an inexpensive deuterium source, via a synergistic combination of light-driven, polyoxometalate-facilitated hydrogen atom transfer and thiol catalysis. This highly efficient, scalable reaction showed excellent deuterium incorporation, a broad substrate scope, and excellent functional group tolerance and selectivity and is therefore a practical method for late-stage modification of synthetic intermediates in medicinal chemistry and for generating libraries of deuterated compounds.

Formyl-selective deuteration of aldehydes with D₂O mediated by the synergistic combination of light-driven, polyoxometalate-facilitated HAT and thiol catalysis is reported.     

Reactivity of pyrrole pigments, 4. Part: Deuteration of 5-arylmethylene-3-pyrrolin-2-ones withd 1-trifluoroacetic acid

5-Arylmethylene-3,4-dimethyl-3-pyrrolin-2-ones on treatment withd ₁-trifluoroacetic acid (d ₁-TFA) undergo deuterium substitution at the carbon atom of the methylene bridge. This electrophilic substitution is related to similar deuteration reactions of verdins (bilatrienes-a,b,c). The results obtained can be interpreted by a free energy relationship, assuming that the field effect, becomes negligible by the influence ofTFA.