Deuteration Of Water Research Articles

On the low ortho-to-para H2 ratio in star-forming filaments

The formation of stars and planetary systems is a complex phenomenon that relies on the interplay of multiple physical processes. Nonetheless, it represents a crucial stage for our understanding of the Universe, and in particular of the conditions leading to the formation of key molecules (e.g. water) on comets and planets. Herschel observations demonstrated that stars form in gaseous filamentary structures in which the main constituent is molecular hydrogen (H2). Depending on its nuclear spin H2 can be found in two forms: ‘ortho’ with parallel spins and ‘para’ where the spins are anti-parallel. The relative ratio among these isomers, the ortho-to-para ratio (OPR), plays a crucial role in a variety of processes related to the thermodynamics of star-forming gas and to the fundamental chemistry affecting the deuteration of water in molecular clouds, commonly used to determine the origin of water in Solar System bodies. Here, for the first time, we assess the evolution of the OPR starting from the warm neutral medium by means of state-of-the-art 3D magnetohydrodynamic simulations of turbulent molecular clouds. Our results show that star-forming clouds exhibit a low OPR (≪0.1) already at moderate densities (∼1000 cm−3). We also constrain the cosmic-ray ionisation rate, finding that 10−16 s−1 is the lower limit required to explain the observations of diffuse clouds. Our results represent a step forward in the understanding of the star and planet formation processes providing a robust determination of the chemical initial conditions for both theoretical and observational studies.

Incorporation of Membrane Proteins Into Bicontinuous Microemulsions Through Winsor‐III System‐Based Extraction

AbstractThe membrane proteins (MP) α‐synuclein (ASYN) and bacteriorhodopsin (BR) were readily incorporated into bicontinuous microemulsions (BμEs) formed by two microemulsion systems: water/heptane/Aerosol‐OT (AOT)/CK‐2,13 and water/dodecane/sodium dodecyl sulfate (SDS)/1‐pentanol. (CK‐2,13 is an alkyl ethoxylate possessing two alkyl tail groups of carbon chain length 2 and 13 and an average degree of ethoxylation of 5.6.) MP were encapsulated in BμEs through preparation of Winsor‐III systems at optimal salinity, with the anionic surfactants AOT and SDS providing the driving force for extraction. Dissolution of ASYN in BμEs greatly increased the former's α‐helicity, similar to ASYN's behavior in the presence of biomembranes, while BμE‐ and vesicle‐encapsulated BR possessed similar secondary structure. Small‐angle neutron scattering (SANS) results clearly demonstrated the direct interaction of MP with the surfactants, resulting in a decrease of surface area per volume for surfactant monolayers due to decreased surfactant efficiency. The SANS signal for ASYN was isolated through the use of neutron contrast matching for the surfactants through partial deuteration of water and oil, one of the first reports of contrast matching for BμEs in the literature. The SANS results of the contrast‐matched sample reflected similar aggregation for ASYN in BμEs as was reported previously for vesicles and SDS solution. This study demonstrates the potential use of BμEs as MP host systems for conducting biochemical reactions such as the conversion of sunlight into adenosine triphosphate by BR and studying the fundamental behavior of MP, such as the role of ASYN dysfunction in Parkinson's disease, as well as for isolation and purification of MP via Winsor‐III‐based extraction.

Simulating the D/H ratio of water formed in the early solar nebula

Our solar system originated from a protoplanetary disk about 4.6 billion years ago. We simulate the formation of this disk by a three-stage model of the solar nebula (SN) which describes the hydrodynamic and chemical evolution of a cold cloud core consisting of gas and one mass percent dust. Considering the first two stages of this SN-model we have studied the formation and deuteration of water, which is an important precondition of life. During the quasi-stationary stage of the cloud core, corresponding to the first SN stage, water has been formed on the surface of dust grains by the hydrogenation of oxygen. The gas and dust temperatures, which differ at the outer boundary of the core, are nearly 14 K and reach 9 K in its center. Therefore an icy mantle forms on the dust grains in less than 105 years and changes slowly afterwards. Because of the large abundance of hydrogen and a carbon to oxygen (C/O) ratio of 0.44 the major component of this mantle is water ice. We found that the water produced in the gas phase amounts to less than 20 ppm of the water formed on dust grains. In both phases, the deuterium enrichment δD (‰) relative to the Standard Mean Ocean Water varies at 1 AU from 15,050 to 63,100‰ (or a D/H ratio from 2 to 0.5%) and indicates the low formation temperature of water molecules. In the second stage of our SN-model, the collapse of the cold cloud core is simulated using a semi-analytical solution of the magneto-hydrodynamic equations. Due to relatively high temperatures around the center (10^(2-3) K), this range is identified with the hot corino observed in regions of low mass star formation in our galaxy. There, the icy mantles of the grains vanish due to desorption of water molecules from their surfaces. As a result the water to hydrogen ratio in the gas phase increases to 10^(-5)-10^(-4). Since this water was formed in a cold region and a collision related destruction of water molecules (occurring at ~10^5 K) can be neglected everywhere except for the protostellar source in the core center (< 10^(-2) AU), the deuterium enrichment in the outer hot corino (1 AU) reaches δD of 2,210‰ (or D/H of 0.1%) at the end of the main collapse phase. Different reasons for this relatively high value are discussed.

THE HERSCHEL AND IRAM CHESS SPECTRAL SURVEYS OF THE PROTOSTELLAR SHOCK L1157-B1: FOSSIL DEUTERATION

We present the first study of deuteration toward the protostellar shock L1157-B1, based on spectral surveys performed with the Herschel-HIFI and IRAM 30 m telescopes. The L1157 outflow is driven by a low-mass Class 0 protostar and is considered the prototype of the so-called chemically active outflows. The young (2000 yr), bright blueshifted bow shock, B1, is an ideal laboratory for studying the gas chemically enriched by the release of dust mantles due to the passage of a shock. A total of 12 emission lines (up to E_u = 63 K) of CH_(2)DOH, HDCO, and DCN are detected. In addition, two lines of NH_(2)D and HDO are tentatively reported. To estimate the deuteration, we also extracted from our spectral survey emission lines of non-deuterated isotopologues (^(13)CH_(3)OH, H_2 ^(13)CO, H^(13)CN, H_2 ^(13)CO, and NH_3). We infer higher deuteration fractions for CH_(3)OH (D/H = 0.2-2 × 10^(–2)) and H_(2)CO (5-8 × 10^(–3)) than for H_(2)O (0.4-2 × 10^(–3)), HCN (~10^(–3)), and ammonia (≤3 × 10^(–2)). The measurement of deuteration of water, formaldehyde, and methanol in L1157-B1 provides a fossil record of the gas before it was shocked by the jet driven by the protostar. A comparison with gas-grain models indicates that the gas passed through a low-density (≤10^3 cm^(–3)) phase, during which the bulk of water ices formed, followed by a phase of increasing density, up to 3 × 10^4 cm^(–3), during which formaldehyde and methanol ices formed.

INTERSTELLAR ICES AS WITNESSES OF STAR FORMATION: SELECTIVE DEUTERATION OF WATER AND ORGANIC MOLECULES UNVEILED

Observations of star forming environments revealed that the abundances of some deuterated interstellar molecules are markedly larger than the cosmic D/H ratio of 10-5. Possible reasons for this pointed to grain surface chemistry. How- ever, organic molecules and water, which are both ice constituents, do not enjoy the same deuteration. For example, deuterated formaldehyde is very abundant in comets and star forming regions, while deuterated water rarely is. In this article, we explain this selective deuteration by following the formation of ices (using the rate equation method) in translucent clouds, as well as their evolu- tion as the cloud collapses to form a star. Ices start with the deposition of gas phase CO and O onto dust grains. While reaction of oxygen with atoms (H or D) or molecules (H2) yields H2O (HDO), CO only reacts with atoms (H and D) to form H2CO (HDCO, D2CO). As a result, the deuteration of formaldehyde is sensitive to the gas D/H ratio as the cloud undergoes gravitational collapse, while the deuteration of water strongly depends on the dust temperature at the time of ice formation. These results reproduce well the deuterium fractionation of formaldehyde observed in comets and star forming regions and can explain the wide spread of deuterium fractionation of water observed in these environments.

Deuteration of Water Enables Self‐Organization of Phospholipid‐Based Reverse Micelles

Phospholipid-based reverse micelles are composed of branched cylinders. Their branching points are known to attract themselves and to slide along branches. The rate of this sliding is governed by the lifetime of H(D)-bonded water bridges between phospholipid molecules. This lifetime is increased when the water is deuterated. On condition that the water contains at least 40 D atoms%, water/dipalmitoylphosphatidylcholine (DPPC)/deuterated pyridine reverse micelles with the composition 1.1:1:250 (v/v) have been shown to self-organize into a liquid crystal in the 310-316 K temperature range. The mechanism of this self-organization is unraveled by following the FTIR and (1)H NMR spectra of more concentrated micelles upon heating. During the preparation of micelles, pyridine-(D(+))H(+) ions are formed. They give rise to hydron transfers, under the influence of the DPPC electric charges, evidenced by two broad FTIR absorptions above (BB1) and below (BB2) the nu(C-O) stretch. These hydron transfers occur along strong (D(+))H(+) bonds of pyridinium ions with pyridine (BB1) and DPPC C=O groups (BB2). The proton transfers at the interface of micelles, relayed in the continuous pyridine medium, create a tenuous link between separated micelles, thus facilitating their organization. Upon heating, DPPC heads shrink and DPPC chains expand to make wedge-shaped DPPC molecules. The micelles then change in shape: cylinders constrict and enclosed water drifts towards branching points, which swell. Branching points of neighboring micelles come into contact. Due to the deuteration of water these contacts are prolonged and H bonds are formed between DPPC molecules located in each branching point. Upon storage at 39 degrees C, these branching points fuse. The lateral diffusion of DPPC molecules becomes free, as evidenced by a narrowing of all (1)H NMR resonances. Upon further heating, reorganization into a liquid crystal occurs.

Investigation of isotope effects with the nuclear-electronic orbital approach

This paper addresses fundamental issues that arise in the application of the nuclear-electronic orbital (NEO) approach to systems with equivalent quantum nuclei. Our analysis illustrates that Hartree-Fock nuclear wave functions do not provide physically reasonable descriptions of systems comprised of equivalent low-spin fermions or equivalent bosons. The physical basis for this breakdown is that the ionic terms dominate due to the localized nature of the nuclear orbitals. Multi-configurational wave functions that include only covalent terms provide physically reasonable descriptions of these types of systems. The application of the NEO approach to a variety of chemical systems is presented to elucidate the isotope effects on the geometries and electronic wave functions. Deuteration of hydrogen halides, water, ammonia, and hydronium ion decreases the bond length and the magnitude of negative partial atomic charge on the heavy atom. These results are consistent with experimental spectroscopic data. Deuteration at the beta position for formate anion and a series of amines increases the magnitude of negative partial atomic charge on the protonation site for the unprotonated species. This observation is consistent with the experimentally observed increase in basicity upon deuteration at the beta position for carboxylic acids and amines.

Isotopomeric Conformational Change in Anisole–Water

The deuteration of water produces the conformational change shown in the figure in the anisole⋅⋅⋅water complex. The value of the θ angle decreases from 138 to 128°, and the secondary interaction O⋅⋅⋅HMe is replaced by O⋅⋅⋅HPh. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2005/z461860_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Striking changes in molecular recognition by deuteration of aqueous binary solvents

Oxidation of a pair of associating thiols 1 and 2 with oxygen, each with a binding site [—C(O)NHC(O)NH—] and a recognition site (R1 or R2), is examined at various temperatures in aqueous binary solvents of water or deuterium oxide with ethanol, acetonitrile or methanol. The selectivity (r)—a measure of the degree of molecular recognition in the oxidation—represented by the logarithmic ratio of the yield of the unsymmetrical disulfide (4) to twice that of the symmetrical disulfide (3) was examined as a function of the mole fractions of water (xw) and deuterium oxide (xdo). It is found that, on deuteration of aqueous binary solvents containing ethanol (xw= 0.50 and 0.75), the temperature dependence of molecular recognition (r) alters strikingly from a clear bell-shaped type (a maximum at 35°C) to a plateau-like type in the range 20–70°C. It is clarified further that, in aqueous acetonitrile at xw= 0.20 and 0.75, deuteration of water causes the temperature dependence of r to become fairly dull. In contrast, it is found that the deuteration effect in water–methanol is much less than that in water–ethanol or in water–acetonitrile. Furthermore, conversion of the NH groups in 1 and 2 to the ND groups occurs very quickly. A possible cause of the large deuterium effect is discussed. Copyright © 2005 John Wiley & Sons, Ltd.

Infrared spectroscopy of OD vibrators in minerals at natural dilution: hydroxyl groups in talc and kaolinite, and structural water in beryl and emerald.

An infrared (IR) study of natural deuteration is conducted on minerals containing hydroxyl groups (talc and kaolinite) and channel-water-bearing minerals (beryl and emerald). In talc, the OD valence vibration is located at 2710 cm(-1), corresponding to OD groups surrounded by 3 Mg atoms. In kaolinite, the OD valence vibrations are located at 2671 cm(-1) (inner OD group), 2712, 2706, and 2700 cm(-1) (three inner-surface OD groups). In beryl and emerald, natural deuteration of channel water is observed for the first time by infrared microspectroscopy. In beryl from Minas Gerais (Brazil), the OD profiles are characterized by four bands at 2735, 2686, 2672, and 2641 cm(-1). In emeralds from Colombia and Brazil, the OD profiles are characterized by five or four bands, respectively, at 2816, 2737, 2685, 2673, and 2641 cm(-1) (Colombia) and 2730, 2684, 2672, and 2640 cm(-1) (Brazil). The band at 2816 cm(-1) can be assigned to -OD or OD(-), and bands at 2686-2684, 2673-2672, and 2641-2640 cm(-1) can be assigned to type-I and type-II HOD molecules. The band at 2737-2730 cm(-1) is partially disturbed by combination bands of the mineral. Such OD profiles are different from those obtained by artificial deuteration at higher OD dilution.

Structural changes of the molecular complexes of pyridines with water and demixing phenomena in aqueous solutions

Demixing phenomena in the aqueous solutions of organic molecules are considered due to the temperature induced structural changes of the hydrogen bonds between water and organic molecules. The lower and upper critical solution points are attributed to the appearance of the “critical” concentration of the complexes with one hydrogen bond between a single water molecule and single solute molecule. Namely, the hydrogen bonded pair complexes are responsible for the formation of the strongly associated water clusters around solute molecules that may be followed by separation of the homogeneous solution on water-rich and organic-rich phases. The extension of the immiscibility gap upon strengthening of the hydrogen bonds between water and pyridine is obtained. Experimentally observed changes of the lower and upper critical solution temperatures upon the deuteration of water, addition of salts, and presence of the alkyl substituents in the solute pyridine molecules are well reproduced in the framework of the proposed model.

Low cost production of perdeuterated biomass using methylotrophic yeasts

AbstractThree strains of methylotrophic yeasts, Candida boidinii, Pichia angusta (previously Hansenula polymorpha) and Pichia Pastoris, were studied for their capacity to grow on methanol in deuterated media. Growth rates, determined relative to the extent of deuteration of water and/or methanol, showed that water deuteration was the major limiting factor. After adaptation to deuterium by progressive transfer through media of increasing deuteration, growth rates were diminished relative to those obtained on hydrogenated media of identical salts composition: the two Pichia species retained the highest growth rates (μ=0.02 h−1) in the fully deuterated medium. Perdeuterated biomass (16 g) was obtained in a 1 liter fed‐batch fermentation and the extent of deuteraton of isolated ergosterol has been shown to be 97.5% by mass spectrometric analysis.

Transport calculations of the influence of physical factors on depth-dose distributions in boron neutron capture therapy

Distributions of thermal neutron fluence and capture gamma ray absorbed dose rates were evaluated, taking into consideration various physical factors relevant to boron neutron capture therapy. The use of a larger neutron irradiation aperture was associated with an increase in thermal neutron fluence and capture gamma ray absorbed dose rates. Radiation leakage was more significant with smaller phantoms. Attenuation of thermal neutron fluence rates by 10B suggested that there was an optimal 10B concentration (<100 PPM) for a given tumour. Deuteration of water allowed better penetration of thermal neutrons with less capture gamma rays and is potentially applicable for the treatment of deep-seated brain tumours.

Increased neutron penetration in partially deuterated water: application to neutron capture therapy.

Theoretically, partial deuteration of body water should allow significantly increased neutron penetration in tissue. To evaluate the possible usefulness of partially deuterated water in neutron capture therapy (NCT), neutron flux density distributions were measured in a 23 x 16.5 cm (length x diameter) cylinder for incident thermal and epithermal neutron beams, at 20 and 40 at. % deuteration of water. Relative to neutron flux densities in nondeuterated water, flux densities increased significantly with increasing depth and increasing levels of deuteration. For example, at a depth of 6 cm, flux density was increased approximately 20% to 50% for 20 to 40 at. % deuteration. In a clinical situation, this would increase tumor dose by approximately 30%. Further benefits include the reduced hydrogen neutron capture and the chemical radioprotective effects of partial deuteration for photon radiation.

The use of heavy water in boron neutron capture therapy of brain tumours

A theoretical analysis is presented from which it is concluded that transient partial deuteration of body water for neutron capture therapy would significantly enhance radiation produced by the neutron-boron reaction at the deep margins of brain tumours and reduce effective gamma radiation to normal brain tissues by 50% or more. The analysis deals only with totally thermalised incident neutrons.

Uptake of 125I-iododeoxyuridine in mouse organs during deuteration of body water: Evidence for a thymus-specific effect

The effects of body water deuteration on mammalian DNA synthesis in vivo during the deuterium equilibration period in the body were studied. Young adult mice were given 15% or 30% D 2O in the drinking water for 4, 10 or 21 days. Control mice were given distilled water. Eighteen hours prior to sacrifice, 125IUdR, a conveniently monitored synthetic analogue of the DNA precursor thymidine, was injected intravenously. Although neither radioiodine activity of the total body nor body weight varied significantly among the three groups, thymic radioactivity per g tissue was significantly lower in mice given 30% D 2O and, to a lesser extent, in mice given 15% D 2O than in the control group. In contrast, intestine and hemopoietic bone marrow displayed minor changes in 125IUdR incorporation. This reduction of 125IUdR incorporation is discussed in relation to the particular importance of thymidine reutilization in the thymus.