scholarly journals The mechanism of glucose 6-phosphate–d-myo-inositol 1-phosphate cyclase of rat testis. The involvement of hydrogen atoms

1968 ◽  
Vol 108 (1) ◽  
pp. 125-129 ◽  
Author(s):  
J. E. G. Barnett ◽  
D. L. Corina
Keyword(s):  
Hydrogen Atom ◽  
Isotope Effect ◽  
Ternary Complex ◽  
Aldol Condensation ◽  
Hydrogen Atoms ◽  
Original Activity ◽  
Rat Testis ◽  
Inositol 1 ◽  
Apparent Loss

Comparison of the initial 3H/14C ratios in specifically labelled d-glucose 6-phosphates with the final ratios in myo-inositol produced by glucose 6-phosphate–d-myo-inositol 1-phosphate cyclase from rat testis showed that, during the conversion, the hydrogen atoms at C-1 and C-3 were fully retained, one hydrogen atom was lost from C-6, and that at C-5 was apparently retained to the extent of 80–90%. The loss of 3H could not be stimulated by addition of unlabelled NADH, and when unlabelled substrate was used 3H from [3H]NADH and [3H]water was not incorporated. Treatment of the enzyme with charcoal abolished the activity, and this was restored to 25–50% of the original activity by NAD+. The charcoal-treated enzyme again apparently gave 85% retention of hydrogen with [5−3H]glucose 6-phosphate as substrate in the presence of NAD+ alone, but the retention was decreased to 65% with excess of NADH. The results are interpreted as indicating that the cyclization proceeds by an aldol condensation in which C-5 is oxidized by NAD+ in a tightly-bound ternary complex, and that the apparent loss of 3H when untreated enzyme is used is due to an isotope effect. It is suggested that after treatment with charcoal some exchange of NADH with an external pool may take place.

scholarly journals The stereospecificity of the reduction of nitrate by reduced nicotinamide-adenine dinucleotides catalysed by Candida utilis preparations

1982 ◽  
Vol 205 (3) ◽  
pp. 581-584 ◽  
Author(s):  
D D Davies ◽  
P Kenworthy
Keyword(s):  
Hydrogen Atom ◽  
Nitrate Reductase ◽  
Isotope Effect ◽  
Candida Utilis ◽  
Kinetic Isotope Effect ◽  
The Other ◽  
Nicotinamide Adenine ◽  
Hydrogen Atoms ◽  
Kinetic Isotope ◽  
High Degree

The reduction of nitrate by reduced nicotinamide-adenine dinucleotides, catalysed by extract of Candida utilis, exhibits an apparent high degree of stereospecificity for the ‘B’ methylene hydrogen atom of NADPH and mixed stereospecificity for the methylene hydrogen atoms of NADH. Purified nitrate reductase, on the other hand, exhibits ‘A’ stereospecificity for NADH and NADPH. The apparent switch of stereospecificity from the ‘B’ to the ‘A’ side of NADPH, which occurs after purification of the enzyme, is partly explained by the fact that in crude extracts nitrate is reduced completely to ammonia. Nitrite does not accumulate but is reduced to ammonia by nitrite dehydrogenase, which is ‘B’-specific, so that up to 75% of hydrogen removed from NADPH during the reduction of nitrate could occur from the ‘B’ side. A further increase in the removal of hydrogen from the ‘B’ side of NADPH could be the kinetic isotope effect that is observed when [‘A’-3H]NADPH is the reductant, the H-C bond being cleaved 2.3 times faster than the 3H-C bond. The mixed stereospecificity observed with NADH has been traced to an uncharacterized enzyme that catalyses a ‘B’-specific exchange between NAD+ and NADH. This reaction is discussed in relation to the possibility that it may explain other cases of apparent mixed stereospecificity that have been reported.

Formation of surface layer of hydrogen in pure aluminum

2019 ◽  
Vol 484 (1) ◽  
pp. 56-60
Author(s):  
D. A. Indejtsev ◽  
E. V. Osipova
Keyword(s):  
Surface Layer ◽  
Hydrogen Atom ◽  
Ab Initio ◽  
Pure Aluminum ◽  
Hydrogen Atoms ◽  
Energy Characteristics ◽  
Aluminum Crystal

Hydrogen atom behavior in pure aluminum is described by ab initio modelling. All main energy characteristics of the system consisting of hydrogen atoms in a periodic aluminum crystal are found.

scholarly journals The photolysis of ammonia

1940 ◽  
Vol 175 (961) ◽  
pp. 187-207 ◽  
Keyword(s):  
Hydrogen Atom ◽  
Preceding Paper ◽  
Ammonia Molecule ◽  
Experimental Techniques ◽  
Hydrogen Atoms ◽  
Atom Concentration ◽  
Important Discrepancy

It has been shown in the preceding paper that the hypothesis that hydrazine is responsible for the anomalously low hydrogen atom concentration in the decomposition of ammonia must be abandoned. In order to explain this important discrepancy some new experimental techniques require to be developed which will settle the matter without appeal to further hypotheses. There are two general explanations of the discrepancy: (1) the hydrogen atoms are not produced as fast as that calculated on the assumption that every ammonia molecule absorbing a quantum necessarily decomposes, (2) that some entity not yet recognized removes hydrogen atoms at a rate faster than that at which they normally recombine. In this paper methods will be described in which these two problems are solved, and finally there is a discussion of the photochemistry of ammonia in the light of the new results obtained during these experiments.

scholarly journals Relationship between the Behavior of Hydrogen and Hydrogen Bubble Nucleation in Vanadium

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 322
Author(s):  
Zhengxiong Su ◽  
Sheng Wang ◽  
Chenyang Lu ◽  
Qing Peng
Keyword(s):  
Hydrogen Atom ◽  
First Principles ◽  
Bound States ◽  
Hydrogen Molecule ◽  
Vacancy Cluster ◽  
Bubble Nucleation ◽  
Hydrogen Bubble ◽  
First Principles Calculations ◽  
Hydrogen Atoms ◽  
Macroscopic Deformation

Hydrogen plays a significant role in the microstructure evolution and macroscopic deformation of materials, causing swelling and surface blistering to reduce service life. In the present work, the atomistic mechanisms of hydrogen bubble nucleation in vanadium were studied by first-principles calculations. The interstitial hydrogen atoms cannot form significant bound states with other hydrogen atoms in bulk vanadium, which explains the absence of hydrogen self-clustering from the experiments. To find the possible origin of hydrogen bubble in vanadium, we explored the minimum sizes of a vacancy cluster in vanadium for the formation of hydrogen molecule. We show that a freestanding hydrogen molecule can form and remain relatively stable in the center of a 54-hydrogen atom saturated 27-vacancy cluster.

60Co γ-RADIOLYSIS OF HYDROGEN HALIDES AT 77 °K

1966 ◽  
Vol 44 (2) ◽  
pp. 191-197
Author(s):  
R. C. Rumfeldt ◽  
D. A. Armstrong
Keyword(s):  
Liquid Phase ◽  
Hydrogen Atom ◽  
Experimental Error ◽  
Dose Dependence ◽  
Solid Matrix ◽  
Reactive Intermediate ◽  
Hydrogen Atoms ◽  
Hydrogen Halides ◽  
Atoms And Molecules ◽  
The Difference

Yields of hydrogen formed in the 60Co γ-radiolyses of pure polycrystalline samples of HBr and HCl at 77 °K decrease with increasing dose in the range 0 to 1 × 1018 eV per g. The true initial yields are G(H2)solidHClat77°K = 6.3 ± 0.2 and G(H2)solidHBrat77°K = 12.3 ± 0.3. Within experimental error these are the same as the respective liquid-phase yields at −79 °C. For doses in excess of 2 × 1018 eV per g the dose dependence is no longer significant and the yields tend toward plateau values of 3.2 ± 0.1 and 10.3 ± 0.1 for HCl and HBr respectively. The dose dependence of the hydrogen yields is attributed to the scavenging of a reactive intermediate by the halogen atoms and molecules which accumulate in the solid matrix as the dose increases.In independent experiments with an apparatus of the Klein–Scheer type it was shown that hydrogen atoms react readily with films of HBr at 77 °K. There is, however, no evidence of a significant reaction with HCl at this temperature. The difference in behavior of the two hydrogen halides may be explained by their different activation energies for reaction with hydrogen atoms. The results of the γ-radiolyses are discussed in the light of these experiments and it is suggested that the dose dependence may be a result of the scavenging of an ionic intermediate rather than a thermal hydrogen atom.

Photolyse du butène-1 dans l'ultraviolet à vide

1973 ◽  
Vol 51 (17) ◽  
pp. 2853-2859 ◽  
Author(s):  
Guy J. Collin
Keyword(s):  
Double Bond ◽  
Hydrogen Atom ◽  
Kinetic Energy ◽  
Thermal Energy ◽  
Hydrogen Atoms ◽  
Excited Molecules

The vacuum u.v. photolysis of 1 -butene was studied in the 147–105 nm region. The main products formed from the fragmentation of excited molecules are allene, 1,3-and 1,2-butadienes, ethylene, and acetylene. The addition of a hydrogen atom to the double bond produces mainly secondary butyl radicals (91%) at 147 nm. At 123.6 nm, this proportion becomes 82%. Thus at shorter wavelengths (10 and 11.6–11.8 eV), hydrogen atoms are produced with a kinetic energy higher than the thermal energy.

Mechanism and stereochemistry of enzymic reactions involved in porphyrin biosynthesis

1976 ◽  
Vol 273 (924) ◽  
pp. 117-136 ◽  
Keyword(s):  
Schiff Base ◽  
Hydrogen Atom ◽  
Carbon Atom ◽  
Pyridoxal Phosphate ◽  
Hydrogen Atoms ◽  
Bond Forming ◽  
Aminolaevulinic Acid

5-Aminolaevulinate synthetase catalyses the condensation of glycine and succinyl-CoA to give 5-aminolaevulinic acid. At least two broad pathways may be considered for the initial C—C bond forming step in the reaction. In pathway A the Schiff base of glycine and enzyme bound pyridoxal phosphate ( a ) undergoes decarboxylation to give the carbanion ( b ) which then condenses with succinyl-CoA with the retention of both the original C2 hydrogen atoms of glycine. In pathway B, loss of a C2 hydrogen atom gives another type of carbanion ( c ) that reacts with succinyl-CoA. Evidence has been presented to show that the initial C—C bond forming event occurs via pathway B which involves the removal of the pro R hydrogen atom of glycine. Subsequent mechanistic and stereochemical events occurring at the carbon atom destined to become C5 of 5-aminolaevulinate have also been delineated.

scholarly journals DISPERSION INTERACTION OF ATOMS WITH SINGLE-WALLED CARBON NANOTUBES DESCRIBED BY THE DIRAC MODEL

2011 ◽  
Vol 03 ◽  
pp. 555-563 ◽  
Author(s):  
YU. V. CHURKIN ◽  
A. B. FEDORTSOV ◽  
G. L. KLIMCHITSKAYA ◽  
V. A. YUROVA
Keyword(s):  
Carbon Nanotubes ◽  
Hydrogen Atom ◽  
Interaction Energy ◽  
Hydrogen Molecule ◽  
Single Walled Carbon Nanotubes ◽  
Hydrogen Atoms ◽  
Single Walled Carbon ◽  
Atoms And Molecules ◽  
Proximity Force Approximation ◽  
Walled Carbon Nanotubes

We calculate the interaction energy and force between atoms and molecules and single-walled carbon nanotubes described by the Dirac model of graphene. For this purpose the Lifshitz-type formulas adapted for the case of cylindrical geometry with the help of the proximity force approximation are used. The results obtained are compared with those derived from the hydrodymanic model of graphene. Numerical computations are performed for hydrogen atoms and molecules. It is shown that the Dirac model leads to larger values of the van der Waals force than the hydrodynamic model. For a hydrogen molecule the interaction energy and force computed using both models are larger than for a hydrogen atom.

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