Equivalent Protons Research Articles

2D 13C-coupled HMQC-ROESY: a probe for NOEs between equivalent protons

2D 13C-coupled HMQC-ROESY: a probe for NOEs between equivalent protons

One-bond C–H NMR coupling constants in 1,2,4-trioxanes: a reversed perlin effect

In a reversal of the Perlin effect, the values of 1JC–H for the equatorial protons at C(3) and C(6) in 1,2,4-trioxanes are less than those for the corresponding axial protons; this is ascribed to homoanomeric interactions between equatorially directed nonbonding electron pairs on oxygen and the equatorial C(3)–H or C(6)–H σ* orbitals.

Spatial and Temporal Features of 0.64-35MeV Protons in the Space Station Environment: EXOS-C Observations.

The spatial and temporal features of the peak proton flux detected near the equator in the integral energy channel of 0.64-35MeV by S-1 telescope on board the EXOS-C mission were studied for a period of three years (1984-86). The equatorial zone (±30°geomagnetic latitude) proton data obtained for the angle between the telescope axis and the magnetic field direction in the range of 50°-130°and at the peak efficiency of the instrument, were sorted out from a study of the orientation of the telescope axis and calculation of the response function of the telescope. The data, after freed from the major influence of the South Atlantic Anomaly, and subsequently analyzed, revealed some new results contrary to the earlier observation (MORITZ, 1972) in the altitude range of 350 to 850km. The spatial distribution shows that the global profile of the peak proton flux is aligned with the profile of the minimum magnetic field, and, the peak proton population straddles the minimum magnetic field equator with a full-width-at-half-maximum of about 19°. Also, the pitch angle distribution of the equatorial proton population is found to have the anisotropy index in the range 7 to 10. Further, the proton flux shows altitude, L, and longitude dependences. The flux increases as h1.43 and L4.25-7.50 (corresponding to different equatorial pitch angles). Besides, in the longitude range 180° 5MeV) protons, has been used to infer the presence of a major low energy component and a minor high energy component. In the study of temporal features, comparison of absolute fluxes during two solar epochs shows that the proton flux during the solar minimum in 1984-86 was, at least, 40 times less than that during the solar maximum condition in 1982, possibly, due to lesser amount of hydrogen escape to the exosphere during the minimum condition, and thereby causing less precipitation of low energy particles in the equatorial atmosphere.

Group Travel Time of EM Waves with Frequencies near the Ion Cyclotron Frequency in the Two-ion Magnetosphere

The oblique propagation of electromagnetic (EM) waves with frequencies below the equatorial proton cyclotron frequency is investigated for a two-ion magnetospheric plasma. Attention is focused on the wave group travel time along a geomagnetic field line rom the equatorial wave source region to the ionosphere or the location where the wave is reflected. It is found that the coupling between eft- and right-hand polarised waves occurring at a crossover frequency significantly modifies features of the frequency-time spectrum. ecause of this modification, the spectral tone change of Pc 1 waves observed on the ground (e.g. Dowden 1966; Gendrin and Laurent 1979) is not caused solely by dispersion effects in a multi-component plasma.

Broadband-decoupled proton spectroscopy

Proton NMR spectra are presented in a form that incorporates chemical-shift effects but excludes spin-spin splittings, as if homonuclear broadband decoupling had been employed. By Fourier transformation of spin echoes modulated by proton-proton coupling, a two-dimensional J spectrum is obtained. A 50 ms purging pulse at the end of the evolution period suppresses antiphase product-operator terms; this changes the character of the two-dimensional spin-multiplet patterns and ensures that the signals are in the pure absorption mode. In the limit of weak coupling, each multiplet pattern possesses C 4 symmetry and a software “symmetry filter” separates overlapping multiplets and rejects all other signal components. By the appropriate projection of the processed J spectrum, a one-dimensional spectrum is obtained with narrow singlet responses at the chemical-shift frequencies and no spin-spin splittings. The peak heights are proportional to the numbers of equivalent protons at each site. A separate spin-multiplet pattern from each site is available in the other frequency dimension ( F 1). The technique can be incorporated into more complicated experiments such as spin-lattice relaxation studies.

Synthesis, reactivity, and NMR studies of dilithiated (E)-1,4-bis(trimethylsilyl)but-2-ene and (E)-1,4-bis(trimethylsilyl)-2,3-dimethylbut-2-ene

(Z)-1, 4-Dilithio-1,4-bis(trimethylsilyl)but-2-ene and 1,4-dilithio-1,4-bis(trimethylsilyl)-2,3-dimethylbut-2-ene adducts of TMEDA (≡N,N,N′,′-tetramethylethylenediamine), [{Li(TMEDA)}{(MeSiCHCH)}] (3) and [{Li(TMEDA)}((MeSiCHCMe)}] (4), respectively, have been prepared by dimetalation of the corresponding (E)-but-2-ene using n-BuLi(TMEDA) in hexane. Assignment of the Z configuration of the dianions with Li atoms bridging the ipso carbons (C) is based on NMR data: Magnetically equivalent protons attached to the ipso carbons (C) couple to Li (J = ca. 1 Hz) in both compounds, lack of coupling of the protons attached to C with the lithiums in 3, and NOE enhancements for HLi HOESY experiments. The Z configuration is also consistent with the structures of two isolated silyl derivatives of 3; treatment with ClSiMe gives (Z)-1,1,4, 4-tetrakis(trimethylsilyl)but-2-ene (5), and with ClSiMe it yields the (Z, Z)-1, 6-disilacyclodeca-3, 8-diene [(MeSiCHC(H)=C(H)CH(SiMe)SiMe}] (6). Compound 3 is a potent reducing agent, affording (E, E)-1, 4-bis(trimethylsilyl)buta-1, 3-diene (7) and metal when treated with HgCl (yield of 7 71%) or CaCl. X-ray diffraction data for 5 revealed a distorted Z double bond, the C-C-C angles at the sp carbon centers being “opened up” to 130.2° (mean): Crystals are monoclinic, space group P2/n, with α = 11.595 (4) A, b = 12.205 (1) A, c = 17.569 (6) A, β = 107.33 (2)°, V = 2373 (1) A, and Z = 4.

Measurement of the integral characteristics of radiation fields of medium-energy nucleons by plastic scintillation detectors

Abstract We have developed a method for measuring the fluences of neutrons and protons with energies above 10–20 MeV and the corresponding dose equivalents by two plastic scintillation detectors of different sizes with an accuracy of 20%, and also a method for determining the total dose equivalent of neutrons and protons by one detector with an accuracy of 40% in mixed fields of hadrons behind the proton accelerator shielding.

1-Naphthyl Acetate-Dependent Medium Acidification by Zea mays L. Coleoptile Segments

Zea mays L. cv INRA 5a coleoptile segments ecidify the incubation medium on the addition of 1-naphthyl acetate (1-NA). The buffering capacity of the bathing solution increases during 1-NA stimulated medium acidification. The solution bathing the 1-NA treated coleoptile segment was analyzed by high performance liquid chromatography. A considerable amount of acetic acid was detected in the bathing solution used to measure 1-NA-dependent medium acidification. For the first time, the data demonstrate directly the release of acetic acid from 1-NA. The extent of medium acidification was proportional to 1-NA concentration. Simultaneous measurement of medium acidification and acetate content upon addition of 1-NA showed that both processes were temporally correlated. The stoichiometry of proton equivalents to acetate ion was 0.966. Addition of 50 micromolar N,N'-dicyclohexylcarbodiimide had little effect on 1-NA-dependent medium acidification. The results indicate that 1-NA is hydrolyzed in the extracellular space of coleoptile cells.

The preparation and characterization of the diaquo- forms of several incomplete corrinoids: Cobyric acid, cobinamide, and three isomeric cobinic acid pentaamides

The preparation of the diaquo- forms of the incomplete corrinoids, cobyric acid, cobinamide, and three isomeric cobinic acid pentaamides, from the corresponding aquocyanocorrinoids has been accomplished. The compounds were characterized by electronic absorption spectra, pk a values, and HPLC/TLC behavior. Upon titration, the acids exhibited three pK a values, but only the pK a corresponding to the carboxylic acid involved the transfer of a full equivalent of protons. In addition, the progress of diaquo- to dihydroxo-titration, and the spectrum of the final products indicated a complex process. These diaquocorrinoids appear to be unstable, and should be stored in solution, frozen, under an inert atmosphere.

A phosphoranide (10‐P‐4) anion coordinating to transition metals, as a Lewis base and a π‐acceptor

AbstractThe reaction of 10‐P‐5 hydridophosphorane 6 with KH provides the 10‐P‐4 potassium phosphoranide anion 7a. Anion 7a reacts with CpFe(CO)2I and BrAu(PEt3) to replace the halide with the phosphoranide as a monodentate ligand forming 8 and 9. The X‐ray structure of 8 shows that the equatorial—Fe(CO)2Cp ligand of 8 makes the apical PO bonds (1.824 Å) longer than the PO bonds (1.80 Å) of the phosphoranide oxide anion 10. The PO bonds (1.75 Å) of 6, with an equatorial proton ligand, are still shorter. This provides evidence that the—Fe(CO)2Cp ligand is not only a sigma‐acceptor Lewis acid ligand, but also a pi‐donor that transfers electrons into the OPO three‐center bond's anti‐bonding orbital to increase its P—O bond lengths. It is a better pi‐donor than the O− pi‐donor of phosphoranide oxide 10.

Structure of dimethylammonium bromide in solutions in aprotic solvents

The structure of the dimethylammonium bromide molecule in solution has been studied on the basis of IR absorption spectra and low-temperature1H NMR spectra. An analysis of the spectroscopic characteristics of the compounds shows that the most preferable of the possible structures is an ion pair with equivalent NH protons and two hydrogen bonds, which form a stable four-membered ring.

Analysis of myo-inositol phosphates by 2D 1H-n.m.r. spectroscopy

2D 1H-N.m.r. spectroscopy applied to phosphorylated myo-inositols can indicate the number and the sites of phosphorylation, and up to three isomers can be completely analyzed simultaneously. The resonance of the sole equatorial proton (H-2) is shifted furthest downfield (to ∼4.7 p.p.m.) when C-2 is phosphorylated; when C-5 is unphosphorylated, the H-5 resonance has the lowest chemical shift (∼ 3.3 p.p.m.). The number of sites of phosphorylation can be determined from the sum of the chemical shifts for the resonances in a given myo-inositol phosphate and, based on the data presented, an algorithm can be constructed that will identify any myo-inositol phosphate on the basis of the chemical shifts.

Gas-phase inorganic chemistry: laser spectroscopy of calcium and strontium monocarboxylates

The CaBH4-and SrBH, free radicals were synthesized by the reaction of Ca or Sr vapor with diborane, The A2Al-X2AI and B2E-X2AI electronic transitions were detected by laser-induced fluorescence. The spectra are consistent with tridentate molecular structures with three bridging hydrogens and C3 symmetry. The tetrahydroborate anion (BH,-) forms a large number of interesting ionic and covalent complexes with metals.'S2 The coordination between the metal and the BH, ion invariably occurs through bridging hydrogens, and rapid interconversion between the various coordination modes is known in the liquid phase.'q2 BH4- is a commonly used reducing agent. Nevertheless, very little is known about the spectroscopic properties of the metal-BH, complexes, particularly in the gas phase. Of the alkaline earth borohydrides, only Be(BH4)2 has been analyzed in the gas phase, but the molecular structure remains uncertain. Gundersen, Hedberg, and Hedberg3 studied the Be(BH4)2 structure using electron diffraction methods, while Nible8 examined the infrared and Raman spectra. The gas-phase NMR spectrum shows only a single set of equivalent protons, consistent with fluxional be- ha~ior.~ A recent theoretical calculation by Stanton, Lipscomb, and BartletP has provided new insight into this long-standing problem. In contrast to the covalent Be(BH4)2, the alkali borohydrides and the heavier alkaline earth borohydrides are all ionic solids with low vapor pressures.'s2 We report here on the discovery of the gas-phase calcium and strontium monoborohydride free radicals, CaBH, and SrBH,. These molecules are made by the reaction of Ca and Sr vapors with diborane, B2H6 The observation of CaBH, completes the isoelectronic pblock family of molecules, CaBH,, CaCH3,' CaNH2,8 CaOH? and CaF.IO We have pre- viously studied many monovalent derivatives of Ca and Sr in our laboratory, including carboxylates,' I azides,12 i~ocyanates,'~ ~lopentadienides ,'~ acetylide~,'~ formamidates,16 pyrrolates, alkanamides,'* and alko~ides.'~ CaBH, and SrBH, are the first examples of gas-phase metal monoborohydrides to be experimentally characterized. However, there has been considerable theoretical activity in this area. Ab initio predictions for the properties of LiBH,,225 NaBH4,23-26 KBH424 and CUBH,~, are available in the literature. The structures are all predicted to be fluxional with either tridentate

Deuteron excitation as an alternative in PIXE analysis

In comparison with protons deuterons show several advantageous features when used to induce X-ray emission for elemental analysis, such as lower bremsstrahlung radiation, higher penetration range and reduction of the charge collected in the target. On the other hand, a high background due to scattering on the chamber material was observed. Beam loss ratios in samples of different thicknesses are presented for deuterons of 4.2 MeV and for the equivalent protons of 2.1 MeV. An extensive study of atmospheric aerosols using 4.2 MeV deuterons is described.

Coenzyme models. Part 52. Diastereo-differentiating hydrogen transfer in 5-deazaflavin oxidation of alcohols and amines

5-Deuteriated 5-deazaflavinophanes (dFI(n)D) were synthesized in which N-3 in the isoalloxazine group and O-2′ in the 10-(2-hydroxyphenyl) group were linked by a –(CH2)n– chain (n= 8 and 10). 1H NMR studies established that NaBH4 reduction of dFI(8)D to the reduced form dFlred(8)D, in which ring inversion is inhibited because of a short (CH2)8 strap, gives an axial C-5 proton (Hax). This indicates that hydrogen is exclusively incorporated into the axial C-5 position. In contrast, NaBH4 reduction of dFI(10)D to dFlred(10)D, in which ring inversion is allowed because of a long (CH2)10 strap, gave an axial and an equatorial proton (Hax and Heq) in the ratio 1 : 1. This indicates that hydrogen is primarily incorporated into the axial C-5 position but is rapidly exchanged through ring inversion. Oxidation of alcohols and amines by dFI(n)D gave 1H NMR spectra similar to those obtained after NaBH4 reduction. Therefore we conclude that hydrogen from these substrates is also transferred to the axial C-5 position. The ‘axial preference’, which is generally observed for 5-deazaflavin-mediated redox reactions, was rationalized in terms of the stereoelectronic effect.

Lignans of Forsythia intermedia

Leaf and stem material of Forsythia intermedia contains four main lignans and their O-glucosides. These were identified as the dibenzylbutyrolactone derivatives (−)-arctigenin, arctiin [(−)-arctigenin 4′- O-glucoside], matairesinol and (−)-matairesinol 4′- O-glucoside, together with the furofuran lignans (+)-phillygenin, phillyrin [(+)-phillygenin 4- O-glucoside], (+)-epipinoresinol and (+)-epipinoresinol 4′- O-glucoside. The lignan contents varied according to tissue type and season. Full spectral data for the lignans are presented. The 1H NOE difference spectra recorded for phillygenin and epipinoresinol necessitate the reversal of earlier chemical shift assignments for axial and equatorial protons on C-9 of furofuran lignans having one axial and one equatorial aryl group (the epi series).

Agonist‐evoked changes in cytosolic pH and calcium concentration in human platelets: studies in physiological bicarbonate.

1. Cytosolic pH (pHi) and calcium concentration ([Ca2+]i) have been investigated in the presence and absence of physiological HCO3- in human platelets co-loaded with the fluorescent indicators BCECF and Fura-2. Basal pHi and changes evoked by butyrate, thrombin, platelet activating factor (PAF), ADP and phorbol ester were investigated, as were the effects of removing external Na+. 2. In the presence of physiological HCO3- and CO2, basal pHi was 7.02 +/- 0.04 compared with 7.15 +/- 0.05 in the absence of HCO3-. Estimated cytosolic buffering power was reduced from 35.6 +/- 3.0 to 14.5 +/- 0.4 mM/pH unit by the omission of HCO3-. 3. Thrombin evoked an immediate acidification of 0.03 +/- 0.01 pH units in the presence of HCO3- and 0.07 +/- 0.01 pH units in its absence. The acidifications were followed by a slow alkalinization. The final pHi was 0.10 +/- 0.01 units above basal in the presence of HCO3- and 0.08 +/- 0.02 units above basal in the absence of HCO3-. The initial acidification was significantly greater in the absence of HCO3-. The subsequent increase in pHi was similar in the presence and absence of this ion, but the calculated loss of proton equivalents was greater in the presence of HCO3-. 4. Replacement of extracellular Na+ with N-methyl-D-glucamine resulted in a fall in basal pHi and abolished recovery from thrombin-evoked acidification in both the presence and absence of HCO3-. 5. In the presence of HCO3-, PAF and ADP evoked an intracellular acidification similar to that caused by thrombin. However, with PAF and ADP, the subsequent recovery in pHi was slow and did not rise above basal levels. Phorbol dibutyrate, an activator of protein kinase C, evoked a similar elevation in pHi of 0.04 +/- 0.01 units over 3 min in the presence and absence of HCO3-. 6. Stopped-flow fluorimetric measurements were made of both BCECF and Fura-2 fluorescence in the presence of HCO3-. In the presence and absence of external Ca2+, thrombin-evoked rises in [Ca2+]i peaked before any cytoplasmic alkalinization occurred. ADP evoked rapid elevations in [Ca2+]i, but caused no alkalinization.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of extracellular pH and D‐lactate efflux on regulation of intracellular pH during isotonic contractions in a molluscan muscle: A 31p‐nuclear magnetic resonance study

AbstractIsotonic contractions were electrically induced in isolated radula protractor muscles of the whelk Busycon canaliculatum, mounted and superfused under anoxic conditions in a special 5 mm phosphorus nuclear magnetic resonance (31P‐NMR) probe. 31P‐NMR spectra showed that there was a decrease in intracellular pH (pHi) from 7.29 to 7.01 during the time course of 30 min of contractile activity. Subsequent biochemical analysis of the tissue and superfusion medium showed that D‐lactate and, to a much lesser extent, alanopine and octopine were the major glycolytic end products. Approximately 75% of the total D‐lactate produced was released into the medium. When the superfusate pH was changed from 7.8 to 7.2, a much more pronounced intracellular acidification took place, as the pHi fell to 6.80. However, there was no significant effect on the extent of release of D‐lactate from the muscle. Elevation of the superfusate pH to 8.2 had no significant effect on final pHi or D‐lactate efflux. D‐lactate efflux was reduced when α‐cyanohydroxycinnamic acid or L‐lactate was added to the superfusate at pH 7.8. These treatments had no significant effect on the final pHi. Movement of proton equivalents and D‐lactate efflux are not tightly linked in this muscle system.

The composition, temperature, and density structure of cold ions in the quiet terrestrial plasmasphere: GEOS 1 results

We present a comprehensive study of the composition, and the density and temperature distributions of the thermal (energy≤110 eV) ion population in the terrestrial plasmasphere under quiet geomagnetic conditions. The data were collected by the Ion Composition Experiment (ICE) on board the European Space Agency's GEOS 1 satellite and cover the period from June 1977 to May 1978. For the data reduction we employ a method based on the modulation of the detector count rates by the rotation of the spacecraft. We find typical quiet time proton densities to vary smoothly between ∼10² cm−3 (L ≈ 6) and 2×10³ cm−3 (L ≈ 3). In the local time sector 1700–2200 the equatorial proton concentration obeys an inverse fourth power dependence with dipole L. He+ is a major ionic component in all L ranges investigated. Its concentration relative to H+ is highly variable, ranging from ∼1% to, on occasion, over 100%. The most frequent values we obtain lie in the range ∼2–6%. The averaged variation of He+ with dipole L in the 1700–2200 local time range shows a somewhat more rapid decrease with increasing L than does H+. The temperatures in the quiet plasmasphere are between 4×10³ K and 1.5×104 K and generally exhibit a slow increase with L value. The average radial temperature gradient near the equator is ∼0.15 K/km. The main ionic constituents are usually in thermal equilibrium throughout the plasmasphere. There are indications that the ionic component is in a state of thermal equilibration with the electronic component in the outer plasmasphere. Using alternate passes in the same region, we discuss the poststorm recovery of the plasmasphere on L shells >4 for both H+ and He+. Data are also presented on the minor ions O+, O++, D+, and He++. The O+ densities around L ≈ 3 are ≲1 cm−3, and the densities of O++ are comparable. Cases are shown where the mass/charge = 2 ion is predominantly D+ and others where it is mainly He++. Typical densities of this ion in the L range 2.6–3.6 are a few tenths per cubic centimeter. With one exception we found these minor ions to share a common temperature with the main constituents of the plasmasphere. The results of our survey are compared with previous studies and with theoretical modeling. In particular, the GEOS 1 H+ temperature structure is in substantial agreement with those from the Plasma Composition Experiment (PCE) on ISEE 1 and the retarding ion mass spectrometer (RIMS) on DE 1. We confirm the enhanced O++ to O+ density ratio in the equatorial plasmasphere with respect to values in the mid‐latitude ionosphere. Our observations on this ratio are compared with the predictions of three theoretical works.

Electron nuclear double resonance of the first excited triplet state of trans-stilbene in a diphenylacetylene-TCNB single crystal

The first excited triplet state of trans-stilbene, contained as an impurity in diphenylacetylene-TCNB single crystal has been investigated by ENDOR spectroscopy. The hyperfine tensors of six pairs of equivalent protons of trans-stilbene have been measured. They show that in this host crystal the trans-stilbene has a centre of symmetry. The isotropic couplings compare well with those of the trans-stilbene radical anion. The calculated dipolar tensors agree with the experimental ones if the trans-stilbene molecule is assumed as planar and the in-plane principal direction x of the zero-field splitting tensor makes an angle of 12° with the central double bond. With such orientation the trans-stilbene is found to substitute one diphenylacetylene molecule with minimum distortion of the crystal lattice.