Line-broadening Effects Research Articles

Use of dialysis fibers for the study of aerobic cells.

The suitability of a perifusion system for the study of renal tubules trapped in different types of dialysis fibers has been investigated. First, the equilibration times across the fiber membranes were estimated by following the penetration of the dysprosium tripolyphosphate shift reagent inside the fibers using 23Na nuclear magnetic resonance. These times ranged from less than 1 min for microfibers to 30 min for some large diameter fibers. When cortical tubules were introduced into cuprophan dialysis microfibers (200 microns internal diameter) and perifused by rapid recirculation of cell culture medium, metabolic viability, as determined by a linear glucose and ammonia production from glutamine and lactate, was found to exceed 10 (dog) or 3 h (rat), an unprecedented time period for such structures. As evidenced by the sensitivity to furosemide, the lumen of thick ascending limb tubules was kept open by including 50 mM mannitol in the perifusate. Fibers with large internal diameters (1100 microns) were found to be less suitable owing to the slow equilibration rates with the intrafiber compartment. All types of fibers showed minimal line-broadening effects on the 31P nuclear magnetic resonance signals.

Two-dimensional proton NMR of three spin-labeled derivatives of bovine pancreatic trypsin inhibitor

Three nitroxide spin-labeled monoderivatives of bovine pancreatic trypsin inhibitor were prepared with the amino-specific reagent succinimidyl 1-oxy-2,2,5,5-tetramethyl-3-pyrroline-3-carboxylate. The monoderivatives were purified by ion-exchange and affinity chromatography. Thin-layer maps of tryptic peptides of the monoderivatives showed that the spin-label was incorporated at either the alpha-amino group, Lys-15, or Lys-26. Two-dimensional J-correlated 1H NMR spectra of the monoderivatives were recorded. Spectra were also recorded after reduction by ascorbic acid of the nitroxide label to hydroxylamine. With the nitroxide label present, significant line-broadening effects on many of the cross peaks in the spectra were observed. The extent of line broadening for the C alpha H-NH cross peaks was qualitatively correlated with the distance between the labeled amino group and the average C alpha H-NH position in the crystal structure. The spin-label affects cross peaks of protons within approximately 15 A. This study suggests that it is feasible to accumulate sufficient intramolecular distances in order to determine protein solution structures with the aid of distance geometry algorithms.

1H NMR investigation of cytochrome cd1: complexes with electron-donor proteins.

Mixtures of the dissimilatory nitrite reductase cytochrome cd1 from Pseudomonas aeruginosa and potential electron-donating proteins were prepared in both fully oxidized and fully reduced states and examined by 1H NMR spectroscopy. The relatively narrower lines of the donor proteins enabled them to be clearly observed in spectra in the presence of significant amounts of the high molecular weight cd1. Mixtures of the physiological donor (Pseudomonas ferrocytochrome c-551) and ferrocytochrome cd1 showed specific line-broadening effects on the resonances of c-551 that depended on the mole ratio of c-551 to cd1. The experimental broadening fit a model in which c-551 is in intermediate or fast exchange between free solution and a complex with cd1, with an association constant for the complex in excess of 10(4) M-1. The model yields a minimum estimate for the forward bimolecular rate constant of 5 X 10(7) M-1 s-1 and suggests that the actual value may be much larger. The complexation was independent of pH in the range of 6-8, was independent of ionic strength over a salt concentration range of 20-1000 mM, and possessed a low thermal activation barrier. Mixtures of ferricytochrome c-551 and ferricytochrome cd1 showed no observable NMR perturbations, indicating that any hypothetical complex involving the oxidized forms must follow different dynamical and/or equilibrium conditions. No observable NMR perturbations existed in spectra of mixtures of cd1 and mammalian cytochrome c or Pseudomonas azurin in either oxidation state.

酸添加によるアルカロイドの｀１´Ｈ‐ＮＭＲスペクトルの変化 立体化学決定法としての可能性

The specific line-broadening effects caused by the addition of a small amount of acid were noted for some 'H-NMR of stemotinine [1] and isostemotinine [2]. The molecular structure of [1] has recently been established by X-ray analysis, we could correlate the line-broadening effect with the stereochemistry of the spiro-lactone moieties of [1] and [2]. Since line-broadening was found to be induced by partial salt formation of the tertiary amino group, it may be widely observed with other alkaloids and may afford a versatile supplementary tool for the stereochemical study of alkaloids.

Profile refinement of powder diffraction patterns using the Voigt function

The Voigt function has been incorporated as a peak-shape description into a program for the refinement of constant-wavelength X-ray and neutron diffraction patterns. The results obtained for neutron diffraction are encouraging and indicate that the Voigt function describes the symmetrical component of the profile peak shape to high accuracy even in the presence of substantial line broadening from particle-size effects. In contrast with approximations to the Voigt function, such as the pseudo-Voigt and Pearson VII functions, the present treatment allows the angular dependences of line-broadening effects resulting from particle-size and instrumental contributions to be coded independently from each other in the Rietveld technique. The present treatment, which details improvements to the symmetrical component of the peak shape, does not offer a fully rigorous description of the peak shape as asymmetry corrections such as those given by Howard [J. Appl. Cryst. (1982), 15, 615–620] are not included.

Selective production of Li-, Be-, and B-like K vacancy states in fast Ne projectiles studied by zero-degree Auger spectroscopy.

High-resolution measurements of Ne K Auger electrons have been performed using multiply charged $^{20}\mathrm{Ne}$ projectiles in collisions with He, ${\mathrm{CH}}_{4}$, and Ar at impact energies of 70 and 100 MeV. Kinematic line-broadening effects were substantially reduced by observing the electrons at 0\ifmmode^\circ\else\textdegree\fi{} with respect to the beam axis. For the He-gas target the outer-shell electronic configuration of the incident ions is essentially retained during K-shell ionization. Thus, B-, Be-, and Li-like electron configurations were selectively produced for incident ions of ${\mathrm{Ne}}^{4+}$, ${\mathrm{Ne}}^{5+}$, and ${\mathrm{Ne}}^{6+}$, respectively. For target gases ${\mathrm{CH}}_{4}$ and Ar, Li-like lines are found to be strongly excited, independent of the initial charge state of the projectiles.

Conformational studies by dynamic nuclear magnetic resonance. Part 30. Exchange kinetics between the rotamers of 2-acyl-furans and -thiophenes

Low-temperature 13C n.m.r. spectra allowed the observation of two different groups of signals, corresponding to the O,O-anti- and O,O-syn-rotamers, of a number of 2-acylfurans with the following alkyl groups bonded to carbonyl: Me, Et, Pri, But, pentan-3-yl. The ratios of these rotamers in dimethyl ether were thus obtained, and the barriers for the syn-anti interconversion were found to decrease with increasing bulkiness of the alkyl groups. Although separate 13C signals could not be detected for the rotamers of the corresponding 2-acylthiophenes, line-broadening effects nonetheless allowed measurement of the interconversion barriers. Lanthanide-induced shift experiments carried out on the latter derivatives (at both 1H and 13C frequencies) showed that in all the 2-acylthiophenes investigated the S,O-syn rotamers are predominant.

Amine inversion in proteins. A 13C-NMR study of proton exchange and nitrogen inversion rates in N epsilon,N epsilon,N alpha,N alpha-[13C]tetramethyllysine,N epsilon,N epsilon,N alpha,N alpha-[13C]tetramethyllysine methyl ester, and reductively methylated concanavalin A.

Exchange rates were calculated as a function of pH from line widths of methylamine resonances in 13C-NMR spectra of N epsilon,N epsilon,N alpha,N alpha-[13C]tetramethyllysine (TML) and N epsilon,N epsilon,N alpha,N alpha-tetramethyllysine methyl ester (TMLME). The pH dependence of the dimethyl alpha-amine exchange rate could be adequately described by assuming base-catalyzed chemical exchange between two diastereotopic methyl populations related by nitrogen inversion. Deprotonation of the alpha-amine was assumed to occur by proton transfer to (1) OH-, (2) water, (3) a deprotonated amine or (4) RCO2-. Microscopic rate constants characterizing each of these transfer processes (k1, k2, k3 and k4, respectively) were determined by fitting the rates calculated from line width analysis to a steady-state kinetic model. Using this procedure it was determined that for both TML and TMLME k2 approximately equal to 1-10 M-1 s-1, k3 approximately equal to 10(6) M-1 s-1 and ki, the rate constant for nitrogen inversion was about 10(8)-10(9) s-1. Upper limits of 10(12) and 10(3) M-1 s-1 could be determined for k1 and k4, respectively. A similar kinetic analysis was used to explain pH-dependent line-broadening effects observed for the N-terminal dimethylalanyl resonance in 13C-NMR spectra of concanavalin A, reductively methylated using 90% [13C]formaldehyde. From exchange data below pH 4 it could be determined that amine inversion was limited by the proton transfer rate to the solvent, with a rate constant estimated at 20 M-1 s-1. Above pH 4, exchange was limited by proton transfer to other titrating groups in the protein structure. Based upon their proximity, the carboxylate side chains of Asp-2 and Asp-218 appear to be likely candidates. The apparent first-order microscopic rate constant characterizing proton transfer to these groups was estimated to be about 1 X 10(4) s-1. Rate constants characterizing nitrogen inversion (ki), proton transfer to OH- (k1) and proton transfer to the solvent (k2) were estimated to be of the same order of magnitude as those determined for the model compounds. On the basis of our results, it is proposed that chemical exchange processes associated with base-catalyzed nitrogen inversion may contribute to 15N or 13C spin-lattice relaxation times in reductively methylated peptides or proteins.

Conformational studies by dynamic nuclear magnetic resonance. Part 26. Interconversion barriers between syn- and anti-conformers of isomeric thiophenecarbaldehydes

The low-temperature 13C n.m.r. spectra (25.16 MHz) of thiophene-2- and -3-carbaldehyde [(1) and (2)] display line-broadening effects due to the exchange between their S,O-syn- and S,O-anti-conformers. In both cases the free energy of activation for rotation of the –CHO moiety was measured, the values being 10.15 and 8.5 kcal mol–1 for (1) and (2), respectively. In the case of thiophene-3-carbaldehyde (2) the signals of both conformers were detected, the ratios being 97:3 at –140 and 93:7 at –100 °C in favour of the S,O-anti-conformer. In thiophene-2-carbaldehyde (1) the minor conformer (S,O-anti) was present in too small an amount to be unambiguously detected by a conventional spectrometer, but spectra taken with a superconducting instrument (75.48 MHz) revealed ca. 1.5% of this conformer at –100 °C.

Image plane detector for the Dynamics Explorer Fabry-Perot interferometer

A compact twelve-channel photon-counting device based on existing Generation II imaging technology has been developed for use as the image-plane detector of the Dynamics Explorer Fabry-Perot interferometer. The device has an S-20 photocathode, three-microchannel plate electron multiplication stages, and an equal-area concentric-ring segmented anode whose geometry mimics that of the interference ring pattern produced by a plane etalon. The twelve channels sample equal and contiguous intervals in the spectrum. The purpose of the development has been to utilize the signal multiplex advantage of a multichannel detector in the measurement of Doppler shifts and line-broadening effects for naturally occurring atmospheric emission features of low intensity. The design, testing, calibration, and flight performance of the novel detector system are presented. In addition, measured emission line profiles at high resolution from the satellite instrument are presented to illustrate the operation of the device.

The interaction of cyanocobalamin and some of its analogs with manganese(II) and gadolinium(III)

The influence of the paramagnetic ions Mn 2+ and Gd 3+ on the proton-decoupled 13C nuclear magnetic resonance spectra of three cyanocobalamin-monocarboxylic acids has been observed. The paramagnetic ions bind preferentially to the free carboxylate groups and cause the broadening of specific carbon resonances adjacent to these groups. These specific line-broadening effects have been used to assign the carbonyl carbons of the a-, f-, and g-acetamide side chains and have allowed us to confirm and/or correct the assignments of several carbon resonances that were assigned tentatively before.

Standard Addition Technique for Quantitative Trace Gas Analysis Using Derivative Infrared Diode Laser Spectroscopy

The method of standard additions has been applied to the determination of moisture in flowing gases using a derivative diode laser spectrometer to monitor infrared absorption. The suitability of derivative spectroscopy for standard addition analysis is discussed in terms of stability of the blank and linearity of response. It is shown that by using the method of standard additions in spectroscopic determinations, line-broadening effects due to the components of the bulk gas are automatically compensated and do not influence analytical accuracy. Simple experimental procedures are outlined for making additions and the use of standards several orders of magnitude more concentrated than the unknown is validated experimentally.

Fast reaction kinetics by e.s.r. methods

Kinetic information can be obtained from e.s.r. spectra both through the determination of radical concentrations as a function of conditions and through line-broadening effects. Applications of the former method have usually been combined with radical generation either by photolysis within the spectrometer cavity or by a rapid redox reaction in conjunction with a flow system; the scope and limitations of the method are discussed, and the examples chosen reveal several structurereactivity relationships. The method based on line-broadening is applicable to processes which occur on a time-scale which is of the same order as appropriate hyperfine splitting intervals for the radicals concerned; the examples chosen give information about the rates of conformational changes. INTRODUCT ION The electron spin resonance spectra of free radicals yield information of four types: hyperfine splittings, g-factors, line-widths, and concentrations. The first two in turn provide information about structural features of the radicals; and both line-widths and concentrations can give kinetic information. The first phase of the application of e.s.r. to organic radicals, beginning in about 1960, was largely concerned with the elucidation of structural features, but in the last decade kinetic applications have become at least as important. This Paper will be concerned mainly with the kinetic data which can be derived from measurements of radical concentrations as a function of reaction conditions. This is because the method is applicable to radicals and their reactions of all types; rate constants up to the diffusion—controlled limit can be determined. In contrast, line-width measurements can yield rate constants only when these are within a relatively small range. STATIC SYSTEMS: PHOTOCHEMICAL TECHNIQUES Photolysis, particularly of peroxides (frequently di-t-butyl peroxide, DTBP) has been widely used to initiate radical reactions for e.s.r. study. The success of the method depends on the efficiency of the photolysis coupled with the fact that alkoxyl radicals react very rapidly with most organic compounds; in spite of the rapidity with which the resulting radicals usually react further, a steady-state radical concentration which is above the limit detectable by e.s.r. (ca. 1O-7M) can be produced. For example, consider the simple system in which all alkoxyl radicals RO. are scavenged by a compound R'H to give radicals R' which decay only by bimolecular combination to give non-radical (molecular) products: k. RO—OR in 2R0• (1) RO + R'H—IROH + R' (2) k 2R' ) molecular products (3)

Temperature dependence of infrared absorption by the water vapor continuum near 1200 cm^−1

Infrared absorption by the water vapor continuum near 1200 cm(-1) has been measured with a lead-tin-telluride diode laser over a 40.5-m optical path. The measurements were made as a function of temperature from 333 K to 473 K; thus, they overlap and extend previous measurements made at temperatures between 293 K and 388 K. Over the entire temperature range studied here, the continuum extinction coefficient increases quadratically with water-vapor partial pressure as expected for the relatively high partial pressures used in these measurements. At temperatures below 398 K. our measured extinction coefficients agree well with previously reported data. At higher temperatures, however, the extinction coefficient is almost independent of temperature and is substantially larger than predicted by empirical formulas. Values of the self-broadening coefficient for water vapor have been extracted from the experimental data, and a possible interpretation of the results involving both dimer and line-broadening effects is presented.

Effect of non-Arrhenius self-diffusional behavior on quasielastic neutron scattering and Mössbauer linewidth

The application of quasielastic-neutron-scattering or Mössbauer experiments to resolve the disputed origin of non-Arrhenius self-diffusional behavior in crystals is proposed. For that purpose, the related line-broadening effects are analyzed in terms of both the prevailing ’’two-defect model’’ and the ’’one-defect model’’ in its formulation, for example, by Gilder and Lazarus. The orientation dependence of the width of diffusion-broadened quasielastic and Mössbauer lines is found to differ for the two models. More importantly, however, it is shown that interpretation of line-broadening data in terms of the two models yields diffusion coefficients which cannot simultaneously agree with tracer data. A numerical analysis is presented for vacancy-induced self-diffusion in bcc crystals, such as sodium metal.

Magnetic-resonance line-broadening effects associated with crystalline imperfections

It is shown that contrary to the usual assumption, the magnetic-resonance line-broadening effects due to mosaiclike structures and crystalline strains from imperfections are not completely separable. We have found that the angular behavior of the line broadening associated with the off-diagonal elements of the strains is the same type as that arising from a mosaiclike structure.

Studies of individual carbon sites of hen egg white lysozyme by natural abundance carbon 13 nuclear magnetic resonance spectroscopy. Assignment of the nonprotonated aromatic carbon resonances to specific residues in the sequence.

The resonances of nonprotonated aromatic carbons in natural abundance 13C NMR spectra of hen egg white lysozyme are assigned to specific residues of the amino acid sequence. Chemical shift considerations, the effect of pH, and partially relaxed Fourier transform NMR spectra are used to assign each resonance to one of the seven types of nonprotonated aromatic carbons of amino acid residues. Spectra of chemically modified lysozyme samples yield various assignments to specific residues in the sequence. Line-broadening effects caused by binding of the relaxation probes Gd3+ and 4-N-acetamido-2,2,6,6-tetramethylipiperidine-1-oxyl yield specific assignments which are fully consistent with those based on chemical modifications. The effects of paramagnetic shift reagents and amino sugar inhibitors do not yield any obvious specific assignments. The effect of pH on the chemical shift of Cgamma of His-15 yields a pKalpha in agreement with published values, and indicates that the imidazole form of His-15 exists mainly (or entirely) as the Nepsilon3-H tautomer. The effect of pH on the chemical shifts (measured up to pH 8.8, at 38 degrees) of Czeta and Cgamma of the 3 tyrosine residues yields crude pKalpha values of 9.5 and 10 for Tyr-23 and one of the other tyrosines, respectively. The 3rd tyrosine residue does not exhibit titration behavior.

N.M.R. spectra of the carbolines. II. 14N quadrupolar and exchange broadening of spectral lines

The n.m.r, spectra of carbazole and the carbolines were previously reported to show unusual line broadening effects under certain conditions. It is found that for the proton in position 9 both chemical exchange and 14N quadrupolar relaxation are responsible for the large line widths observed, while for protons in the ?pyridine? ring chemical exchange is the more important effect. The nature of this exchange is still uncertain, the rate being critically dependent on solvent and sample purity as well as temperature.

Electron Spin Resonance Spectra of Azine – Alkali Metal Triple Ions in Ethereal Solvents

Electron spin resonance spectroscopy has been used to study triple ions formed between pyrazine and tetramethylpyrazine and the cations Li+, Na+, K+ in dimethoxyethane, tetrahydrofuran, and 2-methyl-tetrahydrofuran. Differential line-broadening effects are reported within the hyperfine splitting patterns of the alkali metals incorporated into the triple ions, and a possible application of such effects to the study of ionic association is described.

X-ray line broadening by porous crystals

The application of X-ray line-broadening techniques to the determination of the crystallite size for certain materials is inappropriate since the microstructure of such materials may produce equivalent broadening of powder lines. For substances such as oxides prepared by low-temperature dehydroxylation, a regular porous microstructure is observed within single-crystal pseudomorphs of the original hydroxide. Line-broadening effects are calculated using an idealized model for such a crystal based on electron microscope studies of magnesias. Results are compared with published data for magnesias.