Ppm Signal Research Articles

Shift reagent enhanced concurrent 23Na and 1H magnetic resonance spectroscopic studies of transcellular sodium distribution in the dog brain in vivo.

The intracellular to extracellular sodium distribution is one of the primary determinants of action potentials necessary for the electrical function of organs such as brain, heart and skeletal muscle. The ability of shift reagent enhanced 23Na MRS to directly measure the intracellular and extracellular sodium distribution in brain is controversial and centers on the relative contributions of bulk magnetic susceptibility and hyperfine interactions to the observed chemical shifts. In this study, infusion of dysprosium (III) triethylenetetraminehexacetate (Dy(TTHA)-3), resulted in a 23Na MRS spectrum of dog brain with two well resolved peaks at 9 and 0.4 ppm. The 9 ppm peak corresponded to the resonance seen in aspirated blood. After disruption of the blood brain barrier, the single peak at 0.4 ppm split into two peaks at 3 and 0 ppm. The ability of Dy(TTHA)-3 enhanced 23Na MRS to follow global changes in brain sodium distribution was tested during cardiac arrest. The expected rapid Na influx into the intracellular space produced a marked decrease in the 3 ppm signal and a parallel increase in the 0 ppm peak. This is consistent with the assignment of the 3 ppm peak as interstitial sodium and the 0 ppm peak as intracellular sodium.

Temperature influence on the Al13 complex in partially neutralized aluminum solutions: a 27Al nuclear magnetic resonance study

Stepwise heating to 85°C in the NMR apparatus does not notably change the monomer and tridecamer (Al13) concentrations in a 0.2M Al(NO3)3 solution neutralized with 0.2M NaOH up to an OH/Al molar ratio of 2.4. Upon heating the fourfold coordinated 27Al NMR signal of Al13 at 63.3 ppm and the very broad sixfold coordinated 27Al NMR signal of Al13 at 12 ppm exhibit an increasing intensity and decreasing linewidth, due to diminishing ‘missing intensity’ and ‘quadrupole relaxation’, respectively. An analogous effect for a Na2CO3 neutralized 0.2M AlCl3 solution confirmed that the 12 ppm signal must be assigned to the sixfold coordinated Al of the Al13 complex. The surface ratio of fourfold coordinated Al to sixfold coordinated Al of the Al13 complex experimentally established is smaller than the theoretical 1 : 12 ratio. During heating, a more intensive exchange interaction between monomer and other Al-species is proposed without any effect on the actual concentrations. High symmetry in the Al13 complex is determined at elevated preparation temperatures from the decreasing linewidth of the 63.3 ppm resonance. Above 85°C the tridecamer transforms to other species, which cannot be observed with NMR.

27Al quadrupole nutation and 1H 27Al cross-polarization solid-state NMR studies of ultrastable zeolite Y with fast magic-angle spinning

1H 27Al cross-polarization magic-angle spinning (PC/MAS) NMR has been used to monitor selectively the non-framework aluminium (Al NF) species in dealuminated zeolite Y (Si/Al=4.0–14). 27Al quadrupole nutation with fast (12.5 kHz) MAS and radiofrequency excitation fields up to 220 kHz reveals resonances of 0, 30, 56 and 62 ppm, all of which have been assigned. The quadrupole coupling constant, C Q, of the site responsible for the 30 ppm signal changes significantly with the degree of dealumination, from 4.5–5 MHz (at Si/Al=4.0) to > 6 MHz (at Si/Al=9). The corresponding isotropic chemical shifts are in the range 41–57 ppm. We conclude that the non-framework matter contains four-,five-and six-coordinated aluminium.

A “high resolution” NMR study of ionic transport in the hydrate of ammonium ferrocyanide

Ammonium ferrocyanide monohydrate has been studied by NMR at 270 MHz and 500 MHz. Two chemically shifted (separation = 3.55 ppm) signals observed are attributed to the NH 4 + and H 2O protons. From the temperature dependence of the line-widths and the chemical shifts, both NH 4 + and H 2O are concluded to take part in diffusion.

Determination of Ditalimfos by Liquid Chromatography

Abstract A liquid chromatographic (LC) method for the determination of ditalimfos, 0,0-diethyI phthalimidophosphonothioate, is described. Bonded phase high precision LC using a mixture of n-hexane and chloroform as eluant afforded a capacity factor (k') of 2.3 for the analyte. Ditalimfos could be detected at 0.5 ppm (signal to noise ratio > 3) using ultraviolet detection at 254 nm. The detector afforded a linear response from 0.2 to 10.9 mg/mL when 10 μL of solution was injected and the coefficient of variation was ±0.5%. Structurally related fungicides and several common insecticides were successfully separated from the analyte under the chromatographic conditions of analysis.

Analyses of the chemical structures of melanoidins by 13C NMR, 13C and 15N CP-MAS NMR spectrometry.

Nondialyzable melanoidins, which were prepared from a glucose-glycine system at 95°C for 7, 26 and 44 hr, were subjected to NMR analyses before and after ozonolysis. On 13C CP-MAS NMR, signals in the regions of 10-50, 60-75, 105-115 (I), 130-140 (II), 170-180 and 190-205 (III) ppm were observed for the melanoidins. The signals of I, II and III completely disappeared on ozone-treatment. These findings indicate that the melanoidins were composed mainly of saturated and aliphatic carbons. The 13C NMR spectra of glucose (1-13C)-glycine melanoidins showed that C-1 carbons originating from glucose in the melanoidins were distributed at the positions of aliphatic alkyl methyl (IV), saturated, unsaturated or aromatic and carbonyl (V) carbons. The signals of IV and V disappeared on ozone-treatment. Studies using glycine-2-13C revealed that most of the glycine is incorporated into the melanoidins. On 15N CP-MAS NMR, weak broad signals in the region of 0 - 70 ppm and strong signals in the region of 70-120 ppm with a shoulder at 120-170 ppm (VI) were observed for the melanoidins. The signals of VI disappeared on ozonetreatment. The main linkage of nitrogen (70-120ppm) was remarkably shifted from that of the original glycine and was determined to be a conjugated enamine linkage.

Cobalt(II) as an NMR probe for the investigation of the coordination sites of conabulmin

Conalbumin and transferrin in the presence of bicarbonate bind metal(III) and also metal(II) ions, although the former oxidation number is preferred. ▪In the absence of oxidizing agents, the cobalt(II) derivatives can be prepared; the conalbumin derivative is particularly inert and both 1:1 and 1:2 cobalt to protein derivatives have been characterized during this research. The 60 MHz proton spectra of cobalt(II) conalbumin recorded in water is shown in Fig. 1. It was obtained using an appropriate pulse sequence (modified DEFT [1]) to suppress the slowly relaxing signals of water and of the diamagnetic protons of the protein. The same sequence was used to evaluate the longitudinal relaxation times of the isotropically shifted signals through a saturation recovery type of experiment. The spectrum shows several well shaped resonances. Within the resolution determined by the linewidth, no difference was observed between the 1:1 and 1:2 derivatives. Assignment of the signals can be attempted through the analysis of the T −1 1 values which are mainly determined by the distance from the paramagnetic center. There is a very broad signal downfield at 100 ppm with a T 1 of 1 ms. Position [2, 3] and T 1 indicate that the signal is due to a histidine Hα. Another quite similar signal is detected when measuring T 1 under the peaks at +67 and +58 ppm. This is a second histidine Hα. The other peaks at 67 and 58 ppm in the same position as peaks found for other tetrahedral and five coordinate cobalt (II) proteins which have been assigned as histidine Hβ protons [2, 3]; even the T 1 values (7−11 ms) are consistent with the assignment. There are then four peaks upfield at −37, −51, −90 and −105 ppm with T 1 values ranging from 2 to 4 ms. They could be the four ortho signals of the two proposed tyrosinate ligands. The signals at −30 and −20 ppm may be assigned to two of the four meta protons of the tyrosinates since the T 1 values of 35 ms indicate a larger proton metal distance. The other two meta signals could be under the intense absorption in the diamagnetic region. Two resonances are still to be assigned, i.e.. that at 31 ppm of intensity 2 and at 19 ppm of intensity 1. Both of them have a T 1 of 11 ms, i.e. they are due to protons relatively close to the metal. The one at 19 ppm could be assigned to a meta signal of a tyrosinate bent in such a way as to give rise to a short proton metal distance. However, a proton of a CH 2 attached to a histidine in a α position seems to fit better with the characteristics of the signal. The assignment of the peak at 31 ppm of intensity two is important even for the chemical implications. It is reasonable to assign the signal to two additional histidine Hβ protons. The spectrum recorded in D 2O after allowing the apo-protein to exchange with D 2O for a week at 35 °C shows that the intensity of the 31 ppm signal is halved, while the signal at +67 ppm disappears. If we assign the 67 ppm signal and one of the 31 ppm signals to histidine NH protons, then at +58 and the residual signal at +31 ppm can be assigned as histidine 4H protons. Based on the present assignment, the NMR spectrum confirms the nature of the ligands in iron transfer proteins and suggests that: i) the histidines bind with the nitrogen close to CH 2; ii)the tyrosinates are in the apical positions of a pseudooctahedral chromophore since only such positions have been found to provide large upfield dipolar shifts.

Studies in fluorinated 1,3-diketones and related compounds Part XII. Synthesis and spectroscopic studies of some new polyfluorinated 1,3-diketones, and their copper 1,3-diketonates

New polyfluorinated 1,3-diketones have been prepared from polyfluorinated acetophenones and appropriate esters in the presence of sodamide. The corresponding copper 1,3-diketonates have been obtained by treating a methanolic solution of polyfluorinated 1,3-diketone with methanolic solution of copper acetate. The polyfluorinated 1,3-diketones have been characterized by elemental as well as by spectral studies, viz: I.R., 1H N.M.R. and 19F N.M.R. In I.R., characteristic absorptions observed are: CF stretching bands (1300 − 1000) cm −1, CF deformation modes (900 − 700 cm −1) and intramolecular hydrogen bonding (3000 − 2500 cm −1). In 1H N.M.R. methine ( = C H ) signal is observed at δ 6.2 − 6.8 ppm and enolic proton resonance signal at δ 13 − 15 ppm indicating the presence of strong hydrogen bonding in such polyfluorinated 1,3-diketones.

An Optical-Frequency Pulse-Position-Modulation Experiment

This paper describes an optical-frequency pulse-position-modulation experiment using a GaAs luminescent diode as the source and either a pin or an avalanche photodiode as the detector. The experimental system transmits an audio band from 300 Hz to 3.4 kHz at an 8-kb/s repetition rate. Timing synchronization between the transmitter and receiver has been accomplished by two methods: by transmitting a separate clock signal and by recovering the timing from the ppm signal itself. Data show, with each scheme, peak-signal-to-rms-noise ratios of 70 dB can be achieved with the required average optical power at the receiver being − 73 dBm with a pin detector and − 88 dBm with an avalanche detector.

The Spectrum of a TDM PPM Signal

The spectrum of a time-division-multiplexed (TDM) pulse-position-modulated (PPM) signal consists of three parts-the continuous part, which is simply the sum of the continuous parts of the spectra of the separate channels; lines on harmonics of the maximum overall pulse-repetition frequency (PRF), which are also independent of any permutation among the channels; and the lines on the other harmonics of the single-channel PRF. Simple expressions are found for all three parts under the assumption that <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N - m - n</tex> channels are empty, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</tex> are unmodulated, and the remaining <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</tex> contain independent, identically uniformly distributed pulse positions. A complicated expression is found for the variances of the lines in the last part of the spectrum under a random choice of the modulated and unmodulated channels, and a simple approximation is presented for it.

Estimation of Delay of M PPM Signals in Laguerre Communications

In this note the maximum likelihood detector for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> pulse-position-modulated (PPM) signals in Laguerre communications is derived. A decision-directed maximum likelihood estimator for the delay of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">M</tex> PPM signals is discussed.

The structure of least-mean-square linear estimators for synchronous&amp;lt;tex&amp;gt;M&amp;lt;/tex&amp;gt;-ary signals (Corresp.)

Several authors have shown that the structure of the least-mean-square linear estimator of the sequence of random amplitudes in a synchronous pulse-amplitude-modulated signal that suffers intersymbol interference and additive noise is a matched filter whose output is periodically sampled and passed through a transversal filter (tapped delay line). It is our purpose in this paper to generalize this result to synchronous m -ary signals (e.g., FSK, PSK, PPM signals). We prove that the structure of the least-mean-square linear estimator of the sequence of random parameters in a synchronous m -ary signal, which suffers intersymbol interference and additive noise, is a parallel connection of m matched filters followed by tapped delay lines. A similar structure is derived for the continuous waveform estimator of a synchronous m -ary signal. Finally, we present a structure for estimation-decision detection of synchronous m -ary signals, which is based on least-mean-suare linear estimates of a posteriori probabilities.

Homoadamantane. II Analysis of the NMR Spectrum of Homoadamantane

Abstract Due to a fortuitous coincidence of chemical shifts, the nmr spectra of diamondoid hydrocarbons are often exceedingly simple. At 60 MHz the spectrum of adamantane consists of superimposed bands due to the two types of protons present2 A field strength corresponding to 220 MHz3 is needed (Fig. 1A) to cleanly separate bridgehead (δ = 1.87 ppm) and methylene (1.74 ppm) signals. The three kinds of protons in diamantane have even smaller chemical shift differences, and only a single, relatively sharp peak (1.68 ppra) at 100 MHz is seen in the nmr spectrum of this molecule. 4 Noradamantane (II)5 possesses five different types of hydrogens, but even the 220 MHz spectrum (Fig. 1B) shows only three distinct bands: the two broad bridgehead singlets (2.40 and 2.10 ppm) and the multiplet near 1.6 ppm due to the three types of methylene protons. In striking contrast to this behavior, the nmr spectrum of homoadamantane (III) (Fig. 1C, 2A) is unexpectedly complex. In this communication we report the analysis of ...

Numerical optimization techniques applied to PPM signal design

A computer-oriented algorithm is developed for designing optimum waveforms for a pulse-position-modulation communication system. Nonlinear modulation threshold effects are incorporated directly into the design by introducing constraints on the sidelobe peaks of the autocorrelation function. The search is performed over the class of signals satisfying constraints on average power, peak power, and bandwidth. The optimum signal in this class is the one whose autocorrelation function has the sharpest central peak while the sidelobe peaks are below the specified constraint level. Numerical results for a realistic problem are presented, and the effect of introducing the correlation and peak power constraints is studied. It is shown that a large reduction in the sidelobe peaks is possible with relatively little loss in the sharpness of the central peak.

Optimal control techniques applied to PPM signal design

Optimal control techniques are used to derive necessary conditions for designing optimum waveforms for pulse-position modulation communication systems. Nonlinear modulation threshold effects are incorporated directly into the design by introducing constraints on the side-lobe peaks of the autocorrelation function. The search is performed over the class of signals satisfying constraints on the average power, peak power, and bandwidth. The optimum signal in this class is the one whose autocorrelation function has the sharpest central peak while the side-lobe peaks are below the specified constraint level. The necessary conditions are obtained by treating the correlation constraints as functional constraints on the state-variables and applying Neustadt's abstract variational theory. The conditions are in the form of differential-difference equations of the advanced and retarded type which appear to be extremely difficult to solve analytically.

Unusual Spin-Spin Couplings in NMR Spectra of Alkyl Ammonium Salts

The NMR spectrum of tetraethylammonium iodide in D2O has quartet signals at 1.37 ppm and triplet signals split into 1: 1: 1 triplets at 3.42 ppm. This splitting is attributed to coupling with N14.