14N ultra-wideline (UW), 1H{15N} indirectly-detected HETCOR (idHETCOR) and 15N dynamic nuclear polarization (DNP) solid-state NMR (SSNMR) experiments, in combination with plane-wave density functional theory (DFT) calculations of 14N EFG tensors, were utilized to characterize a series of nitrogen-containing active pharmaceutical ingredients (APIs), including HCl salts of scopolamine, alprenolol, isoprenaline, acebutolol, dibucaine, nicardipine, and ranitidine. A case study applying these methods for the differentiation of polymorphs of bupivacaine HCl is also presented. All experiments were conducted upon samples with naturally-abundant nitrogen isotopes. For most of the APIs, it was possible to acquire frequency-stepped UW 14N SSNMR spectra of stationary samples, which display powder patterns corresponding to pseudo-tetrahedral (i.e., RR′R′′NH+ and RR′NH2+) or other (i.e., RNH2 and RNO2) nitrogen environments. Directly-excited 14N NMR spectra were acquired using the WURST-CPMG pulse sequence, which incorporates WURST (wideband, uniform rate, and smooth truncation) pulses and a CPMG (Carr-Purcell Meiboom-Gill) refocusing protocol. In certain cases, spectra were acquired using 1H → 14N broadband cross-polarization, via the BRAIN-CP (broadband adiabatic inversion – cross polarization) pulse sequence. These spectra provide 14N electric field gradient (EFG) tensor parameters and orientations that are particularly sensitive to variations in local structure and intermolecular hydrogen-bonding interactions. The 1H{15N} idHETCOR spectra, acquired under conditions of fast magic-angle spinning (MAS), used CP transfers to provide 1H–15N chemical shift correlations for all nitrogen environments, except for two sites in acebutolol and nicardipine. One of these two sites (RR′NH2+ in acebutolol) was successfully detected using the DNP-enhanced 15N{1H} CP/MAS measurement, and one (RNO2 in nicardipine) remained elusive due to the absence of nearby protons. This exploratory study suggests that this combination of techniques has great potential for the characterization of solid APIs and numerous other organic, biological, and inorganic systems.

/pdf/natural-abundance-14n-and-15n-solid-state-nmr-of-1njdrbdltj.pdf

Natural abundance 14N and 15N solid-state NMR of pharmaceuticals and their polymorphs

14N-NQR based device for detection of explosives in landmines

https://bilder.buecher.de/zusatz/20/20830/20830285_lese_1.pdf

Nuclear quadrupole resonance spectroscopy

Nuclear quadrupole resonance (NQR) is a solid-state radio frequency (RF) spectroscopic technique that allows for the detection of many narcotics and highly explosive substances. Unfortunately, the practical use of NQR is often restricted by the presence of strong RF interference (RFI). In this letter, extending our recent work on stochastic NQR (sNQR), we propose acquiring signal-of-interest free samples, containing only corrupting signals, and exploiting them to reduce the effects of RFI on conventional NQR (cNQR) measurements. Similar to the sNQR case, the presented detectors are able to substantially outperform previous cNQR detectors when RFI is present.

Countering Radio Frequency Interference in Single-Sensor Quadrupole Resonance

Publisher Summary This chapter gives the account of the detection of explosive devices. The detection can be classified into two schemes — ”seeing” the device and detecting a certain component which is common to all devices. X-ray imaging is a model example of the previous scheme. It gives an image of the contents of anitem under inspection. It is presented upon the operator to be acquainted with the explosive device. Metal detection is a very good example of the latter scheme. Almost all land mines contain no less than a little quantity of metal that can be detected through a metal detector. Evidently, many guiltless objects contain metal. The problem is separating the guiltless from the hazardous. To detect the explosive device without any hesitation is to detect it with the help of devices. The thermal neutron analysis and dual-energy X-ray give the specificity and issues of radiation, which can be challenging in some situations. This chapter discusses the nuclear quadrupole resonance (NQR). NQR stimulates and detects the radio frequency (RF) signals from certain nuclei in molecules of interest and are called explosives.

Nuclear Quadrupole Resonance Detection of Explosives

A number of methods for cancelling magnetoacoustic and piezoelectric ringing signals in the spectroscopy of the nuclear quadrupole resonance are presented. The suggested methods include using the sequence (ϕ0)ϕ-(τ-ϕx-2τ-ϕ
 y
 -2τ-ϕ−x
 -2τ-ϕ−y
 -τ)
 n
 and a multipulse analog of the two-pulse Hahn sequence with the first pulse replaced by a short steady-state sequence. Another method presented is the method of orthogonal effective fields for a fast saturation of the quadrupole spin system which can be used for subtracting the magnetoacoustic and piezoelectric components from the signal. The suggested methods can be used for the practical purposes of detecting explosive substances and narcotics.

Multipulse sequences for explosives detection by NQR under conditions of magnetoacoustic and piezoelectric ringing

Modification of the steady-state free precession (SSFP) multipulse technique for the effective detection of nuclear quadrupole resonance (NQR) signals was studied. This modification is based on the use of the preparatory pulse in the SSFP pulse sequences. It was shown that under certain conditions the total intensity of accumulated NQR signal can be increased. Experimental results of applying the proposed technique to nitrogen-14 NQR in the sample of sodium nitrite (NaNO2) are presented and convincingly demonstrate the technique’s effectiveness.

Modified multipulse technique for the effective detection of pure nuclear quadrupole resonance

Pure Nuclear Quadrupole Resonance (NQR) is a very promising method for the detection and identification of illicit materials such as explosives and narcotics. NQR based machines are able to test closed luggage for illicit materials not readily identifiable by other methods. The application of the pure NQR method for screening of airport luggage is discussed. An advanced NQR machine which is a mid-sized luggage scanner has been developed by QRSciences Limited for use primarily in airports. The basic design, performance and some characteristics of this machine are reported.

The Detection of Explosives in Airport Luggage Using the Direct Nuclear Quadrupole Resonance Method

Some dynamical properties of nitrogen-14 quadrupolar spin-system with non-symmetric electric field gradient tensor

A study of multipulse sequences that can be used for the detection of HMX (N4(CH2)4(NO2)4) has been undertaken. On the basis of this study, a general method for experimentally optimizing multipulse sequences for the efficient detection of substances is proposed. The relaxation parameters and signal intensities for the nitrogen-14 spectral lines of a polycrystalline HMX sample were measured and the lines that are the most important for practical purposes were chosen.

W. P. Chisholm

Papers

Multipulse sequences for explosives detection by NQR under conditions of magnetoacoustic and piezoelectric ringing

Modified multipulse technique for the effective detection of pure nuclear quadrupole resonance

The Detection of Explosives in Airport Luggage Using the Direct Nuclear Quadrupole Resonance Method

Some dynamical properties of nitrogen-14 quadrupolar spin-system with non-symmetric electric field gradient tensor

Methods for optimizing the detection of HMX by nuclear quadrupole resonance