¹⁵N‐NMR Spectroscopy—New Methods and Applications [New Analytical Methods (28)]

Abstract

The nitrogen nucleus is the third most important probe (after ' H and I3C) for structural investigations of organic and bioorganic molecules by NMR spectroscopy. For a long time, however, the insufficient sensitivity and low natural abundance of the I5N isotope hampered detection of the I5N nucleus, and the quadrupolar I4N nucleus proved unsuitable for the study of larger molecules with several nonequivalent nitrogen atoms. The advent of new techniques, such as pulse sequences and polarization transfer, in conjunction with the use of high-field magnets and large-sample probe heads largely solved the detection problem. As a result, the last few years have seen a dramatic development of "N-NMR spectroscopy as a versatile method for studying molecular structure, both in isotropic (liquid) and anisotropic (solid) phases. The scope of chemical applications extends from inorganic, organometallic, and organic chemistry to biochemistry and molecular biology, and includes the study of reactive intermediates, biopolymers, enzyme-inhibitor complexes, and nitrogen metabolism. Two-dimensional NMR techniques offer additional possibilities for detailed studies of biological systems. Pages 383-486Angew Chem. Inr. Ed. Engl. 25 (1986) 383-413 0 VCH Verlagsgesellschajl mbH. 0-6940 Weinheim. 1986 0S70-0833/86/05~15-0383 . $ 02.50/0 Anyen, Chem. Int. Ed. Engl. 25 (1986) 383-413

Polycationic Salts V [1]. 15N NMR Spectra of Amines, Ammonium Salt Monomers, and Polymers of Styrene Based Trialkylammonium Salts

“…The 15 N chemical shift values of the nitrogen atom in position 1 of N-methylimidazole [14] are essentially the same in the three solvents, but the nitrogen atom in position 3 of the imidazole ring is substantially shifted in water and methanol, possibly due to some hydrogen bonding.…”

“…Vinylbenzyltri-n-alkylammonium chloride monomers were investigated further. Vinylbenzyltrimethylammonium chloride (13) had a chemical shift value similar to 11, the -value of vinylbenzyltriethylammonium chloride (14) was similar to that of 12 (Table 4).…”

“…The 15 N NMR spectra were measured using a GE 300 MHz NMR spectrometer with an observation frequency of 30.45 MHz for 15 N. The non-decoupled 15 N NMR spectra were calibrated against external formamide (À267.8 ppm) and are referenced to the delta () scale with nitromethane set to zero [13,14]. Previous standardizations used liquid ammonia (À381.9 ppm) [14].…”

Trifluoromethyl phosphaalkenes of the type F3CPC(OR)NR2: Synthesis, spectroscopic investigations, and ligand properties [1]

“…The high field shift of ca 40 relative to RCOOR' absorption is due to thep-donor effect of the MezN substituent. It is known that an increasing n-donor strength of R in such compounds cuts down the lone pair participation of the OR' group in the resonance stabilization and results in a high field shift of the I7O NMR signal of the OR' fragment [7, 131. The preferred participation of the lone pair of the Me2N substituent in the p / r conjugation of 1 is confirmed by the 15N NMR spectrum with a signal at 6 = 95.8 (2J(PN) = 16.3 Hz), indicating a bonding situation similar to that of nitrogen in amides or enamino ketones [14]. The interesting correlation of chemical shifts SN/SP of analogous compounds with bicoordinated N and P [ 151 at present cannot be verified for corresponding F3CE=C systems (E = N, P) because 6 values of such derivatives, e.g.…”

14N NMR spectra of molecular nitrogen in SDS/pentanol swollen lamellar phases

“…[1] In spite of its very high natural abundance, 99.632%, [2] 14 N, spin quantum number I = 1, progressively lost popularity in favor of the I = 1/2 isotope, 15 N. [1] An important contribution to the NMR success of 15 N is the work of Professor Paul S. Pregosin, who has been paying attention to it since the beginning of his research activity, [3 -6] when the acquisition of signals from 15 N was still a daunting task. Nowadays, 15 N is more frequently employed for the structural determination of biomacromolecules in solution owing to the availability of increasingly stronger magnetic fields and new pulse sequences tailored to overcome the problem of poor sensitivity together with advanced techniques of isotopic enrichment.…”