Magnetic Resonance in Chemistry

Silva Elipe, Maria Victoria; Donovan, Neil; Krull, Robert; Pooke, Donald; Colson, Kimberly L.

doi: 10.1002/mrc.4795pmid: N/A

Zhang, Yunzhi; Xu, Hui; Casabianca, Leah B.

doi: 10.1002/mrc.4751pmid: 29771468

The interactions between small molecule drugs or dyes and nanoparticles are important to the use of nanoparticles in medicine. Noncovalent adsorption of dyes on nanoparticle surfaces is also important to the development of nanoparticle dual‐use imaging contrast agents. In this work, solution‐state NMR is used to examine the noncovalent interaction between a near‐infrared cyanine dye and the surface of polystyrene nanoparticles in solution. Using 1D proton NMR, we can approximate the number of dye molecules that associate with each nanoparticle for different sized nanoparticles. Saturation‐Transfer Difference NMR was also used to show that protons near the positively charged nitrogen in the dye are more strongly associated with the negatively charged nanoparticle surface than protons near the negatively charged sulfate groups of the dye. The methods described here can be used to study similar drug or dye molecules interacting with the surface of organic nanoparticles.

Rusakov, Yury Yu; Rusakova, Irina L.; Krivdin, Leonid B.

doi: 10.1002/mrc.4752pmid: 29775489

Four‐component density functional theory calculations of 31P NMR chemical shifts have been performed for the representative series of 56 phosphine chalcogenides in order to investigate an influence of different functional groups on the heavy atom relativistic effect on the NMR chemical shifts of light phosphorous atoms (Heavy Atom on Light Atom effect). The validity of the 4‐component density functional theory approach used for the wide‐scale calculations of the phosphorous chemical shifts in a wide series of phosphine chalcogenides has been confirmed on a small series of 5 representative compounds with the aid of high‐quality coupled cluster singles and doubles calculations taking into account solvent, vibrational, and the relativistic corrections in comparison with the experiment.

Guo, Chengchen; Yarger, Jeffery L.

doi: 10.1002/mrc.4753pmid: 29808623

Gold nanoparticles have attracted considerable attention in recent research because of their wide applications in various fields such as material science, electrical engineering, physical science, and biomedical engineering. Researchers have developed many methods for synthesizing different kinds of gold nanoparticles, where the sizes and surface chemistry of the nanoparticles are considered to be the two key factors. Traditionally, the sizes of nanoparticles are determined by electron microscopy whereas the surface chemistry is characterized by optical spectroscopies such as infrared spectroscopy and Raman spectroscopy. Compared with that, nuclear magnetic resonance (NMR) spectroscopy provides a more advanced and convenient way for size determination and surface chemistry investigations by combining one‐ and multiple‐dimensional NMR spectroscopy and diffusion‐order NMR spectroscopy. Here, we show a thorough study that NMR spectroscopy can be applied to characterize small thiol‐protected gold nanoparticles, including size determination, surface chemistry investigation, and structural study. The results show that the nanoparticles' sizes determined by NMR agree well with transmission electron microscopy results. Furthermore, the ligand densities of nanoparticles were determined by quantitative NMR spectroscopy, and the structures of ligands capped on the surfaces were studied thoroughly by one‐ and multiple‐dimensional NMR spectroscopy. In this work, we establish a general method for researchers to characterize nanostructures by using NMR spectroscopy.

Nieto, Carla I.; Cabildo, Pilar; García, M. Ángeles; Claramunt, Rosa M.; Elguero, José; Alkorta, Ibon

doi: 10.1002/mrc.4754pmid: 29806195

The X‐ray crystal structure of 2‐benzyl‐1H‐benzimidazole, 2BnBzIm, was determined at 293 K showing no dynamic phenomena (disorder) of any class. On the other hand, some 13C NMR signals were absent in the CPMAS spectrum (100 MHz, 300 K). We decided to carry out variable‐temperature SSNMR and discovered that the missing signals are ortho and meta carbons of the phenyl ring of the benzyl group. Line‐shape analysis and the Eyring equation were used to determine the barrier, which was compared with the calculated DFT for the gas phase that it is much lower.

Jeong, Keunhong; Min, Sein; Chae, Heelim; Namgoong, Sung Keon

doi: 10.1002/mrc.4756pmid: 29856897

Parahydrogen is a potentially significant source of hyperpolarization. However, a heat exchanger at an ultralow temperature, which is normally sustained wastefully using liquid nitrogen, is essential for the generation of hyperpolarized parahydrogen. In order to cut down on the use of liquid nitrogen, we employed a cryogenic storage dewar as the key component of our home‐built parahydrogen generator, which lasted over 20 days with a single filling. Small concentrations of an unsaturated compound in a mixture were identified by hydrogenation in a principle‐based experiment involving the use of hyperpolarization and phase difference. Less than 1 μl of styrene in 1 ml of chloroform was identified in a single scan with a 43 MHz benchtop nuclear magnetic resonance (NMR) spectrometer following hydrogenation with 50% parahydrogen. This method can potentially undergo a significant development through the use of high‐field NMR techniques, higher parahydrogen concentrations, and increased scan times for data collection, among others. Because hydrogenation with parahydrogen induces a phase reversal during attachment to unsaturated CC bonds, it may be possible to detect many other unsaturated bonds in organic molecules. All in all, this study not only broadens the research on parahydrogen‐based unsaturated‐bond detection, but also facilitates the use of hyperpolarization by a broader range of researchers through the introduction of a long‐lasting home‐built parahydrogen generator.

Nguyen, Huong Giang Thi; Nguyen, Vinh Ngoc; Kamounah, Fadhil S.; Hansen, Poul Erik

doi: 10.1002/mrc.4760pmid: 29920769

In a conventional Mannich reaction using piperidine, hydroxypiperidines, morpholine, and N‐methylpiperazine with usnic acid, a deacetylation was observed resulting in a substitution at C‐2, a loss of an acetyl group, and a Mannich base with a stabilized enol. The enol has a hydrogen bond to the nitrogen of the secondary amine. The structure was investigated by nuclear magnetic resonance and deuterium isotope effects on 13C chemical shifts as well as with density functional theory calculations to study the changed hydrogen bond pattern. It was found that the hydrogen bond involving the OH‐9 group in chloroform forms a strong hydrogen bond than in usnic acid itself and that this hydrogen bond becomes even stronger in the more polar solvent, dimethylsulfoxide. Tautomerism was observed in the Mannich base as demonstrated by deuterium isotope effects on chemical shifts. The position of the tautomeric equilibrium depends on the solvent, and the position of the equilibrium governs the strength of the OH‐9…O═C hydrogen bond.

Bigler, Peter; Furrer, Julien

doi: 10.1002/mrc.4762pmid: 29907970

Long‐range heteronuclear single quantum correlation (LR‐HSQC) experiments may be applied as an alternative to heteronuclear multiple‐bond correlation (HMBC) experiments for detecting long‐range correlations but has never enjoyed popularity for that purpose. To the best of our knowledge, the exact reasons have not yet been fully established. For both experiments, it is widely accepted that the evolution of proton–proton homonuclear couplings JHH′ during the polarization transfer delays Δ leads to significant losses, and that the intensity of the observable coherence is zero when JHH′ matches the condition Δ = 0.5/JHH′. Here, we analyze the influence of JHH′ on the intensity of long‐range correlations in HMBC and LR‐HSQC spectra. We show that for both experiments long‐range correlations will not be canceled because of homonuclear couplings JHH′. Our theoretical and experimental results definitely establish and validate the superiority of HMBC‐based experiments among the family of heteronuclear long‐range correlation experiments: (a) the overall cross peak's intensity is higher, and (b) in LR‐HSQC experiments, the intensity of the long‐range cross peaks is additionally influenced in an unwanted way by the magnitude and number of passive homonuclear proton–proton couplings JHH′.