Several parameters in NMR depend on the magnetic field strength. Field-cycling NMR is an elegant way to explore the field dependence of these properties. The technique is well developed for solution state and in relaxometry. Here, a shuttle system with magic-angle spinning (MAS) detection is presented to allow for field-dependent studies on solids. The function of this system is demonstrated by exploring the magnetic field dependence of the solid-state photochemically induced nuclear polarization (photo-CIDNP) effect. The effect allows for strong nuclear spin-hyperpolarization in light-induced spin-correlated radical pairs (SCRPs) under solid-state conditions. To this end, 13C MAS NMR is applied to a photosynthetic reaction center (RC) of the purple bacterium Rhodobacter (R.) sphaeroides wildtype (WT). For induction of the effect in the stray field of the magnet and its subsequent observation at 9.4 T under MAS NMR conditions, the sample is shuttled by the use of an aerodynamically driven sample transfer technique. In the RC, we observe the effect down to 0.25 T allowing to determine the window for the occurrence of the effect to be between about 0.2 and 20 T.

The alkylating potential of p-nitrostyrene oxide (pNSO)--a compound used as a substrate to study the activity of epoxide hydrolases as well as in polymer production and in the pharmaceutical industry--was investigated kinetically. The molecule 4-(p-nitrobenzyl)pyridine (NBP), as a model nucleophile for DNA bases, was used as an alkylation substrate. In order to gain insight into the effect of the hydrolysis of pNSO, as well as the hydrolysis of the NBP-pNSO adduct on the pNSO alkylating efficiency, these two competing reactions were studied in parallel with the main NBP-alkylation reaction. The following conclusions were drawn: (i) pNSO reacts through an S(N)2 mechanism, with NBP to form an adduct, pNSO-NBP (AD). The rate equation for the adduct formation is: r = d[AD]/dt = k(alk)[NBP][pNSO]-k(hyd)(AD) [AD] (k(alk), and k(hyd)(AD) being the alkylation rate constant and the NBP-pNSO adduct hydrolysis rate constant, respectively); (ii) the alkylating capacity of pNSO, defined as the fraction of initial alkylating agent that forms the adduct, is similar to that of mutagenic agents as effective as β-propiolactone. The instability of the pNSO-NBP adduct formed could be invoked to explain the lower mutagenicity shown by pNSO; (iii) the different stabilities of the α and β-adducts formed between NBP and styrene oxides show that the alkylating capacity f = k(alk)[NBP]/(k(alk)[NBP] + k(hyd)) (k(hyd) being the pNSO hydrolysis rate constant) as well as the alkylating effectiveness, AL = f/k(hyd)(AD), are useful tools for correlating the chemical reactivity and mutagenicity of styrene oxides; (iv) a pNSO-guanosine adduct was detected.

Water analysis is one of the most important issues in environmental chemistry. The increasing scale of water contamination owing to the presence of nitrate and nitrite in the environment has converted it into one of the most serious public health problems in modern society. Here an easy colorimetric method for determining nitrite in water is reported. The method is based on the reaction of nitrite with minoxidil in acidic media, which gives nitrosominoxidil as a product that shows an absorption band in the λ = 315–330 nm range. Minoxidil was the first drug approved by the U.S. Food and Drug Administration as a treatment against alopecia (hair loss), thus leading minoxidil to be one of the most popular and commonly used drugs that can be purchased freely at low cost on the market in the form of topical solutions. The experiment can be completed over 3.5 h, and it can be extended to include a kinetic mechanistic study of the nitrosation reaction. The nitrite detection range makes the method suitable for environmental, food, and physiological analytical applications. By using a brand-name product, student curiosity and interest is kept high throughout the experiment. Finally, questions are provided in the student handout, requiring the students to engage further in topics associated with the context of this practical work.

Acrylamide (AA), an industrially produced reactive molecule, is used worldwide. The US EPA and IARC have classified this molecule as a probable human carcinogen. In this work, the alkylating potential of AA was investigated kinetically. The conclusions drawn are as follows: (i) AA shows alkylating ability on the nucleophile 4-( p-nitrobenzyl)pyridine (NBP), a trap for alkylating agents with nucleophilic characteristics similar to those of DNA bases; (ii) the rate equation for the NBP-AA adduct formation is as follows: r ¼ k alk AA ½ NBP ½ ; (ii) the thermoentropic term, TD z S u , is the main term responsible for the lower reactivity of AA as an alkylating agent; (iii) the value of the Gibbs energy of activation, D z G u , for the NBP alkylation reaction by AA is consistent with the conclusions of epidemiologic studies concerning the carcinogenicity of this substance; (iv) the results obtained here may be useful when working with hydrophilic/lipophilic media, such as in Food Science, since the dielectric constant of the medium, where alkylation occurs, influences the reaction rate, and alkylation can be inhibited by lowering the dielectric constant of the medium.