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There is a growing interest in developing paramagnetic nanoparticles as responsive magnetic resonance imaging (MRI) contrast agents, which feature switchable T1 image contrast of water protons upon biochemical cues for better discerning diseases. However, performing an MRI is pragmatically limited by its cost and availability. Hence, a facile, routine method for measuring the T1 contrast is highly desired in early‐stage development. This work presents a single‐point inversion recovery (IR) nuclear magnetic resonance (NMR) method that can rapidly evaluate T1 contrast change by employing a single, optimized IR pulse sequence that minimizes water signal for "off‐state" nanoparticles and allows for sensitively measuring the signal change with "switch‐on" T1 contrast. Using peptide‐induced liposomal gadopentetic acid (Gd3+‐DTPA) release and redox‐sensitive manganese oxide (MnO2) nanoparticles as a demonstration of generality, this method successfully evaluates the T1 shortening of water protons caused by liposomal Gd3+‐DTPA release and Mn2+ formation from MnO2 reduction. Furthermore, the NMR measurement is highly correlated to T1‐weighted MRI scans, suggesting its feasibility to predict the MRI results at the same field strength. This NMR method can be a low‐cost, time‐saving alternative for pre‐MRI evaluation for a diversity of responsive T1 contrast systems. [ABSTRACT FROM AUTHOR]

Superparamagnetic iron oxide (SPIO) nanoparticles have been introduced as contrast agents for clinical applications in magnetic resonance imaging. Recently, SPIO has been also used for tracking cells. However, NMR relaxation of water molecules behaves differently in a SPIO solution and SPIO-loaded cells. In this study, we used water-in-oil-in-water double emulsions to mimic cellular environments. The MR relaxation induced by the SPIO-loaded vesicles and SPIO solution indicates that T2* is sensitive to the iron concentration alone, and the behavior was very similar in both SPIO-loaded vesicles and SPIO solution. However, T2 relaxation of water in SPIO-loaded vesicles was faster than that in a SPIO solution. In addition, the contribution of water inside and outside the vesicles was clarified by replacing H2O with D2O, and water inside the vesicles was found to cause a nonlinear iron concentration dependency. The studied dilution revealed that vesicle aggregation undergoes a structural transition upon dilution by a certain amount of water. R2* relaxation is sensitive to this structural change and shows an obvious nonlinear iron concentration dependency when the SPIO loading is sufficiently high. Random walk simulations demonstrated that in the assumed model, the vesicles aggregate structures causing the differences between R2* and R2 relaxation of water in vesicles in the presence of SPIO particles. [ABSTRACT FROM AUTHOR]

Double-quantum-filtered NMR and T1 inversion-recovery spectroscopy were employed to exploit the temperature-dependent dynamics of D2O confined in MCM-41. Samples with three pore sizes of 1.58, 2.03, and 2.34 nm and two D2O contents were investigated. The reorientation correlation times of confined D2O in variously sized pores exhibit different temperature dependencies. The results reveal that the D2O molecules at fast motion site remain mobile below ∼225 K and a liquid-liquid phase transition occurs around this temperature for all samples studied. This temperature is thought to be unreachable for supercooled D2O. Particularly, in 20 wt % D2O loaded samples with pore diameters of 1.58 and 2.03 nm, the reorientational correlation times of D2O at fast motion site exhibit Arrhenius behavior between 225 and 290 K, while other samples show power law dependency. Thus, a liquid phase of the fragile type in bigger pores changes to the strong type in samples with smaller pores. [ABSTRACT FROM AUTHOR]

Studies the photodissociation of water at 157 nm using the hydrogen atom from Rydberg tagging time-of-flight technique. Measurement of vibrational state distribution from the OH product from the water photodissociation; Underestimation of the relative populations for the high vibrationally excited OH products measured by the laser-induced fluorescence technique.

Investigates the isotope effects on the molecular hydrogen elimination of ethylene. Photodissociation of ethylene at 157 nanometer excitation; Types of molecular elimination processes; Enumeration of ethylene-chemical dissociation channels.

Examines oxygen photodissociation at 157 nanometer excitation using the photofragmentation transnational spectroscopic technique. Determination of relative yields and anisotropy parameters of product channels; Observation of anisotropy mixing of dissociation in the dissociation channel; Mechanism of oxygen dissociation through Schumann-Runge band.

Analyzes the photodissociation dynamics of OCIO using the photofragment translational spectroscopic technique. Discussion on chemical dissociation channels; Dissociation behavior of the molecules in Rydberg electronic states; Results of the anisotropy parameter measurements.

The line shape analyses of (super 2)H double quantum filtered (DQF) nuclear magnetic resonance (NMR) and T1 measurements were used to investigate the dynamics of water adsorbed on MCM-41. It was found that there are three sites for water adsorption on MCM-41, namely a slow site, a fast site I, and a fast site II.

Abstract: Contrast enhancement agents are often employed in magnetic resonance imaging (MRI) for clinical diagnosis and biomedical research. However, the current theory on MRI contrast generation does not consider the ubiquitous presence of macromolecular crowders in biological systems, which poses the risk of inaccurate data interpretation and misdiagnosis. To address this issue, herein the macromolecular crowding effects on MRI contrast agent are investigated with the 1H relaxation rate of water in aqueous solutions of Dotarem with different concentrations of macromolecules. Two representative macromolecular crowder systems are used: polyethylene glycol (with no specific secondary structure) and bovine serum albumin (with compact secondary and tertiary structures). The water 1H relaxation rates in various solutions are measured in a fixed magnetic field and in variable magnetic fields. The results show significant crowding effects for both crowders. The relaxation rate is proportional to the concentration of the MRI contrast agent but shows conspicuous superlinearity with respect to the concentration of the crowder. The size of polyethylene glycol does not affect the relaxivity of water in Dotarem solutions. The above effects are verified with T1‐ and T2‐weighted NMR microimages. These results highlight the importance of the effect of macromolecular crowding on the MRI contrast agent and are valuable for understanding the mechanism of MRI contrast agents and designing new‐generation MRI contrast agents. [ABSTRACT FROM AUTHOR]