I. Solomon

Bio: I. Solomon is an academic researcher. The author has contributed to research in topics: Nuclear Overhauser effect & Hydrofluoric acid. The author has an hindex of 1, co-authored 1 publications receiving 608 citations.

Nuclear Magnetic Interactions in the HF Molecule

Abstract: Magnetic relaxation times of hydrogen and fluorine in anhydrous hydrofluoric acid cannot be accounted for on the assumption of a pure dipole‐dipole interaction between the hydrogen and the fluorine nuclei in the same molecule. However, the introduction, in the Hamiltonian, of a scalar term AI·S resulting from the indirect electron‐coupled interaction between the two nuclei removes all the discrepancies between the calculated and observed decay times. Although the splitting due to this scalar term is smeared out by the rapid chemical exchange of the protons with the traces of water present in the acid, the nuclear Overhauser effect provides the extra parameter required to separate the dipole‐dipole interaction from the scalar interaction and to calculate separately the scalar splitting and the exchange rate of the protons. The value obtained for the splitting is A/h=615 cps.The same method has been applied to investigate the structure of the HF molecule in solutions. The experimental results can be explain...

NMR‐Relaxation Mechanisms of O17 in Aqueous Solutions of Paramagnetic Cations and the Lifetime of Water Molecules in the First Coordination Sphere

Abstract: An investigation was made of the temperature and frequency dependence of T2 for O17 in aqueous solutions containing Mn2+, Fe2+, Co2+, Ni2+, and Cu2+. This represented an extension of the studies previously performed in this laboratory on these ions. Virtually all of the temperature effects predicted by the modified Bloch equations for a two‐species system were verified experimentally. Rates of exchange of water molecules between the bulk of the solution and the first coordination sphere of the paramagnetic cations were determined for all the ions studied. Activation energies for exchange were measured and electronic T1's and coupling constants were determined in some cases. Evidence was found for a tetrahedral Co2+(H2O)4 species in aqueous solutions near 100°C. The data for cupric ion were interpreted in terms of six coordinated water molecules in a distorted octahedron, with a ratio of ∼105 existing for the axial‐water‐exchange rate over that of the equatorial waters. The rates of exchange were compared ...

Proton Relaxation Times in Paramagnetic Solutions. Effects of Electron Spin Relaxation

Abstract: The proton relaxation time in solutions of paramagnetic ions depends, among other factors, on the relaxation time of the electron spins, τs. It is shown that the latter, for ions of the iron group, is determined mostly by the distortion of the hydrated complex by collisions with other water molecules. The theory provides a quantitative explanation for the decrease in T2 in Mn++ (and other) solutions in very high magnetic fields. The experimentally observed field and temperature dependence of the proton relaxation times, T1 and T2, for ions of the iron group is compared with theory and the features which depend on τs are stressed.

Proton Relaxation Times in Paramagnetic Solutions

Abstract: An exchange interaction is postulated between the electron spin and proton spin in adjacent water‐molecules in paramagnetic solutions. In combination with the long electron spin relaxation times for Mn++ and Gd+++, an explanation is given why T1/T2 for protons is much larger than unity in solutions of these particular ions in high magnetic fields, whereas T1 is about equal to T2 in other solutions or in low fields.

Lanthanide probes for bioresponsive imaging.

Abstract: The chemistry of the less familiar elements is a fascinating topic especially for the inorganic minded. The lanthanides, or rare earths, comprise the 5d block of the periodic table and represent a huge array of applications from catalysis to lasers, and of course, imaging agents.1 Recent advances in luminescence and magnetic resonance microscopy have, in part, been stimulated by extraordinary success in the development of new lanthanide probes. The unique properties of the lanthanides provide for a deep tool chest for the chemist, biologist and the imaging scientist to exploit, and that exploitation is in full swing. In this review we focus on two classes of lanthanide probes that are subsets of the larger area of metalloimaging: luminescent and magnetic lanthanides. In Section 2 we discuss the general design and photophysical properties of lanthanides and how these parameters are tuned to develop bioresponsive probes for optical imaging. In Section 3 we provide a brief description of how MR images are acquired and the how MRI contrast agents are engineered to respond to biological events of interest. These guiding principles have driven research that has produced a truly diverse number of new agents that are target specific and bioresponsive (or bioactivatable). While other imaging modalities utilize lanthanide-based probes, these topics are beyond the scope of this review. We direct the reader to explore some excellent reviews in the important areas of radiometals and multimodal imaging.2–5

Intrinsic motions along an enzymatic reaction trajectory

Abstract: The mechanisms by which enzymes achieve extraordinary rate acceleration and specificity have long been of key interest in biochemistry. It is generally recognized that substrate binding coupled to conformational changes of the substrate-enzyme complex aligns the reactive groups in an optimal environment for efficient chemistry. Although chemical mechanisms have been elucidated for many enzymes, the question of how enzymes achieve the catalytically competent state has only recently become approachable by experiment and computation. Here we show crystallographic evidence for conformational substates along the trajectory towards the catalytically competent 'closed' state in the ligand-free form of the enzyme adenylate kinase. Molecular dynamics simulations indicate that these partially closed conformations are sampled in nanoseconds, whereas nuclear magnetic resonance and single-molecule fluorescence resonance energy transfer reveal rare sampling of a fully closed conformation occurring on the microsecond-to-millisecond timescale. Thus, the larger-scale motions in substrate-free adenylate kinase are not random, but preferentially follow the pathways that create the configuration capable of proficient chemistry. Such preferred directionality, encoded in the fold, may contribute to catalysis in many enzymes.