Direct and cost-efficient hyperpolarization of long-lived nuclear spin states on universal (15)N2-diazirine molecular tags.

Conventional magnetic resonance (MR) faces serious sensitivity limitations which can be overcome by hyperpolarization methods, but the most common method (dynamic nuclear polarization) is complex and expensive, and applications are limited by short spin lifetimes (typically seconds) of biologically relevant molecules. We use a recently developed method, SABRE-SHEATH, to directly hyperpolarize (15)N2 magnetization and long-lived (15)N2 singlet spin order, with signal decay time constants of 5.8 and 23 minutes, respectively.

Accessing long lived (1)H states via (2)H couplings.

In this paper we demonstrate long-lived states involving a pair of chemically equivalent protons, with lifetimes ∼30 times T1 up to a total lifetime of ∼117s at high field (8.45T). This is demonstrated on trans-ethylene-d2 in solution, where magnetic inequivalence gives access to the long-lived states.

Long-lived polarization protected by symmetry.

In this paper we elucidate, theoretically and experimentally, molecular motifs which permit Long-Lived Polarization Protected by Symmetry (LOLIPOPS). The basic assembly principle starts from a pair of chemically equivalent nuclei supporting a long-lived singlet state and is completed by coupling to additional pairs of spins. LOLIPOPS can be created in various sizes; here we review four-spin systems, introduce a group theory analysis of six-spin systems, and explore eight-spin systems by simulation.

Accessing long-lived disconnected spin-1/2 eigenstates through spins > 1/2.

Pairs of chemically equivalent (or nearly equivalent) spin-1/2 nuclei have been shown to create disconnected eigenstates that are very long-lived compared with the lifetime of pure magnetization (T1). Here the classes of molecules known to have accessible long-lived states are extended to include those with chemically equivalent spin-1/2 nuclei accessed by coupling to nuclei with spin > 1/2, in this case deuterium. At first, this appears surprising because the quadrupolar interactions present in nuclei with spin > 1/2 are known to cause fast relaxation.

Measuring long-lived 13C2 state lifetimes at natural abundance.

Long-lived disconnected eigenstates (for example, the singlet state in a system with two nearly equivalent carbons, or the singlet-singlet state in a system with two chemically equivalent carbons and two chemically equivalent hydrogens) hold the potential to drastically extend the lifetime of hyperpolarization in molecular tracers for in vivo magnetic resonance imaging (MRI). However, a first-principles calculation of the expected lifetime (and thus selection of potential imaging agents) is made very difficult because of the large variety of relevant intra- and intermolecular relaxation mechanisms. As a result, all previous measurements relied on costly and time consuming syntheses of (13)C labeled compounds.

Multicontrast nonlinear optical microscopy with a compact and rapid pulse shaper.

Homodyne detection can dramatically enhance measurement sensitivity for weak signals. In nonlinear optical microscopy it can make accessible a range of novel, intrinsic, contrast like nonlinear absorption and nonlinear phase contrast. Here a compact and rapid pulse shaper is developed, implemented, and demonstrated for homodyne detection in nonlinear microscopy with high-repetition rate mode-locked femtosecond lasers.

Accurately determining single molecule trajectories of molecular motion on surfaces.

This paper presents a method for simultaneously determining multiple trajectories of single molecules from sequential fluorescence images in the presence of photoblinking. The tracking algorithm is computationally nondemanding and does not assume a model for molecular motion, which allows one to determine correct trajectories even when a distribution of movement speeds is present. We applied the developed procedure to the important problem of monitoring surface motion of single molecules under ambient conditions.

Micrometer-scale translation and monitoring of individual nanocars on glass.

Nanomachines designed to exhibit controlled mechanical motions on the molecular scale present new possibilities of building novel functional materials. Single molecule fluorescence imaging of dye-labeled nanocars on a glass surface at room temperature showed a coupled translational and rotational motion of these nanoscale machines with an activation energy of 42 +/- 5 kJ/mol. The 3 nm-long dye-labeled carborane-wheeled nanocars moved by as much as 2.