ABSTRACT
Phosphorus-31 magnetic resonance spectroscopic imaging (31P-MRSI) provides valuable non-invasive in vivo information on tissue metabolism but is burdened by poor sensitivity and prolonged scan duration. Ultra-short echo time (UTE) acquisitions minimize signal loss when probing signals with relatively short spin-spin relaxation time (T2), while also preventing first-order dephasing. Here, a three-dimensional (3D) UTE sequence with a rosette k-space trajectory is applied to 31P-MRSI at 3T. Conventional chemical shift imaging (CSI) employs highly regular Cartesian k-space sampling, susceptible to substantial artifacts when accelerated via undersampling. In contrast, this novel sequence's "petal-like" pattern offers incoherent sampling more suitable for compressed sensing (CS). These results showcase the competitive performance of UTE rosette 31P-MRSI against conventional weighted CSI with simulation, phantom, and in vivo leg muscle comparisons.
ABSTRACT
Denaturants such as the guanidinium cation unfold proteins at molar concentrations, which interferes with ultraviolet- and infrared-based spectroscopy measurements. Dodine denatures some proteins cooperatively at a thousand-fold lower concentration, allowing for spectroscopy measurements. Nonetheless, dodine's microscopic mechanism of interaction with proteins is not understood. We probe the effect of dodine on α-helices and tertiary structure by investigating the stability of the small helical protein B. Experiments show that dodine promotes formation of helical structure (a kosmotropic effect), while inducing the loss of tertiary structure (a chaotropic effect). Although dodine destabilizes native protein structure, it does not lower the thermal denaturation midpoint temperature of protein B. All-atom simulations reveal the cause for both observations: The denaturant action of dodine's guanidyl headgroup is counteracted by its aliphatic tail, which stabilizes amphipathic helices and associates with an expanded protein core. The Janus-like behavior of headgroup and tail make dodine a simultaneous stabilizer-destabilizer or "kosmo-chaotrope".
