PKA-activation mechanism revised: Many hormone receptors stimulate production of cyclic AMP (adenosine monophosphate), which activates PKA (protein kinase A). The textbook view suggests that activation releases the catalytic subunit of the enzyme from its complex with the regulatory subunit. Smith et al. closely monitored activation of PKA in cultured human cells and found that dissociation of the holoenzyme was not necessary for activation. The kinase, which binds anchoring proteins that localize it in the cell, appears to be restricted to acting within about 200 Å of such anchoring proteins. Thus, PKA activity is more precisely targeted within the cell than previously anticipated. Science , this issue p. 1288

The thermostable four-coordinate divalent lanthanide (Ln) bis-amidinate complexes [Ln(Piso)₂] (Ln = Tb, Dy; Piso = {(NDipp)₂C^tBu}, Dipp = C₆H₃ⁱPr₂-2,6) were prepared by the reduction of parent five-coordinate Ln(III) precursors [Ln(Piso)₂I] (Ln = Tb, Dy) with KC₈; halide abstraction of [Ln(Piso)₂I] with [H(SiEt₃)₂][B(C₆F₅)] gave the respective Ln(III) complexes [Ln(Piso)₂][B(C₆F₅)]. All complexes were characterized by X-ray diffraction, ICP-MS, elemental analysis, SQUID magnetometry, UV-vis-NIR, ATR-IR, NMR, and EPR spectroscopy and ab initio CASSCF-SO calculations. These data consistently show that [Ln(Piso)₂] formally exhibit Ln(II) centers with 4fⁿ5d_z2¹ (Ln = Tb, n = 8; Dy, n = 9) valence electron configurations. We show that simple assignments of the f-d coupling to either L-S or J-s schemes are an oversimplification, especially in the presence of significant crystal field splitting. The coordination geometry of [Ln(Piso)₂] is intermediate between square planar and tetrahedral. Projecting from the quaternary carbon atoms of the CN₂ ligand backbones shows near-linear C···Ln···C arrangements. This results in strong axial ligand fields to give effective energy barriers to magnetic reversal of 1920(91) K for the Tb(II) analogue and 1964(48) K for Dy(II), the highest values observed for mononuclear Ln(II) single-molecule magnets, eclipsing 1738 K for [Tb(C₅ⁱPr₅)₂]. We tentatively attribute the fast zero-field magnetic relaxation for these complexes at low temperatures to transverse fields, resulting in considerable mixing of m_J states.

The magnetic moments and isotope shifts of the neutron-deficient francium isotopes $^{202\mathrm{\text{-}}205}\mathrm{Fr}$ were measured at ISOLDE-CERN with use of collinear resonance ionization spectroscopy. A production-to-detection efficiency of 1% was measured for $^{202}\mathrm{Fr}$. The background from nonresonant and collisional ionization was maintained below one ion in ${10}^{5}$ beam particles. Through a comparison of the measured charge radii with predictions from the spherical droplet model, it is concluded that the ground-state wave function remains spherical down to $^{205}\mathrm{Fr}$, with a departure observed in $^{203}\mathrm{Fr}$ ($N=116$).

The search for materials with improved mechanical and biological properties is a major challenge in tissue engineering. This paper investigates, for the first time, the use of Polyethylene Terephthalate Glycol (PETG), a glycol-modified class of Polyethylene Terephthalate (PET), as a potential material for the fabrication of bone scaffolds. PETG scaffolds with a 0/90 lay-dawn pattern and different pore sizes (300, 350 and 450 µm) were produced using a filament-based extrusion additive manufacturing system and mechanically and biologically characterized. The performance of PETG scaffolds with 300 µm of pore size was compared with polycaprolactone (PCL). Results show that PETG scaffolds present significantly higher mechanical properties than PCL scaffolds, providing a biomechanical environment that promotes high cell attachment and proliferation.

The CRIS setup at CERN-ISOLDE is a laser spectroscopy experiment dedicated to the high-resolution study of the spin, hyperfine structure and isotope shift of radioactive nuclei with low production rates (a few per second). It combines the Doppler-free resolution of the in-flight collinear geometry with the high detection efficiency of resonant ionisation. A recent commissioning campaign has demonstrated a 1% experimental efficiency, and as low as a 0.001% non-resonant ionisation. The current status of the experiment and its recent achievements with beams of francium isotopes are reported. The first identified systematic effects are discussed.status: publishe

The magnetic dipole moments and changes in mean-square charge radii of the neutron-rich ${}^{218m,219,229,231}\mathrm{Fr}$ isotopes were measured with the newly installed Collinear Resonance Ionization Spectroscopy (CRIS) beam line at the On-Line Isotope Mass Separator (ISOLDE), CERN, probing the $7s^2{S}_{1/2}$ to $8p^2{P}_{3/2}$ atomic transition. The $\delta {\langle r^2\rangle }^{A,221}$ values for ${}^{218m,219}\mathrm{Fr}$ and ${}^{229,231}\mathrm{Fr}$ follow the observed increasing slope of the charge radii beyond $N=126$. The charge radii odd-even staggering in this neutron-rich region is discussed, showing that ${}^{220}\mathrm{Fr}$ has a weakly inverted odd-even staggering while ${}^{228}\mathrm{Fr}$ has normal staggering. This suggests that both isotopes reside at the borders of a region of inverted staggering, which has been associated with reflection-asymmetric shapes. The $g{(}^{219}\mathrm{Fr})=+0.69\left(1\right)$ value supports a $\pi 1h_{9/2}$ shell-model configuration for the ground state. The $g{(}^{229,231}\mathrm{Fr})$ values support the tentative $I^{\pi }{(}^{229,231}\mathrm{Fr})=(1/2^{+})$ spin and point to a $\pi s_{1/2}^{-1}$ intruder ground-state configuration.