Deamination process in the formation of a copper(II) complex with glutamic acid and a new ligand derived from guanidinoacetic acid: Synthesis, characterization, and molecular modeling studies

The effect of guanidinium functionalization on the structural properties and anion affinity of polyelectrolyte multilayers

Poly(allylamine hydrochloride) (PAH) is chemically functionalized with guanidinium (Gu) moieties in water at room temperature. The resulting PAH-Gu is used to prepare polyelectrolyte multilayers (PEMs) with poly(sodium 4-styrene sulfonate) (PSS) via layer-by-layer deposition. The polyelectrolyte (PE) adsorption processes are monitored real-time by optical reflectometry and a quartz crystal microbalance with dissipation monitoring (QCM-D). Compared to the reference PSS/PAH PEMs, the PSS/PAH-Gu PEMs show a lower amount of deposited PE materials, lower wet thickness, higher stability under alkaline conditions and higher rigidity. These differences are rationalized by the additional Gu-SO3(-) interactions, also affecting the conformation of the PE chains in the PEM. The interactions between the PEMs and various sodium salts (NaCl, NaNO3, Na2SO4 and NaH2PO4) are also monitored using QCM-D. From the changes in the frequency, dissipation responses and supportive Reflection Absorption Infrared Spectroscopy it is concluded that Gu-functionalized PEMs absorb more H2PO4(-) compared to the Gu-free reference PEMs. This can be understood by strong interactions between Gu and H2PO4(-), the differences in the anion hydration energy and the anion valency. It is anticipated that compounds like the presented Gu-functionalized PE may facilitate the further development of H2PO4(-) sensors and ion separation/recovery systems.

Pulsed electron spin resonance resolves the coordination site of Cu²(+) ions in α1-glycine receptor

Herein, we identify the coordination environment of Cu²(+) in the human α1-glycine receptor (GlyR). GlyRs are members of the pentameric ligand-gated ion channel superfamily (pLGIC) that mediate fast signaling at synapses. Metal ions like Zn²(+) and Cu²(+) significantly modulate the activity of pLGICs, and metal ion coordination is essential for proper physiological postsynaptic inhibition by GlyR in vivo. Zn²(+) can either potentiate or inhibit GlyR activity depending on its concentration, while Cu²(+) is inhibitory. To better understand the molecular basis of the inhibitory effect we have used electron spin resonance to directly examine Cu²(+) coordination and stoichiometry. We show that Cu²(+) has one binding site per α1 subunit, and that five Cu²(+) can be coordinated per GlyR. Cu²(+) binds to E192 and H215 in each subunit of GlyR with a 40 μM apparent dissociation constant, consistent with earlier functional measurements. However, the coordination site does not include several residues of the agonist/antagonist binding site that were previously suggested to have roles in Cu²(+) coordination by functional measurements. Intriguingly, the E192/H215 site has been proposed as the potentiating Zn²(+) site. The opposing modulatory actions of these cations at a shared binding site highlight the sensitive allosteric nature of GlyR.