Azodicarboxylate-Mediated Peptide Cyclisation: Application to Disulfide Bond Formation in Solution and Solid Phase

Cyclic peptides are important molecules, playing key roles in protein architecture, as chemical probes, and increasingly as crucial structural elements of clinically-useful therapeutics. Herein we report methodology using azodicarboxylates as efficient reagents for the facile synthesis of cyclic peptides through a disulfide bridge. The utility of this approach in both solution and solid-phase, and compatibility with common amino acid side chain functionalities is demonstrated, resulting in cyclic peptides in good yield and purity. This approach has significant potential application for synthesis of molecules of biological or therapeutic significance.     

Cover Feature: Hg(II)⋅d8[M] Interactions: Are they Metallophilic Interactions or Spodium Bonds? (ChemPhysChem 24/2023)

Some literature reports have shown the existence of short Hg(II)⋅⋅⋅d⁸[M] (M=Pd, Pt) contacts between linear Hg(II) and square planar d⁸[M] complexes that have been defined as heterometallophilic interactions. Linear L−Hg(II)−L complexes exhibit a π-hole or positive belt of electrostatic potential at the Hg atom, whereas late transition metals can serve as effective electron donors through their filled d_z2 orbitals. This study provides compelling evidence that Hg(II)⋅⋅⋅d⁸[M] interactions should be more appropriately termed spodium bonds.     

The influence of a weak magnetic field in the Renormalization-Group functions of (2 + 1)-dimensional Dirac systems

The experimental observation of the renormalization of the Fermi velocity v _F as a function ofdoping has been a landmark for confirming the importance of electronic interactions ingraphene. Although the experiments were performed in the presence of a perpendicularmagnetic field B, the measurements are well described by arenormalization-group (RG) theory that did not include it. Here we clarify this issue, forboth massive and massless Dirac systems, and show that for the weak magnetic fields atwhich the experiments are performed, there is no change in the renormalization-groupfunctions. Our calculations are carried out in the framework of the Pseudo-quantumelectrodynamics (PQED) formalism, which accounts for dynamical interactions. We includeonly the linear dependence in B, and solve the problem using two differentparametrizations, the Feynman and the Schwinger one. We confirm the results obtainedearlier within the RG procedure and show that, within linear order in the magnetic field,the only contribution to the renormalization of the Fermi velocity for the massive casearises due to electronic interactions. In addition, for gapped systems, we observe arunning of the mass parameter.     

Methylmercury determination in biota by solid-phase microextraction matrix effect evaluation

Aqueous-phase alkylation followed by, headspace solid-phase microextraction (SPME) for mercury speciation in biota, was developed a decade ago. Despite this, matrix effects in this technique have not yet been addressed. In this paper, the importance of these effects has been assessed and overcome by standard addition calibration. Furthermore, improvements were made in the extraction of methylmercury (MeHg) from biological matrixes by optimizing the matrix digestion procedure (temperature and digestion time) and the SPME parameters (aliquot volume of digested samples, extraction temperature and fibre coating), which aimed to minimize the matrix effects. Accordingly, samples were alkaline digested (KOH, 25%, w/v, 60 degrees C, 180 min) and an aliquot was propylated using an aqueous NaBPr(4) solution, headspace SPME sampling and, finally, by using GC-pyrolysis (Py)-atomic fluorescence spectrometry (AFS) determination. The procedure developed was validated using dogfish muscle reference material NRCC DORM-2.     

Energetics of flavone and flavanone

In this work, we have determined the experimental standard (p° = 0.1 MPa) molar enthalpies of formation, in gas phase, of flavone and flavanone.These results were obtained by combining the standard molar enthalpies of formation in the condensed phase with the standard molar enthalpies of sublimation. The former values were derived from combustion experiments in oxygen, at T = 298.15 K, in a static bomb calorimeter. The values of the standard molar enthalpies of sublimation were obtained by Calvet microcalorimetry and corrected to T = 298.15 K.High-level density functional theory calculations using the B3LYP hybrid exchange–correlation energy functional with extended basis sets and more accurate correlated computational techniques of the MCCM/3 suite have been performed for the compounds.The obtained results, experimental and computational, for flavone and flavanone were compared with those obtained for chromone and chromanone, respectively.     

Toward a better description of gallo-phosphate materials in solid-state NMR: 1D and 2D correlation studies

We show that weak 2J(71Ga-O-31P), typically approximately 12 Hz in GaPO4, can be used to efficiently establish heteronuclear 31P-71Ga correlation using a MAS HMQC experiment in gallo-phosphate materials. The experiment demonstrated for cristobalite GaPO4 is then applied to Ga(PO3)3, where it allows the differentiation of the signature of three different Ga sites overlapping in the 1D spectrum.     

Matrix Algebras in Non-Hermitian Quantum Mechanics

In principle, non-Hermitian quantum equations of motion can be formulated using as a starting point either the Heisenberg's or the Schrödinger's picture of quantum dynamics. Here it is shown in both cases how to map the algebra of commutators, defining the time evolution in terms of a non-Hermitian Hamiltonian, onto a non-Hamiltonian algebra with a Hermitian Hamiltonian. The logic behind such a derivation is reversible, so that any Hermitian Hamiltonian can be used in the formulation of non-Hermitian dynamics through a suitable algebra of generalized (non-Hamiltonian) commutators.
These results provide a general structure (a template) for non-Hermitian equations of motion to be used in the computer simulation of open quantum systems dynamics.     

Conditions and evidence for non-integrability in the Friedmann-Robertson-Walker Hamiltonian

This is an example of application of Ziglin-Morales-Ramis algebraic studies in Hamiltonian integrability, more specifically the result by Morales, Ramis and Simó on higher-order variational equations, to the well-known Friedmann-Robertson-Walker cosmological model. A previous paper by the author formalises said variational systems in such a way allowing the simple expression of notable elements of the differential Galois group needed to study integrability. Using this formalisation and an alternative method already used by other authors, we find sufficient conditions whose fulfilment for given parameters would entail very simple proofs of non-integrability – both for the complete Hamiltonian, a goal already achieved by other means by Coelho et al, and for a special open case attracting recent attention.