Homogeneity and variation of donor doping in Verneuil-grown SrTiO3:Nb single crystals

The homogeneity of Verneuil-grown SrTiO3:Nb crystals was investigated. Due to the fast crystal growth process, inhomogeneities in the donor dopant distribution and variation in the dislocation density are expected to occur. In fact, for some crystals optical studies show variations in the density of Ti(3+) states on the microscale and a cluster-like surface conductivity was reported in tip-induced resistive switching studies. However, our investigations by TEM, EDX mapping, and 3D atom probe reveal that the Nb donors are distributed in a statistically random manner, indicating that there is clearly no inhomogeneity on the macro-, micro-, and nanoscale in high quality Verneuil-grown crystals. In consequence, the electronic transport in the bulk of donor-doped crystals is homogeneous and it is not significantly channelled by extended defects such as dislocations which justifies using this material, for example, as electronically conducting substrate for epitaxial oxide film growth.

Site selective C-H functionalization of Mitragyna alkaloids reveals a molecular switch for tuning opioid receptor signaling efficacy

Mitragynine (MG) is the most abundant alkaloid component of the psychoactive plant material "kratom", which according to numerous anecdotal reports shows efficacy in self-medication for pain syndromes, depression, anxiety, and substance use disorders. We have developed a synthetic method for selective functionalization of the unexplored C11 position of the MG scaffold (C6 position in indole numbering) via the use of an indole-ethylene glycol adduct and subsequent iridium-catalyzed borylation. Through this work we discover that C11 represents a key locant for fine-tuning opioid receptor signaling efficacy. 7-Hydroxymitragynine (7OH), the parent compound with low efficacy on par with buprenorphine, is transformed to an even lower efficacy agonist by introducing a fluorine substituent in this position (11-F-7OH), as demonstrated in vitro at both mouse and human mu opioid receptors (mMOR/hMOR) and in vivo in mouse analgesia tests. Low efficacy opioid agonists are of high interest as candidates for generating safer opioid medications with mitigated adverse effects.

Hypervalent Iodine Based Reversible Covalent Bond in Rotaxane Synthesis

Reversible covalent bonds play a significant role in achieving the high-yielding synthesis of mechanically interlocked molecules. Still, only a handful of such bonds have been successfully employed in synthetic procedures. Herein, we introduce a novel approach for the fast and simple preparation of interlocked molecules, combining the dynamic bond character of bis(acyloxy)iodate(I) anions with macrocyclic bambusuril anion receptors. The proof of principle was demonstrated on rotaxane synthesis, with near-quantitative yields observed in both the classical and "in situ" approach. The rotaxane formation was confirmed in the solid-state and solution by the X-ray and NMR studies. Our novel approach could be utilized in the fields of dynamic combinatorial chemistry, supramolecular polymers, or molecular machines, as well inspire further research on molecules that exhibit dynamic behavior, but owing to their high reactivity, have not been considered as constituents of more elaborate supramolecular structures.

Unsubstituted Bambusurils: Post-Macrocyclization Modification of Versatile Intermediates

A new bambusuril derivative, (H)BU[6], lacking substituents on the ureidic nitrogen atoms, has been isolated and characterized. This macrocycle was prepared by the deprotection of bambusuril (PMB)BU[6]. (H)BU[6] is attractive for use as a starting compound for the preparation of other bambusuril derivatives, which was demonstrated via propargylation and the copper-catalyzed click reaction performed on the macrocycle.

Dynamic Interactions in Synthetic Receptors: A Guest Exchange Saturation Transfer Study

The accumulated knowledge regarding molecular architectures is based on established, reliable, and accessible analytical tools that provide robust structural and functional information on assemblies. However, both the dynamicity and low population of noncovalently interacting moieties within studied molecular systems limit the efficiency and accuracy of traditional methods. Herein, the use of a saturation transfer-based NMR approach to study the dynamic binding characteristics of an anion to a series of synthetic receptors derived from bambusuril macrocycles is demonstrated. The exchange rates of BF₄ ^- are mediated by the side chains on the receptor (100 s^-1 <k_ex <5000 s^-1 ), which play a critical role in receptor-anion binding dynamics. The signal amplification obtained with this approach allows for the identification of different types of intermolecular interactions between the receptor and the anion, something that could not have been detected by techniques hitherto used to study molecular assemblies. These findings, which are supported by a computational molecular dynamic study, demonstrate the uniqueness and added value of this NMR method.

[Long-term study of disorders of heart rhythm in patients with chronic diseases of the respiratory system]

The authors investigated the incidence of arrhythmias by the method of continuous recording of ECG tracings according to Holter in 16 patients with chronic respiratory diseases three times in the course of two years. The incidence of arrhythmias was very frequent, more serious disorders (class 3 or a higher class according to Lown's classification) were very rare. The authors provided evidence of a great variability in the incidence of arrhythmias in the same patients during different periods of investigation. They did not reveal a relationship between the incidence of arrhythmias and the degree of functional affection of the lungs, the severity of hypoxaemia and the drop of the maximum aerobic capacity of the lungs. They did not find a relationship between the incidence of arrhythmias and the pressure in the pulmonary artery, or the size of the right or left ventricle or the thickness of their wall. The authors do not consider the finding of arrhythmias in patients with chronic lung disease an unequivocally serious finding, as reported sometimes in the literature.