Full elucidation of the functions and homeostatic pathways of biological copper requires tools that can selectively recognize and manipulate this trace nutrient within living cells and tissues, where it exists primarily as Cu . Buffered at attomolar concentrations, intracellular Cu is, however, not readily accessible to commonly employed amine and thioether-based chelators. Herein, we reveal a chelator design strategy in which phosphine sulfides aid in Cu coordination while simultaneously stabilizing aliphatic phosphine donors, producing a charge-neutral ligand with low-zeptomolar dissociation constant and 10 -fold selectivity for Cu over Zn , Fe , and Mn . As illustrated by reversing ATP7A trafficking in cells and blocking long-term potentiation of neurons in mouse hippocampal brain tissue, the ligand is capable of intercepting copper-dependent processes. The phosphine sulfide-stabilized phosphine (PSP) design approach, which confers resistance towards protonation, dioxygen, and disulfides, could be readily expanded towards ligands and probes with tailored properties for exploring Cu in a broad range of biological systems.

Fragile X syndrome (FXS)—caused by FMR1 gene silencing—is a severe neurodevelopmental disorder characterized by intellectual disabilities that are often comorbid with seizures, sensory hypersensitivities, anxiety, social deficits, and repetitive behaviors. Neuronal hyperexcitability is an overarching neurophysiological characteristic of FXS that may underlie FXS symptoms. About 33% of Fmr1 KO mice from our colony exhibit spontaneous seizures, a newly observed phenotype that more closely parallels seizures in FXS, compared to the audiogenic seizure phenotype in Fmr1 KO mice. In addition, we and others show that Fmr1 KO mice, like individuals with FXS, have cortical EEG gamma‐band power alterations, and at the single‐cell level, have hyperexcitable pyramidal neurons in multiple brain regions. We are using a combinatorial approach—from behavioral to EEG to single‐cell experiments—to advance FXS drug discovery. Based on our observations of altered brain expression and in vivo function of serotonin 1A receptors (5‐HT1ARs) in Fmr1 KO mice and correction of the audiogenic seizure phenotype by our novel 2‐aminotetralin‐type 5‐HT1R modulator, FPT, we are testing the hypothesis that selectively activating 5‐HT1ARs prevents seizures and corrects neurophysiological abnormalities. We evaluated the efficacy of FPT (5.6 mg/kg), a potent and efficacious 5‐HT1AR agonist, to correct EEG abnormalities in Fmr1 KO mice. We also tested the antiepileptic effects of the selective 5‐HT1AR agonist, NLX‐112 (0.25‐2.5 mg/kg), and are currently testing the effects of FPT and NLX‐112 on CA1 pyramidal neuron hyperexcitability in Fmr1 KO mice. In parallel experiments, we are evaluating the pharmacology of FPT and NLX‐112 at each of the 5‐HT G protein‐coupled receptors. Recordings from above the left somatosensory cortex showed a significantly elevated high gamma (65‐100 Hz) power ratio in Fmr1 KO mice relative to control mice at baseline (n=16, P=0.0357) and after vehicle injection (n=16, P=0.0066), a genotype difference that FPT eliminated (n=15‐16, P=0.6279). Comparisons between baseline and first injection conditions also revealed an increased delta power in Fmr1 KO mice relative to controls. Separately, NLX‐112 prevented audiogenic seizures in Fmr1 KO mice (n=10‐12, P≤0.0002), and preliminary data suggest NLX‐112 and FPT modulate CA1 pyramidal neuron activity. For example, FPT (10 µM) showed a reversible reduction of firing frequency of hippocampal CA1 neurons in Fmr1 KO mice (n=8, P<0.05). Forthcoming experiments will include evaluating the effects of NLX‐112 on cortical EEG activity in Fmr1 KO and control mice and the effects of chronic NLX‐112 and FPT on spontaneous seizures in Fmr1 KO mice. Tests of the selective 5‐HT1AR antagonist, WAY100635, will be conducted to examine a 5‐HT1AR mechanism underlying positive outcomes of NLX‐112 and FPT. At present, our convergent data suggest that 5‐HT1AR activation may ameliorate neuronal hyperexcitability, at multiple levels of analysis, in Fmr1 KO mice. Potent and selective 5‐HT1AR agonists might ...

Full elucidation of the functions and homeostatic pathways of biological copper requires tools that can selectively recognize and manipulate this trace nutrient within living cells and tissues, where it exists primarily as CuI. Buffered at attomolar concentrations, intracellular CuI is, however, not readily accessible to commonly employed amine and thioether‐based chelators. Herein, we reveal a chelator design strategy in which phosphine sulfides aid in CuI coordination while simultaneously stabilizing aliphatic phosphine donors, producing a charge‐neutral ligand with low‐zeptomolar dissociation constant and 1017‐fold selectivity for CuI over ZnII, FeII, and MnII. As illustrated by reversing ATP7A trafficking in cells and blocking long‐term potentiation of neurons in mouse hippocampal brain tissue, the ligand is capable of intercepting copper‐dependent processes. The phosphine sulfide‐stabilized phosphine (PSP) design approach, which confers resistance towards protonation, dioxygen, and disulfides, could be readily expanded towards ligands and probes with tailored properties for exploring CuI in a broad range of biological systems.

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Equivalent circuit models of a stripline have been proposed previously but most of them are either in a very complex form or are only able to model striplines in homogeneous media. In this work, modal decomposition technique is applied and a simple equivalent circuit model for a stripline in inhomogeneous substrate is proposed. Comparison with other models is also presented.