Kβ X-Ray Emission Spectroscopic Study of a Second-Row Transition Metal (Mo) and Its Application to Nitrogenase-Related Model Complexes

In recent years, X-ray emission spectroscopy (XES) in the Kβ (3p-1s) and valence-to-core (valence-1s) regions has been increasingly used to study metal active sites in (bio)inorganic chemistry and catalysis, providing information about the metal spin state, oxidation state and the identity of coordinated ligands. However, to date this technique has been limited almost exclusively to first-row transition metals. In this work, we present an extension of Kβ XES (in both the 4p-1s and valence-to-1s [or VtC] regions) to the second transition row by performing a detailed experimental and theoretical analysis of the molybdenum emission lines. It is demonstrated in this work that Kβ₂ lines are dominated by spin state effects, while VtC XES of a 4d transition metal provides access to metal oxidation state and ligand identity. An extension of Mo Kβ XES to nitrogenase-relevant model complexes shows that the method is sufficiently sensitive to act as a spectator probe for redox events that are localized at the Fe atoms. Mo VtC XES thus has promise for future applications to nitrogenase, as well as a range of other Mo-containing biological cofactors. Further, the clear assignment of the origins of Mo VtC XES features opens up the possibility of applying this method to a wide range of second-row transition metals, thus providing chemists with a site-specific tool for the elucidation of 4d transition metal electronic structure.     

(ω,c)-asymptotically periodic functions,first-order Cauchy problem,and Lasota-Wazewska model with unbounded oscillating production of red cells

In this paper, we study a new class of functions, which we call (ω,c)-asymptotically periodic functions. This collection includes asymptotically periodic, asymptotically antiperiodic, asymptotically Bloch-periodic, and unbounded functions. We prove that the set conformed by these functions is a Banach space with a suitable norm. Furthermore, we show several properties of this class of functions as the convolution invariance. We present some examples and a composition result. As an application, we prove the existence and uniqueness of (ω,c)-asymptotically periodic mild solutions to the first-order abstract Cauchy problem on the real line. Also, we establish some sufficient conditions for the existence of positive (ω,c)-asymptotically periodic solutions to the Lasota-Wazewska equation with unbounded oscillating production of red cells.     

Conformational Effects of Regioisomeric Substitution on the Catalytic Activity of Copper/Calix[8]arene C−S Coupling

Functionalization of the phenolic rim of p-tert-butylcalix[8]arene with phenanthroline to create a cavity leads to formation of two regioisomers. Substitution of positions 1 and 5 produces the known C_2v-symmetric regioisomer 1,5-(2,9-dimethyl-1,10-phenanthroyl)-p-tert-butylcalix[8]arene ( L^1,5 ), while substitution of positions 1 and 4 produces the C_s-symmetric regioisomer 1,4-(2,9-dimethyl-1,10-phenanthroyl)-p-tert-butylcalix[8]arene ( L^1,4 ) described herein. [ Cu(L^1,4)I ] was synthesized from L^1,4 and CuI in good yield and characterized spectroscopically. To evaluate the effect of its cavity on catalysis, Ullmann-type C−S coupling was chosen as proof-of-concept. Selected aryl halides were used, and the results compared with the previously reported Cu(I)/ L^1,5 system. Only highly activated aryl halides generate the C−S coupling product in moderate yields with the Cu(I)/ L^1,4 system. To shed light on these observations, detailed computational investigations were carried out, revealing the influence of the calix[8]arene macrocyclic morphology on the accessible conformations. The L^1,4 regioisomer undergoes a deformation that does not occur with L^1,5 , resulting in an exposed catalytic center, presumably the cause of the low activity of the former system. The 1,4-connectivity was confirmed in the solid-state structure of the byproduct [ Cu(L^1,4 − H) (CH₃CN)₂] that features Cu(I) coordinated inside a cleft defined by the macrocyclic framework.     

Hypertension in Prenatally Undernourished Young-Adult Rats Is Maintained by Tonic Reciprocal Paraventricular–Coerulear Excitatory Interactions

Prenatally malnourished rats develop hypertension in adulthood, in part through increased α₁-adrenoceptor-mediated outflow from the paraventricular nucleus (PVN) to the sympathetic system. We studied whether both α₁-adrenoceptor-mediated noradrenergic excitatory pathways from the locus coeruleus (LC) to the PVN and their reciprocal excitatory CRFergic connections contribute to prenatal undernutrition-induced hypertension. For that purpose, we microinjected either α₁-adrenoceptor or CRH receptor agonists and/or antagonists in the PVN or the LC, respectively. We also determined the α₁-adrenoceptor density in whole hypothalamus and the expression levels of α_1A-adrenoceptor mRNA in the PVN. The results showed that: (i) agonists microinjection increased systolic blood pressure and heart rate in normotensive eutrophic rats, but not in prenatally malnourished subjects; (ii) antagonists microinjection reduced hypertension and tachycardia in undernourished rats, but not in eutrophic controls; (iii) in undernourished animals, antagonist administration to one nuclei allowed the agonists recover full efficacy in the complementary nucleus, inducing hypertension and tachycardia; (iv) early undernutrition did not modify the number of α₁-adrenoceptor binding sites in hypothalamus, but reduced the number of cells expressing α_1A-adrenoceptor mRNA in the PVN. These results support the hypothesis that systolic pressure and heart rate are increased by tonic reciprocal paraventricular–coerulear excitatory interactions in prenatally undernourished young-adult rats.     

QM/MM modeling of the hydroxylation of the androstenedione substrate catalyzed by cytochrome P450 aromatase (CYP19A1)

CYP19A1 aromatase is a member of the Cytochrome P450 family of hemeproteins, and is the enzyme responsible for the final step of the androgens conversion into the corresponding estrogens, via a three‐step oxidative process. For this reason, the inhibition of this enzyme plays an important role in the treatment of hormone‐dependent breast cancer. The first catalytic subcycle, corresponding to the hydroxilation of androstenedione, has been proposed to occur through a first hydrogen abstraction and a subsequent oxygen rebound step. In present work, we have studied the mechanism of the first catalytic subcycle by means of hybrid quantum mechanics/molecular mechanics methods. The inclusion of the protein flexibility has been achieved by means of Free Energy Perturbation techniques, giving rise to a free energy of activation for the hydrogen abstraction step of 13.5 kcal/mol. The subsequent oxygen rebound step, characterized by a small free energy barrier (1.5 kcal/mol), leads to the hydroxylated products through a highly exergonic reaction. In addition, an analysis of the primary deuterium kinetic isotopic effects, calculated for the hydrogen abstraction step, reveals values (～10) overpassing the semiclassical limit for the C? H, indicating the presence of a substantial tunnel effect. Finally, a decomposition analysis of the interaction energy for the substrate and cofactor in the active site is also discussed. According to our results, the role of the enzymatic environment consists of a transition state stabilization by means of dispersive and polarization effects. © 2015 Wiley Periodicals, Inc.     

Aptamer-based detection of thrombin by acoustic method using DNA tetrahedrons as immobilisation platform

The thickness shear mode acoustic method was used to study the binding of thrombin to DNA aptamers immobilised on the gold surface covered by DNA tetrahedrons. The binding of thrombin to conventional aptamers sensitive to fibrinogen (FBT) and heparin (HPT) exosites as well as to HPT in a loop configuration (HPTloop) made it possible to determine the constant of dissociation (K_D) and the limit of detection (LOD). The sensing system composed of a HPTloop was characterised by K_D = (66.7 ± 22.7) nM, which was almost twice as low as that of FBT and HPT. For this biosensor, a lower LOD of 5.2 nM compared with 17 nM for conventional HPT aptamers was also obtained. Less sensitive sensors based on FBT aptamers revealed an LOD of 30 nM which is in agreement with the lower affinity of these aptamers to thrombin in comparison with that of HPT. The surface concentration of DNA tetrahedrons was determined by the electrochemical method using [Ru(NH₃)₆]³⁺ as a redox probe. These experiments confirmed that the “step by step” method of forming the sensing layer, consisting first in chemisorption of DNA tetrahedrons onto a gold surface and then in hybridisation of the aptamer-supporting part with complementary oligos at the top of the tetrahedron, is preferable. In addition, atomic force microscopy was applied to analyse the topography of the gold layers modified stepwise by DNA tetrahedrons, DNA aptamers and thrombin. The height profiles of the layers were in reasonable agreement with the dimensions of the adsorbed molecules. The results indicate that DNA tetrahedrons represent an efficient platform for immobilisation of aptamers.     

Multitarget Drug Discovery for Alzheimer's Disease: Triazinones as BACE‐1 and GSK‐3β Inhibitors

Cumulative evidence strongly supports that the amyloid and tau hypotheses are not mutually exclusive, but concomitantly contribute to neurodegeneration in Alzheimer′s disease (AD). Thus, the development of multitarget drugs which are involved in both pathways might represent a promising therapeutic strategy. Accordingly, reported here in is the discovery of 6‐amino‐4‐phenyl‐3,4‐dihydro‐1,3,5‐triazin‐2(1H)‐ones as the first class of molecules able to simultaneously modulate BACE‐1 and GSK‐3β. Notably, one triazinone showed well‐balanced in vitro potencies against the two enzymes (IC₅₀ of (18.03±0.01) μM and (14.67±0.78) μM for BACE‐1 and GSK‐3β, respectively). In cell‐based assays, it displayed effective neuroprotective and neurogenic activities and no neurotoxicity. It also showed good brain permeability in a preliminary pharmacokinetic assessment in mice. Overall, triazinones might represent a promising starting point towards high quality lead compounds with an AD‐modifying potential.