Methyl esters were produced at several temperatures (10, 35, and 45 °C) by transesterification batch reactions of soybean oil with methanol utilizing KOH and NaOH catalysts. The reactions were monitored by aliquot removal and subsequent proton nuclear magnetic resonance spectroscopy (1H NMR) analysis. 1H NMR analysis allowed for the calculation of the average degree of fatty acid unsaturation (DU = 1.52) in oil and methyl ester. 1H NMR analysis also provided initial rates of methyl ester formation and an activation energy of 27.2 kJ/mol. The time-dependent concentration data revealed substantial reaction progress toward equilibrium after only 120 s at a reduced temperature of 10 °C. Understanding the resonance shifts in the 1H NMR spectra of starting materials and products allows for quantitation of reaction progress that is in good agreement with results obtained using other analytical methods.
The exact positions of critical points in the charge density in enzyme active sites reflects electrostatic preorganization.
A major chemical challenge facing implementation of 225 Ac in targeted alpha therapyan emerging technology that has potential for treatment of diseaseis identifying an 225 Ac chelator that is compatible with in vivo applications. It is unclear how to tailor a chelator for Ac binding because Ac coordination chemistry is poorly defined. Most Ac chemistry is inferred from radiochemical experiments carried out on microscopic scales. Of the few Ac compounds that have been characterized spectroscopically, success has only been reported for simple inorganic ligands. Toward advancing understanding in Ac chelation chemistry, we have developed a method for characterizing Ac complexes that contain highly complex chelating agents using small quantities (μg) of 227 Ac. We successfully characterized the chelation of Ac 3+ by DOTP 8− using EXAFS, NMR, and DFT techniques. To develop confidence and credibility in the Ac results, comparisons with +3 cations (Am, Cm, and La) that could be handled on the mg scale were carried out. We discovered that all M 3+ cations (M = Ac, Am, Cm, La) were completely encapsulated within the binding pocket of the DOTP 8− macrocycle. The computational results highlighted the stability of the M(DOTP) 5− complexes.
In this Perspective, we provide a brief background on the use of aromatic phosphonic acid modifiers for tuning work functions of transparent conducting oxides, for example, zinc oxide (ZnO) and indium tin oxide (ITO). We then introduce our preliminary results in this area using conjugated phosphonic acid molecules, having a substantially larger range of dipole moments than their unconjugated analogues, leading to the tuning of ZnO and ITO electrodes over a 2 eV range as derived from Kelvin probe measurements. We have found that these work function changes are directly correlated to the magnitude and the direction of the computationally derived molecular dipole of the conjugated phosphonic acids, leading to the predictive power of computation to drive the synthesis of new and improved phosphonic acid ligands.
Commercial lithium-ion battery cells were cycled to various depths of discharge at various rates while the relative capacities were periodically measured. After 1000 cycles, lithium cobalt oxide (LiCoO 2) cathode material was extracted from the most severely aged cell. Nanoindentation was performed on individual LiCoO 2 particles. Fractures in these particles exhibited anisotropic behavior, which was confirmed by electron microscopy and diffraction examination indicating both intra-and inter-granular fracture occurred along {001} planes. Computation of the charge density structure for LiCoO 2 indicated that the Li-O bonds along the {001} planes require the lowest energy for cleavage, supporting the experimental findings. Atom probe tomography (APT) analysis indicated the nanoscale composition distributions within specimens from both fresh and cycled material. Among the cycled particles, nanoscale inhomogeneities in the Li content were observed. For APT specimens containing grain boundaries, accumulation of Li (up to 80 at%) on one side of the boundary was observed. Correlation of the electrochemical, mechanical, and compositional results indicates a combination of these mechanical and chemical mechanisms contributed to the measured capacity fade.
Actinium-225 (225Ac) is an excellent candidate for targeted radiotherapeutic applications for treating cancer, because of its 10-day half-life and emission of four high-energy α2+ particles. To harness and direct the energetic potential of actinium, strongly binding chelators that remain stable in vivo during biological targeting must be developed. Unfortunately, controlling chelation for actinium remains challenging. Actinium is the largest +3 cation on the periodic table and has a 6d05f0 electronic configuration, and its chemistry is relatively unexplored. Herein, we present theoretical work focused on improving the understanding of actinium bonding with macrocyclic chelating agents as a function of (1) macrocycle ring size, (2) the number and identity of metal binding functional groups, and (3) the length of the tether linking the metal binding functional group to the macrocyclic backbone. Actinium binding by these chelators is presented within the context of complexation with DOTA4–, the most relevant Ac3+ binding agent for contemporary radiopharmaceutical applications. The results enabled us to develop a new strategy for actinium chelator design. The approach is rooted in our identification that Ac3+–chelation chemistry is dominated by ionic bonding interactions and relies on (1) maximizing electrostatic interactions between the metal binding functional group and the Ac3+ cation and (2) minimizing electronic repulsion between negatively charged actinium binding functional groups. This insight will provide a foundation for future innovation in developing the next generation of multifunctional actinium chelators.
Histone deacetylases (HDACs) are responsible for the removal of acetyl groups from histones, resulting in gene silencing. Overexpression of HDACs is associated with cancer, and their inhibitors are of particular interest as chemotherapeutics. However, HDACs remain a target of mechanistic debate. HDAC class 8 is the most studied HDAC, and of particular importance due to its human oncological relevance. HDAC8 has traditionally been considered to be a Zn-dependent enzyme. However, recent experimental assays have challenged this assumption and shown that HDAC8 is catalytically active with a variety of different metals, and that it may be a Fedependent enzyme in vivo. We studied two opposing mechanisms utilizing a series of divalent metal ions in physiological abundance (Zn ). Extensive sampling of the entire protein with different bound metals was done with the mixed quantum-classical QM/DMD method. Density functional theory (DFT) on an unusually large cluster model was used to describe the active site and reaction mechanism. We have found that the reaction profile of HDAC8 is similar among all metals tested, and follows one of the previously published mechanisms, but the rate-determining step is different from the one previously claimed. We further provide a scheme for estimating the metal binding affinities to the protein. We use the quantum theory of atoms in molecules (QTAIM) to understand the different binding affinities for each metal in HDAC8 as well as the ability of each metal to bind and properly orient the substrate for deacetylation. The combination of this data with the catalytic rate constants is required to reproduce the experimentally observed trend in metal-depending performance. We predict Co 2+ and Zn 2+ to be the most active metals in HDAC8, followed by Fe 2+ , and Mn 2+ and Mg 2+ to be the least active. ■ INTRODUCTIONThe acetylation of lysine residues is an important reversible post-translational modification that modulates protein function, affecting a variety of cellular processes. 1−5 Proteomic surveys 6−8 have identified acetyl-lysine residues in diverse groups of proteins, including transcription factors, 9,10 cell signaling proteins, 11 metabolic enzymes (most prominently acetyl-CoA synthase 12−14 ), structural proteins in the cytoskeleton, 15,16 and HIV viral proteins. 17,18 One of the first discovered examples of lysine acetylation was that occurring in histones, 19,20 the predominant protein components of chromatin. Acetylation of histones has been linked to gene regulation: the addition of an acetyl moiety to histone lysine residues gives rise to an open chromatin structure that facilitates DNA transcription, while the removal of acetyl from histone acetyl-lysine residues is associated with a closed chromatin structure, transcriptional repression, and gene silencing. 21 The enzymes responsible for the addition and removal of acetyl groups are known as histone acetyltransferases (HATs) and histone deacetylases (HDACs) 22−26 for historical reasons, although it is now recog...
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