Investigation of intercalation in graphite electrodes with in-situ imaging

Intercalation in layered materials is a rapidly growing area of research to develop next‐generation energy‐storage and optoelectronic devices, including batteries, sensors, transistors, and electrically tunable displays. Advances in few‐layer intercalation are addressed in the historical context of bulk intercalation (Chapter 1), emphasizing electrochemical techniques, mechanism of intercalation, and optoelectronic properties. Despite immense progress, there is still a critical need for simple devices that enable in-situ characterization of a variety of layered electrodes across the electromagnetic spectrum. In addition, a straightforward method of analyzing staging and calculating transport rates in layered materials from in-situ optical measurements would facilitate direct comparisons between experimental observations and computational models. This work describes efforts to address both of these needs through device design (Chapter 3) and the development of an image analysis platform (Chapter 4). Detailed synthesis, characterization, and electrochemical methods are described in Chapter 2. Engineering electrode materials for optoelectronic and energy storage applications requires a fundamental understanding of intercalation using spatially-resolved techniques. However, spectroscopic methods can have limited spatial resolution and low intensity since the signal passes through electrolyte. In Chapter 3, a device geometry is presented in which the electrolyte is laterally separated from the area probed spectroscopically, so that the signal does not pass through the electrolyte. This geometry enables us to visualize ion transport with optical microscopy and monitor charge transfer with Raman and visible reflectance spectroscopies. In addition, vibrational changes are probed in the mid-IR, a region previously difficult to access due to electrolyte absorption. Our observation of colorful domains (i.e. intercalant islands) that move rapidly during the stage 2-1 transition in Chapter 3 motivated us to investigate origin of these colors and transport rates (Chapter 4). We designed an image analysis program in Python to analyze color patterns and calculate (de)intercalation rates of the moving domains. This multifunctional program enabled us to compare differences in the distribution of transport rates among different domains, colors, and (de)intercalation. Our observations support a substage model of intercalation and suggest that structural features and electrostatic interactions affect ion transport.Doctor of Philosoph

Structural and Energetic Determinants of Apo Calmodulin Binding to the IQ Motif of the NaV1.2 Voltage-Dependent Sodium Channel

SummaryThe neuronal voltage-dependent sodium channel (Nav1.2), essential for generation and propagation of action potentials, is regulated by calmodulin (CaM) binding to the IQ motif in its α subunit. A peptide (Nav1.2IQp, KRKQEEVSAIVIQRAYRRYLLKQKVKK) representing the IQ motif had higher affinity for apo CaM than (Ca2+)4-CaM. Association was mediated solely by the C-domain of CaM. A solution structure (2KXW.pdb) of apo 13C,15N-CaM C-domain bound to Nav1.2IQp was determined with NMR. The region of Nav1.2IQp bound to CaM was helical; R1902, an Nav1.2 residue implicated in familial autism, did not contact CaM. The apo C-domain of CaM in this complex shares features of the same domain bound to myosin V IQ motifs (2IX7) and bound to an SK channel peptide (1G4Y) that does not contain an IQ motif. Thermodynamic and structural studies of CaM-Nav1.2IQp interactions show that apo and (Ca2+)4-CaM adopt distinct conformations that both permit tight association with Nav1.2IQp during gating

The construction and evaluation of tests to determine the ability of fifth and sixth grade pupils to select relevant materials in the social studies

Thesis (M.A.)--Boston Universit

Math Tutoring Choice Board (Version 2)

This choice board invites students and teachers to Draw math comics about mathematical concepts. Create a 3D monument to honor women mathematicians. Make a math story using stop motion animation. Write a poem using the Fibonacci sequence in nature. And many more ways to explore and learn math.https://scholarworks.umass.edu/tecs_ed_materials/1053/thumbnail.jp

Identification of the intermediate allosteric species in human hemoglobin reveals a molecular code for cooperative switching

The 10 ligation species of human cyanomethemoglobin were previously found to distribute into three discrete cooperative free energy levels according to a combinatorial code (i.e., dependent on both the number and configuration of ligated subunits). Analysis of this distribution showed that the hemoglobin tetramer occupies a third allosteric state in addition to those of the unligated (T) and fully ligated (R) species. To determine the nature of the intermediate allosteric state, we have studied the effects of pH, temperature, and single-site mutations on its free energy of quaternary assembly, in parallel with corresponding data on the deoxy (T) and fully ligated (R) species. Results indicate that the intermediate allosteric tetramer has the deoxy (T) quaternary structure. This finding, together with the resolved energetic distribution of the 10 microstates reveals a symmetry rule for quaternary switching - i.e., switching from T to R occurs whenever a binding step creates a tetramer with one or more ligated subunits on each side of the α1β2 intersubunit contact. These studies also reveal significant cooperativity within each α1β2 dimer of the T-state tetramer. The ligand-induced tertiary free energy alters binding affinity within the T structure by 170-fold prior to quaternary switching

Calmodulin and PI(3,4,5)P3 cooperatively bind to the Itk pleckstrin homology domain to promote efficient calcium signaling and IL-17A production

Precise regulation of the kinetics and magnitude of Ca2+ signaling enables this signal to mediate diverse responses, such as cell migration, differentiation, vesicular trafficking, and cell death. Here, we showed that the Ca2+-binding protein calmodulin (CaM) acted in a positive feedback loop to potentiate Ca2+ signaling downstream of the Tec kinase family member Itk. Using NMR (nuclear magnetic resonance), we mapped CaM binding to two loops adjacent to the lipid-binding pocket within the Itk pleckstrin homology (PH) domain. The Itk PH domain bound synergistically to Ca2+/CaM and the lipid phosphatidylinositol-3,4,5-trisphosphate [PI(3,4,5)P3], such that binding to Ca2+/CaM enhanced the binding to PI(3,4,5)P3 and vice versa. Disruption of CaM binding attenuated Itk recruitment to the membrane and diminished release of Ca2+ from the endoplasmic reticulum. Moreover, disruption of this feedback loop abrogated Itk-dependent production of the proinflammatory cytokine IL-17A (interleukin-17A) by CD4+ T cells. Additionally, we found that CaM associated with PH domains from other proteins, indicating that CaM may regulate other PH domain–containing proteins

A Dynamic Pathway for Calcium-Independent Activation of CaMKII by Methionine Oxidation

SummaryCalcium/calmodulin (Ca2+/CaM)-dependent protein kinase II (CaMKII) couples increases in cellular Ca2+ to fundamental responses in excitable cells. CaMKII was identified over 20 years ago by activation dependence on Ca2+/CaM, but recent evidence shows that CaMKII activity is also enhanced by pro-oxidant conditions. Here we show that oxidation of paired regulatory domain methionine residues sustains CaMKII activity in the absence of Ca2+/CaM. CaMKII is activated by angiotensin II (AngII)-induced oxidation, leading to apoptosis in cardiomyocytes both in vitro and in vivo. CaMKII oxidation is reversed by methionine sulfoxide reductase A (MsrA), and MsrA−/− mice show exaggerated CaMKII oxidation and myocardial apoptosis, impaired cardiac function, and increased mortality after myocardial infarction. Our data demonstrate a dynamic mechanism for CaMKII activation by oxidation and highlight the critical importance of oxidation-dependent CaMKII activation to AngII and ischemic myocardial apoptosis