Linh Pham

Tetranuclear Lanthanide(III) Complexes with a Zigzag Topology from the Use of Pyridine-2,6-dimethanol: Synthetic, Structural, Spectroscopic, Magnetic and Photoluminescence Studies

Reaction between Ln(NO3)3·xH2O (x = 5 or 6) and the potentially tridentate (N,O,O) chelating/bridging ligand pyridine-2,6-dimethanol (pdmH2), in the presence of base NEt3, affords a family of isostructural tetranuclear [Ln(III)4(NO3)2(pdmH)6(pdmH2)2](NO3)4 (Ln(III) = Eu(III), Gd(III), Tb(III), Dy(III), Ho(III), Er(III), Yb(III)) complexes with a rare zigzag topology. All complexes contain a [Ln4(μ-OR)6](6+) core with bridging ligation provided by the alkoxido arms of six η(1):η(1):η(2):μ pdmH(-) groups. The Ln(III) ions are eight coordinate with distorted geometries. Direct current magnetic susceptibility studies revealed predominant weak antiferromagnetic exchange interactions between the metal centers, which were quantified in the case of isotropic Gd(III)4 to give J = -0.09(1) cm(-1) and g = 2.00(1). The observation of out-of-phase (χ″M) ac susceptibility signals suggested that the Dy(III)4 analogue might be a molecular nanomagnet. Solid-state photoluminescence studies showed that the Eu(III)4 and Tb(III)4 compounds exhibit intense, sharp, and narrow emission bands in the red and green visible regions, respectively, which arise from the characteristic (5)D0 → (7)FJ and (5)D4 → (7)FJ transitions. The combined results demonstrate the ability of pdmH2 ligand to yield homometallic 4f clusters with interesting magnetic and optical properties.

Magnetic “Molecular Oligomers” Based on Decametallic Supertetrahedra: A Giant Mn49 Cuboctahedron and its Mn25Na4 Fragment

Two nanosized Mn49 and Mn25Na4 clusters based on analogues of the high-spin (S=22) [Mn(III)6Mn(II)4(μ4-O)4](18+) supertetrahedral core are reported. Mn49 and Mn25Na4 complexes consist of eight and four decametallic supertetrahedral subunits, respectively, display high virtual symmetry (O(h)), and are unique examples of clusters based on a large number of tightly linked high nuclearity magnetic units. The complexes also have large spin ground-state values (Mn49: S=61/2; Mn25Na4: S=51/2) with the Mn49  cluster displaying single-molecule magnet (SMM) behavior and being the second largest reported homometallic SMM.

A Chiral, Low-Cytotoxic [Ni15]-Wheel Complex

A new chiral [Ni15] complex with a Schiff-base ligand derived from o-vanillin and L-glutamic acid is presented, emphasizing the properties relevant for biology and materials science. The formation of the complex molecules in solution is confirmed by AFM and dynamic light scattering studies. The compound is weakly antiferromagnetic with considerable admixture of excited states, comprising negligibly interacting [Ni3] units. Studies of the interactions with two cell lines indicate low cytotoxicity.

Capturing reading patterns through a real-time smart camera iris tracking system

A real-time iris detection and tracking algorithm has been implemented on a smart camera using LabVIEW graphical programming tools. The program detects the eye and finds the center of the iris, which is recorded and stored in Cartesian coordinates. In subsequent video frames, the location of the center of the iris corresponding to the previously detected eye is computed and recorded for a desired period of time, creating a list of coordinates representing the moving iris center location across image frames. We present an application for the developed smart camera iris tracking system that involves the assessment of reading patterns. The purpose of the study is to identify differences in reading patterns of readers at various levels to eventually determine successful reading strategies for improvement. The readers are positioned in front of a computer screen with a fixed camera directed at the readers eyes. The readers are then asked to read preselected content on the computer screen, one comprising a traditional newspaper text and one a Web page. The iris path is captured and stored in real-time. The reading patterns are examined by analyzing the path of the iris movement. In this paper, the iris tracking system and algorithms, application of the system to real-time capture of reading patterns, and representation of 2D/3D iris track are presented with results and recommendations.

Effects of Hinge-region Natural Polymorphisms on Human Immunodeficiency Virus-Type 1 Protease Structure, Dynamics, and Drug Pressure Evolution.

Multidrug resistance to current Food and Drug Administration-approved HIV-1 protease (PR) inhibitors drives the need to understand the fundamental mechanisms of how drug pressure-selected mutations, which are oftentimes natural polymorphisms, elicit their effect on enzyme function and resistance. Here, the impacts of the hinge-region natural polymorphism at residue 35, glutamate to aspartate (E35D), alone and in conjunction with residue 57, arginine to lysine (R57K), are characterized with the goal of understanding how altered salt bridge interactions between the hinge and flap regions are associated with changes in structure, motional dynamics, conformational sampling, kinetic parameters, and inhibitor affinity. The combined results reveal that the single E35D substitution leads to diminished salt bridge interactions between residues 35 and 57 and gives rise to the stabilization of open-like conformational states with overall increased backbone dynamics. In HIV-1 PR constructs where sites 35 and 57 are both mutated (e.g. E35D and R57K), x-ray structures reveal an altered network of interactions that replace the salt bridge thus stabilizing the structural integrity between the flap and hinge regions. Despite the altered conformational sampling and dynamics when the salt bridge is disrupted, enzyme kinetic parameters and inhibition constants are similar to those obtained for subtype B PR. Results demonstrate that these hinge-region natural polymorphisms, which may arise as drug pressure secondary mutations, alter protein dynamics and the conformational landscape, which are important thermodynamic parameters to consider for development of inhibitors that target for non-subtype B PR.