Publications

The alternating direction implicit finite difference method (ADIFDM) was used to simulate the steady-state as well as the transient (chronoamperometric) behavior of sphere-cap microelectrodes (SCMs). The necessary steps to implement the ADIFDM for solving the rather complex geometry involved are described. The results for the steady-state behavior are in excellent agreement with a previously suggested anal. soln. making the ADIFDM an excellent tool to develop a comprehensive theory for SCMs. [on SciFinder(R)]

We report here on the fabrication and optimization of composites of conjugated polymer in Sol-Gel and PVA matrices. FTIR spectroscopy as well as other observations show that efficient phase and absorption holograms can be created in the material upon illumination, via the photochromic effect. The main contribution to the absorption change is chain scission and photo-oxidation mechanism. Optimized holographic composites with diffraction efficiencies as high as 26% are shown. Beam interaction between the writing beams is observed for these composites, while the diffraction efficiencies was improved by an order of magnitude.

Computational results for the surface impact of (CH3I)(n) clusters are presented, and the dynamics of formation of molecular products is examined. The mechanism is compared to the high energy bimolecular CH3I + CH3I collision and to other reactions in impact-heated clusters, in particular, the burning of air. The results are discussed in reference to the experimentally: observed formation of molecular iodine (as I-2(-)) in surface collisions of (CH3I)(n)(-) clusters.

An approach to sol-gel film formation is described, involving electrochem. control of pH near a conductive surface, in which methyltrimethoxysilane (MeTMOS) is deposited onto indium tin oxide (ITO) and Au surfaces. The method is based on a 2-step sol-gel prepn. procedure in which MeTMOS is first pre-hydrolyzed and then polycondensed. A const. neg. potential is applied to the electrode surface, increasing the concn. of hydroxyl ions, which act as a catalyst in the condensation process. This results in greater control over the deposition process and thus over film properties. [on SciFinder(R)]

Electrochem. polymn. of 2',5'-bis(1-methylpyrrol-2-yl)thiophene (NSN) was carried out by scanning electrochem. microscopy, using Ru(bpy)33+ as oxidant for the polymn. process and for the ultramicroelectrode surface-distance probe. While this led to deposition of flat layers of polymer on a PMMA substrate, use of the weak oxidant IrCl62- gave sets of thin needles. Micrographs of the various patterns are shown (with resolns. of ≈ 15 μm) and the mechanism of polymn. is discussed. [on SciFinder(R)]

For large molecules, electronically excited stales are denser than can be simply judged from the gap between the ground state and excited states. This is particularly true for large open shell systems, such as peptide cations. In such systems, short laser pulses can be used to prepare initial electronic states that are not stationary. These are non Born-Oppenheimer states, and therefore, the motion of the nuclei is not determined by a single potential. It is argued that such states could offer the possibility of control of reactivity. They can impede the usually facile vibrational energy redistribution, which is characteristic for a motion on a potential surface with a well. After a localized ionization, the dependence of site-selective fragmentation of small peptide ions on time is discussed with computational results based on a Pariser-Parr-Pople Like electronic Hamiltonian. We predict a strong nonstatistical and site selective reactivity on a short time scale and also a dependence on the nature of the initial excitation. Results are presented for the fragmentation of Leu-Leu-Leu-Trp(+) and Ala-Ala-Ala-Tyr(+) ions and are compared with nanosecond laser pulse experiments.

The effective energy threshold for the crossing into an electronically excited state and the post threshold rise of the yield of crossing are discussed. The time-dependent Schrodinger equation for multiple electronic states is solved using the full multiple spawning (FMS) methodology. The quantal results are compared with classical path methods. The potential energy function is of the LEP form including the electronically excited surface. For kinematic reasons, the yield is exponentially small until an effective threshold, at similar to 10 km s(-1), with a steep rise of the yield in the post threshold regime. (C) 1999 Elsevier Science B.V. All rights reserved.

BACKGROUND: Among the approximately 6.5 million fractures suffered in the United States every year, about 15% are difficult to heal. As yet, for most of these difficult cases there is no effective therapy. We have developed a mouse radial segmental defect as a model experimental system for testing the capacity of Genetically Engineered Pluripotent Mesenchymal Cells (GEPMC, C3H10T1/2 clone expressing rhBMP-2), for gene delivery, engraftment, and induction of bone growth in regenerating bone. METHODS: Transfected GEPMC expressing rhBMP-2 were further infected with a vector carrying the lacZ gene, that encodes for beta-galactosidase (beta-gal). In vitro levels of rhBMP-2 expression and function were confirmed by immunohistochemistry, and bioassay. Differentiation was assayed using alkaline phosphatase staining. GEPMC were transplanted in vivo into a radial segmental defect. The main control groups included lacZ clones of WT-C3H10T1/2-LacZ, and CHO-rhBMP-2 cells. New bone formation was measured quantitatively via fluorescent labeling, X-ray analysis and histomorphometry. Engrafted mesenchymal cells were localized in vivo by beta-gal expression, and double immunofluorescence. RESULTS: In vitro, GEPMC expressed rhBMP-2, beta-gal and spontaneously differentiated into osteogenic cells expressing alkaline phosphatase. Detection of transplanted cells revealed engrafted cells that had differentiated into osteoblasts and co-expressed beta-gal and rhBMP-2. Analysis of new bone formation revealed that at four to eight week post-transplantation, GEPMS significantly enhanced segmental defect repair. CONCLUSIONS: Our study shows that cell-mediated gene transfer can be utilized for growth factor delivery to signaling receptors of transplanted cells (autocrine effect) and host mesenchymal cells (paracrine effect) suggesting the ability of GEPMC to engraft, differentiate, and stimulate bone growth. We suggest that our approach should lead to the designing of mesenchymal stem cell based gene therapy strategies for bone lesions as well as other tissues.