Charles D. Spencer

Bio: Charles D. Spencer is an academic researcher from Ithaca College. The author has contributed to research in topics: Lattice constant & Troubleshooting. The author has an hindex of 4, co-authored 6 publications receiving 109 citations.

Digital Design for Computer Data Acquisition

Abstract: This digital electronics text focuses on "how to" design, build, operate and adapt data acquisition systems. The material begins with basic logic gates and ends with a 40 KHz voltage measurer. The approach aims to cover a minimal number of topics in detail.The data acquisition circuits described communicate with a host computer through parallel I/O ports. The fundamental idea of the book is that parallel I/O ports (available for all popular computers) offer a superior balance of simplicity, low cost, speed, flexibility and adaptability. All circuits and software are thoroughly tested. Construction details and troubleshooting guidelines are included. This book is intended to serve people who teach or study one of the following: digital electronics, circuit design, software that interacts outside hardware, the process of computer based acquisition, and the design, adaptation, construction and testing of measurement systems.

Interactions of porphyrins with nucleic acids

Abstract: The interactions of tetrakis(4-N-methylpyridyl)-porphine (H2TMpyP-4) and its copper(II), nickel(II), zinc(II), cobalt(III), iron(III), and manganese(III) derivatives with several nucleic acids have been investigated. Spectrophotometric titrations of H2TMpyP-4 and Cu(II)TMpyP-4 with the synthetic polymer poly(dG-dC) could be analyzed by a nearest-neighbor exclusion model leading to n approximately equal to two base pairs and equilibrium constants of 7.7 X 10(5) M-1 and 8.0 X 10(5) M-1, respectively. The other metal derivatives [except for the nickel(II) porphyrin] do not provide sufficiently large color changes with poly(dG-dC) to allow analysis. In contrast, all of these porphyrins interact with poly(dA-dT) and DNA. For those porphyrins investigated, the binding profiles are not adequately fit by a nearest-neighbor exclusion model but have profiles suggesting that cooperativity effects are important. Spectral and circular dichroic experiments both suggest base specificity. With calf thymus DNA, the copper(II) and nickel(II) derivatives show prominent negative circular dichroism (CD) features and large red shifts and hypochromicity of the Soret absorption band characteristic of GC specificity, as demonstrated with the synthetic polymer. The other metal derivatives show prominent positive induced visible CD features with small red shifts and hypochromicity of the absorption bands in the Soret region characteristic of AT specificity. Only the metal-free derivative has a conservative CD spectrum suggesting distribution among GC and AT sites.

Interaction of cationic porphyrins with DNA: importance of the number and position of the charges and minimum structural requirements for intercalation

Abstract: Thirty-three porphyrins or metalloporphyrins corresponding to the general formula (meso-(N-methyl-4(or 3 or 2)-pyridiniumyl){sub n}(aryl){sub 4-n}porphyrin)M (M = H{sub 2}, Cu{sup II}, or ClFe{sup III}), with n = 2-4, have been synthesized and characterized by UV-visible and {sup 1}H NMR spectroscopy and mass spectrometry. These porphyrins differ not only in the number (2-4) and position of their cationic charges but also in the steric requirements to reach even temporarily a completely planar geometry. Interaction of these porphyrins or metalloporphyrins with calf thymus DNA has been studied and their apparent affinity binding constants have been determined by use of a competition method with ethidium bromide which was applicable not only for all the free base porphyrins but also for their copper (II) or iron (III) complexes. Whatever their mode of binding may be, their apparent affinity binding constants were relatively high and a linear decrease of log K{sub app} with the number of porphyrin charges was observed. Studies of porphyrin-DNA interactions by UV and fluorescence spectroscopy, viscosimetry, and fluorescence energy transfer experiments showed that not only the tetracationic meso-tetrakis(N-methyl-4(or 3)-pyridiniumyl)porphyrins, which both involved four freely rotating meso-aryl groups, but also the corresponding tri- and dicationic porphyrins were able to intercalate into calfmore » thymus DNA. These results show that only half of the porphyrin ring is necessary for intercalation to occur.« less