Thomas E. Johnson

Porphyrin building blocks for modular construction of bioorganic model systems

Abstract We outline a modular building block strategy for the covalent assembly of porphyrin-containing model systems. Molecular design issues for the synthesis of porphyrin dimers, dye-porphyrin dyads, and multi-porphyrin arrays have been used to guide the development of this approach. The major design constraints are to achieve directed coupling of free base and/or metalloporphyrin building blocks in dilute solution under non-acidic non-metalating conditions. A set of 24 porphyrin building blocks has been synthesized. The porphyrins are prepared by reaction of substituted benzaldehydes with pyrrole using the two-step one-flask room temperature porphyrin synthesis. Routes to 7 substituted aldehydes are described. Each porphyrin bears one or four functional groups, and many also are facially-encumbered in order to achieve increased solubility. 12 functional groups that meet the design criteria include those that can be reacted directly in coupling reactions such as active esters, α-chloroacetamido, benzoyl, and iodo groups, and others that require deprotection prior to coupling, such as phthalimidomethyl, FMOC-prolyl, trimethylsilylethynyl, dithiolane, methoxycarbonyl, and trimethylsilylethoxycarbonyl groups. The synthesis of 13 porphyrin dimers and dye-porphyrin dyads has been explored as a testbed for refining strategies for the synthesis of molecular devices containing multiple porphyrins and other components. The coupling strategies investigated have yielded dimers or dyads with subunits linked by amide, butadiyne, ethyne, or thiourea groups. This building block approach should enable rapid assembly of architecturally-defined porphyrin-based model systems.

The relationship of Cpm to squared error loss

The relationship between the capability index Cpm and the expected squared error loss provides an intuitive interpretation of Cpm. By putting the loss in relative terms a user needs only to specify the target and the distance from the target at which th..

Synthesis and properties of weakly coupled dendrimeric multiporphyrin light-harvesting arrays and hole-storage reservoirs

A convergent synthesis employing porphyrin building blocks has afforded dendrimeric multiporphyrin arrays containing n Zn-porphyrins (nxa0=xa04, 8, or 20) and one free base- (Fb-) porphyrin joined via diarylethyne linkers. Size exclusion chromatography was used extensively for purification. The arrays have sufficient solubility in toluene or other solvents for routine handling. With increasing size, the intense near-UV Soret (S0xa0→xa0S2) absorption band broadens, splits, and red shifts due to inter-porphyrin exciton coupling. In contrast, the weaker visible bands (S0xa0→xa0S1) remain essentially unchanged in position or width in proceeding from the monomer all the way to the 21-mer; however, the molecular extinction coefficients of the visible bands scale with the number of porphyrins. Similarly, the one-electron oxidation potentials of the porphyrins are virtually unchanged as the arrays get larger. These results are indicative of relatively weak (but significant) electronic coupling between ground states and between the photophysically relevant lowest-excited-singlet states of the diarylethyne-linked porphyrins; thus, the characteristic properties of the individual units are retained as the architectures increase in complexity. Efficient excited-singlet-state energy transfer occurs among the Zn-porphyrins and ultimately to the sole Fb-porphyrin in each of the arrays, with the overall arrival time of energy at the trapping site increasing modestly with the number of Zn-porphyrinsxa0=xa01 (45xa0ps), 2 (90xa0ps), 8 (105xa0ps), and 20 (220xa0ps). The overall energy-transfer efficiencies are 98%, 96%, 96%, and 92% in the same series. The ground-state hole-storage properties of the 21-mer (Zn20Fb) were examined. Bulk electrolysis indicates that 21 (or more) electrons can be removed from this array (e.g., one hole resides on each porphyrin) to yield a stable “super-charged” nπ-cation radical. Taken together, these results indicate that the convergent building-block synthesis approach affords dendrimeric multiporphyrin arrays with favorable properties for light-harvesting and hole storage.

Investigation of the one-flask synthesis of porphyrins bearing meso-linked straps of variable length, rigidity, and redox activity

Abstract The reactions of 18 dialdehydes have been examined in the two-step one-flask room temperature porphyrin synthesis. Efficient alkylation methods were established for the reaction of diols and diacids with m -bromomethylbenzaldehyde. Dialdehydes linked at the o,o′-or m,m′-positions were converted to strapped porphyrins in yields up to 25%, while the one p,p′-linked dialdehyde that was examined failed to give porphyrin. The resulting porphyrins bear straps joining adjacent meso -positions rather than across the face of the porphyrin. Dialdehydes incorporating rigid groups provided improved yields in some but not all cases. The yield of strapped porphyrin exhibited a maximum at 10 −2 M reactant concentrations. The o,o′-strapped porphyrins exist as atropisomers that are sufficiently stable to interconversion at room temperature to be separable chromatographically. No atropisomers of m,m′-strapped porphyrins could be separated, though some could be observed by 1 H NMR spectroscopy. For two different m,m′-strapped porphyrins, the ΔG ‡ values for interconversion of the atropisomers were found to be 66 and 68 kJ/mol. The outer rings in these strapped porphyrins range in size from 14 to 24 atoms. Five porphyrins with bridging redox-active groups (ferrocene or anthraquinone) have been prepared in one-flask reactions, including a porphyrin bearing one ferrocene and one anthraquinone in straps across adjacent meta-substituted phenyl sites.

Bioeconomic dynamics of a fishery modeled as an S-system

A bioeconomic model of a single species fishery is developed by using a realistic catch-rate function and assuming that a regulatory agency controls exploitation of the fishery by imposing a suitable tax on the catch. The existence of a nontrivial steady state and its stability are examined. The optimal harvesting policy is discussed from the viewpoints of variational calculus and control theory. The fishery is then modeled as an S-system by following the recasting techniques of Savageau and Voit. Numerical examples of the optimal control curves and the yield-effort curves are obtained by executing the ESSYNS algorithm.

Laser Desorption Mass Spectrometry of Synthetic Multiporphyrin Arrays

Laser desorption mass spectrometry and matrix-assisted laser desorption mass spectrometry (MALDI-MS) have been investigated for the analysis of a set of synthetic compounds containing one, two, five, eight or nine porphyrins. Intact singly ionized molecule ions were observed for each compound and the spectra were readily interpretable. The use of a matrix of 4-hydroxy-α-cyano-cinnamic acid greatly diminished the extent of fragmentation. Examination of the resulting mass spectra provides insight into aspects of the MALDI process. The present results show that high molecular weight photochemically active materials that absorb strongly at the wavelength of laser illumination can be analysed effectively and that MALDI-MS is a powerful analytical tool for synthetic chemistry of porphyrin-based molecules with dimensions ranging to 10 nm. The strong molecule ions observed for the largest compounds investigated (Zn8-octamer, Zn9-nonamer) indicates that this method should be applicable to even larger porphyrin arrays.

Optimal Timing of Harvest for the North Carolina Bay Scallop Fishery

Substantial improvement is possible in economic returns for the North Carolina bay scallop fishery by delaying the opening of the season beyond its traditional date. A general bioeconomic harvesting model was developed for use in determining the optimal season opening/closing schedule for a seasonal fishery with the control specified as an on/off switch. One hundred and twenty separate scenarios were created by setting five exogenous variables to reasonable alternative values. The optimal season is contrasted with the unregulated case for each scenario. The optimal opening was typically two to three weeks later than the model of past practices.

Self-assembly of molecular devices containing a ferrocene, a porphyrin and a quinone in a triple macrocyclic architecture

Porphyrinogen self-assembly is compatible with a structurally diverse set of meta-linked dialdehyde building blocks, providing rapid access under gentle conditions to porphyrins bearing redox-active units positioned in a 3-dimensional architecture.

Testing for Harmful Effects of Clam and Scallop Harvesting Techniques in the North Carolina Bay Scallop Fishery

Abstract An open-access fishery model incorporating negative effects from harvesting techniques was developed to derive a bionomic equilibrium harvest rate. The model was applied to the bay scallop fishery in North Carolina. The results suggested that clam kicking and clam raking have had significant negative effects on the bay scallop recruitment process.

Estimation and simulation of 3-systems

A method has been developed to estimate the parameters of systems of nonlinear stochastic differential equations. This method uses quasilinearization at each observation and conditional least squares for the loss function on the one step ahead prediction. This method has been applied to estimate the parameters of a S-system that models the feeding and growth of animals. This application has been programmed in the GAUSS language for IBM/PC microcomputers. A related simulation program has also been programmed in GAUSS and has been used to evaluate the distribution of parameter estimates for a two equation three parameter S-system. Theoretical results for conditional least squares imply assymptopic normality of these parameter estimates. The simulation results for 30 time periods indicate that some parameter estimates approach normality in relatively small samples while others require longer series. The algorithm allows the inclusion of unobserved variables in the S-system. The result is to allow for the possibility of an ARMA error process in the observed variables. The complete listing of the code is available upon request to the author.