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Flavins are photoenzymatic cofactors often exploiting the absorption of light to energize photoinduced redox chemistry in a variety of contexts. Both flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) are used for this function. The study of these photoenzymes has been facilitated using flavin analogs. Most of these analogs involve modification of the flavin ring, and there is recent evidence that adenine (Ade)-modified FAD can affect enzyme turnover, but so far this has only been shown for enzymes where the adenine and flavin rings are close to each other in a stacked conformation. FAD is also stacked in aqueous solution, and its photodynamics are quite different from unstacked FAD or FMN. Oxidized photoexcited FAD decays rapidly, presumably through PET with Ade as donor and Fl* as acceptor. Definitive identification of the spectral signatures of Ade

Lumichrome (7,8-dimethylalloxazine, LC) is a natural photodegradation product and catabolite of flavin coenzymes. Although not a coenzyme itself, LC is used for biosignaling in plants and single-celled organisms, including quorum sensing in the formation of biofilms. The noninvasive detection of in vivo lumichrome would be useful for monitoring this signaling event. For molecules that undergo significant charge redistribution upon light excitation (e.g., intramolecular charge transfer), there are optical detection methods (e.g., second-harmonic generation) that would be well suited to this task. Here, we have used Stark spectroscopy to measure the extent and direction of charge redistribution in photoexcited LC. Stark and low-temperature absorption spectra were obtained at 77 K on LC in ethanol glasses and analyzed using the Liptay analysis to obtain the difference dipole moments and polarizabilities. These data were complemented by a computational analysis of the excited states using density functional theory (DFT) at the TD-B3LYP/6-311+G(2d,p) level of theory.

Radical pair formation and decay are implicated in a wide range of biological processes including avian magnetoreception. However, studying such biological radical pairs is complicated by both the complexity and relative fragility of natural systems. To resolve open questions about how natural flavin–amino acid radical pair systems are engineered, and to create new systems with novel properties, we developed a stable and highly adaptable de novo artificial protein system. These protein maquettes are designed with intentional simplicity and transparency to tolerate aggressive manipulations that are impractical or impossible in natural proteins. Here we characterize the ultrafast dynamics of a series of maquettes with differing electron-transfer distance between a covalently ligated flavin and a tryptophan in an environment free of other potential radical centers. We resolve the spectral signatures of the cysteine-ligated flavin singlet and triplet states and reveal the picosecond formation and recombination of singlet-born radical pairs. Magnetic field-sensitive triplet-born radical pair formation and recombination occurs at longer timescales. These results suggest that both triplet- and singlet-born radical pairs could be exploited as biological magnetic sensors.

The alpha-beta algorithm for searching decision trees is adapted to allow parallel activity in different parts of a tree during the search. The algorithm has been implemented in a procedural simulation language (GASP IV). The simulation environment provides the illusion of multiple software processes and multiple hardware processors. A number of preliminary experiments have been done to gather statistics on run time, nodes scored, and nodes visited. Results indicate that a substantial reduction in time of search occurs because of the use of parallelism. An analytic expression for the storage requirements of the algorithm is derived. The analysis provides an example of the classical tradeoff between time and storage.

The standards ISO 8879 and its related material describes both a text markup scheme and an implementation of a text parser based on that markup scheme. By trying to clarify the relationship between the documents and an implementation, we show that optional SGML features properly belong to separate applications. The result suggests more general and powerful mechanisms which could be obtained.

One recurring theme in the TEI project has been the need to represent non-hierarchical information in a natural way — or at least in a way that is acceptable to those who must use it — using a technical tool that assumes a single hierarchical representation. This paper proposes solutions to a variety of such problems: the encoding of segments which do not reflect a document’s primary hierarchy; relationships among non-adjacent segments of texts; ambiguous content; overlapping structures; parallel structures; cross-references; vague locations.

This article presents a general algorithm for prettyprinting and holophrasting interactively created objects. It is shown how an environment with knowledge of the entities it manipulates can automatically produce cathode-ray tube displays with more helpful contextual information for the user than a traditional display of contiguous lines from a source file.

The CCITT X.400 Series of Recommendations on Message Handling Systems (MHS) define a distributed message exchange model aiming towards the development of an international mail network by interconnecting public and private networks worldwide. The essential functional components of the MHS Model are the User Agents (UAs) and the Message Transfer Agents (MTAs) . Users of the MHS — originators and recipients of messages — request its services through a UA which in turn interacts with the Message Transfer System (MTS). QK-MHS/VM , is an electronic mail system developed at Queen's University under the IBM VM/SP operating system, and is based on the CCITT Recommendations. Design and implementation issues in the development of a remote UA model on a personal computer to be connected to QK-MHS/VM are surveyed in this paper.

Programs written in Euclid can be expected to be verifiable, while those written in Ada can be expected to be portable among the various Ada implementations to be available. The paper describes the construction of a Euclid to Ada translator intended to provide users with both these features. The translator is based on the Toronto Euclid compiler. Development involved using a number of successively larger subsets of the language to be translated.

There is wide agreement on the need for a markup standard for encoding literary texts. The Standard Generalized Markup Language (SGML) seems to provide the best basis for such a standard. But two problems inhibit the acceptance of SGML for this purpose. (1) Computer-assisted textual studies often require the maintenance of multiple views of a document's structure, but SGML is not designed to accommodate such views. (2) An SGML-based standard would appear to entail the keyboarding of more markup than researchers are accustomed to, or are likely to accept. We discuss five ways of dealing with the first problem, and several ways of reducing the burden of markup. We conclude that the problem of maintaining multiple views can be surmounted, though with some difficulty, and that the markup required for an SGML-based standard can be reduced to a level comparable to that of other markup schemes currently in use. Ron Hayter is the Senior Software Developer of Software Exoterica Corporation, Ottawa, Canada. Maria Karibaba obtained the M.Sc. degree in Computing and Information Science at Queen's University and returned to Greece. George Logan is Head of the Department of English at Queen's University, Canada. John McFadden is the President of Software Exoterica Corporation, Ottawa, Canada

This paper describes the application of Hoare-style proof rules for the programming language Modula in the verification of two concurrent programs. In particular, a reasonably large (350 line) system program was verified.

The languages Ada and Euclid are compared and evaluated in the context of three application areas: secure systems, real-time systems, and systems programming. Specific issues considered are verification, robustness, structuring, implementation, functionality, and portability. Programming experiments, supported by the MIT test translator and the Toronto Euclid compiler, are described. The program specifications chosen, Wirth’s p1/0 compiler in Pascal, UNIX levels 0–2 in SPECIAL, the Ada radar track manager example, and the Euclid zone example, were chosen to exercise areas of strength in each language and to represent the applications of interest. Conclusions regarding the suitability of Ada and Euclid for these application areas are given.

Flavins (vitamin B2 and its derivatives) are important blue light sensors and photoredox cofactors. They are also crucial for many proteins that do ground state redox chemistry. Lumichrome (Lc) and lumazine (Lm) are photodegradation products of flavins. Lumazine has been identified as a photoantenna for the cryB protein from Rh. sph., which provides photoregulation of photosynthesis in that cyanobacterium (J. Biol. Chem. 2014, 289:19659-19669). Other studies (J. Biol. Chem. 2009, 284:13068-13076) suggest that archaeal dodecin, a riboflavin-binding protein, may reduce Rbf concentrations photoselectively by an ultrafast electron transfer reaction to produce LC in a manner that preserves cellular integrity. We have used Stark spectroscopy to measure the electronic charge redistribution accompanying light absorption for the lowest optically accessible singlet transitions. Difference dipole moments and changes in the polarizability of the molecules were estimated. These results are discussed in relation to the proteins that incorporate them.