Excited-State Proton Transfer in Hydroxynaphthaldehydes Covalently Bound to Proteins

The kinetics and equilibrium of excited-state proton transfer (ESPT) in 2-hydroxynaphthaldehyde-1 (HNA-2.1) bound to proteins (bovine serum albumin, cytochrome c, and lysozyme) by an alkylamino bond was studied by means of fluorimetric steady-state and time-resolved methods. The results were compared to analogous data for 1-hydroxy naphthaldehyde-4 (HNA-1.4) bound to proteins and for other 2-naphthol derivatives bound to proteins by a sulfonamide bond, Conclusions concerning the influence on ESPT of the mode of binding and of intramolecular hydrogen bonds occurring in the case of HNA-2. 1 were drawn. An intramolecular hydrogen bond enhances the rate of ESPT but the molecular environment in the protein leads to an opposite effect by increasing reorganization energy during proton transfer. The results obtained prove that the mode of binding and the kind of group linking fluorophores to proteins influence considerably the rate and mechanism of ESPT. In naphthol groups bound to proteins by an alkylamino bond, proton dissociation depends strongly on the molecular environment in the macromolecule. This is due to the short length of the alkylamino bridge and its small interaction with electronic orbitals of the aromatic system. Fluorophores bound to proteins by a sulfonamide bond show a higher rate of ESPT, which is due partly to the electron withdrawing effect of the linking arm. The efficiency of ESPT for naphthol groups bound to proteins by a sulfonamide bond is, in most cases, sufficient for acidification of the medium and influence of the proton gradient in biological membranes.     

Method of moments approach and coupled cluster theory

Summary The single reference coupled cluster (CC) approach to the many-electron correlation problem is examined from the viewpoint of the method of moments (MM). This yields generally an inconsistent (overcomplete) set of equations for cluster amplitudes, which can be solved either in the least squares sense or by selective projection process restricting the number of equations to that of the unknowns. These resulting generalized MM-CC equations always contain the standard CC equations as a special case. Since, in the MM-CC formalism, the Schrödinger equation will be approximately satisfied on a subspace spanned by non-canonical configurations, this procedure may be helpful in extending the standard single reference CC theory to quasi-degenerate situations. To examine the potential usefulness of this idea, we explore the linear version of the CC approach for systems with a quasi-degenerate reference, in which case the standard linear theory is plagued with singularities due to the intruder states. Implications of this analysis for the structure of the wavefunction are also briefly discussed.Killam Research Fellow 1987–89     

Intershell nl4f electron correlation effects

The pair correlation energies for some nl4f pairs of the ground state of the Yb atom are calculated for the first time. The partial wave (PW ) increments to the second-order pair energies are generated using numerical first-order radial pair functions obtained as the solution of two-dimensional differential equations. The analysis of the PW s contributions shows the dominant role of the df, fg, and gh PW s for the 4d4f pair, of the pf and dg PW s for the 4p4f and 5p4f pairs, and of the sf and pg PW s for the 4s4f, 5s4f, and 6s4f pairs. A discussion of the similarities and differences of the structure of the correlation energy found in this paper with those calculated earlier for smaller atoms is given.     

COMPARISON OF THE SPECTROSCOPIC PROPERTIES OF 4'-AMINO PHENYLALANINE AS AN UNPROTECTED AMINO ACID AND AS A RESIDUE IN PEPTIDES

Abstract— Ultraviolet absorption and fluorescence spectra of 4'-amino phenylalanine (Aphe) and of some peptides and esters containing Aphe, are characterized. Based on these results, the applicability of Aphe for fluorescence structural investigations of peptides is evaluated. The use of Aphe as an acceptor in fluorescence energy transfer measurements offers the possibility of facilitating the determination of donor fluorescence quantum yield (φ_D) in the absence of energy transfer which usually turns out to be difficult in systems containing donor and acceptor moities. The Aphe residue in peptides also allows a better insight into intramolecular interactions.     

Principle and applications of the protein-purification-parameter screening system

For the purification of a target protein, liquid chromatography is the method of choice, if its activity has to be maintained. The selection of optimum parameters will improve in proportion to the number of individual parameters varied in initial experiments. Here a fast screening method is described, which utilizes automated parallel chromatographic experiments in the batch mode in 96-well plates. The principle of this protein-purification-parameter screening (PPS) system is demonstrated with a mixture of four proteins. An application of PPS for the determination of a purification step of an angiotensin-II-generating enzyme from a crude tissue extract is shown.     

Development and intercalibration of ultraviolet solar actinometers

Ultraviolet (UV) sunlight actinometers were developed based on the photolysis of nitrate and nitrite. Photon exposures ( i.e. time-integrated irradiances) were quantified from the photochemical production of salicylic acid (SA) or p -hydroxybenzoic acid (pHBA) formed by the reaction of the hydroxyl radical with benzoic acid. The solar response bandwidth for the nitrate actinometer in quartz tubing was 322 ± 11 nm during the Spring of 1999, while the response bandwidth of the Mylar D-filtered nitrite actinometer was 355 ± 25 nm. Intercomparisons of the nitrate and nitrite actinometers with a Smithsonian Environmental Research Center SR-18 scanning UV-B radiometer (SERC SR-18) and an Optronics OL-754 spectroradiometer (OL-754) were performed during the summer of 1998, and the winter and spring of 1999. Photon exposures determined by the nitrate actinometer were in excellent agreement with the SERC SR-18, with a slope (95% confidence interval [CI]) of 0.98 ± 0.01 based on SA production and 0.94 ± 0.02 based on pHBA production. Excellent agreement was also found between the nitrite actinometer and the OL-754, with a slope (95% CI) of 1.00 ± 0.01 using SA production and 1.00 ± 0.02 using pHBA production. These actinometers are well suited for use in the water column and are sufficiently sensitive to determine photon exposures below the 0.1% UV light-level.     

Role of Time Scales in the Coupled Epidemic-Opinion Dynamics on Multiplex Networks

Modelling the epidemic’s spread on multiplex networks, considering complex human behaviours, has recently gained the attention of many scientists. In this work, we study the interplay between epidemic spreading and opinion dynamics on multiplex networks. An agent in the epidemic layer could remain in one of five distinct states, resulting in the SIRQD model. The agent’s attitude towards respecting the restrictions of the pandemic plays a crucial role in its prevalence. In our model, the agent’s point of view could be altered by either conformism mechanism, social pressure, or independent actions. As the underlying opinion model, we leverage the q-voter model. The entire system constitutes a coupled opinion–dynamic model where two distinct processes occur. The question arises of how to properly align these dynamics, i.e., whether they should possess equal or disparate timescales. This paper highlights the impact of different timescales of opinion dynamics on epidemic spreading, focusing on the time and the infection’s peak.     

Application of the valence-universal coupled-cluster method based on various model spaces. II. Nonstandard solutions for Be

The impact of the choices of the complete model space (CMS) and of the orbital basis set on the existence, attainability, and properties of the nonstandard solutions of the valence-universal coupled-cluster (VU-CC) methods has been studied for the case of nonlinear equations corresponding to the atomically oriented form of these methods accounting for one- and two-electron excitations (VU-CCSD/R method) and applied to the Be atom. The results for five ¹S states are discussed. In addition to the previously applied CMS defined by the orbital set (2s, 2p) and (2s, 3s), we have employed the CMSs defined by the (2s, 2p, 3s) set. For each of the CMSs several nonstandard solutions are documented. It is found that the energies of the individual states corresponding to standard and nonstandard solutions differ very little. These energies are also almost independent on the choice of CMS. On the other hand, the energies of excited states disclose a strong dependence on the radial structure of the orbital basis set. It is also demonstrated that the magnitudes of the cluster amplitudes representing a set of states depend both on the choice of the CMS and whether they correspond to the standard or nonstandard solutions. © 1996 John Wiley & Sons, Inc.     

First-order impulsive ordinary differential equations with advanced arguments

This paper deals with impulsive advanced ordinary differential equations with boundary conditions. We investigate the existence of solutions and quasisolutions for advanced impulsive differential equations. To obtain such results we apply Schauder's fixed point theorem. Corresponding results are also formulated for differential inequalities.     

Advanced differential equations with nonlinear boundary conditions

We investigate the existence of solutions for advanced differential equations with nonlinear boundary conditions. Sufficient conditions when the problem has extremal solutions or a unique solution are formulated. Linear advanced differential inequalities are also discussed.