Dimer asymmetry in superoxide dismutase studied by molecular dynamics simulation

Summary Molecular dynamics (MD) simulations of 100 ps have been carried out to study the active-site behaviour of the Cu,Zn superoxide dismutase dimer (SOD) in water. The active site of each subunit was monitored during the whole simulation by calculating the distances between functional residues and the catalytic copper. The results indicate that charge orientation is maintained at each active site but the solvent accessibility varies. Analysis of the MD simulation, carried out by using the atomic displacement covariance matrix, has shown a different intra-subunit correlation pattern for the two monomers and the presence of inter-subunit correlations. The MD simulation presented here indicates an asymmetry in the two active sites and different dynamic behaviour of the two SOD subunits.     

Optimal life strategies in organisms exposed to recurrent critical events

The optimal partition of energy between survival and reproduction is considered for a population subject to recurrent and potentially lethal critical events. The best strategy is found by maximizing fitness, a functional derived from the Lotka equation. The dynamics is governed by a second-order, age-varying, nonlinear system. The energy storage and the probability of survival are the state variables, while the amounts of energy placed into and withdrawn from the storage are the controls. The optimal life strategy is shown to be as follows: build up the storage at the very beginning of life, and then progressively deplete it to resist the critical events.This work was partially supported by MURST Project Ricerche sui Fondamenti della Conservazione della Natura. The authors would like to thank C. Ricci for suggesting the problem and C. Matessi for helpful discussion.     

Interior-point algorithm for quadratically constrained entropy minimization problems

In this paper, we develop an interior point algorithm for quadratically constrained entropy problems. The algorithm uses a variation of Newton's method to follow a central path trajectory in the interior of the feasible set. The primal-dual gap is made less than a given in at most steps, wheren is the dimension of the problem andm is the number of quadratic inequality constraints.     

含氮亲核试剂在2-甲磺酰基-5-(3,4,5-三甲氧基苯基)-1,3,4-噁二唑环上取代反应的研究

2,5—二取代—l,3,4—噁二唑化合物具有消炎,抗菌,调节植物生长,杀虫门等广泛的生物活性。作者曾研究了取代胺在2—甲磺酰基—5—(2—苯基—4—喹啉基)—1,3,4—噁二唑化合物环2—位上的亲核加成消去反应,制得了一系列新的2—取代基—5—(2—苯基—4—喹啉基)—1,3,4—噁二唑衍生物,并发现它们具有一定的抗菌活性。在此基础上,我们又研究了含氮亲核试剂在 2—甲磺酰基—5—(3,4,5—三甲氧基苯基)—1,3,4,—噁二唑环2—位上的亲核加成消去反应,制得一系列新的2—取代基—5—(3,4,5—三甲氧基苯基)—1,3,4—噁二唑衍生物。作者用3,4,5—三甲氧基苯甲酰肼在KOH催化下与CS_2反应得到2—巯基—5—(3,4,5—三甲氧基苯基)—l,3,4—噁二唑1,1在NaOH溶液中与Me_2S0_4作用得到2—甲硫醚—5—(3,4,5—三甲氧基苯基)—1,3,4—噁二唑2,2在冰醋酸水溶     

Geminale Azo- und Heteroelement-Funktionen,II: α-Substituierte 2-(4-Chlorphenylazo)-propan-Derivate

The reaction of acetone-4-chlorophenylhydrazone (6) with bromine in the presence of acetamide yields 2-bromo-2-(4-chlorophenylazo)-propane (7) and 2,2-bis(4-chlorophenylazo)propane (8). The unstable heteroallylic bromide7 was subjected without isolation to nucleophilic displacements with a series of heteronucleophiles thereby affording the corresponding 2-(4-chlorophenylazo)-2-propane derivatives9 with the azo- and heteroelement-functions in a geminal position to each other.

Herrn Prof. Dr. Dr. h. c.K. Kratzl mit den besten Wünschen zum 70. Geburtstag gewidmet.     

A practical access to novel 2-amino-5-arylidene-1,3-thiazol-4(5H)-ones via sulfur/nitrogen displacement under solvent-free microwave irradiation

A new effective approach to the synthesis of a small library of 2-amino-5-arylidene-1,3-thiazol-4(5H)-ones was reported using solvent-free reaction conditions under microwave irradiation. In the first step, rhodanines were subjected to Knoevenagel condensation with aryl aldimines according to a facile one-pot protocol. Then the (5Z)-5-arylidene rhodanine derivatives were transformed directly into the corresponding 2-amino-1,3-thiazol-4(5H)-ones by sulfur/nitrogen displacement reaction under microwaves with retention of configuration and good overall yields.     

TheT g displacement measurements: A way to foresee the physical behaviour and the use of glassy polymers

The effect of ageing temperature (belowT _g) on physical ageing of glassy PET has been investigated by differential scanning calorimetry. The position of the glass transition endotherm was found to be strongly dependent on the annealing conditions (time, annealing temperature). A single relaxation time model is proposed for the analysis of physical ageing.The variations of the equilibrium relaxation time _iso with annealing temperature allow the determination of the parameters of the model. Finally, using these constants, one can determine the thermal past and foresee the thermal future of unknown samples which are of prime importance in processes using temperatures around the glass transition temperature.

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Zusammenfassung Mittels DSC wurde der Einfluß der Alterungstemperatur (unterhalbT _g) auf das physikalische Altern von glasartigen PET untersucht. Die Lage der Glasumwandlungsendothermen hängt stark von den Temperungsbedingungen (Dauer, Temperungstemperatur) ab. Es wird ein Relaxationszeitmodell für die Analyse physikalischen Alterns vorgeschlagen.Die Parameter dieses Modelles knnen aus der Änderung der Gleichgewichtsrelaxationszeit _iso mit der Temperungstemperatur ermittelt werden. Unter Benutzung dieser Konstanten kann die thermische Vergangenheit unbekannter Proben bestimmt und die thermische Zukunft derselben vorhergesagt werden, was für Vorgänge bei Temperaturen um den Glasumwandlungspunkt von primärer Wichtigkeit ist.

     

Determining PPARγ-ligand binding affinity using fluorescent assay with cis-parinaric acid as a probe

Upon the study of small-molecules binding to proteins, the traditional methods for calculating dissociation constants (Kd and Ki) have shortcomings in dealing with the single binding site models. In this paper, two equations have been derived to solve this problem. These two equations are independent of the total concentration or initial degree of saturation of receptor and the activity of the competitive molecule. Through nonlinear fitting against these two equations, Kd value of a probe can be obtained by binding assay, and Ki value of a ligand can be obtained by competitive assay. Moreover, only the total concentrations of receptor([R]t), ligand([L]t) and probe([P]t) are required for the data fitting. In this work, Ki values of some typical ligands of PPARγ were successfully determined by use of our equations, among which the Ki value of PPARγ-LY171883 was reported for the first time.     

Novel Electroless Deposition of Cu<Subscript>3</Subscript>Se<Subscript>2</Subscript> Film on Silicon Substrate by a Simple Galvanic Displacement Process

A novel electroless deposition method for depositing highly uniform adhesive thin films of copper selenide (Cu₃Se₂) on silicon substrates from aqueous solutions is described. The deposition is carried out by two coupled galvanic reactions in a single deposition bath containing copper cations, hydrogen fluoride, and selenous acid: the galvanic deposition of copper on silicon and the subsequent galvanic reaction between the deposited copper with selenous acid in the deposition bath. The powder X-ray diffraction and scanning electron microscopy are used to characterize and examine the deposited films.     

Representations of unbounded optimization problems as integer programs

Any optimization problem in a finite structure can be represented as an integer or mixed-integer program in integral quantities.We show that, when an optimization problem on an unbounded structure has such a representation, it is very close to a linear programming problem, in the specific sense described in the following results. We also show that, if an optimization problem has such a representation, no more thann+2 equality constraints need be used, wheren is the number of variables of the problem.We obtain a necessary and sufficient condition for a functionf:SZ, withS Z ⁿ , to have a rational model in Meyer's sense, and show that Ibaraki models are a proper subset of Meyer models.This research was supported by NSF Grant No. GP-37510X1 and ONR Contract No. N00014-75-C0621, NR047-048.