Binary data acquisition from instrumentation with BCD-coded output: a hardware converter and an example of the relative software control

Simple hardware for conversion from BCD into binary code is described. The device is of low cost, performs a 16-bit conversion in a maximum time of 400 nsec, and is able to output the converted number to either an 8-bit or a 16-bit data bus. An example of the software necessary to perform data acquisition from a digital voltmeter by using this converter is also presented.     

Probing fragment complementation by rigid-body docking: in silico reconstitution of calbindin D9k

Fragment complementation is gaining an increasing impact as a nonperturbing method to probe noncovalent interactions within protein supersecondary structures. In this study, the fast Fourier transform rigid-body docking algorithm ZDOCK has been employed for in silico reconstitution of the calcium binding protein calbindin D9k, from its two EF-hands subdomains, namely, EF1 (residues 1-43) and EF2 (residues 44-75). The EF1 fragment has been used both in its wild type and in nine mutant forms, in line with in vitro experiments. Consistent with in vitro data, ZDOCK reconstituted the proper fold of wild-type and mutated calbindin, locating the nativelike structures (i.e., holding a root-mean-square deviation < 1 A with respect to the X-ray structure) among the first 10 top-scored solutions out of 4000. Moreover, the three independent in silico reconstitutions of wild-type calbindin ranked a nativelike structure at the top of the output list, that is, the best scored one. The algorithm has been also successfully challenged in reconstituting the EF2 homodimer from two identical copies of the monomer. Furthermore, quantitative models consisting of linear correlations between thermodynamic data and ZDOCK scores were built, providing a tested tool for very fast in silico predictions of the free energy of association of protein-protein complexes solved at the atomic level and known to not undergo significant conformational changes upon binding.     

Controlled Hopf bifurcation of a storage-ring free-electron laser

Local bifurcation control is a topic of fundamental importance in the field of nonlinear dynamical systems. We discuss an original example within the context of storage-ring free-electron laser physics by presenting a new model that enables analytical insight into the system dynamics. The transition between the stable and the unstable regimes, depending on the temporal overlapping between the light stored in the optical cavity and the electrons circulating into the ring, is found to be a Hopf bifurcation. A feedback procedure is implemented and shown to provide an effective stabilization of the unstable steady state.     

Efficient synthesis of enantiomerically pure alpha-alkyl cyclopropanecarbonitrile derivatives from pyrazolines

[reaction: see text] Thermolysis of enantiopure sulfonyl pyrazolines 4 and 5, easily obtained from (Z)-3-p-tolylsulfinylacrylonitriles (1), afforded sulfonyl cyclopropanes (6, 7) in a completely stereoselective manner in almost quantitative yields. Both cyclopropanes and alkylidenecyclopropanes, containing one or two chiral carbon atoms, one of them being quaternary, were obtained by hydrogenolysis of the C-S bonding and under the conditions reported by Julia, respectively. The highly stereoselective extrusion of nitrogen suggests a concerted mechanism.     

Lattice invariants and the center of the generic division ring

Let be a finite group, let be a -lattice, and let be a field of characteristic zero containing primitive roots of 1. Let be the quotient field of the group algebra of the abelian group . It is well known that if is quasi-permutation and -faithful, then is stably equivalent to . Let be the center of the division ring of generic matrices over . Let be the symmetric group on symbols. Let be a prime. We show that there exist a split group extension of by a -elementary group, a -faithful quasi-permutation -lattice , and a one-cocycle in such that is stably isomorphic to . This represents a reduction of the problem since we have a quasi-permutation action; however, the twist introduces a new level of complexity. The second result, which is a consequence of the first, is that, if is algebraically closed, there is a group extension of by an abelian -group such that is stably equivalent to the invariants of the Noether setting .

     

Aberro-polariscope for the human eye

We have developed an aberro-polariscope that simultaneously measures spatially resolved polarization properties and wave-front aberration in a living human eye. The setup consists of an infrared Hartmann-Shack sensor that incorporates a polariscope. A series of four Hartmann-Shack images corresponding to independent polarization states were recorded. The corresponding wave-front aberration was computed from each image. Moreover, from each set of four images spatially resolved (over the pupil plane) parameters of polarization were also determined. This instrument allows useful information on both the optical and the biomechanical properties of the eye to be obtained.     

Naphthalene analogues of lignans

The methodology for the synthesis of podophyllotoxin and thuriferic acid-type lignans has been applied to derivatives carrying a naphthalene moiety. Starting from the 1,3-dithiane of 2-naphthaldehyde afforded the expected analogues in the 2,1-naphthalene series. The preferred conformations of these compounds are influenced by the bulky naphthalene system. By contrast, 1,8-bridged products were obtained from the 1,3-dithiane of 1-naphthaldehyde. In this series, polycyclic naphthalene lignan analogues were isolated after deprotection and/or desulfurization reactions. The cyclizations produced in this process are due to the proximity between the 3,4,5-trimethoxyphenyl moiety and the reacting C-2 of the 1,3-dithiane ring.     

Molecular dynamics simulations of the ligand-induced chemical information transfer in the 5-HT(1A) receptor

Comparative molecular dynamics simulations of the 5-HT(1A) receptor in its empty as well as agonist- (i.e. active) and antagonist-bound (i.e. nonactive) forms have been carried out. The agonists 5-HT and (R)-8-OH-DPAT as well as the antagonist WAY100635 have been employed. The results of this study strengthen the hypothesis that the receptor portions close to the E/DRY/W motif, with prominence to the cytosolic extensions of helices 3 and 6, are particularly susceptible to undergo structural modification in response to agonist binding. Despite the differences in the structural/dynamics behavior of the two agonists when docked into the 5-HT(1A) receptor, they both exert a destabilization of the intrahelical and interhelical interactions found in the empty and antagonist-bound receptor forms between the arginine of the E/DRY sequence and both D133(3.49) and E340(6.30). For both agonists, the chemical information transfer from the extracellular to the cytosolic domains is mediated by a cluster of aromatic amino acids in helix 6, following the ligand interaction with selected amino acids in the extracellular half of the receptor, such as D116(3.32), S199(5.42), Y195(5.38), and F361(6.51). A significant reduction in the bend at P360(6.50), as compared to the empty and the antagonist-bound receptor forms, is one of the features of the agonist-bound forms that is related to the breakage of the interhelical salt bridge between the E/DRY arginine and E340(6.30). Another structural feature, shared by the agonist-bound receptor forms and not by the empty and antagonist-bound forms, is the detachment of helices 2 and 4, as marked by the movement of W161(4.50) away from helix 2, toward the membrane space.     

Stereodifferentiation of chiral compounds using reversed-phase liquid chromatography coupled with capillary gas chromatography

A method is described for the enantiomeric quantitation of some chiral compounds via online coupling of reversed-phase liquid chromatography-gas chromatography. The evaluation of some variables affecting the experimentation (i.e., the packing material used in the interface, volume of the transferred fraction, desorption time, initial temperature of the interface, and purge time) makes it possible to optimize the recoveries obtained for some chiral terpenes and lactones using a capillary column of beta-cyclodextrin dissolved in OV-1701. The proposed method allows the enantiomeric analysis of aqueous matrices obtaining relative standard deviations lower than 9% and detection limits ranging from 0.26-0.93 ppm for the investigated compounds.