Solid-state structures and conformational studies of four 1,2,3,4-tetrahydroacridine Alzheimer's disease therapeutics

The solid-state structures of four 1,2,3,4-tetrahydroacridines [tacrine hydrochloride monohydrate (1), 7-methoxytacrine hydrochloride monohydrate (2), velnacrine hydrogenmaleate (3) and suronacrine hydrogenmaleate (4)] were determined from single-crystal X-ray diffraction analysis. (1): monoclinic,P2₁/n, a=8.778(1),b=8.521(1),c=17.603(2)Å, =101.34(1)°. (2): monoclinic,C2/c, a=12.326(7),b=18.050(9),c=13.822(8)Å, =113.70(4)°. (3): triclinic, ,a=7.349(2),b=9.417(3),c=12.557(4)Å, =109.62(2), =98.12(2), =101.18(2)°. (4): monoclinic,P2₁/n, a=8.513(6),b=18.74(1),c=13.401(6)Å, =91.21(5)°. FinalR factors for compounds(1)–(4) are 0.047, 0.057, 0.057, 0.11, respectively. The overall arrangement of the common aminotetrahydroacridine skeleton looks similar in all derivatives. However, whereas enantiomerization of the unsubstituted cyclohexenyl rings occurs in (1) and (2), onlyquasi-axially hydroxyl substituted diastereomers are found for (3) and (4). This is presumably due to the different propensities for hydrogen bonding of axially vs. equatorially disposed hydroxyl groups with the hydrogenmaleate anions. Empirical and semiempirical calculations were performed to examine the conformational behavior of the four compounds, bothin vacuo and in solution.     

Solid state conformational parameters in dibenzo[b,f]heteroepin drugs: Crystal structures of 3-methoxy-10-methyl-11-phenyldibenzo[b,f]thiepine and 3-allyloxy-10-ethyl-11-phenyldibenzo[b,f]oxepine

The structures of 3-methoxy-10-methyl-11-phenyldibenzo[b, f]thiepine (I) [C₂₂H₁₈OS, tetragonal,I4₁/a, witha=33.81(1),c=6.065(5)Å,Z=16] and 3-allyloxy-10-ethyl-11-phenyldibenzo[b,f]oxepine (II) [C₂₅H₂₂O₂, mono-clinic,P2₁/c,a=12.115(7),b=16.316(9),c=10.136(7)Å,=105.05(9)°,Z=4] have been determined by the symbolic addition procedure and refined by least-squares method to anR of 0.090 for 784 diffractometer-measured reflections (I) and to anR of 0.083 for 442 reflections (II). The dihedral angle between the phenyl-ring mean planes is 111.3° in (I) and 121.1° in (II), the middle seven-membered ring has the boat conformation, and the tricyclic moiety has twist and skew values of 6° and 0.42 Å in (I) and 0.3° and 0.79 Å in (II). The overall conformational characteristic for the tricyclic (6, 7, 6)-dibenzo[b,f]heteroepin derivatives have been reviewed to gain a better understanding of what requirements may be important for interaction of drugs of this class at the receptor site.     

Multitechnique investigation of conformational features of small molecules: the case of methyl phenyl sulfoxide

The conformational distribution of methyl phenyl sulfoxide (a molecule representative of a very important class of reagents widely used in asymmetric synthesis) has been studied in two different phases of matter (gas phase and solution) by a comprehensive approach including theoretical calculations, microwave spectroscopy, liquid crystal NMR experiments, and atomistic molecular dynamics computer simulations. The aim was to investigate the combined action of intra- and intermolecular interactions in determining the molecule's conformational equilibrium, upon which important physicochemical properties (inter alia, the chemoselectivity) significantly depend. Basically, the results converge in describing the tendency of the molecule to favor stable conformations governed by intramolecular interactions (in particular, the expected optimization between steric repulsion and conjugation of pi systems). However, significant solvent effects (whose "absolute" magnitude is actually difficult to assess, due to a certain "method-dependence" of the results) have been also detected.     

Molecular recognition of chiral conformers: a rotational study of the dimers of glycidol

Two homochiral dimers of glycidol, deriving from two different conformers, have been characterized by rotational spectroscopy in a supersonic expansion.     

Sn-centred icosahedral Rh carbonyl clusters: synthesis and structural characterization and 13C-{103Rh} HMQC NMR studies

The reaction of [Rh(7)(CO)(16)](3-) with SnCl(2).2H(2)O in a 1 : 1 molar ratio under N(2) results in the formation of the new heterometallic cluster, [Rh(12)Sn(CO)(27)](4-), in very high yield (ca. 86%). Further controlled additions of SnCl(2).2H(2)O, or solutions of HCl, or [RhCl(COD)](2), give [Rh(12)(micro-Cl)(2)Sn(CO)(23)](4-). Similarly, addition of HBr to [Rh(12)Sn(CO)(27)](4-) gives the related cluster [Rh(12)(micro-Br)(2)Sn(CO)(23)](4-). Notably, if the addition of SnCl(2).2H(2)O to [Rh(12)Sn(CO)(27)](4-) is carried out under a CO atmosphere, the reaction takes a different course and leads to the formation of the new cluster, [Rh(12)Sn(micro(3)-RhCl)(CO)(27)](4-). All the above clusters have been shown by single-crystal X-ray diffraction studies to have a metal framework based on an icosahedron, which is centred by the unique Sn atom. Their chemical reactivity and (13)C-{(103)Rh} HMQC NMR spectroscopic characterization are also reported.     

Exotic states in the dynamical Casimir effect

Inhibited decoherence has been recently observed in a dissipative two-level system by increasing the strength of the coupling with the reservoir. The system is described by the spin-boson model under a perturbation approach in the delocalized phase regime occurring in weak-coupling limit at zero temperature. Within this scenario, persistence of coherence is found over long times for various low frequency structures of the bosonic environment near a band gap. Special resonances provoke transitions in the long time dynamics if the transition amplitude of the two-level system is greater than the band gap frequency or in absence of any band gap. These transitions may hinder the the loss of coherence in the spin-boson model. Limitations of the approximations are also discussed.     

Screening Clouds and Majorana Fermions

Ken Wilson developed the Numerical Renormalization Group technique which greatly enhanced our understanding of the Kondo effect and other quantum impurity problems. Wilson’s NRG also inspired Philippe Nozières to propose the idea of a large “Kondo screening cloud”. While much theoretical evidence has accumulated for this idea it has remained somewhat controversial and has not yet been confirmed experimentally. Recently a new possibility for observing an analogous crossover length scale has emerged, involving a Majorana fermion localized at the interface between a topological superconductor quantum wire and a normal wire. We give an overview of this topic both with and without interactions included in the normal wire.     

PHOTOBEHAVIOR OF EUGLENA GRACILIS: ACTION SPECTRUM FOR THE STEP-DOWN PHOTOPHOBIC RESPONSE OF INDIVIDUAL CELLS

Abstract—Light-induced behavioral responses of Euglena gracilis have been investigated in single cells by means of a video system coupled to an optical microscope. Light intensity-effect curves at different wavelengths in the near UV and visible range have been determined. From these curves the action spectrum for the step-down photophobic response of Euglena has been calculated. From a comparison with the results obtained using a population method by means of a phototaxigraph, it is concluded that a single photomotile reaction is responsible for cell accumulation, brought about by trapping in the light spot and possibly by phototaxis towards scattered light from organisms already in the light field.     

Nonbinary convolutional codes derived from group character codes

New families of unit memory as well as multi-memory nonbinary convolutional codes are constructed algebraically in this paper. These convolutional codes are derived from the class of group character codes. The proposed codes have basic generator matrices, consequently, they are noncatastrophic. Additionally, the new code parameters are better than the ones available in the literature.