DFT and TDDFT investigation of the Schiff base formed by tacrine and saccharin

Schiff bases have many chemical and biological applications in medicine and pharmaceuticals due to the presence of an imine group (?C=N?). These bases are used in many different fields of technology, and in photochemistry because of their photochromic properties. Here, the structural and electronic properties of the Schiff base formed by tacrine and saccharin (TacSac) were explored using density functional theory with the B3LYP, M06-2X, M06L, and ωB97XD functionals in combination with the 6-311++G(d,p) basis set. The time-dependent formalism was used at the B3LYP/6-311++G(d,p) level to obtain electronic transitions. The calculations were repeated in an implicit solvent model mimicking water, using the polarizable continuum model in conjunction with a solvation model based on a density approach. The results indicate that TacSac cannot form spontaneously, but can be obtained in mild reactions. However, the resulting Schiff base displays different characteristics to its monomers. It also has the potential for use in photochemical intramolecular charge-transfer systems.

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Graphical Abstract Intramolecular charge transfer between HOMO and LUMO of TacSac

     

Subcellular Localization of Carotenoid Biosynthesis in Synechocystis sp. PCC 6803

The biosynthesis pathway of carotenoids in cyanobacteria is partly described. However, the subcellular localization of individual steps is so far unknown. Carotenoid analysis of different membrane subfractions in Synechocystis sp. PCC6803 shows that “light” plasma membranes have a high carotenoid/protein ratio, when compared to “heavier” plasma membranes or thylakoids. The localization of CrtQ and CrtO, two well-defined carotenoid synthesis pathway enzymes in Synechocystis, was studied by epitope tagging and western blots. Both enzymes are locally more abundant in plasma membranes than in thylakoids, implying that the plasma membrane has higher synthesis rates of β-carotene precursor molecules and echinenone.     

Adaptive neuro-fuzzy inference technique for estimation of light penetration in reservoirs

An adaptive neuro-fuzzy inference technique has been adopted to estimate light levels in a reservoir. The data were collected randomly from Doğanci Dam Reservoir over a number of years. The input data set is a matrix with vectors of time, depth, sampling location, and incident solar radiation. The output data set is a vector representing light measured at various depths. Randomization and logarithmic transformations have been applied as preprocessing. One-half of the data have been utilized for training; testing and validation steps utilized one-fourth each. An adaptive neuro-fuzzy inference system (ANFIS) has been built as a prediction model for light penetration. Very high correlation values between predictions and real values on light measurements with relatively low root mean square error values have been obtained for training, test, and validation data sets. Elimination of the overtraining problem was ensured by satisfying close root mean square error values for all sets.     

Distribution of Young's Modulus in Porcine Corneas after Riboflavin/UVA-Induced Collagen Cross-Linking as Measured by Atomic Force Microscopy

Riboflavin/UVA-induced corneal collagen cross-linking has become an effective clinical application to treat keratoconus and other ectatic disorders of the cornea. Its beneficial effects are attributed to a marked stiffening of the unphysiologically weak stroma. Previous studies located the stiffening effect predominantly within the anterior cornea. In this study, we present an atomic force microscopy-derived analysis of the depth-dependent distribution of the Young''s modulus with a depth resolution of 5 µm in 8 cross-linked porcine corneas and 8 contralateral controls. Sagittal cryosections were fabricated from every specimen and subjected to force mapping. The mean stromal depth of the zone with effective cross-linking was found to be 219±67 µm. Within this cross-linked zone, the mean Young''s modulus declined from 49±18 kPa at the corneal surface to 46±17 kPa, 33±11 kPa, 17±5 kPa, 10±4 kPa and 10±4 kPa at stromal depth intervals of 0–50 µm, 50–100 µm, 100–150 µm, 150–200 µm and 200–250 µm, respectively. This corresponded to a stiffening by a factor of 8.1 (corneal surface), 7.6 (0–50 µm), 5.4 (50–100 µm), 3.0 (100–150 µm), 1.6 (150–200 µm), and 1.5 (200–250 µm), when compared to the Young''s modulus of the posterior 100 µm. The mean Young''s modulus within the cross-linked zone was 20±8 kPa (2.9-fold stiffening), while it was 11±4 kPa (1.7-fold stiffening) for the entire stroma. Both values were significantly distinct from the mean Young''s modulus obtained from the posterior 100 µm of the cross-linked corneas and from the contralateral controls. In conclusion, we were able to specify the depth-dependent distribution of the stiffening effect elicited by standard collagen cross-linking in porcine corneas. Apart from determining the depth of the zone with effective corneal cross-linking, we also developed a method that allows for atomic force microscopy-based measurements of gradients of Young''s modulus in soft tissues in general.     

Olfactory sensitivity and odor structure-activity relationships for aliphatic carboxylic acids in CD-1 mice

Using a conditioning paradigm, the olfactory sensitivity of CD-1 mice for a homologous series of aliphatic n-carboxylic acids (ethanoic acid to n-octanoic acid) and several of their isomeric forms was investigated. With all 14 odorants, the animals significantly discriminated concentrations as low as 0.03 ppm (parts per million) from the solvent, and with four odorants the best-scoring animals even detected concentrations as low as 3 ppt (parts per trillion). Analysis of odor structure-activity relationships showed that the correlation between olfactory detection thresholds of the mice for the unbranched carboxylic acids and carbon chain length can best be described as a U-shaped function with the lowest threshold values at n-butanoic acid. A significant positive correlation between olfactory detection thresholds and carbon chain length of the carboxylic acids with their branching next to the functional carboxyl group was found. In contrast, no such correlation was found for carboxylic acids with their branching at the distal end of the carbon chain relative to the functional carboxyl group. Finally, a significant correlation was found between olfactory detection thresholds and the position of the branching of the carboxylic acids. Across-species comparisons suggest that mice are more sensitive for short-chained (C(2) to C(4)) aliphatic n-carboxylic acids than other mammalian species, but not for longer-chained ones (C(5) to C(8)). Further comparisons suggest that odor structure-activity relationships are both substance class- and species-specific.     

A study on the structures of the substituted (aminomethyl)lithium and (thiomethyl)lithium compounds

The structures of substituted (aminomethyl)lithium and (thiomethyl)lithium compounds have been examined. Geometric parameters, charge densities, bond orders, dipole moments and heats of formation for all the members of the two series of monomers and dimers of the units LiCN(R)2 and LiCSR where R=H, CH3(Me), C6H5(Ph) have been calculated. The structures of the three complex compounds containing the same units; [[Li(CH2SMe)(THF)]X], [Li2(CH2SPh)2(THF)4] and [Li2(CH2NPh2)2(THF)3] have also been modeled. Geometry optimizations have been performed with the semiempirical PM3 method. The molecular orbital calculations have been carried out by a self-consistent field method using the restricted Hartree-Fock formalism. Comparisons have been made with the corresponding properties of methyl lithium monomer and dimer. The results show that in all of the nitrogen-containing monomers, the C-Li bonds weaken and the Li-C-H(N) angles decrease due to the coordination of lithium with nitrogen. Substitution of hydrogen atoms by methyl or phenyl groups decreases the Li-N coordination. In the sulfur-containing compounds, sulfur behaves similarly to nitrogen but the changes are smaller because the 3p lone-pair orbital of sulfur is higher in energy than the 2p lone-pair of nitrogen. All the dimers of nitrogen/sulfur-containing methyl lithium derivatives form six-membered rings in which the Li-N(S) coordination is greater than the one in the corresponding monomers. Dimerization reactions have been found to be exothermic and the formation of all the dimers is favored. The results obtained for the three complex structures are comparable to the experimental results reported in the literature.Keywords:     

Upper limb hemimelia in a twin pregnancy which was obtained by an ICSI and PGD in a woman with mosaic Turner's syndrome and the prognosis

Turner's syndrome (TS) is depicted as a total or partial absence of X chromosome, and occurs in approximately 1/2200 of live born females. Generally, mosaic patients are diagnosed following karyotype analysis due to recurrent pregnancy loss, repeated in vitro fertilization (IVF) failure, and a history of malformed babies. The purpose of this case report is to show that even a selection of normal karyotype embryos can result in abnormalities for those with mosaic TS. A 32-year old patient who underwent IVF after ICSI-PGD, and was diagnosed with 45X/46XX karyotype. At the 12-week scan, one of the fetuses had an upper limb hemimelia in one arm, and feticide was applied to that fetus. The patient delivered a healthy, 2980 g female baby at the thirty-eighth week. In mosaic TS pregnancies (even those obtained by ICSI-PGD), fetal anomaly risk is high. Therefore, careful prenatal scanning is needed for these pregnancies.     

Population cycles of autumnal moth, Epirrita autumnata, in relation to birch mast seeding

We investigated the relationship between flowering peaks of the mountain birch, Betula pubescens ssp. czerepanovii, and population levels of the autumnal moth Epirrita autumnata in Ammarnäs, Swedish Lapland, during 1968-2000, and in Budal, Central Norway, during 1972-2000. There was a significant correlation between the two moth series, both of which showed three well-defined population cycles during the study period. In both areas, the population growth index of the moth was negatively related to population size, but also to the number of years since the previous flowering peak of mountain birch. In the northern study area, Ammarnäs, there was an additional positive effect of the winter temperature index, probably due to increased mortality of moth eggs during cold winters. No significant relationships were found between the number of birch female catkins and larval density in the previous 2 years. Both in Ammarnäs and in an area without moth outbreaks in south-eastern Norway, birch flowering was positively related to temperatures during flower bud formation and to the number of years since the previous flowering peak. The results support the idea of a lower content of chemical defence compounds in birch leaves after a mast reproduction, though we cannot exclude the possibility that the negative relationship between flowering and moth population levels was influenced or caused by stress associated with defoliation during moth outbreaks.