Catenation control in the two-dimensional coordination polymers based on tritopic carboxylate linkers and azamacrocyclic nickel(II) complexes

Four new coordination polymer frameworks, namely [(NiL(1))(3)(BTB)(2)]·6H(2)O, [(NiL(2))(3)(BTB)(2)]·6H(2)O, [(NiL(3))(3)(BTB)(2)]·6H(2)O and [(NiL(2))(3)(BTC)(2)]·10.25H(2)O (L(1) = 1,4,8,11-tetraazacyclotetradecane, L(2) = 3-methyl-1,3,5,8,12-pentaazacyclotetradecane, L(3) = 3,10-dimethyl-1,3,5,8,10,12-hexaazacyclotetradecane, BTC(3-) = benzene-1,3,5-tricarboxylate, BTB(3-) = 4,4',4'-benzene-1,3,5-triyl-tribenzoate) were prepared in water-N,N-dimethylformamide solutions. The molecular and crystal structures of these compounds are compared to the related coordination polymers formed by nickel(II) macrocyclic cations to examine the effect of carboxylate linker size on the framework architecture. Luminescent properties of the complexes based on the BTB(3-) bridging ligand are also discussed.     

Surface‐enhanced Raman spectroscopy of DNA from leaves of in vitro grown apple plants

Ultrasensitive Raman measurements of nucleic acids are possible by exploiting the effect of surface‐enhanced Raman scattering (SERS). In this work, the vibrational spectra of eight genomic DNAs from in vitro grown apple leaf tissues (Malus domestica Borkh., Fam Rosaceae, cvs. Florina, Idared, Rebra, Goldrush, Romus 3, Romus 4 and the rootstocks M9 and M26) were analyzed using surface‐enhanced Raman spectroscopy, in the wavenumber range 200–1800 cm⁻¹. SERS signatures, spectroscopic band assignments and structural interpretations of these plant genomic DNAs are reported. Strong dependences of the SERS spectra on genomic DNA amount in the measured sample volume and on time were observed. Similarities of the SERS signals of DNAs from Rebra and Romus 3 leaves were detected. To our knowledge, this is the first SERS study on genomic DNA from leaf tissues. The present work provides a basis for future use of surface‐enhanced Raman spectroscopy to analyze specific plant DNA–ligand interactions or DNA structural changes induced by plants' stress conditions associated with their natural environment. Besides, this study will generate information that is valuable in the development of low‐level plant DNA‐based analytical sensors. Copyright © 2010 John Wiley & Sons, Ltd.     

The Influence of the Magnetic Impurity Content on the Pore Size Distribution Determination via the DDIF Technique

The pore size distribution of porous media can be determined in a completely non-invasive manner using a new nuclear magnetic resonance (NMR) technique which monitors the magnetization decay due to diffusion in internal fields (DDIF). However, using of the DDIF technique is restricted to the low-phase encoding limit when only the relaxation mode and the first-order diffusion mode are excited. In the present work the fulfillment of such a limit is verified for a progressive increase of the magnetic impurity content of the porous media. If the higher order diffusion modes are excited they lead both to a stronger attenuation of the echo signal and to the appearance of ripples in the DDIF spectra which cannot be related to a pore size distribution. The samples used in this study are porous ceramics prepared using the replication technique and the magnetic impurity is iron (III) oxide which is introduced in an increasing concentration inside the porous matrix. All NMR experiments were done on water filling such porous ceramics using a low-field instrument operating at a proton resonance frequency of 20 MHz. The average pore dimension obtained with the DDIF technique in the weak encoding limit indicates a satisfactory agreement with that observed in optical microscopy images.     

On p-superlinear equations with a nonhomogeneous differential operator

We consider a nonlinear elliptic equation driven by a nonhomogeneous differential operator and with a (p?1)-superlinear Carathéodory reaction. Our formulation incorporates as a special case equations monitored by the p-Laplacian. Using variational methods coupled with truncation techniques and comparison principles, we show that the problem has at least five nontrivial smooth solutions.     

Cascade reactions for constructing heterocycles containing a pyrimidino-pyrazino-pyrimidine core using 1,2,4-triazole scaffolds

The regioselective cyclocondensation of aminoethyl-1,2,4-triazoles and glyoxal provides pentacyclic heterocycles in which two 7,8-dihydro-5H-6λ²-[1,2,4]triazolo[1,5-c]pyrimidine systems are connected through CH(OH) bridges generating a central piperazine-2,5-diol ring. The structure of the new compounds was elucidated based on ¹H, ¹³C and ¹⁵N NMR spectroscopic methods. The molecular structure of the parent compound generated from aminoethyl-1,2,4-triazole was established by single crystal X-ray diffraction.     

Crystal smectic E revisited for(E)-N-(biphenyl-4-ylmethylene)-4-butylaniline – mesomorphism,crystal structure and FTIR study

This paper recalls the attention to an interesting compound having aromatic azomethine structure, namely: (E)-N-(biphenyl-4-ylmethylene)-4-butylaniline (PB4A). The molecular structure of PB4A was determined by X-ray single-crystal diffraction analysis. Besides the enantiotropic smectic B and nematic phases, this compound exhibits a monotropic crystal E phase. By polarising optical microscopy and differential scanning calorimetry, we confirmed the existence of these phases. FTIR measurements in attenuated total reflection configuration have been performed to investigate the evolution of significant absorption bands during phase transitions.     

Epithelial Sodium Channel Inhibition by Amiloride Addressed with THz Spectroscopy and Molecular Modeling

THz spectroscopy is important for the study of ion channels because it directly addresses the low frequency collective motions relevant for their function. Here we used THz spectroscopy to investigate the inhibition of the epithelial sodium channel (ENaC) by its specific blocker, amiloride. Experiments were performed on A6 cells’ suspensions, which are cells overexpressing ENaC derived from Xenopus laevis kidney. THz spectra were investigated with or without amiloride. When ENaC was inhibited by amiloride, a substantial increase in THz absorption was noticed. Molecular modeling methods were used to explain the observed spectroscopic differences. THz spectra were simulated using the structural models of ENaC and ENaC—amiloride complexes built here. The agreement between the experiment and the simulations allowed us to validate the structural models and to describe the amiloride dynamics inside the channel pore. The amiloride binding site validated using THz spectroscopy agrees with previous mutagenesis studies. Altogether, our results show that THz spectroscopy can be successfully used to discriminate between native and inhibited ENaC channels and to characterize the dynamics of channels in the presence of their specific antagonist.     

Some Theoretical and Experimental Evidence for Particularities of the Siloxane Bond

The specific features of the siloxane bond unify the compounds based on it into a class with its own chemistry and unique combinations of chemical and physical properties. An illustration of their chemical peculiarity is the behavior of 1,3-bis(2-aminoethylaminomethyl)tetramethyldisiloxane (AEAMDS) in the reaction with carbonyl compounds and metal salts, by which we obtain the metal complexes of the corresponding Schiff bases formed in situ. Depending on the reaction conditions, the fragmentation of this compound takes place at the siloxane bond, but, in most cases, it is in the organic moieties in the β position with respect to the silicon atom. The main compounds that were formed based on the moieties resulting from the splitting of this diamine were isolated and characterized from a structural point of view. Depending on the presence or not of the metal salt in the reaction mixture, these are metal complexes with organic ligands (either dangling or not dangling silanol tails), or organic compounds. Through theoretical calculations, electrons that appear in the structure of the siloxane bond in different contexts and that lead to such fragmentations have been assessed.     

Synthesis and X-ray structure of a fluorinated 1,1-dialkoxy-3-iminoisoindoline acetal,an elusive phthalocyanine precursor

The synthesis of a fluoroalkylated 1,1-dimethoxy-3-iminoisoindoline acetal, the first representative of the halogenated 3-imino-amino-1-acetal class is reported. In contrast to the protio compound, fluoroalkyl groups make the presence of a base unnecessary for its synthesis while stabilizing the amino tautomer as revealed by an X-ray structural analysis - the first atomic-level structural characterization of the 1,1-alkoxy-3-amino(imino) isoindoline scaffold. Dimers present in solid-state are H-bonded and define a motif similar to the stabilizing, reverse wobble one encountered in adenine-cytosine pairs of tRNA. The fluoro acetal forms easily both metallo- and metal-free phthalocyanines, supporting the proposal that acetals might be phthalocyanine intermediates.