Novel Turn-on Fluorescence Probes for Al3+ Based on Conjugated Pyrazole Schiff Base.

One novel turn-on fluorescence probe founded on conjugated pyrazole Schiff base for detecting Al3+ was invented. The UV-vis and fluorescence spectrometer were employed to explore optical properties of this probe. The results got from those experiments indicated that this fluorescence probe manifested excellent sensitivity and selectivity for Al3+ compared with other cations examined(Ag+, Co2+, Mg2+, Cu2+, Ni2+, Pb2+,and Zn2+). In addition, this probe displayed a more rapid response and remained stable between pH 6 and 9 by investigating the fluorescence intensity under different response time and various pH values. Remarkably, the detection limit for Al3+ could lower to 1.0×10-9M. Therefore, the probe could be potentially applied to the environment for the detection of Al3+, and the availability in biological range of pH that could be further studied to make this probe apply to biological systems in the future.

Experimental and theoretical studies of the products of addition-elimination reactions between benzil dihydrazone and three isomeric chlorobenzaldehydes.

A series of mono- and di-Schiff bases formed between benzil dihydrazone {BDH; systematic name: (1Z)-[(2E)-2-hydrazinylidene-1,2-diphenylethylidene]hydrazine} and three isomeric chlorobenzaldehydes were designed and synthesized to be used as model compounds to help to explain the reaction mechanisms for the formation of Schiff bases. These compounds are 1-(2-chlorobenzylidene)-2-{2-[2-(2-chlorobenzylidene)hydrazin-1-ylidene]-1,2-diphenylethylidene}hydrazine (BDHOCB), and the 3-chloro (BDHMCB) and 4-chloro (BDHPCB) analogues, all having the formula C28H20Cl2N4. Surprisingly, only di-Schiff bases were obtained; our attempts to push the reaction in favour of the mono-Schiff bases all failed. Density functional theory (DFT) calculations were performed to explain the trend in the experimental results. In the case of the systems studied, the type of Schiff base produced exhibits a clear dependence on the HOMO-LUMO energy gaps (ΔE(HOMO-LUMO)), i.e. the product is mainly governed by its stability. The compounds were characterized by single-crystal X-ray diffractometry, elemental analysis, melting point, (1)H NMR and (13)C NMR spectroscopy. The structural features of the three new Schiff bases are similar. For instance, they have the same chemical formula, all the molecules have a symmetrical double helix structure, with each Ph-C=N-N=C-Ph arm exhibiting an anti conformation, and their supramolecular interactions include intermolecular π-π and weak C-H...π stacking interactions. The crystal systems are different, however, viz. triclinic (space group P1¯) for BDHPCB, monoclinic (space group P2(1)/n) for BDHOCB and orthorhombic (space group Pnna) for BDHMCB.

1-(2-Hy-droxy-eth-yl)pyrrole-2,5-dione.

The asymmetric unit of the title compound, C(6)H(7)NO(3), contains two mol-ecules (A and B) related by a non-crystallographic twofold pseudo-axis. The mol-ecules are joined in the (AABB)(n) manner by O-H⋯O hydrogen bonds between their hy-droxy groups, thus forming C(2) chains along the a-axis direction. Neighboring mol-ecules of the same kind (A and A, or B and B) are related by inversion centers, so that all hy-droxy H atoms are disordered other two sets of sites with half occupancies (superimposed O-H⋯O and O⋯H-O fragments). The mol-ecules are further linked by C-H⋯O inter-actions, which can be considered to be weak hydrogen bonds.

exo,exo-4-(2-Hy-droxy-eth-yl)-10-oxa-4-aza-tricyclo-[5.2.1.0]dec-8-ene-3,5-dione.

In the crystal of the title compound, C(10)H(11)NO(4), the hy-droxy group forms an O-H⋯O(carbon-yl) hydrogen bond with an adjacent molecule, so forming chains which extend along (010). Further weak C-H⋯O hydrogen-bonding associations give an infinite three-dimensional network structure.

A two-dimensional undulating Ag(I) coordination polymer constructed of Ag-C and Ag-O bonds: poly[[[µ3-(5,6-η):κO(2):κO(2)-(±)-(1S,2S,3R,4R)-3-carboxy-7-oxabicyclo[2.2.1]hept-5-ene-2-carboxylato]silver(I)] monohydrate].

The title coordination polymer, {[Ag(C(8)H(7)O(5))]·H(2)O}(n), is built from Ag(+) cations and singly protonated dehydronorcantharidin (SP-DNC) anions, with a distorted trigonal-planar geometry at the metal centre. The coordination number of Ag(I) is three (with one Ag-π bond and two Ag-O bonds, one from each of three different SP-DNC ligands), if only formal Ag-ligand bonds are considered, but can be regarded as five if longer weak Ag···O interactions are also included. The two-dimensional corrugated-sheet coordination polymer forms a non-interpenetrating framework with (4.8(2)) topology. Disordered water molecules are sandwiched between the sheets.

Effect of metal ions on radical type and proton-coupled electron transfer channel: sigma-radical vs pi-radical and sigma-channel vs pi-channel in the imide units.

The mechanism of proton transfer (PT)/electron transfer (ET) in imide units, and its regulation by hydrated metal ions, was explored theoretically using density functional theory in a representative model (a nearly planar and cisoid complex between uracil and its N(3)-dehydrogenated radical, UU). In UU (sigma-radical), PT/ET normally occurs via a seven-center, cyclic proton-coupled sigma-electron sigma-channel transfer (PC(sigma)E(sigma)T) mechanism (3.8 kcal/mol barrier height) with a N(3)-->N(3') PT and an O(4)-->O(4') ET. Binding of hydrated metal ions to the dioxygen sites (O(2)/O(2') or/and O(4)/O(4')) of UU may significantly affect its PT/ET cooperative reactivity by changing the radical type (sigma-radical <--> pi-radical) and ET channel (sigma-channel <--> pi-channel), leading to different mechanisms, ranging from PC(sigma)E(sigma)T, to proton-coupled pi-electron sigma-channel transfer (PC(pi)E(sigma)T) to proton-coupled pi-electron pi-channel transfer (PC(pi)E(pi)T). This change originates from an alteration of the ordering of the UU moiety SOMO/HDMO (the singly occupied molecular orbital and the highest doubly occupied molecular orbital), induced by binding of the hydrated metal ions. It is a consequence of three associated factors: the asymmetric reactant structure, electron cloud redistribution, and fixing role of metal ions to structural backbone. The findings regarding the modulation of the PT/ET pathway via hydrated metal ions may provide valuable information for a greater understanding of PT/ET cooperative mechanisms, and an alternative way for designing imide-based molecular devices, such as molecular switches and molecular wires.

4,4'-(Phenyl-imino)dibenzaldehyde.

The asymmetric unit of the title compound, C(20)H(15)NO(2), contains one half-molecule with the central N atom and two C atoms of the benzene moiety lying on a twofold rotation axis. Weak C-H⋯O inter-actions join the mol-ecules together into an infinite three-dimensional network.

Methyl pyrazine-2-carboxyl-ate.

The title compound, C(6)H(6)N(2)O(2), is approximately planar [r.m.s. deviation = 0.0488 (3) Å]. In the crystal, weak inter-molecular C-H⋯O and C-H⋯N inter-actions join the mol-ecules into an infinite three-dimensional network.

Theoretical study on the gas-phase acidity of multiple sites of Cu+-adenine and Cu2+-adenine complexes.

The acidities of multiple sites in Cu(+)-adenine and Cu(2+)-adenine complexes have been investigated theoretically. To compare, the acidities of adenine (A) and adenine radical cation (A(*+)) have also been included. The results clearly indicate that the acidities of C-H and N-H groups in Cu(+/2+)-adenine are significantly enhanced relative to the neutral adenine. The acidic order for a given site on adenine and adenine derivatives is as follows: Cu(2+)-adenine > A(*+) > Cu(+)-adenine > A. For Cu(+)-adenine and Cu(2+)-adenine, N3-coordination exhibits N9-H acid, and N1- and N7-coordination exhibits N6-H(a) and N6-H(b) acid, respectively. Additionally, it is found that C2-H group is surprisingly acidic in the coordination complexes. Calculations in aqueous solution reveal that our results can be extrapolated to aqueous solution. Analyses of the electronic properties interpret the highest acidity of Cu(2+)-adenine among the adenine derivatives studied. Also, Electrostatic potential calculations of [A(-H(+))](-) and [A(-H(+))](*) indicate that the removal of H(a) or H(b) from the amino group favors the bidentate coordination, which provides a dative bond from the deprotonated N and the original coordination ligand to copper ion besides the electrostatic interaction between them and thereby stabilizes the [A(-H(+))](-)/[A(-H(+))](*). NBO analysis confirms the electrostatic potential result.

Characterizing the properties of the N7,N9-dimethylguaninium chloride ion pairs: prospecting for the design of a novel ionic liquid.

The structures, infrared spectra, and electronic properties of the N7,N9-dimethylguaninium chloride have been studied. The interaction of one cation with one to four Cl anions and one Cl anion with two cations were investigated. Fifteen stable conformers are obtained. It is found that there are four acidic regions in the vicinity of the guaninium cations. In these regions, the cation could H-bond with one to three Cl anions but no more than three nearest anions. One Cl anion could H-bond with two cations. Additionally, evidence of a Cl...pi interaction between the anion and cation is observed. Among these structures, one cation interaction with two anions and two cations interaction with one anion have the larger interaction energies than the other series. Natural bond orbital analyses and molecular orbitals reveal that the charge transfer from anion(s) to the cation(s) occurs mainly through either the Cllp --> sigma C-H, Cllp --> sigma N-H, or Cllp --> pi C8-N7 interactions. The interaction between Cl and sigma (C/N-H) or pi C-N produces a small bond order. This indicates that the Cl...H (Cl...pi) interaction exhibits a weak covalent character and suggests a strong ionic H-bond (Cl...pi bond). What's more, formation of Cl...H/Cl...pi bond decreases the bond order of the associated C/N-H bond or C8-N7 bond. In addition, examination of vibrational spectrum of each conformer explains the origin of H-bonding character.

Theoretical prediction of the p53 gene mutagenic mechanism induced by trans-4-hydroxy-2-nonenal.

The reaction mechanism of guanine with trans-4-hydroxyl-2-nonenal (4-HNE) and the mutagenic mechanism induced by adducts have been theoretically predicted at a molecular level from the energy point of view. 4-HNE directly reacts with guanine via three steps, yielding eventually four main diastereoisomers: trans-4-HNE-dG adducts. A concerted six-atom-centered transition state is proposed for the first step, while the last two steps are involved in four-membered-ring transition states. The third step is the rate-determining step. The studies of base pairing properties of trans-4-HNE-dG adducts with A, T, C, A*, and T* together with the relationship between the mutation and structure of trans-4-HNE-dG indicate that syn- and anti-conformations of trans-4-HNE-dG around the glycosidic bond are favorable for pairing with A* and T*, respectively, in the parental generation. As a result, the GC --> CG or GC --> TA mutation may be generated from the syn-4-HNE-dGA* during replication. Nevertheless, anti-4-HNE-dGT* creates GC --> TA mutation or nonmutagenesis. Moreover, syn-4-HNE-dGA* has a slightly higher probability to be generated than anti-4-HNE-dGT* in the parental generation; therefore, the GC to TA transversion is predominant among the mutations. In addition, no correlation between the mutations and the stereochemistry of C6 and C8 of trans-4-HNE-dG adducts was found in this work. Our mutational results have interpreted well a part of the discrete experimental observations, but the mutagenic process itself has not previously been characterized, through either computation or experiment.