CH2 Spacer Research Articles

Synthesis, characterisation and extraction behaviour of calix[4]arene-based phosphonic acidsElectronic supplementary information (ESI) available: Tables S1–S3 and Figs. S1 and S2. See http://www.rsc.org/suppdata/p2/b1/b105489a/

Three new bis(phosphonic) acids were prepared by derivatization of p-tert-butylcalix[4]arene on the lower rim by –(CH2)xPO3H2 groups and were fully characterized by NMR spectroscopy; some of them were further investigated by X-ray analysis. The compounds obtained were tested as extractants for La3+, Eu3+, Yb3+ and Th4+ in 0.1–1 M HNO3. Structural details of the complex HLn(H2L1)2 where Ln = Y, La, Eu were elucidated by NMR techniques in solution. The extraction efficiencies decrease with increasing length of the CH2 spacer; the dependence is not monotonic, and an extraordinary selectivity was observed for Yb. The extraction efficiency of Ln3+ for all of the ligands studied increased significantly with decreasing ionic radius.

The possibility of intra-molecular nematic order via chain folding in perylene-containing polyimides: a molecular dynamics study

Perylene containing main-chain polyimides are candidate materials for the photogenerator layer of electrophotographic devices. These polymers are semi-crystalline as synthesized. Annealing improves the crystallinity while causing subtle changes in the X-ray diffraction pattern and a red-shift in the UV–vis absorption spectrum. Molecular dynamics simulations of linear chains of …Pe–C12–Pe… led to chain folded collapsed structures. It is known that a minimum chain length of 150 CH2 units is required, in the case of linear alkanes, for stable folding to occur. However, the strong attractive π interaction between the perylene units causes the chain to fold, with as few as 12 CH2 spacer units. This shows that both intra and intermolecular nematic order can occur in these systems, the former caused by chain folding.

Ruthenium-(II)/-(III) terpyridine complexes incorporating imine functionalities. Synthesis, structure, spectroscopic and electrochemical properties †

A new class of ruthenium terpyridine complexes of the type [RuII(trpy)(L1–6)Cl] 1–6 (trpy = 2, 2′∶6′, 2′′-terpyridine; L1–3 = o-−OC6H3(R)C(R′)NCH2C6H5 and L4–6 = o-−OC6H3(R)CH(R′)NNC6H5; where R = H or p-NO2 and R′ = H or CH3) have been synthesized. The “free” ligands incorporating a NH spacer o-−OC6H3(R)C(R′)NNHC6H5 (HL4–6) have undergone imine to azo tautomerism on co-ordination to the ruthenium terpyridine moiety in the complexes 4–6, whereas those having a CH2 spacer (HL1–3) remain unaltered on co-ordination. The diamagnetic, neutral complexes 1–6 exhibit strong MLCT transitions in the visible region and intraligand transitions in the UV region. A significant shift in MLCT band energy has been observed depending on the ligand field strength of the co-ordinated L. The complexes display a reversible ruthenium(III)–ruthenium(II) couple in the potential range of 0.12–0.63 V and a quasi-reversible ruthenium(IV)–ruthenium(III) couple in the range of 1.21–1.85 V versus SCE. The higher ligand field strength of the co-ordinated L4–6 compared to the co-ordinated L1–3 is reflected in the observed metal redox processes. The reduction of the co-ordinated terpyridine has been observed near −1.3 V. The complexes exhibit moderately strong emissions from the lowest energy MLCT bands in the range 661–690 nm in EtOH–MeOH (4∶1 v/v) at 77 K. The quantum yields of the complexes (Φ = 0.006–0.09) are found to be reasonably sensitive to the nature of the co-ordinated L. The oxidised complexes 3+ and 6+ have been isolated in the solid state as their perchlorate salts. The crystal structure of 3+ exhibits pseudo-octahedral trans geometry with regard to the relative disposition of the imine nitrogen (N4) of L3 and the central pyridyl group of the trpy ligand. The one-electron paramagnetic complexes show 1∶1 conductivity and display ligand-to-metal charge transfer bands near 600 and 400 nm and intraligand transitions in the UV region. The observed rhombic EPR spectra at 77 K corresponding to the distorted octahedral geometry have been analysed to furnish values of axial (Δ) and rhombic (V) distortion parameters as well as the energies of the two expected ligand field transitions (ν1 and ν2) within the t2 shell.

Quantum Chemical Calculations of the Electronic States and Fluorescence Properties of Carbazolyl- and Carbazolylmethylene-Substituted Diacetylenes

The carbazolyldiacetylenes show very different fluorescence behaviors depending on how the carbazolyl (Cz) moiety is connected to the diacetylenic backbone. In fact, when Cz is attached to the backbone through one or more CH2 spacer(s) fluorescence properties are observed which are closely related to those of the fluorescent Cz group. On the contrary, almost no fluorescence is observed when Cz is directly attached to the backbone. In this paper, these phenomena are studied quantum chemically and an explanation for the observed facts is provided. The relevant excited states are studied in detail, showing that in the lowest singlet excited state a considerable intramolecular charge transfer occurs from Cz to the backbone when they are directly bonded.

Synthesis and properties of new calixarene-based ditopic receptors for the simultaneous complexation of cations and carboxylate anions

Calix[4]arene tetramide mono(thio)urea derivatives 5a,b and 9 are able to solubilize solid sodium salts of different anions in CDCl3 thanks to their ability to complex simultaneously the cation at the lower rim and the anion at the upper rim. Therefore they behave as ditopic receptors. Binding studies in [2H6]DMSO performed only on the thiourea derivatives allowed us to establish that these receptors complex carboxylates better than spherical anions and that receptor 9 having the thiourea group directly connected to the aromatic nucleus is more efficient than 5a, which has a CH2 spacer between the two units; in the latter case good selectivity for the acetate anion is observed. Complexation of sodium ion by the amide groups at the lower rim causes an increase in the anion binding properties of receptor 9 and has little effect on receptor 5a. This is explained by the effects of the cation encapsulation on the hydrogen bonding ability of the thiourea units in the two receptors.

Synthesis and characterization of polymers containing 4‐cyanobiphenyl‐based side groups for nonlinear optical applications, 3. Poly(p‐chloromethylstyrene) derivatives

AbstractPoly[p‐(4′‐cyanobiphenyl‐4‐yloxymethyl)styrene]s (PCBMS) were prepared by chemical modification of poly(p‐chloromethylstyrene) with the sodium salt of 4‐cyano‐4′‐hydroxybiphenyl or free radical polymerization of p‐(4′‐cyanobiphenyl‐4‐yloxymethyl)‐styrene (CBMS). The latter method appeared to be a good one for the preparation of polymers with high glass transition temperature and high chromophore content if performed in dimethyl sulfoxide. There was no real evidence for liquid crystal properties in the resulting polymers, which resemble typical amorphous isotropic polymers. This indicates that these polymers should be considered to be polyethylene containing the benzyl ether of 4‐cyano‐4′‐hydroxybiphenyl as the mesogenic group attached directly to the backbone, and not as polystyrenes containing the cyanobiphenyl group attached to the backbone through a OCH2spacer. Some preliminary Corona poling experiments were performed, and the second harmonic generation coefficients d31 and d33, were measured by Maker fringe analysis. Interestingly, the ratio of d33 to d31 was found to be 6, which is much larger than the value of 3 predicted by the molecular statistical model for electric field poling of isotropic systems. This was attributed to conformational constraints on chromophore ordering as expected in such polymers containing no flexible spacer.

Distance dependence of nonadiabaticity in the branching between C–Br and C–Cl bond fission following 1[n(O),π*(C=O)] excitation in bromopropionyl chloride

These experiments on bromopropionyl chloride investigate a system in which the barrier to C–Br fission on the lowest 1A″ potential energy surface is formed from a weakly avoided electronic configuration crossing, so that nonadiabatic recrossing of the barrier to C–Br fission dramatically reduces the branching to C–Br fission. The results, when compared with earlier branching ratio measurements on bromoacetyl chloride, show that the additional intervening CH2 spacer in bromopropionyl chloride reduces the splitting between the adiabatic potential energy surfaces at the barrier to C–Br fission, further suppressing C–Br fission by over an order of magnitude. The experiment measures the photofragment velocity and angular distributions from the 248 nm photodissociation of Br(CH2)2COCl, determining the branching ratio between the competing primary C–Br and C–Cl fission pathways and detecting a minor C–C bond fission pathway. While the primary C–Cl:C–Br fission branching ratio is 1:2, the distribution of relative kinetic energies imparted to the C–Br fission fragments show that essentially no C–Br fission results from promoting the molecule to the lowest 1A″ potential energy surface via the 1[n(O),π*(C=O)] transition; C–Br fission only results from an overlapping electronic transition. The results differ markedly from the predictions of statistical transition state theories which rely on the Born–Oppenheimer approximation. While such models predict that, given comparable preexponential factors, the reaction pathway with the lowest energetic barrier on the 1A″ surface, C–Br fission, should dominate, the experimental measurements show C–Cl bond fission dominates by a ratio of C–Cl:C–Br=1.0:<0.05 upon excitation of the 1[n(O),π*(C=O)] transition. We compare this result to earlier work on bromoacetyl chloride, which evidences a less dramatic reduction in the C–Br fission pathway (C–Cl:C–Br=1.0:0.4) upon excitation of the same transition. We discuss a model in which increasing the distance between the C–Br and C=O chromophores decreases the electronic configuration interaction matrix elements which mix and split the 1n(O)π*(C=O) and np(Br)σ*(C–Br) configurations at the barrier to C–Br bond fission in bromopropionyl chloride. The smaller splitting between the adiabats at the barrier to C–Br fission increases the probability of nonadiabatic recrossing of the barrier, nearly completely suppressing C–Br bond fission in bromopropionyl chloride. Preliminary ab initio calculations of the adiabatic barrier heights and the electronic configuration interaction matrix elements which split the adiabats at the barrier to C–Br and C–Cl fission in both bromopropionyl chloride and bromoacetyl chloride support the interpretation of the experimental results. We end by identifying a class of reactions, those allowed by overall electronic symmetry but Woodward–Hoffmann forbidden, in which nonadiabatic recrossing of the reaction barrier should markedly reduce the rate constant, both for ground state and excited state surfaces.

Mechanics of glycerinated muscle fibers using nonnucleoside triphosphate substrates

We have investigated the ability of the photoaffinity, nonnucleotide ATP analogues, 2-[(4-azido-2-nitrophenyl) amino] ethyl triphosphate (NANTP) and 2-[(4-azido-2-nitrophenyl) amino] propyl triphosphate (PrNANTP), to support active contraction in glycerinated rabbit psoas fibers. At millimolar concentrations, in the absence of calcium, both analogues relaxed fibers. In the presence of calcium, MgNANTP produced isometric tension and stiffness that were one-half to two-thirds the values obtained in MgATP. Maximum shortening velocity and the calcium-activated, myofibrillar catalyzed rate of hydrolysis were approximately the same for MgNANTP as for MgATP. With MgNANTP as the substrate, increasing concentrations of the diphosphate analogue, MgNANDP, inhibited shortening velocity but did not change isometric tension. The addition of increased concentrations of orthophosphate (P) decreased tension while shortening velocity increased. Thus, the effects of the hydrolysis products of NANTP were quite similar to those observed previously for ADP and P in the presence of MgATP. Taken together, these observations show that MgNANTP binds to, and functions in the active site of myosin in a manner quite analogous to MgATP. Thus, the aryl azido group should serve as a valid photoaffinity label for the purine portion of the active site. In contrast, MgPrNANTP, which differs from MgNANTP only in an extra CH2 spacer between the nitrophenyl ring and the triphosphate moiety did not support isometric tension or active shortening in the presence of calcium. Fiber stiffness increased in the presence of calcium and MgPrNANTP, with a calcium-activated, myofibrillar MgPrNANTPase which was about half that obtained with MgATP. Thus, in the presence of MgPrNANTP, cross-bridges appeared to be cycling through states that were attached to actin, but not producing force.

Functionalization of polysterene. II synthesis of chelating polymers by alkylation of 4-aminomethylpolystyrene

A synthetic strategy to obtain chelating polymers via a one-step functionalization of selected macromolecular networks, such as macroporous styrene-divinylbenzene copolymers, is presented. The conversion of chloromethylpolystyrene to aminomethylpolystyrene in a Delepine reaction by way of hexamethylenetetramine addition to the chloride, followed by acid hydrolysis, provides a nucleophilic polymer of high activity. It can be alkylated with a variety of disubstituted benzylhalides (2-acyl-4-chloromethylphenols, 3-picolylchloride, 5-chloromethyl-8-hydroxyquinoline) to yield chelating polymers with strong affinity for transition metal ions. The metal complexing properties of the polymers agree well with estimated properties from known K 1 values of the parent ligands in homogenous media. The chelating polymers, 5A, 6A and 7A show very good reversibility in metal binding and release, and good kinetic behaviour due to the hydrophilic nature of the -CH 2NHCH 2-spacer group between the backbone and the chelating group.