Isomerisation in the chemistry of platinacyclobutane complexes

The platinacyclobutane complexes PtCl₂L₂(C₃H₅Me)], L  pyridine, CD₃CN, or tetrahydrofuran, exist as mixtures of isomers containing P$\text{tCH}{}_2\text{CHMeC}$H₂ or P$\text{tCHMeCH}{}_2\text{CH}{}_2$ groups in rapid equilibrium. Decomposition occurs in some cases to give [PtCl₂L(CH₃CH₂CHCH₂)]. Stereospecific skeletal isomerisation also occurs in metallocyclobutanes containing the groups P$\text{tCHRCHRC}$H₂  P$\text{tCHRCH}{}_2\text{C}$HR, when R  aryl further decomposition gives ν-allylplatinum complexes.     

Observations on clear solution silicalite-1 growth by nanoslabs

Several research groups have reported the presence of nanometer-sized particles (nanoslabs) in clear solutions, which precipitate the crystalline MFI (ZSM-5) structure. Debate about the growth mechanism for Al-free ZSM-5 (silicalite-1) has revolved around growth by small silicate units (monomers, dimers, etc.) from solution vs growth by nanoslab addition. A model developed for precipitation of uniform sized colloids by addition of sub-colloidal precursor units has been adapted for this zeolite synthesis system. Parameter values were adjusted for the simulation results to match experimental observations from work reported previously, at least to the extent possible. The model involved the simultaneous solution of up to 6000 ordinary differential equations, and required computation times of up to 24 h. The results shed light on the crystal growth mechanism, but pose questions for further investigations of the nucleation mechanism.     

In silico engineering of tailored ink-binding ability at molecular printboards.

Molecular recognition between guest ink molecules and beta-cyclodextrin (beta-CD) cavities at self-assembled monolayers provides a molecular printboard for nanopatterning applications. We recently used molecular dynamics (MD) simulations to describe the specificity of ink-printboard binding and here extend the simulations to include charged cyclodextrin hosts, necessary to broaden the chemistry of molecular printboards and bind charged inks such as the ferrocenium cation. Shifting to high pH, or alternatively grafting a charged sidearm onto beta-CD, created three distinct types of anionic beta-CD cavity and we used electronic structure calculations and MD simulations to measure host-guest charge transfer and binding strengths. We find that steric recognition of uncharged organic molecules is retained at the charged printboards, and that improved guest-host electrostatic contacts can strengthen binding of larger inks while penalising small inks, enhancing the level of discrimination. A prudent choice of complementary host-guest shape and charge states thus provides a means of tuning both ink binding strength and specificity at molecular printboards.     

Photoelectron spectra of polyunsaturated [4,4,2]propellanes

The photoelectron spectra of the six propellanes 1 to 6 have been recorded. Those bands which correspond to ejection of an electron from a π-orbital have been assigned, using the concept of through bond and through space interaction. Homoconjugative interaction between the π-systems of the two butadiene moieties of 6 is of the same order as that of the π-orbitals in norbornadiene.     

Synthesis of the ladybug alkaloids (±)-propyleine and (±)-isopropyleine. Modification of the published structure of propyleine

The total syntheses of the ladybug alkaloids (±)-propyleine and (±)-isopropyleine are described. Evidence that the alkaloid propyleine is actually a rapidly interconverting mixture of propyleine and a previously unknown isomer isopropyleine is presented.     

High-yield solvothermal formation of magnetic CoPt alloy nanowires

One-dimensional (1D) magnetic nanomaterials have attracted much attention recently because of their applications in magnetic recording and spintronics. Nevertheless, it remains a challenge to prepare free-standing magnetic nanowires in high yield. This Communication reports the successful high-yield synthesis of an interesting 1D ferromagnetic CoPt alloy by direct decomposition of platinum acetylacetonate and cobalt carbonyl compound in ethylenediamine solvent through a solvothermal reaction. The CoPt alloy nanowires obtained have a tunable diameter of 10-50 nm and a length along the longitudinal axis of up to several microns, depending on crystallization temperature and reaction time. A unique formation mechanism involving coarsening and ripening under solvothermal conditions was discovered. This research opens new opportunities in synthesizing nanomaterials through low-temperature solvothermal processes.     

Channel flow cell studies on the evaluation of surface pretreatments using phosphoric acid or polymaleic acid for calcite stone protection

The dissolution kinetics of surface-pretreated and weathered calcite was investigated in dilute acid using a channel flow cell with microdisk detection. Two pretreatments were studied, polymaleic acid and phosphoric acid. Treatment with polymaleic acid was shown to significantly passivate calcite but to a lesser extent than the phosphoric acid and the former coating was found to be less effective for protection of calcite from acid attack. However, treatment of calcite with phosphoric acid resulted in the passivation of calcite from acid attack which strongly inhibited dissolution, an effect that was enhanced even further after exposure to the environment.     

Mechanistic study of stereoselective gas-phase reactions of phosphenium ions with cis- and trans-1,2-diaminocyclohexanes

The 1,3-dioxolane-2-phosphenium ion, 1,3-benzodioxole-2-phosphenium ion, and o-biphenylenephosphenium ion are reported to react in a stereoselective manner with cis- and trans-1,2-diaminocyclohexanes in the gas phase in a Fourier transform ion cyclotron resonance mass spectrometer. Elimination of NH3 from an addition product was observed only for the trans isomer. Several reaction mechanisms were experimentally and computationally examined (B3LYP/6-31G(d)//HF/6-31G(d) + ZPVE level of theory). The most plausible mechanism is initiated by addition of one of the amino groups to the electrophilic phosphorus atom followed by proton transfer between the amino groups. A change to a diaxial conformation for the trans isomer facilitates anchimeric assistance by the now nucleophilic phosphorus atom as the C-N bond breaks to release NH3. Intramolecular proton transfer competes with the conformational change and ultimately leads to ethylene glycol elimination. The transition states for the critical steps of these two reactions are calculated to be nearly equal in magnitude, which rationalizes the observation of both reactions for the trans-diamine. In contrast, the adduct of the cis isomer can eliminate NH3 via a concerted 1,2-hydride shift without a need for a conformational change. However, the barrier associated with this reaction was found to be substantially greater than for proton transfer between the N- and O-atoms. The latter reaction dominates and ultimately leads to ethylene glycol elimination.     

Electrophotographic and microwave photodielectric studies on titanium dioxide pigments in the solid state

In this paper, we report some novel preliminary findings on the photoactivity of titanium dioxide pigments using photoconductive and microwave dielectric techniques. A variety of pigment types were investigated by both methods, including the two crystalline forms of titanium dioxide, anatase and rutile, and a variety of coated pigments. Analysis of the data obtained indicates that there are possible relationships between the photoconductive and photodielectric results, and that these may be used to characterize the pigment types rapidly. Photoconductive measurements were carried out on pigmented films of poly(N-vinylcarbazole) (PVK). Uncoated pigments were found to be more photoconductive than coated pigments with the anatase modification being the more active. It is believed that the pigments act as “trapping” sites to the holes produced by PVK, and that the more photoactive the pigment, the easier it is to regenerate the holes. Various factors influence the band gap of the pigment and these have a significant effect on the photoactivity and photoconductivity of the pigment samples. These include the presence of traps and recombination centres (present as coatings on the surface of the pigment particle) and impurities which can act as acceptors or donors.

Microwave dielectric measurements were carried out on the different anatase and rutile pigments, each exhibiting a different microwave resonant frequency loss depending on the nature of the crystalline modification and the coating. However, on illumination on the pigments with polychromatic light in the microwave cavity, the resonant frequency losses exhibit shifts, the nature of which depend on the pigment type and the coating. Thus the anatase pigments exhibit greater responses than the rutile pigments, particularly with regard to the shift in the resonant frequency values and the change in the Q factor of the resonant peak. The resonant frequency values of the anatase samples are also higher than those obtained for the rutile samples. Furthermore, the frequency shifts are in opposite directions, with the anatase modification exhibiting a more rapid shift to lower frequencies and rutile a slower shift to higher frequencies. It appears that, when the anatase samples are irradiated, their dielectric properties change from those characteristic of a conductor-like material to those of an insulator-like material. However, these changes are reversible once the illumination is terminated. With the rutile samples, irradiation increases the resonant frequency values and hence their dielectric constants. Thus the pigments appear to become more like conductors.     

Rapid assay for hard tissue collagen cross-links using isocratic ion-pair reversed-phase liquid chromatography

Following a detailed study, a rapid and sensitive assay for the naturally fluorescent collagen cross-links pyridinoline and deoxypyridinoline has been developed using ion-pair reversed-phase high-performance liquid chromatography in the presence of 1-octanesulphonic acid (OSA). Pyridinoline and deoxypyridinoline were separated on an Exsil 100 ODS, 5-microns column (100 mm X 4.6 mm I.D.) using 25 mM sodium formate, 5 mM OSA and 1 mM ethylenediaminetetraacetic acid adjusted to pH 3.25, containing 20% (v/v) methanol. The mobile phase flow-rate was 1.5 ml/min. Compounds were detected by their natural fluorescence (xenon lamp; excitation wavelength 290 nm, emission wavelength 400 nm). Peak areas were linear to 25 pmol injected for pyridinoline and 20 pmol injected for deoxypyridinoline (r = 0.99). Intra-assay coefficients of variation for urinary extracts were 7.65 and 9.07% (n = 10), respectively. Limit of detection (signal-to-noise ratio = 5) was 200 fmol injected. Quantification of the cross-links in acid hydrolysates and human urine samples was possible in under 15 min.