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A new synthesis of poly(methyl methacrylate) vinylterminated macromonomer is performed using the disproportionation between propagating methyl methacrylate radical and nitroxide TEMPO. The ability of the macromonomer to polymerize and copolymerize with styrene and poly(ethylene glycol) methacrylate was confirmed by GPC and isothermal calorimetry.

The monocyclic 1,4-benzoquinone, HU-331, the direct oxidation product of cannabidiol, inhibits the catalytic activity of topoisomerase II but without inducing DNA strand breaks or generating free radicals, and unlike many fused-ring quinones exhibits minimal cardiotoxicity. Thus, monocyclic quinones have potential as anti-cancer agents, and investigation of the structural origins of their biological activity is warranted. New syntheses of cannabidiol and (±)-HU-331 are here reported. Integrated synthetic protocols afforded a wide range of polysubstituted resorcinol derivatives; many of the corresponding novel 2-hydroxy-1,4-benzoquinone derivatives are potent inhibitors of the catalytic activity of topoisomerase II, some more so than HU-331, whose monoterpene unit replaced by a 3-cycloalkyl unit conferred increased anti-proliferative properties in cell lines with IC50 values extending below 1 mM, and greater stability in solution than HU-331. The principal pharmacophore of quinones related to HU-331 was identified. Selected monocyclic quinones show potential for the development of new anticancer agents.

A comparison of chlorido-gallium functionalized alkoxides as precursors for aerosol-assisted chemical vapor deposition (AACVD) was carried out. Variable-temperature (VT)-NMR studies were used to probe the fluxional behavior of these alkoxides in solution, and hence their utility as precursors. The synthesis involved the initial isolation of the dimer [GaCl(NMe2)2]2 via a salt metathesis route from GaCl3 and 2 equiv of LiNMe2. This dimer was then reacted with 4 equiv of HOCH2CH2CH2NEt2, resulting in the formation of Ga[μ-(OCH2CH2CH2NEt2)2GaCl2]3 (1). Mass spectrometry and VT-NMR confirmed the oligomeric structure of 1. Tuning of the ligand properties, namely, the chain length and substituents on N, resulted in formation of the monomers [GaCl(OR)2] (R = CH2CH2NEt2, (2); CH2CH2CH2NMe2, (3)). VT-NMR studies, supported by density functional theory calculations, confirmed that the ligands in both 2 and 3 possess a hemilabile coordination to the gallium center, owing to either a shorter carbon backbone (2) or less steric hindrance (3). Both 2 and 3 were selected for use as precursors for AACVD: deposition at 450 °C gave thin films of amorphous Ga2O3, which were subsequently annealed at 1000 °C to afford crystalline Ga2O3 material. The films were fully characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, UV–visible spectroscopy, and energy dispersive X-ray analysis., A comparison of chlorido-gallium functionalized alkoxides for use as precursors toward gallium oxide (Ga2O3) via aerosol-assisted chemical vapor deposition was carried out. Variable-temperature NMR studies were used to probe the fluxionality of these alkoxides in solution, combined with computational modeling of their dynamic behavior and hence their utility as precursors. Thin films of gallium oxide were deposited, and full characterization of the films was carried out.

A range of novel β-nitroacetamides with an alkenyl- or alkynyl tether were synthesized using the deprotonative or conjugate addition nitro-Mannich reaction. They were subjected to radical denitration-cyclisation with a 10 equivalent excess of tributyltin hydride, catalytic AIBN in refluxing benzene to explore the structural and electronic requirements for efficient cyclisation. Cyclisations of the β-nitroacetamides were successful in most cases, undergoing 5-exo-trig cyclisation to give the desired cyclopentyl or indanyl structures. Radical 1,4-translocation of a phenyl group was observed in several cases. Diastereoselectivity was low, with 2 or 3 of 4 possible diastereoisomers observed in most cases. Further purification by crystallisation allowed the isolation of some as single diastereoisomers. It was found that higher yields were obtained by increasing the substitution or reducing the degrees of freedom of the tether between the nitro group and the radical acceptor.

Four new conjugated microporous polymers (CMPs) were synthesized by a Buchwald-Hartwig (BH) cross-coupling reaction of tri-and tetrafunctionalized precursors to yield materials with tunable surface area and pore size distribution. This approach yielded LPCMP1-4, CMPs with significantly higher Brunauer-Emmett-Teller (BET) surface areas (more than 5 times higher) than other related BH-based CMPs. These CMPs possess not only high BET specific surface areas and high chemical and thermal stabilities, but also exhibit outstanding swellability. To the best of our knowledge, swellable behavior was studied in great detail for CMPs for the first time, with the greatest degree of swelling for methanol reaching 16.5 and 16.3 mL g -1 for LPCMP1 and LPCMP3, respectively. Owing to their excellent swellability, we further studied the adsorption capacity of these CMPs for different toxic organic vapors (including toluene and methanol). LPCMP1 and LPCMP3 adsorbed 124 and 117 mg g -1 toluene, respectively, at saturated vapor pressure. For methanol, the adsorption capacities of LPCMP1 and LPCMP3 were up to 250 and 215 mg g -1, respectively, which are the highest recorded values when compared with published data for CMPs, HCPs, MOFs, and porous carbons. These materials are promising candidates for the removal and elimination of hazardous organic vapors and chemical warfare agents. Moreover, all the polymers show high sensitivity to nitroaromatic explosives. LPCMP2 and LPCMP4 exhibit high selectivity for TNT and may be suitable as new candidates to selectively detect TNT for security or environmental applications.

The relative strength of noncovalent interactions between a thioether sulfur atom and various π systems in designed top pan molecular balances was determined by NMR spectroscopy. Compared to its oxygen counterpart, the sulfur atom displays a remarkable ability to interact with almost equal facility over the entire range of π systems studied, with the simple alkene emerging as the most powerful partner. With the exception of the O⋅⋅⋅heteroarene interaction, all noncovalent interactions of sulfur with π systems are favoured over oxygen.

The combustion of mercury(II) thiocyanate to form "Pharaoh's serpents" is a spectacular reaction first described nearly two centuries ago. The large volume of distinctive yellow branches that grow from a tiny quantity of flaming reactants makes this an enchanting demonstration, often used to depict the magic of chemistry. In recent years several videos of this bizarre process have "gone viral" online. Formally, the reaction should yield a carbon nitride with the ideal formula C 3 N 4 along with HgS. However, since early characterization attempts there has been little further study of the materials produced. Herein we apply modern characterization techniques to reinvestigate the nature of the carbon nitride and its intimate relationship to the HgS produced. The HgS phase forms nanoparticles that decorate the surfaces of a C 3 N 4 foam matrix. Both of these compounds are important wide-gap semiconductors and we propose that the "Pharaoh's serpents reaction" could be used to produce a potentially important heterojunction nanocomposite materials that could be useful optoelectronic and photocatalytic applications.

Herein we report a retro-Michael deconjugation pathway of thiol-pyridazinedione linked protein bioconjugates to provide a novel cleavable linker technology. We demonstrate that the novel pyridazinedione linker does not suffer from off-target modification with blood thiols (e.g., glutathione, human serum albumin (HSA)), which is in sharp contrast to an analogous maleimide linker.

Twisting is cool Rubber bands that are stretched and held in an extended shape for a while will extract heat from their surroundings as they are allowed to relax, owing to a reversal of stress-induced crystallization, which is an exothermic process. Wang et al. examine the potential for solid-state cooling of twisted fibers, along with configurations such as supercoiling, for materials including natural rubber, polyethylene, and nickel-titanium fibers. The cooling is related to the change in entropy of the material as it is mechanically deformed. Science , this issue p. 216

Crystalline layered carbon nitrides can be inter-converted by simple ion exchange process allowing their properties to be tuned., The development of processes to tune the properties of materials is essential for the progression of next-generation technologies for catalysis, optoelectronics and sustainability including energy harvesting and conversion. Layered carbon nitrides have also been identified as of significant interest within these fields of application. However, most carbon nitride materials studied to date have poor crystallinity and therefore their properties cannot be readily controlled or easily related to their molecular level or nanoscale structures. Here we report a process for forming a range of crystalline layered carbon nitrides with polytriazine imide (PTI) structures that can be interconverted by simple ion exchange processes, permitting the tunability of their optoelectronic and chemical properties. Notable outcomes of our work are (a) the creation of a crystalline, guest-ion-free PTI compound that (b) can be re-intercalated with ions or molecules using “soft chemistry” approaches. This includes the intercalation of HCl, demonstrating a new ambient pressure route to the layered PTI·xHCl material that was previously only available by a high-pressure-high-temperature route (c). Our work also shows (d) that the intercalant-free (IF-) PTI material spontaneously absorbs up to 10 weight% H2O from the ambient atmosphere and that this process is reversible, leading to potential applications for membranes and water capture in dry environments.

As one of the first semi-synthetic plastics produced industrially, cellulose acetate (CA)-based artefacts represent valued items in museum collections and archives which, however, present stability issues. High temperature and relative humidity conditions have long been known to promote changes in CA properties, for instance, due to the deacetylation of CA polymer chains and the loss of plasticiser from the polymer matrix. However, there is a need for improved methods for the quantification of plasticiser loss and CA deacetylation. In this context, this contribution presents a new approach for enabling the investigation of plasticiser loss and deacetylation degradation processes in historic plasticised CA-based artefacts which is based on high-resolution proton nuclear magnetic resonance spectroscopy (1H NMR). The proposed methods allow for simple and fast quantification of diethyl phthalate contents and average degree of substitution (DS), while requiring no need for extractive separation between the plasticiser and the CA polymer matrix prior to analysis. Both methods are demonstrated by their application towards a series of reference samples, historic artefacts and artificially aged plasticised CA materials. Our analysis indicates that plasticiser content and DS can be accurately quantified by using high-resolution 1H NMR and both methods have been compared to analyses performed using infrared spectroscopy.

The use of biomass-sourced chemical feedstocks creates a conflict over land use between food and fuel/chemical production. Such conflict could be reduced by making use of the annual 1.3 Pg food waste resource. Oleic acid is available from seed oils such as pumpkin, grape, avocado and mango. Its esterification with diols 1,3-propanediol, resorcinol and orcinol was used to form diesters and the naturally occurring norspermidine was used to prepare a diamide, all under ambient conditions. These compounds were then epoxidized and polymerized. When esterification was followed by epoxidation and subsequent curing at elevated temperature with p-phenylenediamine or diethylenetriamine, hard insoluble resins were formed. When the sequence was changed such that the epoxidized oleic acid was first reacted with cis-1,2-cyclohexanedicarboxylic anhydride and then esterified with orcinol and resorcinol, insoluble crosslinked polymers were also obtained. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3159–3170

Transparent conductive indium-tin oxide (ITO) thin films, electrochemically intercalated with alkali (Li+, Na+, K+, Rb+, Cs+), alkali earth (Mg+2, Ca+2), or complex NH $_{4}^{+}$ ions, show tunable superconducting transitions with dome-shaped behavior of T c versus electron density around the maximum at ∼ 5 K. On field cooling, the transition into the superconducting state is accompanied by a paramagnetic response, i.e., an increase of magnetization, rather than the usual diamagnetic Meissner response. We provide an extensive study of this so-called paramagnetic Meissner effect (PME), using DC SQUID, transport measurements and a variety of sample sizes and growth conditions. We show that the PME in electrochemically doped ITO films results from a higher T c at the sample edges than at the center of disk-shaped samples, causing flux to be expelled towards the center of the disk, following the flux-compression theory of Koshelev and Larkin. Changing to the opposite spatial T c profile largely removes the paramagnetic response. The paramagnetic magnetization is strongly influenced by sample geometry and flux pinning conditions. The reduction of pinning defects by thermal annealing removes the paramagnetic response. An alternation of the external magnetic field restores the usual Meissner diamagnetism.

Based on detailed analysis of newly acquired NMR data, we show that the previously revised structure of tagetitoxin is incorrect. A new structure of tagetitoxin is proposed which is consistent with the NMR and MS data.

A comparative study using NMR spectroscopy and designed top-pan molecular balances demonstrates that the noncovalent interaction of a hydroxy group with π-deficient pyrazine and quinoxaline units involves a lone pair-heteroarene interaction which is much stronger and solvent independent when measured relative to the classical π-facial hydrogen bond to a benzene ring. Alkyl fluorides also prefer the heteroarene rings over the benzene ring. The attractive interaction between a quinoxaline and a terminal alkyne is also stronger than the intramolecular hydrogen bond to an arene.

Amides of benzo-fused cyclic amines can undergo a ring-opening reaction with TfOH. In benzene, the intermediate carbocation is trapped by phenylation. However, the cinnamamide of 2-phenyl-1,2-dihydroindole with TfOH in CHCl3 undergoes a novel cascade reaction to form a tetrahydro-azadibenzazulene-11-one.

Two different axial symmetries of the119Snchemical shiftanisotropy(CSA) intin dioxidewith theasymmetryparameter (η) of 0 and 0.27 were reported previously based on the analysis of MASNMR spectra. By analyzing the static powder pattern, we show that the119Sn CSA is axially symmetric. A nearly axial symmetry and the principal axis system of the119Sn chemical shift tensor in SnO2were deduced from periodic scalar-relativistic density functional theory (DFT) calculations of NMR parameters. The implications of fast small-angle motions on CSA parameters were also considered, which could potentially lead to a CSA symmetry in disagreement with acrystal symmetry. Our analysis of experimental spectra usingspectral simulationsand iterative fittings showed that MAS spectra recorded at relatively high frequencies do not show sufficiently distinct features in order to distinguish CSAs with η≈0 and η≈0.4. The example of SnO2shows that both the MASlineshapeand spinning sideband analyses may overestimate the η value by as much as ∼0.3 and ∼0.4, respectively. The results confirm that a static powder pattern must be analysed in order to improve the accuracy of the CSA asymmetry measurements. The measurements on SnO2nanoparticlesshowed that the asymmetry parameter of the119Sn CSA increases for nm-sized particles with a larger surface area compared to μm-sized particles. The increase of the η value for tin atoms near the surface in SnO2was also confirmed by DFT calculations.

(1)H NMR chemical shifts have been obtained in the solvents deuterochloroform and dimethyl sulfoxide. The difference in the chemical shifts of an OH or NH group in these two solvents, Δδ = δ(DMSO) - δ(CDCl3), can be converted into the hydrogen bond acidity, A, of the group using the equation A = 0.0065 + 0.133Δδ. The NMR A value, ANMR, can be used as a quantitative assessment of intramolecular hydrogen bonding. We list values of Δδ and ANMR for 55 compounds containing an OH group and 60 compounds with an NH group. For the hydroxy compounds, if A0.5 then the OH group is not part of an intramolecular hydrogen bond, but if A0.1 then the OH group forms part of an intramolecular hydrogen bond. For NH compounds, if A0.16 the NH group is not part of an intramolecular hydrogen bond, and if A0.05 the NH group is part of an intramolecular hydrogen bond. No comparison compounds are needed, and the method is extremely simple. We further show how it is possible to relate intramolecular hydrogen bonding to the actual effect on values of a number of physicochemical, environmental, and biochemical properties.

Graphite particles (0.505 mm) were oxidized to graphite oxide with KClO3 in a H2SO4/HNO3 mixture. Graphite and graphite oxide particles were modified by reaction with SO2 at 630 °C. Thiolysis with sodium dodecane-1-thiolate and aminolysis with dodecane-1-amine of these particles occurred with the insertion of the organic moiety in the carbon matrix. Graphite microparticles (6.20 µm) were oxidized by H2SO4/ KMnO4/ H2O2 mixture and were exfoliated to graphene oxide sheets (MPGO). MPGO was modified by reaction with SO2 at 630 °C. The modified MPGO was refluxed in DMSO with dodecane-1-thiol, dodecane-1-amine, and hexadecane-1-bromide. The reactions occurred with the insertion of the organic moiety in the carbon matrix, according to the X-ray photoelectron and nuclear magnetic resonance spectra. Mechanisms for the reactions were postulated using the atom inventory technique. Despite the structural differences, graphite, graphite oxide, and graphene oxide present the same selectivity for aminolysis and thiolysis reactions, with respect to the oxidized and non-oxidized intermediates of the reduction of SO2, as was found for the activated carbon. Copyright © 2014 John Wiley & Sons, Ltd.

N-Cinnamoyl-9-aminoanthracenes cyclise with PPA or triflic acid to form novel 2-azahexacyclo[10.6.6.0(1,5).0(6,11).0(13,18).0(19,24)]tetracosa-6(11),7,9,13,15,17,19(24),20,22-nonaen-3-ones. In contrast, both N-cinnamoyl-N-methyl-9-(2-aminomethyl)anthracene and N-cinnamoyl-9-(2-aminoethyl)anthracene undergo an intramolecular Diels-Alder cycloaddition.

Based on detailed analysis of newly acquired NMR data, we show that the previously revised structure of tagetitoxin is incorrect. A new structure of tagetitoxin is proposed which is consistent with the NMR and MS data.

The Pd-mediated oxidation of unsaturated thioacetals gives either allyl or vinyl esters, depending on the substrate structure. We report the characterization of a range of sulfur-stabilized palladium intermediates via a combined computational and experimental NMR approach, demonstrating that the oxidation proceeds via two divergent reaction mechanisms. We were also able to synthesize an unusual sigma-bound Pd complex, via acetoxypalladation of an unsaturated dithiane, which was characterized by X-ray crystallography.

Selective examples of OH...arene, NH2...arene and C-HN[triple bond, length as m-dash]C weak interactions are presented using a flexible dibenzobicyclo[3.2.2]nonane scaffold for detection and comparative characterisation of non-covalent interactions in solution and solid states.

X-ray photoelectron spectroscopy (XPS) allows the analysis of the surface atomic composition of a solid and can be used for mechanistic studies of solid-gas and solid-liquid reactions. The change of atomic composition of a surface after a reaction can be calculated considering hypothetical mechanisms based on the known reactivity of the organic moieties bound to the solid surface. Atom inventory of the elements involved in the reactions was used to quantify the components of the XPS spectrum after the reaction and consequently the change of concentration in at%. The method was used to study the basic hydrolysis and photolysis of the intermediates bound to the carbon matrix after the reduction of SO2 on activated carbon. Consistent mechanisms were postulated for these reactions. Basic hydrolysis hydrolyzed the sultine intermediate, and the attack of hydroxide ion on the episulfide formed a sulfide anion, eliminating S2- in a consecutive step. Laser photolysis of modified activated carbon in t-butanol showed the insertion of the organic moiety in the carbon matrix with expulsion of an SO2 radical anion that oxidized to SO42-. Copyright (C) 2008 John Wiley & Sons, Ltd.

The core structure of the RNA polymerase inhibitor tagetitoxin has been synthesized by one-carbon ring expansion of bridged bicyclic monothioacetals. The key steps are intramolecular ylide formation by reaction between the sulfur atom and a pendant diazoester, followed by an efficient photochemical 1,2-rearrangement to give the desired 9-oxa-3-thiabicyclo[3.3.1]nonane ring system.

The reduction of SO2 on carbons proceeds through reactive intermediates bound to the carbon matrix, which were postulated to be 1,2-oxathiene 2-oxide (or sultine), and 1,3,2-dioxathiolane that decomposes to produce an episulfide and CO2. The reactivity of these intermediates was studied in this work through several reactions, using XPS and NMR spectra to postulate their mechanisms. When modified activated carbon obtained after reaction with SO2 at 630 °C was heated at 900 °C, it was observed that the changes of the XPS spectrum resulted from the forward reaction of decomposition of the oxidized intermediate with S-transfer to produce the episulfide and CO2 and the reverse reaction with expulsion of SO2. Strong bases hydrolyzed the dioxathiolane intermediate and the episulfide. The thiolysis, aminolysis, and reaction of alkyl halides with modified activated carbon occurred with the insertion of the organic moiety in the carbon matrix. Laser photolysis at 266 nm in t-butanol showed insertion of t-butoxide o...

Compounds that comprise the erythrina alkaloid class of natural products are based on a tetracyclic spiroamine framework and exhibit a range of biological activities on the central nervous system. Herein, we report a new and efficient total synthesis of this multiple-ring system based on an intramolecular acylal cyclisation (IAC) approach. Using this methodology, the tetracyclic core was rapidly assembled over a two-step domino process catalysed by a Lewis acid. The effect of heteroatoms, substituents and ring size on the IAC has also been investigated, and the broad application of this procedure is demonstrated by the synthesis of a library of derivatives in good yields with excellent regioselectivity.

An electrochemical sensor is built using vertically grown multi-walled carbon nanotubes (MWNTs) micro-array to detect methanol concentration in water. This study is done for the potential use of the array as methanol sensor for portable units of direct methanol fuel cells (DMFCs). Platinum (Pt) nanoparticles electro-deposited CNTs (Pt/CNTs) electrode shows high sensitivity in the measurement of methanol concentration in water with cyclic voltammetry (CV) measurement at room temperature. Further investigation has also been undertaken to measure the concentration by changing the amount of the mixture of methanol and formic acid in water. We compared the performance of our micro array sensor built with Pt/CNTs electrodes versus that of Pt wire electrode using CV measurement. We found that our Pt/CNTs array sensor shows high sensitivity and detects methanol concentrations in the range of 0.04 M to 0.10 M. In addition, we found that co-use of formic acid as electrolyte enables us to measure up to 1.0 M methanol concentration.

Large surface infrared photonic crystals with reflectance higher than 90% have successfully been synthesized by self-assembling large size SiO 2 spheres, of 0.8-4.5 μm diameters, followed by melt infiltration with the chalcogenide glass Ge 33 As 12 Se 55 and the removal of the SiO 2 spheres by chemical etching. The sphere size and the periodicity of the templates were chosen to guarantee the formation of photonic band gaps of the inverted opals in the targeted IR regions of 3-5 μm and 8-12 μm. Fabrication, structural features and spectral behavior of the reflectance peaks of these chalcogenide glass inverse opals are presented.

Treatment of [Os-3(mu-H)(2)(CO)(10)] with the chiral diphosphines BINAP, tolBINAP [(R)-2,2'-bis(di-4-tolylphosphino)-1,1'-binaphthyl], DIOP [(4R,5R)-(-)-O-isopropenylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino) butane] affords [Os-3(mu-H)(2)(CO)(8)(mu-L)] (L = BINAP (1), tolBINAP (2), DIOP (4)) in high yield. The X-ray structures for 1, 2 and 4 are reported, and structural and spectroscopic comparisons are made between these clusters and [Os-3(mu-H)(2)(CO)(8)(mu-L)] (L = dppm (5), dppe (6), dppp (7)) which were synthesised similarly. Compounds 5 to 7 were previously synthesised by hydrogenation of 1,2-[OS3(CO)(10)(mu-L)] but the route from [Os(mu-H)(2)(CO)(10)] is preferable. The H-bridged Os center dot center dot Os distances are similar in 1, 2 and 4 indicating that these species are formally unsaturated 46-electron clusters. The P center dot center dot center dot P distances vary from 4.24 to 4.30 angstrom in 1 and 2, respectively, to 4.53 angstrom in 4 and there are related changes in the angles associated with the ligand set around the H-bridged osmium atoms. Introduction of the diphosphine ligands completely suppresses the ability to add CO, to insert acetylene to form a mu-eta(1), eta(2)-vinyl compound, and to exchange hydride ligands with styrene-d(8), which are reactions characteristic of [Os-3(mu-H)(2)(CO)(10)], Clusters 2 and 5-7 were also used to examine the potential of natural abundance Os-187 NMR spectroscopy through techniques based on inverse detection by HMQC, HSQC and HMBC spectroscopy. (c) 2005 Elsevier B.V. All rights reserved. (Less)

Photolyses at 254 nm of phenylalanine (Phe) in aqueous solutions, were carried out in the presence of oxidized carbon nanotubes modified by the reaction with SO2 (mNTO). Kinetics of the photolyses were followed by UV spectrophotometry at 220 nm, and the products were characterized by HPLC, XPS, and (13)C-SSNMR. The ratio of the initial rates of photolysis in the presence and absence of mNTO, k*/ko*, showed a systematic decrease. The photolytic decay of Phe occurs with minor formation of tyrosine. The mass of nanotubes produced an exponential attenuation of the photolytic decomposition of Phe. Total carbon analyses (TCA) showed no inorganic carbon formation after the photolyses. The first-order rate constant of photofunctionalization of mNTO by the insertion of phenylalanine onto the nanotube matrix was calculated from TCA to be kin = 30.1 min(-1). Comparison of the XPS spectra of the mNTO before and after the photolysis, using the atom inventory technique, suggests the insertion of Phe along with the extrusion of a sulfide radical anion ((•)S(-)) which undergo subsequent oxidation to SO4(2-). The obtained results show the effects of mNTO on the photolysis of Phe and provide a new method of photofunctionalization of carbon materials, modified by the intermediates of the reduction of SO2, with an organic moiety.

Parchment, a biologically based material obtained from the processed hides of animals such as cattle and sheep, has been used for millennia as a writing medium. Although numerous studies have concentrated on the structure and degradation of collagen within parchment, little attention has been paid to noncollagenous components, such as lipids. In this study, we present the results of biochemical and structural analyses of historical and newly manufactured parchment to examine the potential role that lipid plays in parchment stability. The lipid fraction extracted from the parchments displayed different fatty acid compositions between historical and reference materials. Gas chromatography, small-angle X-ray scattering, and solid-state NMR were used to identify and investigate the lipid fraction from parchment samples and to study its contribution to collagen structure and degradation. We hypothesize that the origin of this lipid fraction is either intrinsic, attributable to incomplete fat removal in the manufacturing process, or extrinsic, attributable to microbiological attack on the proteinaceous component of parchments. Furthermore, we consider that the possible formation of protein-lipid complexes in parchment over the course of oxidative degradation may be mediated by reactive oxygen species formed by lipid peroxidation.

[structure: see text] A modular, flexible solid-phase synthetic route for the preparation of biotinylated cross-linking probes of membrane receptors is described. The route utilizes an orthogonal protection strategy employing a Pd[0] cleavable allyl linker attached to the probe via an aspartate residue. The versatility of the method is illustrated through the synthesis of a number of arvanil-derived cannabinoid receptor ligands displaying either a photoaffinity or a chemical cross-linking group.

In this study four series of single and mixed alkali glass systems were made and investigated using MAS NMR. Additionally the densities of the glasses were measured experimentally, as well as calculated theoretically using Doweidar’s model. MAS NMR was used to obtain a quantitative structural understanding of glasses by calculating the concentrations of bridging and non-bridging oxygens per silicon oxygen tetrahedron as a function of the alkali oxide concentration expressed as Qn. 29Si MAS NMR spectra exhibited a single resonance corresponding closely with Si in a Q2 state. The chemical shift of the 31P MAS NMR peak was attributed to phosphate in an orthophosphate environment. The 29Si NMR spectra are in agreement with the density data. Using Doweidar’s model the proportions of Q2 and Q3 were calculated, showing that all glasses studied are predominantly Q2 in structure, i.e. [ SiO 3 - ] n silica chains which readily dissolve. The changes in the chemical shifts of the Q2 and Q3 species with composition have been interpreted as resulting from the preferential association of Na+ with Q3 and Ca2+ with Q2.

p-Nitrobenzyl amylose xanthate (AmXNB) was synthesized and characterized by C-13 NMR spectroscopy in solution and the solid state. The degree of substitution (DS), calculated from the sulfur content, was 7.0, and this value was similar to that obtained from solid-state C-13 NMR using the signal of C-1 as internal standard. The hydrolysis of AmXNB was studied in 10% (v/v) DMSO with mu = 0.5 (KCl) at 25degreesC. The basic hydrolysis was pseudo-first order, but the water-catalyzed hydrolysis in the pH range 7-9 showed a biphasic plot of In (DeltaAbsorbance) vs time, as has been observed for cellulose xanthate esters, occurring through two parallel reactions with rate constants k'(H2O) (fast) = 5.3 x 10(-5) s(-1) and k"(H2O) (slow) = 3.3 x 10(-6) s(-1). The fast hydrolysis was more than three orders of magnitude faster than that of the O-ethyl analog. The activation parameters were DeltaH(not equal) = 20.5 kcal mol(-1) and DeltaS(not equal) = +10 cal K-1 mol(-1). They showed that the acceleration of the fast hydrolysis of AmXNB and cellulose analogs is due to entropy of activation effect. There is a linear increase of logk'(H2O) (fast) with increase in the concentration of the small Li+ ion that produces an increase of the 3-D hydrogen-bond network of water while the large singly charged iodide ion has a considerable inverse effect. These results are strongly consistent with the theory that the supramolecular catalysis induced by modified polysaccharide esters is due to the 3-D hydrogen-bond network of the water in the solvation shell. Copyright (C) 2003 John Wiley Sons, Ltd.

In the absence of a structure-directing organic molecule, aluminosilicate ZSM-5 is produced directly from high-silica zeolite Y or zeolite β by a simple hydrothermal treatment of the alkali metal hydroxide-treated starting zeolite material. NMR and FTIR results clearly suggest that the majority of the Al(III) species is present in the framework yielding Bronsted acid sites. Addition of an appropriate organic molecule such as tetrapropylammonium bromide or tetrabutylammonium bromide facilitates the formation of ZSM-5 and ZSM-11, respectively. The protonated form of all the ZSM-5 catalysts shows very good catalytic activity for the conversion of methanol to hydrocarbon.

Dynamic properties of perdeuterated pyrazine (pyrazine-d(4)) guest molecules in the layered a-zirconium phosphate host structure have been established from solid-state H-2 NMR lineshape analysis and H-2 NMR spin-lattice relaxation time measurements. Both techniques indicate that the intercalation compound contains two different types of pyrazine-d(4) guest molecules, which undergo different dynamic processes. The relative proportions of the two types of pyrazine-d(4) guest molecules are approximately 30% (component A) and 70% (component B). The pyrazine-d(4) molecules representing component B undergo two-site 180degrees jumps about the N...N axis of the molecule, whereas the pyrazine-d(4) molecules representing component A undergo an effectively isotropic motion. The activation energy for the two-site 180degrees motion of component B is estimated to be 39 kJ mol(-1) from the H-2 NMR spin-lattice relaxation time measurements and 49 kJ mol(-1) from the H-2 NMR line-shape analysis. Structurally, it may be inferred that component B comprises guest molecules for which the N...N axis has a restricted orientation in space, presumably because of direct interactions with the alpha-zirconium phosphate host structure, whereas component A comprises guest molecules that are held rather weakly in the host structure (or on its external surfaces) such that their reorientation is relatively unestricted. Thermogravimetric analysis provides direct evidence for the existence of two different types of pyrazine guest molecules in the alpha-zirconium phosphate host structure, with different strengths of binding and with populations in the approximate ratio 30:70. High-resolution solid-state N-15 NMR and C-13 NMR spectra provide further support for the existence of two different types of pyrazine guest species within the alpha-zirconium phosphate host structure and provide direct evidence that the pyrazine guest molecules of component B are N-protonated (from the host structure).

Potassium chitosan dithiocarbamate (ChitDTC) was synthesized and characterized by elemental analysis and solid-state C-13 NMR spectroscopy. The degree of substitution (DS) (number of substituents per 100 2-amino-2-deoxyglucopyranoside units) and molalities of the groups were calculated for acetylamino, amino and dithiocarbamate substituents in chitin, chitosan and ChitDTC. A comparative study of the retention and exchange of Cu(II) was performed with chitin, chitosan and ChitDTC at 30degreesC, pH 6.0 (0.1 M succinate). The stability constants, K-X, for the heterogenous equilibriumChitX + Cu(II) reversible arrow(KX) ChitXCu(II)were calculated assuming that complexing of Cu(II) ions was largely in a 1:1 ratio with respect to each group. The values of K-X for each group were NHAc 45.1, DTC 3.14 x 10(3), and NH2 1.12 x 10(4). It is proposed that in the presence of succinate, the main species of aqua Cu(II) ion present in solution must be the uncharged Cu(II)-succinate complex that prevents the acetylamino, amino and DTC groups from forming complexes higher than 1: 1. Also, this may explain the fact that the stability constant for DTC was lower than for the amino group. The method allows the characterization of the chelating ability of each group in ChitDTC with respect to metal ions. Copyright (C) 2002 John Wiley Sons, Ltd.

The controlled cleavage of coordination polymers consisting of well-defined large units can be employed for the rational synthesis of high nuclearity clusters. This synthetic concept is demonstrated by the conversion (schematically shown) of a three-dimensional ZnII coordination polymer containing repeating hexameric units with a "twin-anchor" arrangement of the metal ions into the corresponding hexanuclear cluster by reaction with a donor solvent.

Cellulose acetate fibers with magnetic properties have recently attracted much attention because of their potential novel applications in biomedicine such as for cell and protein separations, magnetic resonance imaging contrast agents, and magnetic filters. In this work, as synthesized yttrium iron garnet and gadolinium substituted yttrium iron garnet nanoparticles have been used to generate magnetic filter paper. Garnet nanoparticles dispersed in cellulose acetate polymer solutions were electrospun as free-standing nonwoven fiber mats as well as on cellulose filter paper substrates resulting in magnetic filter papers. The magnetic fibers were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), and superconducting quantum interference device (SQUID) magnetic property measurements. The resulting magnetic polymer nanocomposites can be easily picked up by an external magnet from a liquid medium. Fluorescein isothiocyanate (FITC) labeled bovine serum albumin (BSA) was separated from solution by using the magnetic filter paper.

Rotary resonance recoupling of heteronuclear 13 C − 1 H dipolar interactions in magic angle spinning solid state 13 C NMR spectra (recorded under conditions of 1 H decoupling at frequency ν 1 and magic angle spinning at frequency ν r ) has been studied for three examples of molecular solids (adamantane, ferrocene and hexamethylbenzene) in which substantial molecular motion is known to occur. It is shown that when rotary resonance conditions are satisfied (i.e. ν 1/ ν r = n , for n =1 or 2), the recoupling can lead to motionally averaged Pake-like powder patterns from which information on 13 C − 1 H internuclear distances and/or molecular motion can be derived.

The thermally induced solidstate polymerization reactions in sodium chloroacetate and sodium bromoacetate, leading to poly(hydroxyacetic acid) (polyglycolide) and NaCl and NaBr, respectively, were studied by isothermal in situ solid-state NMR spectroscopy at 120, 130 and 140 degrees C with a time resolution of the order of 5 to 25 min. The nuclei probed were 23Na and 13C, allowing the parent compounds (sodium halogenoacetates) and both reaction products (polymer and alkali halide) to be monitored. For sodium chloroacetate, there is no evidence for the involvement of intermediate phases during the reaction whereas this cannot be excluded for sodium bromoacetate. The crystal structure of sodium bromoacetate was determined directly from powder diffraction data by the Monte Carlo method, and was found to be isostructural with sodium chloroacetate. The topochemical reaction mechanism proposed previously for sodium chloroacetate is thus also applicable for the polymerization reaction in sodium bromoacetate. The mechanistic and kinetic information obtained from our in situ solid-state NMR investigations is compared and contrasted with information obtained from other in situ probes of the polymerization reactions in these materials.

In this paper we report on synthesis and characterisation of the first phosphonate and phosphonic acid-modified porous silicas and polysilsesquioxanes. The organosilicon phosphonates [(EtO)3Si(CH2)3PO(OEt)2] 1 and [(EtO)3Si(CH2)2PO(OEt)2] 2 have been used to introduce phosphonate and phosphonic acid functionalities to silica and a polysilsesquioxane. Compounds 1 and 2 have been fully characterised (1H, 29Si, 31P and 13C NMR and elemental analysis). Xerogels [from tetraethylorthosilicate (TEOS) or 1,4-bis(triethoxysilyl)benzene (BTESB), and 1 or 2] bearing functionality of the type [On/2(EtO)3 − nSi(CH2)mPO(OEt)2] and, after treatment with concentrated HCl, functionality of the type [On/2(EtO)3 − nSi(CH2)mPO(OH)2], (n can be 0–2, m = 2 or 3) were synthesised and characterised using solid state 29Si, 31P and 13C NMR spectroscopy, elemental analyses and porosimetry measurements. High surface area mesoporous phosphonic acid-modified silicas with a narrow pore size distribution are described.

In the crystal structure of triphenylmethanol (Ph3COH), the molecules form hydrogen-bonded tetramers, with the oxygen atoms positioned approximately at the corners of a tetrahedron. In the average crystal structure, three of the Ph3COH molecules (denoted as “basal”) in the tetramer are related to each other by a 3-fold rotation axis and the fourth molecule (denoted as “apical”) lies on this axis. Previously, the dynamic properties of the hydrogen-bonding arrangement have been probed through solid-state 2H NMR spectroscopic investigations of Ph3COD. There are two dynamically distinguishable types of hydroxyl hydrogen atoms (deuterons), denoted d1 and d3, with relative populations in the ratio 1:3. Each d1 deuteron undergoes three-site 120° jumps by rotation about the C−OD bond, with equal populations of the three sites involved in this motion. Each d3 deuteron undergoes two-site 120° jumps by rotation about the C−OD bond, with equal populations of the two sites involved in this motion. In the present paper...

The halogenopentacarbonylrhenium(I) compounds react with 2,6-bis(diphenylphosphinosulfide) pyridine (L) under mild conditions to yield ionic complexes of general formulae, fac-[Re₂(CO)₃L]⁺ [Re2(CO) ₆(μ-X) )₃]⁻ (X=Cl, Br or I), in which the ligand adopts a facial terdentate bonding mode. A synthesis of [Re(CO)₃L]⁺ [SbF₆]⁻ was carried out to establish the presence of the cation, fac-[Re(CO)₃L]⁺, in the complexes. The character of the anions was confirmed by negative ion MALDI-TOF mass spectrometry. The cation is fluxional; the P–phenyl rings oriented towards the metal moiety exhibit restricted rotation at low temperature. The free energy of activation, ΔG †, for hindered rotation is ca. 47 kJ mol⁻¹ for all complexes. Solid-state₃ ¹P NMR data are reported for the free ligand and for the complexes, [Re(CO)₃L][SbF₆] and [Re(CO)₃L][Re₂(CO)₆(μ-X)₃] (X=Cl, Br or I).

A new approach is presented for the analysis of wideline H-2 NMR lineshapes, based on automated fitting of simulated spectra to experimental spectra using either 'downhill simplex' or simulated annealing algorithms. This approach provides an objective assessment of the level of agreement between experimental and simulated H-2 NMR spectra, and removes much of the subjectivity that is characteristic of the traditional approach involving trial-and-error variation of the parameters used in the simulation, followed by visual comparison between experimental and simulated H-2 NMR spectra to assess the quality of fit. Applications of our new approach are reported for the analysis of (i) static H-2 NMR powder patterns, (ii) the temperature dependence of H-2 NMR powder patterns in the intermediate motion regime (including the case of fitting experimental spectra with poor signal-to-noise ratio) and (iii) the dependence of quadrupole echo 2H NMR spectra on the echo delay. Quantitative details relating to the dynamic properties of thiourea-d(4) in its pure crystalline phase and in the chlorocyclohexane-thiourea-d(4) inclusion compound are presented, in addition to the motion of the guest molecules iri the benzenetricarbonylchromium-d(6)-thiourea inclusion compound and the pyrazine-d(4)-alpha-zirconium phosphate intercalation material. (C) 1998 John Wiley & Sons, Ltd.

The dynamic properties of dioctanoyl peroxide guest molecules within the urea host tunnel structure in the dioctanoyl peroxide/urea inclusion compound have been investigated by incoherent quasielastic neutron scattering (IQNS) and solid state 2H nuclear magnetic resonance (NMR) techniques. The IQNS investigations were carried out on samples of urea inclusion compounds containing perdeuterated urea to ensure that the incoherent scattering is dominated by the dioctanoyl peroxide guest molecules. Using semioriented polycrystalline samples, translational motions of the guest molecules along the tunnel were investigated separately from reorientational motions of the guest molecules about the tunnel axis. The 2H NMR experiments used dioctanoyl peroxide deuterated selectively in both the α CD2 groups and urea with natural isotopic abundance. The dynamic models that have been found to describe the translational and reorientational motions of the guest molecules from the IQNS and 2H NMR data are discussed in detai...

Reaction of pentane-2,4-dione, pyridine-2-carboxylic acid or pyridine-2,6-dicarboxylic acid with trimethylplatinum(IV) gives dimeric complexes of general formulate fac-[PtMe3L](2), in which the ionised ligand acts in a chelating and a bridging fashion. High-resolution solid-state Pt-195 NMR data shows that the two platinum atoms are equivalent; the chemical shielding anisotropy and the principal components of the shielding tensor are reported. The complexes are soluble in co-ordinating solvents, yielding monomeric species of general formulae fac-[PtMe3L(solvent)], which are fluxional. The pyridine adducts, fac-[PtMe3L(py)] (L = pentane-2,4-dionato or pyridine-2-carboxylato), are also stereochemically non-rigid. The energetics of the dynamic processes have been studied by standard H-1 NMR band shape analysis techniques; Delta G( double dagger) (298 K) is in the range 69-86 kJ mol(-1). Solid-state C-13, and solution-state C-13 and Pt-195 NMR data are also reported. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.

Incoherent quasielastic neutron scattering (IQNS) has been used to investigate the dynamic properties of cyclohexane guest molecules within the tunnel/cage host structure in the cyclohexane/thioure...