Disruption Of Lattice Research Articles

Re-yellowing of chromium-contaminated soil after reduction-based remediation: Effects and mechanisms of extreme natural conditions

Chromium (VI) in soil poses a significant threat to the environment and human health. Despite efforts to remediate Cr contaminated soil (Cr-soil), instances of re-yellowing have been observed over time. To understand the causes of re-yellowing as well as the influence of overdosed chemical reductant in remediating Cr-soil, experiments on excess reducing agent interference and soil re-yellowing mechanisms under different extreme conditions were conducted. The results show that the USEPA method 3060A & 7196A combined with K2S2O8 oxidation is an effective approach to eliminate interference from excess FeSO4 reducing agents. The main causes of re-yellowing include the failure of reducing agents, disruption of soil lattice, and interactions between manganese oxides and microorganisms. Under various extreme conditions simulated across the four seasons, high temperature and drought significantly accelerated the failure of reducing agents, resulting in the poorest remediation effectiveness for Cr-soil (91.75 %). Dry-wet cycles promoted the formation of soil aggregates, negatively affecting Cr(VI) removal. While these extreme conditions caused relatively mild re-yellowing (9.46 %–16.79 %) due to minimal soil lattice damage, the potential risk of re-yellowing increases with the failure of reducing agents and the release of Cr(VI) within the lattice. Prolonged exposure to acid rain leaching and freeze-thaw cycles disrupted soil structure, leading to substantial leaching and reduction of insoluble Cr, resulting in optimal remediation effectiveness (94.37 %–97.73 %). As reducing agents gradually and the involvement of the water medium, significant re-yellowing occurred in the remediated soil (51.52 %). Mn(II) in soil enriched relevant microorganisms, and the Mn(IV)-mediated biological oxidation process was also one of the reasons for soil re-yellowing.

Evaluation of a Three-Fluid Nozzle Spraying Process for Facilitating Spray Drying of Hydrophilic Polymers for the Creation of Amorphous Solid Dispersions.

Amorphous solid dispersions (ASDs) enable formulations to improve the solubility of poorly soluble active pharmaceutical ingredients (APIs). The amorphous state is reached through the disruption of the crystalline lattice of an API resulting in an increased apparent solubility with faster disintegration. Nevertheless, this form is characterized by a high-energy state which is prone to re-crystallization. To ensure a stable ASD, excipients, e.g., polymers that form a matrix in which an API is dispersed, are used. The applicable polymer range is usually linked to their solubility in the respective solvent, therefore limiting the use of hydrophilic polymers. In this work, we show the applicability of the hydrophilic polymer, polyvinyl alcohol (PVA), in spray-dried solid dispersions. Using a three-fluid nozzle approach, this polymer can be used to generate ASDs with a targeted dissolution profile that is characterized by a prominent spring and desired parachute effect showing both supersaturation and crystallization inhibition. For this purpose, the polymer was tested in formulations containing the weakly basic drug, ketoconazole, and the acidic drug, indomethacin, both classified as Biopharmaceutics Classification System (BSC) class II drugs, as well as the weakly basic drug ritonavir classified as BCS IV. Furthermore, ritonavir was used to show the enhanced drug-loading capacity of PVA derived from the advantageous viscosity profile that makes the polymer an interesting candidate for spray drying applications.

Single source with series modifications: New method for preparing modified clay to control harmful algae blooms

Modified clay (MC) is an effective and eco-friendly material that is widely used for controlling harmful algae blooms (HABs). In this study, a new method—single source with series modifications (SSSM)—was optimized for preparing a high-quality MC, and aluminum-rich clay (kaolin) was activated with a multistep treatment that included calcination (Cal), acid etching with alkali neutralization (Al–An), and raw clay supplementation and aging (RSA). The results showed that the removal efficiency of Prorocentrum donghaiense by the SSSM–MC exceeded 85%; Cal, Al–An, and RSA were indispensable processing steps for preparing the best MC with the SSSM method. The changes occurring in the mineral structure and chemical composition of kaolin treated by the different steps were characterized by FT-IR, XRD, 27Al-NMR and Al-Ferron. Surface dehydroxylation and disruption of the kaolin lattice after calcination significantly changed the aluminum structure from AlVI to AlV and AlIV. The relatively reactive AlV was readily released from the kaolin lattice with acid etching, and it subsequently reacted with external OH– to generate different polyhydroxyaluminum species because alkali was added during the Al–An step. The acidity of the above complex was further decreased by RSA, greatly increasing the yield of SSSM–MC while assuring the quality.

Biomimetic ion substituted and Co-substituted hydroxyapatite nanoparticle synthesis using Serratia Marcescens

Biomimicry is becoming deep-rooted as part of bioceramics owing to its numerous functional advantages. Naturally occurring hydroxyapatite (HA) apart from primary nano structures are also characterised by various ionic substitutions. The ease of accommodating such key elements into the HA lattice is known to enhance bone healing properties of bioceramics. In this work, hydroxyapatite synthesized via biomimetic approach was substituted with individual as well as multiple cations for potential applications in bone repair. Ion substitutions of Sr, Mg and Zn was carried out on HA for the first time by using Serratia grown in a defined biomineralization medium. The individual ions of varying concentration substituted in Serratia HA (SHA) (Sr SHA, Mg SHA and Zn SHA) were analysed for crystallinity, functional groups, morphology and crystal size. All three showed decreased crystallinity, phase purity, large agglomerated aggregates and needle-shaped morphologies. Fourier transform infrared spectroscopy (FTIR) spectra indicated increased carbonate content of 5.8% resembling that of natural bone. Additionally, the reduced O–H intensities clearly portrayed disruption of HA lattice and subsequent ion-substitution. The novelty of this study lies primarily in investigating the co-substitution of a combination of 1% Sr, Zn and Mg in SHA and establishing the associated change in bone parameters. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images clearly illustrated uniform nano-sized agglomerates of average dimensions of 20–50 nm length and 8–15 nm width for Sr SHA; 10–40 nm length and 8–10 nm width for both Zn SHA and Mg SHA and 40–70 nm length and 4–10 nm width in the case of 1% Sr, Zn, Mg SHA. In both individual as well as co-substitutions, significant peak shifts were not observed possibly due to the lower concentrations. However, cell volumes increased in both cases due to presence of Sr2+ validating its dominant integration into the SHA lattice. Rich trace ion deposition was presented by energy dispersive X-ray spectroscopy (EDS) and quantified using inductively coupled plasma optical emission spectrometer (ICP-OES). In vitro cytotoxicity studies in three cell lines viz. NIH/3T3 fibroblast cells, MG-63 osteosarcoma cells and RAW 264.7 macrophages showed more than 90% cell viability proving the biocompatible nature of 1% Sr, Zn and Mg in SHA. Microbial biomineralization by Serratia produced nanocrystals of HA that mimicked “bone-like apatite” as evidenced by pure phase, carbonated groups, reduced crystallinity, nano agglomerates, variations in cell parameters, rich ion deposition and non-toxic nature. Therefore ion-substituted and co-substituted biomineralized nano SHA appears to be a suitable candidate for applications in biomedicine addressing bone injuries and aiding regeneration as a result of its characteristics close to that of the human bone.

Gas‐Phase Fluorination of Hexagonal Boron Nitride

Hexagonal boron nitride (hBN) has received much attention in recent years as a 2D dielectric material with potential applications ranging from catalysts to electronics. hBN is a stable covalent compound with a planar hexagonal lattice and is relatively unreactive to most chemical environments, making the chemical functionalization of hBN challenging. Here, a simple, scalable strategy to fluorinate hBN using a direct gas-phase fluorination technique is reported. The nature of fluorine bonding to the hBN lattice and their chemical coordination are described based on various characterization studies and theoretical models. The fluorine functionalized hBN shows a bandgap reduction and displays a semiconducting behavior due to the fluorination process. Additionally, the fluorinated hBN shows significant improvement in its thermal and friction properties, which could be substantial in applications such as lubricants and thermal fluids. Theory and simulations reveal that the enhanced friction properties of fluorinated hBN result from reduced inter-planar interaction energy by electrostatic repulsion of intercalated fluorine atoms between hBN layers without significant disruption of the in-plane lattice. This technique paves the way for the fluorination of several other 2D structures for various applications such as magnetism and functional nanoscale electronic devices.

EXCITONS IN FUNCTION TO THE BINDING COEFICIENT IN MONOCRISTALLINE SILICON BASE.

The exciton is a particle formed between one or more electrons intermediate levels with one or more holes in the valence band. These two particles are bonded by electrical interactions. These interactions are modeled by a coupling coefficient denoted b. Thus in this article, a study of the variation of the excess excitons density in the base in function to the binding coefficient was done. This study shows that, the excess excitons density is zero at the junction of the base and the space charge zone. By cons, in depth, the excitons density increases as a function to the coupling coefficient. Indeed, when one enters deep, interactions between holes and electrons become very important modeled by a high coupling coefficient. These result a reduction of the excess minority carriers mobility in the base and the formation of exciton complexes, hence the increase of the excess excitons density in the base. The reduction of the excess excitons density at the rear face is due to a very high excitons recombination in this region. This is due to a lack adhesion of the metal contact and disruption of the crystal lattice in this region. When the cell is under polychromatic light, the excess excitons density in the base is very high compared to that obtained when the cell is in dark.

Factors affecting electron beam damage in calcite nanoparticles

We report electron fluence thresholds for the degradation of calcite nanoparticles under electron irradiation by both conventional and scanning TEM (CTEM and STEM), using time resolved phase contrast imaging and EDX spectroscopy at both 80 kV and 300 kV accelerating voltages. We show that the degradation pathway of calcite involves disruption of the crystal lattice with the evolution of pores and transformation to calcium oxide and carbon dioxide. Depending on irradiation conditions (CTEM or STEM), the calcium oxide formed can be either amorphous or crystalline, with the formation of the latter apparently being hindered by hydrocarbon contamination build up in STEM. For a given electron flux, irradiation at 300 kV prolongs the characteristic lifetime of the calcite lattice as compared to irradiation at 80 kV but with a corresponding reduction in both image contrast and energy dispersive X-ray (EDX) signal, consistent with the change in inelastic mean free path for electron scattering. STEM offers significant benefits over CTEM, however only in the presence of hydrocarbon contamination, increasing the fluence threshold for the detection of irradiation induced faults in the calcite lattice from 2.7 × 107 e− nm-2 for 300 kV CTEM to over 1.8 × 108 e− nm-2 for 300 kV STEM. This work forms a framework for reliable identification of discrete particle crystallinity in nominally amorphous, nanoscale calcium carbonate particles which is of importance for fundamental studies of crystallisation and also for the process control during the synthesis of such surfactant stabilised nanoparticles for application as over-based fuel detergents.

Reductions in ATPase activity, actin sliding velocity, and myofibril stability yield muscle dysfunction in Drosophila models of myosin-based Freeman-Sheldon syndrome.

Using Drosophila melanogaster, we created the first animal models for myosin-based Freeman–Sheldon syndrome (FSS), a dominant form of distal arthrogryposis defined by congenital facial and distal skeletal muscle contractures. Electron microscopy of homozygous mutant indirect flight muscles showed normal (Y583S) or altered (T178I, R672C) myofibril assembly followed by progressive disruption of the myofilament lattice. In contrast, all alleles permitted normal myofibril assembly in the heterozygous state but caused myofibrillar disruption during aging. The severity of myofibril defects in heterozygotes correlated with the level of flight impairment. Thus our Drosophila models mimic the human condition in that FSS mutations are dominant and display varied degrees of phenotypic severity. Molecular modeling indicates that the mutations disrupt communication between the nucleotide-binding site of myosin and its lever arm that drives force production. Each mutant myosin showed reduced in vitro actin sliding velocity, with the two more severe alleles significantly decreasing the catalytic efficiency of actin-activated ATP hydrolysis. The observed reductions in actin motility and catalytic efficiency may serve as the mechanistic basis of the progressive myofibrillar disarray observed in the Drosophila models as well as the prolonged contractile activity responsible for skeletal muscle contractures in FSS patients.

Metallocene-catalyzed ethylene−α-olefin isomeric copolymerization: A perspective from hydrodynamic boundary layer mass transfer and design of MAO anion

This study reports a novel conceptual framework that can be easily experimented to evaluate the effects of hydrodynamic boundary layer mass transfer, methylaluminoxane (MAO) anion design, and comonomer steric hindrance on metallocene-catalyzed ethylene polymerization. This approach was illustrated by conducting homo- and isomeric copolymerization of ethylene with 1-hexene and 4-methyl-1-pentene in the presence of bis(n-butylcyclopentadienyl) zirconium dichloride (nBuCp)2ZrCl2, using (i) MAO anion 1 (unsupported [MAOCl2]−) and pseudo-homogeneous reference polymerization, and (ii) MAO anion 2 (supported Si−O−[MAOCl2]−) and in-situ heterogeneous polymerization. The measured polymer morphology, catalyst productivity, molecular weight distribution, and inter-chain composition distribution were related to the locus of polymerization, comonomer effect, in-situ chain transfer process, and micromixing effect, respectively. The peak melting and crystallization temperatures and %crystallinity were mathematically correlated to the parameters of microstructural composition distributions, melt fractionation temperatures, and average lamellar thickness. These relations showed to be insightful. The comonomer-induced enchainment defects and the eventual partial disruption of the crystal lattice were successfully modeled using Flory and Gibbs–Thompson equations. The present methodology can also be applied to study ethylene−α-olefin copolymerization, performed using MAO-activated non-metallocene precatalysts.

CPNA-1, a copine domain protein, is located at integrin adhesion sites and is required for myofilament stability in Caenorhabditis elegans.

We identify cpna-1 (F31D5.3) as a novel essential muscle gene in the nematode Caenorhabditis elegans. Antibodies specific to copine domain protein atypical-1 (CPNA-1), as well as a yellow fluorescent protein translational fusion, are localized to integrin attachment sites (M-lines and dense bodies) in the body-wall muscle of C. elegans. CPNA-1 contains an N-terminal predicted transmembrane domain and a C-terminal copine domain and binds to the M-line/dense body protein PAT-6 (actopaxin) and the M-line proteins UNC-89 (obscurin), LIM-9 (FHL), SCPL-1 (SCP), and UNC-96. Proper CPNA-1 localization is dependent upon PAT-6 in embryonic and adult muscle. Nematodes lacking cpna-1 arrest elongation at the twofold stage of embryogenesis and display disruption of the myofilament lattice. The thick-filament component myosin heavy chain MYO-3 and the M-line component UNC-89 are initially localized properly in cpna-1-null embryos. However, in these embryos, when contraction begins, MYO-3 and UNC-89 become mislocalized into large foci and animals die. We propose that CPNA-1 acts as a linker between an integrin-associated protein, PAT-6, and membrane-distal components of integrin adhesion complexes in the muscle of C. elegans.

Galectin-3 Protein Regulates Mobility of N-cadherin and GM1 Ganglioside at Cell-Cell Junctions of Mammary Carcinoma Cells

Galectin-3 binding to cell surface glycoproteins, including branched N-glycans generated by N-acetylglucosaminyltransferase V (Mgat5) activity, forms a multivalent, heterogeneous, and dynamic lattice. This lattice has been shown to regulate integrin and receptor tyrosine kinase signaling promoting tumor cell migration. N-cadherin is a homotypic cell-cell adhesion receptor commonly overexpressed in tumor cells that contributes to cell motility. Here we show that galectin-3 and N-cadherin interact and colocalize with the lipid raft marker GM1 ganglioside in cell-cell junctions of mammary epithelial cancer cells. Disruption of the lattice by deletion of Mgat5, siRNA depletion of galectin-3, or competitive inhibition with lactose stabilizes cell-cell junctions. It also reduces, in a p120-catenin-dependent manner, the dynamic pool of junctional N-cadherin. Proteomic analysis of detergent-resistant membranes (DRMs) revealed that the galectin lattice opposes entry of many proteins into DRM rafts. N-cadherin and catenins are present in DRMs; however, their DRM distribution is not significantly affected by lattice disruption. Galectin lattice integrity increases the mobile fraction of the raft marker, GM1 ganglioside binding cholera toxin B subunit Ctb, at cell-cell contacts in a p120-catenin-independent manner, but does not affect the mobility of either Ctb-labeled GM1 or GFP-coupled N-cadherin in nonjunctional regions. Our results suggest that the galectin lattice independently enhances lateral molecular diffusion by direct interaction with specific glycoconjugates within the adherens junction. By promoting exchange between raft and non-raft microdomains as well as molecular dynamics within junction-specific raft microdomains, the lattice may enhance turnover of N-cadherin and other glycoconjugates that determine junctional stability and rates of cell migration.

Back Cover: Double Single-Crystal-to-Single-Crystal Transformation and Small-Molecule Activation in Rhodium NHC Complexes (Angew. Chem. Int. Ed. 35/2011)

Chemical transformations that occur in single crystals without disruption of the crystal lattice are rare, particularly for organometallic complexes. C. Crudden and co-workers describe a dinitrogen–rhodium complex with an N-heterocyclic carbene in their Communication on page 8100 ff. that undergoes two back-to-back single-crystal-to-single-crystal transformations to O2 and CO complexes.

X‐ray diffraction, Raman, and differential thermal analyses of the thermal aging of a Kevlar®‐PBI blend fabric

AbstractA previous study of the effects of thermal aging on the tensile properties of a fabric made of a 60–40 wt % blend of Kevlar and PBI fibers has shown that exposure to elevated temperatures between 190 and 320°C results in a rapid decrease in tensile breaking force retention. In this article, X‐ray diffraction and Raman spectroscopy analyses were carried out to evaluate the consequences of thermal aging on the material's crystallinity. Differential thermal analyses were also undertaken to examine the evolution of the glass transition temperature of PBI following thermal exposure. X‐ray diffraction profiles show a gradual increase in the crystallinity with temperature and aging time, whereas a complete disappearance of spectral lines for aged samples in Raman analysis suggests instead a decrease in crystallinity as a consequence of exposure to elevated temperatures. The seemingly contradictory outcome obtained when using the two techniques led to the proposal of a new, alternative hypothesis to explain the observed results. This hypothesis involves two simultaneous events that occur during thermal aging: the increase of crystallite size in the direction parallel to coplanar sheets, and the disruption of the crystalline lattice in the direction perpendicular to those sheets. The glass transition temperature of PBI was found to shift towards the lower temperatures after thermal aging, a phenomenon that can be associated with random polymer chain scission caused by thermal aging. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

A Classification System to Assess the Crystallization Tendency of Organic Molecules from Undercooled Melts

Assessing the viability of an amorphous formulation strategy is of great importance in an era of drug discovery where a large percentage of new molecules have solubility limited dissolution rates, and disruption of the crystal lattice is a potential strategy to improve this process. The objective of the current study was to evaluate the glass forming ability (GFA) of a large data set of organic molecules and also to evaluate potential links between GFA and glass stability (GS). The crystallization tendency from the undercooled melt was evaluated for a group of 51 organic molecules and separated into three separate classes [class (I), class (II), class (III)] based upon the presence/absence of observable crystallization during a heating/cooling/heating cycle, as measured using differential scanning calorimetry (DSC). Class (I) molecules were further delineated based upon the observation of a crystalline [class (I-A)] or amorphous [class (I-B)] solid after quench cooling in liquid N(2). Principal component analysis (PCA) of various physiochemical descriptors suggested that molecules with low GFA tended to be low molecular weight (MW), rigid structures while class (III) molecules tended to be higher MW, more complex structures. For select compounds, it was observed that crystallization from the glassy state was much faster for compounds with a lower GFA. It is believed that nuclei are quenched into the glass during cooling for class (I-B) and (II) molecules, leading to more facile crystallization below T(g). In addition, these quenched in nuclei are also thought to be responsible for the recrystallization observed for these classes of molecules upon heating above T(g). In conclusion, the DSC screening method and classification scheme may be a useful tool to quickly assess the GFA and potential GS of new chemical entities during early drug development.

Mutating the Converter–Relay Interface of Drosophila Myosin Perturbs ATPase Activity, Actin Motility, Myofibril Stability and Flight Ability

We used an integrative approach to probe the significance of the interaction between the relay loop and converter domain of the myosin molecular motor from Drosophila melanogaster indirect flight muscle. During the myosin mechanochemical cycle, ATP-induced twisting of the relay loop is hypothesized to reposition the converter, resulting in cocking of the contiguous lever arm into the pre-power stroke configuration. The subsequent movement of the lever arm through its power stroke generates muscle contraction by causing myosin heads to pull on actin filaments. We generated a transgenic line expressing myosin with a mutation in the converter domain (R759E) at a site of relay loop interaction. Molecular modeling suggests that the interface between the relay loop and converter domain of R759E myosin would be significantly disrupted during the mechanochemical cycle. The mutation depressed calcium as well as basal and actin-activated MgATPase ( V max) by ∼ 60% compared to wild-type myosin, but there is no change in apparent actin affinity ( K m). While ATP or AMP-PNP (adenylyl-imidodiphosphate) binding to wild-type myosin subfragment-1 enhanced tryptophan fluorescence by ∼ 15% or ∼ 8%, respectively, enhancement does not occur in the mutant. This suggests that the mutation reduces lever arm movement. The mutation decreases in vitro motility of actin filaments by ∼ 35%. Mutant pupal indirect flight muscles display normal myofibril assembly, myofibril shape, and double-hexagonal arrangement of thick and thin filaments. Two-day-old fibers have occasional “cracking” of the crystal-like array of myofilaments. Fibers from 1-week-old adults show more severe cracking and frayed myofibrils with some disruption of the myofilament lattice. Flight ability is reduced in 2-day-old flies compared to wild-type controls, with no upward mobility but some horizontal flight. In 1-week-old adults, flight capability is lost. Thus, altered myosin function permits myofibril assembly, but results in a progressive disruption of the myofilament lattice and flight ability. We conclude that R759 in the myosin converter domain is essential for normal ATPase activity, in vitro motility and locomotion. Our results provide the first mutational evidence that intramolecular signaling between the relay loop and converter domain is critical for myosin function both in vitro and in muscle.

Converter Domain Residue R759 Interaction with Relay Loop Residue N509 in Drosophila Muscle Myosin is Critical for Motor Function, Myofibril Stability and Flight Ability

We used an integrative approach to probe the significance of the interaction between the relay loop and converter domain of Drosophila melanogaster skeletal muscle myosin. We generated a transgenic line expressing myosin with a mutation in the converter domain (R759E) at the relay loop interaction site. The mutation depresses calcium, basal or actin-activated MgATPase values (Vmax) by ∼60% and actin sliding velocity ∼35% compared to wild-type myosin. Ultrastructure of two-day-old adult fibers shows cracking and frayed myofibrils with some disruption of the myofilament lattice which becomes more severe in one-week-old adults. Flight ability is reduced in two-day-old flies compared to controls and is absent in 1-week-old adults. Thus appropriate interaction between the relay loop and converter domain is essential for normal motor function, myofibril stability and locomotion. To examine the specificity of this interaction, we used a compensatory mutational approach to attempt to restore the function of the R759E mutant myosin. Our modeling indicates that relay loop residues N509 and D511 interact with converter domain residue R759. To verify our model, we generated two transgenic lines that express R759E and either the N509K or D511K mutations. Interestingly, calcium, basal, and actin stimulated ATPase values are restored to 70% and actin sliding velocity is restored to 90% in N509K/R759E but not in D511K/R759E. Structurally fibers from 2-day or one-week -old adults appear morphologically normal in N509K/R759E and their flight ability is like wild type. However, D511K/R759E myofibrils do not show any improvement compared to R759E and flight ability is worse than R759E. Overall, our results reveal the critical interaction between the converter domain with relay loop residues and their role in myosin motor function and myofibril assembly/stability.

Structural and dynamical surface properties of phosphatidylethanolamine containing membranes

The hydration of solid dimyristoylphosphatidylethanolamine (DMPE) produces a negligible shift in the asymmetric stretching frequency of the phosphate groups in contrast to dimyristoylphosphatidylcholine (DMPC). This suggests that the hydration of DMPE is not a consequence of the disruption of the solid lattice of the phosphate groups as occurs in DMPC. The strong lateral interactions between NH 3 and PO 2 − groups present in the solid PEs remain when the lipids are fully hydrated and seem to be a limiting factor for the hydration of the phosphate group hindering the reorientation of the polar heads. The lower mobility is reflected in a higher energy to translocate the phosphoethanolamine (P–N) dipoles in an electrical field. This energy is decreased in the presence of increasing ratios of PCs of saturated chains in phosphoethanolamine monolayer. The association of PC and PE in the membrane affecting the reorientation of the P–N groups is dependent of the chain–chain interaction. The dipole potentials of PCs and PEs mixtures show different behaviors according to the saturation of the acyl chain. This was correlated with the area in monolayers and the hydration of the P–N groups. In spite of the low hydration, DMPE is still able to adsorb fully hydrated proteins, although in a lower rate than DMPC at the same surface pressure. This indicates that PE interfaces posses an excess of surface free energy to drive protein interaction. The relation of this free energy with the low water content is discussed.

On thin ice: surface order and disorder during pre-melting

The effect of temperature on the structure of the ice Ih (0001) surface is considered through a series of molecular dynamics simulations on an ice slab. At relatively low temperatures (200 K) a small fraction of surface self-interstitials (i.e. admolecules) appear that are formed exclusively from molecules leaving the outermost bilayer. At higher temperatures (ca. 250 K), vacancies start to appear in the inner part of the outermost bilayer exposing the underlying bilayer and providing sites with a high concentration of dangling hydrogen bonds. Around 250-260 K aggregates of molecules formed on top of the outermost bilayer from self-interstitials become more mobile and have diffusivities approaching that of liquid water. At approximately 270-280 K the inner bilayer of one surface noticeably destructures and it appears that at above 285 K both surfaces are melting. The observed disparity in the onset of melting between the two sides of the slab is rationalised by considering the relationship between surface energy and the spatial distribution of protons at the surface; thermodynamic stability is conferred on the surface by maximising separations between dangling protons at the crystal exterior. Local hotspots associated with a high dangling proton density are suggested to be susceptible to pre-melting and may be more efficient at trapping species at the external surface than regions with low concentrations of protons thus potentially helping ice particles to catalyse reactions. A preliminary conclusion of this work is that only about 10-20 K below the melting temperature of the particular water potential employed is major disruption of the crystalline lattice noted which could be interpreted as being "liquid", the thickness of this film being about a nanometre.

Photocyclization of 2,4,6-triethylbenzophenones in the solid state

Photocyclization of 2,4,6-triethylbenzophenones (TEBPs) into ( E)- or ( Z)-benzocyclobutenols (( E)- or ( Z)-CBs) is E-selective in solution. By contrast, upon solid-state photolysis, TEBP-3,4-diCl and especially TEBP-4- t-Bu gave ( Z)-CB relative to ( E)-CB with a much higher proportion than that in solution. For TEBP-4- t-Bu, the most major product in the solid state is an indanol derivative (Inol) ( E/ Z/Inol=1:3.9:10.3 at 9% conversion). On the basis of the X-ray crystallographic analysis, Inol and ( Z)-CB are both topochemical products. Notably, the relative proportion of ( E)-CB increased with increased conversion, namely with increased disruption of the crystal lattice. The DFT calculation of highly hindered 2,6-diisopropylbenzophenone (DIBP) was also conducted. These results in conjunction with the previous results on 2,4,6-triisopropylbenzophenones (TIBPs) indicate that CB is formed either via trans-enol followed by its conrotatory ring-closure (paths a and d) or through direct cyclization of biradical (BR) (path b) as shown in Scheme 1. Normally the former route is faster. However, in the crystalline state or in the case of sterically hindered phenyl ketones, path b tends to be adopted.

Rheology and Neutron Scattering of Block Copolymer Solutions

Non-Newtonian flow behavior was examined for butadiene-styrene (BS) diblock and BSB triblock copolymers dissolved in a S-selective solvent, dibutyl phthalate (DBP). Spherical domains of the non-solvated B blocks were arranged on a bcc lattice in both solutions at equilibrium, as revealed from small-angle neutron scattering (SANS). The solutions exhibited significant thinning under steady flow, which was well correlated with the disruption of the bcc lattice detected with SANS. The lattice disruption was most prominent at a shear rate comparable to the frequency of B/S concentration fluctuation. For the BS/DBP solution, the recovery of the lattice structure after cessation of flow was the slowest for the most heavily disrupted lattice, as naturally expected. In contrast, for the BSB/DBP solution, the recovery rate was insensitive to the magnitude of lattice disruption. This peculiar behavior of the BSB solution suggests that the rate-determining step of the recovery in this solution is the transient B/S mixing required for reformation of the S bridges connecting the B domains.