Slow Equilibrium Research Articles

Reaction of platinum(II) diamine and triamine complexes with selenomethionine

We have reacted [Pt(dien)Cl]Cl, [Pt(en)(D2O)2]2+, and [Pt(Me4en)(D2O)2]2+ [Me4en=N,N,N′,N′-tetramethylethylenediamine] with selenomethionine (SeMet). When [Pt(dien)Cl]Cl is reacted with SeMet, [Pt(dien)(SeMet-Se)]2+ is formed; two Se–CH3 resonances are observed due to the different chiralities at the Se atom upon platination. In a reaction of [Pt(dien)Cl]Cl with an equimolar mixture of SeMet and Met, the SeMet product forms more quickly though a slow equilibrium with approximately equal amounts of both products is reached. [Pt(Me4en)(D2O)2]2+ reacts with SeMet to form [Pt(Me4en)(SeMet-Se)(D2O)]2+ initially but forms [Pt(Me4en)(SeMet-Se,N)]+ ultimately. One stereoisomer of the chelate, assigned to the R chirality at the Se atom, dominates within the first few minutes of reaction. [Pt(en)(D2O)2]2+ forms a variety of products depending on reaction stoichiometry; when one equivalent or less of SeMet is added, the dominant product is [Pt(en)(SeMet-Se,N)]+. In the presence of excess SeMet, [Pt(en)(SeMet-Se)2]2+ is the dominant initially, but displacement of the en ligand occurs leading to [Pt(SeMet-Se,N)2] as the eventual product. Displacement of the en ligand from [Pt(en)(SeMet-Se,N)]+ does not occur. In reactions of K2PtCl4 with two equivalents of SeMet, [Pt(SeMet-Se,N)2] is formed, and three sets of resonances are observed due to different chiralities at the Se atoms. Only the cis geometric isomers are observed by 1H and 195Pt NMR spectroscopy.

Enhanced permanganate chemiluminescence

The significant enhancement of acidic potassium permanganate chemiluminescence by Mn(II) results from the concomitant presence of permanganate and Mn(III) in the reagent solution, which enables rapid production of the excited Mn(II) emitter with a wide range of analytes. Furthermore, the key Mn(III) co-reactant can be quickly generated by reducing permanganate with sodium thiosulfate, instead of the slow (~24 h) equilibration required when Mn(ii) is used. The emission from reactions with analytes such as tyrosine and fenoterol was over two orders of magnitude more intense than with the traditional permanganate reagent.

Intra- and inter-monomeric transfers in the light harvesting LHCII complex: the Redfield–Förster picture

We further develop the model of energy transfer in the LHCII trimer based on a quantitative fit of the linear spectra (including absorption (OD), linear dichroism (LD), circular dichroism (CD), and fluorescence (FL)) and transient absorption (TA) kinetics upon 650 nm and 662 nm excitation. The spectral shapes and relaxation/migration rates have been calculated using the combined Redfield-Förster approach capable of correctly describing fast relaxation within strongly coupled chlorophyll (Chl) a and b clusters and slow migration between them. Within each monomeric subunit of the trimeric complex there is fast (sub-ps) conversion from Chl's b to Chl's a at the stromal side accompanied by slow (>10 ps) equilibration between the stromal- and lumenal-side Chl a clusters in combination with slow (>13 ps) population of Chl's a from the 'bottleneck' Chl a604 site. The connection between monomeric subunits is determined by exciton coupling between the stromal-side Chl's b from the two adjacent subunits (Chl b601'-608-609 cluster) making a simultaneous fast (sub-ps) population of the Chl's a possible from both subunits. Final equilibration occurs via slow (>20 ps) migration between the Chl a clusters located on different monomeric subunits. This migration includes up-hill transfers from the red-most Chl a610-611-612 clusters located at the peripheral side in each subunit to the Chl a602-603 dimers located at the inner side of the trimeric LHCII complex.

Meizothrombin Is Unexpectedly Zymogen-Like: Its Slow Conversion to Proteinase Dominates Thrombin Production by Prothrombinase

AbstractAbstract 2215The proteolytic activation of prothrombin catalyzed by prothrombinase is a paradigm for zymogen activation resulting from ordered cleavage at multiple sites. Initial cleavage at Arg320 forms meizothrombin (mIIa). The associated conversion of zymogen to proteinase is instrumental in facilitating further processing at Arg271 to yield thrombin. A full kinetic explanation for this process remains obscure and controversial because of the limitations of standard kinetic approaches. We now uncover novel facets of this reaction by rapid kinetic studies to approximate single catalytic turnover. Product formation was measured continuously by stopped flow using Dansyl arginine (3-ethyl-1,5-pentanediyl) amide (DAPA) or discontinuously using rapid quenching and analysis by SDS-PAGE or peptidyl substrate cleavage following rapid mixing of preformed prothrombinase (0.3 μM) with prothrombin (0.3 μM). Prothrombin cleavage, assessed discontinuously, was essentially complete within 0.2 seconds. The results indicated initial cleavage at Arg320 to form mIIa followed by subsequent cleavage at Arg271 to produce thrombin. However, product formation measured continuously with DAPA, yielded a pronounced lag and proceeded ∼20-30-fold more slowly. The intermediate, mIIa, which is expected to bind DAPA was invisible to the continuous measurements. Analysis was further simplified using a recombinant prothrombin variant, which is exclusively cleaved at Arg320 to produce mIIa and not processed further. Continuous detection of proteinase formation by stopped flow proceeded ∼30-fold more slowly than cleavage at Arg320 measured discontinuously. These findings indicate that rapid cleavage at the Arg320 site is followed by an unexpectedly slow reaction (t½ ∼ 0.5–1 s) in which the cleaved product matures to form a competent active site. This conclusion was further tested employing stable mIIa prepared by the action of Ecarin on recombinant prothrombin variants that were not degraded further even without occluding the active site. Stopped flow kinetic studies for the binding of DAPA to these variants revealed markedly biphasic traces. The data could be globally analyzed according to a two step mechanism with an initial slow equilibrium between zymogen-like and proteinase forms in which only the proteinase form can bind the active site ligand. The zymogen- like and proteinase forms were approximately equally populated and interconverted slowly (t½ ∼ 0.5 s). These findings independently corroborate the conclusions from the kinetic studies of prothrombin cleavage. Accordingly, inclusion of this slow step could explain profiles of prothrombin depletion, transient formation of mIIa and the final appearance of thrombin seen in the action of prothrombinase on prothrombin. Zymogen-like mIIa accumulates at much higher concentrations than would be predicted from knowledge of the kinetics of the individual cleavage steps because its slow maturation to proteinase is required for further cleavage at Arg271. Thus, the rate-limiting maturation of mIIa to proteinase plays a dominant role in regulating thrombin formation. Furthermore, while mIIa is a poor catalyst for many of substrates of thrombin, it retains the ability to bind thrombomodulin and function in the anticoagulant pathway. As a result of its unexpectedly zymogen-like character and slow conversion to proteinase, mIIa produced as an intermediate by prothrombinase would be resistant to inhibition in plasma and thereby potentially be dispersed by flowing blood to exert its selectively anticoagulant functions distant from its site of production. Disclosures:No relevant conflicts of interest to declare.

Cryopreservation of hormonally induced sperm for the conservation of threatened amphibians with Rana temporaria as a model research species

The survival of hundreds of threatened amphibian species is increasingly dependent on conservation breeding programs (CBPs). However, there is an ongoing loss of genetic variation in CBPs for most amphibians, reptiles, birds, and mammals. Low genetic variation results in the failure of CBPs to provide genetically competent individuals for release in supplementation or rehabitation programs. In contrast, in the aquaculture of fish the perpetuation of genetic variation and the production of large numbers of genetically competent individuals for release is accomplished through the cryopreservation of sperm. Successful protocols for the cryopreservation of amphibian sperm from excised testes, and the use of motile frozen then thawed sperm for fertilisation, have been adapted from those used with fish. However, there have been no protocols published for the cryopreservation of amphibian hormonally induced sperm (HIS) that have achieved fertility. We investigated protocols for the cryopreservation of amphibian HIS with the European common frog ( Rana temporaria) as a model research species. We induced spermiation in R. temporaria through the intraperitoneal administration of 50 μg LHRHa and sampled HIS through expression in spermic urine. Highly motile HIS at a concentration of 200 × 10 6/mL was then mixed 1:1 with cryodiluents to form cryosuspensions. Initial studies showed that; 1) concentrations of ∼15 × 10 6/mL of HIS achieve maximum fertilisation, 2) TRIS buffer in cryodiluents did not improve the recovery of sperm after cryopreservation, and 3) high concentrations of DMSO (dimethylsulphoxide) cryoprotectant reduce egg and larval survival. We then compared four optimised cryopreservation protocols for HIS with the final concentrations of cryodiluents in cryosuspensions of; 1) DMSO, (½ Ringer Solution (RS), 10% sucrose, 12% DMSO); 2) DMSO/egg yolk, (½ RS, 10% sucrose, 12% DMSO, 10% egg yolk), 3) DMFA, (½ RS, 10% sucrose, 12% dimethylformamide (DMFA)), and 4) MIS/glycerol, (Motility Inhibiting Saline (MIS), 5% glycerol, 2.5% sucrose, 5% egg yolk). Cryosuspensions were frozen in LN 2 vapour, stored in LN 2, thawed in 40° C water bath, and activated by slow equilibration with 1:3 dilutions of cryosuspensions with 20 mM/L NaCl. Protocol efficacies were assessed through the post-thaw percentage of; 1) sperm motility, 2) sperm membrane integrity, 3) fertilisation, 4) fertilised eggs hatching, and 5) larval survival from fertilised eggs to 7 d. The DMFA cryodiluent proved superior to the DMSO based cryodiluents in recovery of sperm motility and fertility after cryopreservation. MIS/glycerol cryodiluent provided low sperm viability and no fertility. Considering the ease of obtaining HIS from many Rana species, the success of our protocols offer the potential for the perpetuation of the genetic variation of the 42 threatened Rana species and the 193 threatened Ranid species in total.

Unusual biophysics of immune signaling-related intrinsically disordered proteins

Intrinsically disordered (ID) regions, the regions that lack a well-defined three-dimensional structure under physiological conditions, are preferentially located in the cytoplasmic segments of plasma membrane proteins, many of which are known to be involved in cell signaling. This is in line with our studies that demonstrated that cytoplasmic domains of signaling subunits of immune receptors, including those of ζ, CD3ε, CD3δ and CD3γ chains of T cell receptor, Igα and Igβ chains of B cell receptor as well as the Fc receptor γ chain represent a novel class of ID proteins (IDPs). The domains all have one or more copies of an immunoreceptor tyrosine-based activation motif, tyrosine residues of which are phosphorylated upon receptor engagement in an early and obligatory event in the signaling cascade. Our studies of these IDPs revealed several unusual biophysical phenomena, including (1) the specific dimerization of disordered protein molecules, (2) the fast and slow dimerization equilibrium, depending on the protein, (3) no disorder-to-order transition and the lack of significant chemical shift and peak intensity changes upon dimerization or interaction with a well-folded partner protein and (4) the dual mode of binding to model membranes (with and without folding), depending on the lipid bilayer stability. Here, I highlight several of these studies that not only facilitate a rethinking process of the fundamental paradigms in protein biophysics but also open new perspectives on the molecular mechanisms involved in receptor signaling.

Streptococcus pyogenes Ser/Thr Kinase-regulated Cell Wall Hydrolase Is a Cell Division Plane-recognizing and Chain-forming Virulence Factor

Cell division and cell wall synthesis are closely linked complex phenomena and play a crucial role in the maintenance and regulation of bacterial virulence. Eukaryotic-type Ser/Thr kinases reported in prokaryotes, including that in group A Streptococcus (GAS) (Streptococcus pyogenes Ser/Thr kinase (SP-STK)), regulate cell division, growth, and virulence. The mechanism of this regulation is, however, unknown. In this study, we demonstrated that SP-STK-controlled cell division is mediated under the positive regulation of secretory protein that possesses a cysteine and histidine-dependent aminohydrolases/peptidases (CHAP) domain with functionally active cell wall hydrolase activity (henceforth named as CdhA (CHAP-domain-containing and chain-forming cell wall hydrolase). Deletion of the CdhA-encoding gene resulted in severe cell division and growth defects in GAS mutants. The mutant expressing the truncated CdhA (devoid of the CHAP domain), although displayed no such defects, it became attenuated for virulence in mice and highly susceptible to cell wall-acting antibiotics, as observed for the mutant lacking CdhA. When CdhA was overexpressed in the wild-type GAS as well as in heterologous strains, Escherichia coli and Staphylococcus aureus, we observed a distinct increase in bacterial chain length. Our data reveal that CdhA is a multifunctional protein with a major function of the N-terminal region as a cell division plane-recognizing domain and that of the C-terminal CHAP domain as a virulence-regulating domain. CdhA is thus an important therapeutic target.

Introduction of 2,4-dichlorophenoxyacetic acid into soil with solvents and resulting implications for bioavailability to microorganisms

Slow equilibration of introduced chemicals through tortuous pore space limits uniform substrate distribution in soil biodegradation studies. The necessity of introducing poorly soluble xenobiotics via organic solvents, the volume of which is minimized to limit toxicity, likely also affects xenobiotic distribution. Our objective was to investigate relative effects of carrier solvent choice and volume on xenobiotic distribution, apparent solvent toxicity, and soil degradation of 2,4-dichlorophenoxy acetic acid. Incubations using four carrier solvents ranging in properties showed that the fraction of 2,4-D mineralized was a hyperbolic function of solvent volume used (0.02–10 μl g−1), attributed to compensating effects of herbicide bioavailability and solvent toxicity. Substrate concentration influenced mineralization of herbicide introduced with organic carriers, but not water. Fraction of material readily desorbed increased when water was the carrier. Results suggest that solvent toxicity should be balanced with uniformity of substrate distribution when using organic carriers in soils. Substrate bioavailability is a ubiquitous issue in terrestrial microbiology research, thus limitations observed herein broadly apply to microbiology questions about introduced substances in soil. We advocate the development of tools to characterize variable conditions among soil compartments, estimates of substrate bioavailability, and linkage of this information to microbial data.

Acceptor switching and axial rotation of the water dimer in matrices, observed by infrared spectroscopy

Several isotopologues of the water dimer have been studied in different matrices (Ne, Ar, Kr, and p-H(2)) at very low temperatures. A fine structure, which is more or less matrix independent and very similar for different intramolecular fundamentals of the same isotopologic dimer, is present on the high wavenumber side of the main component. The bound OD (OH) stretches of the donor have temperature dependent components. The fine structure and temperature dependency is interpreted as evidence for acceptor switching and rotation of the water dimer around its O-O axis in the matrices studied here. The slow nuclear spin equilibration in H(2)O inhibits the thermal equilibration between the acceptor switching states in H(2)O-DOH and H(2)O-DOD. The condensed environment slows down the acceptor switching rate compared to the gas phase. The antisymmetric stretch of the proton acceptor is assigned by combining information from different matrices with the rotation-acceptor switching model.

Mechanisms and specificity of factor XIa and trypsin inhibition by protease nexin 2 and basic pancreatic trypsin inhibitor

Factor XIa (FXIa) inhibition by protease nexin-2 (PN2KPI) was compared with trypsin inhibition by basic pancreatic trypsin inhibitor (BPTI). PN2KPI was a potent inhibitor of FXIa (K(i) ∼ 0.81 nM) and trypsin (K(i) ∼ 0.03 nM), but not of other coagulation proteases (thrombin, FVIIa, FIXa, FXa, FXIIa, plasmin, kallikrein, K(i) > 185 nM). PN2KPI was ∼775-fold more potent than BPTI in FXIa inhibition, but both exhibited similar potencies against trypsin. Studies of FXIa and trypsin inhibition by PN2KPI and BPTI and P1 site swap mutants (PN2KPI-R15 K, BPTI-K15 R) demonstrated that FXIa inhibition by PN2KPI and P1 site swap mutants and trypsin inhibition by PN2KPI and BPTI conform to a single-step, slow equilibration inhibitory mechanism, whereas FXIa-inhibition by BPTI follows a classical, competitive inhibitory mechanism. Mutation of P1 impaired FXIa inhibition by PN2KPI-R15 K ∼14-fold, enhanced FXIa inhibition by BPTI-K15 R ∼150-fold, and had no effect on trypsin inhibition. Arginine at the P1 site of either PN2KPI or BPTI confers high affinity and specificity for FXIa, whereas either arginine or lysine suffices for trypsin inhibition. Thus, PN2KPI is a highly specific inhibitor of FXIa among coagulation enzymes, but the flexibility of trypsin renders it susceptible to inhibition by both wild-type and mutant forms of PN2KPI and BPTI.

NMR structure of the protein NP_247299.1: comparison with the crystal structure

The NMR structure of the protein NP_247299.1 in solution at 313 K has been determined and is compared with the X-ray crystal structure, which was also solved in the Joint Center for Structural Genomics (JCSG) at 100 K and at 1.7 Å resolution. Both structures were obtained using the current largely automated crystallographic and solution NMR methods used by the JCSG. This paper assesses the accuracy and precision of the results from these recently established automated approaches, aiming for quantitative statements about the location of structure variations that may arise from either one of the methods used or from the different environments in solution and in the crystal. To evaluate the possible impact of the different software used for the crystallographic and the NMR structure determinations and analysis, the concept is introduced of reference structures, which are computed using the NMR software with input of upper-limit distance constraints derived from the molecular models representing the results of the two structure determinations. The use of this new approach is explored to quantify global differences that arise from the different methods of structure determination and analysis versus those that represent interesting local variations or dynamics. The near-identity of the protein core in the NMR and crystal structures thus provided a basis for the identification of complementary information from the two different methods. It was thus observed that locally increased crystallographic B values correlate with dynamic structural polymorphisms in solution, including that the solution state of the protein involves a slow dynamic equilibrium on a time scale of milliseconds or slower between two ensembles of rapidly interchanging conformers that contain, respectively, the cis or trans form of the C-terminal proline and represent about 25 and 75% of the total protein.

Iridium Compounds with κ-P,P,Si(biPSi) Pincer Ligands: Favoring Reactive Structures in Unsaturated Complexes

The structure, coordination properties, insertion processes, and dynamic behavior in solution of the five-coordinate complexes [IrXH(biPSi)] (biPSi = kappa-P,P,Si-Si(Me){(CH(2))(3)PPh(2)}(2); X = Cl (1), Br (2), or I (3)) have been investigated. The compounds are formed as mixtures of two isomers, anti and syn, in slow equilibrium in solution. The equilibrium position depends on the halogen and the solvent. Both isomers display distorted square-based pyramidal structures in which the vacant position sits trans to silicon. The equatorial plane of the syn isomer is closer to the T structure due to distortions of steric origin. The small structural differences between the isomers trigger remarkable differences in reactivity. The syn isomers form six-coordinate adducts with chlorinated solvents, CO, P(OMe)(3), or NCMe, always after ligand coordination trans to silicon. The anti isomers do not form detectable adducts with chlorinated solvents and coordinate CO or P(OMe)(3) either trans to silicon (kinetic) or trans to hydride (thermodynamic). NCMe coordinates the anti isomers exclusively at the position trans to hydride. Qualitative and quantitative details (equilibrium constants, enthalpies, entropies, etc.) on these coordination processes are given and discussed. As a result of the different coordination properties, insertion reagents such as acetylene, diphenylacetylene, or the alkylidene resulting from the decomposition of ethyl diazoacetate selectively insert into the Ir-H bond of 1-syn, not into that of 1-anti. These reactions give five-coordinate syn alkenyl or alkyl compounds in which the vacancy also sits trans to silicon. Acetylene is polymerized in the coordination sphere of 1. The nonreactive isomer 1-anti also evolves into the syn insertion products via anti<-->syn isomerizations, the rates of which are notably dependent on the nature of the insertion reactants. H(2) renders anti<-->syn isomerization rates of the same order as the NMR time scale. The reactions are second order (k(obs) = k(anti<-->syn)[H(2)]) and do not involve H(2)/IrH hydrogen atom scrambling. A possible isomerization mechanism, supported by MP2 calculations and compatible with the various experimental observations, is described. It involves Ir(V) intermediates and a key sigma Ir-(eta(2)-SiH) agostic transition state. A similar transition state could also explain the anti<-->syn isomerizations in the absence of oxidative addition reactants, although at the expense of high kinetic barriers strongly dependent on the presence of potential ligands and their nature.

Excited Stilbene: Intramolecular Vibrational Redistribution and Solvation Studied by Femtosecond Stimulated Raman Spectroscopy

Excited-state relaxation of cis- and trans-stilbene is traced with femtosecond stimulated Raman spectroscopy, exploiting S(n) <-- S(1) resonance conditions. For both isomers, decay in Raman intensity, shift of spectral positions, and broadening of the bands indicate intramolecular vibrational redistribution (IVR). In n-hexane this process effectively takes 0.5-0.7 ps. Analysis of the intensity decay allows us to further distinguish two phases for trans-stilbene: fast IVR within a subset of modes (approximately 0.3 ps) followed by slower equilibration over the full vibrational manifold (approximately 0.9 ps). In acetonitrile IVR completes with 0.15 ps; this acceleration may originate from symmetry breakage induced by the polar solvent. Another process, dynamic solvation by acetonitrile, is seen as spectral narrowing and characteristic band shifts of the C=C stretch and phenyl bending modes with 0.69 ps. Wavepacket motion is observed in both isomers as oscillation of low-frequency bands with their pertinent mode frequency (90 or 195 cm(-1) in trans-stilbene; 250 cm(-1) in cis-stilbene). Anharmonic coupling shows up as a modulation of high-frequency peak positions by phenyl/ethylene torsion modes of 57 and 90 cm(-1). Decay and shift of the 90 cm(-1) inverse Raman band within the first 0.3 ps suggests a gradual involvement of phenyl/ethylene torsion in relaxation. In cis- and trans-stilbene, low-frequency spectral changes are found within 0.15 ps, indicating an additional ultrafast process.

Mechanisms of Successful Drug Action

The mechanism of drug action (MoA) couples molecular interactions to a physiological response. MoA includes the molecular target and the mechanism that communicates the response. The MoA defines the molecular descriptor (such as KI, kon, koff, and conformational state) for a biochemically efficient mechanism and optimal therapeutic index. Target‐focused drug discovery that is driven solely by equilibrium binding, without consideration for MoA and the molecular descriptors for an optimal therapeutic index, is a common practice in drug discovery today. In order to better understand the role of MoA in drug discovery we analyzed the MoAs of New Molecular Entities (NMEs) approved by the US FDA between 1999 and 2008. Data was collected from the product labels approved by the FDA and reports describing the discovery process. We identified that approximately 20% of the NMEs were first in class and/or had novel MoAs. Target‐focused approaches accounted for less than half of the novel MoAs and these targets were generally biologically well validated with molecular descriptors that included irreversible and slow kinetics, state dependence, induced conformations and equilibrium binding. The majority of the novel MoAs were identified from compound‐focused drug discovery by compound screening in physiological assays and modification of natural substances.

Influence of Pt II and Pd II coordination on the equilibrium of 2,2′-dipyridylketone (dpk) with its hydrated gem-diol form (dpk·H 2O)

2,2′-Dipyridylketone (dpk), when acting as a chelating ligand for Pd II or Pt II, is in slow equilibrium with its corresponding gem-diol form (dpk·H 2O). In D 2O, equilibrium constants K = (dpk·H 2O)/(dpk) change from ca. 0.04 for the free ligand to ca. 3 in the corresponding complexes with cis-[Pt(H 2O) 2] 2+. In solution, species of both ligands can be identified and differentiated by 1H NMR spectroscopy, and in the trinuclear μ-OH bridged Pt II complex [Pt 3( μ-OH) 3(dpk·H 2O) 2(dpk)](NO 3) 3·4.5H 2O ( 4), both types of ligands are present simultaneously in a ratio of (dpk·H 2O):(dpk) = 2. As demonstrated with a series of Pd II complexes containing dpk·H 2O and dpk ligands, a straightforward differentiation is possible when DMSO- d 6 is used as solvent, because then also the OH protons of dpk·H 2O are observable. It is also shown that monocrystalline [PdCl 2(dpk·H 2O)] ( 1), when dissolved in DMSO- d 6, partially converts, with loss of H 2O, to [PdCl 2(dpk)].

Photocatalysis of chloroform degradation by μ-dichlorotetrachlorodipalladate(II)

Abstract Unlike other chlorometallate complexes that catalyze the photodecomposition of haloalkanes through photodissociation of a chlorine atom, both PdCl 4 2 - and Pd 2 Cl 6 2 - catalyze chloroform decomposition through a process that appears to involve C–H bond breakage from an excited state association complex with chloroform. This would account for the greatly retarded rate of decomposition in CDCl3 and for the generation of CCl4 as a side product. In chloroform, Pd 2 Cl 6 2 - and PdCl 4 2 - are in slow equilibrium with each other. The rate for the conversion of Pd 2 Cl 6 2 - – PdCl 4 2 - in chloroform at 23 °C obeys the expression (0.03 M−1 s−1) [ PdCl 4 2 - ][Cl−]. The equilibrium constant, K = [ Pd 2 Cl 6 2 - ][Cl−]2/[ PdCl 4 2 - ]2, was estimated to be 3 × 10−3 M in CHCl3.

AFM Investigations of Phase Separation in Supported Membranes of Binary Mixtures of POPC and an Eicosanyl-Based Bisphosphocholine Bolalipid

Supported membranes prepared from binary mixtures of DOPC and the bolalipid C(20)BAS have been examined by atomic force microscopy (AFM). The supported membranes are phase separated to give a thicker DOPC-rich phase and a thinner bolalipid-rich phase for a range of lipid compositions. These results confirm an earlier prediction from mean field theory that phase separation is the thermodynamically stable state for membranes containing approximately equimolar C(20)BAS and double chain monopolar lipids with chain lengths exceeding 15 carbons. Hydrophobic mismatch between the monopolar lipid hydrocarbon chains and the membrane spanning bolalipid chains was suggested to provide the driving force for phase separation. The AFM results also show that the morphology of the mixed POPC:C(20)BAS supported membranes varies significantly with the conditions used to prepare the vesicles and supported membrane samples. The complex membrane morphologies observed are attributed to the interplay of several factors, including a compositionally heterogeneous vesicle population, exchange of lipid between the vesicle solution and solid substrate during formation of the supported membrane, and slow equilibration of domains due to pinning of the lipids to the solid support.

Solvent Effect in Dynamic Superstructures from Au Nanoparticles and CdTe Nanowires: Experimental Observation and Theoretical Description

Solvent effects on luminescence in nanocolloids are typically related to changes in the dielectric constant around the light-emitting species, but they can have a completely different nature in complex dynamic nanoscale assemblies. Hybrid superstructures were assembled from Au nanoparticles (NPs) and CdTe nanowires (NWs) via poly(ethylene glycol) (PEG) bridges and provide the first example of solvent-responsive dynamic nanoscale assemblies from NWs. The photoluminescence (PL) intensity of the CdTe NWs was found to be dependent on the hydrophilic/hydrophobic balance of the solvent (water, methanol, ethanol, and 2-propanol) surrounding the superstructure and displayed slow equilibration kinetics. PL gradually decreased over a period of 2000 s by ca. 50% for ethanol and ca. 70% for 2-propanol, whereas it remained constant for water and methanol. This phenomenon was attributed to the solvent dependence of the radius of gyration (RF) of the PEG bridges between the NPs and NWs, which swells in ethanol and 2-pro...

Clinoptilolite Adsorption Capability of Ammonia in Pig Farm

In this paper, clinoptilolite, as an adsorbing material, which adsorption capability of ammonia was studied. Clinoptilolite is a porous crystal material, which adsorption properties of clinotiolite are strongly related to the framework structure, which has performance for the physical adsorption and ion exchange. China is in rich of nature clinoptilolite, which is cheap and suitable for extensive application in pig house. The experiment indicated that clinoptilolite had a characteristic of “rapid adsorption, slow equilibrium”, it took 3hours to reach adsorption equilibrium, clinoptilolite's particle size, moisture content and dosage had important effects on saturation adsorption time and ammonia adsorption capacity. With decreasing the particle size, clinoptilolite adsorption capacity increased, and the higher ammonia concentration, the better adsorption effect in the “rapid adsorption” phase. Different clinoptilolite's moistures also played an important role for adsorption effect, in the “rapid adsorption” phase, the effect was the best when moisture content of clinoptilolite was 40%; in the phase of “slow equilibrium”, wet clinoptilolite adsorption would be better than the natural, the rank was: 40%>50%>30%>20%>60%>the natural. By regression analyze, when moisture content was 42%, adsorption capability could be the best. Besides, clinoptilolite adsorption capacity was studied, per unit saturation adsorption capacity of 10g nature clinoptilolite was 0.09mg/g, 20g nature clinoptilolite's was 0.13mg/g. Therefore, it could be seen that increasing the amount of clinoptilolite would improve the total and units clinoptilolite adsorption capacity. Considering the significant sorption for ammonia, the method of clinoptilolite adsorption could be simple and economic, it should be foreseeable that clinoptilolite adsorption would have a good prospect for air purification in pig farm.

Permeability of Model Stratum Corneum Lipid Membrane Measured using Quartz Crystal Microbalance: Non-Fickian Diffusion and Transient Membrane Swelling

The stratum corneum (SC) is the outermost layer of the epidermis. Stacked intercellular lipid membranes found in the SC play a crucial role in regulating transport of water through the skin. In this work, we present a new method to determine the water permeability of a model SC lipid membrane using a quartz crystal microbalance (QCM) [Langmuir, 2009, 25 (10), 5762-5766]. We investigate a model SC lipid membrane comprising an equimolar mixture of brain ceramide (CER), cholesterol (CHO) and palmitic acid (PA), and use QCM to determine the diffusivity (D), solubility (S) and permeability (P) of water vapor. We have found that the water transport in model skin lipid membranes can not be described in terms of Fickian process as the effective diffusion constant depends on the thickness of the lipid bilayer stacks. This may be due to slow equilibration process related to the membrane hydration. Using polarity-sensitive probe, PRODAN, we have found that the time scale of slow equilibration process is ∼ 10 hrs, which may explain the non-Fickian behavior of a skin lipid membrane.