bluuebunny/crossref_metadata_2025_split huggingface dataset:
High‐pressure differential thermal analysis of lamellar to lamellar and lamellar to non‐lamellar lipid phase transitions
Authors: Landwehr A. , Winter R. 
Published: July 2012

AbstractHydrated phospholipids, which provide model systems for lipid membranes, display a variety of polymorphic phases, depending on their molecular structure and environmental conditions. In this study, high hydrostatic pressure has been used as a physical parameter to study the thermodynamic properties and phase behaviour of phospholipid systems, and because high pressure is a characteristic feature of certain natural membrane environments. We built a new high‐pressure differential thermal analysis (DTA) apparatus, which allowed us to study the calorimetric properties and the temperature and pressure dependent phase behaviour of lipid systems up to temperatures of 360 K and pressures of 250 MPa. In particular, we focussed on the effect of pressure on lamellar to lamellar and on lamellar to non‐lamellar phase transitions of phospholipid systems, differing in lipid chain saturation and headgroup structure. The possible biophysical implications of this study are discussed.
Zero length column chromatography to characterise microporous sorbents by means of kinetic data
Authors: Micke A. , Bülow M. , Kočiřik M. 
Published: July 2012

AbstractAlternative methods for simulation of ZLC chromatography behaviour are presented. The phenomena of accumulation in the fluid phase, non‐linearity of the adsorption isotherm and inlet concentration disturbance are analysed. Models for pure diffusion and barrier limited sorption kinetics for the ZLC chromatography are compared. In addition the asymptotic behaviour of the model solutions for small times is examined.
Conformational order of amphiphilic chain molecules in lyotropic liquid‐crystalline phases
Authors: Schnepp Werner , Schmidt Claudia 
Published: July 2012

AbstractThe nonionic surfactant hexa(ethyleneglycol) n‐dodecyl methylether in aqueous liquid‐crystalline phases is studied by deuterium NMR Spectroscopy. From the quadrupole splittings of the surfactant, which is deuterated either in the hydrophobic alkyl chain or in the hydrophilic oxyethylene chain, order profiles of both the alkyl and oxyethylene moiety are obtained. Characteristic features of the order profiles are related to the conformations of the surfactant molecules. The observed temperature dependence of the quadrupole splittings is explained by changes of the conformational equilibrium.
Comparison between IR‐emission spectra of CaO ‐ Al2O3‐melts (1873 K) and IR‐absorption spectra (293 K)
Authors: Mausbach Klaus , Nowack Norbert , Schlegelmilch Franz 
Published: July 2012

AbstractThe IR‐emission of CaO ‐ Al2O3‐melts (1873 K) is caused by IR‐active molecular vibrations of AlO‐ and AlO‐complexes. In the CaO ‐ Al2O3‐melts the equilibrium AlO + O2‐ ⟺ AlO dominates. At lower temperatures (1000°C) the formation of condensed AlO‐complexes was observed (solid phases).
Two‐dimensional phase transitions in electrochemically formed adlayers on gold
Authors: Hölzle M. H. , Kolb D. M. 
Published: July 2012

AbstractTwo‐dimensional phase transitions occurring during electrodeposition of the first Cu monolayer onto Au(111) at underpotentials or during adsorption of coumarin from solution at Au(111) and the reconstructed Au(100)‐ (hex) electrodes have been studied by cyclic voltammetry and potential step experiments. Rising current transients were observed for both systems, indicating the presence of nucleation‐and‐growth phenomena during monolayer formation. However, phase transitions in the adlayers were observed only for the densely packed gold surfaces, and not for the more open surfaces of Au(100)‐(1×1) or Au(110). A comparison between experiment and classical model transients revealed that surface imperfections may have to be taken into account when working with solid electrodes, rather than with mercury for which these models have been derived.
Prewetting of helium on weak binding substrates
Authors: Taborek P. , Rutledge J. E. 
Published: July 2012

AbstractRecent theoretical and experimental work has shown that alkali metal surfaces have extremely weak potentials for physical adsorption, which leads to very unusual thermodynamic properties of adsorbed films. We have used a microbalance adsorption isotherm technique to investigate the phase diagram of He films on cesium. This experimental system has provided the first example of a surface which is not wet by superfluid helium, and the first experimental observation of the prewetting line. Near the wetting temperature Tw ≈ 2 K, we have observed large hysteresis effects associated with the nucleation of the thin phase. At higher temperatures, the prewetting line terminates at a prewetting critical point T ≈ 2.5 K. This system is particularly well suited to surface phase transition studies, since the interaction parameters can be tuned continuously by varying the thickness of the cesium substrate, or by doping the film with 3He.
Spinodal decomposition in thin polymer films
Authors: Krausch Georg , Dai Chi‐An , Kramer Edward J. , Bates Frank S. 
Published: July 2012

AbstractWe have studied the influence of the boundary surfaces on spinodal decomposition in thin films of a critical polymer mixture. The wetting layer formed during spinodal decomposition is found to grow as t1/3 and the corresponding composition vs. depth profiles exhibit dynamic scaling behavior. For sufficiently thin films, the effects of the two boundary surfaces interfere and the overall domain structure is found to be strongly thickness dependent.
Universal order‐parameter profiles for critical adsorption and the extraordinary transition: A comparison of ϵ expansion and Monte Carlo results
Authors: Smock M. , Diehl H. W. , Landau D. P. 
Published: July 2012

AbstractThe universal, scaled order parameter profiles P± (z/ξ) for critical adsorption of a fluid or fluid mixture onto a wall or interface, and for the extraordinary transition of the semi‐infinite Ising model, are discussed theoretically, where z is the distance from the interface, ξ(T) is the bulk correlation length, and the subscript + (‐) refers to the approach from above (below) Tc. Recent results to first order in the ϵ = 4–d expansion are extrapolated to d = 3 space dimensions and compared with new Monte Carlo results. In order to obtain meaningful extrapolations it is crucial that both the exponential decay at large ζ as well as the known algebraic behavior P±(ζ)∼ζ−β/v small ζ be correctly reproduced. To this end a recently developed novel RG scheme involving a z dependent amplitude renormalization is used. Reasonable agreement of our extrapolations with the Monte Carlo results and some experimental results is obtained.
Primary products of the elementary reactions of CH2CO with F, Cl, and OH in the gas phase
Authors: Grußdorf J. , Nolte J. , Temps F. , Wagner H. Gg. 
Published: July 2012

AbstractThe absolute yields of the primary products of the reactions of CH2OH with F and Cl atoms and OH radicals were measured in the gas phase at room temperature using a discharge flow apparatus connected to a Far Infrared Laser Magnetic Resonance (FIR‐LMR) spectrometer. Quantitative determinations of the reaction pathways were carried out by employing reference reactions with known product yields. The measurements yielded the branching ratios for the following channelsmagnified imageThus, the main reaction channels were found to be addition of the F, Cl, or OH, respectively, to the CH2 moiety followed by elimination of CO.
Electronic transitions of salicylaldehydeethylenediimine and its Cu(II) complexes
Authors: Hoshi Toshihiko , Inomaki Yoshihiro , Wada Mikiko , Yamada Yasunori , Okubo Jun , Kobayashi Michio , Inoue† Hiroyasu 
Published: July 2012

AbstractElectronic absorption spectra of Salicylaldehydeethylenediimine (salen) and its Cu(II) complexes have been measured in various media at various temperatures. It is found that salen takes an enol‐imine‐type structure in cyclohexane and exists as an equilibrium mixture of enol‐imine and keto‐amine type species in alcoholic media. The polarization spectrum of salen‐Cu(II) measured in the stretched PVA film shows that 282, ∼ 290, ∼ 250, and 230.4 nm bands are polarized along the longer‐molecular‐axis, and 354, 273.0, 242.4 and ∼ 220 nm bands along the shorter‐molecular‐axis. The 242.4 and ∼ 250 nm bands can be assigned to intramolecular charge transfer (CT) transitions between the metal ion and ligand and between the two π‐electronic systems of the ligand, respectively. The complex of salen‐Cu(II) forms a dimer in EPA (ether: isopentane: ethanol = 5:5:2 in volume) at low temperatures. The first two bands of the monomer at 380 and 362 nm are blue‐shifted by the dimer formation, and appear at 370 and 351 nm, respectively, and the 278 nm monomer band splits into two bands at 275 and 267 nm. These spectral changes on the dimer formation are well reproduced by an extended PPP calculation.
Near‐infrared spectroscopic investigations on phase behaviour and hydrogen‐bonding of polar substances in supercritical chlorotrifluoromethane. Part I — phase behaviour
Authors: Ochel Henning , Schneider Gerhard M. 
Published: July 2012

AbstractThe phase behaviour of fluid mixtures of polar substances in supercritical chlorotrifluoromethane CClF3 was investigated at pressures up to 100 MPa and temperatures from 323 K to 398 K. The measurements were performed by high pressure near‐infrared spectroscopy using the analytical method. An optical high pressure cell equipped with sapphire windows and fibre optics was used. The total substance concentration was obtained from the first overtone region of C‐H stretching vibration (1600–1800nm), as well as from the second overtone region (1150–1300 nm) and its combination with other vibrational molecular modes (2100–2350 nm). Solubilities of dodecanoic acid, hexadecanoic acid, their corresponding methyl esters, δ‐valerolactam and δ‐caprolactam in the supercritical gas are presented. The influence of molecular properties on the phase behaviour is discussed.
Magnetic relaxation and molecular motions in liquid 3,5‐dimethylpyridine
Authors: Suchański W. , Kempka M. , Peplińska B. , Pająk Z. 
Published: July 2012

AbstractThe nuclear spin‐lattice relaxation times of 14N have been measured as a function of temperature for liquid 3,5‐dimethylpyridine. These results together with the values of the 13C spin‐lattice relaxation times and the factor of nuclear Overhauser enhancement for the ring C2,6 and C4 carbons presented previously [15], have been analyzed in terms of relative influence of molecular shape and attractive dipolar forces on anisotropy of the molecular reorientations. Principal components of the rotational diffusion tensor have been determined.
Molecular dynamics study of the dielectric constant of water under high pressure and temperature conditions
Authors: Wasserman Evgeny , Wood Bernard , Brodholt John 
Published: July 2012

AbstractThe static dielectric constant of a water model (extended simple point charges, SPC/E) was evaluated by molecular dynamics simulations in the (N, V, E) ensemble for temperatures ranging from T = 324 K to 1278 K and densities from 0.257 g/cm3 to 1.1108 g/cm3. The dielectric constants calculated from fluctuations of the total dipole moment of the simulation box in the absence of an external field, and those obtained from the polarization response to an applied field were demonstrated to be consistent. Simulations within the pressure‐temperature range (up to 500 MPa and 823 K) of available experimental data yield dielectric constant in very good agreement with experiment. It appears therefore that the SPC/E potential model can be used for the simulation of the dielectric properties of supercritical water and of aqueous solutions under supercritical conditions.
Precise viscosity measurements of binary liquid mixtures of acetonitrile‐water and 1,3‐dimethyl‐2‐imidazolidinone‐water
Authors: Wode H. , Seidel W. 
Published: July 2012

AbstractViscosities of binary aqueous mixtures of Acetonitrile (AN) and 1,3‐Dimethyl‐2‐imidazolidinone (Dimethylethyleneurea, DMEU) have been measured at atmospheric pressure and temperatures of 20, 25, 30, 35 and 40°C over the entire concentration region by means of Ubbelohde capillary viscometers, type 0c. For a set of 6 viscometers kinetic energy correction functions (Hagenbach‐Couette correction) have been experimentally determined for each viscometer using tridistilled water and commercially available liquids. Further corrections accounted for buoyancy and surface tension. Viscosity measurements were carried out with at least three, usually 5 to 6 viscometers, giving viscosities with an estimated uncertainty of 0.3%. Hydrodynamic volumes were determined from relative viscosity vs. concentration curves by means of the viscosity‐B‐coefficient and compared to van der Waals volumes calculated using increments for functional groups from the literature. Our data indicate the formation of associated species of DMEU and water.
Free radicals of isatoic anhydride and its derivatives as studied by in situ electrochemical‐ESR‐technique
Authors: Petr A. , Dunsch L. , Neudeck A. , Oesterreich Nadja , Mann M. , Domschke G. 
Published: July 2012

AbstractThe electrochemical reduction of isatoic anhydride and its derivatives was studied by simultaneous electrochemical and ESR‐measurements. For the first time 9 new radicals were characterized by its formal redox potentials, hyperfine coupling constants, g‐factors and lifetimes. The advantage of measuring the kinetic data in stagnant and renewed electrolyte combined with accumulation of the ESR‐spectra is demonstrated in the case of shortlived radicals. It is shown that the electrochemical reduction of isatoic structures follows a self protonation mechanism.
Electrolytic conductivity of mixed electrolyte solutions
Authors: Vink Hans 
Published: July 2012

AbstractElectrolytic conductivity of mixed electrolyte solutions has been studied theoretically and experimentally on the basis of recent phenomenological theories of conductivity. For 1:1 electrolytes a generalised mixture rule is deduced, applicable to mixtures of any number of ionic species. For mixtures of dissimilar electrolytes the simple mixture rule does not apply. However, for mixtures of 1:1 electrolytes with electrolytes of other charge type (2:2, 2:1 electrolytes), when the 1:1 electrolyte is present in marginal quantities, a modified additivity rule is established. In this case the 1:1 electrolyte can be used to probe the properties of the dominant electrolyte in the solution.
capillary wave study of linear and branched polysiloxanes at the air/water interface
Authors: Runge F. E. , Yu H. , Woermann D. 
Published: July 2012

AbstractThe surface properties of two commercially available polysiloxanes, AK 1000 and AV 1000, have been examined at the air/water (A/W) interface in terms of the surface quasi‐elastic light scattering technique (SLS) in conjunction with surface pressure‐area (II–A) isotherm studies. Both are found to form stable, insoluble and promptly equilibrating monolayers at A/W. Being a mixture of linear poly(dimethylsiloxanes) (PDMS), AK 1000 is shown to follow the well established surface properties of PDMS. On the other hand, AV 1000, a mixture of linear and phenylsiloxane‐branched PDMS, referred to as PPMS, shows a different isotherm. The profiles of the surface dynamic viscoelastic parameters deduced from SLS, i.e., the surface dilational elasticity, ϵd, and the corresponding viscosity, K, relative to the surface mass density, γ, are rather different. The magnitudes of ϵd and K for both monolayers are comparable, while small but distinct differences are observed. In particular, in the high surface mass density region, the dynamic surface viscosity of PPMS films is about twice that of PDMS, but all values are still in the regime of very small viscosities (K< 5×10−8 kg/s). These findings are discussed in the context of the differences found in thermocapillary experiments between the two polymers.
Orientational disorder in solids composed of the ellipsoid‐shaped molecules trichloromethyltrimethylsilane, Cl3CSi(CH3)3, t‐Butyltrichlorosilane, (CH3)3CSiCl3, and t‐Butyldimethylchlorosilane, (CH3)3CSi(CH3)2Cl
Authors: Bräuninger Sigmar , Dou Shi‐Qi , Fuess Hartmut , Schmahl Wolfgang , Strauß Roman , Weiss Alarich 
Published: July 2012

AbstractThe ethane structure‐related molecules Cl3CSi(CH3)3 (1), (H3C)3CSiCl3 (2), and (CH3)3CSi(CH3)2Cl (3) crystallize from the melt to an orientational disordered body centered cubic (plastic) phase I, Im3m, Z = 2. By DTA/DSC the following thermodynamic data have been determined (temperatures in K, ΔH in kJ mol−1). (1): Tm = 405.3; ΔHm = 7.36; ΔSm/R = 2.17; TI,II = 285.5; ΔHI,II = 11.16; ΔSI,II/R = 4.68. (2): Tm = 373.4; ΔHm = 6.69; ΔSm/R = 2.13; TI,II = 206.4; ΔHI,II = 6.01; ΔSI,II/R = 3.45. (3): Tm = 358.1; ΔHm = 5.66; ΔSm/R = 1.87; TI,II = 203.6; ΔHI,II = 7.75; ΔSI,II/R = 4.51. At 293 K the lattice constants of the bcc unit cells are (1): 796.6 (2) pm (303 K), (2): 794.5 (7) pm, (3): 803.6 (9) pm.(1) Shows a two line 35Cl NQR spectrum (νi in MHz, T = 77 K) with ν1 = 37.213, ν2 = 37.033, fade out temperature Tf = 253 K; (2): Doublet, ν1 = 19.060, ν2 = 18.260, Tf = 177 K; (3): ν = 16.786, Tf = 200 K.The 1H‐NMR line width and the second moment M2 (1H) of (2) show the orientationally disordered state above TI,II, hysteresis in TI,II, the freezing‐in of the t‐butyl group rotation below TI,II, and a freezing‐in of the individual CH3 group rotation below 100 K.
The role of RNA structure in RNA replication
Authors: Biebricher Christof K. 
Published: July 2012

AbstractRNA replication by RNA replicases has two puzzling features: (i) its selectivity, i.e. only a few RNA species can be replicated, (ii) strand separation, i.e., a single‐stranded RNA template is used to produce a complementary replica; both template and replica are liberated as single‐stranded RNA. Sequence comparison of a great number of replicating RNA species did not reveal sequence homologies except for the invariant ends. However, a structural element required for the replication has been identified: 5′ termini were found to be involved in intramolecular base‐pairing while the 3′ termini were not. Artificially designed short RNA sequences having this structural property were synthesized and found to replicate. The results suggest that the RNA structures of template and replica participate directly in catalyzing the replication, in particular in the separation of strands during RNA replication.
Protein mediated networks. Random chemistry
Authors: Kauffman Stuart 
Published: July 2012

AbstractMathematical models of complex reaction systems suggest that such systems can exhibit a phase transition from subcritical to supracritical behavior. Supracritical behavior occurs if the diversity of substrates and potential catalysts exceeds a threshold. I will explore practical experimental avenues to study this phase transition, its role in creating libraries of organic molecules for drug discovery, approaches to study the emergence of collectively autocatalytic sets of peptides and other polymers, and a potential constraint on cells to remain subcritical.
Emergence of order in small autocatalytic sets maintained far from equilibrium: Application of a probabilistic receptor affinity distribution (RAD) model
Authors: Lancet Doron , Kedem Ora , Pilpel Yizhaq 
Published: July 2012

AbstractWe examined the behavior of auto‐catalytic sets of polymers by a computer simulation. Polymers are allowed to interact with each other, whereby each polymer molecule may catalyze the formation and degradation of others. The system is subjected to a set of thermodynamic and kinetic constraints, including a constant influx of free energy, which keeps the system away from chemical equilibrium and thus enables the effect of catalysis. The system is found to continuously change and probe many possible values in the composition space. In this simulation we make use of a Receptor Affinity Distribution (RAD) model to predict the probabilities of interaction and catalysis. Our results indicate that initially random sets of polymers, under the assumptions of the model, might accumulate information (i.e., clustering in the composition space). Sets will occupy a limited region of composition space, and temporarily reproduce themselves or disperse and give rise to other sets.
Determination of the rate constant and of product branching ratios in the reaction of CH3O2 with OCl between 233 and 300 K
Authors: Kukui A. S. , Jungkamp T. P. W. , Schindler R. N. 
Published: July 2012

AbstractThe reaction CH3O2 + OCl→prod (1) has been investigated in the temperature range 233–300 K using discharge flow mass‐spectrometric technique. A rate constant k1 (300 K) = (2.5±0.3) 10−12cm3 molecule−1 s−1 has been obtained observing the pseudo‐first‐order decay of CH3O2 radicals. The observed temperature dependence is described byk1(233–300 K) = (2.0±0.1)10−12exp((80±50)/T)cm3 molecule−1 s−1.The reaction channel (1a) CH3O2 + OCl→CH3OCl + O2 leading to CH3OCl formation was identified and found to be negatively temperature dependent withk1a(233–300 K) = (1.5±0.3)·10−14exp ((920±200)/T)cm3 molecule−1 s−1.It is shown that HCHO and HOCl result from the secondary reaction of OCl with CH3O.
Oxidative decarboxylation of cyclohexane monocarboxylic acid as a degenerate branching chain reaction II. Mechanism
Authors: Héberger K. , Keszler Á. , Vidóczy T. , Gál D. , Cotarca Livius , Delogu Pietro 
Published: July 2012

AbstractBased on the experimental results obtained studying the oxidative decarboxylation of cyclohexane monocarboxylic acid and published earlier, a mechanism is suggested, according to which in the thermal oxidation two main chain carrier radicals exist: tertiary and secondary peroxy radicals yielding cyclohexanone as well as hydroxy and keto acids in parallel reaction sequences. Carbon dioxide is formed in both pathways independently.The corresponding hydroperoxide molecules, formed during oxidation, decompose partly into radicals and partly into molecules resulting in degenerate branching and chemiluminescence phenomena, respectively. The rate determining termination is the cross combination process between secondary and tertiary peroxy radicals.The combinatorial generation of the mechanism of the thermal process and its reduction enabled the construction of the sequence network of the formation of products indicating that the primary attack of the hydrogen abstraction (secondary or tertiary) determines the product distribution.
Von der Entropie zur Information — die physikalische Chemie der belebten Materie
Authors: Eigen Manfred 
Published: July 2012

AbstractHundred years ago physical chemistry was mainly concerned with equilibrium properties of macroscopic systems of matter. Energy and entropy were the basic concepts underlying various applications of the laws of thermodynamics. Particle physics and cosmology of our times have uncovered the limits of our understanding of these basic concepts. We had to learn “how strange the universe” is, before we may realize “how simple it is” (J.A. Wheeler, 1973). Physical chemistry of our days is increasingly dealing with material self‐organization far from equilibrium. A new concept is that of molecular storage and processing of information. This concept provides a physico‐chemical understanding of living matter. The paper describes necessary and sufficient conditions for generating information in molecular systems. The theoretical results are confronted with experimental findings obtained in vitro and in vivo.