Effect of inorganic salts on the aggregation behavior of branched block polyether at air/water and n-heptane/water interfaces

The effect of inorganic salts (CaCl₂, MgCl₂, NaCl, NaI and NaSCN) on the aggregation behavior of a synthesized polyether with seven poly (ethylene oxide)-b-poly (propylene oxide)-b-poly (ethylene oxide) (PEO-PPO-PEO) arms attached to a tetraethylenepentamine core (simplified AE73) at air/water and n-heptane/water interfaces has been investigated by interfacial tension and oscillating bubble methods. The additions of NaCl, CaCl₂, and MgCl₂ may facilitate the micellization of AE73 and increase its maximum interfacial excess concentration (Γ_max) due to the “salting out” effect, while NaSCN induces opposite effect and NaI exerts little influence. The adsorption kinetics of AE73 is controlled not only by the diffusion between the bulk solution and the interfacial layer but also by the energetic and steric barriers generated by the already adsorbed molecules. The adsorption relaxation time of AE73 is reduced with the addition of salts and this phenomenon is more prominent at the n-heptane/water interface. The “salting in” ions decrease the dilational modulus of AE73 while the “salting out” ions induce an opposite effect. The mechanisms of the interaction between inorganic ions and the polyether were discussed; the difference in aggregation behavior between linear and branched block polyethers were also compared.     

Simulation of EPR spectra of ThBr8:Pa4+ in the incommensurable phase

At T = 95 K β-ThBr₄ undergoes a phase transition from a “high-temperature” phase with space group I_41/amd to a structure with an incommensurable distortion wave along the crystallographic c axis. The modulation can be thought to consist of a combination of a “rotation” and a “twist” of the Br atoms in the plane perpendicular to the c axis. The EPR spectra at 4.2 K show the characteristic “edge singularities” of the incommensurable structure. A model is presented for the simulation of these spectra. It is based on the “twist” component of the modulation only.     

Zur Definition von Selektivität,Spezifität und Empfindlichkeit von Analysenverfahren

The three metric, functional concepts named in the title can be defined without arbitrariness and their values may be calculated for any multicomponent-analytical procedure from the relation of the measurable physical quantities x _ito the contents c _kwhich are to be determined. This relation is mathematically a “mapping” (achieved by systems of functions). The system of “analytical functions” (x _i→ c _k) is the inverse of the system of “calibration functions” (c _k→ x _i) which alone can be directly gained by experiments. The ‘calibration matrix” (γik) whose elements γ_ik are the “partial sensitivities” \(\tfrac{{\partial x_i }}{{\partial c_k }}\) represents the system in first approximation but only locally, i.e. for the respective constitution of the sample. The “sensitivity” of the analytical procedure as a whole, is numerically given by the determinant of this matrix; the “selectivity” is derived from the condition that the inversion of the calibration system to the analytical system (of functions) shall be possible by an iteration process. “Specificity” is defined in analogy to selectivity. In the appendix it is explained why selectivity is the strongest means to reduce the expenditure for the complete calibration of multicomponent analyses to a realistic and tolerable degree.     

Phase behavior of water-in-supercritical carbon dioxide microemulsion with sodium salt of bis(2,2,3,3,4,4,5,5-octafluoro-1-pentanol) sulfosuccinate

The fluorinated analogues of AOT surfactant, sodium salt of bis(2,2,3,3,4,4,5,5-octafluoro-1-pentanol) sulfosuccinate, which has CO₂-philic chains and a hydrophilic head group, was synthesized for forming water-in-CO₂ microemulsion. The cloud point of this surfactant was measured and the supercritical fluid-phase behavior of water-in-CO₂ microemulsion was investigated by using a variable-volume view cell apparatus. It was found that the phase behavior of microemulsion is affected by the concentrations of water and surfactant in CO₂, molar ratio of water to surfactant (W_o = [water]/[surfactant]), and the amount of CO₂. From this experiment, we found out another cloudy point which exists above the homogeneous microemulsion region. We defined this point as “upper cloud point” and general cloud point as “lower cloud point. The region which exists between these two cloud points was defined as “stable region of microemulsion”. Conditions for the formation of water-in-CO₂ microemulsion were obtained at temperatures up to 370.15 K.     

Long range 13C1H coupling constants at bridgehead carbons in some naphthalene and quinoline derivatives, “cross” ring and “through” ring interactions

The ³J_CH couplings at bridgehead carbons in naphthalene and quinoline derivatives have been classified as “through” ring and “cross” ring interactions. Further divisions of the couplings have been introduced in an attempt to rationalize the interactions such that they may be used for structural assignments. The influence of central π-bond order and of the heterocyclic nitrogen atom on the couplings has been discussed. From a study of the ³J couplings at C-9 and C-10 in 45 quinoline derivatives the coupling constant ranges observed were “through” ring (via 9,10-bond): J₉₄ 4.9–6.1 Hz, J₉₅ 5.5–7.3 Hz, J_10.8 4.1–5.3 Hz; “cross” ring: J₉₂ 11.0–13.5 Hz, J₉₇ 6.7–9.8 Hz, J_10.3 4.4–7.3 Hz, J_10.6 5.2–9.1 Hz.     

Preparation of hexagonal MoO3 by “Chimie Douce” reaction with NO2

The metastable hexagonal form of MoO₃ has been successfully prepared starting from the ammonium molybdate, using a “Chimie Douce” reaction with NO₂ gas. The lattice parameters of the as-prepared material were determined by XRD analysis to be: a = 10.633(2) Å and c = 3.719(1) Å. The composition of this material obtained by physical and chemical analysis is MoO₃, 0.09 H₂O, showing that a small amount of water molecules remained while there were no more ammonium ions in this structure. The structural transformation from hexagonal to stable orthorhombic α-MoO₃ phase was observed at 350°C. It was also shown that NO₂ reaction is a very useful method to remove topotactically ammonium ions from a parent structure at low temperature. This “Chimie Douce” process appears to be very promising for obtaining new metastable oxides with large tunnels or interlayer distances.     

Molecular orbital theory of the hydrogen bond. 24. Ground-state water–uracil complexes

Ab initio SCF calculations with the STO -3G basis set have been performed to investigate the structural, energetic, and electronic properties of mixed water–uracil dimers formed at the six hydrogen-bonding sites in the uracil molecular plane. Hydrogen-bond formation at three of the carbonyl oxygen sites leads to cyclic structures in which a water molecule bridges N₁? H and O₂, N₃? H and O₂, and N₃? H and O₄. Open structures form at O₄, N₁? H, and N₃? H. The two most stable structures, with energies of 9.9 and 9.7 kcal/mole, respectively, are the open structure at N₁? H and the cyclic one at N₁? H and O₂. These two are easily interconverted, and may be regarded as corresponding to just one “wobble” dimer. At 1 kcal/mole higher in energy is another “wobble” dimer consisting of an open structure at N₃? H and a cyclic structure at N₃? H and O₄. The third cyclic structure at N₃? H and O₂ collapses to the “wobble” dimer at N₃? H and O₄. The two “wobble” dimers are significantly more stable than the open dimer formed at O₄, which has a stabilization energy of 5.4 kcal/mole. Uracil is a stronger proton donor to water through N₁? H than N₃? H, owing to a more favorable molecular dipole moment alignment when association occurs through H₁. Hydration of uracil by additional water molecules has also been investigated. Dimer stabilization energies and hydrogen-bond energies are nearly additive in most 2:1 water:uracil structures. There are three stable “wobble” trimers, which have stabilization energies that vary from 7 to 9 kcal/mole per water molecule. Hydrogen-bond strengths are slightly enhanced in 3:1 water:uracil structures, but the cooperative effect in hydrogen bonding is still relatively small. The single stable water–uracil tetramer is a “wobble” tetramer, with two water molecules which are relatively free to move between adjacent hydrogen-bonding sites, and a stabilization energy of approximately 8 kcal/mole per water molecule. Within the rigid dimer approximation, successive hydration of uracil is limited to the addition of one, two, or three water molecules.     

Hydration of gas-phase gramicidin S (M + 2H)2+ ions formed by electrospray: The transition from solution to gas-phase structure

The hydration of doubly protonated gas-phase ions of gramicidin S formed by electrospray ionization was investigated. Under “gentle” electrospray conditions, a near Gaussian distribution of (M + 2H + nH₂O)²⁺ ions with n up to 50 can be readily formed. These extensively hydrated gas-phase ions should have structures similar to those in solution. For intermediate extents of hydration, the “naked” or unsolvated ion is present in unusually high abundance. This is attributed to a competition between solvation of the charges by water vs intramolecular self-solvation via hydrogen bonding. In addition, “magic” numbers of attached water molecules are observed for n = 8, 11, and 14. These magic numbers are attributed to favorable arrangements of water molecules surrounding the charge and surface of the peptide in the gas phase. These results are indicative of a gentle stepwise transformation from the solution-phase structure of the ion to the preferred gas-phase structure as solvent evaporates from the hydrated ions.     

Reactivity of cis dichlorodiammineplatinum(II) (cisplatin) toward selected nucleophiles

Results are reported for the reaction of cis-dichlorodiammineplatinum(II) (“cisplatin”) with various nucleophiles in aqueous solution at constant ionic strength (μ = 0.5) and 30°C. The reactivity is described in terms of linear free energy relationships between the logarithm of the second order rate constants and two established indices of nucleophilicity, i.e. electrode potentials, E° and nucleophilic reactivity constants, n_Pt^o (based on reactivity of trans-[Pt(PY)₂Cl₂] in methanol). New nucleophilic reactivity constants, (n_Pt^o)′are reported based on “cisplatin” reactivity in water.     

Dependence of kinetics of copper sulfate pentahydrate dehydration on water vapor pressure

The dependence of the growth rate v_g of nuclei during CuSO₄·5H₂O dehydration upon water vapor pressure P_H2O has been investigated. At small P_H2O (less than 1 Torr at 50°C), v_g falls rapidly with decreasing P_H2O, and simultaneously v_g anisotropy disappears. At P_H2O = 1–9 Torr, v_g for elliptic and round nuclei is constant and independent of P_H2O. The influence of initially keeping the samples in water vapor upon the kinetics of the following dehydration has been studied. Treatment by water vapor leads to slowing of dehydration and increasing its degree of transformation. On the basis of data obtained a kinetic interpretation of the Topley-Smith effect has been proposed.     

Specific features of the radiolysis of water and aqueous solutions of H2 and O2 by mixed n,γ-radiation with a high portion of the neutron component

A previously unknown feature of the kinetics of the radiolysis of water and hydrogen, oxygen, and hydrogen peroxide solutions has been discussed. By calculation, it has been revealed that concentration oscillations of the radiolysis products can appear during irradiation of the solution with fast neutrons or mixed n,γ-radiation with a high portion of the neutron component. The period and amplitude of the oscillations depend on the temperature, the dose rate, and the ratio of n/γ radiation components. It has been shown that oscillations cannot be excited during γ-radiolysis under any conditions. It is suggested that the mechanism of the oscillations is similar to the Belousov-Zhabotinsky reaction mechanism. A chain reaction proceeds in the irradiated system, in which the reactants H₂O₂ (“reducing agent”), “oxidizing agent” OH radicals initiating the chain, and the “catalyst” are introduced from the outside. Hydrogen molecules produced by the action of radiation play the role of the “catalyst”, and H₂O molecules formed in the secondary reactions are the “deactivated form of the catalyst”. Hydrogen atoms and hydrated electrons propagate the chain. Oxygen formed in both spurs and the secondary reactions is the “inhibitor” terminating the chain reaction.     

Enantiodivergent formation of a chiral cytosine crystal by removal of crystal water from an achiral monohydrate crystal under reduced pressure

An achiral nucleobase cytosine forms an achiral monohydrate crystal (space group: P2₁/c) by crystallization from a water solution. It was found that the removal of crystal water under reduced pressure at room temperature afforded a chiral crystal of anhydrous cytosine (P2₁2₁2₁). The crystal chirality of anhydrous cytosine corresponds to the enantiotopic crystal face of the achiral monohydrate; therefore, when the enantiotopic b¹-face is exposed to the reduced pressure, dehydration occurred in the direction from the b¹-face to provide [CD(+)310_KBr]-cytosine crystal. In contrast, dehydration from the b²-face gave the opposite enantiomorphous [CD(?)310_KBr]-cytosine crystal. The correlation between enantiotopic faces and the formed crystal chirality is opposite to that from dehydration by heating. The formed chiral cytosine crystals act as a chiral trigger for asymmetric autocatalysis with enantioenrichment amplification of pyrimidylalkanol.     

Thermal analysis of boron complexes containing ligands of the type R-C(CH2OH)3

The thermal behaviours of certain salts of the complex “ethriol-” and “methriolboric” acids have been investigated by means of Derivatograph and IR spectra. It is shown that compounds of this type decompose in three main stages on heating: 1) the crystallization water is lost, 2) the condensation water is lost and dimers are formed containing bridge bonds B₄-O-B₄; 3) up to 600–700? all the organic matter is lost; the residue is the corresponding borate (1 ∶ 1). The possibility of performing a fast full analysis by means of the TG and DTG curves has been demonstrated.     

Molecular orbital theory of the hydrogen bond. 25. Water–uracil complexes in excited n → π states

Hydrogen bonding of uracil with water in excited n → π* states has been investigated by means of ab initio SCF -CI calculations on uracil and water–uracil complexes. Two low-energy excited states arise from n → π* transitions in uracil. The first is due to excitation of the C₄? O group, while the second is associated with excitation of the C₂? O group. In the first n → π* state, hydrogen bonds at O₄ are broken, so that the open water–uracil dimer at O₄ dissociates. The “wobble” dimer, in which a water molecule is essentially free to move between its position in an open structure at N₃? H and a cyclic structure at N₃? H and O₄ in the ground state, collapses to a different “wobble” dimer at N₃? H and O₂ in the excited state. The third dimer, a “wobble” dimer at N₁? H and O₂, remains intact, but is destabilized relative to the ground state. Although hydrogen bonds at O₂ are broken in the second n → π* state, the three water–uracil dimers remain bound. The “wobble” dimer at N₁? H and O₂ changes to an excited open dimer at N₁? H. The “wobble” dimer at N₃? H and O₄ remains intact, and the open dimer at O₄ is further stabilized upon excitation. Dimer blue shifts of n → π* bands are nearly additive in 2:1 and 3:1 water:uracil structures. The fates of the three 2:1 water:uracil trimers and the 3:1 water:uracil tetramer in the first and second n → π* states are determined by the fates of the corresponding excited dimers in these states.     

Absolute configuration and biosynthesis of tiliageine

Tracer experiments on Tiliacora racemosa Colebr established that tiliageine has “S” and “R” configuration at the asymmetric centres C₁ and C'₁ respectively. The experiments also prove that tiliageine is biosynthesised in the plants from N-methylcoclaurine.     

Modular Synthesis of Furans with up to Four Different Substituents by a trans-Carboboration Strategy

Propargyl alcohols, on treatment with MHMDS (M=Na, K), B₂(pin)₂, an acid chloride and a palladium/copper co-catalyst system, undergo a reaction cascade comprised of trans-diboration, regioselective acylation, cyclization and dehydration to give trisubstituted furylboronic acid pinacol ester derivatives in good yields; subsequent Suzuki coupling allows a fourth substituent of choice to be introduced and hence tetrasubstituted (arylated) furans to be formed. In terms of modularity, the method seems unrivaled, not least because each product can be attained by two orthogonal but convergent ways (“diagonal split”). This asset is illustrated by the “serial” formation of a “library” of all twelve possible furan isomers that result from systematic permutation of four different substituents about the heterocyclic core.     

Magnetic properties and dye adsorption capacities of silica–hematite nanocomposites with well-defined structures prepared in surfactant solutions

Silica–hematite (α-Fe₂O₃) nanocomposites were synthesized by addition of aqueous solution containing ferrous ions (Fe²⁺), cetyltrimethylammonium bromide (CTAB) as a surfactant and tert-butanol (t-butanol) as a cosurfactant into colloidal silica solution. At alkaline atmosphere, silica surface with negative charges electrostatically attracts positively-charged iron hydroxide nuclei or particles which are stabilized by cationic CTAB molecules, and then silica–iron compound composites could be formed. Finally, the silica–hematite composite particles were obtained after calcination at 800 °C for 4 h. Through these processes, two types of composites having “core–shell type” or “decorated type” could be achieved. Morphology, BET surface area, crystallinity and magnetic properties of samples were analyzed by using TEM, BET, XRD and VSM, respectively. The “decorated type” composites had larger BET surface area and better magnetization. Also, to estimate the application in water treatment, adsorption properties of composites were studied through methylene blue (MB) adsorption which was characterized by UV–vis spectroscopy, involving collection of composites with neodymium magnet.     

Steric diversion—I : Addition of halogens and pseudo-halogens to isolongifolene

Addition of halogens (Cl₂, Br₂) and pseudo-halogens (ICl, halogen azides, NOCl) to solongifolene does not yield any “normal” addition products due to severe steric hindrance to the approach of counter ion at C-7. Initially formed halogenonium ions undergo elimination or rearrangement to give “abnormal” products. The term Steric Diversion is suggested to describe this switch over from the “normal” route.     

Preparation of LiZnPO4·H2O via a novel modified method and its non-isothermal kinetics and thermodynamics of thermal decomposition

The single phase ??-LiZnPO₄·H₂O was directly synthesized via solid-state reaction at room temperature using LiH₂PO₄·H₂O, ZnSO₄·7H₂O, and Na₂CO₃ as raw materials. XRD analysis showed that ??-LiZnPO₄·H₂O was a compound with orthorhombic structure. The thermal process of ??-LiZnPO₄·H₂O experienced two steps, which involved the dehydration of one crystal water molecule at first, and then the crystallization of LiZnPO₄. The DTA curve had the one endothermic peak and one exothermic peak, respectively, corresponding to dehydration of ??-LiZnPO₄·H₂O and crystallization of LiZnPO₄. Based on the iterative iso-conversional procedure, the average values of the activation energies associated with the thermal dehydration of ??-LiZnPO₄·H₂O, was determined to be 86.59?kJ?mol^?1. Dehydration of the crystal water molecule of ??-LiZnPO₄·H₂O is single-step reaction mechanism. A method of multiple rate iso-temperature was used to define the most probable mechanism g(??) of the dehydration step. The dehydration step is contracting cylinder model (g(??)?=?1?(1???)^1/2) and is controlled by phase boundary reaction mechanism. The pre-exponential factor A was obtained on the basis of E _a and g(??). Besides, the thermodynamic parameters (??S ^??, ??H ^??, and ??G ^??) of the dehydration reaction of ??-LiZnPO₄·H₂O were determined.