Self-assembly of Quasi-monocrystal CdCO3 Nanorings

Hierarchical CdCO3 nanostructures with complex morphologies, such as tetrago- nal, pentagonal and hexagonal nanorings, can be prepared via self-assembly of nanocrystals in a solvothermal environment. XRD pattern indicated that the product is trigonal CdCO3 phase (PDF#850989) with cell constants a = 6.112  and α = 47.4o. Based on our experimental results, a possible nanoring formation mechanism was proposed.     

The thermal stability of fully charged and discharged LiCoO2 cathode and graphite anode in nitrogen and air atmospheres

Polyethylene glycol (PEG) compounds and mixtures have many properties that make them suitable for thermal applications in buildings, such as having high heat of fusion, phase change repeatability, chemical stability, non-corrosive behavior, and low-cost. In this study, we developed a number of PU rigid foams incorporated with three types of PEGs, as new insulation materials provided with an enhanced thermal capacity, and sought their suitability for various applications such as layer of floor and ceiling coverings in constructions, insulations in controlled temperature transportation packaging, inner coverings of automobile seats, etc. In order to investigate the thermal properties of PEG-containing PU foams, differential scanning calorimeter (DSC) tests were conducted first. Then, a two-layer concrete–PU foam system was designed in the laboratory conditions to examine the insulation performances via using a computer-aided thermal measurement setup which was sensitive to the simulated environmental temperature changes. The PU-PEG composites produced here can be helpful for the design of thermal insulators. PUI, including 44% PEG 600, exhibited fairly efficient thermal regulation under moderate ambient temperature conditions, whereas PUII (49% PEG 1000) is suitable for temperature control in both mild and hot surroundings. PUIII, containing 53% PEG 1500, showed suitable heat storage and thermal stability characteristics. PUIV, containing 38% PEG 600/PEG 1000/PEG 1500, also confirmed good thermal and durability characteristics. The blend of three PEGs is suitable for preventing discontinuous thermal regulation when the external temperature increases or decreases. PU foams containing PEGs can be assumed to be leak-resistant, which is promising for their industrial applications.     

Microfluidic synthesis of tunable poly-(N-isopropylacrylamide) microparticles via PEG adjustment

We present a microfluidic droplet method to synthesize a series of tunable poly(N-isopropylacrylamide) (PNIPAM) microparticles by the addition of polyethylene glycols (PEGs). The PEGs are used as porogens and could be removed simply by washing step. By varying molecular weights and concentrations of the PEGs, morphologies and temperature-sensitive properties of the formed PNIPAM microparticles are flexibly tuned. It is found that PEG of lower molecular weight induces smaller micropore sizes, and results in faster response rate. The volume changes prior to and after shrinkage can also be regulated by the addition of PEGs due to tuned homogeneities of micropores. The microparticles tuned by PEG1000 with ratio of added PEGs to NIPAM of 2:1 respond the fastest (120 s), whereas with ratio of added PEGs to NIPAM of 1:1 display largest volume change (1/γ=12.12). This simplicity and controllability of tunable microparticles synthesis are appealing for various applications ranging from chemical delivery, drug release control, to optical applications.     

On the formation and structure of nanometric polyhedral foams: toward the dry limit

High surface area, high porosity, nanometric polygonal silica foams with hierarchically connected and uniformly sized pore systems are reported here. We observe a remarkable increase in foam cell sizes from mesoscopic to macroscopic dimensions upon swelling the self-assembled template with oil. The resultant structures resemble classical macroscopic soap foams and display, among other features, Plateau borders and volume fractions approaching the dry limit of 100%. In well-developed foams of this kind, dimensionally isometric polyhedral cells are connected by relatively short, flat cylindrical mesopores through polyhedral faces and micropores through the walls. For one sample, with approximately 75 nm diameter primary foam cells, we infer three separate sets of cell-connecting mesopores puncturing tetragonal, pentagonal, and hexagonal faces of the component polyhedra. A multiple step model of foam formation is discussed where an organic silica precursor progressively hydrolyzes and condenses as a growing flexible shell from the core-corona interface of oil-swollen triblock copolymer micelles or microemulsion droplets, inducing a clouding phenomena in the otherwise stabilizing poly(ethylene oxide) chains, leading to aggregation, deformation, and jamming to high volume fractions.     

Lantern-Type Divanadium Complexes with Bridging Ligands: Short Metal−Metal Bonds with High Multiple Bond Orders

Vanadium forms binuclear complexes with a variety of ligands often containing V≡V triple bonds. Many tetragonal divanadium paddlewheel complexes with bridging bidentate ligands have been experimentally characterized. This research exhaustively treats model tetragonal, trigonal, and digonal paddlewheel-type divanadium complexes V₂L_x (L=formamidinate, guanidinate, and carboxylate; x=2, 3, 4), each in the three lowest-energy spin states. The V−V formal bond orders are obtained from metal−metal MO diagrams for representative structures. A number of short V−V multiple bonds of order 3, 3.5, and 4 are found in these model complexes. The short V≡V triple bonds and singlet ground state predicted here for the model tetragonal complexes correspond well with the limited experimental results for the series of known tetragonal paddlewheels. Digonal divanadium lanterns with very short V−V quadruple bonds are predicted as interesting synthetic targets. The V−V bond distances are categorized into distinct ranges according to the formal bond order values from 0.5 to 4. These bond length ranges are compared with the ranges compiled for other divanadium complexes including carbonyl complexes.     

Sol–gel transition behavior of biodegradable three‐arm and four‐arm star‐shaped PLGA–PEG block copolymer aqueous solution

Two types of temperature‐sensitive biodegradable three‐arm and four‐arm star‐shaped poly(DL ‐lactic acid‐co‐glycolic acid‐b‐ethylene glycol) (3‐arm and 4‐arm PLGA–PEG) were successfully synthesized via the coupling reaction of 3‐arm and 4‐arm PLGA and α‐monocarboxyl‐ω‐monomethoxypoly(ethylene glycol) (CMPEG). In dilute aqueous solutions, star PLGA–PEGs showed the temperature‐ and concentration‐dependent formation and aggregation of micelles over specific concentration and specific temperature. With increasing the molecular weight and the relative hydrophobicity of hydrophobic PLGA block, critical micelle temperature (CMT) decreased. Aqueous solution of 4‐arm PLGA–PEG started to form micelles at lower temperature and showed sharper temperature‐dependent growth in micelle size. These results are due to the enhanced hydrophobicity of PLGA block. On the other hand, at high concentration, two types of 3‐arm and 4‐arm PLGA–PEG showed sol–gel–sol transition behavior as the temperature was increased. The 3‐arm and 4‐arm PLGA–PEG showed sol–gel transition at higher polymer concentrations (above 24 wt %) than the PEG–PLGA–PEG triblock copolymer. As the molecular weight and the relative hydrophobicity of PLGA block increased, the critical gel concentration (CGC) decreased. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 888–899, 2006     

Contrasting oxide crystal chemistry of Nb and Ta:: The structures of the hexagonal bronzes BaTa2O6 and Ba0.93Nb2.03O6

The high-temperature hexagonal forms of BaTa₂O₆ and Ba_0.93Nb_2.03O₆ have P6/mmm symmetry with unit-cell parameters a=21.116(1) Å, c=3.9157(2) Å and a=21.0174(3) Å, c=3.9732(1) Å, respectively. Single crystal X-ray structure refinements for both phases are generally consistent with a previously proposed model, except for displacements of some Ba atoms from high-symmetry positions. The structures are based on a framework of corner- and edge-connected Nb/Ta-centred octahedra, with barium atoms occupying sites in four different types of [0 0 1] channels with hexagonal, triangular, rectangular and pentagonal cross-sections. The refinements showed that the non-stoichiometry in the niobate phase is due to barium atom vacancies in the pentagonal channels and to extra niobium atoms occupying interstitial sites with tri-capped trigonal prismatic coordination. The origin of the non-stoichiometry is attributed to minimisation of non-bonded Ba-Ba repulsions. The hexagonal structure is related to the structures of the low-temperature forms of BaNb₂O₆ and BaTa₂O₆, through a 30° rotation of the hexagonal rings of octahedra centred at the origin.     

聚对二氧环己酮/聚乙二醇多嵌段共聚物的合成与表征

首先合成双端羟基的聚对二氧环己酮预聚物(PPDO)和双端羧基的聚乙二醇预聚物(PEG),然后以丁二酸酐/二环己基碳二亚胺(DCC)将PPDO与PEG偶联共聚,得到PPDO/PEG多嵌段共聚物.通过1H-NMR和GPC表征了聚合物的结构和分子量.采用差示扫描量热法(DSC)和热重分析(TGA)研究了共聚物的结晶性能和热稳定性.用透析法制备了共聚物纳米粒子,并用动态光散射(DLS)表征了共聚物纳米粒子的粒径及分散度,结果表明,随着共聚物亲水链段PEG含量的增加,其纳米粒子更易形成,粒子粒径随共聚物分子量增大而增大.     

Stabilization ofEscherichia coli penicillin G acylase by polyethylene glycols against thermal inactivation

The effects of five polyethylene glycol (PEG) compounds of different molecular weight on the thermal stability of penicillin G acylase (PGA) obtained from a mutant ofEscherichia coli ATCC 11105 have been investigated. The molecular weights of PEG compounds were 400, 4000, 6000, 10,000, and 15,000. The thermal inactivation mechanisms of both native and PEG-containing PGA were considered to obey first order inactivation kinetics during prolonged heat treatments. Optimal concentrations of PEGs at molecular weights of 400,4000, 6000,10,000, and 15,000 were found to be 250,150,150,100, and 50 mM, respectively. The greatest enhancement of thermostability was observed with PEG 4000 and PEG 6000, as a nearly 20-fold increase above 50°C. PGA showed almost the same temperature activity profile and optimal temperature values both in the presence and absence of PEG. The addition of PEGs did not cause any change in the optimal temperature value of PGA, but the parametersV _m ,K _m , the activation energy, and thek _cat values of enzyme were markedly decreased because of the mixed inhibition by PEG compounds. The type of inhibition was found to be hyperbolic uncompetitive.     

Sandwich Fibrous PEG Encapsulations for Thermal Energy Storage

Phase change materials (PCMs) textiles have been developed for personal thermal management (PTM) while limited loading amount of PCMs in textiles reduced thermal buffering effect. In this work, we proposed a sandwich fibrous encapsulation to store polyethylene glycol (PEG) with PEG loading amount of 45 wt %, which consisted of polyester (PET) fabrics with hydrophobic coating as protection layers, polyurethane (PU) nanofibrous membranes as barrier layers and PEG-loaded viscose fabric as a PCM-loaded layer. The leakage was totally avoided by controlling weak interfacial adhesion between protection layer and melting PEG. The sandwich fibrous PEG encapsulations had an overall melting enthalpy value ranging from 50 J/g to 78 J/g and melting points ranging from 20 °C to 63 °C by using different PEGs. Besides, introduction of Fe microparticles in PCM-loaded layer enhanced thermal energy storage efficiency. We believe that the sandwich fibrous PEG encapsulation has a great potential in various fields.     

Lantern-type dinickel complexes: An exploration of possibilities for nickel–nickel bonding with bridging bidentate ligands

Many binuclear nickel complexes have Ni Ni distances suggesting Ni Ni covalent bonds, including lantern-type complexes with bridging bidentate ligands. This DFT study treats tetragonal, trigonal, and digonal lantern-type complexes with the formamidinate, guanidinate, and formate ligands, besides some others. Formal bond orders (ranging from zero to two) are assigned to all the Ni Ni bonds on the basis of MO occupancy considerations. A VB-based electron counting approach assigns plausible resonance structures to the dinickel cores. Model tetragonal complexes with the dimethylformamidinate and the dithioformate ligands have singlet ground states whose non-covalently bonded Ni Ni distances are close to those in their experimentally known counterparts. Trigonal dinickel complexes are unknown, but are predicted to have quartet ground states with Ni Ni bonds of order 0.5. The model digonal complexes are predicted to have triplet ground states, but the predicted Ni Ni bond lengths are longer than those found in their experimentally known counterparts. This could owe to inadequate treatment of electron correlation by DFT in these short Ni Ni bonds with their multiconfigurational character. All the Ni Ni bond distances here are categorized into ranges according to the Ni Ni bond orders of 0, 0.5, 1, 1.5, and 2, no Ni Ni bonds of order higher than two being identified. The Ni Ni bonds of given order in these lantern-type complexes are consistently shorter than the corresponding Ni Ni bonds in dinickel complexes having carbonyl ligands, attributable to the metal metal bond lengthening effect of CO ligands.     

The effect of molecular crowding with nucleotide length and cosolute structure on DNA duplex stability

The thermodynamics of DNA duplex structures in the presence of high concentrations of cosolutes in solution were investigated to discern nucleic acid structures and functions in living cells. In the presence of ethylene glycol (EG) and poly(ethylene glycol) (PEG) (MW = 200-8000), the stability of the oligomer DNA duplexes with differing nucleotide length varied, depending on the nucleotide length as well as the size of PEG. It was also revealed that the decrease of water activity is the primary factor for destabilization of the short (8-mer) duplex by addition of high molecular weight PEGs as well as low molecular weight PEGs and other low molecular weight cosolutes. In addition, the number of water molecules taken up per base pair formation was the same for all the PEGs and for 1,2-dimethoxyethane, which was greater than in the cases of glycerol, EG, 1,3-propanediol, and 2-methoxyethanol, suggesting that the solvation of nucleotides may differ, depending on the cosolute structure. These findings are useful not only for understanding nucleic acid structures and functions in cells but also for the design of oligonucleotides applicable for cells, such as antisense nucleic acids, RNAi, and DNA chips.     

Amplifying the macromolecular crowding effect using nanoparticles

The melting temperature (T(m)) of DNA is affected not only by salt but also by the presence of high molecular weight (MW) solutes, such as polyethylene glycol (PEG), acting as a crowding agent. For short DNAs in a solution of low MW PEGs, however, the change of excluded volume upon melting is very small, leading to no increase in T(m). We demonstrate herein that by attaching 12-mer DNAs to gold nanoparticles, the excluded volume change was significantly increased upon melting, leading to increased T(m) even with PEG 200. Larger AuNPs, higher MW PEGs, and higher PEG concentrations show even larger effects in stabilizing the DNA. This study reveals a unique and fundamental feature at nanoscale due to geometric effects. It also suggests that weak interactions can be stabilized by a combination of polyvalent binding and the enhanced macromolecular crowding effect using nanoparticles.     

Ternary early-transition-metal palladium pnictides Zr3Pd4P3, Hf3Pd4P3, HfPdSb, and Nb5Pd4P4

Several ternary palladium pnictides of the early transition metals have been prepared by arc-melting of the elemental metals and the binary pnictides ZrP, HfP, HfSb2, or NbP, and their structures have been determined by X-ray diffraction methods. The phosphides M3Pd4P3 (M = Zr, Hf) adopt a new structure type (Pearson symbol oP40), crystallizing in the orthorhombic space group Pnma with Z = 4 and unit cell parameters of a = 16.387(2), b = 3.8258(5), and c = 9.979(1) A for Zr3Pd4P3 and a = 16.340(2), b = 3.7867(3), and c = 9.954(1) A for Hf3Pd4P3. The antimonide HfPdSb was identified by powder X-ray diffraction (orthorhombic, Pnma, Z = 4, a = 6.754(1) A, b = 4.204(1) A, and c = 7.701(2) A) and confirmed to be isostructural to ZrPdSb, which adopts the TiNiSi-type structure. The phosphide Nb5Pd4P4 adopts the Nb5Cu4Si4-type structure, crystallizing in the tetragonal space group I4/m with Z = 2, a = 10.306(1) A, and c = 3.6372(5) A. Coordination geometries of pentacapped pentagonal prisms for the early transition metal, tetracapped distorted tetragonal prisms for Pd, and tricapped trigonal prisms for the pnicogen are found in the three structures; tetracapped tetragonal prisms for Nb are also found in Nb5-Pd4P4. In common with many metal-rich compounds whose metal-to-nonmetal ratio is equal or close to 2:1, the variety of structures formed by these ternary palladium pnictides arises from the differing connectivity of pnicogen-filled trigonal prisms. Pnicogen-pnicogen bonds are absent in these structures, but metal-metal bonds (in addition to metal-pnicogen bonds) are important interactions, as verified by extended Hückel band structure calculations on Zr3Pd4P3.     

Large thermoelectric figure of merit in hexagonal phase of 2D selenium and tellurium

We found a large thermoelectric figure of merit in the hexagonal phase of 2D selenium and tellurium from first-principles calculations. The hexagonal phase (α) is obtained from three atomic layers truncated along the [001] direction of trigonal Te and Se bulk in the equilibrium structure. We found the α-Se structure dynamically stable. The calculated electronic structures of α-Se and α-Te show interesting semiconductor character for both electronic and optoelectronic applications. Furthermore, the obtained elastic properties show that hexagonal tellurene is a softer material than selenene. The thermoelectric figure of merit for hexagonal 2D phase (∼1.0) is larger than those reported for the tetragonal 2D phase (∼0.75) of selenium and tellurium. Additionally, the computed electrical and phonon transport parameters indicate that selenene and tellurene are promising thermoelectric materials; both offer an alternative to recovering residual heat and transforming it into electricity.     

Allowed boundary sequences for fused polycyclic patches and related algorithmic problems

We consider sequences that encode boundary circuits of fused polycycles made up of polygonal faces with p sides, p < or = 6. We give a constructive algorithm for recognizing such sequences when p = 5 or 6. A simpler algorithm is given for planar hexagonal sequences. Hexagonal and pentagonal sequences of length at most 8 are tabulated, the former corresponding to planar benzenoid hydrocarbons CxHy with y up to 14.     

The effects of melt annealing and counterpart's molecular weight on the thermal properties and phase morphology of poly(L‐lactide)‐based blends

The thermal properties and phase morphology of poly(L ‐lactide) (PLLA)‐based blends have been studied. Two poly(ethylene glycol)s (PEGs) with molecular weight (MW) of about 1,500 (1.5k) g/mol and 2,000,000 (2M) g/mol, respectively, were used as counterparts. The blends were annealed at a preselected temperature of 200 °C for either 2 min or 30 min before the characterizations. Both PEGs were determined to enhance the crystallizability of PLLA. After a 2‐min process of annealing, the PEG(1.5k)'s crystallization efficiency on PLLA has been noted to increase with the increase of its content. Conversely, PEG(2M)'s crystallization efficiency declined with the increase of its content. Extending the annealing time has evidently changed the PEGs' crystallization effect on PLLA. Moreover, the PEG(1.5k) has, to a greater extent, brought about the depression of PLLA's melting temperature by increasing its content, and this depression increased with the annealing time. The blends exhibited lower thermal stability than those of the parent components, particularly for the PEG(1.5k)‐included system with a higher PEG content. Regardless of the annealing time, the PEG(1.5k)‐included blends have shown homogeneous melt morphology under light microscope, whereas the PEG(2M)‐included blends have displayed phase‐separated melt morphology. In addition to the composition, PEG's MW and annealing time influence the crystalline morphology of the blends. The ringed PLLA spherulites have appeared mostly in the 2‐min annealed PEG(1.5k)‐included blends. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1497–1510, 2009     

Distinct columnar and lamellar liquid crystalline phases formed by new bolaamphiphiles with linear and branched lateral hydrocarbon chains

A universal building block for the convergent synthesis of a wide variety of different T-shaped ternary amphiphiles was developed and used for the synthesis of a series of new liquid-crystalline materials composed of a rigid biphenyl core with polar glycerol groups at both ends and linear or branched alkyl chains in a lateral position. In addition, compounds with bulky achiral (2,4,6-trimethylphenoxy, adamantane-1-carboxylate, benzoate) or chiral (menthyl or cholesteryl) substituents attached to the end of the lateral alkyl chain were also investigated. In all cases the lateral chains were connected to the aromatic core by an ether linkage. The effect of the ether linking unit on mesophase stability and mesophase type is discussed with respect to conformational effects. The liquid-crystalline phases were investigated by polarizing microscopy, calorimetry, and X-ray diffraction of surface aligned samples. Upon enlarging the lateral chains a series of different polygonal cylinder phases was observed, which were replaced by lamellar phases and a non-cylinder hexagonal columnar phase by further increasing the size of these substituents. Remarkably, only pentagonal, hexagonal, and giant hexagonal cylinder phases could be observed, whereas mesophases composed of cylinders with a smaller number of sides are missing. No distinct chirality effects were observed for the menthyl- and cholesteryl-substituted compounds. However, the rodlike shape of the polycyclic cholesteryl core leads to a unique phase structure combining an organization of the alicyclic cholesteryl cores perpendicular to the layer planes and the aromatic biphenyl cores parallel to the layer planes.     

Determination of poly(ethylene glycol)s by both normal-phase and reversed-phase modes of high-performance liquid chromatography

A normal-phase HPLC system using an amino column has been developed to characterise oligomers of poly(ethylene glycol)s (PEGs) of average M_r 400 to 2000 with derivatisation by dinitrobenzoate. Normal-phase HPLC with gradient elution using ternary solvents of hexane, dichloromethane and methanol has produced a baseline resolution for oligomers of PEG 400, 600 and 1000, while PEG 1000 and 2000 were analysed by using binary solvents of acetonitrile and water. Mixtures of PEGs have been determined by these HPLC systems. PEG 400 in a textile finish has also been determined with satisfactory recovery. It has been found that the hydroxyl group of solvents in normal-phase HPLC plays an important role in resolution and retention of PEG oligomers. Derivatisation efficiency for PEGs by dinitrobenzoyl chloride and quantitative determination of derivatised PEGs by HPLC have been studied. A reversed-phase (RP) mode of HPLC was examined for determination of PEG 400 oligomers. The normal-phase system provided greater resolution for oligomers of PEGs.     

The new structure type Gd3Ni7Al14

The crystal structure of Gd₃Ni₇Al₁₄ (trigadolinium heptanickel tetradecaaluminide) belongs to a family of two‐layer structures and can be described as an assembly of interpenetrating centred straight prisms. For the Ni atoms, trigonal prisms (Al₄Gd₂ and Al₆) are observed, the Al atoms are inside tetragonal (Ni₂Al₂Gd₄, Ni₂Al₄Gd₂, Al₄Gd₄, Ni₄Al₄ and Al₈) and pentagonal (Ni₄Al₆ and Al₁₀) prisms, while the Gd atoms are at the centres of pentagonal (Ni₄Al₆) and hexagonal (Ni₄Al₈) prisms. In each case, the true coordination polyhedron is a capped prism, also including atoms from the same layer. The structural features of Gd₃Ni₇Al₁₄ are similar to those of the intermetallides PrNi₂Al₃ and ZrNiAl. In all these structures, Ni‐centred trigonal prisms form infinite columns via common triangular faces. The columns share prism edges and form a three‐dimensional framework with six‐membered rings in the (001) plane in the case of the PrNi₂Al₃ and ZrNiAl types. In the case of Gd₃Ni₇Al₁₄, six‐membered rings are also observed, but only two‐thirds of the rings are interconnected via prism edges.