A comparison between polysulfone,zirconia and organo-mineral membranes for use in ultrafiltration

In this paper, representative polymeric (a PSf/PVP membrane), ceramic (a ZrO₂ membrane) and organo-mineral (a ZrO₂/PSf membrane) ultrafiltration membranes, all in the tubular configuration, are being compared for their basic membrane properties, and for the typical ultrafiltration application of protein recovery of cheese whey. These three different membranes with a quite similar pore size (the cut-off values for each of the three membranes were comprised between 25 000 and 50 000 Dalton) showed pure water permeability coefficients between 135 and 1250 l/h m² bar. The highest pure water flux was found for the organo-mineral membrane, the lowest for the polymeric membrane. By FESEM analysis of the top-surfaces (skin) of both the PSf/PVP and the ZrO₂/PSf membrane a strong difference in surface-porosity was found. These results were claimed to partially explain the difference in pure water flux. From SEM pictures of the cross-section of the ZrO₂/PSf membrane it could also be seen that the skin layer thickness is smaller, at these places where particles are present near the skin-surface, compared to the rest of the membrane as well as to the skin of the PSf/PVP membrane. These latter observations were also used to further explain the flux difference between the PSf/PVP and the ZrO₂/PSf membrane.     

A chromatographic comparison of the pore structure of zirconia high performance liquid chromatographic materials made by the polymerization induced colloidal aggregation and the Oil Emulsion methods

Summary The pore structures of zirconium oxide particles prepared by two different methods (PICA and Oil Emulsion processes) are compared. Nitrogen sorptometry and size exclusion chromatography are used to characterize the two different types of particles. Significant and unexpected differences were found in the accessible pore volumes and the bed packing densities of the two materials. The PICA material was found to have a higher totally included and totally excluded volume than would be normally expected. The chromatographic method provides results which are more useful for the application of these materials to separation sciences.     

Depth-sensing indentation applied to polymers: A comparison between standard methods of analysis in relation to the nature of the materials

Mechanical data (hardness and elastic modulus) from instrumented indentation testing are often extracted assuming linear elasticity in the initial portion of the unloading. The method is nowadays widely accepted as a convenient tool to interpret depth-sensing data, however it is a matter of controversy when applied to polymer materials due to their time-dependent behavior. More recently, Loubet and co-workers applied continuous stiffness measurements (CSM), consisting of superimposing a small oscillation to the quasi-static component of loading, to the study of the mechanical properties of polymers and proposed a new model to account for the apparent increase in the contact area detected at the first stages of contact. The present work offers a comparative study between the Loubet’s model using CSM and the procedure yielding a single reading from the onset of unloading. A wide range of thermoplastic polymer materials including glassy and semicrystalline polymers have been investigated. The most important equations employed for each method are summarized and the advantages and disadvantages of employing one procedure or the other are discussed. The differences found between the results obtained from both approaches are discussed in relation to the nature of the polymer material. A comparison between mechanical data extracted from indentation measurements and from classical dynamic mechanical analysis is offered.     

KNiB4O6F3: A Layered Fluorooxoborate with Charge-Oriented Ordering

A layered fluorooxoborate, KNiB₄O₆F₃, contains a new (B₄O₆F₄)⁴⁻ group built of one planar (BO₃)³⁻ triangle and three tetrahedral (BO₃F)⁴⁻ units. Those units are joined together by sharing the oxygen atoms to form a 2-dimensinal (BO_3/2F)₃BO_3/2)_∞ layer. K⁺ and Ni²⁺ occupy on the sides with F⁻ and O²⁻ of the (BO_3/2F)₃BO_3/2)_∞ layer with a high (positive charge) to high (negative charge) and low to low coordination. Such kind of charge-oriented ordering is found to be governed by the stabilization energy of Coulomb interaction of the cations in certain sites. It is hoped that this mechanism of ordering may provide an additional tool for designing new structures with favourable properties, such as ferroelectrics or nonlinear optical materials.     

A Ten‐membered Dimetallacycle with an [Ag···Ag]2+ Dication Bridged by Two P,N Ligands

The reaction of silver hexafluoridoantimonate with Ph₂PCH₂PPh₂NSiMe₃ ( 1 ) in dichloromethane produces the dimeric complex [Ag(μ‐Ph₂PCH₂PPh₂NSiMe₃)]₂[SbF₆]₂ ( 2 ), in which two heterobifunctional ligands 1 in the dication are N, P‐chelated in a head‐to‐tail fashion to a [Ag ··· Ag]²⁺ unit that exhibits an Ag ··· Ag contact of 2.8530(6) Å. Quantum theory of atoms‐in‐molecules (QTAIM) analysis of the bonding revealed an attractive interaction between the two silver atoms.     

Furan derivatives of tellurium: Synthesis and structural comparison with the thiophene analogues

α-Bromo-2-acetylfuran adds oxidatively to elemental tellurium and aryltellurium(II) bromide at ambient temperature to afford (2-furoylmethyl)tellurium(IV) dibromides, (FuCOCH₂)₂TeBr₂ (1b) and Ar(FuCOCH₂)TeBr₂ (Fu = 2-C₄H₃O; Ar = 1-C₁₀H₇, 2b; 2,4,6-Me₃C₆H₂, 3b). The iodo analogues 1c-3c can be obtained by metathesis of the bromides with an alkali iodide. Condensation reactions of the parent methyl ketone with Te(IV) chlorides results in the corresponding chloro analogues, (FuCOCH₂)₂TeCl₂ (1a) and Ar(FuCOCH₂)TeCl₂ (2a, 3a and Ar = 4-MeOC₆H₄ (4a)). These diorganotellurium dihalides are reduced with aqueous bisulfite to diorganotellurides 1-3, which can be oxidized readily with dihalogens to the desired diorganotellurium(IV) dihalides. The tellurated furan derivative, bis(2-furyl)tellurium(II), Fu₂Te (5), obtained by detelluration of bis(2-furyl)ditelluride with electrolytic copper, gives crystalline bis(2-furyl)tellurium(IV) dichloride (5a) upon chlorination. Crystal structures of Te(IV) compounds 1a, 1b, 2a-4a, and the telluride 3 together with its thiophene analogue (2,4,6-Me₃C₆H₂)((2-C₄H₃S)COCH₂)Te, 6 have been studied. Among the Te(IV) compounds, the functionalized organic moiety, FuCOCH₂-, behaves as a (C, O) chelating ligand, resulting in a intramolecular 1,4-Te?O secondary bonding interaction. Such an interaction is absent in Te(II) compounds 3 and 6, though they differ in the conformation adopted by the organic ligand. The chalcogen atoms in the heteroaroyl moiety are trans in 3 but cis in 6 which also possesses intermolecular Te?O interaction in its lattice.     

A novel coordination polymer with dicyanamide ligand: multi-dimensional architecture stabilized by hydrogen bonding

A novel dicyanamide (dca) complex, [Cu(pn)(dca)₂]_n (pn=1,2-diaminopropane), was synthesized and characterized. X-ray diffraction analysis reveals that the title complex crystallizes in the monoclinic space group C2/c with β=96.662(6)°, Z=8, and R₁=0.0476, wR₂=0.1094. The complex exhibits one-dimensional zigzag chain structure constructed by μ_1,5-dca bridges. The coordination geometry around the copper atom was a distorted square-pyramid. The spectroscopic and magnetic properties have also been discussed.     

Metallic monoboronyl compounds: Prediction of their structure and comparison with the cyanide analogues

A theoretical study of monoboronyls of different metals has been carried out. We have chosen Mg as representative of s‐block elements, Al for the p‐block, and Group 11 metals (Cu, Ag, and Au) for the d‐block. Different behaviors are observed: bonding through the oxygen atom is preferred in the case of Al, for all Group 11 monoboronyls bonding through the boron atom prevails and both interactions give rise to almost isoenergetic compounds in the case of Mg. Predictions for the spectroscopic parameters relevant for rotational and vibrational spectroscopy of the different competitive species are provided. Al and Group 11 boronyls have relatively high dissociation energies, whereas Mg boronyl has moderate dissociation energy. The molecular structure of metal boronyls has been rationalized through an analysis of the bonding. The similarities and differences between metal boronyls and their isoelectronic cyanide analogues have been discussed. © 2017 Wiley Periodicals, Inc.     

氨基己酸为配基的新型弱阳离子交换/疏水双功能色谱固定相对蛋白质的分离纯化

以硅胶为基质、氨基己酸为配基制备了一种新型弱阳离子交换/疏水（WCX/HIC）双功能混合模式色谱固定相。该固定相配基具有一定的疏水性且含有羧基,在高盐浓度下表现为HIC的性质,可作为HIC固定相使用;在低盐浓度条件下表现为离子交换的性质,可作为WCX固定相使用。分别考察了该介质在WCX和HIC两种模式下对标准蛋白质的分离性能,并与商品柱进行比较。结果表明,所合成的WCX/HIC双功能固定相在WCX和HIC两种模式下对蛋白质均有较高的分离度和选择性,且分离能力与商品柱相当,两种模式下标准蛋白质的质量和活性回收率均大于93%,表明该柱具有“一柱二用”的功能,适于生物大分子的分离纯化。基于此双功能色谱柱构建的在线单柱二维液相色谱（2DLC-1C）可在60 min内实现8种蛋白质的快速分离。在70 min内完成了对蛋清中溶菌酶的二维纯化,纯度可达到98.3%。该技术中一根色谱柱可当作两根色谱柱使用,对蛋白质组学研究和重组蛋白药物的生产具有重要的应用价值。     

The consequences of cation radical fluorination theory—I : A comparison of various theoretical scenarios with experiment for carbocyclic-aromatics,using CNDO/2 and INDO calculations

Various of the possible scenarios (Table 1) derived from cation radical fluorination theory are examined critically in the light of experiment. The predictions of the theory are made using CNDO/2 and some INDO calculations, and these are compared with the known experimental results for benzene, benzotrifluoride, naphthalene, anthracene and phenanthrene. It is concluded that cation radical theory must be broadly correct; it works well for monocyclic hydrocarbon compounds, assuming product control to be via spin or charge density in the intermediates (cations, radicals, cation-radicals), with sequence 3 (Table 1) preferred. In the absence of any modifying hypothesis, however, control of products by spin or charge density alone cannot explain the experimental results for the polycyclic substrates. The most plausible modifications appear to be product control via Wheland intermediate stability (sequence 7, Table 1) and/or rapid rearrangements.     

Quenching of chlorophyll a singlets and triplets by carotenoids in light-harvesting complex of photosystem II: comparison of aggregates with trimers

Laser-induced changes in the absorption spectra of isolated light-harvesting chlorophyll a/b complex (LHC II) associated with photosystem II of higher plants have been recorded under anaerobic conditions and at ambient temperature by using multichannel detection with sub-microsecond time resolution. Difference spectra (ΔA) of LHC II aggregates have been found to differ from the corresponding spectra of trimers on two counts: (i) in the aggregates, the carotenoid (Car) triplet–triplet absorption band (ΔA>0) is red-shifted and broader; and (ii) the features attributable to the perturbation of the Q_y band of a chlorophyll a (Chla) by a nearby Car triplet are more pronounced, than in trimers. Aggregation, which is known to be accompanied by a reduction in the fluorescence yield of Chla, is shown to cause a parallel decline in the triplet formation yield of Chla; on the other hand, the efficiency (100%) of Chla-to-Car transfer of triplet energy and the lifetime (9.3 μs) of Car triplets are not affected by aggregation. These findings are rationalized by postulating that the antenna Cars transact, besides light-harvesting and photoprotection, a third process: energy dissipation within the antenna. The suggestion is advanced that luteins, which are buried inside the LHC II monomers, as well as the other, peripheral, xanthophylls (neoxanthin and violaxanthin) quench the excited singlet state of Chla by catalyzing internal conversion, a decay channel that competes with fluorescence and intersystem crossing; support for this explanation is presented by recalling reports of similar behaviour in bichromophoric model compounds in which one moiety is a Car and the other a porphyrin or a pyropheophorbide.     

Methylamine interaction with proteins of photosystem II: A comparison with biogenic polyamines

Biogenic polyamines are essential for cell growth and differentiation. The interaction of polyamines with protein of photosystem II (PSII) are well investigated, while there has been no report on the effect of monoamines complexation on photosynthetic oxygen evolution. This study was designed to investigate the interaction of methylamine with proteins of PSII, using PSII-enriched submembrane fractions with various concentrations of methylamine. Fourier transformed infrared (FTIR) and fluorescence spectroscopic methods were used in order to determine the methylamine binding mode, the protein conformational changes, and the effect of amine interaction on photosynthetic oxygen evolution. Spectroscopic evidence showed that methylamine interacts with protein (H-bonding) through polypeptide CO, C–N and NH groups with major perturbations of protein secondary structure. Major reduction of α-helix from 50% (free PSII) to 35% with an increase of β-sheet from 10% (free PSII) to 16% was observed in methylamine-PSII complexes. At very low methylamine concentration, no inhibition of oxygen-evolution occurred, while at higher amine content (12 mM), 100% inhibition was observed. Chlorophyll (Chl) fluorescence measurements indicated the inhibition mainly affects the oxygen evolving complex (OEC) of PSII. Comparisons of the effects of methylamine with biogenic polyamine spermine, spermidine and putrescine showed a similar mode of binding with protein (H-bonding) through polypeptide CO, C–N and NH groups. However, major alterations of the protein secondary structure are induced by monoamine and not by polyamines.     

A Diazabutadiene stabilized Nickel(0) Cyclooctadiene Complex: Synthesis,Characterization and the Reaction with Diphenylacetylene

The reaction of [Ni(COD)₂] with one equivalent of DAB^Mes (DAB^Mes = (2,4,6‐Me₃C₆H₂)N=C(Me)‐C(Me)=N(2,4,6‐Me₃C₆H₂)) affords a mixture of the compound [Ni(DAB^Mes)₂] ( 2 ) and starting material [Ni(COD)₂]. The crystallographically characterized, diamagnetic complex 2 can be obtained in a stoichiometric reaction of [Ni(COD)₂] and two equivalents of DAB^Mes. This reaction can be accelerated by addition of 1‐chloro‐fluorobenzene or methyl iodide. In the presence of 1‐chloro‐fluorobenzene, [Ni(DAB^Mes)(COD)] ( 3 ) is available via reaction of [Ni(COD)₂] and one equivalent of DAB^Mes. The crystallographically characterized complex 3 reacts with diphenylacetylene to afford [Ni(DAB^Mes)(Ph‐C≡C‐Ph)] ( 4 ). A long‐wavelength absorption band in the UV‐Vis spectrum of this compound has to be assigned to a mixed MLCT/LL′CT transition, as quantum chemical calculations reveal.     

A triphenylamine double-decker: from a delocalized radical cation to a diradical dication with an excited triplet state

The redox properties and electronic structures of polycationic species were examined using a triphenylamine double-decker species. The double-decker has a strong electron-donating ability, and the spin in the radical cation is delocalized over the whole caged skeleton, despite no direct transannular π-π interaction between two TPA decks. Moreover, the diradical dication has spin-singlet character, despite the meta-phenylene linkage.     

Cooperative near-IR to visible photon upconversion in Yb3+-doped MnCl2 and MnBr2: comparison with a series of Yb3+-doped Mn2+ halides

Yb3+-doped MnCl2 and MnBr2 crystals exhibit strong red upconversion luminescence under near-infrared excitation around 10 000 cm(-1) at temperatures below 100 K. The broad red luminescence band is centred around 15 200 cm(-1) for both compounds and identified as the Mn2+ 4T1g-->6A1g transition. Excitation with 10 ns pulses indicates that the upconversion process consists of a sequence of ground-state and excited-state absorption steps. The experimental VIS/NIR photon ratio at 12 K for an excitation power of 191 mW focused on the sample with a 53 mm lens is 4.1% for MnCl2:Yb3+ and 1.2% for MnBr2:Yb3+. An upconversion mechanism based on exchange coupled Yb3+-Mn2+ ions is proposed. Similar upconversion properties have been reported for RbMnCl3:Yb3+, CsMnCl3:Yb3+, CsMnBr3:Yb3+, RbMnBr3:Yb3+, Rb2MnCl4:Yb3+. The efficiency of the upconversion process in these compounds is strongly dependent on the connectivity between the Yb3+ and Mn2+ ions. The VIS/NIR photon ratio decreases by three orders of magnitude along the series of corner-sharing Yb3+-Cl--Mn2+, edge-sharing Yb3+-(Cl-)2-Mn2+ to face-sharing Yb3+-(Br-)3-Mn2+ bridging geometry. This trend is discussed in terms of the dependence of the relevant super-exchange pathways on the Yb(3+)-Mn2+ bridging geometry.     

A practical valence bond method: a configuration interaction method approach with perturbation theoretic facility

The previously developed valence bond configuration interaction (VBCI) method (Wu, W.; Song, L.; Cao, Z.; Zhang, Q.; Shaik, S., J. Phys. Chem. A, 2002, 105, 2721) that borrows the general CI philosophy of the MO theory, is further extended in this article, and its methodological features are improved, resulting in three accurate and cost-effective procedures: (a) the effect of quadruplet excitation is incorporated using the Davidson correction, such that the new procedure reduces size consistency problems, with due improvement in the quality of the computational results. (b) A cost-effective procedure, named VBCI(D, S), is introduced. It includes doubly excited structures for active electrons and singly excited structures for inactive pairs. The computational results of VBCI(D, S) match those of VBCISD with much less computational effort than VBCISD. (c) Finally, a second-order perturbation theory is utilized as a means of configuration selection, and lead to considerable reduction of the computational cost, with little or no loss in accuracy. Applications of the new procedures to bond energies and barriers of chemical reactions are presented and discussed.     

A novel dimeric zinc(II) complex with a tripodal peptide ligand: a structure stabilized by ligand sharing

The crystal structure of a novel dimeric zinc(II) complex, [ZnL(H₂O)]₂(ClO₄)₂·4H₂O (L?=?N-(bis(2-pyridyl)methyl)-2-pyridinecarboxamide), has been determined by X-ray diffraction. In this complex each planar N_py–N_amido–N_py moiety of the ligand coordinates to one zinc ion and the pendant pyridine of one [ZnL] unit completes the coordination sphere of a [ZnL] neighbor. Units of the complex are connected in a two-dimensional network by intermolecular hydrogen bonds. The thermodynamic properties of the ligand with bivalent metal ions Co(II), Ni(II), Cu(II) and Zn(II) were studied by potentiometric titration and the order of the stability constants is in agreement with the Irving–Williams series. The dimeric complex is stabilized through ligand sharing, as confirmed by the crystal structure and thermodynamic properties.     

Spinodal decomposition of two homopolymers with their block copolymer: A comparison of models

The dynamics of phase separation in the presence of a diblock copolymer have been studied using ternary and quaternary models of spinodal decomposition. The ternary model treats the block copolymer as a third component that is compatible with each of the mutually incompatible homopolymers. The quaternary model treats the block copolymer as a pair of specially constrained homopolymers. Both models predict core-shell morphologies with the copolymer concentrated at the interface. Both models predict larger domain sizes and less sharp phase boundaries in the early stages of spinodal decomposition. In the late stages, domain sizes are largest for the system of homopolymers without copolymer and smallest when a system containing copolymer is modeled as a quaternary blend. The scaling exponent observed for the quaternary model was s = 0.25 ± 0.02 compared to s ≅ 0.3 for the homopolymers without copolymer and for the ternary model. The quaternary model predicts internal phase separation within a pure diblock copolymer, whenever the corresponding homopolymers are sufficiently incompatible. © 1996 John Wiley & Sons, Inc.     

A multireference configuration interaction study with singles and doubles of some mesoionic rings: reaction and activation free energies for the ring-opening reaction

For the first time, multireference configuration interaction with singles and doubles (MR-CISD) calculations (including extensivity corrections, MR-CISD+Q) have been performed to study the ring-opening reactions of the following mesoionic rings and their 2, 3, and 4 methyl-substituted derivatives: ( a ) 1,3-oxazol-5-one, ( c ) 1,3-oxazol-5-thiolate, and ( d ) 1,3-thiazol-5-thiolate. The ring-opening reaction of the parent 1,3-thiazol-5-one mesoionic ring ( b ) has also been studied. The effect of methyl and S replacement on the reaction and activation free energies (ΔG and ΔG^†, respectively) is studied. For a , the effect of methyl replacement on C2 is almost negligible, while on N3 and C4, it is significantly larger, especially in the latter position. The open structure (ketene form) of a is considerably more stable, and the replacement of the exocyclic O by S stabilizes the ketene tautomer even more and increases ΔG^† considerably. On the other hand, replacement of the endocyclic O by S (yielding b ) completely prevents the formation of the open structure, while replacement of both endo and exo atoms strongly stabilizes the cyclic structure and leads to a remarkably high value of ΔG^†. In some cases, the relative polarity of the stationary points is used to estimate how ΔG and ΔG^† are expected to change as one goes from the gas phase to aprotic polar solvents. A linear correlation between the multiconfigurational character of the mesoionic rings and ΔG^† has been observed, and such correlation is used to estimate the ΔG^† values for the methyl-substituted c and d . The largest barrier (13.78 kcal/mol) has been obtained for the 4-methyl-1,3-thiazol-5-thiolate (4-m- d ).