Controllable mineralization of calcium carbonate on regenerated cellulose fibers

Gel–forming fibers (GF fibers) can serve as nucleation sites to prepare calcium carbonate (CaCO₃) because they can adsorb large amounts of Ca²⁺ due to their porous structure. In this paper, mineralization behavior of CaCO₃ on GF fibers in ethanol–water mixed solvents without any additives has been investigated. The results showed that some crystals covered the fibers, while others were embedded in fibers. Twin–sphere based vaterite, zonary and rodlike calcite with large aspect ratio could be prepared successfully. The effect of ethanol content inside GF fibers, concentration of Ca²⁺ and CO₃^2‐, mineralization time, miscibility between alcohol and water, and temperature were studied. Lastly, a possible mineralization mode was suggested. This work could provide a new method to prepare inorganic/polymer hybrid materials. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Exciton Migration and Surface Trapping for a Photonic Crystal Displaying Charge‐Recombination Fluorescence

A compact donor–acceptor molecular dyad has been synthesized by attaching an N,N‐dimethylamino fragment to a naphthalic anhydride residue. The dyad shows fluorescence from an intramolecular charge‐transfer state (i.e., charge‐recombination fluorescence) in solution, with the photo‐physical properties being strongly dependent on the solvent polarity. Similar emission is seen for single crystals of the target compound, the molecules being aligned head‐to‐head, although time‐resolved emission profiles display dual‐exponential kinetics. A second polymorph with the head‐to‐tail alignment also gives rise to two lifetimes that differ somewhat from those of the first structure, which are assigned to bulk and surface‐bound molecules. Growing the crystal in the presence of Rhodamine B localizes the dye around the surface. Excitation of the crystal is followed by sub‐ps exciton migration along the aligned stacks, with occasional crossing to adjacent stacks and trapping at the surface. Rhodamine B present at very low levels acts as the acceptor for excitons entering the surface layer. Crystals embedded in a polyester resin form an artificial light‐harvesting antenna able to sensitize an amorphous silicon solar cell.     

Conformational dimorphism in o‐nitrobenzoic acid: alternative ways to avoid the O…O clash

Polymorphism is a challenging phenomenon and the competitive packing alternatives which are characteristic for polymorphs may be encountered for essentially rigid molecules. A second crystal form of the well known compound o‐nitrobenzoic acid, C₇H₅NO₄, an important intermediate in the production of dyes, pharmaceuticals and agrochemicals, is described. Although obtained serendipitously, its intra‐ and intermolecular features match expectations from database searches and theoretical calculations. O—H…O hydrogen‐bonded carboxylic acid dimers represent the building blocks in both polymorphs. For steric reasons and in agreement with a calculated potential energy surface, the carboxylic acid and nitro groups cannot simultaneously be coplanar with the benzene ring but have to tilt. In the well established crystal form, this out‐of‐plane torsion is more pronounced for the nitro substituent. In contrast, the new polymorph is characterized by a major tilt of the carboxylic acid group. The molecules in both alternative crystal forms achieve a similar compromise with respect to acceptable intramolecular O…O contacts.     

A new crystalline form of αβ‐d‐lactose prepared by oven drying a concentrated aqueous solution of d‐lactose

A new crystalline form of αβ‐d ‐lactose (C₁₂H₂₂O₁₁) has been prepared by the rapid drying of an approximately 40% w/v syrup of d ‐lactose. Initially identified from its novel powder X‐ray diffraction pattern, the monoclinic crystal structure was solved from a microcrystal recovered from the generally polycrystalline mixed‐phase residue obtained at the end of the drying step. This is the second crystalline form of αβ‐d ‐lactose to be identified and it has a high degree of structural three‐dimensional similarity to the previously identified triclinic form.     

New solvents for cellulose: Hydrazine/thiocyanate salt system

The hydrazine/thiocyanate system was found to be an excellent solvent for cellulose. The solubility and solution properties were investigated. Even at room temperature, the combinations of hydrazine and lithium, sodium, and potassium thiocyanate had high dissolution power for cellulose, up to an 18% (w/w) maximum, unrelated to the polymorph, whereas a combination with ammonium thiocyanate exhibited a solubility difference among celluloses I, II, and III. The effect of the temperature cycling of the system for the rapid dissolution of cellulose was investigated thermodynamically. In these systems, a high concentration of salts was necessary to effect the cellulose dissolution; this suggested that an undissociated salt–solvent complex played an important role in the cellulose dissolution as implied by electroconductivity measurements of the hydrazine/salt system. Gel and liquid‐crystal formation was observed in all systems above 4 and 6% (w/w) cellulose concentrations, respectively. The values of both critical concentrations were quite similar to those observed in the ammonia/ammonium thiocyanate system studied earlier in our laboratories. The gelation temperature was between approximately 10 and 50 °C, depending on the salt and cellulose concentration. The dependence of the cellulose solubility on the degree of polymerization was also examined. It is suggested that these solvent systems have great potential for the fiber and film formation of cellulose. © 2002 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 601–611, 2002; DOI 10.1002/pola.10135     

Microemulsion‐Facilitated Crystallization of Carbamazepine

The crystallization patterns of carbamazepine precipitated from a confined microemulsion reservoir were studied by DSC, TGA, Powder XRD, single crystal XRD, SEM, and optical microscopy. The results suggest that interfacial fast nucleation and slow growth from O/W microemulsion leads to a selective, large, and better‐ordered single crystals of dihydrate form with primitive monoclinic unit cell with parameters a=10.16 Å, b=28.70 Å, c=4.93 Å, β=103.33°, cell volume of 1400.7 ų, and space group P21/c. The crystal structure, as well as the habit, are strongly influenced by the heat dissipation and prefered molecular orientation at the interface.     

表面活性剂AEO-3对β沸石合成的促进作用

在常规β沸石的水热合成体系中加入非离子型表面活性剂脂肪醇聚氧乙烯醚(AEO-3),按照n_(Al_2O_3)∶n_(SiO_2)∶n_(Na_2O)∶nTEAOH∶n_(H_2O)∶n_(AEO-3)∶n_(C_2H_5OH)=(0.28～1)∶40∶1.55∶10∶640∶(0.45～7.69)∶11.37的配料比,考察其作为助剂对β沸石合成的影响。实验发现,与常规合成体系相比,AEO-3的加入可促进硅铝酸盐溶胶的生成并增加了其均匀化程度,同时增加了产品收率。所合成样品的X射线衍射、N_2和Ar吸附-脱附、扫描电镜、固体核磁和正癸烷吸附的表征结果表明,表面活性剂AEO-3的加入使β沸石的纳米晶粒更加完整与均匀,提高了结晶度和微孔体积,并使得收率提高。所合成的β沸石的骨架硅铝比提高,酸强度增加。另外,AEO-3的加入提高了β沸石结构中的手性多形体A的比例。     

ECNU‐36: A Quasi‐Pure Polymorph CH Beta Silicate Composed of Hierarchical Nanosheet Crystals for Effective VOCs Adsorption

A quasi‐pure C_H polymorph of microporous zeolite beta, named ECNU‐36, was obtained as a highly crystalline silicate using 1,5‐bis(tetramethylimidazolium) hydroxide as organic structure‐directing agent (OSDA) in fluoride media. An appropriate concentration of free fluoride in the synthetic mother liquor was crucial to purify the C_H‐phase. The framework structure of ECNU‐36 consists of polymorph C_H (>95 %) and polymorph B, elucidated by a combination of PXRD data, DIFFaX simulation, EDT, and HRTEM techniques. For the first time, the framework structure of beta C_H polymorph was directly confirmed and solved using electron diffraction data. The pure‐silica ECNU‐36 showed an unusual crystal morphology, composed of stacked nanosheets, with typical 17 nm thickness and exposed {100} facets, which exhibited attractive adsorption performance for hydrocarbons and aromatics.     

2,2’-二(4-羟基苯基)丙烷与四丁基铵包合物([(n-C4H9)4N]＋• [(C15H15O2)2H]－)的两种同质异晶体

合成了2,2’-二(4-羟基苯基)丙烷为主体分子的四丁基铵包合物, [(n-C4H9)4N]＋•[(C15H15O2)2H]－, 并通过单晶Ｘ射线衍射法对其进行了晶体结构测定, 发现该包合物的晶体存在两种同质异晶体. 结果表明, 晶型1属单斜晶系, C2/c空间群, 晶胞参数a＝2.8199(2) nm, b＝0.92730(8) nm, c＝2.1450(3) nm, β＝130.050(1)°, Z＝4, R1＝0.0771, wR2＝0.2452; 晶型2属三斜晶系, P`1空间群, 晶胞参数a＝1.0895(1) nm, b＝1.2331(2) nm, c＝1.7244(2) nm, α＝108.137(2)°, β＝94.458(2)°, γ＝100.172(2)°, Z＝2, R1＝0.0697, wR2＝0.2176. 晶型1中2,2’-二(4-羟基苯基)丙烷阴离子的氢键链构成管道式主体晶格, 正四丁基铵阳离子被包合在这些管道中; 晶型2中2个独立的2,2’-二(4-羟基苯基)丙烷阴离子分别形成氢键主体层, 它们交替排列并与夹在其间的正四丁基铵阳离子形成类三明治层状包合物.     

The structural properties of a noncentrosymmetric polymorph of 4‐aminobenzoic acid

The crystal structure of a polymorph of 4‐aminobenzoic acid (PABA), C₇H₇NO₂, at 100 K is noncentrosymmetric, as opposed to centrosymmetric in the structures of the other known polymorphs. The two crystallographically independent PABA molecules form pseudocentrosymmetric O—H...O hydrogen‐bonded dimers that are further linked by N—H...O hydrogen bonds into a three‐dimensional network. The benzene rings stack in the b direction. The CO₂ moieties are bent out slightly from the benzene ring plane.