Optical enrichment of dansyl-rac-amino acids by formation of crystalline inclusion complexes with cyclodextrins

Optical enrichment from racemic dansyl-leucine, dansyl-norleucine, and dansyl-phenylalanine with both beta- and gamma-cyclodextrins in water is reported. Initial crystallization yielded the dansyl-L-Leucine isomer complexed in excess with beta-cyclodextrin with an optical purity of 62-78% depending on experimental conditions. The optical purities obtained for L-norleucine and L-phenylalanine were 71 and 64%, respectively. The optical purity can be increased with continued recrystallization. The dansyl-D-leucine isomer was obtained in the mother liquor with an optical purity of 54-93% depending on experimental conditions. The optical purities obtained for D-norleucine and D-phenylalanine were 72 and 58%. The optical purity of the isomer depended on the molar ratio of host:guest and the pH value of the solution. Optimum enrichment of both enantiomers was achieved with host:guest ratios of 2:1 and 3:1. Although maximum crystalline yield of the dansyl-leucine/CD inclusion complex was obtained at a pH of 3.5, optical purity of both enantiomers was less than that obtained at other pHs. The influence of the molar ratio of host:guest and the pH value of the solution are discussed. This method is suitable for large-scale enantiomeric separations.     

Crystallization, sequence, and preliminary crystallographic data for an antipeptide Fab 50.1 and peptide complexes with the principal neutralizing determinant of HIV-1 gp120.

X-ray quality crystals of an Fab fragment from an antipeptide monoclonal antibody (R/V3-50.1) that recognizes the principal neutralizing determinant (PND) of the gp120 glycoprotein of human immunodeficiency virus type 1 (HIV-1) (MN isolate) were grown as uncomplexed and peptide complexed forms. Crystals of the free Fab grew from high salt in orthorhombic space groups P2(1)2(1)2(1) and I222 and from polyethylene glycol in space groups P1 and P2(1). Seeds from either the P1 and P2(1) native (uncomplexed) Fab crystals induced nucleation of crystals of the Fab complexed to a 16-residue synthetic peptide corresponding to the PND when streak seeded into preequilibrated solutions of this complex. Data were collected from these complex crystals and from each of the four native Fab forms to at least 2.8 A resolution. The genes for the variable domain of the Fab were cloned and sequenced and the primary amino acid sequence was deduced from this information. Knowledge of the three-dimensional structure of this Fab-peptide complex will be important in the understanding of the PND of HIV-1 and its recognition by neutralizing monoclonal antibodies.     

5,5'-Dithio-bis(2-nitrobenzoic acid) modification of cysteine improves the crystal quality of human chloride intracellular channel protein 2

Structural studies of human chloride intracellular channel protein 2 (CLIC2) had been hampered by the problem of generating suitable crystals primarily due to the protein containing exposed cysteines. Several chemical reagents were used to react with the cysteines on CLIC2 in order to modify the redox state of the protein. We have obtained high quality crystals that diffracted to better than 2.5 Å at a home X-ray source by treating the protein with 5,5′-dithio-bis(2-nitrobenzoic acid) (DTNB). After solving the crystal structure of CLIC2, we found that the DTNB had reacted with the Cys¹¹⁴, and made CLIC2 in a homogenous oxidized state. This study demonstrated that the DTNB modification drastically improved the crystallization of CLIC2, and it implied that this method may be useful for other proteins containing exposed cysteines in general.     

Silver(I) coordination networks constructed with di-2-pyrazinylmethanediol

The new ligand di-2-pyrazinylmethanone (di-2-pyrazinyl ketone), (2-C₄H₃N₂)₂CO, has been synthesized, and two silver(I) coordination polymers of its hydrated gem-diol (2-C₄H₃N₂)₂C(OH)₂, namely {Ag[(2-C₄H₃N₂)₂C(OH)₂](CF₃SO₃)}_∞ (1) and {Ag[(2-C₄H₃N₂)₂C(OH)₂](CF₃CO₂)}_∞ (2), have been characterized by X-ray crystallography. A (4,4) net was found in compound 1. In the case of 2, the silver(I) atom functions as a rare five-connected node to conjunct the (2-C₄H₃N₂)₂C(OH)₂ ligands into an extended coordination network which can be viewed as an α-Po topology of the NaCl-type.     

Probability distributions of enantiomeric excess in unstirred and stirred crystallization of 1,1'-binaphthyl melt.

Crystallization of 1, l'-binaphthyl from its melt can generate optical activity spontaneously. Since crystallization is a stochastic process, the enantiomeric excess (ee) generated in each crystallization varies randomly. We investigated the qualitative features of probability distribution of the ee for crystallization at two temperatures, 150 degrees C and 152 degrees C, at which conglomerate crystallization occurs. No clear transparent crystals were produced at either temperature, indicating that the solid states formed in the melt were polycrystalline. The ee randomly fluctuated from run to run, with an average of 26.9% and 2.7% when the crystallization was carried out at 152 degrees C, and 150 degrees C, respectively. The spread of the probability distribution is also substantially different. We also studied the probability distribution of ee in stirred crystallization at different stirring RPM. The results show probability distribution's broadening and evolution to a bimodality with increasing stirring RPM--a typical behavior in symmetry-breaking transitions. These results shed light on the nature of enantioselectivity in secondary nucleation and crystal growth.     

空间格局和物种组合对三个植物种行为的影响

以青藏高原东部高寒草甸弃耕地种子大小不同的3个常见物种：2个1年生物种鼬瓣花（Galeopsis bifida）和菊叶香藜（Chenopodium foetidum）及1个2年生物种四数獐牙菜（Swertia tetraptera）为试验材料,通过单播、2个、3个物种的混播,分别以2个密度（高密度和低密度）,按照随机或者种内积聚的空间格局形式播种,研究空间格局、物种组合对不同种子大小植物行为的影响。结果表明：1）空间格局和物种组合对3物种的出苗率没有显著影响,但在一定程度上影响着物种竞争能力等级,大种子鼬瓣花在种间竞争中占据着优势地位,小种子菊叶香藜在种内集聚格局下获益;四数獐牙菜的种子大小介于二者之间,其种间竞争的结果表现复杂;2）集聚格局下菊叶香藜的幼苗死亡率低,地上生物量比随机格局下显著高;集聚格局下鼬瓣花死亡率高,通过密度-格局作用,高密集聚下的地上生物量才表现显著较低;3）与其他物种混播相比,鼬瓣花单播下死亡率高,地上生物量低;当混播中存在四数獐牙菜时,菊叶香藜的死亡率比单播下高,物种组合对其地上生物量没有显著影响;四数獐牙菜与鼬瓣花混播时死亡率最低,3个物种混播时其死亡率最高。     

Structure of dystrophia myotonica protein kinase

Dystrophia myotonica protein kinase (DMPK) is a serine/threonine kinase composed of a kinase domain and a coiled‐coil domain involved in the multimerization. The crystal structure of the kinase domain of DMPK bound to the inhibitor bisindolylmaleimide VIII (BIM‐8) revealed a dimeric enzyme associated by a conserved dimerization domain. The affinity of dimerisation suggested that the kinase domain alone is insufficient for dimerisation in vivo and that the coiled‐coil domains are required for stable dimer formation. The kinase domain is in an active conformation, with a fully‐ordered and correctly positioned αC helix, and catalytic residues in a conformation competent for catalysis. The conserved hydrophobic motif at the C‐terminal extension of the kinase domain is bound to the N‐terminal lobe of the kinase domain, despite being unphosphorylated. Differences in the arrangement of the C‐terminal extension compared to the closely related Rho‐associated kinases include an altered PXXP motif, a different conformation and binding arrangement for the turn motif, and a different location for the conserved NFD motif. The BIM‐8 inhibitor occupies the ATP site and has similar binding mode as observed in PDK1.     

Hybrid Perovskites: Effective Crystal Growth for Optoelectronic Applications

Outstanding material properties of organic‐inorganic hybrid perovskites have triggered a new insight into the next‐generation solar cells. Beyond solar cells, a wide range of controllable properties of hybrid perovskites, particularly depending on crystal growth conditions, enables versatile high‐performance optoelectronic devices such as light‐emitting diodes, photodetectors, and lasers. This article highlights recent progress in the crystallization strategies of organic–inorganic hybrid perovskites for use as effective light harvesters or light emitters. Fundamental background on perovskite crystalline structures and relevant optoelectronic properties such as optical band‐gap, electron‐hole behavior, and energy band alignment are given. A detailed overview of the effective crystallization methods for perovskites, including thermal treatment, additives, solvent mediator, laser irradiation, nanostructure, and crystal dimensionalityis reported offering a comprehensive correlation among perovskite processing conditions, crystalline morphology, and relevant device performance. Finally, future research directions to overcome current practical bottlenecks and move towards reliable high performance perovskite optoelectronic applications are proposed.     

Conjugated Polymers Based on Difluorobenzoxadiazole toward Practical Application of Polymer Solar Cells

To advance polymer solar cells (PSCs) toward real‐world applications, it is crucial to develop materials that are compatible with a low‐cost large‐scale manufacturing technology. In this context, a practically useful polymer should fulfill several critical requirements: the capability to provide high power conversion efficiencies (PCEs) via low‐cost fabrication using environmentally friendly solvents under mild thermal conditions, resulting in an active layer that is thick enough to minimize defects in large‐area films. Here, the development of new photovoltaic polymers is reported through rational molecular design to meet these requirements. Benzodithiophene (BDT)‐difluorobenzoxadiazole (ffBX)‐2‐decyltetradecyl (DT), a wide‐bandgap polymer based on ffBX and BDT emerges as the first example that fulfills the qualifications. When blended with a low‐cost acceptor (C₆₀‐fullerene derivative), BDT‐ffBX‐DT produces a PCE of 9.4% at active layer thickness over 250 nm. BDT‐ffBX‐DT devices can be fabricated from nonhalogenated solvents at low processing temperature. The success of BDT‐ffBX‐DT originates from its appropriate electronic structure and charge transport characteristics, in combination with a favorable face‐on orientation of the polymer backbone in blends, and the ability to form proper phase separation morphology with a fibrillar bicontinuous interpenetrating network in bulk‐heterojunction films. With these characteristics, BDT‐ffBX‐DT represents a meaningful step toward future everyday applications of polymer solar cells.