“Crystal memory” Affects the Properties of Peptide Hydrogels – The Case of the Cyclic Tyr-Tyr dipeptide

In this work a relationship between the crystal form and morphology and rheological properties of peptide-based hydrogels is examined. We show, that under favorable circumstances a correlation between a starting solid material and a self-assembly processes in solution can exist, leading to different properties of a resulting soft matter. This observation, together with an in-depth analysis of the influence of stereochemistry of self-assembled (ll ) and (dl ) Tyr-Tyr cyclic dipeptides (cYY) on the observed relationship between gelation and crystallization allowed us to gain a deeper understanding of the peptide hydrogelation processes at a molecular level, using liquid state NMR, rheological studies and scanning electron microscopy. In the course of our studies, several crystal forms of (ll )-cYY has been discovered and described in details using single crystal X-ray diffraction, as well as advanced solid state NMR, X-ray diffraction of powders, thermal analysis, FTIR, circular dichroism and crystal structure prediction (CSP) calculations. Subsequently, we found that while (ll )-cYY easily assembles into hydrogels with different properties depending on the starting solid form, (dl )-cYY always precipitated as one crystal form in the tested conditions. Molecular-level justification for this observation is given.     

Combinatorial Crystal Synthesis: Structural Landscape of Phloroglucinol:1,2‐bis(4‐pyridyl)ethylene and Phloroglucinol:Phenazine

A large number of crystal forms, polymorphs and pseudopolymorphs, have been isolated in the phloroglucinol‐dipyridylethylene (PGL:DPE) and phloroglucinol‐phenazine (PGL:PHE) systems. An understanding of the intermolecular interactions and synthon preferences in these binary systems enables one to design a ternary molecular solid that consists of PGL, PHE, and DPE, and also others where DPE is replaced by other heterocycles. Clean isolation of these ternary cocrystals demonstrates synthon amplification during crystallization. These results point to the lesser likelihood of polymorphism in multicomponent crystals compared to single‐component crystals. The appearance of several crystal forms during crystallization of a multicomponent system can be viewed as combinatorial crystal synthesis with synthon selection from a solution library. The resulting polymorphs and pseudopolymorphs that are obtained constitute a crystal structure landscape.     

Two Crystal Forms of a Hydrated 2:1 β-Cyclodextrin Fluconazole Complex: Single Crystal X-ray Structures,Dehydration Profiles,and Conditions for Their Individual Isolation

Inclusion complexes between cyclodextrins (CDs) and active pharmaceutical ingredients (APIs) have potential for pharmaceutical formulation. Since crystallization of a given complex may result in the isolation of multiple crystal forms, it is essential to characterize these forms with respect to their structures and physicochemical properties to optimize pharmaceutical candidate selection. Here, we report the preparation and characterization of two crystallographically distinct hydrated forms of an inclusion complex between β-cyclodextrin (β-CD) and the antifungal API fluconazole (FLU) as well as temperature–concentration conditions required for their individual isolation. Determination of crystal water contents was achieved using thermoanalytical methods. X-ray analyses revealed distinct structural differences between the triclinic (TBCDFLU, space group P1) and monoclinic (MBCDFLU, space group C2) crystal forms. Removal of the crystals from their mother liquors led to rapid dehydration of the MBCDFLU crystal, while the TBCDFLU crystal was stable, a result that could be reconciled with the distinct packing arrangements in the respective crystals. This study highlights (a) the importance of identifying possible multiple forms of a cyclodextrin API complex and controlling the crystallization conditions, and (b) the need to characterize such crystal forms to determine the extent to which their physicochemical properties may differ.     

Backbone flexibility on conjugated polymer's crystallization behavior and thin film mechanical stability

Extensive efforts have been made to develop flexible electronics with conjugated polymers that are intrinsically stretchable and soft. We recently systematically investigated the influence of conjugation break spacers (CBS) on the thermomechanical properties of a series n-type naphthalene diimide-based conjugated polymer and found that CBS can significantly reduce chain rigidity, melting point, as well as glass transition temperature. In the current work, we further examined the influence of CBS on the crystallization behaviors of PNDI-C3 to C6, including isothermal crystallization kinetics, crystal polymorphism and subsequently time-dependent modulus, in a holistic approach using differential scanning calorimetry, X-ray scattering, polarized optical microscopy, atomic force microscopy, and pseudo-free-standing tensile test. Results demonstrate that increasing the length of CBS increases the crystallization half-time by 1 order of magnitude from PNDI-C3 to PNDI-C6 from approximately 10³ to 10⁴ s. The crystallization rate shows a bimodal dependence on the temperature due to the presence of different polymorphs. In addition, crystallization significantly affects the mechanical response, a stiffening in the modulus of nearly three times is observed for PNDI-C5 when annealed at room temperature for 12 h. Crystallization kinetic is also influenced by molecular weight (MW). Higher MW PNDI-C3 crystallizes slower. In addition, an odd–even effect was observed below 50°C, odd-number PNDI-Cxs (C3 and C5) crystallize slower than the adjacent even-numbered PNDI-Cxs (C4 and C6). Our work provides an insight to design flexible electronics by systematically tuning the mechanical properties through control of polymer crystallization by tuning backbone rigidity.     

An overview on 12-polyurethane: Synthesis, structure and crystallization

The knowledge on linear aliphatic polyurethanes n-PUR has increased significantly due to a series of works made in these last years and published in recent literature. An overview of 12-polyurethane (12-PUR) embracing its synthesis, thermal properties, crystal structure and crystallization is given in this paper. The purpose is to provide a representative example able to reflect comprehensively the state of the art reached for the whole family. The synthesis of 12-PUR was accomplished in good yield and with acceptable molecular weight from 12-amino-1-dodecanol by applying a two-step method without isolation of the isocyanate alcohol precursor. 12-PUR is a semicrystalline polymer with an equilibrium melting temperature of 157 °C. It adopts a layered crystal structure similar to the α-form of nylons with chains in fully-extended conformation and arranged in hydrogen-bonded sheets in the antiparallel mode. This structure is thermally stable up to melting and is unable to undergo Brill transition. 12-PUR crystallized from dilute solution affording well-shaped lamellar crystals with a thickness of 8-9 nm and from the melt yielding either banded or fibrillar spherulitic textures displaying negative birefringence. Isothermal crystallization of 12-PUR from the melt took place with heterogeneous nucleation, while both crystallization rate and the finally attained crystallinity degree were highly depending on crystallization temperature.     

Synthesis of NiO Crystals Exposing Stable High-Index Facets

Metal oxides exposing high-index facets are potentially impactful in catalysis and adsorption processes owing to under-coordinated ions and polarities that alter their interfacial properties compared to low-index facets. Here, we report molten-salt syntheses of NiO particles exposing a variety of crystal facets. We show that for a given anion (nitrate or chloride), the alkali cation has a notable impact on the formation of crystals exposing {311}, {611}, {100}, and {111} faces. Based on a parametric analysis of synthesis conditions, we postulate that the crystallization mechanism is governed by the formation of growth units consisting of Ni^II complexes whose coordination numbers are determined by temperature and the selection of anion (associated to the coordination sphere) and alkali cation (associated with the outer coordination sphere). Notably, our findings reveal that high-index facets are particularly favored in chloride media and are stable under prolonged periods of catalysis and steaming.     

Simulations of calcite crystallization on self-assembled monolayers

This paper presents simulations of calcium carbonate ordering in contact with self-assembled monolayers. The calculations use potential-based molecular dynamics to model the crystallization of calcium carbonate to calcite expressing both the (00.1) and (01.2) surfaces. The effect of monolayer properties: ionization; epitaxial matching; charge density; and headgroup orientation on the crystallization process are examined in detail. The results demonstrate that highly charged surfaces are vital to stimulate ordering and crystallization. Template directed crystallization requires charge epitaxy between both the crystal surface and the monolayer. The orientation of the headgroup appears to make no contribution to the selection of the crystal surface.     

Mesocrystals: inorganic superstructures made by highly parallel crystallization and controlled alignment

Controlled self-organization of nanoparticles can lead to new materials. The colloidal crystallization of non-spherical nanocrystals is a reaction channel in many crystallization reactions. With additives, self-organization can be stopped at an intermediary step-a mesocrystal-in which the primary units can still be identified. Mesocrystals were observed for various systems as kinetically metastable species or as intermediates in a crystallization reaction leading to single crystals with typical defects and inclusions. The control forces and mechanism of mesocrystal formation are largely unknown, but several mesocrystal properties are known. Mesocrystals are exiting examples of nonclassical crystallization, which does not proceed through ion-by-ion attachment, but by a modular nanobuilding-block route. This path makes crystallization more independent of ion products or molecular solubility, it occurs without pH or osmotic pressure changes, and opens new strategies for crystal morphogenesis.     

Synthesis of NiO Crystals Exposing Stable High‐Index Facets

Metal oxides exposing high‐index facets are potentially impactful in catalysis and adsorption processes owing to under‐coordinated ions and polarities that alter their interfacial properties compared to low‐index facets. Here, we report molten‐salt syntheses of NiO particles exposing a variety of crystal facets. We show that for a given anion (nitrate or chloride), the alkali cation has a notable impact on the formation of crystals exposing {311}, {611}, {100}, and {111} faces. Based on a parametric analysis of synthesis conditions, we postulate that the crystallization mechanism is governed by the formation of growth units consisting of Ni^II complexes whose coordination numbers are determined by temperature and the selection of anion (associated to the coordination sphere) and alkali cation (associated with the outer coordination sphere). Notably, our findings reveal that high‐index facets are particularly favored in chloride media and are stable under prolonged periods of catalysis and steaming.     

Controllable Zeolite AST Crystallization: Between Classical and Reversed Crystal Growth

Crystal growth mechanisms govern a wide range of properties of crystalline materials. Reversed crystal growth is one of the nonclassical mechanisms observed in many materials. However, the reversed crystallization starting from amorphous aggregates and the key factors driving this growth remain elusive. Here, we describe a characteristic model of reversed crystal growth representing the inner structure and crystallinity development of aggregates studied by microscopy and nano X-ray computed tomography. By adjusting the synthesis conditions, the fundamental function of the structure-directing agent, which determines the crystallization pathway, was revealed. As a result, the crystal growth mode can be “switched” from the classical route at a low ratio of SDA/framework elements to reversed growth at a high ratio. Our findings provide further insights into crystal growth control, which is crucial for improving synthesis protocols and designing various forms of crystalline materials.     

μ-氧-双[meso-四(对烷氧基苯基)卟啉合铁(III)]的合成、表征和液晶性

设计合成了未见文献报道的μ-氧-双[meso-四(对烷氧基苯基)卟啉合铁(III)]配合物9个, 研究了其合成、分离、纯化方法, 用MS, ¹H NMR, IR, UV, 元素分析等方法剖析确证了目标化合物的结构, 其结构我们认为是μ-氧桥联的二聚体结构, 且存在两种典型空间构象结构(重叠式和交叉式), 表现为同一系列化合物存在四类¹H NMR谱. 用差示扫描量热仪和偏光显微镜研究了这9个化合物的液晶性, 发现9个化合物均具有液晶性, 多为升温降温互变液晶, 具有丝状光学织构. 有一至三个中介相, 相变起始温度最低为－6 ℃, 最高为210 ℃; 相变区间最宽为301 ℃, 最窄为50 ℃; 清亮点(T_c)最高315 ℃, 最低147 ℃. 考察了烷氧基链长、配位金属离子及配合物分子空间结构对液晶性能的影响. 我们认为这种μ-氧桥联的二聚体结构比单层平面卟啉及其金属配合物具有更好的液晶性.     

New 1:1 and 2:1 salts in the `dl‐norvaline–maleic acid' system as an example of assembling various crystal structures from similar supramolecular building blocks

Molecular salts and cocrystals of amino acids have potential applications as molecular materials with nonlinear optical, ferroelectric, piezoelectric, and other various target physical properties. The wide choice of amino acids and coformers makes it possible to design various crystal structures. The amino acid–maleic acid system provides a perfect example of a rich variety of crystal structures with different stoichiometries, symmetries and packing motifs built from the molecular building blocks, which are either exactly the same, or differ merely by protonation or as optical isomers. The present paper reports the crystal structures of two new salts of the dl ‐norvaline–maleic acid system with 1:1 and 2:1 stoichiometries, namely dl ‐norvalinium hydrogen maleate, C₅H₁₂NO₂⁺·C₄H₃O₄⁻, (I), and dl ‐norvalinium hydrogen maleate–dl ‐norvaline, C₅H₁₂NO₂⁺·C₄H₃O₄⁻·C₅H₁₁NO₂, (II). These are the first examples of molecular salts of dl ‐norvaline with an organic anion. The crystal structure of (I) has the same C ₂²(12) structure‐forming motif which is common for hydrogen maleates of amino acids. The structure of (II) has dimeric cations. Of special interest is that the single crystals of (I) which are originally formed on crystallization from aqueous solution transform into single crystals of (II) if stored in the mother liquor for several hours.     

含少量共聚组分聚乙烯熔体拉伸薄膜的形态结构

利用透射电子显微学(TEM)和示差扫描量热学(DSC)等方法研究了含少量丁烯-1组分(摩尔分数为0.64%)的聚乙烯共聚物(PE100)熔体拉伸高取向薄膜的形态结构. 结果表明, 在PE100熔体拉伸薄膜中, 除存在高取向片晶结构外, 还含有大量的纤维晶, 纤维晶平行于拉伸方向, 穿过几个片晶区, 平均直径约为12 nm. 模拟实验结果表明, 纤维晶的生成源于聚乙烯共聚物中的超高分子量组分, 但不同于传统意义上的伸直链纤维晶, 其形态特征应为晶桥结构. 由此提出了晶桥结构纤维晶模型, 该模型不但有助于深入理解和认识聚合物取向结晶机理, 同时也为该材料的高性能化提供了理论依据.     

Crystalline polymorphism and molecular structure of sodium pravastatin

In this work different crystallization processes of sodium pravastatin are explored and a new polymorph is obtained. The analytical results of powder X-ray diffraction (PXRD) and thermal analysis for this new polymorph indicate that it is different from the polymorphs previously reported. This new crystal form shows different physical-chemical properties than the previous forms, such as crystallographic structure, thermal behavior, and melting point, 181.5 degrees C. Besides, all crystallization processes previously reported use an aprotic solvent as antisolvent. However, we propose a new crystallization process for sodium pravastatin that uses only protic solvents, overcoming industrial scaling and environmental problems. Variable-temperature PXRD experiments show a transformation between different crystal forms in the range of 80-120 degrees C. Solid-state 13C NMR, reported in this work for the first time, and Fourier transform infrared (FT-IR) studies of some polymorphs show some differences in intermolecular interactions, especially with carboxylate and hydroxyl groups. Quantum mechanical calculations of the pravastatin molecule are also presented for the first time, obtaining a molecular structure similar to the experimental structure existing within the crystal lattice of the tert-octylamonium salt of pravastatin.     

Rationalization of the Color Properties of Fluorescein in the Solid State: A Combined Computational and Experimental Study

Fluorescein is known to exist in three tautomeric forms defined as quinoid, zwitterionic, and lactoid. In the solid state, the quinoid and zwitterionic forms give rise to red and yellow materials, respectively. The lactoid form has not been crystallized pure, although its cocrystal and solvate forms exhibit colors ranging from yellow to green. An explanation for the observed colors of the crystals is found using a combination of UV/Vis spectroscopy and plane‐wave DFT calculations. The role of cocrystal coformers in modifying crystal color is also established. Several new crystal structures are determined using a combination of X‐ray and electron diffraction, solid‐state NMR spectroscopy, and crystal structure prediction (CSP). The protocol presented herein may be used to predict color properties of materials prior to their synthesis.     

Modular Design of Domain Assembly in Porous Coordination Polymer Crystals via Reactivity-Directed Crystallization Process

The mesoscale design of domain assembly is crucial for controlling the bulk properties of solids. Herein, we propose a modular design of domain assembly in porous coordination polymer crystals via exquisite control of the kinetics of the crystal formation process. Employing precursors of comparable chemical reactivity affords the preparation of homogeneous solid-solution type crystals. Employing precursors of distinct chemical reactivity affords the preparation of heterogeneous phase separated crystals. We have utilized this reactivity-directed crystallization process for the facile synthesis of mesoscale architecture which are either solid-solution or phase-separated type crystals. This approach can be also adapted to ternary phase-separated type crystals from one-pot reaction. Phase-separated type frameworks possess unique gas adsorption properties that are not observed in single-phasic compounds. The results shed light on the importance of crystal formation kinetics for control of mesoscale domains in order to create porous solids with unique cooperative functionality.     

尿素晶体介电性能的量子化学计算

利用量子化学的第一性原理,在自洽场理论水平上对尿素晶体的线性和非线性光学介电性质进行了定量计算,获得了与实验值相符的理论计算结果.提供了一种解决分子晶体量子化学理论计算的新思路.     

Creation of Ternary Multicomponent Crystals by Exploitation of Charge‐Transfer Interactions

Four new ternary crystalline molecular complexes have been synthesised from a common 3,5‐dinitrobenzoic acid (3,5‐dnda) and 4,4′‐bipyridine (bipy) pairing with a series of amino‐substituted aromatic compounds (4‐aminobenzoic acid (4‐aba), 4‐(N,N‐dimethylamino)benzoic acid (4‐dmaba), 4‐aminosalicylic acid (4‐asa) and sulfanilamide (saa)). The ternary crystals were created through the application of complementary charge transfer and hydrogen‐bonding interactions. For these systems a dimer was created through a charge‐transfer interaction between two of the components, while hydrogen bonding between the third molecule and this dimer completed the construction of the ternary co‐crystal. All resulting structures display the same acid ??? pyridine interaction between 3,5‐dnba and bipy. However, changing the third component causes the proton of this bond to shift from neutral OH ??? N to a salt form, O^? ??? HN⁺, as the nature of the group hydrogen bonding to the carboxylic acid was changed. This highlights the role of the crystal environment on the level of proton transfer and the utility of ternary systems for the study of this process.     

Highly Luminescent Linear Complex Arrays of up to Eight Cuprous Centers

Linearly arranged metal atoms that are embedded in discrete molecules have fascinated scientists across various disciplines for decades; this is attributed to their potential use in microelectronic devices on a submicroscopic scale. Luminescent oligonuclear Group 11 metal complexes are of particular interest for applications in molecular light‐emitting devices. Herein, we describe the synthesis and characterization of a rare, homoleptic, and neutral linearly arranged tetranuclear Cu^I complex that is helically bent, thus representing a molecular coil in the solid state. This tetracuprous arrangement dimerizes into a unique octanuclear assembly bearing a linear array of six Cu^I centers with two additional bridging cuprous ions that constitute a central pseudo‐rhombic Cu^I₄ cluster. The crystal structure determinations of both complexes reveal close d¹⁰???d¹⁰ contacts between all cuprous ions that are adjacent to each other. The dynamic behavior in solution, DFT calculations, and the luminescence properties of these remarkable complexes are also discussed.