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Author(s):  
Georgia Zacharopoulou

The objective of the paper is the compilation, review and dissemination of updated scientific knowledge on lime theory and technology in the field of heritage conservation.The strong evidence of the last decade’s research on the positive effect of the-not demonstrable by a chemical equation-‘key’ missing link of the maturation process is highlighted. It is demonstrated that the exceptional performance characteristics of durable lime based mortars predominately rely on the capacity for rapid, efficient and extensive carbona-tion of the air-hardening phase of limes, in particular when matured (nanoparticle wet slaked) lime putties are used; and on the chemical and mechanical stability of the strength components (principally CSHs) of the hydraulic phase of limes, which is higher in their more crystalline forms of historical lime-pozzolan mixtures than in their amorphous forms of modern cements. Hence, physicochemical adhesion and cohesion bonds both at the lime matrix and at the binder/aggregate interfaces are ensured imparting minimization of cracks and durability to lime based mortars and historic masonries.The comprehensive documentation of the former leads to optimal materials and procedures to preserve our cultural heritage. Resumo O objectivo do presente artigo é a compilação, revisão e disseminação do actual conhecimento científico sobre teoria e tecnologia da cal no campo da conservação do património. Com base na investigação da última década, são destacados os fortes indícios do efeito positivo-não demonstrável por equação química-do elo perdido ‘chave’, o processo de maturação. É demonstrado que as excepcionais características de desempenho das argamassas à base de cal mais duráveis dependem predominantemente das suas capacidades para uma rápida, eficiente e extensa carbonatação da fase de presa aérea da cal, em particular quando é usada cal em pasta com maior tempo de maturação (extinção húmida ao nível das nanopartículas); e da estabilidade química e mecânica dos com-ponentes de resistência (principalmente silicatos de cálcio hidratados (CSHs)) da fase hidráulica da cal, que é mais elevada nas for-mas mais cristalinas das misturas históricas de cal e pozolana do que nas formas amorfas dos cimentos modernos. Deste modo são asseguradas as ligações fisico-químicas por adesão e por coesão, quer na matriz de cal, quer nas interfaces ligante/agregado, conferindo minimização de fissuras e durabilidade a argamassas à base de cal e alvenarias históricas. Uma abrangente documentação destes proces-sos permitirá a obtenção de materiais e procedimentos progressivamente mais adequados à preservação do nosso património cultural. Palavras-chave Maturação; Cal em pasta; Argamassa de cal; Componentes de resistência; Estabilidade estrutural.


Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1440
Author(s):  
Yanan Wang ◽  
Yong Wang ◽  
Jin Cheng ◽  
Haibiao Chen ◽  
Jia Xu ◽  
...  

The amorphous form of a drug usually exhibits higher solubility, faster dissolution rate, and improved oral bioavailability in comparison to its crystalline forms. However, the amorphous forms are thermodynamically unstable and tend to transform into a more stable crystalline form, thus losing their advantages. In order to investigate and suppress the crystallization, it is vital to closely monitor the drug solids during the preparation, storage, and application processes. A list of advanced techniques—including optical microscopy, surface grating decay, solid-state nuclear magnetic resonance, broadband dielectric spectroscopy—have been applied to characterize the physicochemical properties of amorphous pharmaceutical solids, to provide in-depth understanding on the crystallization mechanism. This review briefly summarizes these characterization techniques and highlights their recent advances, so as to provide an up-to-date reference to the available tools in the development of amorphous drugs.


Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3330
Author(s):  
Antonietta Cozzolino ◽  
Guglielmo Monaco ◽  
Christophe Daniel ◽  
Paola Rizzo ◽  
Gaetano Guerra

Delta (δ) and epsilon (ε) co-crystalline forms of syndiotactic polystyrene with a carboxylic acid guest were obtained by sorption of liquid hexanoic acid in syndiotactic polystyrene films exhibiting delta and epsilon nanoporous-crystalline forms. The characterization study is facilitated by axially stretched syndiotactic polystyrene films, used both for polarized FTIR spectra and for WAXD fiber patterns. Particularly informative are two carbonyl-stretching FTIR peaks, attributed to monomeric and dimeric hexanoic acid. The dichroism of these carbonyl peaks indicates that both delta and epsilon phases are able to include hexanoic acid as isolated guest molecules, while only the epsilon phase is also able to include dimeric hexanoic acid molecules in its crystalline channels. The inclusion of both isolated and dimeric hexanoic acid species in the epsilon form crystalline channels produces extremely fast hexanoic acid uptakes by syndiotactic polystyrene epsilon form films.


2021 ◽  
Author(s):  
Tomohiko Nishiuchi ◽  
Hikaru Sotome ◽  
Risa Fukuuchi ◽  
Kenji Kamada ◽  
Hiroshi Miyasaka ◽  
...  

Since the discovery of the triphenylmethyl (trityl) cation 120 years ago, a variety of aromatic cations having various colors and luminescence properties have been rigorously studied. Many, differently substituted trityl cations have been synthesized and their optical properties have been elucidated. However, the optical properties of the parent, non-substituted and highly reactive trityl cation, which was observed to be very weakly luminescent, have not been subjected to detailed investigation. In the effort described herein, we explored the optical nature of non-substituted trityl hexafluorophosphate (PF6) in the crystalline state. Trityl PF6 was found to exist as two crystal polymorphs including a yellow (Y) and an orange (O) form. Moreover, we observed that these crystalline forms display crystalline-state emission with different colors. The results of X-ray crystallographic analysis showed that the two polymorphs have totally different molecular packing arrangements. Furthermore, an investigation of their optical properties revealed that the O-crystal undergoes a distinct color change to yellow upon cooling as a consequence of a change in the nature of the charge transfer interaction between the cation and PF6 anion, and that both the Y and O crystal exhibit phosphorescence.


2021 ◽  
Vol 77 (10) ◽  
pp. 615-620
Author(s):  
Duyen N. K. Pham ◽  
Zachary S. Belanger ◽  
Andrew R. Chadeayne ◽  
James A. Golen ◽  
David R. Manke

The crystal structures of the hydrochloride salts of nine substituted tryptamines, namely, 1-methyltryptammonium chloride, C11H15N2 +·Cl−, (1), 2-methyl-1-phenyltryptammonium chloride, C17H19N2 +·Cl−, (2), 5-methoxytryptammonium chloride, C11H15N2O+·Cl−, (3), 5-bromotryptammonium chloride, C10H12BrN2 +·Cl−, (4), 5-chlorotryptammonium chloride, C10H12ClN2 +·Cl−, (5), 5-fluorotryptammonium chloride, C10H12FN2 +·Cl−, (6), 5-methyltryptammonium chloride, C11H15N2 +·Cl−, (7), 6-fluorotryptammonium chloride, C10H12FN2 +·Cl−, (8), and 7-methyltryptammonium chloride, C11H15N2 +·Cl−, (9), are reported. The seven tryptamines with N—H indoles, (3)–(9), show very similar structures, with N—H...Cl hydrogen-bonding networks forming two-dimensional sheets in the crystals. These sheets are combinations of R 4 2(8) and R 4 2(18) rings, and C 2 1(4) and C 2 1(9) chains. Substitution at the indole N atom reduces the dimensionality of the hydrogen-bonding network, with compounds (1) and (2) demonstrating one-dimensional chains that are a combination of different rings and parallel chains.


Molecules ◽  
2021 ◽  
Vol 26 (17) ◽  
pp. 5361
Author(s):  
M. John Plater ◽  
William T. A. Harrison

In this study, treatment of anhydrous trazodone powder with ammonium carbamate in warm water crystallised two new polymorphs or dihydrates of trazodone after 5 h, whose structures were determined by X-ray single crystal diffraction. Each dihydrate contains infinite zigzag hydrogen-bonded chains of water molecules, which are stabilised by the N4 acceptor atom of the piperazine ring and the pendant carbonyl O1 atom of the triazole ring, as well as other water molecules. The strong dipole moment expected for the O1 atom makes it a good hydrogen bond acceptor for stabilising the chains of water molecules. Each molecule of trazodone has a similar conformation in both hydrates, except for the propyl chains, which adopt different conformations: anti-gauche in the β hydrate (triazole N-C-C-C and C-C-C-piperazine N) and anti-anti in the γ hydrate. Both piperazine rings adopt chair conformations, and the exocyclic N-C bonds are in equatorial orientations. The Hirshfeld surfaces and two-dimensional fingerprint plots for the polymorphs were calculated using CrystalExplorer17, which indicated contacts significantly shorter than the sum of the van der Waals radii in the vicinity of the piperazine N4 and triazole O1 atoms corresponding to the strong hydrogen bonds accepted by these atoms.


Molecules ◽  
2021 ◽  
Vol 26 (17) ◽  
pp. 5318
Author(s):  
Szymon Sip ◽  
Natalia Rosiak ◽  
Andrzej Miklaszewski ◽  
Patrycja Talarska ◽  
Ewa Dudziec ◽  
...  

The amorphous form of carvedilol phosphate (CVD) was obtained as a result of grinding. The identity of the obtained amorphous form was confirmed by powder X-ray diffraction (PXRD), different scanning calorimetry (DSC), and FT-IR spectroscopy. The process was optimized in order to obtain the appropriate efficiency and time. The crystalline form of CVD was used as the reference standard. Solid dispersions of crystalline and amorphous CVD forms with hydrophilic polymers (hydroxypropyl-β-cyclodextrin, Pluronic® F-127, and Soluplus®) were obtained. Their solubility at pH 1.2 and 6.8 was carried out, as well as their permeation through a model system of biological membranes suitable for the gastrointestinal tract (PAMPA-GIT) was established. The influence of selected polymers on CVD properties was defined for the amorphous form regarding the crystalline form of CVD. As a result of grinding (four milling cycles lasting 15 min with 5 min breaks), amorphous CVD was obtained. Its presence was confirmed by the “halo effect” on the diffraction patterns, the disappearance of the peak at 160.5 °C in the thermograms, and the changes in position/disappearance of many characteristic bands on the FT-IR spectra. As a result of changes in the CVD structure, its lower solubility at pH 1.2 and pH 6.8 was noted. While the amorphous dispersions of CVD, especially with Pluronic® F-127, achieved better solubility than combinations of crystalline forms with excipients. Using the PAMPA-GIT model, amorphous CVD was assessed as high permeable (Papp > 1 × 10−6 cm/s), similarly with its amorphous dispersions with excipients (hydroxypropyl-β-cyclodextrin, Pluronic® F-127, and Soluplus®), although in their cases, the values of apparent constants permeability were decreased.


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