A critique of using epitaxial criterion to discriminate between protogenetic and syngenetic mineral inclusions in diamond.

Distinguishing syngenetic from protogenetic inclusions in natural diamonds is one of the most debated issues in diamond research. Were the minerals that now reside in inclusions in diamonds born before the diamond that hosts them (protogenesis)? Or did they grow simultaneously and by the same reaction (syngenesis)? Once previously published data on periclase [(Mg,Fe)O] and magnesiochromite (MgCr2O4) inclusions in diamond have been re-analysed, we show that the main arguments reported so far to support syngenesis between diamond and its mineral inclusions, definitely failed. Hence: (a) the epitaxial relationships between diamond and its mineral inclusion should no longer be used to support syngenesis, because only detecting an epitaxy does not tell us which was the nucleation substrate (there are evidences that in case of epitaxy, the inclusion acts as a nucleation substrate); (b) the morphology of the inclusion should no longer be used as well, as inclusions could be protogenetic regardless their shapes. Finally, we advance the hypothesis that the majority of inclusions in diamonds are protogenetic, e.g., they are constituent of rocks in which diamonds were formed and not products of reactions during diamond growth.

101 contact twins in gypsum experimentally obtained from calcium carbonate enriched solutions: mineralogical implications for natural gypsum deposits.

Gypsum twins are frequently observed in nature, triggered by a wide array of impurities that are present in their depositional environments and that may exert a critical role in the selection of different twin laws. Identifying the impurities able to promote the selection of specific twin laws has relevance for geological studies aimed at interpreting the gypsum depositional environments in ancient and modern deposits. Here, the effect of calcium carbonate (CaCO3) on gypsum (CaSO4·2H2O) growth morphology has been investigated by performing temperature-controlled laboratory experiments with and without the addition of carbonate ions. The precipitation of twinned gypsum crystals has been achieved experimentally (101 contact twin law) by adding carbonate to the solution, and the involvement of rapidcreekite (Ca2SO4CO3·4H2O) in selecting the 101 gypsum contact twin law was supported, suggesting an epitaxial mechanism. Moreover, the occurrence of 101 gypsum contact twins in nature has been suggested by comparing the natural gypsum twin morphologies observed in evaporitic environments with those obtained in experiments. Finally, both orientations of the primary fluid inclusions (of the negative crystal shape) with respect to the twin plane and the main elongation of sub-crystals that form the twin are proposed as a fast and useful method (especially in geological samples) to distinguish between the 100 and 101 twin laws. The results of this study provide new insights into the mineralogical implications of twinned gypsum crystals and their potential as a tool to better understand natural gypsum deposits.

Epitaxies of Ca sulfates on calcite. II. The main {010}, {001} and {100} forms of bassanite epi-deposited on the {10.4} substrate form of calcite.

2D and 3D epitaxies of the main {010}, {001} and {100} forms of deposited bassanite (CaSO4·0.5H2O) on {10.4} calcite (CaCO3) as a substrate are described to provide a theoretical crystallographic background for the replacement of calcite by bassanite both in nature and in the laboratory and by weathering linked to cultural heritage. First, epitaxy in the third dimension, perpendicular to the investigated interfaces, has been verified in order to establish whether adsorption/absorption can occur (as anomalous mixed crystals) at the bassanite/calcite epi-contacts. Secondly, and by applying the Hartman-Perdok method, 2D lattice coincidences have been obtained from the physical-geometric matches of bonds running in the common directions within the elementary slices facing the substrate/deposit interfaces. This research represents the second and more detailed part of a wider program extended to the epi-interactions between the following pairs: (i) {010}-gypsum/{10.4}-calcite (just published); (ii) bassanite/{10.4}-calcite (the present work); and (iii) anhydrite (CaSO4)/{10.4}-calcite (coming soon).

Encapsulation of Acyclovir in new carboxylated cyclodextrin-based nanosponges improves the agent's antiviral efficacy.

Cyclodextrin-based nanosponges (NS) are solid nanoparticles, obtained from the cross-linking of cyclodextrins that have been proposed as delivery systems for many types of drugs. Various NS derivatives are currently under investigation in order that their properties might be tuned for different applications. In this work, new carboxylated cyclodextrin-based nanosponges (Carb-NS) carrying carboxylic groups within their structure were purposely designed as novel Acyclovir carriers. TEM measurements revealed their spherical shape and size of about 400 nm. The behaviour of Carb-NS, with respect to the incorporation and delivery of Acyclovir, was compared to that of NS, previously investigated as a drug carrier. DSC, XRPD and FTIR analyses were used to investigate the two NS formulations. The results confirm the incorporation of the drug into the NS structure and NS-Acyclovir interactions. The Acyclovir loading into Carb-NS was higher than that obtained using NS, reaching about 70% (w/w). In vitro release studies showed the release kinetics of Acyclovir from Carb-NS to be prolonged in comparison with those observed with NS, with no initial burst effect. The NS uptake into cells was evaluated using fluorescent Carb-NS and revealed the nanoparticle internalisation. Enhanced antiviral activity against a clinical isolate of HSV-1 was obtained using Acyclovir loaded in Carb-NS.

Cyclodextrin-based nanosponges encapsulating camptothecin: physicochemical characterization, stability and cytotoxicity.

Camptothecin (CAM), a plant alkaloid and a potent antitumor agent, has a limited therapeutic utility because of its poor aqueous solubility, lactone ring instability and serious side effects. Cyclodextrin-based nanosponges (NS) are a novel class of cross-linked derivatives of cyclodextrins. They have been used to increase the solubility of poorly soluble actives, to protect the labile groups and control the release. This study aimed at formulating complexes of CAM with three types of beta-cyclodextrin NS obtained with different cross-linking ratio (viz. 1:2, 1:4 and 1:8 on molar basis with the cross-linker) to protect the lactone ring from hydrolysis and to prolong the release kinetics of CAM. Crystalline (F(1:2), F(1:4) and F(1:8)) and paracrystalline NS formulations were prepared. XRPD, DSC and FTIR studies confirmed the interactions of CAM with NS. XRPD showed that the crystallinity of CAM decreased after loading. CAM was loaded as much as 21%, 37% and 13% w/w in F(1:2), F(1:4) and F(1:8), respectively while the paracrystalline NS formulations gave a loading of about 10% w/w or lower. The particle sizes of the loaded NS formulations were between 450 and 600nm with low polydispersity indices. The zeta potentials were sufficiently high (-20 to -25mV) to obtain a stable colloidal nanosuspension. The in vitro studies indicated a slow and prolonged CAM release over a period of 24h. The NS formulations protected the lactone ring of CAM after their incubation in physiological conditions at 37 degrees C for 24h with a 80% w/w of intact lactone ring when compared to only around 20% w/w of plain CAM. The cytotoxicity studies on HT-29 cells showed that the CAM formulations were more cytotoxic than plain CAM after 24h of incubation.

Effect of alkylcarbonates of gamma-cyclodextrins with different chain lengths on drug complexation and release characteristics.

Alkylcarbonates of gamma-cyclodextrins were produced and their inclusion complexes with four poorly water-soluble drugs of different structures and solubilities were prepared. The alkylcarbonates and the alkylcarbonate drug complexes were characterized by DSC and XRPD; the physical mixtures were used as control. Solubility capacities were evaluated by phase solubility studies. The effect of alkyl chain length on the complexation and release behaviour was investigated as well. The XRPD patterns of alkylcarbonates showed that the derivatives lose the original crystallinity of gamma-cyclodextrins. The series of alkylcarbonates formed inclusion complexes with the drugs considered. Both XRPD and DSC analyses did not show neither the reflections of the crystalline structures nor the melting peaks of the drugs, respectively. These gamma-cyclodextrin derivatives can improve drug solubility and influence the drug release rates while the alkyl chain length may affect these properties.