Teaching a large-scale crystallography school with Zoom Webinar.

In order to address the loss of crystallographic training opportunities resulting from the cancelation of conventional schools around the world due to the COVID-19 pandemic, we have started an online crystallography school with live lectures and live Q&A using Zoom Webinar. Since we were trying to reach a large audience in a relatively short period, we have limited the school to ten 1 h lectures covering practical aspects of small molecule crystallography including data collection, data processing, and structure solution. In the school, we also covered some advanced topics that students commonly see in their work: absolute structure determination, twinning, and disorder. To round out the education, we provided lectures on macromolecular crystallography and powder diffraction. For students to practice on their own, we used freely available data reduction and structure solution software, as well as datasets with which to practice. To give students credit for course completion, we provided an online exam and an electronic certificate of completion. In this editorial, we will provide some insight into the issues of holding lectures with up to 750 students of very diverse backgrounds and review the efficacy of the school in teaching crystallography for the two cohorts of students.

Pharmacognostical standardization and antidiabetic activity of Syzygium cumini (Linn.) barks (Myrtaceae) on streptozotocin-induced diabetic rats.

BACKGROUND: The objectives of the present study were phytochemical and pharmacological screening of bark of Syzygium cumini on streptozotocin (STZ)-induced diabetic Wistar albino rats. METHODS: Dose selection was made on the basis of acute oral toxicity study (300-5,000 mg/kg b.w.) as per OECD guidelines. Rats were made diabetic by a single dose of STZ at 50 mg/kg b.w. intraperitoneally. The effect of Syzygium cumini extracts (500 mg/kg) on postprandial blood glucose level was determined in fasted diabetic and normal rats. Blood glucose levels were measured at 0, 30, and 90 min after the glucose administration in the OGTT study. The bark extracts were administered orally at the dose of 500 mg/kg for 21 days in the chronic study. Glibenclamide (2.5 mg/kg) was used as a standard drug for activity comparison. Statistical analyses were performed using one-way ANOVA followed by Bonferroni's multiple comparison tests. RESULTS: The phytochemical screening showed positive results for triterpenes/steroids, glycosides, carbohydrates, alkaloids, flavonoids, saponins, tannins and amino acids. Administration of Syzygium cumini extracts 30 min before oral glucose loading significantly suppressed (p<0.001) the rise in postprandial blood glucose levels in treated rats compared to control rats but less significant than glibenclamide. Daily, continuous oral treatment of STZ-induced diabetic with various extract of Syzygium cumini for 3 weeks resulted in significant reductions in fasting blood glucose levels compared with diabetic controls. The ethanol and aqueous extracts were most active. CONCLUSIONS: This study brings out the evidence regarding phytochemistry and pharmacological activities of Syzygium cumini.

The first framework solid composed of vanadosilicate clusters.

In this Communication, we report the first example of a network structure composed of vanadosilicate clusters. We utilized hydrothermal conditions to synthesize a polyoxovanadogermanate (POVG): (C4H14N2)4[V14O44(GeOH)8].6H2O. By substituting SiO2 for GeO2 in the synthesis, a framework solid, H4V18O46(SiO)8C4H12N2)4.(H2O)] .4H2O, is formed in which isostructural vanadosilicate clusters are linked by five-coordinate vanadium with a (VO)O2N2 environment. The charge-compensating organic amine, 1,4-diaminobutane, in the POVG is covalently bonded to the linking vanadium polyhedra in the framework solid.

(K4Li4)Al8Ge8O32.8H2O: an Li+-exchanged potassium aluminogermanate with the zeolite gismondine (GIS) topology.

The title compound, lithium potassium dialuminium digermanium octaoxide dihydrate, (K,Li)-(Al,Ge)-GIS (GIS is gismondine), is the result of a 50% Li(+) exchange into the K-(Al,Ge)-GIS structure. The (K,Li)-(Al,Ge)-GIS structure was determined from a 4 x 4 x 2 micro m octahedral single crystal at the ESRF synchrotron X-ray source. The ion exchange results in a symmetry transformation from I2/a for K-(Al,Ge)-GIS to C2/c for (K,Li)-(Al,Ge)-GIS. The structural change is due to disordering of K(+) ions with Li(+) ions along the [001] channel and ordering of water molecules in the [101] channels. The distance between sites partially occupied by K(+) ions increases from 2.19 (3) A in K-(Al,Ge)-GIS to 2.94 (3) A in (K,Li)-(Al,Ge)-GIS. The Li(+) ions occupy positions along the twofold axis at the intersection of the eight-membered-ring channels in a twofold coordination with water molecules. For the four closest framework O(2-) anions, the Li.O distances are 3.87 (4) A.

Sandia octahedral molecular sieves (SOMS): structural and property effects of charge-balancing the M(IV)-substituted (M = Ti, Zr) Niobate framework.

Sandia octahedral molecular sieves (SOMS) is an isostructural, variable composition class of ion exchangers with the general formula Na(2)Nb(2-x)M(IV)(x)O (6-x)(OH)(x).H(2)O (M(IV) = Ti, Zr; x = 0.04-0.40) where up to 20% of the framework Nb(V) can be substituted with Ti(IV) or Zr(IV). This class of molecular sieves is easily converted to perovskite through low-temperature heat treatment (500-600 degrees C). This report provides a detailed account of how the charge imbalance of this Nb(V)-M(IV) substitution is compensated. X-ray powder diffraction with Rietveld refinement, infrared spectroscopy, thermogravimetric analysis, (23)Na MAS NMR, and (1)H MAS NMR were used to determine how the framework anionic charge is cation-balanced over a range of framework compositions. All spectroscopic evidence indicated a proton addition for each M(IV) substitution. Evidences for variable proton content included (1) increasing OH observed by (1)H MAS NMR with increasing M(IV) substitution, (2) increased infrared band broadening indicating increased H-bonding with increasing M(IV) substitution, (3) increased TGA weight loss (due to increased OH content) with increasing M(IV) substitution, (4) no variance in population on the sodium sites (indicated by Rietveld refinement) with variable composition, and (5) no change in the (23)Na MAS NMR spectra with variable composition. Also observed by infrared spectroscopy and (23)Na MAS NMR was increased disorder on the Nb(V)/M(IV) framework sites with increasing M(IV) substitution, evidenced by broadening of these spectral features. These spectroscopic studies, along with ion exchange experiments, also revealed the effect of the Nb(V)/M(IV) framework substitution on materials properties. Namely, the temperature of conversion to NaNb(1-x)M(IV)(x)O(3) (M = Ti, Zr) perovskite increased with increasing Ti in the framework and decreased with increasing Zr in the framework. This suggested that Ti stabilizes the SOMS framework and Zr destabilizes the SOMS framework. Finally, comparing ion exchange properties of a SOMS material with minimal (2%) Ti to a SOMS material with maximum (20%) Ti revealed the divalent cation selectivity of these materials which was reported previously is a function of the M(IV) substitution in the framework. A thorough investigation of this class of SOMS materials has revealed the importance of understanding the influence of heterovalent substitutions in microporous frameworks on material properties.