X-ray structures of fifty year old crystals of cholesterol iodide forms I and II

  The molecular framework of steroids was firmly established from the successful X-ray analysis of cholesteryl iodide crystals over fifty years ago. At the time, this was a triumph for the rapidly developing technique of X-ray crystallography. We describe here new analyses of cholesteryl iodide using crystals of forms I and II^(A) which are at least 50 years old. Comparison of these two structures reveals subtle differences in the geometry of the steroid skeleton, the attached side chain and the covalently bound iodine. The crystals of both forms occur in the same monoclinic space group, P2₁, with similar but nevertheless different unit cells, particularly in the b-axis length. As a consequence, there are subtle differences in the packing mechanisms of the two polymorphs. The two forms were originally classified by Bernal and Crowfoot, on the basis of their studies of more than 60 crystals of sterols and sterol derivatives, as “normal, type A - the common form” (corresponding to form II) and “reverse or type B” (corresponding to form I), respectively. Those crystals of form I which have survived for almost 55 years are poor X-ray diffractors at room temperature and have been analysed at liquid N temperature, diffracting well under these conditions. Form II crystals diffract well at room temperature and for this reason the crystals were not cooled. The main differences in geometry occur in the side-chain which is disordered in the room temperature form II crystals, whilst the individual ring conformations in the steroid skeleton are similar, ring A being a strained chair, ring B a 7α/8β half-chair, ring C a symmetrical chair and D a 13β/14α half-chair. (A) Originally denoted Forms B and A respectively. See Additional Note (A) for explanation.

Effect of Soil Type: Qualitative and Quantitative Analysis of Phytochemicals in Some Browse Species Leaves Found in Savannah Biome of South Africa

In semi-arid regions, browse plant species are used as feed and for medicinal purposes for both animals and humans. The limitation of the utilization of these species to medicinal purposes or as feed for livestock is a lack of knowledge on the concentration level of phytochemicals and other bioactive compounds found in these plants. The study sought to assay the qualitative and quantitative bioactive constituents of some browse species found in the savannah biome of South Africa, viz. Adansonia digitate, Androstachys johnsonii, Balanites maughamii, Berchemia discolor, Berchemia zeyheri, Bridelia mollis hutch, Carissa edulis, Catha edulis, Colophospermum mopane, Combretum Imberbe, Combretum molle, Combretum collinum, Dalbergia melanoxylon, Dichrostachys cinerea, Diospros lycioides, Diospyros mespiliformis, Euclea divinorum, Flueggea virosa, Grewia flava, Grewia flavescens, Grewia monticola, Grewia occidentalis, Melia azedarach, Peltophorum africanum, Prosopis velutina, Pseudolachnostylis maprouneifolia, Pterocarpus rotundifolius, Schinus molle, Schotia brachypetala, Sclerocarya birrea, Searsia lancea, Searsia leptodictya, Searsia pyroides, Senegalia caffra, Senegalia galpinii, Senegalia mellifera, Senegalia nigrescens, Senegalia polyacantha, Strychnos madagascariensis, Terminalia sericea, Trichilia emetic, Vachellia erioloba, Vachellia hebeclada, Vachellia karroo, Vachellia nilotica, Vachellia nilotica subsp. Kraussiana, Vachellia rechmanniana, Vachellia robusta, Vachellia tortilis, Vachellia tortilis subsp. raddiana, Vangueria infausta, and Ziziphus mucronata. These browse species’ leaf samples were harvested from two provinces (Limpopo and North-West) of South Africa. The Limpopo province soil type was Glenrosa, Mispah, and Lithosols (GM-L), and the soil types in the North-West Province were Aeolian Kalahari Sand, Clovelly, and Hutton (AKS-CH). The harvested browse samples were air dried at room temperature for about seven days and ground for analysis. The methanol and distilled water extracts of the browse species leaves showed the presence of common phytoconstituents, including saponins, flavonoids, tannins, phenols, cardio glycosides, terpenoids, and phlobatannins, as major active compounds in browse species leaves. In the quantitative analysis, phytochemical compounds, such as soluble phenols, insoluble tannins, and condensed tannins, were quantified for common species found in both sites. Two-way ANOVA and multivariate analysis were used to test soil type and species effect on soluble phenols, insoluble tannins, and condensed tannins of woody species. Dichrostachys cinerea (0.1011% DM) in GM-L soil type and Z. mucronata (0.1009% DM) in AKS-CH soil type showed the highest (p < 0.05) concentration of soluble phenols. In AKS-CH soil type, D. cinerea (0.0453% DM) had the highest insoluble tannins concentration, while V. hebeclada had the lowest (0.0064% DM) insoluble tannins content. Vacchelia hebeclada had lower (p < 0.05) condensed tannins concentration levels than all other browse plants in both soil types. Under multivariate analysis tests, there was a significant effect (p < 0.001) of soil type, species, and soil type x species interaction on soluble phenols, insoluble tannins, and condensed tannins of woody species. In this study, most of the woody species found in GM-L soil type showed a lower amount of tannins than those harvested in AKS-CH soil type. There is a need to identify the amount of unquantified phytochemicals contained in these browse species and valorize the high-bioactive-compound browse species to enhance and maximize browsing of these browse species for animal production.     

In‐line Particle Size Measurement for Control of Jet Milling

Jet milling is suitable for the production of very fine powders with a well‐defined particle size distribution (PSD). The major disadvantage of the process is the poor energy efficiency. In practice jet mills have to be operated below their maximum capacity in order to avoid the production of off‐specification material, due to operation disturbances. Therefore, it is important to automate operation with a real‐time PSD instrument for quality control. In this paper, a study for in‐line particle size measurement using laser diffraction is presented to improve operation control. This measurement system uses a novel CMOS pixel array, which has a robust and flexible feature for the application. It also includes an in‐line cell system, where direct measurement is implemented in the product particle stream coming from the mill and an air purge for the cell window allows continued operation. Experiments were conducted on a 10‐inch spiral jet mill pilot plant with alpha‐Al₂O₃ as test material. The milling process is investigated by varying the operational conditions. The measurement results are useful to build a grinding model for control purpose.     

Lyophilized Drug-Loaded Solid Lipid Nanoparticles Formulated with Beeswax and Theobroma Oil

Solid lipid nanoparticles (SLNs) have the potential to enhance the systemic availability of an active pharmaceutical ingredient (API) or reduce its toxicity through uptake of the SLNs from the gastrointestinal tract or controlled release of the API, respectively. In both aspects, the responses of the lipid matrix to external challenges is crucial. Here, we evaluate the effects of lyophilization on key responses of 1:1 beeswax–theobroma oil matrix SLNs using three model drugs: amphotericin B (AMB), paracetamol (PAR), and sulfasalazine (SSZ). Fresh SLNs were stable with sizes ranging between 206.5–236.9 nm. Lyophilization and storage for 24 months (4–8 °C) caused a 1.6- and 1.5-fold increase in size, respectively, in all three SLNs. Zeta potential was >60 mV in fresh, stored, and lyophilized SLNs, indicating good colloidal stability. Drug release was not significantly affected by lyophilization up to 8 h. Drug release percentages at end time were 11.8 ± 0.4, 65.9 ± 0.04, and 31.4 ± 1.95% from fresh AMB-SLNs, PAR-SLNs, and SSZ-SLNs, respectively, and 11.4 ± 0.4, 76.04 ± 0.21, and 31.6 ± 0.33% from lyophilized SLNs, respectively. Thus, rate of release is dependent on API solubility (AMB < SSZ < PAR). Drug release from each matrix followed the Higuchi model and was not affected by lyophilization. The above SLNs show potential for use in delivering hydrophilic and lipophilic drugs.     

An unusual conformational similarity of two peptide folds featuring sulfonamide and carboxamide on the backbone

Two folded peptides featuring carboxamide and sulfonamide at the core of the peptide fold have been shown to possess almost similar conformational features, despite the well-known fact that carboxamides and sulfonamides have strikingly different hydrogen-bonding and geometrical preferences.     

Localization: The effect of a weak magnetic field

The effect of a weak magnetic field on the diffusion of noninteracting electrons in a disordered system is studied in a nonlinear-model context. The effective Lagrangian describing the soft modes of the system in the weak field limit is derived. The result does not have the simple form that has been suggested by several authors. Therefore the crossover of the system under a weak perturbing magnetic field is not analogous to that found in spin systems.     

A comparison of the AMBER*, OPLSAA and HF potential energy surfaces for a series of diastereomeric cyclic urea HIV-1 inhibitors

The LM:MC conformational search method was used to identify the low energy structures on the OPLS-AA/GBSA(water) and AMBER*/GBSA(water) surfaces for a diastereomeric series of cyclic urea molecules that have been shown to be potent inhibitors of the HIV-1 protease enzyme. The lowest energy structures from each search were then subjected to geometry optimization and frequency analysis using the HF/6-311G** method in conjunction with the self-consistent reaction field (SCRF) treatment for water. A comparison of the diastereomeric energies and structures indicates that the OPLSAA/GBSA(water) surface is in good agreement with the HF/6-311G**/SCRF(water) surface.     

The determination of molybdenum in water and biological samples by graphite furnace atomic spectrometry after polyurethane foam column separation and preconcentration

A system for molybdenum separation and enrichment aiming its determination in water and biological samples by graphite furnace atomic absorption spectrometry (GFAAS) is proposed. The procedure is based on the sorption of the molybdenum (VI) thiocyanate complex onto a mini-column packed with polyurethane foam (PUF). The elution is accomplished by a 3.0 mol l⁻¹ nitric acid solution. Flow variables were optimized and an enrichment factor of 10 as well as a limit of detection (LOD) (3 s) of 0.08 μg l⁻¹ in the sample solution were achieved. The coefficient of variation showed values of 3 and 2% for molybdenum solutions of 2.0 and 10.0 μg l⁻¹, respectively. The accuracy of the method was confirmed by the good concordance between found and certified values in the analysis of certified reference materials (CRMs) (CASS-3 Nearshore Seawater, NIST 1547 Peach Leaves, NIST 1515 Apple Leaves and NIST 1572 Citrus Leaves). The procedure was also applied for the molybdenum determination in mineral waters as well as in produced water samples. The results obtained for the mineral water samples compared well with those obtained by ICP-MS. Concerning the produced water samples, in spite of their large salinity, recoveries of 90 to 120% at the 1 μg l⁻¹ were observed.