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INTRODUCTION: Despite viral suppression due to combination antiretroviral therapy (cART), HIV-associated neurocognitive disorders (HAND) continue to affect half of people with HIV, suggesting that certain antiretrovirals (ARVs) may contribute to HAND. METHODS: We examined the effects of nucleoside/nucleotide reverse transcriptase inhibitors tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) and the integrase inhibitors dolutegravir (DTG) and elvitegravir (EVG) on viability, structure, and function of glutamatergic neurons (a subtype of CNS neuron involved in cognition) derived from human induced pluripotent stem cells (hiPSC-neurons), and primary human neural precursor cells (hNPCs), which are responsible for neurogenesis. RESULTS: Using automated digital microscopy and image analysis (high content analysis, HCA), we found that DTG, EVG, and TDF decreased hiPSC-neuron viability, neurites, and synapses after seven days of treatment. Analysis of hiPSC-neuron calcium activity using Kinetic Image Cytometry (KIC) demonstrated that DTG and EVG also decreased the frequency and magnitude of intracellular calcium transients. Longer ARV exposures and simultaneous exposure to multiple ARVs increased the magnitude of these neurotoxic effects. Using the Microscopic Imaging of Epigenetic Landscapes (MIEL) assay, we found that TDF decreased hNPC viability and changed the distribution of histone modifications that regulate chromatin packing, suggesting that TDF may reduce neuroprogenitor pools important for CNS development and maintenance of cognition in adults. CONCLUSION: This study establishes human preclinical assays that can screen potential ARVs for CNS toxicity to develop safer cART regimens and HAND therapeutics.

Ga-MIL-53 is a metal-organic framework (MOF) that exhibits a “breathing effect,” in which the pore size and overall MOF topology can be influenced by temperature, pressure, and host-guest interactions. The phase control afforded by this flexible framework renders Ga-MIL-53 a promising material for guest storage and sensing applications. In this work, the structure and behavior of four Ga-MIL-53 phases ( as , ht , enp and lt ), along with CO 2 adsorbed within Ga-MIL-53 at various loading levels, has been investigated using 69/71 Ga solid-state NMR (SSNMR) experiments at 21.1 T and 9.4 T. 69/71 Ga SSNMR spectra are observed to be very sensitive to distortions in the octahedral GaO 6 secondary building units within Ga-MIL-53; by extension, Ga NMR parameters are indicative of the particular crystallographic phase of Ga-MIL-53. The evolution of Ga NMR parameters with CO 2 loading levels in Ga-MIL-53 reveals that the specific CO 2 loading level offers a profound degree of control over the MOF phase, and the data also suggests that a re-entrant phase transition is present. Adsorption of various organic compounds within Ga-MIL-53 has been investigated using a combination of thermal gravimetric analysis (TGA), powder X-ray diffraction (pXRD) and 69/71 Ga SSNMR experiments. Notably, pXRD experiments reveal that guest adsorption and host-guest interactions trigger unambiguous changes in the long-range structure of Ga-MIL-53, while 69/71 Ga SSNMR parameters yield valuable information regarding the effect of the organic adsorbates on the local GaO 6 environments. This approach shows promise for the ultra-wideline investigation of other quadrupolar metal nuclei in MIL-53 ( e.g. , In-MIL-53) and MOFs in general, particularly in regards to adsorption-related applications.

In this work, we report the results of a detailed structural study of a promising bioceramic material silicocarnotite Ca 5 (PO 4 ) 2 SiO 4 (SC) synthesized from mechanochemically treated nanosized silicon-substituted hydroxyapatite by annealing at 1000 °C. This novel synthetic approach represents an attractive and efficient route towards large-scale manufacturing of the silicocarnotite-based bioceramics. A combination of solid-state nuclear magnetic resonance (NMR), powder X-ray crystallography and density function theory (DFT) calculations has been implemented to characterize the phase composition of the prepared composite materials and to gain insight into the crystal structure of silicocarnotite. The phase composition analysis based on the multinuclear solid-state NMR has been found in agreement with X-ray powder diffraction indicating the minority phases of CaO (5–6 wt%) and residual silicon-apatite (7–8 wt%), while the rest of the material being a fairly crystalline silicocarnotite phase (86–88 wt%). A combination of computational (CASTEP) and experimental methods was used to address the anionic site disorder in the silicocarnotite crystal structure. Distorted [OPO 3 ] pyramids have appeared as an important structural motif in the SC crystal structure. The ratio between regular [PO 4 ] and distorted [OPO 3 ] tetrahedra is found between 2:1 and 3:1 based on XRD experiments and CASTEP calculations. The natural abundance 43 Ca magic angle spinning NMR spectra of silicocarnotite are reported for the first time.

The recent re-emergence of Zika virus (ZIKV)1, a member of the Flaviviridae family, has become a global emergency. Currently, there are no effective methods of preventing or treating ZIKV infection, which causes severe neuroimmunopathology and is particularly harmful to the developing fetuses of infected pregnant women. However, the pathology induced by ZIKV is unique among flaviviruses, and knowledge of the biology of other family members cannot easily be extrapolated to ZIKV. Thus, structure-function studies of ZIKV proteins are urgently needed to facilitate the development of effective preventative and therapeutic agents. Like other flaviviruses, ZIKV expresses an NS2B-NS3 protease, which consists of the NS2B cofactor and the NS3 protease domain and is essential for cleavage of the ZIKV polyprotein precursor and generation of fully functional viral proteins. Here, we report the enzymatic characterization of ZIKV protease, and we identify structural scaffolds for allosteric small-molecule inhibitors of this protease. Molecular modeling of the protease-inhibitor complexes suggests that these compounds bind to the druggable cavity in the NS2B-NS3 protease interface and affect productive interactions of the protease domain with its cofactor. The most potent compound demonstrated efficient inhibition of ZIKV propagation in vitro in human fetal neural progenitor cells and in vivo in SJL mice. The inhibitory scaffolds could be further developed into valuable research reagents and, ultimately, provide a roadmap for the selection of efficient inhibitors of ZIKV infection.

This article investigates the theme of childhood being a leading topic in a majority of socially focused texts, especially in public service announcements (PSA). Very often, the deep meaning of PSA texts is conveyed through the metaphor. Nowadays we can see that a traditional verbal metaphor is giving its way to more elaborate and complex type – visual metaphor. Thus it becomes vital to research such metaphorical structures, where the transfer is performed using an iconic semiotic system and by correlation of visual metaphor with a verbal one. This transfer of the verbal code into the code of images has a great persuasive potential essential for PSA's effectiveness. It means that all advantages of metaphoric “packing” of the information can be actualized by the verbal code sufficiently enhanced by the visual code. One of the key tasks of the present research is to develop and test a method of analyzing socially oriented polycode metaphorical texts, connected with the issues of childhood, and to check their effectiveness. We detect the tools of constructing visual cognitive metaphor, determine the strategies used, and evaluate the persuasive effect of the visual metaphor used in PSA discourse.

The paper considers the role of interactive forms of teaching, the project method in particular, in the implementing action and student-centered approach in the formation of socio-cultural and professional competences. The project method appears as a pedagogical technique, which is based not on integration of actual knowledge, but its application and acquisition of new knowledge and skills, including self-education. This determines the obvious advantage of this method in the study of disciplines, containing creative component, in the field of advertising in particular. Moreover, the most important advantages of the project method are the following: ensuring a high level of cognitive interest and students’ motivation, integration of theoretical knowledge into practice, development of the individuality, development and realization of students’ creative abilities. The paper concludes by presenting professional competencies, developed within project method.

The paper focuses on application of conceptual blending theory to reconstruction of the region's media-image. The authors determine the peculiarities of perception of Siberia by the representatives of American culture; detect image-making and metaphorical potentials of the concept “Siberia”. By the means of content analysis, the authors detect the mental spaces blended more frequently and explain how the constructed blends influence the image of Siberia. The methodology of the research may be used in PR or marketing practice for the purpose of place branding and creation of a country's positive image. This work was supported by the Russian humanitarian scientific fund (RGNF) under Grant 15-14-55002 “Reconstruction of Siberian Region Image”.

The feasibility of obtaining (75)As and (1)(21/123)Sb NMR spectra for solids at high and moderate magnetic field strengths is explored. Arsenic-75 nuclear quadrupolar coupling constants and chemical shifts have been measured for arsenobetaine bromide and tetraphenylarsonium bromide. Similarly, (121/123)Sb NMR parameters have been measured for tetraphenylstibonium bromide and potassium hexahydroxoantimonate. The predicted pseudo-tetrahedral symmetry at arsenic and the known trigonal bipyramidal symmetry at antimony in their respective tetraphenyl-bromide "salts" are reflected in the measured (75)As and (121)Sb nuclear quadrupole coupling constants, CQ((75)As)=7.8MHz and CQ((121)Sb)=159MHz, respectively. Results of density functional theory quantum chemistry calculations for isolated molecules using ADF and first-principles calculations using CASTEP, a gauge-including projector augmented wave method to deal with the periodic nature of solids, are compared with experiment. Although the experiments can be time consuming, measurements of (75)As and (121)Sb NMR spectra (at 154 and 215MHz, respectively, i.e., at B0=21.14T) with linewidths in excess of 1MHz are feasible using uniform broadband excitation shaped pulse techniques (e.g., WURST and WURST-QCPMG).

Zika virus (ZIKV) targets neural progenitor cells in the brain, attenuates cell proliferation, and leads to cell death. Here, we describe a role for the ZIKV protease NS2B-NS3 heterodimer in mediating neurotoxicity through cleavage of a host protein required for neurogenesis. Similar to ZIKV infection, NS2B-NS3 expression led to cytokinesis defects and cell death in a protease activity-dependent fashion. Among binding partners, NS2B-NS3 cleaved Septin-2, a cytoskeletal factor involved in cytokinesis. Cleavage of Septin-2 occurred at residue 306 and forced expression of a non-cleavable Septin-2 restored cytokinesis, suggesting a direct mechanism of ZIKV-induced neural toxicity. Video Abstract: Mechanisms by which Zika virus leads to microcephaly are poorly understood. Here, Li et al. demonstrate the Zika protease, required for viral replication, associates with host proteins and cleaves Septin-2, a protein required for neural cell division.

The in vitro neuralization of hESCs has been widely used to generate central and peripheral nervous system components from neural precursors (Bajpai et al., 2009; Curchoe et al., 2010), most often through an intermediate “rosette” stage. Here we confirm that hESC derived neuro-epithelial rosettes express many characteristics of the developing embryonic neural plate (Aaku-Saraste et al., 1996), characterized by expression of the tight junction proteins ZO-1 and N-Cadherin. Moreover, neuro-epithelial rosettes display a characteristic acetylated alpha tubulin cytoskeletal arrangement (similar to that observed in the developing embryonic neural plate) (Bhattacharyya et al., 1994). Demonstrated here for the first time MKLP was observed in a hESC model system. We found MKLP expression in small particles in between mitotic spindles, large particles aggregating in the lumen of neuroepithelial rosettes, and we did not observe MKLP in the nucleus of hESC derived neural precursors as previously described in the HeLa cell line. We observed MKLP + particles in aggregations in the lumen of “early” rosette structures. Furthermore, we observed that MKLP + particle aggregations can also be lost from the lumens of hESC derived neuro-epithelial rosettes, similar to a phenomenon observed in the developing neural tube in vivo (Marzesco et al., 2005). We determined that this loss of MKLP + particles occurs from “late” as opposed to “early” stage neuro-epithelial rosettes (characterized by junction type). Disrupting the apical-basal polarization of “early” stage rosettes with a 1% Matrigel overlay (Krtolica et al., 2007) nearly ablates MKLP particle aggregation in the lumen of rosettes, demonstrating that the apical-basal polarity of early NE cells is necessary for lumenal MKLP particle aggregation. We conclude that early hESC derived neuro-epithelial rosettes can model early neurulation events, such as the transition from neural plate like cells to neural tube like cells (i.e. symmetric to asymmetric NE cell division) demonstrated by polarized MKLP particle inheritance and distribution using junction type as a measure of stage.

SummaryThe transcription factor SOX2 is widely known to play a critical role in the central nervous system; however, its role in peripheral neurogenesis remains poorly understood. We recently developed an hESC-based model in which migratory cells undergo epithelial to mesenchymal transition (EMT) to acquire properties of neural crest (NC) cells. In this model, we found that migratory NC progenitors downregulate SOX2, but then start re-expressing SOX2 as they differentiate to form neurogenic dorsal root ganglion (DRG)-like clusters. SOX2 downregulation was sufficient to induce EMT and resulted in massive apoptosis when neuronal differentiation was induced. In vivo, downregulation of SOX2 in chick and mouse NC cells significantly reduced the numbers of neurons within DRG. We found that SOX2 binds directly to NGN1 and MASH1 promoters and is required for their expression. Our data suggest that SOX2 plays a key role for NGN1-dependent acquisition of neuronal fates in sensory ganglia.

The elucidation of mechanisms underlying telencephalic neural development has been limited by the lack of knowledge regarding the molecular and cellular aspects of the ganglionic eminence (GE), an embryonic structure that supplies the brain with diverse sets of GABAergic neurons. Here, we report a comprehensive transcriptomic analysis of this structure including its medial (MGE), lateral (LGE) and caudal (CGE) subdivisions and its temporal dynamics in 12.5 to 16 day-old rat embryos. Surprisingly, comparison across subdivisions showed that CGE gene expression was the most unique providing unbiased genetic evidence for its differentiation from MGE and LGE. The molecular signature of the CGE comprised a large set of genes, including Rwdd3, Cyp26b1, Nr2f2, Egr3, Cpta1, Slit3, and Hod, of which several encode cell signaling and migration molecules such as WNT5A, DOCK9, VSNL1 and PRG1. Temporal analysis of the MGE revealed differential expression of unique sets of cell specification and migration genes, with early expression of Hes1, Lhx2, Ctgf and Mdk, and late enrichment of Olfm3, SerpinE2 and Wdr44. These GE profiles reveal new candidate regulators of spatiotemporally governed GABAergic neuronogenesis.

We tested a "standard" cryopreservation protocol (slow cooling with 10% DMSO) on the human embryonic stem cell (hESC) line H9 containing an Oct-4 (POU5F1) promoter-driven, enhanced green fluorescent protein (EGFP) reporter to monitor maintenance of pluripotency. Cells were cooled to -80 degrees C in cryovials and then transferred to a -80 degrees C freezer. Cells were held at -80 degrees C for 3 days ("short-term storage") or 3 months ("long-term storage"). Vials were thawed in a +36 degrees C water bath and cells were cultured for 3, 7, or 14 days. Propidium iodide (PI) was used to assess cell viability by flow cytometry. Control cells were passaged on the same day that the frozen cells were thawed. The majority of cells in control hESC cultures were Oct-4 positive and almost 99% of EGFP+ cells were alive as determined by exclusion of PI. In contrast, the frozen cells, even after 3 days of culture, contained only 50% live cells, and only 10% were EGFP-positive. After 7 days in culture, the proportion of dead cells decreased and there was an increase in the Oct-4-positive population but microscopic examination revealed large patches of EGFP-negative cells within clusters of colonies even after 14 days of culturing. After 3 months of storage at -80 degrees C the deleterious effect of freezing was even more pronounced: the samples regained a quantifiable number of EGFP-positive cells only after 7 days of culturing following thawing. It is concluded that new protocols and media are required for freezing hESC and safe storage at -80 degrees C as well as studies of the mechanisms of stress-related events associated with cell cryopreservation.

Objective Lentiviral transduction is an established method for efficiently modifying the gene expression program of primary cells, but the ability of the introduced construct to persist as an episome has not been well studied. Material and Methods Here we investigated this issue in lethally irradiated female mice injected with 300 or 3000 doubly sorted male lin neg , Sca-1 high , c-kit high , Thy-1.1 low mouse bone marrow cells that had been exposed in vitro to self-inactivating lentivirus vector encoding a green fluorescence protein (GFP) cDNA. Seven to sixteen months later, bone marrow cells from primary mice were injected into secondary female recipients and another 8 months later into tertiary female recipients. Integration study was performed on individual spleen colonies by Southern blot analysis. Inverse polymerase chain reaction (PCR) and sequence of amplified vector-derived DNA was used to verify Southern blot results. Results Spleen colony-forming cell study revealed that a small fraction of the spleen colonies contained integrated provirus as shown by Southern blot analysis. Unexpectedly, many spleen colonies were found to contain a nonintegrated episomal form of the provirus, which was confirmed by an inverse PCR analysis. In some of the spleen colonies containing only the episomal form, GFP-expressing cells were also detected. Lentiviral sequences were present in hematopoietic tissues of primary mice but not in other tissues. Conclusions These results demonstrate that lentiviral vectors produce episomal circles in hematopoietic stem cells that can be transferred through many cell generations and expressed in their progeny.

The static and magic angle spinning NMR solid-state spectra of Re6Te15 and a series of Re6–Te cluster compounds demonstrate the positive and negative 125Te NMR chemical shifts indicating that the [Re6] cluster distorts strongly magnetic field at the neighboring Te sites. The local magnetic field is decreased at the facial tellurium sites (Teface) and enhanced at the apexial tellurium sites (Teapex). The facial and sagittal sections of the Re6–Te clusters were reconstructed from analysis of Teface and Teapex NMR spectra, respectively.

The identification of the genes regulating neural progenitor cell (NPC) functions is of great importance to developmental neuroscience and neural repair. Previously, we combined genetic subtraction and microarray analysis to identify genes enriched in neural progenitor cultures. Here, we apply a strategy to further stratify the neural progenitor genes. In situ hybridization demonstrates expression in the central nervous system germinal zones of 54 clones so identified, making them highly relevant for study in brain and neural progenitor development. Using microarray analysis we find 73 genes enriched in three neural stem cell (NSC)-containing populations generated under different conditions. We use the custom microarray to identify 38 “stemness” genes, with enriched expression in the three NSC conditions and present in both embryonic stem cells and hematopoietic stem cells. However, comparison of expression profiles from these stem cell populations indicates that while there is shared gene expression, the amount of genetic overlap is no more than what would be expected by chance, indicating that different stem cells have largely different gene expression patterns. Taken together, these studies identify many genes not previously associated with neural progenitor cell biology and also provide a rational scheme for stratification of microarray data for functional analysis.

This overview paper includes both published and original data of the current state of the field of 51 V NMR in solid-state chemistry. Advantages and shortcomings of different NMR techniques in their applications to vanadium are discussed on the examples of their application to various vanadia based systems (including individual highly crystalline compounds, solid solutions, glasses, catalysts). New correlations between local structure of vanadium atoms and NMR parameters allowing to discriminate at least seven different types of vanadium sites (tetrahedral sites of Q0, Q1 and Q2 types; trigonal pyramids of 3=1 and 3=2 (V2O5 like) types; tetragonal pyramids of 4=1, 4=2 types) are proposed. It is demonstrated that competent combination of different NMR approaches permits now not only to describe different vanadium sites in highly crystalline and amorphous materials, but also to insight into the structural aspects of disorder in crystallinity as well as to reveal the behavior of different functional groups at elevated temperatures. The influence of low valence vanadium atoms on 51 V NMR spectra is also discussed.

Earlier mutagenesis of the red fluorescent protein drFP583, also called DsRed, resulted in a mutant named Fluorescent Timer (Terskikh, A., Fradkov, A., Ermakova, G., Zaraisky, A., Tan, P., Kajava, A. V., Zhao, X., Lukyanov, S., Matz, M., Kim, S., Weissman, I., and Siebert, P. (2000) Science 290, 1585--1588). Further mutagenesis generated variants with novel and improved fluorescent properties. The mutant called AG4 exhibits only green fluorescence. The mutant, called E5up (V105A), shows complete fluorophore maturation, eventually eliminating residual green fluorescence present in DsRed. Finally, the mutant, called E57 (V105A, I161T, S197A), matures faster than DsRed as demonstrated in vitro with purified protein and in vivo with recombinant protein expressed in Escherichia coli and Xenopus leavis. Comparative analysis of the mutants in the context of the crystal structure of DsRed suggests that mutants with free space around the fluorophore mature faster and more completely.

We examine correlation and relativistic effects on Pb–Pb and Pb–O interactions in β -PbO with ab initio quantum calculations and 207 Pb NMR chemical-shift-tensor analysis. We find a covalent-like Pb 2+ –Pb 2+ interaction accounts for many facets of the NMR spectroscopy and the X-ray absorption near-edge structure, as well as other spectroscopic properties. This covalent effect arises from the relativistic properties of the 6 p 3/2( m =±1/2) and 6 p 3/2( m =±1/2) orbitals. The existence of such interactions in lead (II) oxides other than β -PbO may explain NMR and optical spectra of these materials as well.

Phage display is a powerful method of isolating of antibody fragments from highly diverse naive human antibody repertoires. However, the affinity of the selected antibodies is usually low and current methods of affinity maturation are complex and time-consuming. In this paper, we describe an easy way to increase the functional affinity (avidity) of single chain variable fragments (scFvs) by tetramerization on streptavidin, following their site-specific biotinylation by the enzyme BirA. Expression vectors have been constructed that enable addition of the 15 amino acid biotin acceptor domain (BAD) on selected scFvs. Different domains were cloned at the C-terminus of scFv in the following order: a semi-rigid hinge region (of 16 residues), the BAD, and a histidine tail. Two such recombinant scFvs directed against the carcinoembryonic antigen (CEA) were previously selected from human non-immune and murine immune phage display libraries. The scFvs were first synthesized in Escherichia coli carrying the plasmid encoding the BirA enzyme, and then purified from the cytoplasmic extracts by Ni-NTA affinity chromatography. Purified biotinylated scFvs were tetramerized on the streptavidin molecule to create a streptabody (StAb). The avidity of various forms of anti-CEA StAbs, tested on purified CEA by competitive assays and surface plasmon resonance showed an increase of more than one log, as compared with the scFv monomer counterparts. Furthermore, the percentage of direct binding of 125I-labeled StAb or monomeric scFv on CEA-Sepharose beads and on CEA-expressing cells showed a dramatic increase for the tetramerized scFv (80%), as compared with the monomeric scFv (20%). Interestingly, the percentage binding of 125I-labeled anti-CEA StAbs to CEA-expressing colon carcinoma cells was definitely higher (80%) than that obtained with a reference high affinity murine anti-CEA mAb (30%). Another advantage of using scFvs in a StAb format was demonstrated by Western blot analysis, where tetramerized anti-CEA scFv could detect a small quantity of CEA at a concentration 100-fold lower than the monomeric scFv.

27 Al MAS NMR spectroscopy has been used to study the surface aluminium compounds formed upon interaction of the supported TiCl 4 /donor/MgCl 2 catalyst with AlEt 3 in the presence or absence of the external donor. Similarly with the catalyst without any donors [A.G. Potapov, V.V. Terskikh, V.A. Zakharov, G.D. Bukatov, J. Mol. Catal. A: Chem., 145 (1999) 147], the AlEt 2 Cl formed adsorbs on the catalyst surface. It was found that there is no influence of internal and/or external donors on the state of aluminium in adsorbed AlEt 2 Cl in spite of a decrease of the aluminium content in the presence of external donor.

The catalytic hydrodechlorination of chlorobenzene with Ni/C, Pd/C and Ni 98 Pd 2 /C in ethanol was studied with 2 D and 13 C{ 1 H} NMR. Two dechlorination routes of this reaction (ionic and free-radical) are suggested depending upon the nature of the active hydrogen species. At the same time two competitive sources of hydrogen for hydrogenolysis of the CCl bond – molecular hydrogen and solvent (ethanol) molecules – are readily apparent from experiments with molecular deuterium.

Multinuclear 23 Na, 39 K, 133 Cs, 17 O, 51 V magnetic resonance studies of the M 2 S 2 O 7 -V 2 O 5 (M=Na, K, Cs) systems in the temperature range 20–650°C have been performed for vanadium oxide mole fractions, X(V 2 O 5 ), in the range 0–0.5. At ambient temperature the melt-quenched glassy samples exhibit a three-dimensional network of vanadium oxosulfate complexes. Octahedral coordination of vanadium atoms is found in the glassy samples at all compositions studied, in accordance with 51 V NMR spectra. Alkali cations are distributed randomly within an anion network. At high vanadium concentration the structure of vanadium sites in the glasses is very similar to that found in Cs 4 (VO) 2 O(SO 4 ) 4 , whereas for small vanadium contents the vanadium sites are separated by additional sulfate ligands. Heating to the glass-transition temperature, T g , and above, leads to jumps of the alkali cations between different sites. The mobility of pyrosulfate groups is accompanied by dissociation to SO 4 2− and SO 3 . At the elevated temperature the mobility of SO 3 molecules is sufficient to participate in chemical exchange with the sulfate groups of the network. Addition/splitting mechanism involving SO 3 has been proposed to be responsible for random fluctuations of the 51 V nuclear quadrupole tensor at given vanadium network sites with characteristic correlation time τ c . For 10 −8 τ c −6 s the 51 V NMR line became unobservable. For Cs-containing samples the increase of the temperature is accompanied by fast crystallization. In this case a cooperative motion of the anion network, caused by bond breaking and bond formation, dominates at temperatures around T g . The NMR spectra of alkali metals were found to be very characteristic for the structure of the network formed in melts between V 2 O 5 and M 2 S 2 O 7 . 17 O, 23 Na, 39 K, 133 Cs spectra recorded at 500°C point to the formation of different species and rapid exchange between them. A change of the local vanadium environment in melts takes place at X(V 2 O 5 )∼0.1 and 0.3 most probably due to the formation of dimeric and polymeric V(V) complexes, possibly (VO) 2 O(SO 4 ) 4 4− and (VO 2 SO 4 ) n n − . Correlation time of 51 V quadrupole tensor fluctuations for samples with X(V 2 O 5 )∼0.1–0.5 is higher than 10 −8 s, which makes 51 V NMR spectra unobservable in the region 400–500°C, whereas for more dilute samples, τ c is determined mainly by the size of the vanadium-sulfate species making 51 V spectra of these samples observable. The dependence of 51 V chemical shift on the vanadium concentration indicates a change of coordination number in the system M 2 S 2 O 7 -V 2 O 5 from tetrahedral in pure V 2 O 5 to octahedral in dilute samples. The structure of supported catalysts is very similar to the structure of bulk melts (M 2 S 2 O 7 -V 2 O 5 ), the main difference revealed is lower mobility of all structural units (such as metal cations, SO 4 2− and SO 3 ) for the supported melts.

Solid Pb3O4 has been studied with 207Pb nuclear magnetic resonance (NMR) spectroscopy. The 207Pb NMR chemical-shift tensor of the Pb2+ site has principal values of delta11 = 1980 +/- 5 ppm, delta22 = 1540 +/- 5 ppm, and delta33 = -1108 +/- 10 ppm; delta(iso) = 804 +/- 10 ppm. The chemical-shift tensor of the Pb4+ site is axial, with principal values delta(parallel) = -1009 +/- 3 ppm and delta(perpendicular) = 1132 +/- 3 ppm; delta(iso) = -1091 +/- 3 ppm. The Pb4+-Pb2+ scalar coupling constant J(Pb-Pb) = 2.3 +/- 0.1 kHz. The main contribution to the Pb2- chemical-shift anisotropy is proposed to arise from an exchange interaction in the Pb2+-Pb2+ pairs, conventionally regarded as molecular [Pb2]4+ ions.

129Xe NMR spectroscopy was used to study xenon adsorption on V2O5/TiO2/SiO2 catalysts with varying ratio of supported vanadia and titania components. These catalysts were chosen because of their strong electron-accepting (Lewis) acidity. Xenon atoms despite their large polarizability exhibit weak basic properties. The specific interactions of adsorbed xenon atoms with the strongest Lewis acidic sites were detected with 129Xe NMR. It was demonstrated that a possibility of such interactions should be taken properly into account when studying porous solids by the adsorption of gaseous xenon.

27 Al NMR MAS method has been used to study the surface aluminium compounds forming during the treatment of supported TiCl4/MgCl2 catalyst with organoaluminium compounds (OAC) of various composition (AlEt3, AlOct3, AlEt2Cl). Dialkylaluminium chloride has been found to be the main surface compound in the case of trialkylaliminium. Three surface species of dialkylaluminium chloride have been identified: one of them corresponds to 5-coordinated aluminium; the other two correspond to 6-coordinated aluminium with different alkyl-to-chlorine ratio. The relative amounts of surface species depend on the conditions of OAC reaction with catalysts and OAC composition. After polymerization of ethylene or propylene on trioctylaluminium-treated catalysts (polymer yield ca. 1 g/1 g catalyst), the signals of 5-coordinated aluminium disappear from the 27 Al NMR spectra of the catalysts.

α-PbO and β-PbO have been studied with 207 Pb NMR-MAS spectroscopy in the solid state. The 207 Pb NMR chemical-shift tensor in α-PbO is axial, with principal values δ ⊥ =3030±5, δ ‖ =−270±5, and δ iso =1930±10 ppm. In β-PbO, the 207 Pb NMR powder spectrum is approximately represented by a single non-axial tensor with principal values δ 11 =2820, δ 22 =2760, δ 33 =−1000, δ iso =1525±10 ppm and η =0.024, although there appears to be an overlap of two very similar patterns. Using normal-coordinate analysis, the 207 Pb magnetic shielding tensor is represented as a sum of contributions from separate Pb–O and Pb–Pb interactions. It is shown that Pb–O and Pb–Pb contributions are of the same order of magnitude. A potential underlying relativistic reason for the abnormal Pb–Pb interaction is revealed.

The Te–O and Te–Te bonds in TeO 2 have been studied from 125 Te NMR single crystal data. The 125 Te NMR chemical shift tensor has principal components δ 11 =727.5, δ 22 =1586.2 and δ 33 =2065.8 ppm. The 125 Te magnetic shielding tensor is represented as a sum of constituents characterising the off-ionic parts of the separated Te–Te and Te–O interactions. It is shown that the Te–Te exchange interaction is associated with a strong polarization of the Te 4+ ion under the intramolecular electric field and with tunneling of 5s 2 electrons along the Te–Te bonds.

The 27 Al NMR MAS spectra of surface species of aluminum-containing compounds AlEt 3 − n Cl n ( n = 0–3) on MgCl 2 have been measured. The data obtained indicate that 5- and 6-coordinated aluminum compounds form on the MgCl 2 surface. The majority of the AlCl 3 supported in small amounts on MgCl 2 was found to be 4-coordinated.

Vanadium and tungsten oxide supported on TiO{sub x}/Al{sub 2}O{sub 3} catalysts have been studied by solid state NMR spectroscopy. {sup 1}H-MAS NMR spectra demonstrated that basic AlOH groups are involved in anchoring TiO{sub x} and VO{sub x} species. A certain percentage of the AlOH groups are located in positions, probably in the bulk of the alumina particles, where they remain inaccessible for interaction with titania, vanadia, or tungsten oxide. Titania modification of the Al{sub 2}O{sub 3} surface leads to formation of bridging hydroxyls, namely Ti(OH)Ti and (or) Ti(OH)Al. Hydroxyl groups coordinated to Ti atoms are involved in anchoring vanadium and tungsten oxide species. VOH (and probably WOH) groups are formed when this ternary oxide phase is dispersed on the TiO{sub x}/Al{sub 2}O{sub 3} support. {sup 51}V-NMR spectra indicated that tungsten oxide participates in the formation of the structure of the mixed oxide surface complexes. {sup 15}N-NMR spectroscopy of adsorbed N{sub 2}O permitted the detection of strong Lewis acid sites on these multicomponent supported oxide catalysts. The acid strength of (V{sub 2}O{sub 5}-WO{sub 3}) on TiO{sub x}/Al{sub 2}O{sub 3} catalysts turned out to be comparable to that of the TiO{sub x}/Al{sub 2}O{sub 3} support material. 39 refs., 9 figs., 2 tabs.

1H magic-angle spinning nuclear magnetic resonance (MAS NMR) spectra of TiO chi/SiO2 catalysts suggest the interaction of surface TiO chi species with Si-OH groups of the silica. Simultaneously, Ti-OH groups from surface titania species appear. The distribution of TiO chi species over SiO2 is non-uniform, since a considerable part of surface OH groups remains unreacted with supported titania. Supported vanadia species interact both with Si-OH and Ti-OH groups. 51V NMR spectra suggest the interaction of vanadia with supported titania species and show the non-uniform distribution of titania over the SiO2 surface. Deposition of titania as well as vanadia produces strong electron-accepting (Lewis) sites which interact with the terminal N atom of adsorbed N2O molecules, resulting in a downfield shift of the resonance in 15N NMR spectra. The acid strength of electron-accepting sites is similar in both cases. Only about 10% of the total amount of supported titania and vanadia create Lewis sites.

Combined1H,15N and13C NMR studies have been performed to elucidate the role of proton donating (Bronsted) and electron accepting (Lewis) sites in isomerization and disproportionation of n-pentane catalyzed by sulfate-promoted zirconia.1H NMR MAS of proton sites in a series of sulfate-promoted zirconia as well as in ZrO2 and Zr(SO4)2 has revealed a variety of surface OH groups that differ in their chemical shifts. Their amounts as function of sample preparation procedure and evacuation temperature have been measured. Lewis acidic sites have been characterized by15N NMR of adsorbed N2. The results have shown that the most active zirconia catalysts have very strong Lewis acidic sites with a concentration of several μmol/g. Their amount has been found to decrease on increase of an evacuation temperature of samples up to 600°C. The numbers of Bronsted and Lewis sites have been correlated with the catalytic activity in reaction of n-pentane isomerization measured by in situ1H MAS NMR. Effects of catalyst treatment temperature and addition of CO and H2O have been studied. No correlation between the catalyst's activity in the reaction of n-pentane isomerization and the number and types of surface OH groups has been found. At the same time, the proportionality between the activity and the amount of the most strong Lewis sites detected by15N NMR of adsorbed N2 has been revealed. The products of n-pentane conversion over sulfate-promoted zirconia have been identified by13C MAS NMR. The role of Lewis and Bronsted acidic sites in n-pentane isomerization and disproportionation is discussed.

The rate of ethylene epoxidation over AgAl2O3 supported catalysts demonstrates the drastic increase at a mean size of Ag particles about 400–500 A. The integral intensity of the 109Ag NMR line from Ag metal particles of the same catalysts increases in the same range of particle sizes. This is due to the large line broadening of the signal from the Ag particles of which the sizes are less than 400–500 A. The self-consistent calculations of the electronic structure of semi-infinite Ag(111) crystal show the large deviation of the local density of electronic states and 109Ag NMR Knight shifts for the first surface layers of Ag compared with Ag bulk.