Comparative studies on mammalian Hoxc8 early enhancer sequence reveal a baleen whale-specific deletion of a cis-acting element

Variations in regulatory regions of developmental control genes have been implicated in the divergence of axial morphologies. To find potentially significant changes in cis-regulatory regions, we compared nucleotide sequences and activities of mammalian Hoxc8 early enhancers. The nucleotide sequence of the early enhancer region is extremely conserved among mammalian clades, with five previously described cis-acting elements, A-E, being invariant. However, a 4-bp deletion within element C of the Hoxc8 early enhancer sequence is observed in baleen whales. When assayed in transgenic mouse embryos, a baleen whale enhancer (unlike other mammalian enhancers) directs expression of the reporter gene to more posterior regions of the neural tube but fails to direct expression to posterior mesoderm. We suggest that regulation of Hoxc8 in baleen whales differs from other mammalian species and may be associated with variation in axial morphology.     

Selectivity engineering in isopropylation of mesitylene with isopropyl alcohol over cesium substituted heteropolyacid supported on K-10 clay

Alkylation of aromatics catalyzed by solid acids constitutes a class of reactions of both academic and industrial importance. Among alkylation reactions, isopropylation of aromatic compounds has attracted considerable attention. Use of propylene as alkylating agent at very high temperatures leads to coke formation which results in deactivation of the catalyst. The use of isopropanol (IPA) as an alkylating agent is attractive when propylene is not readily available. In situ dehydration of IPA leads to prolonged activity since water of reaction suppresses coke formation. Further, IPA dehydration also generates diisopropyl ether which itself is an excellent alkylating agent. Alkylation of mesitylene with propylene or IPA results in the formation of 2-isopropyl-mesitylene (2-IPMT), which is almost extensively used as a precursor in a number of industrial chemicals. This work covers the evaluation of clay-supported heteropolyacids and sulfated zirconia. A variety of solid acid catalysts such as K-10 clay, sulfated zirconia, Filtrol-24, 20% w/w dodecatungstophosphoric acid (H₃PW₁₂O₄₀, DTP) supported on K-10 montmorillonite clay and 20% w/w cesium substituted dodecatungstophosphoric acid (Cs_2.5H_0.5PW₁₂O₄₀, Cs-DTP) supported on K-10 montmorillonite clay were investigated for the liquid phase isopropylation of mesitylene to 2-IPMT using IPA at much milder conditions vis-à-vis other catalysts reported so far. 20% w/w Cs-DTP/K-10 clay was found to be the best catalyst which gives 98% conversion of limiting component, IPA and 98% selectivity towards the desired product, 2-IPMT after 2 h of total reaction time. This catalyst could be reused without any further chemical treatment, eliminating the effluent disposal problems. The reaction was carried out without using any solvent and the process subscribes to the principles of green chemistry. The catalytic activity is in the following order: 20% w/w Cs-DTP/K-10 clay (most active) > 20% w/w DTP/K-10 clay > Filtrol-24 > Sulfated zirconia > K-10 clay (least active). The effect of various operating parameters and catalyst reusability were also systematically investigated. A mathematical model was proposed to probe into the intricate reaction kinetics and mechanism consistent with the experimental results. The reaction is free from any external mass transfer as well as intraparticle diffusion limitations and is intrinsically kinetically controlled. An overall second order kinetic equation was used to fit the experimental data, under the assumption that all the species are weakly adsorbed on the catalytic sites.     

5th International Symposium on Electrochemical Impedance Spectroscopy Marilleva (Trento), Italy, June 2001

Preface

5th International Symposium on Electrochemical Impedance Spectroscopy Marilleva (Trento), Italy, June 2001     

Iron Nitrate/TEMPO: a Superior Homogeneous Catalyst for Oxidation of Primary Alcohols to Nitriles in Air

A highly practical, one‐step, facile synthesis of aromatic, heteroaromatic, allylic and aliphatic nitriles from primary alcohols catalyzed by ferric nitrate [Fe(NO₃)₃⋅9H₂O] in the presence of TEMPO, aqueous ammonia and air at room temperature is described.

     

Optical studies of ZnO/Ag nanojunctions

Ag/ZnO nano-hetero-junctions were synthesized by an electrochemical route. The optical absorption spectroscopy and photoluminescence studies reveal the reaction mechanism at the junction. Optical absorption spectra indicate presence of well-defined ZnO excitonic feature along with the Ag surface plasmon absorption feature at 400 nm. Moreover, ZnO green photoluminescence appears on junction formation with Ag. Detailed analysis of emission and excitation processes indicate that efficient charge transfer is taking place from ZnO to Ag. Ag is also responsible for creation of levels in the HOMO-LUMO gap of ZnO. This finding may be of relevance so far as p-type doping in ZnO is concerned.     

Combinations of closely situated cis-acting elements determine tissue-specific patterns and anterior extent of early Hoxc8 expression

We have used a transgene mutation approach to study how expression domains of Hoxc8 are established during mouse embryogenesis. A cis-regulatory region located 3 kb upstream from the Hoxc8 translational start site directs the early phase of expression. Four elements, termed A, B, C, and D, were previously shown to direct expression to the neural tube. Here we report that a fifth element, E, located immediately downstream of D directs expression to mesoderm in combination with the other four elements. These elements are interdependent and partially redundant. Different combinations of elements determine expression in different posterior regions of the embryo. Neural tube expression is determined minimally by ABC, ABD, or ACD; somite expression by ACDE; and lateral plate mesoderm expression by DE. Neural tube and lateral plate mesoderm enhancers can be separated, but independent somite expression has not been achieved. Furthermore, mutations within these elements result in posteriorization of the reporter gene expression. Thus, the anterior extent of expression is determined by the combined action of these elements. We propose that the early phase of Hoxc8 expression is directed by two separate mechanisms: one that determines tissue specificity and another that determines anterior extent of expression.     

Multiple phases of expression and regulation of mouse Hoxc8 during early embryogenesis

Hox genes are expressed in dynamic patterns during embryogenesis consistent with their role in axial specifications. To study the distribution of mouse Hoxc8, a homeodomain containing protein, we raised monoclonal antibodies against the least conserved portion of Hoxc8. Using these antibodies, we have examined early and mid-gestation embryos for the distribution of the protein. At the end of gastrulation Hoxc8 is expressed in the caudal portion of the embryo. In the neural tube, an early phase when all cells express Hoxc8 is distinguished from a late phase with predominant expression in differentiating neurons. A comparison of this expression pattern with that of a reporter gene under the control of the early Hoxc8 enhancer demarcates three separate regulatory components: (1) initiation and establishment; (2) maintenance; and (3) downregulation. We propose that Hoxc8 expression during embryogenesis is established in multiple phases. Possible regulatory mechanisms involved in generating such a complex domain of Hox gene expression are discussed.     

Conserved regulatory element involved in the early onset of Hoxb6 gene expression

When administered before training to 23-day-old Long-Evans rats, scopolamine hydrobromide significantly impaired both contextual and auditory-cue fear conditioning in a dose-dependent manner. Methylscopolamine which does not cross the blood-brain barrier, however, had no effect on either form of conditioned fear. Scopolamine administered up to 3 h after training also impaired both forms of fear conditioning when administered following a single pairing of the auditory cue and shock. When rats received three pairings, however, a posttraining treatment with scopolamine only impaired contextual fear conditioning. These results suggest that central cholinergic systems are involved in the posttrial processes that establish the memory trace for the conditioning experience.     

Cobalt selenide thin film: photovoltaic and impedance spectral studies by simple chemical grown technique

A thin film of cobalt selenide is deposited on the fluorescence tin oxide-coated glass surface material using a simple chemical growth technique. In this article, we report on the study of photoelectrochemical characteristics (PEC), including current–voltage, capacitance–voltage characteristics, photovoltaic power output, and spectral response in dark and light conditions. For the above parameter study, we prepared using cobalt selenide and carbon electrode (using polysulfide as electrolyte), the battery configuration is expressed as n-CoSe/NaOH (1 M)?+?Na₂S (1 M)?+?S (1 M)/C (graphite). The performance of the cobalt selenide thin film material the resulted values of respective series (R_S) and shunt (R_Sh) resistance 2.280 kΩ and 1.224 Ω, respectively. The efficiency and fill factor of these PEC cells were found to be 0.899 and 28.72%. The junction ideality value are found to be (n_D) is 0.69 in the dark and 2.72 in the light (n_L). The M–S plots are constructed using C^?2 against applied bias voltage (with respect to SCE) for CoSe PEC cell. The positive slope of the M–S plot confirms n-type conductivity of the CoSe films. The carrier density values of the samples obtained from the M–S plots varied from 3.48?×?10¹⁴ cm^?3.