Stabilization of germanium(IV) aquafluorocompounds in host-guest type complexes with crown ethers. synthesis,crystal structure and ir spectra of the complexes [(GeF5-H2O)2-(H2-1,10-Diaza-l 8-Crown-6)] and [(trans-GeF4 · 2H2O) · 18-Crown-6·2H2O]

Stable products have been obtained from the interaction of GeO₂-HF solution with 18-membered crown ethers, 1,10-diaza-l8-crown-6 and 18-crown 6. Complexes were characterized by X-ray analysis and IR spectroscopy. Both Ge(IV) aquafluorocompounds are isostructural with their Si analogues. It was established that in the host-guest type complexes the germanium moiety as a central atom has been stabilized in the form of octahedral complexes. The host-guest interaction occurs by means of O-H(W)...O_cr, OH...F and N-H...F hydrogen bonds.     

Capillary electrophoresis

The most important characteristics of capillary electrophoresis are studied. Principles of the technique, instrumentation employed and the most important applications are described.     

Thermotropicity of fully aromatic polyesters based on 3,4′-dicarboxydiphenyl ether

3,4′-Substituted aromatic monomers, consisting of two phenylene units joined together by linking groups such as ketone or methylene, have recently been used for the preparation of quasi-rigid fully aromatic thermotropic polymers, based on conformational isomerism, with accessible transition temperatures. In this work the polyester of 3,4′-dicarboxydiphenyl ether and hydroquinone is considered: an Ullmann condensation has been carried out for the preparation of the asymmetric monomer, and low-temperature solution polycondensation has been used to synthesize the polymer. Although a liquid crystalline behavior could be expected, the polyester melts to an isotropic phase. Several copolymers have been prepared, by partially substituting either the asymmetric monomer with terephthalic acid or hydroquinone with different diphenols. The attempt to decrease the stability of the crystalline phase did not lead to significant results. The appearance of the nematic phase in some samples has been attributed to an increased chain stiffness, expressed in terms of persistence length as derived from molecular dynamics (MD) simulations.     

Evaluation of a fibre optic device in solution equilibria studies. Application to 3-hydroxybenzoic acid ionization

The use of a fibre optic device for spectrophotometric measurements in solution equilibria studies is presented. In particular the precision obtainable with such equipment is evaluated as a function of different experimental conditions, such as path length, averaging time and stirring of the solution. Analysis of 3-hydroxybenzoic acid ionization is presented to assess the results obtained in the study of an equilibrium system.     

QUANTIFICATION OF PYRIMIDINE DIMERS AND APURINIC SITES IN DNAs OF UNIFORM LENGTH

Abstract— A new simple in vitro assay for the determination of pyrimidine dimers and/or apurinic/apyrimidinic sites in non-radioactive DNA has been developed. In this procedure, DNA substrates of uniform length-which may be supercoiled, partially relaxed, relaxed or linear-are treated with agents which produce specific single strand nicks at the site of the lesion. The number of lesions per molecule can be expressed as a function of the amount of single-stranded molecules left intact after the specific nicking treatment. Unreacted molecules, which retain the original uniform length, are separated from the other smaller reaction products by electrophoresis on an alkaline agarose gel. In the case of circular molecules, the substrate is linearized by the use of an appropriate restriction endonuclease before loading on the gel. The amount of intact DNA molecules is obtained by integrating the corresponding peak of absorption after densitometric scan of the negative of the gel picture. This assay can detect up to eight damaged sites per duplex molecule. This method could be particularly useful when dealing with mixtures of DNA with different degrees of supercoiling or for comparisons between linear and circular DNA substrates.     

Stereoselective synthesis of constrained azacyclic hydroxyethylene isosteres as aspartic protease inhibitors: dipolar cycloaddition and related methodologies toward branched pyrrolidine and pyrrolidinone carboxylic acids

The synthesis of three vicinally substituted azacyclic carboxylic acids in enantiopure form was achieved from a common alpha-amino aldehyde originating from l-leucine. Pyrrolidines and pyrrolidinones were elaborated from alpha,beta-unsaturated gamma-hydroxy-delta-amino acids via azomethine ylide 1,3-dipolar addition and conjugate addition/cyclization strategies, respectively. The azacyclic amino acids were incorporated in a pseudopeptide now encompassing a hydroxyethylene isostere. Low nanomolar inhibition of BACE1, an enzyme implicated in the cascade of events leading to plaque formation in Alzheimer's disease, was found with a pyrrolidinone analogue.     

Structure of Dibenzocrown Ethers and their H-Bonded Adducts.1. [1.5]Dibenzo-18-Crown-6 and Biphenyl-20-Crown-6: Complexes with Amidosulfuric Acid

The interaction of the amidosulfuric acid NH ₃ SO ₃ with 15 distal and proximal dibenzocrown ethers, including diphenyloxide, diphenylsulfide and biphenyl ones leads to the stable (1:1) complexes only in the case of [2.4]- and [1.5]dibenzo-18-crown-6 and biphenyl-20-crown-6. According to the data of the X-ray analysis, in the two last adducts the amidosulfuric acid coordinates to hexadentate crown ethers in a zwitterion form through a near-ideal ‘tripod’ arrangement to alternate crown oxygen atoms. The conformations of crown molecules are different in complexes and in initial macrocyclic ligands.This revised version was published online in July 2005 with a corrected issue number.     

Dye-sensitized solar cells under ambient light powering machine learning: towards autonomous smart sensors for the internet of things

The field of photovoltaics gives the opportunity to make our buildings ‘‘smart’’ and our portable devices “independent”, provided effective energy sources can be developed for use in ambient indoor conditions. To address this important issue, ambient light photovoltaic cells were developed to power autonomous Internet of Things (IoT) devices, capable of machine learning, allowing the on-device implementation of artificial intelligence. Through a novel co-sensitization strategy, we tailored dye-sensitized photovoltaic cells based on a copper(ii/i) electrolyte for the generation of power under ambient lighting with an unprecedented conversion efficiency (34%, 103 μW cm⁻² at 1000 lux; 32.7%, 50 μW cm⁻² at 500 lux and 31.4%, 19 μW cm⁻² at 200 lux from a fluorescent lamp). A small array of DSCs with a joint active area of 16 cm² was then used to power machine learning on wireless nodes. The collection of 0.947 mJ or 2.72 × 10¹⁵ photons is needed to compute one inference of a pre-trained artificial neural network for MNIST image classification in the employed set up. The inference accuracy of the network exceeded 90% for standard test images and 80% using camera-acquired printed MNIST-digits. Quantization of the neural network significantly reduced memory requirements with a less than 0.1% loss in accuracy compared to a full-precision network, making machine learning inferences on low-power microcontrollers possible. 152 J or 4.41 × 10²⁰ photons required for training and verification of an artificial neural network were harvested with 64 cm² photovoltaic area in less than 24 hours under 1000 lux illumination. Ambient light harvesters provide a new generation of self-powered and “smart” IoT devices powered through an energy source that is largely untapped.

Indoor light harvesters enable machine learning on fully autonomous IoT devices at 2.72 × 10¹⁵ photons per inference.     

Comparison of micellar electrokinetic chromatography, liquid chromatography, and microbiologic assay for analysis of cephalexin in oral suspensions

Two well-accepted methodologies, based on a microbiologic assay (MA) and liquid chromatography (LC), and a novel methodology using micellar electrokinetic chromatography (MEKC), were compared for the determination of cephalexin in commercially available and simulated samples of oral suspensions. The MA, described in the Brazilian Pharmacopeia, was performed with a strain of Staphylococcus aureus ATCC 6538 as the test organism, following the cylinder-plate method. The LC analysis followed the European Pharmacopoeia, 3rd Ed., and was used with minor modifications. The MEKC analysis was based on a previous work of the group. Estimates of the repeatability relative standard deviations of the MA, LC, and MEKC methods in the analysis of a commercial sample were 0.34, 0.42, and 0.37%, respectively. The recovery obtained with LC was 99.90 +/- 1.11%; for MEKC, it was 100.09 +/- 0.56%. Although the 3 methodologies were statistically equivalent for the determination of cephalexin in oral suspensions, MA gave suitable repeatability despite being nonspecific and time-consuming. MEKC provided faster analysis and higher column efficiency, whereas LC presented superior sensitivity. The results indicated that MEKC can be used as an alternative method to MA and LC in routine quality control laboratories.