Hydrogen‐Bonding‐Driven Enantioselective Resolution against the Kazlauskas Rule To Afford γ‐Amino Alcohols by Candida rugosa Lipase

Most lipases resolve secondary alcohols in accordance with the “Kazlauskas rule” to give the R enantiomers. In a similar manner to other lipases, Candida rugosa lipase (CRL) exhibits R enantioselectivity towards heptan‐2‐ol, although the enantiomeric ratio (E) is low (E=1.6). However, unexpected enantioselectivity (i.e., S enantioselectivity, E=58) of CRL towards 4‐(tert‐butoxycarbonylamino)butan‐2‐ol, which has a similar chain length to heptan‐2‐ol, has been observed. To develop a deeper understanding of the molecular basis for this unusual enantioselectivity, we have conducted a series of molecular modeling and substrate engineering experiments. The results of these computational and experimental analyses indicated that a hydrogen bond between the Ser450 residue and the nitrogen atom of the carbamate group is critical to stabilize the transition state of the S enantiomer.     

Ultrastructure of dermal denticles in sharpnose shark (Rhizoprionodon lalandii) (Elasmobranchii,Carcharhinidae)

The presence of denticles in the external surface, oral cavity, fins, and clasper of Elasmobranchii has been widely reported. These structures, called body denticles, may be observed on the body surface of sharks. Dermal and oral denticles are made up by a basal plate that is embedded in the dermis, forming a peduncle that grows from the base to the crown. These denticles may protect the skin against abrasion, and improve hydrodynamics and gill arches function. Rhizoprionodon lalandii is a widely distributed and very common species in Brazilian coastal areas. The aims of this study was to compare the morphology of oral and body denticles of R. lalandii to understand the implications of these structures in the behavior of these animals. Morphological analysis showed that there are differences between dermal and oral denticles, which are related to their role in different body regions. Body denticles have three cusps, and well‐defined crests and ridges, and literature data suggest that suggest that hydrodynamics is their main function. Most of the oral denticles have only one cusp, and their morphology and distribution showed that their main functions are preparing food to be swallowed and protecting the oral cavity against abrasion. Microsc. Res. Tech. 78:859–864, 2015. © 2015 Wiley Periodicals, Inc.     

A Fully-Differential Complementary Hartley VCO in 0.18 m CMOS Technology

In this letter, a new complementary Hartley (C-Hartley) voltage controlled oscillator (VCO) with fully differential outputs is proposed, in which the self-biasing configuration is introduced to solve the biasing difficulty of a Hartley VCO by employing a five-port transformer. The proposed C-Hartley VCO with the center frequency of 5.6 GHz is implemented in a 1P6M 0.18 $mu$m CMOS process. The measurement result shows that the phase noise is ${-}123.6$ dBc/Hz at 1 MHz offset frequency, while dissipating 6.5 mA from 1.6 V supply with the FOM of ${-}188.5$ dBc.      

Transfer of mercury and methylmercury along macroinvertebrate food chains in a floodplain lake of the Beni River, Bolivian Amazonia

We have evaluated the mercury and methylmercury transfers to and within the macroinvertebrate communities of a floodplain lake of the Beni River basin, Bolivia, during three hydrological seasons and in two habitats (open water and vegetation belt). Using the stable isotopes δ¹³C and δ¹⁵N, six trophic chains were identified during a previous study. Four are based on only one source: seston, organic matter from the bottom sediment, periphyton and macrophytes. Two are based on mixed sources (seston and periphyton in one case, periphyton and macrophytes in the other). During sampling, we found only one taxon that had surface sediment organic matter as food source and very few taxa whose trophic source was constituted by macrophytes. The periphyton was the most important source during all seasons; it produced the longest chain, with three trophic positions. Whatever the season and trophic source, all collected macroinvertebrates contained methyl mercury and the latter was biomagnified in all trophic chains that we identified. The biomagnification of methylmercury through invertebrate trophic chains accurately reflected the existence and length of these chains. Biomagnification was virtually non-existent in the sediment-based chain, low and restricted to the dry season in the macrophyte-based chain. It was significant in the seston-based chain, but limited by the existence of only two trophic levels and restricted to the wet season. Finally, it was very effective in the periphyton-based chain, which offers the highest rate of contamination of the source but, above all, the largest number of trophic levels.     

Computational-fluid-dynamics study of a Kenics static mixer as a heat exchanger for supercritical carbon dioxide

The thermal efficiency of a Kenics^® KM static mixer used to pre-heat supercritical carbon dioxide, under high pressure conditions, is studied using computational fluid dynamics (CFD). A mesh sensitivity analysis is performed and the CFD model is validated against experimental results on heat transfer with conventional and supercritical fluids. Three turbulent models - standard k-?, RNG k-?, and k-ω - are employed to model the flow and heat transfer under high pressure conditions; the effects of large variations of the physical properties in the pseudo-critical region of the fluid are also studied. The RNG k-? model gives results that are closer to the experimental data than the other two turbulence models. The numerical results show that the static mixer has a thermal efficiency more than three times higher than that of a conventional empty pipe heat exchanger with similar heat transfer area.     

Background arsenic concentrations in Southeastern Spanish soils

The arsenic content in the province of Granada (SE Spain) was quantified, based on 93 soils at two different depths and their corresponding parent materials. The arsenic concentrations fit a log-normal distribution. Four different statistical procedures to estimate the arsenic background range in the region were tested. Upper background limits clearly exceeded limits reported for natural soils when based on the Tukey box plot or means and standard deviations of the dataset (M+/-2sdev) or of the calculated distribution function (Mf+/-2sigma) but not when based on median values (Md+/-2MAD). The relative cumulative frequency curve not only adequately estimates the background range but also delivers a clear and detailed visualisation of the data distribution and identifies subpopulations with specific background ranges related to combinations of parent materials and degree of soil development.     

Determination of IgG levels in bovine bulk milk samples from different regions of Spain

Colostrum addition to milk for consumption is an unlawful practice. Furthermore, the higher whey protein/casein ratio of colostrum compared with milk causes severe technological problems. A high concentration of immunoglobulins has been generally accepted as an index of colostrum presence in milk. In this work, the levels of IgG have been determined by a non-competitive ELISA in 3,248 bulk bovine milk samples from different regions of Spain throughout one year. The mean value for IgG concentration obtained from all the samples was 0.257±0.122 mg/ml, within the range generally considered as acceptable for mature milk. The mean concentration obtained for all the samples collected in the spring was 0.288±0.125 mg/ml, significantly higher than the values found at the other seasons. The finding of some samples with very high values of IgG would suggest that the determination of immunoglobulin levels periodically would be a good parameter to control milk quality.     

Thermophysical properties of medium grain rough rice (<Emphasis Type="Italic">LIDO cultivar</Emphasis>) at medium and low temperatures

Bulk density, specific heat capacity, bulk thermal conductivity and bulk thermal diffusivity of medium-grain rough rice (LIDO cultivar) have been studied. Specific heat was determined by DSC, thermal conductivity by the probe method and bulk thermal conductivity indirectly from bulk density, specific heat capacity and bulk thermal conductivity. All the thermal properties have been determined at different moisture contents and temperatures used during cooling and storage operations and the effect of these variables has been investigated. It has been shown that moisture content has the greatest effect on specific heat and bulk thermal conductivity. Temperature also affected these thermal properties, but to a smaller extent. Mathematical expressions have been developed to determine each of these thermophysical properties as a function of moisture content and temperature.List of Abbreviations and Symbols C_p Specific heat capacity (kJ/kg °C) - k Bulk thermal conductivity (W/m °C) - T Temperature (ºC) - W Moisture content (%, d.b.) - Bulk thermal diffusivity (m²/s) - Bulk density (kg/m³)     

Effect of calcium chloride on the volatile pattern and sensory acceptance of dry-fermented sausages

The effect of calcium chloride addition used in combination with starter cultures (lactic acid bacteria and staphylococci) was studied in the development of dry-fermented sausage aroma and final sensory acceptance. Volatile compounds were extracted by solid-phase micro extraction and analysed by gas chromatography-mass spectrometry. A paired comparison test was done to determine which sausage was preferred. The addition of calcium chloride 0.05% showed an important effect on volatile generation during ripening by inhibiting the generation of lipid oxidation products and promoting the generation of methyl branched alcohols and ethyl esters that contribute to proper sausage aroma. However, other compounds such as 3-methyl-butanoic acid and acetic acid, detected in high quantities in the 0.05% calcium added batch, may impart rancid and cheese-like notes that can negatively affect the final aroma. Moreover, the amount of calcium chloride used is important because larger amounts (0.5%) favoured the lipid oxidation producing a rejection from consumers.