Molecular Basis for the Enantioselective Ring Opening of β‐Lactams Catalyzed by Candida antarctica Lipase B

Lipase B from Candida antarctica (CAL‐B) catalyzes the slow, but highly enantioselective (E>200), ring‐opening alcoholysis of two bicyclic and two 4‐aryl‐substituted β‐lactams. Surprisingly, the rate of the reaction varies with the nature of the alcohols and was fastest with either enantiomer of 2‐octanol. A 0.5‐g scale reaction with 2‐octanol as the nucleophile in diisopropyl ether at 60 °C yielded the unreacted β‐lactam in 39–46% yield (maximum yield is 50%) with ≥96% ee. The product β‐amino acid esters reacted further by polymerization (not isolated or characterized) or by hydrolysis due to small amounts of water in the reaction mixture yielding β‐amino acids (7–11% yield, ≥96% ee). The favored enantiomer of all four β‐lactams had similar 3‐D orientation of substituents, as did most previously reported β‐lactams and β‐lactones in similar ring‐opening reactions. Computer modeling of the ring opening of 4‐phenylazetidin‐2‐one suggests that the reaction proceeds via an unusual substrate‐assisted transition state, where the substrate alcohol bridges between the catalytic histidine and the nitrogen of the β‐lactam. Computer modeling also suggested that the molecular basis for the high enantioselectivity is a severe steric clash between Ile189 in CAL‐B and the phenyl substituent on the slow‐reacting enantiomer of the β‐lactam.     

Effect of processing on thiamin and riboflavin contents of some high-yielding rice varieties of punjab

Six high-yielding varieties of rice (Oryza sativa L) were taken and subjected to 6 and 8% degree of milling. The raw rice and the parboiled rice were analysed microbiologically for thiamin and riboflavin contents. Milled parboiled rice contained more thiamin and riboflavin that milled raw rice at both the levels of milling because parboiling of paddy results in inward diffusion of water-soluble vitamins to the endosperm. The thiamin content of brown rice is reduced after parboiling. The loss may be due to the partial decomposition of thiamin during the stages of parboiling, but the riboflavin content of brown rice is found to be increased after parboiling.     

A rapid tissue testing methodology for optimum potassium fertilization of potato grown under subtropical short-day conditions

Field experiments were conducted at the Central Potato Research Station, Jalandhar (Punjab) during 1989–90 and 1990–91 on a sandy loam soil (Typic Ustochrept) to develop a tissue testing methodology for determining the optimum dose of K to be applied as a side dressing at the time of earthing up, based on leaf tissue analysis. The sixteen treatments consisted of all combinations of four levels of K applied as basal at planting and as side dressing at the time of earthing-up (30 days after planting (DAP) in two potato cultivars, Kufri Jyoti and Kufri Chandramukhi. The combined application of basal and side dressed K was superior in increasing tuber yield of potato compared to their individual application. The concentration of K in leaf blade or petiole at the early stages (29–40 DAP) was more related to basal K than to basal+ side dressed K, while at the later stages (40–60 DAP) it was more related to basal+side dressed K than to basal K. This suggests the need to apply both basal as well as side-dressed K to maintain a high K concentration in the leaf tissues throughout the crop growth cycle.A methodology to estimate the optimum dose of K to be side dressed from leaf tissue analysis is described. Critical K concentrations in leaf tissues at different growth stages are reported for both potato cultivars.     

Transgenic monocyte chemoattractant protein-1 (MCP-1) in pancreatic islets produces monocyte-rich insulitis without diabetes: abrogation by a second transgene expressing systemic MCP-1

Monocyte chemoattractant protein-1 (MCP-1) is a CC chemokine that attracts monocytes and T lymphocytes in vitro; however, its in vivo functions are poorly understood. To address this question, we constructed transgenic mice expressing MCP-1 controlled by an insulin promoter. These mice developed a chronic insulitic infiltrate composed of F4/80+ monocytes with minor populations of CD4+, CD8+, and B220+ cells. Despite persistent transgene expression, the insulitis never progressed, and blood glucose levels remained normal. Thus, MCP-1 alone is sufficient to elicit a monocytic infiltrate, but not to activate elicited cells. These results differ from those obtained with another transgenic model using the mouse mammary tumor virus long terminal repeat, in which mice expressed substantial MCP-1 in several organs but had no infiltrates. However, mice expressing both transgenes had minimal insulitis, indicating that high systemic levels of MCP-1 prevented monocytes from responding to local MCP-1. Thus, the ability of MCP-1 to elicit monocytic infiltration depends on its being expressed at low levels in an anatomically restricted area.     

Particle coarsening behavior of α-β titanium alloys

A systematic study was undertaken to develop particle coarsening relationships in terms of time, temperature, and volume percents of phases and to determine the rate-controlling mechanisms for the coarsening of α-β Ti-Mn and Ti-V alloys. This investigation is confined to equiaxed-type α+ β microstructures. For a given alloy anc te nperature, the coarsening of particles refers to the growth of particles under essentially constant volume percents of the component phases. The coarsening exponents increased from 0 24 to 0.29 and from 0.28 to 0.32 for Ti-V and Ti-Mn systems, respectively, when the temperature was increased from 973 to 1073 K. In addition, it was found that the activation energy chances as the temperature is increased from 973 to 1108 K for the Ti-Mn system. Based on these results, it is suggested that the rate-controlling mechanism for particle coarsening changes from mixed (bulk + grain-boundary) diffusion control toward bulk diffusion control when the temperature is increased from 973 to 1108 K for the Ti-Mn system. Similarly, for the Ti-V system, it is suggested that the rate-controlling mechanism changes from grain-boundary diffusion control toward mixed diffusion control when the temperature is increased from 973 to 1073 K. These results clearly indicate that the rate-controlling mechanism depends on temperture as well as the diffusivities of the alloying elements. This paper is based on a presentation made in the symposium “Interfaces and Surfaces of Titanium Materials” presented at the 1988 TMS/AIME fall meeting in Chicago, IL, September 25–29, 1988, under the auspices of the TMS Titanium Committee.     

High‐Performance Microwave‐Derived Multi‐Principal Element Alloy Coatings for Tribological Application

The authors report the development of Al_xCoCrFeNi (x = 0.1 to 3) high entropy alloy (HEA) coatings using a simple and straightforward microwave technique. The microstructure of the developed coatings is composed of a cellular structure and diffused interface with the substrate. The microstructure of the HEA coatings varies as a direct function of Al content. An increase in Al fraction shows structural transformation from FCC to BCC along with the evolution of σ and B₂ as the major secondary phases. The diffusion of Mo from the substrate enhances the mixing entropy and promotes σ‐phase formation. The HEA coatings show significantly high hardness compared to SS316L substrate steel (227 HV) with a maximum value of 726 HV observed for three‐molar composition. The fracture toughness exhibits an inverse correlation with the Al fraction with the highest value of around 49 MPa m^1/2 observed for Al_0.1CoCrFeNi coating. The equimolar coating composition shows lowest erosion rates among all the tested samples due to optimum combination of the mechanical properties. The erosion resistance of the equimolar coating is 2 to 5 times higher than steel substrate and around 1.5 times higher than the non‐equimolar counterparts depending upon the impingement angles.

     

Performance enhancement of visible light communication (VLC) system incorporating WMZCC-OCDMA codes and PDM-QPSK-DSP data encoding

Multi-user optical code division multiplexing (OCDMA) in visible light communication (VLC) is an imminent domain for providing an even distribution of available bandwidth and improved security. Q4R1Zero cross-correlation (ZCC) codes are widely reported, and improved performance is offered by them due to insignificant multiple access interference (MAI). However, practically, MAI exists in ZCC codes due to adjacent weights (W) in the code matrix rows for each user. Therefore, a novel ZCC code with a nonadjacent W is designed in this work to eradicate MAI limitations and is named weight managed ZCC codes (WMZCC). An indoor 100 Gbps/User OCDMA-VLC system is realised using polarisation division multiplexed quadrature phase shift keying (PDM-QPSK) and digital signal processing (DSP). Incorporation of DSP in the coherent receiver compensates the effects of dispersion and nonlinear effects and also performs phase estimation. Further, a state-of-the-art comparison of WMZCC codes with diagonal identity matrix (DIM) and zero cross-correlation resultant weight (ZCCRW) codes has been performed in terms of log symbol error rate (SER), Q factor, error vector magnitude percentage (EVM%) and log bit error rate (BER) log at different VLC lengths, Q4R1Transmitter half angles (THA), incidence half angles (IHA) and optical concentrators (cm²). Constellations are analysed with and without DSP, and according to the author's best knowledge, a 100 Gbps VLC system for five users covering 6 m at −3.42 log BER is demonstrated for the first time. Results revealed that weight management in WMZCC codes makes its performance improve as compared with ZCCRW and DIM codes.     

Novel space-vector-based harmonic elimination inverter control

This paper presents a novel space-vector-based pulsewidth modulation (PWM) strategy which closely approximates in “real time” the switching angles of the selective harmonic elimination PWM (HEPWM) strategy. The strategy uses only conventional regular-sampling techniques and does not require any of the intensive offline computations which are characteristic of optimized PWM strategies, thereby allowing a simple and efficient digital signal processor implementation     

Haematological and biochemical studies on experimental Theileria annulata infection in crossbred calves

The aim of the present study was to clarify the effects of O2 diffusion limitation resulting from hypoxic interventions on O2 uptake (V.O2) in unloaded (that is, near-zero initial force) and loaded skeletal muscle in a high-frequency stimulation. We measured V.O2, muscle venous PO2 (PvO2) and initial force in gastrocnemius-plantaris muscle in situ of anesthetized dogs: (1) during hypoxic hypoxia at 1 Hz tetanic stimulation, and (2) during hypoxia induced by the perfusion with high O2-affinity erythrocytes (having a low value of PO2 at 50% saturation of hemoglobin (P50)) at 4 Hz twitch stimulation. Averaged unloaded V.O2 during normoxia was 10.2 ml.min-1.100 g-1 at averaged blood flow of 74 ml.min-1.100 g-1 (n = 6). Hypoxic hypoxia of a decreased O2 delivery (arterial O2 concentration x flow) significantly decreased both unloaded and loaded V.O2 with a decrease in PvO2 (p<0.05). The unloaded V.O2 was reduced to 8.5 ml.min-1.100 g-1. Low P50-hypoxia decreased V.O2 at high and low initial force conditions with a decrease in PvO2 (p<0.05) at the same O2 delivery. If these decreases in V.O2 correspond with a decrease in V.O2 at zero initial force (unloaded V.O2), the unloaded V.O2 value is calculated to be 7.57 ml.min-1.100 g-1 from V. O2-initial force data. Despite the different conditions of O2 delivery, the unloaded V.O2 decreased by both hypoxia showed similar values. Thus the decreased unloaded V.O2 does not seem to be derived from only the limited O2 delivery. Some other factors such as the limitation of O2 diffusion may contribute to the decreased V.O2.