Efficient Chemical and Enzymatic Syntheses of FAD Nucleobase Analogues and Their Analysis as Enzyme Cofactors**

Flavin adenine dinucleotide (FAD) is an essential redox cofactor in cellular metabolism. The organic synthesis of FAD typically involves coupling flavin mononucleotide (FMN) with adenosine monophosphate, however, existing synthesis routes present limitations such as multiple steps, low yields, and/or difficult-to-obtain starting materials. In this study, we report the synthesis of FAD nucleobase analogues with guanine/cytosine/uracil in place of adenine and deoxyadenosine in place of adenosine using chemical and enzymatic approaches with readily available starting materials, achieved in 1–3 steps with moderate yields (10–57 %). We find that the enzymatic route using Methanocaldococcus jannaschii FMN adenylyltransferase (MjFMNAT) is versatile and can produce these FAD analogues in high yields. Further, we demonstrate that Escherichia coli glutathione reductase is capable of binding and using these analogues as cofactors. Finally, we show that FAD nucleobase analogues can be synthesized inside a cell from cellular substrates FMN and nucleoside triphosphates by the heterologous expression of MjFMNAT. This lays the foundation for their use in studying the molecular role of FAD in cellular metabolism and as biorthogonal reagents in biotechnology and synthetic biology.     

Effect of chromium on the mechanical properties of powder-processed Fe–0.45 wt.% P alloys

The present investigation shows the role of chromium in Fe–P binary and Fe–P–Cr ternary alloys. The compositions are characterized in terms of microstructure, porosity content, hardness and tensile properties. The alloys were made using a hot powder forging technique. In this process mild steel encapsulated powders were hot forged into slabs. Then the slabs were hot rolled and annealed to relieve the residual stresses. Densifications as high as 98.9% of theoretical density have been realized. Microstructures of these alloys consist of single-phase ferrite only. Both Fe–0.45P and Fe–0.45P–3Cr alloys showed very high strength. As forged and hot rolled Fe–0.45P alloy showed low elongation. It was observed that, the addition of Cr to Fe–P based alloys caused an increase in strength associated with the reduction in ductility. Alloys developed in the present investigation were capable of hot working to very thin gage of sheets and wires.     

Modeling and Testing for Timing Faults in Synchronous Sequential Circuits

Even with proper design, integrated circuits and systems can have timing problems because of physical faults or variation of parameters. The authors introduce a fault model that takes into account timing related failures in both the combinational logic and the storage elements. Using their fault model and the system's requirements for proper operation, the authors propose ways to handle flipflop-to-flipflop delay, path selection, initialization, error propagation, race-around, and anomalous behavior. They discuss the advantages of scan designs like LSSD and the effectiveness of random delay testing.     

Low cycle fatigue behavior of Ti-6AI-2Sn-4Zr-6Mo: Part II. Cyclic deformation behavior and low cycle fatigue

A series of strain-controlled low cycle fatigue tests have been carried out on Ti-6-2-4-6 at room temperature primarily for solution-treated and aged material. Tension-compression testing at R = 1 produced softening, irrespective of the morphology of the primary α. The amount of softening increased with increasing strain. Tension-tension testing for R = 0 produced strengthening. Unaged specimens showed behavior similar to aged material for both R = ?1 and R = 0 testing. Annealing at 621 °C produced hardening for R = ?1 and softening for R = 0 testing. Aging at 210 °C of R = ?1 specimens produced strengthening. Fatigue life data revealed longer fatigue life for equiaxed (E) structures than for Widmanstätten plus grain boundary (W +GB)α structures. ForEα, increasing α particle size tends to reduce fatigue life. For W +GBα alloys the situation is more complex, and both a decrease and increase in fatigue life may be seen for increasing particle sizes. There is also a prior β grain size dependency. As a result of softening, the slope of the log Δε _p/2 vs logN _f curve continuously decreases with increasingN. Explanations of the softening and hardening behavior in terms of dislocation rearrangement are offered. An explanation of the role of microstructure on fatigue life has been offered in the companion paper.     

Optimization of test parallelism with limited hardware overhead

The main considerations for built-in self-test (BIST) for complex circuits are fault coverage, test time, and hardware overhead. In the BIST technique, exhaustive or pseudo-exhaustive testing is used to test the combinational logic in a register sandwich. If register sandwiches can be identified in a complex digitial system, it is possible to test several of them in parallel using the built-in logic block observation (BILBO) technique. Concurrent built-in logic block observation (CBILBO) technique can further improve the test time, but it requires significant hardware overhead. A systematic scheduling technique is suggested to optimize parallel tests of register sandwiches. Techniques are proposed to deal with shared registers for parallel testing. The proposed method attempts to reduce further the test time while only modestly increasing the hardware overhead.     

2-nitroglycals as powerful glycosyl donors: application in the synthesis of biologically important molecules

[Reaction: see text]. The biological significance of oligosaccharides and glycoconjugates is profound and wide-ranging. For example, the mucins have attracted attention because of their role in fundamental cellular processes such as fertilization, parasitic infection, inflammation, immune defense, cell growth, and cell-cell adhesion. Increased expression of mucins is implicated in malignant transformation of cells. Antifreeze glycoproteins also are of interest because they are important for the survival of many marine teleost fishes that live in polar and subpolar waters. The synthesis of glycoconjugates requires methods for glycoside bond formation, the most difficult aspect of which is the assembly of monosaccharide building blocks. This Account discusses a valuable addition to the repertoire of methods for glycoconjugate synthesis: an approach that involves 2-nitroglycal concatenation. For a long time, methods for glycosylation via glycosyl donor generation required either an anomeric oxygen exchange reaction or anomeric oxygen retention. In the case of an anomeric oxygen exchange reaction, activation of the glycosyl donors demands a promoter in at least equimolar amounts. However, anomeric oxygen retention, such as base-catalyzed formation of O-glycosyl trichloroacetimidates, can be activated by catalytic amounts of acid or Lewis acid. Alternatively, glycals, which are readily available from sugars, can be an attractive starting material for glycoside bond formation. Their nucleophilic character at C-2 permits reactions with oxygen, nitrogen, and sulfur electrophiles that under high substrate stereocontrol generally lead to three-membered rings; ring opening under acid catalysis furnishes the corresponding glycosides, whichdepending on the electrophile Xare also employed for 2-deoxyglycoside synthesis. Glycals also can be transformed into derivatives that have at C-2 an electron-withdrawing group and are amenable to Michael-type addition. A good example are 2-nitroglycals. In this case, glycoside bond formation is achieved under base catalysis and leads to 2-deoxy-2-nitroglycosides. These intermediates are readily converted into 2-amino-2-deoxyglycosides, which are constituents of almost all glycoconjugates. This 2-nitroglycal concatenation has been extensively investigated with 2-nitrogalactal derivatives. When alcohols are used as nucleophiles and strong bases used as catalysts, the result is primarily or exclusively the alpha-galacto-configured adducts. Some studies show that weaker bases may lead to preferential formation of the beta-galacto-configured products instead. The reaction was very successfully extended to other nucleophiles and also to other 2-nitroglycals that undergo base-catalyzed stereoselective Michael-type additions. Thus, 2-nitroglycals are versatile synthons in glycoconjugate and natural-products synthesis, and it is foreseeable that many more applications will be based on these readily available and highly functionalized skeletons.     

Effect of chromium on the corrosion behaviour of powder-processed Fe-0.45wt% P alloys

The corrosion behaviour of Fe-0.45P with/without addition of chromium, prepared by powder forging route was studied in different environments. The corrosion studies in acidic (0.25M H₂SO₄ solution of pH 0.6) and neutral/marine (3.5% NaCl solution of pH 6.8) solutions were conducted using Tafel Extrapolation method. The rate of corrosion in alkaline medium (0.5M Na₂CO₃ + 1.0M NaHCO₃ solution of pH 9.4) was measured using linear polarization technique. The studies compare electrolytic Armco iron with Fe-P alloys. It was observed that, chromium improved the resistance to corrosion in acidic and marine environments. The corrosion rates were minimal in alkaline medium and low in neutral solution.     

Fuel wood consumption pattern of tribal communities in cold desert of the Lahaul valley, North-Western Himalaya, India

Fuel wood is the primary source of energy in rural areas of the Himalaya. Lack of resources, extremely low temperature and xeric climatic conditions of the study region (Khoksar – 3200 m, Jahlma – 3000 m, Hinsa – 2700 m and Kuthar – 2600 m) of cold desert of the Lahaul valley has led to serious deforestation due to excessive use of fuel wood in the past. On the basis of family sizes, fuel wood consumption was recorded less in large family as compared to small family. The fuel wood is used for various activities such as cooking, water heating, room heating, lighting and livestock rearing, etc. Fuel wood consumption was highest in high altitude villages as compared to low altitude villages irrespective of family size. Fuel wood consumption of 4.32 ± 0.99 kg/capita/day was highest at Khoksar for small family during winter season followed by the autumn (2.25 ± 0.15 kg/capita/day) and summer (1.38 ± 0.13 kg/capita/day). The labour energy expenditure for fuel wood collection was also highest for Khoksar (91.91 MJ/capita/year), followed by Hinsa (61.29 MJ/capita/year), Kuthar (52.01 MJ/capita/year) and Jahlma (51.89 MJ/capita/year), respectively. It was found that fuel wood consumption in the study region was influenced by the local cold climate and season of the year. The present information on fuel wood consumption pattern at different altitudes would be helpful in designing appropriate technologies to develop energy plantations in the region.     

Assessing vulnerability exploitability risk using software properties

Attacks on computer systems are now attracting increased attention. While the current trends in software vulnerability discovery indicate that the number of newly discovered vulnerabilities continues to be significant, the time between the public disclosure of vulnerabilities and the release of an automated exploit is shrinking. Thus, assessing the vulnerability exploitability risk is critical because this allows decision-makers to prioritize among vulnerabilities, allocate resources to patch and protect systems from these vulnerabilities, and choose between alternatives. Common vulnerability scoring system (CVSS) metrics have become the de facto standard for assessing the severity of vulnerabilities. However, the CVSS exploitability measures assign subjective values based on the views of experts. Two of the factors in CVSS, Access Vector and Authentication, are the same for almost all vulnerabilities. CVSS does not specify how the third factor, Access Complexity, is measured, and hence it is unknown whether it considers software properties as a factor. In this work, we introduce a novel measure, Structural Severity, which is based on software properties, namely attack entry points, vulnerability location, the presence of the dangerous system calls, and reachability analysis. These properties represent metrics that can be objectively derived from attack surface analysis, vulnerability analysis, and exploitation analysis. To illustrate the proposed approach, 25 reported vulnerabilities of Apache HTTP server and 86 reported vulnerabilities of Linux Kernel have been examined at the source code level. The results show that the proposed approach, which uses more detailed information, can objectively measure the risk of vulnerability exploitability and results can be different from the CVSS base scores.     

Effect of carbon on corrosion resistance of powder-processed Fe-0·35%P alloys

The corrosion behaviour of phosphoric irons containing 0.35 wt % P, 2% copper, 2% nickel, 1% silicon, 0.5% molybdenum, with/without 0.15% carbon prepared by powder forging route were studied in different environments. The various environments chosen were acidic (0.25 M H₂SO₄ solution of pH 0.6), neutral/marine (3.5% NaCl solution of pH 6.8) and alkaline (0.5 M Na₂CO₃ + 1.0 M NaHCO₃ solution of pH 9.4). The corrosion studies were conducted using Tafel extrapolation and linear polarization methods. The studies also compare Armco iron with phosphoric irons. It was observed that the addition of carbon improved the corrosion resistance of a Fe-0.35%P-2%Ni-2%Cu-1%Si-0.5%Mo alloy in all the environments. Corrosion rates were highest in acid medium, minimal in alkaline medium and low in neutral solution. SEM/EDAX was used to characterize the compositions.