K intermediate

An intere.sting example in the context of waste minimization is the manufacture of the vitamin K intermediate, menadione. Traditionally it was produced by stoichiometric oxidation of 2-methylnaphthalene with chromium trioxide (Eqn. (8)), which generates 18 kg of solid, chromium containing waste per kg of menadione. Catalytic alternatives have been reported, but selectivities tend to be rather low owing to competing oxidation of the second aromatic ring (the. selectivity in the classical process is only 50-60%). The best results were obtained with a heteropolyanion as catalyst and O2 as the oxidant (Kozhevnikov, 1993). 

Anti-Stokes picosecond TR spectra were also obtained with pump-probe time delays over the 0 to 10 ps range and selected spectra are shown in Figure 3.33. The anti-Stokes Raman spectrum at Ops indicates that hot, unrelaxed, species are produced. The approximately 1521 cm ethylenic stretch Raman band vibrational frequency also suggests that most of the Ops anti-Stokes TR spectrum is mostly due to the J intermediate. The 1521 cm Raman band s intensity and its bandwidth decrease with a decay time of about 2.5 ps, and this can be attributed the vibrational cooling and conformational relaxation of the chromophore as the J intermediate relaxes to produce the K intermediate.This very fast relaxation of the initially hot J intermediate is believed to be due to strong coupling between the chromophore the protein bath that can enable better energy transfer compared to typical solute-solvent interactions. ... 

The picosecond TR experiments described above for BR reveal that a hot unrelaxed J intermediate with a highly twisted structure forms and then vibrationally cools and conformationally relaxes within 3ps to form the K intermediate. Subsequently, an isomerization induced protein conformational change takes place during 20-100 ps to produce the KL inermediate. ... 

Dynamic nuclear polarisation (DNP) enhanced 15N CP MAS NMR has been exploited by Mark-Jurkauskas et al.79 in the studies of intermediates of the bacteriorhodopsin photocycle. The data for L intermediate were similar to those found for 13-ds,15-anti retylidene chloride, while those for K intermediate were similar to those of acid blue bacteriorhodopsin in which the Schiff base counterion was neutralised (Table 3). The 15N chemical shifts observed have shown that for bacteriorhodopsin, the Schiff base in K intermediate state loses contact with its counterion and establishes a new one in L intermediate state. The proton energy stored at the beginning in the electrostatic modes has been transformed to torsional modes. The transfer of energy is facilitated by the reduction of bond order alternation in the polyene chain when the counterion interaction is initially broken and is driven by the attraction of the Schiff base to a new counterion. 3D CP MAS experiments of NCOCX, NCACX, CONCA and CAN(CO)CA types have been used in studies of proteorhodopsin.71... 

In terms of temperature regions, low-temperature combustion occurs over the range 298-550 K, whereas high-temperature combustion mechanisms dominate at temperatures over 1000 K. Intermediate temperatures, from 550 to 700 K, demonstrate an unusual phenomenon called the negative temperature coefficient (NTQ, which is observed for methane and larger hydrocarbon fuels. As shown in Fig. 3, when the correct alkylperoxy radical chemistry is included in a fuel s combustion mechanism, a NTC range exists (Fig. 3, plot C) where an increase in temperature causes a decrease... 

A palladium(II)-exchanged polystyrene sulfonic acid resin (Dowex 50W, H form) catalyzes the oxidation of 2-methylnaphthalene with 60% aqueous H2O2 (reaction 27), affording 2-methyl-l,4-naphthoqu1none (menadione) in 55-60% yield at 90-97% conversion. 3 Menadione is a commercially important vitamin K intermediate and these results compare favourably with those obtained in existing industrial processes that employ stoichiometric quantities of chromium trioxide in sulfuric acid. 

Generally speaking, s can be tended to zero by various methods without assuming S, bs, and bg to be constant. In this case, many different asymptotes arise. Their difference is associated with the fact that, at given 9 and cg, the values of w are independent of bs and be and the equations for "slow motions [the first part of eqn. (148)] contain parameters 1/S and bg/S. For example, at fixed bg, S and V, bs can be tended to zero ba -> 0. Then the rates of elementary reactions which are linear with respect to intermediates, will have an order of smallness e. But if the reaction also involves the participation of k intermediates as initial reactants, the order of smallness for w is equal to ek. Let kmin be the lowest order with respect to intermediates that can... 

Table 22 Different contributions to the final transition moment T <— So for free ethylene. Transition moments are shown for both the triplet and singlet manifold of states. 0 denotes ground, k intermediate and f the final states. The last two columns describe the final contribution to the transition moment from state k. Term(k) is the k+l th term of the final sum and Sum(k) is the accumulative term. AEk is equal to 3Ek —1 Eo for the triplet manifold and equal to -3 E for the singlet manifold.

Fig. 25.11. Sankey energy flow diagram for a 1000ton/day sulfur-burning double absorption sulfuric acid plant (feed gas 10% S02). A Blower B Sulphur furnace C Waste heat boiler D Catalyst bed 1 E Steam superheater F Catalyst bed 2 G Boiler H Catalyst bed 3 J Intermediate heat exchangers K Intermediate absorber L Converter bed 4 M Economizer N Final absorber O Air dryer P Acid coolers. (Courtsey Lurgi GmbH, Frankfurt, Germany.)...

QKO/1QKP Wild type, low temperature K intermediate with 35 % occupancy 2.1 X-ray, CLP... 

At 77 K, the K intermediate is stable for several minutes. A static BR-K difference spectrum is obtained as follows 1) in the dark, cool the sample to 77 K 2) obtain... 

Example 4.3. Radioactive decay. A long-lived radioisotope A decays the k intermediates X, X2, etc., are very short-lived the final product P is stable ... 

Schiffs base, but the spectra for the M-412 intermediate indicate that this proton is lost. The deprotonation of the Schiffs base is apparently after the K intermediate [262], and proposed to be during the L to M transition [209,263,264], Reprotonation of the nitrogen is suggested to occur during the M-412 to 0-640 conversion [265], Part of the blue-shift in the formation of M-412 is, of course, explained by the fact that, in model retinal compounds, loss of the proton leads to a 440-380 nm shift [266], but other effects must also be present. Circumstantial evidence, which includes the finding of 13-cis retinal in M-like intermediates stabilized under somewhat denaturing conditions [198,267], favors the idea that the retinal is isomerized in the M intermediate, as do the more direct resonance Raman data [268,269], In fact, the K and L intermediates seem already to contain the 13-c/i isomer of retinal, as indicated by extraction of 13-c/i retinal from the L intermediate [270] and spectroscopic data on the K and L intermediates [271-274], The resonance Raman spectroscopy of bacteriorhodopsin photointermediates has been recently reviewed [275],... 

Extraction of the proton allows the carboxylase to carbox-ylate the glutamate residue. The vitamin K intermediate is converted to vitamin K oxide, which must be reduced back to vitamin K. Vitamin K oxide is recycled back to vitamin K by vitamin K epoxide reductase arid vitamin K quinone reducta.se. Both of these enzymes are dithiol dependent and are inhibited by the 4-hydroxycoumarin anticoagulants. 

Imai et al. [83] studied the reduction of NO by carbon present in activated carbon fibers. Particles of a-FeOOH were present on the fibers in order to absorb NO in a dimerized form. Iron hydroxide enhances NO decomposition and N2 formation at 473 K. Intermediate steps were the disproportionation of NO into N2O and NO2. NO2 was reduced by carbon to CO2 and NO again. 

Unlike visual rhodopsins that bleach upon illumination, archaeal rhodopsins exhibit photocycle. This is highly advantageous in ultrafast spectroscopic studies and these techniques have been extensively applied in addition to low-temperature spectroscopy [2,12,13]. In particular, bacteriorhodopsin has been regarded historically as the model system to test new spectroscopic methods. As in visual rhodopsins, the light absorption of archaeal rhodopsins causes formation of red-shifted primary intermediates [68]. The primary K intermediate can be stabilized at 77 K. Time-resolved visible spectroscopy of bacteriorhodopsin reveals the presence of the precursor, called the J intermediate [12,13]. The J intermediate is more red-shifted (7.max -625 nm) than the K intermediate (2rn ix -590 nm). The excited state of bacteriorhodopsin possesses blue-shifted absorption, which decays nonexpo-nentially. The two components of the stimulated emission decay at about 200 and 500 fs [69]. The J intermediate is formed in <500 fs, and converted to the K intermediate within 3 ps [12,69]. 

Fuchs E, Weber K. Intermediate filaments Structure, dynamics, 77. function and disease. Ann Rev Biochem. 1994 63 345-382. 

R)-(+)-C1tronella1 Is a useful, k Intermediate for the preparation of several Important, optically active compounds such as citronellol, 1-menthol, muscone, and a-tocopherolThe optical purity of citronellal from natural sources Is at most 77% ee, however. This new procedure gives (R)- +)-cltronellal of high optical purity (over 95% ee). 

---