Effective generation

With eveiy change in ion concentration, there is an electrical effect generated by an electrochemical cell. The anion membrane shown in the middle has three cells associated with it, two caused by the concentration differences in the boundaiy layers, and one resulting from the concentration difference across the membrane. In addition, there are ohmic resistances for each step, resulting from the E/I resistance through the solution, boundary layers, and the membrane. In solution, current is carried by ions, and their movement produces a fric tion effect manifested as a resistance. In practical applications, I R losses are more important than the power required to move ions to a compartment wim a higher concentration. 

In transforming bis-ketone 45 to keto-epoxide 46, the elevated stereoselectivity was believed to be a consequence of tbe molecular shape — tbe sulfur ylide attacked preferentially from tbe convex face of the strongly puckered molecule of 45. Moreover, the pronounced chemoselectivity was attributed to tbe increased electropbilicity of the furanone versus the pyranone carbonyl, as a result of an inductive effect generated by tbe pair of spiroacetal oxygen substituents at tbe furanone a-position. ... 

A natural question to ask is whether the basic model can be modified in some way that would enable it to correctly learn the XOR function or, more generally, any other non-linearly-separable problem. The answer is a qualified yes in principle, all that needs to be done is to add more layers between what we have called the A-units and R-units. Doing so effectively generates more separation lines, which when combined can successfully separate out the desired regions of the plane. However, while Rosenblatt himself considered such variants, at the time of his original analysis (and for quite a few years after that see below) no appropriate learning rule was known. 

The setup in Figure 1-7 becomes an effective generator of nearly monochromatic x-rays when various elements inserted in the sample position are irradiated by x-rays of energy sufficient to excite the characteristic spectra that is, when by x-ray excitation the characteristic... 

The steric effect generated by the gem-dimethyl group of the thietane ring on the adjacent sp2 carbon atom makes the cycloaddition in these cases more sluggish compared with those of the parent thietane dioxide (6b)190. These cycloadditions provide a convenient entry into the strained thiabicyclo [2.2.0] hexane system (e.g. 287, 288 equation 107). 

A further importance of cysteines lies in the palmitoylation of chemokine receptors. Many chemokine receptors have cysteine residues in their carboxy-terminal regions. In other GPCRs, these have been implicated in palmitoylation and in the anchoring of the carboxy-terminus to the plasma membrane. This effectively generates a fourth intracellular loop in the receptors. Studies on CCR5 have identified a three-cysteine cluster in the carboxy-terminus that is... 

Ah/At = 7.4 and A /Ax = 1.8 and isotopic activation energy differences that are within the experimental error of zero. The values of the two A-ratios correspond to a Swain-Schaad exponent of 3.4, not much different from the semiclassical expectation of 3.3. The a-secondary isotope effects are 1.19 (H/T), 1.13 (H/D), and 1.05 (D/T), which are exactly at the limiting semiclassical value of the equilibrium isotope effect. The secondary isotope effects generate a Swain-Schaad exponent of 3.5, again close to the semiclassical expectation. At the same time that the isotope effects are temperature-independent, the kinetic parameter shows... 

The books, however, cannot yet be closed. Although the flexibilities of the yeast enzyme at 25 °C and thermophilic enzyme at 65 °C are similar, and although both show unmistakeable evidence of tunneling, the nature of the tunneling process appears to be different. This is another instance in which the temperature dependences of the isotope effects generate a complex and ill-understood picture. 

The halogen molecule is comprised of two halogen atoms each with seven electrons in their outer shell. Sharing of the unpaired electrons creates a stable molecule in which each atom has now acquired an octet of electrons in its outer shell. By absorbing energy, we have removed this stabilization and effectively generated halogen atoms, which are our radicals. 

The nucleophile in biological Claisen reactions that effectively adds on acetyl-CoA is almost always malonyl-CoA. This is synthesized from acetyl-CoA by a reaction that utilizes a biotin-enzyme complex to incorporate carbon dioxide into the molecule (see Section 15.9). This has now flanked the a-protons with two carbonyl groups, and increases their acidity. The enzymic Claisen reaction now proceeds, but, during the reaction, the added carboxyl is lost as carbon dioxide. Having done its job, it is immediately removed. In contrast to the chemical analogy, a carboxylated intermediate is not formed. Mechanistically, one could perhaps write a concerted decarboxylation-nucleophilic attack, as shown. An alternative rationalization is that decarboxylation of the malonyl ester is used by the enzyme to effectively generate the acetyl enolate anion without the requirement for a strong base. 

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