Using analytical electron microscopy of freeze-dried cryosections, physiologic elements were visualized within individual cells across the human inner stratum corneum. Human corneocytes undergo systematic changes in element composition as they advance through this region. Phosphorus is largely excluded from the stratum corneum, undergoing a precipitous drop in concentration at the granular/stratum corneum interface. The cellular potassium concentration has a profile similar to that of phosphorus but with a slower decline, thus migrating further into the stratum corneum. In contrast, the cellular chloride concentration increases in the innermost corneocyte layer, increases further in the subsequent layer or two (as potassium declines), and then decreases to values comparable to those in the innermost corneocyte. The cellular sodium concentration (per unit volume of tissue) is relatively unaltered in transit across the inner stratum corneum. The initial potassium and chloride movements are oppositely directed and have the appearance of creating an electrical charge imbalance. The position-dependent alterations in corneocyte elemental composition may reflect sequential stages of chemical maturation occurring intracellularly during stratum corneum transit, an example of which is the breakdown of filaggrin that occurs over this same region of the inner stratum corneum.
Sir:In spite of considerable evidence in support of the transient existence of substituted silaethenes,' direct evidence for the intermediacy of the parent compound, [H2Si=CH2] (la), is lacking. Since l a has been implicated as a product in the vacuum-ultraviolet photolysis of methylsilane,2 and since it has been the subject of several theoretical ~t u d i e s ,~ definitive evidence for just the formation of l a would be of considerable value. Additional information concerning the chemical behavior of l a would help to answer the following question: "Is the general chemical behavior of [H2Si=CH2] similar to that reported for its di-, tri-, and tetrasubstituted derivatives?"We wish to report the first generation of la, a very reactive transient intermediate, which can be chemically trapped when generated in the presence of a suitable substrate. Gas phase thermolysis (560°, nitrogen flow system) of silacy~lobutane~ generates l a as indicated in eq 1. When
HzSQ
[H,Si=CHJ + CH2=CHz(1) la generated in the absence of a trapping reagent l a forms an intractable, high molecular weight polymer. However, if silacyclobutane is copyrolyzed with a suitable trapping reagent, reasonable yields of 1 : 1 adducts (or their derivatives) are obtained as indicated in Scheme I. The reaction produ c t~~ of [H2Si=CH2], presented in Scheme I together with those of the more thoroughly studied 1,l-dimethyl-1-silaethene,Ib in our opinion provide convincing evidence for the existence of [H2Si=CH2] as a transient intermediate.The reactions summarized in Scheme I indicate that both [H2Si=CH2] (la) and [Me2Si=CH2] (lb) show similar behavior toward more reactive trapping reagents such as Ph2C=O and (Me2Si0)3.6 However, l a reacts differently than l b when generated either in the presence of less reactive substrates such as CH3CN or Sic14 or in the absence of a trapping reagent. Under these conditions l a does not form appreciable quantities of either a 1:l adduct or volatile selfcondensation products such as ( H~S~C H Z ) , , ( n = 2, 3, or 4),
N2Scheme I R /CH2\
A selective synthesis for both 1-and 4-alkyl vinyl itaconate regioisomers is presented. Polymerization experiments with these two monomers reveal that only 4-vinyl itaconic acid (3a) and 1-alkyl 4-vinyl itaconates (e.g., 8) lead to cyclopolymers. A synthesis of the -lactone repeating unit found in the cyclopolymer confirms the structure and stereochemistry of the polymer.Recently, there has been growing synthetic interest in the use of free radical cyclizations to prepare five-membered rings. This approach has been utilized, for example, to construct small carbocycles such as alkaloids,1,2 lactams,1 23
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