Biomimetic polyorganosiloxanes: model compounds for new materials

Abstract

The chemistry of N-organosilylalkyl-substituted heterocyclic bases (thymine, adenine and cytosine) is described, covering the structures of model compounds, the synthesis of substituted oligo-siloxanes and a preliminary report of the synthesis of a poly(organosiloxane) with pendant N-alkyl(heterocycle) functionalities. N-Alkenylthymines CH2=CH(CH2)(n)T (T = thymine, n = 1 (1), 2 (2), 3 (3)) have been prepared and 2 hydrosilylated to form PhMe2Si(CH2)4T (5). Alternatively, 5 was prepared by reaction of PhMe2Si(CH2)4Br (6) with (O,O-SiMe3)2T, a method which has also been used to prepare PhMe2Si(CH2)4A (7) and PhMe2Si(CH2)4C (8) (A = adenine, C = cytosine). Model di- and tri-siloxanes [Br(CH2)4(Me)2Si]2O (10), Me3SiOSi(Me)2(CH2)4Br (11), PhMe2SiOSi(Me)2(CH2)4Br (12) and (Me3SiO)2(Me)Si(CH2)4Br (13) have been prepared by hydrosilylation of H2C[double bond, length as m-dash]C(H)(CH2)4Br with an appropriate hydrosiloxane and used to prepare Me3SiO(Me)2Si(CH2)4T (14), Me3SiO(Me)2Si(CH2)4A (15) (both from 11), and (Me3SiO)2(Me)Si(CH2)4T (16), (Me3SiO)2(Me)Si(CH2)4A (17) (both from 13). 10 reacts with thymine to give a mixture of the pyrimidocyclophane cyclo-T-N,N-[(CH2)4(Me)2Si]2O (19) and [T(CH2)4Si(Me)2]2O (20), while cytosine reacts similarly to form cyclo-C-N,N-[(CH2)4(Me)2Si]2O (21; as an imine) and [C(CH2)4Si(Me)2]2O (22); adenine only generates [A(CH2)4Si(Me)2]2O (18) in an analogous synthesis. Using a related protocol, polymeric {[MeSi(O)(CH2)4Br]2[Me2SiO]98}n (23) has been converted to {[MeSi(O)(CH2)4T]2[Me2SiO]98}n (24) and {[MeSi(O)(CH2)4A]2[Me2SiO]98}n (25). The structures of 4, 5, 8, 19 and 21, along with a 2 : 1 adduct of 5 with Ni(dithiobiuret)2 (9) are reported.

Noncovalent Bonds through Sigma and Pi-Hole Located on the Same Molecule. Guiding Principles and Comparisons

“…As examples, understanding the forces behind crystal engineering and supramolecular chemistry benefits from a knowledge of σ-hole interactions due to their directionality, strength, and selforganization properties which promote formation of adducts in the solid state [34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52]. The importance of σ-hole bonding has also been verified in the context of anion recognition processes [53][54][55][56][57][58][59][60][61], materials chemistry [62][63][64][65][66][67][68][69][70][71][72], or biochemistry [73][74][75][76][77][78][79][80][81]. An early work connecti...…”

“…The full range of these sorts of bonds, along with their designations, is summarized in Figure 1. processes [53][54][55][56][57][58][59][60][61], materials chemistry [62][63][64][65][66][67][68][69][70][71][72], or biochemistry [73][74][75][76][77][78][79][80][81]. An early work connecting σ-hole bonds with crucial concepts in chemistry occurred when Grabowski recognized that tetrel bonds can be thought of as a preliminary stage of the very important SN2 reaction [82].…”

The Structures of Uncommon Cationic N‐alkenyl Purine and Pyrimidine Bases

“…Despite the use of excess allyl bromide, the bis‐allylation of the bases was unexpected based on our previous experience of this type of reaction with thymine . In both cases the yield is very low, and it might be assumed that the recovered products are minor to other unrecovered species.…”

“…The THF and excess allyl bromide were then removed by reduced pressure and the oil recrystallised once from chloroform to yield 0.11 g of the product 1,3-bis-allylcytosinium bromide (1) as sparingly soluble, air stable, white crystals (9%). 1 7,9 Bis-(allyl)adeninium bromide hydrate (2). Prepared by the same method using bis-(trimethylsilyl)-adenine[1] (5.00 g, 37 mmol) and allyl bromide (11.90 g, 132 mmol).…”

“…We have an on‐going interest in the chemistry of organosiloxane polymers with appended DNA bases in order to harmonize the known beneficial material properties of these polymers with the ability of DNA bases to introduce order through complementary hydrogen bonds . As part of this work, we have had cause to synthesize allyl‐subsituted purine and pyrimidine bases, which, on further hydrosilylation reactions, generate model, organosilyl‐substitued DNA bases . As part of this work, we have isolated three unusual derivatives of cytosine and adenine, which include unique bis‐(allyl)cytosinium or adeninium cations or a (butenyl)adeninium cation with mono‐addition at the unusual N ‐3 site.…”