Commonly used H2S donors include the inorganic salts sodium sulfide (Na2S) and sodium hydrosulfide (NaHS) that cause a transient spike in H2S concentration when dissolved. Slow-release donors have been synthesized, including numerous water-soluble molecules such as GYY4137, and anethole trithione hydroxide (ADT-OH) complexes. Naturally occurring compounds are useful H2S donors, including diallyl disulfide and diallyl trisulfide from garlic, and sulforaphane from broccoli. Applied cysteine analogs thereof such as S-propyl cysteine, and other sulfur-donating molecules like 3-mercaptopyruvate, have a stimulatory effect on endogenous H2S production.
A new synthetic process was developed later by Campbell,321 in which high-molecular-weight PPS (Mn = 35 000–65 000) were obtained directly during polymerization without the postcuring process. The new process involved the use of an alkali metal carboxylate as a polymerization modifier and eliminated the need of curing process in the above-mentioned conventional process to obtain high molecular weight. It has been reported that an soluble polymer with even higher molecular weight of 200 000 could be prepared by the incorporation of a very small amount of a 1,2,4-trichlorobenzene as a comonomer into the polymerization recipe. The mechanism of Campbell’s reaction was traditionally considered to be a nucleophilic substitution. Instead, Heitz et al.12,322 have proposed a one-electron-transfer process, with radical cations as reactive intermediates. However, the general characteristics and responses to reaction variables for this mechanism have not yet been firmly established.
A more recent example of using SNAr polymerization to synthesize poly(arylene sulfide)s was reported by Robb and Knauss323 Poly(thianthrene phenylene sulfide) and poly(thianthrene sulfide) containing the thermally stable thianthrene group were synthesized from the activated monomer 2,7-difluorothianthrene with bis-thiophenoxide and sulfide nucleophiles. The corporation of thianthrene group afforded a variety of potentially useful material properties, such as excellent thermal and thermooxidative characteristics.
In early research on H2S biology, inorganic and organic H2S donors were used in experimental settings. Inorganic salts such as sodium sulfide (Na2S) and sodium hydrosulfide (NaHS) cause a transient spike in H2S concentration when they dissociate in solution.15 There are a number of organic molecules capable of increasing H2S levels, including substrates of H2S-generating enzymes, molecules that liberate H2S spontaneously or after bioactivation, and hybrid molecules that contain an H2S-donating moiety (e.g., anethole dithiolethione-OH and thiobenzamide) conjugated to a known drug. Synthetic H2S donors include 4-methoxyphenyl (morpholino) phosphinodithioate-morpholinium salt (GYY4137), thio-aminoacids (thioglycine and l-thiovaline), N-(benzoylthio) benzamides, and, more recently, dithioper-oxyanhydrides. Naturally occurring compounds such as diallyl disulfide and diallyl trisulfide from garlic and sulforaphane from broccoli have been used as H2S donors.15 There is now an extensive array of new H2S donors in the form of hybrids of H2S with established drug classes and small molecules, and engineered H2S delivery platforms such as nanoparticles, fibers, and polymers.