The recent advances in nanotechnology and the corresponding increase in the use of nanomaterials in products in every sector of society have resulted in uncertainties regarding environmental impacts. The objectives of this review are to introduce the key aspects pertaining to nanomaterials in the environment and to discuss what is known concerning their fate, behavior, disposition, and toxicity, with a particular focus on those that make up manufactured nanomaterials. This review critiques existing nanomaterial research in freshwater, marine, and soil environments. It illustrates the paucity of existing research and demonstrates the need for additional research. Environmental scientists are encouraged to base this research on existing studies on colloidal behavior and toxicology. The need for standard reference and testing materials as well as methodology for suspension preparation and testing is also discussed.

Nanomaterials in the environment: Behavior, fate, bioavailability, and effects

Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

Asymmetric 1,3-Dipolar Cycloaddition Reactions

One of the initial steps in the development of therapeutic agents is the identification of lead compounds that bind to the receptor or enzyme target of interest. Many analogs of these lead compounds are then synthesized to define the key recognition elements for maximal activity. In general, many compounds must be evaluated in both the lead identification and optimization steps. Increasing burdens have been placed on these efforts due to the large number of new therapeutic targets that continue to be identified thorough modern molecular biology methods.1 To address this demand, very powerful chemical and biological methods have been developed for the generation of large combinatorial libraries of peptides2 and oligonucleotides3 that are then screened against a receptor or enzyme to identify high-affinity ligands or potent inhibitors, respectively. While these studies have clearly demonstrated the power of library synthesis and screening strategies, peptides and oligonucleotides generally have poor oral activities and rapid in vivo clearance;4 therefore their utility as bioavailable therapeutic agents is often limited. Due to the favorable pharmacokinetic properties of many small organic molecules (<600-700 molecular weight),5 the design, synthesis, and evaluation of libraries of these compounds6 has rapidly become a major frontier in organic chemistry. Lorin A. Thompson was born in Lexington, KY, in 1970. He received the Bachelor of Science degree from the University of North Carolina, Chapel Hill, in 1992 where he worked under the guidance of Joseph Desimone. He is currently pursuing his doctorate in the laboratory of Jonathan Ellman at UC Berkeley where he is the 1994 Glaxo-Wellcome fellow. His research interests include the development of synthetic methodology for organic library construction.

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Synthesis and Applications of Small Molecule Libraries.

1,2-Amino Alcohols and Their Heterocyclic Derivatives as Chiral Auxiliaries in Asymmetric Synthesis

Benzoyl (1) and thiobenzoyl isocyanates (2) reacted with benzaldehyde arylhydrazones and methylhydrazone to give the corresponding semicarbazones as isolated products respectively. In the reactions with acetone arylhydrazones and methylhydrazone, however, the s-triazolidin-5-ones whose structures corresponded to the ring tautomers of semicarbazones, were isolated as sole products from the reaction of 1, and 2 afforded the (4+2) cycloadducts of 2 to the C=N bond of hydrazones and s-triazolidin-5-ones. It has been found that in some cases, the semicarbazones isomerize into their ring tautomers, and the isomerization obeys good first-order kinetics taking into account the equilibrium. Although 1 did not react with p-tosyl- and benzoylhydrazones, 2 easily added to both hydrazones to yield the corresponding (4+2) cycloadducts.

Studies of Acyl and Thioacyl Isocyanates. XIV. The Reactions of Benzoyl and Thiobenzoyl Isocyanates with Hydrazones

A new porphinogen type compound

2-Substituted Acenaphtho[1,2-d]oxazoles

Methacryloyl isocyanate (MAI) reacted with arylhydrazines (1) to give semicarbazides (2) in good yields. Treatment of (2) with aqueous potassium hydroxide gave the corresponding 1-aryl-3-hydroxy- 1,2,4-triazoles (3), whereas thermal ring closure of (2) afforded isomeric 2,3-dihydro-2-aryl-1,2,4-triazole-3(1H)-ones (4). MAI reacted with benzamidine to give directly 1,3,5-triazine-2(1H)-one (10) by the loss of water. On the other hand, the reaction of MAI with 1,3-diphenyl- guanidine afforded the 1:1 adduct (11), which on thermal decomposition gave the perhydropyrimidin-6(1H)-one (12) and perhydro-1,3,5-triazine- 2,6-dione (13). The pathways for the formation of (4), (12) and (13) are also described

Ring closure reactions of adducts of methacryloyl isocyanate to arylhydrazines and their related compounds

1,3-Diphenylthiazolo[3,4-a]benzimidazole (1) containing tetravalent sulfur reacts as a thiocarbonyl ylide dipole with 6,6-diphenylfulvene to give a mixture of two regioisomeric exo-[4 + 2] adducts and endo-[4 + 2] adduct. The reaction of 1 with tropone and 8,8-dicyanoheptafulvene proceeds via a [4 + 2] cycloaddition to the C4–C5and C1–C2 bond of the addend to afford the exo-adduct and desulfurized compound respectively.

Otohiko Tsuge

Papers

Studies of Acyl and Thioacyl Isocyanates. XIV. The Reactions of Benzoyl and Thiobenzoyl Isocyanates with Hydrazones

A new porphinogen type compound

2-Substituted Acenaphtho[1,2-d]oxazoles

Ring closure reactions of adducts of methacryloyl isocyanate to arylhydrazines and their related compounds

Cycloaddition reactions of 1,3-diphenylthiazolo(3,4-a)benzimidazole with fulvene and tropone systems.