A quantitative structure-reactivity relationship for the Michael-type addition of thiols onto acrylates was determined. Several thiol-containing peptides were investigated by examining the correlation between the second-order rate constant of their addition onto PEG-diacrylate and the pK(a) of the thiols within a peptide. By introducing charged amino acids in close proximity to a cysteine, the pK(a) of the thiol was systematically modulated by electrostatic interactions. Positive charges from the amino acid arginine decreased the pK(a) of the thiol and accelerated the reaction with acrylates while negative charges from aspartic acids showed the opposite effect. A linear correlation between thiolate concentrations and kinetic constants was found, confirming the role of thiolates as the reactive species in this Michael-type reaction. The relevant factors influencing the reactivity were the sign and the number of the neighboring charges, while the position of these charges had little effect on reactivity. These results provide a basis for the rational design of peptides, where the kinetics and thus selectivity of protein/peptide conjugation with polymeric structures via Michael-type addition reactions can be controlled.

Under appropriate conditions, block copolymeric macroamphiphiles will self-assemble in water to form vesicles, referred to as polymersomes. We report here polymersomes that can protect biomolecules in the extracellular environment, are taken up by endocytosis, and then suddenly burst within the early endosome, releasing their contents prior to exposure to the harsh conditions encountered after lysosomal fusion. Specifically, block copolymers of the hydrophile poly(ethylene glycol) (PEG) and the hydrophobe poly(propylene sulfide) (PPS) were synthesized with an intervening disulfide, PEG17-SS-PPS30. Polymersomes formed from this block copolymer were demonstrated to disrupt in the presence of intracellular concentrations of cysteine. In cellular experiments, uptake, disruption, and release were observed within 10 min of exposure to cells, well within the time frame of the early endosome of endolysosomal processing. This system may be useful in cytoplasmic delivery of biomolecular drugs such as peptides, proteins, oligonucleotides, and DNA.

Block copolymers of poly(ethylene glycol)-bl-poly(propylene sulfide) (PEG-PPS) have recently emerged as a new macromolecular amphiphile capable of forming a wide range of morphologies when dispersed in water. To understand better the relationship between stability and morphology in terms of the relative and absolute block compositions, we have synthesized a collection of PEG-PPS block copolymers and quantified their critical aggregation concentration and observed their morphology using cryogenic transmission electron microscopy after thin film hydration with extrusion and after solvent dispersion from tetrahydrofuran, a solvent for both blocks. By understanding the relationship between aggregate character and block copolymer architecture, we have observed that whereas the relative block lengths control morphology, the stability of the aggregates upon dilution is determined by the absolute block length of the hydrophobic PPS block. We have compared results obtained with PEG-PPS to those obtained with poly(ethylene glycol)-bl-poly(propylene oxide)-bl-poly(ethylene glycol) block copolymers (Pluronics). The results reveal that the PEG-PPS aggregates are substantially more stable than Pluronic aggregates, by more than an order of magnitude. PEG-PPS can form a wide variety of stable or metastable morphologies in dilute solution within normal time and temperature ranges, whereas Pluronics can generally form only spherical micelles under the same conditions. On the basis of these results, block copolymers of PEG with poly(propylene sulfide) may present distinct advantages over those with poly(propylene glycol) for a number of applications.

We explore the effects of preparation protocol on the morphology and stability of aggregates from a poly(ethylene glycol-b-propylene sulfide-b-ethylene glycol) triblock copolymer, PEG44−PPS76−PEG44. Fluorescence spectra and excimer formation of the probe molecule pyrene elucidated the various stages of aggregate formation, and cryo-TEM yielded insight into aggregate morphology. When prepared by direct hydration of polymer films, an extraordinary variety of morphologies was formed, ranging from spherical micelles to wormlike micelles, Y-junctions, blackberry micelles, and vesicles. Aging produced more uniform structural ensembles, including wormlike micelles with undulations and eventually spherical micelles, indicating the nonequilibrium nature of the system as initially formed. On the contrary, preparation by dilution from organic solvent yielded only structures that were closer to equilibrium distributions.

Control of nonspecific interactions between bioanalytical surfaces and proteins in the analyte is critical in the design of biosensor systems. Here we explore poly(propylene sulfide-block-ethylene glycol) (PPS−PEG) di- and triblock copolymer adlayers on gold to gain such control. Chemisorption of the PPS block permits a simple dip-and-rinse coating process. We synthesized different architectures of di- and triblock copolymers, varying the molecular weight of PEG between 1.1 and 5 kDa while keeping the PPS block constant at around 4 kDa, thus permitting systematic variations in ethylene glycol surface density in the adlayer. A simple dip-and-rinse process was used to produce PPS−PEG adlayers on gold substrates, which were characterized with surface plasmon resonance (SPR) and further confirmed by ex situ variable angle spectral ellipsometry (VASE), and X-ray photoelectron spectroscopy (XPS). Crowding in the PPS chemisorbed layer seemed to limit the polymer adsorption process. Subsequent exposure of PPS−PEG adlayers to protein adsorption (human serum albumin at 1 mg/mL or full-concentration human serum) was monitored with in situ SPR. Protein adsorption can be reduced up to 97% for human serum albumin and up to 96% for blood serum relative to bare gold substrates. Triblock copolymers were more effective than corresponding diblocks. The possibility to render gold surfaces bioinert is the basis for application in bioanalytical devices.

The equilibrium constant for the keto‐enol tautomerism of 3‐nitrobutan‐2‐one KT = [enol]/[ketone] has been measured in water as 4.57 × 10−3 (pKT = 2.34) by combining the rate constants for ketonisation of the enolate form and pKa of the ketone at 25 °C. The rates of ketonisation were measured by a rapid kinetic technique and the pKa was determined spectrophotometrically and potentiometrically as 5.15. A comparison with 2‐butanone and acetone shows a strong influence of the nitro group in enhancing the acidity of the substrate and in stabilizing the enol relative to the keto tautomer. By means of semiempirical AM1 calculations, good correlations were found between the atomic charge on the acidic hydrogens and the pKa (in water at 25 °C) of both tautomeric forms for a number of simple ketones whose pKas and pKTs are available in the literature. The agreement of experimental acidity constants of the enol, pKaEH, the ketone, pKaKH, and the tautomeric constant, pKT, with predicted values is satisfactory.

Overcoming the ortho/para rule? The regioselectivity of Diels–Alder reactions with neutral electron demand between 1,3‐dienes with alkynes can be controlled by simple cobalt diimine complexes so that the meta‐substituted cycloadducts are generated in good yields and excellent regioselectivity (see scheme; DDQ=2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone).

Finding alternative reaction media to replace polluting organic solvents is one aim of green chemistry. The ultimate green solvent, water, is the cheapest, non-toxic and most readily available reaction medium: three properties which make it an environmentally and economically attractive solvent. However, a fundamental problem in performing reactions in water is that many organic substrates are hydrophobic and not soluble in water. Several approaches are possible in solubilizing these compounds in aqueous media, one of which is carrying out reactions in aqueous solutions of surfactants at concentrations above their critical micellar concentration (cmc). Reactions of iodine with cyclohexene, 1-octene and styrene in water or in the presence of cationic surfactants do not give useful amounts of iodohydrins, but reactions in anionic surfactants give good yields. Iodohydrins are important functionalizable compounds and are readily prepared in the presence of sodium dodecyl sulfate (SDS) or sodium N-dodecanoyl sarcosinate (SANa). The critical conditions for these reactions were optimized with a rigorous statistical approach, the experimental design method. Use of these newly optimized reaction conditions gave high yields in short times for all of the alkenes examined. The use of anionic surfactants in water to form iodohydrins is a valid alternative to methods previously described