ABSTRACT
Syringe-injectable biomaterials and medical devices are important as minimally invasive implants for diagnosis, therapy, and regenerative medicine. Free-standing polymeric nanosheets with a thickness less than 1 µm and a flexural rigidity less than 10-2 nN m are a promising platform of syringe-injectable, implantable devices that provide conformable and long-term stable adhesion to the target biological tissues for in situ delivery of therapeutic materials. Here, we developed free-standing ultrathin films (<1 µm thick) based on polyurethane-based shape-memory polymer (SMP) and magnetic nanoparticles (MNP), termed MNP-SMP nanosheets. With the temperature-mediated shape-memory effect of SMP, we overcome the limitation in the manipulation of the conventional polymer nanosheets. In particular, we demonstrated the following four capabilities using the 710 nm thick MNP-SMP nanosheet with the glass transition temperature (Tg) of 25 °C: (1) syringe-injectability through the medical needles, (2) self-expandability after ejection, (3) conformability and removability on the biological surfaces, and (4) guidability in an external magnetic field. The MNP-SMP nanosheets were readily interfaced with an additional layer of poly(lactic-co-glycolic acid) (PLGA) to extend their functionality as a carrier of molecular and cellular drugs. The MNP-SMP nanosheets will contribute to the development of advanced syringe-injectable medical devices as a platform to deliver drugs, sensors, cells, and engineered tissues to the specific site or lesion in the body for minimally invasive diagnosis and therapy.
ABSTRACT
A diamide armed with a photochromic azobenzene unit and a nucleophilic pyridyl group varied its aggregation/dissociation state depending on the trans/cis geometry of the azobenzene. The catalytic activity of the pyridyl group was closely linked to the aggregation/dissociation state and hence photoirradiation could manipulate the catalytic performance.
Subject(s)
Azo Compounds/chemistry , Light , Ultraviolet Rays , Catalysis , Isomerism , Pyridines/chemistrySubject(s)
Azo Compounds/chemistry , Diamide/chemistry , Hydrogen Bonding , Isomerism , Photochemical Processes , Solubility , Ultraviolet RaysABSTRACT
Solvent-dependent, self-discrimination of diamides is described. Mixing a solution of (R)-1a and (S)-1a, which are valine-derived, bis(2-hydroxyphenyl)diamide-bearing, multiple hydrogen-bonding modules, in dichloromethane immediately led to the formation of a thick suspension comprising a 1:1 heterochiral aggregate of 1a. The solubility of heterochiral 1a was substantially lower in halogenated solvents than in ethyl acetate. A perusal of racemic crystal structures obtained from chloroform and ethyl acetate revealed a significant difference in the crystal-packing pattern, which is likely to be the basis for the pronounced difference in solubility. Specific self-discrimination of 1 a in an ensemble of eight structurally related molecules showcased the specific aggregation through the hydrogen-bonding network of the bis(2-hydroxyphenyl)diamide framework. The low solubility of heterochiral 1a in halogenated solvent was exploited to achieve high stereoselectivity in a catalytic asymmetric reaction by using a low enantiomeric excess sample of 1a.
Subject(s)
Diamide/chemistry , Models, Molecular , Phenols/chemistry , Amino Acids/chemistry , Catalysis , Hydrocarbons, Halogenated/chemistry , Hydrogen Bonding , Ligands , Molecular Structure , Peptides/chemistry , Solvents/chemistry , StereoisomerismABSTRACT
Full details of an anti-selective catalytic asymmetric nitroaldol reaction promoted by a heterobimetallic catalyst comprised of Nd(5)O(O(i)Pr)(13), an amide-based ligand, and NaHMDS (sodium hexamethyldisilazide) are described. A systematic synthesis and evaluation of amide-based ligands led to the identification of optimum ligand 1m, which provided a suitable platform for the Nd/Na heterobimetallic complex. During the catalyst preparation in THF, a heterogeneous mixture developed and centrifugation of the suspension allowed for separation of the precipitate, which contained the active catalyst and which could be stored for at least 1 month without any loss of catalytic performance. The precipitate promoted a nitroaldol (Henry) reaction for a broad range of nitroalkanes and aldehydes under heterogeneous conditions, affording the corresponding 1,2-nitroalkanol in a highly anti-selective (up to anti/syn = >40/1) and enantioselective manner (up to 98% ee). Inductively coupled plasma (ICP) and X-ray fluorescence (XRF) analyses revealed that the precipitate indeed included both neodymium and sodium, which was further supported by high-resolution ESI TOF MS spectrometry.
Subject(s)
Aldehydes/chemical synthesis , Alkanes/chemical synthesis , Organosilicon Compounds/chemistry , Catalysis , Spectrometry, Mass, Electrospray IonizationABSTRACT
Proteins, the functional molecules in biological systems, are sophisticated chemical devices that have evolved over billions of years. Their function is intimately related to their three-dimensional structure and elegantly regulated by conformational changes through allosteric regulators and a number of reversible or unidirectional post-translational modifications. This functional diversification in response to external stimuli allows for an orderly and timely progression of intra- and extracellular events. In contrast, enantioselective catalysts generally exhibit limited conformational flexibility and thereby exert a single specific function. Exploiting the features of conformationally flexible asymmetric ligands and the variable coordination patterns of rare earth metals, we demonstrate dynamic structural and functional changes of a catalyst in asymmetric catalysis, leading to two distinct reaction outcomes in a single flask.
Subject(s)
Molecular Structure , Catalysis , StereoisomerismABSTRACT
A highly enantio- and diastereoselective catalytic asymmetric Mannich-type reaction of alpha-cyanoketones and N-Boc imines promoted by an amide ligand/Sc(OiPr)3 catalyst is described. The similar reaction outcome is obtained with/without precomplexation of catalyst, suggesting that reaction components in a non-ordered conglomerate mixture orchestrate to form an ordered transition state during the reaction. Spectroscopic data and Eyring plot are consistent with this assumption.