Synthesis and properties of crosslinked polyvinylformamide and polyvinylamine hydrogels in conjunction with silica particles

Polyvinylamine hydrogels with silica particles encapsulated (PVAm/silica) were produced by a two‐step synthesis. In the first step, polyvinylformamide/silica (PVFA/silica) hybrids were synthesized from vinylformamide (VFA) and 1,3‐divinylimidazolidin‐2‐one (1,3‐bisvinylethyleneurea, BVU), as the crosslinker, by radical copolymerization in silica/water suspensions using different compositions of VFA/BVU. The target product PVAm/silica was obtained by acidic hydrolysis of the PVFA/silica hydrogels in a second step. The chemical structures of both hydrogels, PVFA/silica and PVAm/silica, respectively, were revealed by solid‐state ¹³C(¹H) cross‐polarity/magic‐angle spinning NMR spectroscopy. Both hydrogels swelled significantly in water. The swelling capacity of the two systems was characterized by the correlation length ξ (or hydrodynamic blob size) of the network meshes with small‐angle neutron scattering experiments. ξ is significantly larger for PVAm/silica than for PVFA/silica, which corresponds to the observed higher swelling capacity of this polyelectrolyte material. Furthermore, the swelling behavior of the hybrid hydrogels was quantitatively described in terms of free swell capacity, centrifuge‐retention capacity, adsorption against pressure, and free swell rate as compared with values of the corresponding copolymer hydrogels. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3144–3152, 2002     

Asymmetric bioreduction of alkenes using ene-reductases YersER and KYE1 and effects of organic solvents

Asymmetric trans-bioreduction of activated alkenes by KYE1 from Kluyveromyces lactis and Yers-ER from Yersinia bercovieri, two ene-reductases from the Old Yellow Enzyme family, showed a broad substrate spectrum with a moderate to excellent degree of stereoselectivity. Both substrate- and enzyme-based stereocontrols were observed to furnish opposite stereoisomeric products. The effects of organic solvents on enzyme activity and stereoselectivity were outlined in this study, where two-phase systems hexane and toluene are shown to sustain bioreduction efficiency even at high organic solvent content.     

Highly efficient visible-light driven photochromism: developments towards a solid-state molecular switch operating through a triplet-sensitised pathway

We introduce a new highly efficient photochromic organometallic dithienylethene (DTE) complex, the first instance of a DTE core symmetrically modified by two Pt(II) chromophores [Pt(PEt(3))(2)(C≡C)(DTE)(C≡C)Pt(PEt(3))(2)Ph] (1), which undergoes ring-closure when activated by visible light in solvents of different polarity, in thin films and even in the solid state. Complex 1 has been synthesised and fully photophysically characterised by (resonance) Raman and transient absorption spectroscopy complemented by calculations. The ring-closing photoconversion in a single crystal of 1 has been followed by X-ray crystallography. This process occurs with the extremely high yield of 80%--considerably outperforming the other DTE derivatives. Remarkably, the photocyclisation of 1 occurs even under visible light (>400 nm), which is not absorbed by the non-metallated DTE core HC≡C(DTE)C≡CH (2) itself. This unusual behaviour and the high photocyclisation yields in solution are attributed to the presence of a heavy atom in 1 that enables a triplet-sensitised photocyclisation pathway, elucidated by transient absorption spectroscopy and DFT calculations. The results of resonance Raman investigation confirm the involvement of the alkynyl unit in the frontier orbitals of both closed and open forms of 1 in the photocyclisation process. The changes in the Raman spectra upon cyclisation have permitted the identification of Raman marker bands, which include the acetylide stretching vibration. Importantly, these bands occur in the spectral region unobstructed by other vibrations and can be used for non-destructive monitoring of photocyclisation/photoreversion processes and for optical readout in this type of efficiently photochromic thermally stable systems. This study indicates a strategy for generating efficient solid-state photoswitches in which modification of the Pt(II) units has the potential to tune absorption properties and hence operational wavelength across the visible range.     

The C-disaccharide alpha-C(1-->3)-mannopyranoside of N-acetylgalactosamine is an inhibitor of glycohydrolases and of human alpha-1,3-fucosyltransferase VI. Its epimer alpha-(1-->3)-mannopyranoside of N-acetyltalosamine is not

The radical C-glycosidation of (-)-(1S,4R,5R, 6R)-6-endo-chloro-3-methylidene-5-exo-(phenylseleno)-7-ox abi cyclo[2. 2.1]heptan-2-one ((-)-4) with 2,3,4, 6-tetra-O-acetyl-alpha-D-mannopyranosyl bromide gave (+)-(1S,3R,4R, 5R,6R)-6-endo-chloro-5-exo-(phenylseleno)-3-endo-(1',3',4', 5'-tetra-O-acetyl-2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)-7-oxabi cyc lo[ 2.2.1]hept-2-one ((+)-5) that was converted into (+)-(1R,2S,5R, 6R)-5-acetamido-3-chloro-2-hydroxy-6-(1',3',4',5'-tetra-O-acetyl)-2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)cyclohex -3-en- 1-yl acetate ((+)-10) and into (+)-(1R,2S,5R, 6S)-5-bromo-3-chloro-2-hydroxy-6-(1',3',4',5'-tetra-O-acetyl-2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)cyclohex -3-en- 1-yl acetate ((+)-19). Ozonolysis of (+)-10 and further transformations provided 2-acetamido-2,3-dideoxy-3-C-(2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)-D-galac tos e (alpha-C(1-->3)-D-mannopyranoside of N-acetylgalactosamine (alpha-D-Manp-(1-->3)CH(2)-D-GalNAc): 1). Displacement of the bromide (+)-19 with NaN(3) in DMF provided the corresponding azide ((-)-20) following a S(N)2 mechanism. Ozonolysis of (-)-20 and further transformations led to 2-acetamido-2,3-dideoxy-3-C-(2', 6'-anhydro-7'-deoxy-D-glycero-D-manno-heptitol-7'-C-yl)-D-talose (alpha-C(1-->3)-D-mannopyranoside of N-acetyl D-talosamine (alpha-D-Manp-(1-->3)CH(2)-D-TalNAc): 2). The neutral C-disaccharide 1 inhibits several glycosidases (e.g., beta-galactosidase from jack bean with K(i) = 7.5 microM, alpha-L-fucosidase from human placenta with K(i) = 28 microM, beta-glucosidase from Caldocellum saccharolyticum with K(i) = 18 microM) and human alpha-1, 3-fucosyltransferase VI (Fuc-TVI) with K(i) = 120 microM whereas it 2-epimer 2 does not. Double reciprocal analysis showed that the inhibition of Fuc-TVI by 1 displays a mixed pattern with respect to both the donor sugar GDP-fucose and the acceptor LacNAc with K(i) of 123 and 128 microM, respectively.     

Effect of added alpha-lactalbumin protein on the phase behavior of AOT-brine-isooctane systems

We have found that the presence of <1 wt% of the globular protein alpha-lactalbumin has a significant impact on the equilibrium phase behavior of dilute sodium bis(ethylhexyl) sulfosuccinate (AOT)/brine/isooctane systems. Nuclear magnetic resonance (NMR), Karl Fischer titration, and ultraviolet spectroscopy were used to determine the surfactant, oil, water, and protein content of the organic and aqueous phases as a function of the total surfactant and protein present. As a small amount of alpha-lactalbumin is added to the mixture, there is a substantial increase (up to 80%) in the maximum water solubility in the water-in-oil microemulsion phase. Dynamic light scattering measurements indicate that this increase is due to a decrease in the magnitude of the (negative) spontaneous curvature of the surfactant monolayer, as droplets swell in size. As the molar ratio of alpha-lactalbumin to AOT surpasses approximately 1:300, the partitioning of water, protein, and surfactant shifts to the excess aqueous phase, where soluble assemblies with positive curvature are detected by dynamic light scattering. Significant amounts of isooctane are solubilized in these aggregates, consistent with the formation of oil-in-water microemulsion droplets. Circular dichroism studies showed that the tertiary structure of the protein in the microemulsion is disrupted while the secondary structure is increased. In light of these findings, the protein most likely expands to a molten-globule type conformation in the AOT interfacial environment, but does not substantially unfold to become an extended chain.     

The pH dependence of phenolphthalein: A 13c NMR study

The pH dependence of the ¹³C NMR spectra of phenolphthalein has been measured and interpreted. The spectrum of the neutral compound 1 is compared with the spectra of the dianion 4, the trianion5 and the carbocation7. At the first time spectroscopic evidence for the carbinol 6 is given.     

Metal-free N-h insertions of donor/acceptor carbenes

Synthetically useful transformations arise from the thermal decomposition of aryldiazoacetates in the presence of primary and secondary amines without the use of a metal catalyst. Thermally generated, free donor/acceptor carbenes directly undergo N-H insertion with amines through selective aza-ylide formation to afford a variety of α-amino esters in 53-96% yields.     

Mesoporous carbon amperometric glucose sensors using inexpensive,commercial methacrylate-based binders

Two ordered, soft-templated mesoporous carbon powders with cubic and hexagonal framework structure and four different commercial, low cost methacrylate-based polymer binders with widely varying physical properties are investigated as screen printed electrodes for glucose sensors using glucose oxidase and ferricyanide as the mediator. Both the chemistry and concentration of the binder in the electrode formulation can significantly impact the performance. Poly(hydroxybutyl methacrylate) as the binder provides hydrophilicity to enable transport of species in the aqueous phase to the carbon surface, but yet is sufficiently hydrophobic to provide mechanical robustness to the sensor. The current from the mesoporous carbon electrodes can be more than an order of magnitude greater than for a commercial printed carbon electrode (Zensor) with improved sensitivity for model glucose solutions. Even when applying these sensors to rabbit whole blood, the performance of these glucose sensors compares favorably to a standard commercial glucose meter with the lower detection limit of the mesoporous electrode being approximately 20 mg dL⁻¹ despite the lack of a separation membrane to prevent non-specific events; these results suggest that the small pore sizes and high surface areas associated with ordered mesoporous carbons may effectively decrease some non-specific inferences for electrochemical sensing.     

A semipermanent coating for preventing protein adsorption at physiological pH in kinetic capillary electrophoresis

Protein adsorption to the inner capillary wall hinders the use of kinetic capillary electrophoresis (KCE) when studying noncovalent protein-ligand interactions. Permanent and dynamic capillary coatings have been previously reported to alleviate much of the problems associated with protein adsorption. The characteristic limitations associated with permanent and dynamic coatings motivated us to look at a third type of coating - semipermanent. Here, we demonstrate that a semipermanent capillary coating, designed by Lucy and co-workers, comprised of dioctadecyldimethylammonium bromide (DODAB) and polyoxyethylene (POE) stearate, greatly reduces protein adsorption at physiological pH - a necessary requirement for KCE. The coating (i) does not inhibit protein-DNA complex formation, (ii) prevents the adsorption of the analytes, and (iii) supports an electoosmotic flow required for many applications of KCE. The coating was tested in three physiological buffers using a well-known DNA aptamer and four proteins that severely bind to bare silica capillaries as standards. For every protein, a condition was found under which the semipermanent coating effectively suppresses protein adhesion. While no coating can completely prevent the adsorption of all proteins, our findings suggest that the DODAB/POE stearate coating can have a broad impact on CE at large, as it prevents the absorption of several well studied, highly adhesive proteins at physiological pH.     

A Bioorthogonal Small‐Molecule‐Switch System for Controlling Protein Function in Live Cells

Chemically induced dimerization (CID) has proven to be a powerful tool for modulating protein interactions. However, the traditional dimerizer rapamycin has limitations in certain in vivo applications because of its slow reversibility and its affinity for endogenous proteins. Described herein is a bioorthogonal system for rapidly reversible CID. A novel dimerizer with synthetic ligand of FKBP′ (SLF′) linked to trimethoprim (TMP). The SLF′ moiety binds to the F36V mutant of FK506‐binding protein (FKBP) and the TMP moiety binds to E. coli dihydrofolate reductase (eDHFR). SLF′‐TMP‐induced heterodimerization of FKBP(F36V) and eDHFR with a dissociation constant of 0.12 μM . Addition of TMP alone was sufficient to rapidly disrupt this heterodimerization. Two examples are presented to demonstrate that this system is an invaluable tool, which can be widely used to rapidly and reversibly control protein function in vivo.