Matrix assisted pulsed laser evaporation of poly(d,l-lactide) thin films for controlled-release drug systems

We report the successful deposition of the porous polymer poly(d,l-lactide) by matrix assisted pulsed laser evaporation (MAPLE) using a KrF* excimer laser (248 nm, τ = 7 ns) operated at 2 Hz repetition rate. The chemical structure of the starting materials was preserved in the resulting thin films. Fluence played a key role in optimizing our depositions of the polymer. We demonstrated MAPLE was able to improve current approaches to grow high quality thin films of poly(d,l-lactide), including a porosity control highly required in targeted drug delivery.     

Adaptive optics interferometer using superspeckles for high resolution deformation measurement

Digital speckle pattern interferometry (DSPI) is a well-known technique for measuring deformations, but it is limited in range by speckle decorrelation. We developed an adaptive interferometer with increased measurement range by combining the DSPI set-up with a pupil filter that generates optical superresolution. As a result, a decrease in the transverse speckle size is observed accompanied with a substantial increase in the longitudinal speckle size. The increase in the speckle correlation length along the optical axis allows for obtaining an out-of-plane deformation measurement over a significantly extended depth. An experimental verification of this concept of superspeckles is presented with an intensity-only LCD spatial light modulator (SLM) acting as a pupil filter. Comparison of speckle correlation fringes with and without the superresolution filter confirms the proposed concept. The present work demonstrates a doubling of the measurement range when using the superresolution interferometer. A standard set-up in which the speckle length is comparably elongated by stopping down the lens has a similar loss of intensity, but its lateral resolution is only half as good.     

Aluminacyclopropene: syntheses, characterization, and reactivity toward terminal alkynes

Reactions of LAl with ethyne, mono- and disubstituted alkynes, and diyne to aluminacyclopropene LAl[eta2-C2(R1)(R2)] ((L = HC[(CMe)(NAr)]2, Ar = 2,6-iPr2C6H3); R1 = R2 = H, (1); R1 = H, R2 = Ph, (2); R1 = R2 = Me, (3); R1 = SiMe3, R2 = C[triple bond]CSiMe3, (4)) are reported. Compounds 1 and 2 were obtained in equimolar quantities of the starting materials at low temperature. The amount of C2H2 was controlled by removing an excess of C2H2 in the range from -78 to -50 degrees C. Compound 4 can be alternatively prepared by the substitution reaction of LAl[eta2-C2(SiMe3)2] with Me3SiC[triple bond]CC[triple bond]CSiMe3 or by the reductive coupling reaction of LAlI2 with potassium in the presence of Me3SiC[triple bond]CC[triple bond]CSiMe3. The reaction of LAl with excess C2H2 and PhC[triple bond]CH (<1:2) afforded the respective alkenylalkynylaluminum compounds LAl(CH=CH2)(C[triple bond]CH) (5) and LAl(CH=CHPh)(C[triple bond]CPh) (6). The reaction of LAl(eta2-C2Ph2) with C2H2 and PhC[triple bond]CH yielded LAl(CPh=CHPh)(C[triple bond]CH) (7) and LAl(CPh=CHPh)(C[triple bond]CPh) (8), respectively. Rationally, the formation of 5 (or 6) may proceed through the corresponding precursor 1 (or 2). The theoretical studies based on DFT calculations show that an interaction between the Al(I) center and the C[triple bond]C unit needs almost no activation energy. Within the AlC2 ring the computational Al-C bond order of ca. 1 suggests an Al-C sigma bond and therefore less pi electron delocalization over the AlC2 ring. The computed Al-eta2-C2 bond dissociation energies (155-82.6 kJ/mol) indicate a remarkable reactivity of aluminacyclopropene species. Finally, the 1H NMR spectroscopy monitored reaction of LAl(eta2-C2Ph2) and PhC[triple bond]CH in toluene-d8 may reveal an acetylenic hydrogen migration process.     

The dimeric mixed‐ligand titana­carborane sandwich [1‐(Cp)‐1‐Ti‐2‐(Me)‐3‐(SiMe3)‐2,3‐C2B4H4]2

The title dimer, bis­[1‐cyclo­penta­dienyl‐2‐methyl‐1‐titana‐3‐tri­methylsilyl‐2,3‐dicarba‐closo‐hexaborane(6)], [Ti(C₅H₅)(C₆­H₁₆­B₄Si)]₂, reveals that the centrosymmetric mol­ecule consists of two bent‐sandwich titanacarboranes bridged by the B—H—Ti bonds. The average bond distances are Ti—B 2.445 (3), Ti—C(cage) 2.334 (2) and Ti—C(Cp) 2.376 (3) Å, and the corresponding bond angles are Cp—Ti—Cp 163.2 (1) and Cp—Ti—Cb (Cb = C₂B₃ face) 139.9 (1)°; the Ti—H separations are 2.10 (2) and 2.19 (2) Å.     

ortho‐Phenylenediamine: An Effective Spacer to Build Highly Magnetic Fe3O4/Au Nanocomposites

1,2‐Diaminobenzene, popularly known as ortho‐phenylenediamine (PDA), is found to be a prototype spacer for the deposition of gold nanoparticles on the surfaces of Fe₃O₄ microspheres. Upon carbonization with PDA, the morphology of the product changes significantly, and the resulting nanocomposites exhibit enhanced magnetism beyond the saturation value of Fe₃O₄. The Fe₃O₄/Au nanocomposites show good surface‐enhanced Raman spectroscopy activity with a detection limit of 10^?15 M .     

Calix[4]arene-based ditopic receptors for simultaneous recognition of fluoride and cobalt(II) ions

A series of calix[4]arene based ditopic receptors possessing bipyridyl and hydrazone units have been synthesized and evaluated for ionic recognition. It has been observed that the synthesized derivatives function as allosteric receptors for simultaneous recognition of Co²⁺and F^? ions through non-covalent interactions. Significant bathochromic shifts in the UV–visible spectrum with a profound colour change promise their use to engineer novel applications.     

A highly diastereoselective synthesis of (E)-B-2-(1-cyclopropyl-1-alkenyl)-1,3,2-dioxaborinanes. Isolation and oxidation to alkyl cyclopropyl ketones

A convenient, novel synthesis of alkyl cyclopropyl ketones based on Z-1-bromo-1-alkenylboronate esters is developed. α-Bromo-(Z)-1-alkenylboronate esters readily available from literature procedures smoothly undergo a reaction with cyclopropylmagnesium bromide in tetrahydrofuran to provide the corresponding ‘ate’ complexes. These ‘ate’ complexes undergo intramolecular nucleophilic substitution reactions to provide the corresponding (E)-1-alkenylboronate esters containing cylcopropyl moiety for the first time in good isolated yields (68-82%). The carbon skeleton present in these intermediates is confirmed by oxidation with hydrogen peroxide and sodium acetate to afford the corresponding alkyl cyclopropyl ketones in good yields (72-85%).     

Microwave promoted methylation of plant polysaccharides

O-Methylation is of outstanding importance in structural polysaccharide chemistry. A novel method for the methylation of polysaccharides using microwave (MW) irradiation is described. Seed gum from Cyamopsis tetragonolobus (Guar) was fully methylated with dimethyl sulphate and sodium hydroxide using 100% microwave power for 4 min in 68% yield. The completely methylated seed gum thus obtained was hydrolyzed by 70% formic acid followed by 0.5N H₂SO₄ under full microwave power for 1.16 and 1.66 min, respectively. The partially methylated monosaccharides were separated and identified.     

Study of electrolyte induced aggregation of gold nanoparticles capped by amino acids

This work reports the electrolyte induced aggregation of gold nanoparticles directly conjugated to amino acid by chemical reduction in aqueous solution. The study was focused on three different classes of amino acids depending on the nature of alpha substituent, viz. l-cysteine, l-leucine, and l-asparagine. The band broadening and the red shift of surface plasmon band with increase in flocculation parameter showed the aggregation of gold nanoparticles with increase in electrolyte concentration and decrease in pH as monitored by UV-visible spectrophotometer. The (1)H NMR spectrum demonstrates that the sulfide bond of cysteine and alpha amino group of leucine and asparagine interact with nanoparticles surface. Furthermore, transmission electron microscope (TEM) and thermogravimetric analysis (TGA) were performed to characterize and to support the fate of stabilization of the gold nanoparticles by amino acid.     

Selective Interactions of O-Methylated Flavonoid Natural Products with Human Monoamine Oxidase-A and -B

A set of structurally related O-methylated flavonoid natural products isolated from Senecio roseiflorus (1), Polygonum senegalense (2 and 3), Bhaphia macrocalyx (4), Gardenia ternifolia (5), and Psiadia punctulata (6) plant species were characterized for their interaction with human monoamine oxidases (MAO-A and -B) in vitro. Compounds 1, 2, and 5 showed selective inhibition of MAO-A, while 4 and 6 showed selective inhibition of MAO-B. Compound 3 showed ~2-fold selectivity towards inhibition of MAO-A. Binding of compounds 1–3 and 5 with MAO-A, and compounds 3 and 6 with MAO-B was reversible and not time-independent. The analysis of enzyme-inhibition kinetics suggested a reversible-competitive mechanism for inhibition of MAO-A by 1 and 3, while a partially-reversible mixed-type inhibition by 5. Similarly, enzyme inhibition-kinetics analysis with compounds 3, 4, and 6, suggested a competitive reversible inhibition of MAO-B. The molecular docking study suggested that 1 selectively interacts with the active-site of human MAO-A near N5 of FAD. The calculated binding free energies of the O-methylated flavonoids (1 and 4–6) and chalcones (2 and 3) to MAO-A matched closely with the trend in the experimental IC_50′s. Analysis of the binding free-energies suggested better interaction of 4 and 6 with MAO-B than with MAO-A. The natural O-methylated flavonoid (1) with highly potent inhibition (IC₅₀ 33 nM; Ki 37.9 nM) and >292 fold selectivity against human MAO-A (vs. MAO-B) provides a new drug lead for the treatment of neurological disorders.