Dip-pen nanolithography in tapping mode

Dip-pen nanolithography (DPN) is becoming a popular nano-patterning technique for depositing materials onto a substrate using the probe of an atomic force microscope (AFM). Here, we demonstrate the deposition of a short synthetic peptide by DPN using the Tapping Mode of AFM rather than the commonly used contact mode. DPN in Tapping Mode requires drive amplitude modifications for deposition, yet allows for gentle imaging of the deposited material and enables deposition on soft surfaces.     

Electron and positron impact excitation of hydrogen from the initially excited 22S state to 32S and 32P states

The total and differential cross sections for the electron and positron impact excitation of hydrogen from its initially excited metastable 2²S state to 3²S and 3²P states are reported. A distorted-wave approximation theory is used for the calculation. The angular correlation parameters, Ly and alignment angle are also reported for 2²S-3²P excitation. For comparison, similar first Born results are also obtained. Interesting features are noted on comparing our distorted wave results with the first Born results as well as with the other available results forn ²S andn ²P (n=2,3) excitations from the ground 1²S state of hydrogen.     

Laser induced breakdown of Ar,N2 and O2 gases using 1.064, 0.532, 0.355 and 0.266 μm radiation

An experimental investigation of laser-induced breakdown using Nd:YAG laser harmonics for argon, nitrogen and oxygen gases is reported. Pressure dependence as well as wavelength dependence of the breakdown threshold irradianceI _th is investigated. The experimental observations for 1.064 and 0.532 m laser wavelengths are in agreement with theoretical calculations which include the effects of multiphoton ionization and cascade ionization.     

Thermal rearrangements of spiro[2.4]hepta-1,4,6-trienes

Thermolysis of spiro[2.4]hepta-1,4,6-triene (1a) at 50 degrees C yielded bicyclo[3.2.0]hepta-1,3,6-triene (5), which dimerized in two different fashions to form cyclobutanes. The 1,2-dimethyl and 1-propyl derivatives of 1a also rearranged at 50 degrees C, but at a faster rate, each yielding a pair of cyclobutane dimers. The structures of these symmetrical dimers were investigated by 1D and 2D NMR and NOE difference spectroscopy. Ab initio calculations indicated that the two strained olefins 1a and 5 had comparable energies about 50 kcal/mol lower than norborna-1(7),2,5-triene, which was thus excluded as a reaction intermediate.     

Self-assembly with degenerate prototropy

This work describes a rational approach for addressing the prototropy-related problems in heterocycle-based self-assembling systems by the use of degenerate prototropy. As a proof of principle, the utility of degenerate prototropy is demonstrated herein by developing heterocycle-based AADD-type self-assembling modules that exist as "single set of protameric pair (duplex)" in both solution and solid states. These self-assembling modules are quickly accessible in good yield by reacting 2-amino-5,5-disubstituted-1H-pyrimidine-4,6-diones, available in one step by the condensation of alpha,alpha-dialkyl malonates and free guanidine, with isocyanates. Evidence from NMR spectroscopy, ESI mass spectrometry, and single-crystal X-ray diffraction studies confirmed the formation of molecular duplexes. The effect of electronic repulsion in duplex formation is also investigated. Their ready synthetic accessibility, remarkably high propensity to crystal formation, and the novel property of degenerate prototropy would make these novel self-assembling molecules promising candidates for many proposed applications.     

Enantioselective synthesis of (R)-phenylephrine hydrochloride

An efficient method for the synthesis of enantiomerically pure (R)-phenylephrine hydrochloride 1 is described using a Sharpless asymmetric dihydroxylation as the key step.     

Stereoselective syntheses of 20-epi cholanic acid derivatives from 16-dehydropregnenolone acetate

A stereoselective total synthesis of naturally occurring 20-epi cholanic acid derivatives has been realized, starting from readily available 16-dehydropregnenolone acetate. The key step of these syntheses involves an ionic hydrogenation of a C-20,22-ketene dithioacetal and deoxygenation of steroidal C-20 tert-alcohols, to set up the unnatural C(20R) configuration with 100% stereoselectivity. The unnatural C-22 aldehydes with C(20R) stereocenters thus obtained were elaborated to 20-epi cholanic acid derivatives. Two derivatives of 20-epi cholanic acid were synthesized and their structures have been confirmed by single crystal X-ray analysis. Catalytic hydrogenation of 16-dehydropregnenolone acetate and 16-dehydropregnenolone in ethanol affords C-5,C-16 tetrahydro products. Crystal structure analysis of one of these products revealed C-5α and C-17α configurations of the hydrogen atoms.     

1,1,1,1-Tetrakis(o-fluorophenylamino)silane tris[titanium(IV) chloride]. Evidence for a new titanium cation [Ti2Cl7]+

Si(NHC₆H₄F-o)₄ · 3TiCl₄ (1) has been obtained from the disproportionation of (CF₃CH₂O)₃SiNHC₆H₄F-o and TiCl₄ in petroleum ether (40–60 °C) at –10 °C. The analytical (elemental analysis, molar conductance) and spectral (i.r., ¹H- and ¹⁹F-n.m.r.) data suggested that (1) behaves as [Si(NHC₆H₄F-o)₄ · Ti₂Cl₇]⁺ [TiCl₅]^–. The presence of these ions has been confirmed by characterising the products of metathetical reactions of (1) with R₄NX (R = Bu and Et; X = I and Br) and with AgNO₃. The data suggest the presence of a new titanium cation [Ti₂Cl₇]⁺.     

Synthesis and characterisation of some new cyanonitrosyl chromium(l) complexes with phenetidines and anisidines

Summary A new series of cyano-substituted nitrosylchromium(I) complexes having octahedral stereochemistry around the metal ion, and of general formula, [CrNO(CN)₂(L)₂(H₂O)] (L =o-,m- andp-phenetidines oro-,m-, andp-anisidines) have been isolated in the solid state by interaction of potassium pentacy-anonitrosylchromate(I) monohydrate with the appropriately substituted aniline. The complexes, which have been characterised by elemental analysis, conductance, molecular weight determination, magnetic measurements, e.s.r. and i.r. spectral studies, contain chromium(I) in a low-spin d⁵-configuration.     

Some Novel Dinuclear phenylboronates of biologically potent β‐enaminoesters: Synthesis,Spectroscopic characterization,antimicrobial activity and their antiandrogenic effect

Organoboron derivatives of biologically potent β‐enamino esters of the type [Where R = CH₃(1a), C₂H₅ (1b), C₃H₇(1c) and C (CH₃)₃ (1d)] have been prepared by the reactions of β‐enamino esters and Phenyl boronic acid [PhB (OH)₂] in 1:2 molar ratio in refluxing tetrahydrofuran (THF). All these derivatives have been characterized by physico‐chemical properties, elemental analyses and molecular weight measurements. The structures of these compounds have been proposed on the basis of IR, ¹H, ¹³C, ¹¹B NMR spectral data and GC‐mass spectrometry. Phenyl boronic acid, β‐enamino esters and their respective phenylboronates derivatives have been screened for the antibmicrobial activities against pathogenic bacteria (B. subtilis and E. coli) and fungi (A. niger and P. peniculosum) to access their growth inhibiting potential. In addition to this, antiandrogenic effect of Ligand, L^aH₂ and its boron derivative (1a) has also been tested in male albino rats.