Role of metal ions in growth and stability of Langmuir-Blodgett films on homogeneous and heterogeneous surfaces

Structure and stability of cadmium arachidate (CdA) Langmuir-Blodgett (LB) films on homogeneous (i.e., OH-, H-passivated Si(001) substrates) and heterogeneous (i.e., Br-passivated Si(001) substrates) surfaces were studied using X-ray reflectivity and atomic force microscopy techniques and compared with those of nickel arachidate (NiA) LB films. While on OH-passivated Si, an asymmetric monolayer (AML) structure starts to grow, on H-passivated Si, a symmetric monolayer (SML) of CdA forms, although for both the films, pinhole-type defects are present as usual. However, on heterogeneous Br-passivated Si substrates, a combination of AML, SML, shifted SML and SML on top of AML (i.e., AML/SML), all types of structures are found to grow in such a way that, due to the variation of heights in the out-of-plane direction, ring-shaped in-plane nanopatterns of CdA molecules are generated. Probably due to stronger head-head interactions and higher metal ion-carboxylic ligand bond strength for CdA molecules compared to NiA, easy flipping of SML on top of another preformed SML, i.e. a SML/SML structure formation was not possible and as a result a wave-like modulation is observed for the CdA film on such heterogeneous substrate. The presence of hydrophilic/hydrophobic interfacial stress on the heterogeneous substrate thus modifies the deposited molecular structure so that the top surface morphology for a CdA film is similar to monolayer buckling while that for NiA film is similar to monolayer collapse.     

Curved kinoform lenses for stigmatic imaging of an axial object at infinity

We report a convenient formulation for the determination of zone spacing and blaze profile for a spherically curved kinoform lens. The method enables one to design the kinoform lens for stigmatic imaging of an axial object at infinity. Some numerical results are presented.     

Synthesis of the necine bases (±)-macronecine and (±)-supinidine via an aza-ene reaction and allylsilane induced ring closure

An aza-ene reaction has been used for the first time for the synthesis of two 5-membered lactam-hydrazides, each with a built-in allylsilane terminator for further elaboration. One of the lactam-hydrazides was transformed via an allylsilane-hydrazonium ion ring closure to a fused tetrahydropyrazole which may be considered as a mono-nitrogen analog of the biologically significant necine bases. A density functional theoretical study (B3LYP/6-21G*) was undertaken to provide insight into the factors that favor a synclinal transition structure of the hydrazonium ion intermediate leading to the tetrahydropyrazole. This stereocontrolled synthesis served as a model for the multi-step conversion of the other lactam-hydrazide, the substituted 2-pyrrolidinone, to necine bases (±)-supinidine and (±)-macronecine. An allylsilane-aldehyde ring closure formed the key step in the synthesis of these natural products.     

Response dynamics of 2-D quantum dots in the presence of time-varying fields: Anharmonicity and pulse shape effects

We explore the pattern of time evolution of different observables in a harmonically confined single carrier 2-D quantum dot when an external time-varying electric field is switched on. A static transverse magnetic field is also present. For given strengths of the confining field, cyclotron frequency, intensity and oscillation frequency of the external field, and pulse shape parameters, the system reveals a long time dynamics that leads to a kind of localization in the unperturbed state space. The presence of cubic anharmonicity in the confining field brings in new features in the dynamics. Frequency dependent linear and non-linear response properties of the dot are analyzed.     

Process and purification for manufacture of a modified insulin intended for oral delivery

Oral delivery of insulin is convenient and physiologically desirable in the treatment of diabetes. However, this route of administration has presented substantial challenges as insulin is degraded enzymatically in the gut, resulting in low bioavailability. We have developed a conjugated insulin product (IN-105) that has high bioavailability and is currently undergoing clinical trials for the treatment of diabetes. A process for the manufacture of IN-105 was developed. Initially, recombinant human insulin was conjugated covalently with a monodisperse, short-chain methoxypolyethylene glycol derivative. The desired product, IN-105, was purified from its closely related species using RP-HPLC and cation exchange chromatography to a purity of 98.5%. The elution pool from cation exchange chromatography was crystallized and lyophilized into the dry active pharmaceutical ingredient.     

Impact of methyl rotor in the excited state level mixing of doubly hydrogen-bonded complexes of 2-pyridone

We have presented in this paper the laser-induced fluorescence excitation and resolved fluorescence spectra of five 1:1 hydrogen-bonded complexes of 2-pyridone (2PY) with formic acid (FA), acetic acid (AA), propanoic acid (PA), formamide (FM), and acetamide (AM). The resolved fluorescence spectra, measured following excitation to different single vibronic levels of the dimers indicate that the intermolecular hydrogen bond vibrations undergo mixing with a number of intramolecular modes of the 2PY moiety in the excited state. A comparison of the emission spectral features of these dimers clearly indicates that the methyl groups belonging to the AA and AM moieties spectacularly accelerate the vibrational energy redistribution (IVR) in the 2PY moiety. On the other hand, although the molecular size of PA is bigger than AA, the spectral features of the 2PY-PA dimer bear signatures of a slower IVR rate compared to those of 2PY-AA. We propose that hyperconjugation of the methyl group with the cyclic hydrogen-bonded network involving AA and AM is responsible for the observed phenomenon.     

Periodic voltammetry as a successful technique for synthesizing CdSe semiconductor films for photo-electrochemical application

Journal of Solid State Electrochemistry - Polycrystalline n-type CdSe thin films were deposited from aqueous bath at room temperature by periodic voltammetry for use in photo-electrochemical (PEC)...     

Guest-Responsive Reversible Electron Transfer in a Crystalline Porous Framework Supported by a Dynamic Building Node

We demonstrate a redox-active, crystalline donor–acceptor (D-A) assembly in which the electron transfer (ET) process can be reversibly switched. This ET process, induced by a guest-responsive structural transformation at room temperature, is realized in a porous, metal–organic framework (MOF), having anthracene (D)–naphthalenediimide (A) as struts. A control MOF structure obtained by a solvent-assisted linker exchange (SALE) method, replacing an acceptor strut with a neutral one, supported the switchable electronic states in the D-A MOF. Combined investigations with X-ray diffraction, spectroscopy, and theoretical analyses revealed the dynamic metal paddle-wheel node as a critical unit for controlling structural flexibility and the corresponding unprecedented ET process.