3′-Amino-5′-carboxymethyl-3′,5′-dideoxy nucleosides for the synthesis of fully amide-linked RNA mimics

A convenient protocol is developed for the synthesis of 3′-[N-(fluorenylmethoxycarbonyl)-amino]-5′-carboxymethyl derivatives of all four natural ribonucleosides from cheap chiral pool compound glucose. Synthesis of fully amide-linked RNA analogues of small oligonucleotides containing, for the first time, all four nucleoside amino acids using standard solid phase Fmoc-chemistry is described.     

Regio‐ and Diastereoselective and Enantiospecific Metal‐Free C(sp3)H Arylation: Facile Access to Optically Active 5‐Aryl 2,5‐Disubstituted Pyrrolidines

Optically active 5‐aryl 2,5‐disubstituted pyrrolidines are the principal structural moiety of many bioactive compounds including natural products and catalysts for asymmetric synthesis. A highly regio‐ and diastereoselective and enantiospecific method for direct C?H arylation of aliphatic amine has been developed. Structurally diverse enantiopure arylated pyrrolidines were synthesized from commercially available starting materials, through a single‐step three‐component reaction under metal‐ and oxidant‐free conditions. Furthermore, the complex analogous structure of CCK antagonist RP 66803 and angiotensin‐converting enzyme inhibitors was easily constructed using the synthesized arylated pyrrolidine derivative. Detailed theoretical calculations (M06‐2X/TZVPP/SMD//M06‐2X/6‐31+G(d,p) level) were also carried to investigate the mechanism and high level of stereocontrol involved in this direct sp³ C?H arylation reaction. Preference for a given regio‐ and stereoselectivity in the arylated product can be explained through elucidation of the mechanism for dehydration, generating azomethine ylide, and for the final re‐aromatization step. The calculated energies reveals that the re‐aromatization step is essentially rate determining, accompanying an activation barrier of Δ^≠${G{{{\rm S}\hfill \atop {\rm L}\hfill}}}$ =25.6 kcal mol^?1.     

A mathematical model describing the thyroid-pituitary axis with time delays in hormone transportation

In the present paper, a mathematical model, originally proposed by Danziger and Elmergreen and describing the thyroid-pituitary homeostatic mechanism, is modified and analyzed for its physiological and clinical significance. The inuence of different system parameters on the stability behavior of the system is discussed. The transportation delays of different hormones in the bloodstream, both in the discrete and distributed forms, are considered. Delayed models are analyzed regarding the stability and bifurcation behavior. Clinical treatment of periodic catatonic schizophrenia is discussed in presence of transportation delays. Numerical simulations are presented to support analytic results.     

THz Spectrum of Methanol-D4 and Microwave Spectrum of Methanol-D1

The sub-THz spectra of CD₃OD have been observed in the frequency ranges of 461-486 GHz and 596-610 GHz using the Backward Wave Oscillator based Technique. The 218 transitions of CD₃OD are newly assigned to J=31 and K=12 in the first three torsional states (n=2). The assigned lines include several new series of both a-type and b-type transitions. These THz transitions combined with the previous published millimeter-wave (MMW) and microwave (MW) data and recently observed high resolution Fourier transform far infrared (FIR) spectra have been used in a global fit. The data set contains 1320 MW, MMW, SMMW and FIR transitions with n=2, J=31 and K=12. Using the reduced torsion-rotational Hamiltonian with 67 parameters the fit converges with an RMS deviation of 277 kHz for the MW transitions and of 0.00024 cm^-1 for the FIR transitions. Thus molecular parameters are well determined. The MW spectrum of CH₂DOH (in the range 97.7 -118.0 and 128.5-146.5 GHz) is also presented which will help astronomers for astrophysical detection and theoretical spectroscopists to get further information on torsion-rotation-vibration interaction in an internal rotor with an asymmetric top.     

Two-dimensional magnetic ordering in a multilayer structure

The effect of confinement from one, two or from all three directions on magnetic ordering has remained an active field of research for almost 100 years. The role of dipolar interactions and anistropy are important to obtain, the otherwise forbidden, ferromagnetic ordering at finite temperature for ions arranged in two-dimensional (2D) arrays (monlayers). We have demonstrated that conventional low-temperature magnetometry and polarized neutron scattering measurements can be performed to study short-range ferromagnetic ordering of in-plane spins in 2D systems using a multilayer stack of non-interacting monolayers of gadolinium ions formed by Langmuir-Blodgett (LB) technique. The spontaneous magnetization could not be detected in the heterogeneous magnetic phase observed here and the saturation value of the net magnetization was found to depend on the sample temperature and applied magnetic field. The net magnetization rises exponentially with lowering temperature and then reaches saturation following a T ln(βT) dependence. The T ln (βT) dependence of magnetization has been predicted from spinwave theory of 2D in-plane spin system with ferromagnetic interaction. The experimental findings reported here could be explained by extending this theory to a temperature domain of βT<1.     

Modulation of SHG responses via supramolecular association/dissociation between two complementary cryptands

Two sets of complementary cryptands are investigated for supramolecular nitro-amino H-bonding interactions in solutions. The D-π-A cryptand and the unsubstituted cryptand forms 1:1 H-bonded structure. Its second harmonic generation capabilities in solution are explored by HRS titration experiments. Supramolecular assembly leads to spontaneous increase of the SHG intensity, which undergoes steady decrease on addition of MeOH due to the breakdown of the H-bonded structure. Thus, NLO responses can be reversibly modulated by applying such supramolecular principles.     

Modelling a single-species closed habitat fishery with spatial heterogeneity and time delay

A mathematical model describing a single species fishery is presented. The coupling effect of intra-species interaction delay of the harvested species and the spatial non-homogeneity of the aquatic environment is studied. The analysis is performed in a finite domain with the help of Neumann boundary value problem which resembles a closed-habitat fishery. Existence, uniqueness and regularity of solutions are demonstrated using the method of upper-lower solution pair. Stability criteria of the system is derived and interpreted from a bio-economic viewpoint.     

Tunable THz Sources and Their Applications

In this paper, the technology aspects of the THz laser and spectrometric devices, developed over the last decade are described and their applications in various fields of science and technology are explained. The THz sources of importance are the optically pumped lasers, solid state devices and the backward wave oscillator (BWO) based systems. The BWO system offers the electronic tuning and multiplexing facility like Fourier transform technology. The time resolved and frequency domain aspects with relative merits are discussed. Non-linear optical methods of production of monochromatic radiation using second harmonic generation (SHG) are also considered. The important areas of space applications are described in detail. Present status and future directions are indicated.     

Studies directed towards the synthesis of botcinolides: synthesis of the nonalactone ring of 2-epibotcinolide

Synthesis of the polyoxygenated nonalactone ring of 2-epibotcinolide was achieved using a highly stereoselective aldol reaction of the titanium enolate from a lactate-derived chiral ketone, a stereoselective dihydroxylation and a Yamaguchi macrolactonization reaction.