Hydration of a B-DNA Fragment in the Method of Atom-atom Correlation Functions with the Reference Interaction Site Model Approximation

We propose an efficient numerical algorithm for solving integral equations of the theory of liquids in the Reference Interaction Site Model (RISM) approximation for infinitely dilute solution of macromolecules with a large number of atoms. The algorithm is based on applying the nonstationary iterative methods for solving systems of linear algebraic equations. We calculate the solvent-solute atom-atom correlation functions for a fragment of the B-DNA duplex d(GGGGG).d(CCCCC) in infinitely dilute aqueous solution. The obtained results are compared with available experimental data and results from computer simulations.Comment: 9 pages, RevTeX, 9 pages of ps figures, accepted for publications in JC

Insertion of carbenes into p-h bonds. 5. f synthesis of new phosphonates and phosphinates in reactions catalysed by cu, pd, rh, ni complexes

Cu(OTf)2 and Cu(acac)2 were found to be the most effective catalysts in the reaction of diazo compounds Ph2CN2 (1a), EtOC(O)CHN2 (lb), MeOC(O)CHN2 (1c), MeC(0)CN2C(O)OMe (1d), Cl-CH2C(O)CHN2 (1e) and CH2N2 (1f) with hydrophosphoryl compounds (MeO)2P(O)H (2a), (t-BuO)2P(O)H (2b), Ph(MeO)P(O)H (2c), (EtO)2P(O)H (2d) and (FORMULA OMITTED) resulting in P-C bond formations. Cu, Pd and Rh acetates and Ni(acac)2 have a much lower efficiency. Chlorines in Cl3CC(O)CH2P(O)(OMe)2 (3k) and Cl2CHC(O)CH2P(0)(OMe)2 (31) are reduced in the copper catalysed Atherton-Todd reaction. © 1992, Taylor & Francis Group, LLC. All rights reserved

Phosphorinane and enol rings in one molecule. Evidence for reciprocal stabilization of half-chair conformations

The X-ray crystal structure of 2-(2′,4′-dioxo-3′-pentyl)-5,5-dimethyl-2-oxo-1,3,2- dioxaphosphorinane (2) reveals significant half-chair distortion of the axially oriented cis-enol ring. The molecule also undergoes in-plane deformations. R(O...O) = 2.410 Å in the enol moiety indicates a very strong hydrogen bonding. The enol content, δ OH and thermodynamic parameters for the axial-equatorial conformational and keto-enol equilibriums were obtained from 1H, 31P NMR and IR measurements in comparison with the planar 4,6-dimethyl isomer (1) containing equatorially oriented enol ring. The X-ray single crystal structure of 5,5-dimethyl-2-(methoxycarbonyl-3′-oxo-2′-butyl)-2-oxo-1,3,2- dioxaphosphorinane (3) reveals the unusual half-chair conformation of the dioxaphosphorinane cycle disposed a trans-enol ring substituent. 1H, 31P NMR and IR solution data support the same structure displays a strong conformational preference while the minor forms are chair conformers with an axial or equatorial cis-enol ring

Stereospecific thionation of 2-ethoxy-1,2-oxaphosphorinane 2-oxide and its derivatives with Lawesson's reagent

The parent phostone, 2-ethoxy-1,2-oxaphosphorinane 2-oxide 1, and derivatives with substituents at the 3-position (methyl, phenyl, and benzyl; compounds 2-4) were convened with Lawesson's reagent to provide the corresponding sulfide analogues 5-8 in moderate yields. The conversion of 2-4 occurred with retention of configuration at the phosphorus center. This was implied from the relative R(f) values and 13C and 31P NMR chemical shifts of the individual isomers and confirmed for the transformation of 3b to 7b by X-ray structures of each of these. Oxidation of 7b, 8a, and 8b with m-chloroperoxybenzoic acid alone led to the corresponding oxides 3b, 4a, and 4b with retention. The presence of trifluoroacetic acid during this oxidation process led to varying degrees of epimerization about phosphorus and was dependent on the relative molar equivalents of this acid

Reactions of diazoacetates with phosphate triesters and thiophosphate triester: >P+-O-C-< and >P+-S-C-< intermediacy formation

Diazoacetates 1a,b undergo BF3 · OEt2 catalyzed carbenoid attack on the oxygen of the phosphoryl double bond of phosphate triesters 2a-c or on the sulfur of thiophosphoryl double band of thiophosphate 9 to form corresponding O-alkoxycarbonylmethylphosphates 3a-c or S-alkoxycarbonylmethylphosphate 13

Equilibrium CH-acidities of dimethyl 2-dimethoxyphosphoryl malonate and its thiophosphoryl analog

The p Ka values of dimethyl 2-dimethoxyphosphoryl malonate and of its thiophosphoryl analog have been measured by transmetallation using the inclusion complex of Li+ with [2.1.1]-cryptand as the metallation agent. © 1994 Plenum Publishing Corporation

THE BEAM ENVELOPE CONTROL IN SC LINAC FOR THE PROTON RADIOTHERAPY

Abstract Proton cancer therapy is conventionally based on normal conducting synchrotrons and cyclotrons. The high electrical power consumption and especial devices necessary to energy variation are main problems of such facilities. Superconducting linacs based on short identical independently phased cavities have a seriously progress and it&apos;s development allow to propose their using for medical application. High accelerating gradient and small capacity losses nearly 10 -4 W/m are main advantages in advance of normal conducting facilities, the energy variation can be realized by means of RF field amplitude and phase variation in a number of cavities. Besides linac structures are lack of unwieldy magnetic system, simplicity of input and output of particles and high current densities. The parameters choose and the optimization for SC linac structure with energy up to 240 MeV and envelope control will discuss in this paper. The simulation was done using BEAMDULAC-SCL cod

Broadband SNAIL parametric amplifier with microstrip impedance transformer

Josephson parametric amplifiers have emerged as a promising platform for quantum information processing and squeezed quantum states generation. Travelling wave and impedance-matched parametric amplifiers provide broad bandwidth for high-fidelity single-shot readout of multiple qubit superconducting circuits. Here, we present a quantum-limited 3-wave-mixing parametric amplifier based on superconducting nonlinear asymmetric inductive elements (SNAILs), whose useful bandwidth is enhanced with an on-chip two-section impedance-matching circuit based on microstrip transmission lines. The amplifier dynamic range is increased using an array of sixty-seven SNAILs with 268 Josephson junctions, forming a nonlinear quarter-wave resonator. Operating in a current-pumped mode, we experimentally demonstrate an average gain of $17 dB$ across $300 MHz$ bandwidth, along with an average saturation power of $- 100 dBm$, which can go as high as $- 97 dBm$ with quantum-limited noise performance. Moreover, the amplifier can be fabricated using a simple technology with just a one e-beam lithography step. Its central frequency is tuned over a several hundred megahertz, which in turn broadens the effective operational bandwidth to around $1.5 GHz$.Comment: 7 pages, 3 figure