Structural and polymer-analogous transformations in cellulose on esterification with polyfunctional acids

Structural transformations of cellulose in ethylenediamine and in liquid ammonia and on subsequent esterification with polyfunctional organic and inorganic acids have been studied.The authors thank Prof. G. A. Petropavlovskii for valuable advice and consultation.Tashkent Institute of Chemical Technology, Tashkent, 700029, ul. T. Shevchenko, 1. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 160–164, January-February, 1995. Original article submitted October 11, 1994.     

Kinetics of the hydrolysis of mixed cellulose derivatives

By acetylating weakly substituted Na and H carboxymethylcelluloses and methylcellulose we have synthesized acetone-soluble highly substituted mixed derivatives of cellulose — acetocarboxymethylcellulose and acetomethylcellulose. Water-soluble products have been obtained from these esters by subsequent deep hydrolysis. The kinetics of the hydrolysis of the acetyl groups in the mixed derivatives obtained have been studied. Rate constants of the hydrolysis reactions have been calculated. The influence of the substituted groups on the acetylation and hydrolysis reactions has been determined.Tashkent Institute of Chemical Technology. Translated from Khimiya Prirodnykh Soedinenii, Vol. 33, No. 1, pp. 102–106, January–February, 1997.     

Density results in the Δ20 e-degrees

We show that the Δ⁰ ₂ enumeration degrees are dense. We also show that for every nonzero n-c. e. e-degree a, with n≥ 3, one can always find a nonzero 3-c. e. e-degree b such that b < a on the other hand there is a nonzero ωc. e. e-degree which bounds no nonzero n-c. e. e-degree. Received: 13 June 2000 / Published online: 3 October 2001     

Transport and magnetic properties of a Zn<Subscript>0.1</Subscript>Cd<Subscript>0.9</Subscript>GeAs<Subscript>2</Subscript> + 10 wt % MnAs composite with magnetic clusters at high pressure

The temperature (T = 77–420 K) dependences of the electrical resistivity and the magnetization, the magnetic-field (H ≤ 5 kOe) and pressure (P ≤ 7 GPa) dependences of the resistivity, the Hall coefficient, and the magnetization have been measured in the Zn_0.1Cd_0.9GeAs₂ + 10 wt % MnAs composite with the Curie temperature T _C = 310 K. The magnetoresistive effect has been observed at high hydrostatic pressure to 7 GPa. At nearly room temperature, the pressure dependence of the magnetization demonstrated a transition from the ferromagnetic to paramagnetic state at P ~ 3.2 GPa that was accompanied by the semiconductor–metal phase transition.     

Maps of Broadband Quantum Memory Based on an Atomic Frequency Comb

Optics and Spectroscopy - The influence of the parameters of an inhomogeneously broadened optical transition in the shape of an atomic frequency comb on dispersion effects in the quantum-memory...     

Hydrogen‐Bond‐Guided Self‐Assembly of Nucleotides on a Receptor‐Array Surface

The hydrogen‐bond‐guided self‐assembly of 5′‐ribonucleotides bearing adenine(A), cytosine (C), uracil (U), or guanine (G) bases from aqueous solution on a lipid‐like surface decorated with synthetic bis(Zn^II–cyclen) (cyclen=1,4,7,10‐tetraazacyclodododecane) metal–complex receptor sites is described. The process was studied by using surface plasmon resonance spectroscopy. The data show that the mechanism of nucleotide binding to the 2D template is influenced by the chemistry of the bases and the pH value of the solution. In a neutral solution of pH 7.5, the process is cooperative and selective with respect to Watson–Crick pairs (A–U and C–G), which form stable double planes in accordance with the Chargaff rule. In a more acidic solution at pH 6.0, the interactions between complementary partners become non‐cooperative and the surface also stabilizes mismatched and wobble pairs due to the pH‐induced changes in the receptor coordination state. The results suggest that hydrogen bonding plays a key role in the self‐assembly of complementary nucleotides at the lipid‐like interface, and the cooperative character of the process stems from the ideal matching of the orientation and chemistry of all the interacting components with respect to each other in neutral solution.