Ab initio MRD-CI investigation of the electronic spectrum of 1-chloromethyl hypochlorite ClCH2OCl in comparison with isomeric dichloromethanol Cl2CHOH

The electronic absorption spectrum of 1-chloromethyl hypochlorite ClCH₂OCl is computed with multi-reference configuration interaction (MRD-CI) methods and compared to isomeric dichloromethanol. While the first dipole-allowed transitions of dichloromethanol Cl₂CHOH are obtained above 7 eV, the corresponding transitions of ClCH₂OCl are obtained at much lower energy, namely 3.66eV (1¹A″ ←[Xtilde]¹A′), 4.96eV (2¹A′←[Xtilde]¹A′), 6.04eV (2¹A″←[Xtilde]¹A′) and 6.67eV (3¹A′ ← [Xtilde]¹ A′). A further strong transition is computed at 7.82eV (4¹A′ ← [Xtilde]¹A′) with a relatively large oscillator strength of ? = 0.4.     

OLIGONUCLEOTIDE PHOTOPRODUCTS FORMED BY PHOTOLYSIS OF POLYRIBOBROMOURIDYLIC ACID

Abstract— Polyribobromouridylic acid was irradiated with 313 nm light at an exposure of ˜ 190 pE/cm*. Oligonucleotides found after RNase hydrolysis of the photolysed poly-rBrU were isolated by DEAE-cellulose chromatography and partially characterized. The dmucleo-tide fraction, found in highest amounts, was not susceptible to hydrolysis by KOH or snake venom phosphodiesterase and may contain a coupled photoproduct. The properties of the dinucleotide were not those of a molecule containing a cyclobutane-type dimer, but were compatible with the properties of a coupled product similar to 5–5'-diuracil. The trinucleotide fraction probably consisted of more than one component. One component may contain a dimeric photoproduct. The tetranucleotide material was sensitive to cleavage into fragments by KOH, and could consist of adjacent photoproducts of the types found in the di- and trinucleotide fractions. The photoproducts formed over a range of lower doses of light were found to have properties similar to those found at high doses.     

Monte Carlo simulations of an amphiphilic polymer at a hydrophobic/hydrophilic interface

Monte Carlo simulations have been carried out for an off-lattice model of an amphiphilic polymer at a hydrophobic/hydrophilic interface. The model system consists of a polynorbornene backbone with poly(ethylene oxide) (PEO) grafts modelled atomistically at an idealized interface between hydrophobic and hydrophilic regions, which are represented by external potentials. Results are presented for the distribution of PEO chain ends, and the density of PEO segments perpendicular to the surface. The latter is used to provide predictions for neutron reflectivity profiles normal to the surface as a function of the lateral confinement of the PEO grafts. At low surface coverage the simulation results are found to be in good agreement with experimental neutron scattering results from similar polymers studied at the water/air interface.     

The electronic spectrum of chloromethanol ClCH2OH in comparison with isomeric methylhypochlorite CH3OCl

Large-scale multi-reference configuration interaction calculations are employed to differentiate in the electronic spectrum between chloromethanol ClCH₂OH and its isomer methylhypochlorite CH₃OCl by certain fingerprints. The first dipole-allowed transitions of the CH₃OCl spectrum are obtained at 4.13 eV(1¹A″ ← X¹A¹) and 5.50eV (2¹ A′ ← X¹A′). in reasonable agreement with prior calculations (4.24eV and 5.58eV) and in accordance with experimental measurements of 4.02 eV and 5.27 eV. For the yet to be observed spectrum of ClCH₂OH the corresponding transitions are predicted at higher energies of 7.32eV for 1¹A″ ← X¹A′ and 7.95eV for 2¹A′ ← X¹A′ and 7.98eV for 2¹A″ ← X¹A′.     

Ab initio and RRKM studies of decomposition and interconversion pathways of ClCH2OH and CH3OCl isomeric species

The photofragmentation and photointerconversion pathways of the CH₃OCl and ClCH₂OH species are studied using quantum mechanical and RRKM theories. Ten possible channels are investigated in total and the relative importance of the various pathways in stratospheric photochemistry is discussed.     

PHOTOLYSIS OF POLYRIBOBROMOURIDYLIC ACID

Abstract— Photolysis of polyribobromouridylic acid with 313 nm light at neutral pH caused extensive debromination and a loss of A₂₈₀ (280–nm absorbance) without comparable increase in A₂₆₀. At an exposure of 190μE/cm ² , strand breakage occurred on the average of one break every 170 BrU residues. Little if any pyrimidine hydrate was produced. Exhaustive RNase hydrolysis of photolysed polymer gave a mixture of mononucleotides and oligonucleotides. The mononucleotide fraction was found to be composed of unaltered BrUMP and contained little if any UMP. Irradiation of the polymer at alkaline pH caused little or no debromination or spectral change.