Robert Kołos

CELL ADHESION TO POLYMERIC SURFACES: EXPERIMENTAL STUDY AND SIMPLE THEORETICAL APPROACH

In a medium without serum, the initial adhesion of L1210 cells to nonsulfonated and sulfonated polymer surfaces was investigated. In the case of sulfonated polymer surfaces, the relative number of adhering cells strongly increases with an increase of the interfacial surface tension; that is, adhesion strongly depends on the surface density of sulfonic groups. However, in the case of nonsulfonated polymer surfaces, the relative number of adhering cells is high and independent of the interfacial surface tension. To extend the basic knowledge of these phenomena, a semi-empirical quantum chemical computational study was undertaken. Simple probe molecules were chosen that mimic the chemical properties of functional groups present on polymeric surfaces. The energies of interaction between these molecules and ones representing the midchain polypeptide building blocks were calculated. To discuss the steric effects involved in similar interactions on real surfaces, a simple model of polymeric surfaces was proposed. Also the interactions among such surfaces and the short hydrated polypeptide chain were studied at the molecular mechanics level of theory. The derived intermolecular energy parameter was found to change in parallel to the number of adhered cells within the two groups of substrata under study: nonsulfonated and sulfonated. The computational results suggest the possible existence of differently arranged cell membrane protein centers responsible for docking to these two types of surfaces.

EVIDENCE FOR DIACETYLENE CATION AS THE CARRIER OF A DIFFUSE INTERSTELLAR BAND

High-quality spectra acquired at three different observatories point to the presence of a new diffuse interstellar band (DIB) at 5069 ?. The spectral profile of this DIB matches published laboratory measurements of the diacetylene cation A 2? u -X 2? g (0-0) low-temperature gas-phase optical absorption. HC4H+ is approximately 60-80 times less abundant than CH along the analyzed lines of sight. Only an upper limit could presently be inferred from the search for an analogous band of the triacetylene cation HC6H+, expected at 6001.1 ?, which implies the HC6H+ to HC4H+ ratio of less than ~1/3.

Matrix isolation IR spectroscopic and ab initio studies of C3N− and related species

Coupled cluster calculations were carried out for C(3)N(-), CCNC(-), C(3)N, CCNC, C(3)N(+), and C(3)O. They support the experimental identification of the C(3)N(-) ion by means of matrix isolation infrared (IR) spectroscopy. The anion was generated in electric discharges through the cyanoacetylene isotopomers HC(3) (14)N, HC(3) (15)N, and (2)HC(3)N, trapped in cryogenic rare gas matrices (Ne, Ar, Kr), and detected via its two most intense IR absorption bands, assigned to the nu(1) and nu(2) stretching vibrations. C(3)N(-) appears to be quite a stable anion, with a vertical detachment energy predicted to be as high as 4.42 eV. A large equilibrium electric dipole moment of 3.10 D facilitates the investigation of C(3)N(-) by microwave spectroscopy and radio astronomy. Various structural parameters and spectroscopic properties have been calculated for all tetra-atomic species considered.

The infrared spectroscopy of HNCCC: matrix isolation and density functional theory study

Abstract Infrared spectra of UV-photolysed argon matrices doped with cyanoacetylene reveal the presence of HNCCC, a carbene (imine) isomer of the parent molecule. The identification of three stretching bands is based on deuterium and nitrogen-15 substitution experiments and on a B3LYP/6-311++G ** density functional theory study. The detection of this energetically unfavourable isomer is facilitated by the high absolute intensity of its IR absorption.

HCNCC - the possible isomer of cyanoacetylene

Abstract HCNCC, the exotic linear rearrangement of cyanoacetylene, is a probable interstellar molecule. The Letter compares CCSD(T)/aug-cc-pVTZ energies of five cyanoacetylene isomers, and predicts properties of the HCNCC ground singlet electronic state: geometry, equilibrium rotational constant, electric dipole moment and vibrational frequencies – based on the coupled-clusters and density functional theory (B3LYP/aug-cc-pVTZ) studies.

IR Low‐Temperature Matrix and ab Initio Study on β‐Alanine Conformers

For the first time the argon-matrix low-temperature FTIR spectra of beta-alanine are recorded. They reveal a quite complicated spectral pattern which suggests the presence of several beta-alanine conformers in the matrix. To interpret the spectra, the eighteen beta-alanine conformers, stable in the gas phase, are estimated at the B3LYP and MP2 levels combined with the aug-cc-pVDZ. Ten low-energy structures are reoptimized at the QCISD/aug-cc-pVDZ and B3LYP and MP2 levels by using the aug-cc-pVTZ basis sets. Assignment of the experimental spectra is undertaken on the basis of the calculated B3LYP/aug-cc-pVDZ anharmonic IR frequencies as well as careful estimation of the conformer population. The presence of at least three beta-alanine conformers is demonstrated. The detailed analysis of IR spectra points to the possible presence of five additional beta-alanine conformers.

Matrix-isolated products of cyanoacetylene dissociation

Abstract The photolysis at 193 and 222 nm of matrix-isolated cyanoacetylene yields isocyanoacetylene, identified by its stretching fundamentals. Another carbene isomer, HNCCC, has been tentatively identified. The possibility of CCCN radical detection is discussed.

Spectroscopy of cyanodiacetylene in solid argon and the photochemical generation of isocyanodiacetylene

Following the measurements of UV and mid-IR spectra of cyanodiacetylene, H-(CC)2-CN, isolated in low temperature Ar matrices, the first photochemical study on this compound and on its 2H isotopomer was carried out with the laser light tuned to 267 nm and with far-UV discharge lamps. Evidence for the formation of isocyanodiacetylene, H-(CC)2-NC, was found in infrared absorption spectra interpreted with the aid of available theoretical predictions.

Spectroscopic identification of 2,4-pyrimidinedithiol; an experimental matrix isolation and ab initio Hartree-Fock and density functional theory study

2,4-Pyrimidinedithiol (the dithiol form of 2,4-dithiouracil) was generated by UV (lambda > 335 nm) irradiation of the dithione form of 2,4-dithiouracil isolated in low-temperature argon or nitrogen matrices. The IR and UV spectra of the photoproduct are reported. The dithiol form of 2,4-dithiouracil was identified by comparison of the experimental spectrum with the spectrum theoretically predicted for this form at the HF/6-31 (d,p) and DFT(B-3LYP)/6-31 (d,p) levels. This comparison resulted also in assignment of the bands observed in the IR spectrum of 2,4-pyrimidinedithiol to the theoretically predicted normal modes.

CAN H2CCC BE THE CARRIER OF BROAD DIFFUSE BANDS

The recent assignment of two broad diffuse interstellar bands (DIBs) near 4882 and 5450 A to the propadienylidene (l-C{sub 3}H{sub 2}) molecule is examined using a statistically meaningful sample of targets. Our spectra clearly show that the strength ratio of two broad DIBs is strongly variable, contrary to what should be observed if both features are due to l-C{sub 3}H{sub 2}, since the proposed transitions are lifetime broadened and start from the same level. Moreover, even in directions where the 4882 DIB and 5450 DIB are strong, the third expected l-C{sub 3}H{sub 2} band, in the 5165-5185 A region, is absent. Another puzzling characteristic of l-C{sub 3}H{sub 2} as the proposed carrier of both broad diffuse bands is its column density of several 10{sup 14} cm{sup -2}, inferred from the equivalent width of the 5450 DIB. This value is one order of magnitude higher than N(CH) toward the same objects and two to three orders of magnitude higher than N(H{sub 2}CCC), measured at radio frequencies in absorption, for comparable samples of the diffuse medium. We conclude that the proposed identification of broad DIBs is unjustified.