J. Bok

Metalation of 5,10,15,20‐tetrakis(1‐methyl‐4‐pyridyl)porphyrin in silver colloids studied via time dependence of surface‐enhanced resonance Raman spectra

In SERS-active systems, when a free base porphyrin is adsorbed at a roughened metal surface, the metal ion may be incorporated into the porphyrin core. We have investigated the metalation kinetics of 5,10,15,20-tetrakis(1-methyl-4-pyridyl)porphyrin (TMPyP), reflected in the time evolution of its SERRS spectra. To establish proper metalation Raman markers, resonance Raman spectra of the free base and chemically Ag metalated TMPyP forms were measured under different conditions. The increase in intensity of the 395 cm-1 line, the decrease in intensity of the 329 cm-1 line, the reduction of the 1337+1360 cm-1 doublet to one strong line at 1340 cm-1 and the vanishing of the 1140 cm-1 medium line (the last exceptionally for 514.5 nm excitation) were found to be suitable markers for quantitative analysis. All other spectral changes related to metalation may coincide with effects caused by other variations of the porphyrin state. Time evolution of the porphyrin metalation was studied in various Ag colloid systems, with or without phosphate anions, citrate and/or Triton X-100. Time-dependent SERRS spectra of TMPyP were recorded within periods from minutes to several hours. Factor analysis of the SERRS spectra proved that the spectral changes were induced by only one phenomenon (metalation). The SERRS spectra were decomposed into the spectrum of the free base TMPyP and that of its Ag metalated form, and the metalation kinetics were determined by means of the time dependence of the metalated form portion in the SERRS spectrum. The results show a remarkable reliance on the state of the metal surface.

CdTe and CdZnTe crystals for room temperature gamma-ray detectors

Abstract CdTe(Cl) detectors from CdTe single crystals, grown by the Bridgman method from Te-rich melt, were fabricated. The quality of the detectors was tested with 57Co and 241Am sources. In the 57Co spectrum low noise is demonstrated by the presence of a 14 keV peak and good resolution ≈7 keV (FWHM) evident from the separation of 122 and 136 keV peaks. A review is given of the state-of-the-art properties of (CdZn)Te single crystals prepared for substrates in the Institute of Physics of Charles University. The quality of samples is tested by measurements of the diffusion length of minority carriers, from which the mobility–lifetime product is evaluated.

Refractive index of CdTe: Spectral and temperature dependence

The refractive index of CdTe was determined from interference maxima in the transparency region from 10 to 295 K. Parameters in a four-oscillator model were fitted to experimental data and an empirical formula for the refractive index is given.

Raman spectroscopic study of triplex‐like complexes of polyuridylic acid with the isopolar, non‐isosteric phosphonate analogues of diadenosine monophosphate

The formation of poly(rU) complexes with diadenosine monophosphate (3′–5′) and its four isopolar, non-isosteric phosphonate analogues was studied by means of Raman spectroscopic titration. A set of mixed samples containing the diadenosine monophosphate or monophosphonate and the poly(rU) at various concentration ratios was prepared. The room temperature spectra of mixed solutions were treated by factor analysis and decomposition of the Raman marker bands. For all the species studied, the results revealed an exclusive presence of the triplex-like complexes, i.e. complexes with a 1:2 stoichiometric ratio of the adenosine to uridine units, the Raman spectra of which exhibit all the features typical of the poly(rU)·poly(rA)·poly(rU) triple-helical structure. The individual molar fractions of the free ApA dimer, the free poly(rU) and the triplex-like complex do not fit classical equilibrium equation, because the binding ability of the adenosine dimers to poly(rU) falls significantly for small ApA molar fractions. This tendency is strongest for the natural diadenosine phosphate (3′–5′) and weakest for two analogues in which the —CH2— group in the modified internucleotide linkage is situated closer to the 5′-position. Copyright

Metallation kinetics of a free base porphyrin in surface-enhanced resonance Raman scattering active Ag colloid system as a probe of porphyrin–nucleic acids interaction

Abstract Complexes of the cationic free base 5,10,15,20-tetrakis (1-methyl-4-pyridyl) porphyrin with DNA, double-stranded poly(dA-dT) and poly(dG-dC) polynucleotides have been studied by using surface-enhanced resonance Raman scattering spectroscopy (SERRS). SERRS spectra of these complexes have been recorded during time-scale varying from minutes to days, and the differences in the course of the porphyrin metallation, indicating different accessibility of the metal surface for the porphyrin core in the case of particular complexes, have been monitored. The results obtained for the three studied systems are in very good agreement with the expected dominant types of the porphyrin interaction with the nucleic acids, i.e., intercalation in the case of poly(dG-dC) and external binding in the case of poly(dA-dT).

Preparation of Semi-Insulating CdTe:In by Post-Grown Annealing After Elimination of Te Inclusions

Annealing under Cd-saturated overpressure within the temperature range of 700-800degC was used for elimination of Te inclusions in high resistive In-doped CdTe. Te inclusions were significantly reduced by annealing and only residual inclusions with dimensions less than 1 mum remained in the material. All annealed samples were converted to the high conductive n-type after Cd-saturated annealing. Annealing finished by quenching at 550degC, 650degC, and 750degC under various Cd/Te overpressures was used to find an annealing conditions leading to the preparation of a semi-insulating material. The range of optimal overpressures was found to be very narrow and keeping these conditions during annealing and quenching is practically impossible. The semi-insulating material was prepared by means of Te-rich annealing finished by slow cooling. The annealing temperature, In doping concentration, and cooling regime were observed to strongly affect the preparation of semi-insulating material.

A Thought Construction of Working Perpetuum Mobile of the Second Kind

The previously published model of the isothermal Maxwell demon as one of models of open quantum systems endowed with the faculty of selforganization is reconstructed here. It describes an open quantum system interacting with a single thermodynamic bath but otherwise not aided from outside. Its activity is given by the standard linear Liouville equation for the system and bath. Owing to its selforganization property, the model then yields cyclic conversion of heat from the bath into mechanical work without compensation. Hence, it provides an explicit thought construction of perpetuum mobile of the second kind, contradicting thus the Thomson formulation of the second law of thermodynamics. No approximation is involved as a special scaling procedure is used which makes the employed kinetic equations exact.

A universal computer-controlled UV-VIS spectrometer with high resolution monochromator

Abstract A modular UV-VIS spectrometer based on a high-resolution monochromator was computerized using an 8-bit CBM 8296 microcomputer. The hardware of the microcomputer was extended with serial and 64-bit parallel interfaces and with graphics. To control the spectrometer a set of machine code routines was created; they are simply callable from the users program written in BASIC.

Explicit Solvent Molecular Dynamics Simulation of Duplex Formed by the Modified Oligonucleotide with Alternating Phosphate/Phosphonate Internucleoside Linkages and its Natural Counterpart

Abstract Impact of the internucleoside linkage modification by inserting a methylene group on the ability of the modified oligonucleotide to hybridize with a natural DNA strand was studied by fully solvated molecular dynamics (MD) simulations. Three undecamer complexes were analyzed: natural dT11.dA11 duplex as a reference and two its analogs with alternating modified and natural linkages in the deoxyadenosine chain. The isopolar, non-isosteric modified linkages were of 5′-O-PO2-CH2-O-3′ (5′PC3′) or 5′-O-CH2-PO2-O-3′ (5′CP3′) type. Simulations were performed by using the AMBER 5.0 software package with the force field completed by a set of parameters needed to model the modified segments. Both modifications were found to lead to double helical complexes, in which the thymidine strand as well as deoxyriboses and unmodified linkages in the adenosine strand adopted conformations typical for the B-type structure. For each of the two conformational richer modified linkages two stable conformations were found at 300 K: the -ggt and ggt for the 5′PC3′ and ggg, tgg for the 5′CP3′, respectively. Both modified chains adopted helical conformations with heightened values of the inclination parameter but without affecting the Watson-Crick hydrogen bonds.

Concentration dependent behavior of the free base porphyrins in Ag colloid/porphyrin SERS-active system studied via the metalation kinetics

Abstract Metalation of 5,10,15,20-tetrakis(1-methyl-4-pyridyl) porphyrin (TMPyP), adsorbed on laser-ablated Ag colloid was investigated as a function of the porphyrin concentration. Factor analysis and further treatment of the results provided parameters of the metalation kinetics. High sensitivity to the concentration of the TMPyP molecules was demonstrated when qualitative differences were obtained for the concentrations below and above the covering limit.