K. Vacek

Models of pigment-protein interactions in photosynthetic systems: Tetraphenylporphyrin complexes with polycationic sequential polypeptides. Absorption, circular dichroism and fluorescence properties

Abstract Absorption and circular dichroism spectra and steady state and time-resolved fluorescence of complexes of 5,10,15,20-tetrakis (4-carboxyphenyl)porphyrin with sequential helical polypeptides (L-Lys-L-Ala) n , (L-Lys-L-Ala-L-Ala) n , and (L-Lys-L-Ala-L-Ala-L-Ala) n are studied. Changes of electronic transition energies, induction of optical activity and two-component fluorescence decay with components t 1 = 2–3 ns and t 2 = 180 ps characterize the complexed pigment. Dependence of these changes on relative number of lysine amino acids in polypeptide primary structures was observed and is discussed in terms of perturbational influence of polypeptide molecular field on mixing of porphyrin electronic states.

Site-selection and Shpolskii spectroscopy of model photosynthetic systems

Low temperature (T= 10 K) site‐selection fluorescence and excitation spectra of both isolated pheophorbide‐a molecules (I PHEO) and pheophorbide covalently bonded to the synthetic l‐lysyl‐l‐alanyl‐l.‐alanine polypeptide (B PHEO) were measured in dimethylformamide (DMF) matrices. The fluorescence spectra display sharp vibronic lines at different wavenumbers for different dye laser excitation wavelengths, superimposed on a broad band background. Spectral analysis provides frequencies of normal vibrations (FNV) and site distribution functions (SDF). The FNV and SDF of I PHEO in DMF have been found to show good agreement with other chlorophyll‐like molecules. A covalent binding between the polypeptide and PHEO molecules produces only slight changes in FNV but significant broadenings and shifts to lower energies in SDF. The fluorescence spectra of I PHEO in a typical Shpolskii matrix (n‐octane) were also measured and found to exhibit sharp non‐shifting vibronic lines for all wavelengths and kinds of excitation. A general model explaining both site‐selection and Shpolskii spectroscopy is presented.

Luminescence of direct-and indirect-gap electron-hole plasma in TlBr

Abstract Luminescence of TlBr crystals highly excited by a nanosecond pulsed-dye laser (3.4 eV) at the bath temperature ∼ 8.5 K was studied. Two emission lines labeled A (∼ 2.98 eV) and B (∼ 2.62 eV) were found, which show typical behavior of the electron-hole plasma recombination radiation. The A-line is assigned to the recombination of e-h pairs in the direct gap ( X + 6 − X - 3 ) and the B-line to the simultaneous recombination in the indirect gap ( X + 6 − R - 6 ). Condensation of carriers into an electron-hole liquid was not observed.

ПРИГОТОВЛЕНИЕ И ХАРА КТЕР ПОВЕРХНОСТИ ПЛАСТИНОК AgBr

AbstractРазработан метод при готовления монокрис таллических пластин ок AgBrдля оптических изме рений. На образцах с оп ределенным содержанием нечисто т изучалисъ некоторы е явления, связанные с приготовлением обр азцов и их механическ им состоянием.

Fröhlich coherent vibrations and raman scattering

Coherent vibration systems are very likely composed of oscillating protein molecules located in the closed surface of the plasma membrane. Except short periods in the cell life, the distribution of the oscillating molecules corresponds to the condition of the minimum energy of the generated electromagnetic field. In this case the Raman scattering is hardly possible.

Multiple quantum terms in the fröhlich kinetic equation

Abstract Energy stored in a coherent state may shift the vibration system into a highly nonlinear region where strong interaction without the help of the heat bath may be significant. Multiple quantum processes of this type are analyzed.

Low temperature laser fluorescence and excitation spectra of free base phthalocyanine in normal alkanes matrices (Shpolskii effect)

Excitation and fluorescence spectra of free base phthalocyanine were studied in matrices of normal alkanes (C8H18, C12H26, C16H34) at low temperatures (5 to 30 K). Narrow band excitation of fluorescence using a pulsed tunable dye laser was used for site selection to eliminate ambiguities due to impurities and multiple sites. Fluorescence and excitation spectra show quasiline structure. Multiplicity of 0-0 transitions depends on the chain length of normal alkanes. The spectra and frequencies of normal vibrations are compared with those of phthalocyanine in other n-alkanes (C9H20, C10H22) and noble gas matrices (Ar, Ne) under different excitation conditions.

Computer simulation of the Fröhlich coherent vibrations

In a nonlinear vibration system with energy supply the lowest frequency mode may be coherently excited as was predicted by Fröhlich. Computer simulation of nonlinear vibration systems reveals that even the higher frequency modes may be excited. The conditions for higher frequency modes excitation are specified. Coherent states may be excited in the time period less than about one hour after switching on the energy supply.

Some remarks on photoluminescence of AgCl crystals excited by laser or after deformation

This paper summarizes and analyses our experimental results obtained on photoluminescence of AgCl crystals excited by ruby and u.v. laser in first part, and after and during deformation in second part. The influence of pressure on AgCl photoluminescence is explained by means of a qualitative model based on charged dislocations for both the elastic and plastic regions of the deformation curve.

ВЛИЯНИЕ ДАВЛЕНИЯ HA ПО ГЛОЩЕНИЕ ГАЛОГЕНИДО В СЕРЕБРА I

AbstractИзучалось влияние да вления на границу nогл ощения чиСтых монокр исталлов AgBr, AgClи AgI.Поглощение изме рялоСь при температу ре −180 °С. Обнаружено смеще ние границы поглощен ия в сторону ультраφиолетовой ча сти спектра. Смещение объясняется в соотно шении с работой Биллига [7],ра сширением запрещенн ой зоны вследствие умен ьшения постоянной ре шетки кристалла под влиянием давления.