Prof. Svetlana Zheludeva was an eminent scientist, a remarkable representative of Russian scientific community. The famous French scientist Georges Cuvier once said: “Those, who are born with the noble capacity to enlighten people, can feel the power and indescribable fascination of truth they are searching for”. This is certainly true of Prof. Zheludeva. All her life through she was admiring the “miracles of the universe”; she was untiring in her quest for knowledge and love for science. The people, who were happy enough to know her personally, remember her bright eyes, her emotional and enthusiastic manner of discussing the results of research. At the same time, in the course of such discussions her reasoning was sharp and critical; she had a skeptical mind that could not bear lack of judgement.
Prof. Zheludeva’s distinctive feature was her ability to grasp the essence of problem quickly and then sum it up in a clear and succinct manner. She was also remarkable for considering things from a new and unexpected angle; where everyone else saw just a handful of pieces, she managed to see the whole jigsaw puzzle at a single glance. She would transform her interlocutor’s vague speculations into plain statements, immediately detecting his strong and weak points.
It was in her nature to carry all the tasks through, to search for an exhaustive solution for every problem. Having set a task to herself, she acted firmly and decisively, guided by her high principles and never intimidated by any obstacles. And she succeeded, thanks to her excellent managerial skills and power of persuasion.
Prof. Zheludeva’s main sphere of research was the development of new high-resolution spectrally selective methods of studying the structure and properties of new materials with the use of x-rays and synchrotron radiation. She was daring in her research. Her curiosity and original mind always made her look for something unexpected; with her excellent memory and logic, she could quickly master a new method or field of research. While sincerely admiring other scientists’ achievements, Prof. Zheludeva was never subdued by authorities to the point of losing the independence of her own thought. So it was in the late 1980s, when she started to study layered synthetic microstructures by means of x-ray standing waves. The method is based on the simultaneous registration of x-ray reflection and secondary radiation (such as characteristic fluorescence) excited by incident x-ray beam under total external reflection or Bragg diffraction. This method is unique in the sense that it allows, literally, to scan a thin film in the direction of the normal to the surface and directly locate the atoms of a certain type, inside as well as on the surface of a nanostructure.
This field of research was then dominated by the studies by American (Bedzyk M.) and Japanese (Matsushita T.) scientists. These studies were well-known, and their authority was virtually indisputable. But it did not prevent Svetlana Zheludeva from starting her own research in this field, that was completely new to her, and within a short time she managed to obtain considerable results.
Among her most interesting works of this period there are studies of penetration of metal ions into layered organic structures; it was demonstrated how x-ray standing waves can be used to locate the ions within molecular films, that is, the basis was laid for studying diffusion processes in molecular electronic objects and the transport functions of cellular membrane models. Impressive results were got in the course of experimental measurements with ultrathin x-ray waveguide layered structures.
The results of these studies were published in a number of articles that quickly made Svetlana Zheludeva known in the scientific community. The general style of these articles deserves a special mention. Svetlana did not ever do things with indifference; she was inspired by her subject, and none of her works can be called dull or offhand. At the same time, her strict, exacting mind could not tolerate slapdash work and charlatanry in science. In her articles the problem is clearly outlined from the very start, the argumentation is logical, the definitions are clear-cut; there were no place there for doubtful hypotheses or vague speculations. All of her studies are characterized by the truly scientific approach to the subject, by independence and originality of thought.
The results of this research form the basis for Svetlana Zheludeva’s doctoral dissertation “Method of Long-Period X-ray Standing Waves for Characterizing Layered Nanostructures,” successfully defended in 1995. This work had demanded years of painstaking studies and a lot of experiments. Some research in this field had been done before her, but only fragmentarily, with reference to single facts. In Svetlana’s dissertation the whole bulk of results of her research is summed up, and a new x-ray method for studying nanomaterials is presented in a clear, detailed and scientifically substantiated manner.
In the late 1990s administrative work at IC RAS (in the capacity of deputy director) and at the Ministry of Science and Education took much of Prof. Zheludeva’s time and energy, but, nevertheless, the research retained primary importance and determined everything else. Being a mature scientist already, Svetlana was never tired to acquire knowledge. She would not miss an opportunity to listen to an interesting report; notwithstanding her huge workload, she always found the time to discuss a new scientific problem, and she was equally attentive while listening to a member of Academy of Sciences and to a young researcher. She did not claim the status of absolute scientific truth for her private opinion, and she rejoiced at her colleagues’ success, forgetting her own troubles and preoccupations.
Prof. Zheludeva did not only know how to deal with complicated scientific problems; due to her remarkable intuition of a researcher she managed to choose and set to herself most crucial tasks. Among such tasks one should mention the study of bioorganic molecular layers on liquid surfaces. Ordered bioorganic nanosystems are of interest especially because their composition and morphology make them an adequate model of cellular membranes. X-ray studies of bioorganic layers on liquid surface allow to get unique information about membrane models in the conditions most resembling natural, when protein molecules retain their conformational structure, nativity, the structured character of protein-lipid connections and functional activity. The results of this kind of research help to obtain information about the properties, principles of functioning and changes in molecular structure of biological membranes in physiological conditions and under exposure of a cell to pathological effects.
The main difficulties in the course of experimental measurements of molecular layers on liquid surfaces are connected with the fact that one cannot tilt a sample (that is, a Langmuir bath filled with water) in order to change the angle between the beam and liquid surface, the way it is done with solid samples; one has to deflect the beam. It poses a considerable problem from the point of view of x-ray equipment; as a result, the study of bioorganic layers on liquid surface remains difficult to perform for the majority of experimenters, notwithstanding the great potential of the method. Nowadays this kind of research is being done only in some scientific centers (mainly at synchrotron radiation sources) and remains fragmentary.
Experimental measurements on liquid with the help of x-ray standing waves are even harder to perform, as it is necessary to accumulate for a long time the extremely low-intensive fluorescent signal from weakly-scattering bioorganic films. In the process of long-term (often hours-long) measurements the liquid evaporates, and thus the level of reflecting surface changes uncontrollably. Besides, the prolonged and intensive x-ray radiation damages the molecular layer itself, and its surface considerably shrinks.
The first measurements on the air/water borderline using x-ray standing waves method were done by a group of American scientists (Bloch J.M., Yun W.B.). Their task was to study the segregation of metal ions from the solution towards the air/water interface; they obtained information concerning the concentration profile of different elements in the solution near the interface. But the study of a single monolayer on liquid surface was Prof. Zheludeva’s achievement. The x-ray reflectivity and the fluorescence yield measurements were performed at the open undulator beamline ID10B at the European Synchrotron Radiation Facility (ESRF), Grenoble, France. The first objects chosen for the research were metal-substituted phthalocyanines that form stable monolayers on liquid surfaces and contain metal ions. The location of metal ions within them is known, and so the main problem, crucial for the development of the method in question, was to adapt the x-ray fluorescent measurements equipment for studying organic monolayers on liquid surface, bearing in mind all the above-mentioned experimental problems.
A series of experiments that followed (performed at ESRF) was aimed at investigations of self-assembling processes in a protein-lipid system on a water subphase where protein and phospholipid molecules were free to move over the water subphase. In order to form an ordered protein-lipid film on the water subphase protein-lipid mixture of alkaline phosphatase and phosphatidylinositol has been injected under the phospholipid monolayer preliminarily deposited on the water subphase by Langmuir method. XRSW measurements revealed the presence of trace Ni contaminations incorporated from the water subphase in the protein-lipid film. Numerical analysis of the XRSW fluorescence data allowed to locate the position of P, Zn and Ni ions and to obtain the information on the distribution of protein and phospholipid molecules over the depth of the film that has been formed on the water subphase. The protein-lipid film was found to separate into layered structure, the protein molecules arranged themselves by self-assembling into a pure protein layer containing no phospholipid molecules. Two layers of the proposed model appeared to satisfy the conditions which provide the resonance enhancement of the wave field within these layers.
One of the remarkable traits of Prof. Zheludeva’s character was her patriotism where Russian science was concerned. Even dealing with strictly scientific matters, she acted as a statesman preoccupied with preservation and development of the scientific potential of our country. Everything she did was marked by sincere aspiration for the success of Russian science. The study of bioorganic films on liquid surface, that started to be performed so fruitfully in France at ESRF, could be continued at this international center, but Prof. Zheludeva made the decision to create an analogous experimental station at Kurchatov Center of Synchrotron Radiation and Nanotechnology, in order to initiate the development in Russia of a priority scientific school for studying structural characteristics of functionally active bioorganic nanosystems on liquid surface. It demanded a whole complex of measures, from solving technical and methodological problems to the creation of up-to-date experimental equipment for carrying out x-ray fluorescence measurements at a synchrotron source. Not to mention the fact that, in order to equip the station with the necessary x-ray instrumentation, one had to find the sources of substantial financial support. To start this most challenging project one had to be really daring and to believe in Russian science firmly.
An original optical system was elaborated at the station to manage the falling beam: the angle between synchrotron radiation beam and the surface of a horizontally fixed sample is changed by means of successive reflection of the beam from two mirrors of full external x-ray reflection. The first mirror reflects a horizontal beam, and the second points it at the sample at a changing angle. The first mirror helps to vary this angle from zero value with the use of the whole front of the beam. During the whole experiment this way of managing a falling beam allows not to move the bath and to leave the beam on the surface of the sample fixed. Unfortunately, this work remained unfinished; at the moment separate units of the station are being assembled and adjusted.
The life of Prof. Svetlana Zheludeva, albeit relatively short, was remarkably integral, lived efficiently, on a grand scale, and beneficially for the people around her.