An Integrated Approach to Structure Verification Using Automated Procedures

Cobas Gómez Carlos Juan, Bernstein Michael, Sykora Stanislav,
Chapter 12 in Structure Elucidation in Organic Chemistry: The Search for the Right Tools,
edited by Bravo Jorge and Cid Maria-Magdalena, Wiley-VCH 2015, ISBN 978-3527333363. Kindle reader code: B00RZD4CG8.

Spectroscopic methods - of which nuclear magnetic resonance (NMR) is one of the most vital players - have almost entirely replaced those old 'wet chemistry'-based approaches and the art has become a science. The fact that any automatic structure verification (ASV) system measures the degree of compatibility between a proposed molecular structure and the available spectroscopic data is of fundamental importance. This chapter presents a brief survey of existing computer-based verification systems. It reviews the rudiments of NMR data acquisition and processing. The chapter also presents the well-known theory on signal processing to lay the basis required to ensure a minimum level of data quality. It shows some practical examples as well as some general recommendations that could be followed in the conditions commonly used in the context of verification by NMR.

DOI: 10.1002/9783527664610.ch12. Also available for the Kindle reader.

Multinuclear nanoliter one-dimensional and two-dimensional NMR spectroscopy
with a single non-resonant microcoil

Fratila R.M., Gomez M.V., Sykora S., Velders A.,
Nature Communications, 5, Article number: 3025 (2014).

Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical technique, but its low sensitivity and highly sophisticated, costly, equipment severely constrain more widespread applications. Here we show that a non-resonant planar transceiver microcoil integrated in a microfluidic chip (detection volume 25 nl) can detect different nuclides in the full broad-band range of Larmor frequencies (at 9.4 T from 61 to 400 MHz). Routine one-dimensional (1D) and two-dimensional (2D), homo- and heteronuclear experiments can be carried out using the broad-band coil set-up. Noteworthy, heteronuclear 2D experiments can be performed in a straightforward manner on virtually any combination of nuclides (from classical 1H–13C to more exotic combinations like 19F–31P) both in coupled and decoupled mode. Importantly, the concept of a non-resonant system provides magnetic field-independent NMR probes; moreover, the small-volume alleviates problems related to field inhomogeneity, making the broad-band coil an attractive option for, for example, portable and table-top NMR systems.

DOI: 10.1038/ncomms4025.

Automatic assignment of ¹H-NMR spectra of small molecules

Cobas C., Seoane F., Vaz E., Bernstein M.A., Dominguez S., Péres M., Sykora S.,
Magnetic Resonance in Chemistry, 51, 649-654 (2013).

A novel data-evaluation procedure for the automatic atom to peak or multiplet assignment of 1H-NMR spectra of small molecules has been developed using a fast and robust expert system. The applicability and reliability of the method are demonstrated by comparison of a manually assigned database of 1H-NMR spectra with the assignments produced by the automatic procedure. The results of this analysis show an excellent success ratio, indicating that this new algorithm can have a major impact as a time saving tool for the organic chemist. A new graphical feature used to illustrate both the stability and quality of the elementary assignments is also introduced.

DOI: 10.1002/mrc.3995.

Optimization and Automation of Quantitative NMR Data Extraction

Bernstein M.A., Sykora S., Peng C., Barba A., Cobas C.,
Analytical Chemistry, 85, 5778-5786 (2013).

NMR is routinely used to quantitate chemical species. The necessary experimental procedures to acquire quantitative data are well-known, but relatively little attention has been applied to data processing and analysis. We describe here a robust expert system that can be used to automatically choose the best signals in a sample for overall concentration determination and determine analyte concentration using all accepted methods. The algorithm is based on the complete deconvolution of the spectrum which makes it tolerant of cases where signals are very close to one another and includes robust methods for the automatic classification of NMR resonances and molecule-to-spectrum multiplets assignments. With the functionality in place and optimized, it is then a relatively simple matter to apply the same workflow to data in a fully automatic way. The procedure is desirable for both its inherent performance and applicability to NMR data acquired for very large sample sets.

DOI: 10.1021/ac400411q.

PERFIDI filters to suppress and/or quantify relaxation time components in multi-component systems:
An example for fat-water systems

Bortolotti V., Fantazzini P., Gombia M., Greco D., Rinaldin G., Sykora S.,
J.Magn.Reson., 206, 219-226 (2010).

Parametrically Enabled Relaxation FIlters with Double and multiple Inversion (PERFIDI) is an experimental NMR/MRI technique devised to analyze samples/voxels characterized by multi-exponential longitudinal relaxation. It is based on a linear combination of NMR sequences with suitable preambles composed of inversion pulses. Given any standard NMR/MRI sequence, it permits one to modify it in a way which will attenuate, in a predictable manner and before data acquisition, signals arising from components with different r rates (r = 1/T₁). Consequently, it is possible to define relatively simple protocols to suppress and/or to quantify signals of different components. This article describes a simple way to construct low-pass, high-pass and band-pass PERFIDI filters. Experimental data are presented in which the method has been used to separate fat and water proton signals. We also present a novel protocol for very fast determination of the ratio between the fat signal and the total signal which avoids any time-consuming magnetization recovery multi-array data acquisition. The method has been validated also for MRI, producing well T₁-contrasted images.

DOI: 10.1016/j.jmr.2010.07.010.
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PERFIDI: Parametrically Enabled Relaxation Filters with Double and multiple Inversion

Sykora S., Bortolotti V., Fantazzini P.,
Magn.Reson.Imaging, 25, 529-532 (2007).

We present a novel approach to the NMR / MRI analysis of complex samples with a non-trivial distribution of longitudinal relaxation rates R1. The method, denominated PERFIDI, aims at separating signals arising from components with different R1's prior to actual data acquisition. Given any standard NMR / MRI pulse sequence, by itself insensitive to differences in R1's, it can be combined with a PERFIDI preamble which functions as a preliminary R1 filter and confers on the original technique sensitivity to the R1 dimension. The article states the principles of the approach, including the way of accounting for instrumental imperfections, and shows how to build PERFIDI filters with specific filter profile functions. Using terms borrowed from electronics, these are classified as low-pass, high-pass and band-pass types. Also included are an experimental verification example and a discussion of potential applications of PERFIDI in various NMR areas.

DOI: 10.1016/j.mri.2006.12.001.
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Technical Aspects Of Fast Field Cycling

by Ferrante Gianni Mario, Sykora Stanislav,
in Advances in Inorganic Chemistry, Vol.57, pp.405-470, Editors van Eldik R., Bertini I., Elsevier 2005, ISBN 978-0120236572.

This work reviews the current state-of-the-art of Fast-Filed-Cycling NMR Relaxometry from the technical as well as methodological points of view. Apart from a general exposition of the principles of the technique, it includes also the experience of the Authors who accepted the challenge and developed the relevant technology from its home-made stage to an industrial series production. The review provides an in-depth insight particularly useful for operators of FFC NMR instrumentation who carry out the actual measurements of NMRD relaxation profiles.

DOI: 10.1016/S0898-8838(05)57009-0.
View the Index and/or the draft version of the review. 176 references.

A Proton NMR Relaxation Study of Hen Egg Quality

Laghi L., Cremonini M.A., Placucci G., Sykora S., Wright K., Hills B.
Magn.Reson.Imaging, 23, 501-510 (2005).

A quantitative analysis of NMR proton relaxation in hen egg albumen and yolk is undertaken to research the causes of quality loss during the first few days of storage and to access the feasibility of an on-line NMR sensor of internal egg quality. It is shown that the change in the transverse relaxation in thick egg albumen mainly results from an increase in proton exchange rate resulting from a pH increase attributed to loss of carbon dioxide by diffusion through the eggshell. The results suggest that the low field T₁ is the best relaxation time indicator of albumen quality.

DOI: 10.1016/j.mri.2004.12.003.
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The Limits of NMR Imaging.

Sykora S., Magn.Reson.Imaging 9, 833-838 (1991).

The limits of isotropic spatial resolution in NMR imaging are estimated starting from an explicit formula for S/N ratio. It is shown that the limit is essentially imposed by the sensitivity of the NMR experiment. The required acquisition time is of course also a factor, but since it increases with the 7th power of resolution, changing acquisition time from quite short to excessively long will cause only a relatively modest increase of the latter. For 1H NMR microscopy (samples of the order of 1cm in diameter), there is an "impossible" barrier of about 40 microns even at high fields (e.g., 300 MHz) for samples rich in hydrogen. On the other hand, there is no particularly sharp degradation of resolution when going to lower fields (e.g., 10 MHz), or hydrogen-poor samples, or some of the heteronuclei (e.g., 23Na). Consequently, NMR microscopy applications requiring isotropic voxel sizes of 100-500 microns have good chances of success even at surprisingly low fields/concentrations.

DOI: 10.1016/0730-725X(91)90384-X.
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Pulsed 1H NMR Relaxation in Crystalline Syndiotactic Polystyrene.

Capitani D., Segre A.L., Grassi A., Sykora S.,
Macromolecules 24, 623-624 (1991).

This is a brief Note with no Abstract. Its main conclusions are:
(i) The pulse 1H NMR technique is capable of discriminating between polymorphous polystyrenes.
(ii) T1 relaxation gives a clear warning on the intensities used in CP-MAS techniques, regardless of contact times.
Spectral intensity differences might be due to difference in proton relaxation times.
(iii) An optimal temperature can be found, where the difference between T1 relaxations is the highest;
at this temperature ... 13C CP-MAS might be carried out to give the best results.
(iv) The value of the maxima defines a scale T1δ<T1γ<T1σ<T1β. The order of this scale matches the solubility scale and solvent permeability of the four mesomorphous forms. Since O2 adsorption shortens T1 relaxation, it seems possible to correlate these values to the amount of sorbed O2.

DOI: 10.1021/ma00002a046.
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Risonanza Magnetica Nucleare in Medicina

Ruffato C., Bonera G., Sykora S., Buttazzoni L., Paolucci G.,
Piccin Nuova Libreria, Padova 1984.

Questa monografia sul imaging tramite la Risonanza Magnetica Nucleare (RMN) era la seconda pubblicata in lingua italiana e la prima che non fosse una traduzione bensì un'opera originale. Per lungo tempo, essa è stata utilizzata come libro di testo per i corsi di specializzazione nell'ultimo anno dei corsi di fisica medica. Oggi (2007) essa è già ampiamente obsoleta ma, a quanto mi risulti, non vi è tuttora un testo alternativo del genere scritto in italiano.
 
[This book was the second Italian language text on Magnetic Resonance Imaging (MRI) and the first one which is not a translation but an original work. For a long time, it has been used as a textbook for last-year students specializing in medical physics. Today (2007) it is quite obsolete but, as far as I know, there is still no alternative text of its kind written in Italian.]

Book index    |    Part III    |    Part IV

Correlation between iodine number and proton relaxation times in maize oil.

Brosio E., Conti F., Di Nola A., Sykora S., J.Food Technol. 16, 67-72 (1981).

We have found a good correlation between the iodine number of maize oil and an empirical parameter related to the proton T1 relaxation time determined by means of low resolution pulsed nuclear magnetic resonance spectroscopy. This result opens a way to fast and reliable determination of the iodine number during oil hydrogenation.

DOI: 10.1111/j.1365-2621.1981.tb00997.x .
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A Pulsed Low Resolution NMR Study on Crystallization and Melting Processes of Cocoa Butter.

Brosio E., Conti F., Di Nola A., Sykora S., J.Am.Oil Chem.Soc. 57, 78-82 (1980).

Pulsed low resolution nuclear magnetic resonance (NMR) was employed to measure the "melting" curves of different series of cocoa butter samples. The samples were prepared from completely liquid phase by cooling and tempering them at different temperatures Tc for varying times Δt. The "melting" curves were measured while keeping the sample at a fixed temperature Tm. The complex shape of each curve was interpreted in terms of cocoa butter polymorphism, and the results were compared with with data obtained by other techniques available in the literature. Using just two tempering temperatures (+7C and -18C), we were able to distinguish four solid phases and identify them with the phases II, III, IV and V described in the literature. Our data are in full agreement with literature. Several novel results have been also found. These include the kinetic constants of the melting processes of phases II and III, the rate constants of solidification of phase V, the conversion of phase III into phase IV before melting at temperatures >30C, and the growth of phase V out of phase II at -18C (including the rate constant of this process).
We are convinced that NMR may serve as a principal tool in fat polymorphism investigations, especially if it is combined with other techniques such as differential scanning calorimetry. Its advantage, apart from rapidity of measurement, is the fact that the measurement itself does not interfere with the melting or solidification process studied. On the other hand, it does not distinguish in a direct way between different solid phases present in the sample; this can be done only in inference from the behavior upon melting.

DOI: 10.1007/BF02674367.
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Experimental Noise in Data Acquisition and Evaluation.
II. Signal-to-Noise Measurements in NMR.

Sykora S., Vogt J., Bruker Report 2/79, 17-18 (1979).

The simple way of estimating the signal-to-noise ratio (S/N) in HR-NMR spectra consists of estimating the height of a standard peak (p) and the peak-to-peak amplitude of a segment of the spectrum containing only noise (n) and setting S/N = 2.5*(p/n). This Note investigates to which extent such a procedure can be considered objective and reliable. The maximum and the minimum of a segment of noise with n data points is a well-defined random variable whose statistical properties can be easily analysed. In particular, its median and quantiles for any confidence level are given by explicit formulae. From these it follows that the standard method depends too much of the size of the noise segment and should be therefore replaced by a more sophisticated method.

DOI not available. See full text

Experimental Noise in Data Acquisition and Evaluation.
I. Noise Amplitude Distribution Function on High Resolution FT-NMR Instruments.

Sykora S., Vogt J., Bruker Report 2/79, 15-17 (1979).

The noise reaching the analog-digital converter of a HR-NMR instrument has been analyzed for any deviations from normal distribution. Several statistical normality tests had been employed, such as skewness, kurtosis, second and fourth moment and the correlation between them. It has been found that any such deviation, if present at all, is below the threshold of detection at 95% confidence level. Tentative reasons for this fact are listed. The fact that the noise is indeed normal implies that standard data averaging techniques are indeed the optimal ones and it has no sense to look for better ones.

DOI not available. See full text

Low-Resolution, Pulsed NMR Studies of Water Binding and of Exchangeable Hydrogen Content in Solids.

Brosio E., Conti F., Paci M., Sykora S., J.Magn.Reson. 34, 593-597 (1979).

Solids with exchangeable hydrogens are treated with D2O. The free-induction decay in a pulsed hydrogen NMR experiment is then interpreted in terms of the fraction of hydrogens in the sample which have been made mobile by this treatement. Data are provided for the hydrogen of starch in durum wheat semolina.

DOI: 10.1016/0022-2364(79)90144-6.
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Moisture determination in starch-rich food products by pulsed nuclear magnetic resonance.

Brosio E., Conti F., Lintas C., Sykora S., J.Food Technol. 13, 107-116 (1978).

The possibility of applying the low resolution pulsed NMR technique to moisture determination in starch-rich low-fat food products is described. The water content of the samples is measured from the liquid to solid ratio. The evaluation of the ratio depends upon the way of extrapolating the free induction decay (FID). The values of the extrapolation coefficients for the liquid and solid phases are measured and their dependence upon the sample water content is given. The method of standard addition for converting the percentage of moisture obtained in terms of hydrogen content to percentage in weight is described. The error statistical analysis is also reported.

DOI: 10.1111/j.1365-2621.1978.tb00784.x .
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Impiego della Risonanza Magnetica Nucleare a bassa risoluzione nella scienza e tecnologia degli alimenti

Brosio E., Chiacchierini E., Conti F., Lintas C., Sykora S., Rivista della Società Italiana di Scienza dell'Alimentazione 7, 309-314 (1978).

Un articolo introduttivo risalente ai tempi dei primi tentativi di promozione della RMN a bassa risoluzione nel campo agro-alimentare. Ho tentato di promuovere il campo sia per l'interesse personale sia perchè ciò faceva parte del mio lavoro alla Bruker. Durante gli anni 70 e 80, però, i risultati erano piuttosto modesti.
[An introductory article from the period of first attempts to promote low-resolution NMR in the agro-alimentary field. I was trying to promote the field both out of my own interest and as a part of my work for Bruker. In the 70's and 80's, however, the results were relatively modest.]

In Italian. DOI not available.
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Vibrational Corrections in NMR Spectra of Oriented Molecules

Sykora S., Vogt J., Bösiger H., Diehl P., J.Magn.Reson. 36, 53-60 (1979).

Nuclear magnetic resonance of oriented molecules provides a convenient and precise technique for determination of molecular geometry. The precision is often high enough for the effect of the vibrational motions to be felt. In this paper the vibrational corrections are discussed in detail, and a novel formulation is presented which, apart from its simplicity, provides distinct advantages in numerical calculations. Although this formulation has not been published so far, a computer program based on it has been used extensively and with excellent results by the authors and their collaborators for several years.

DOI: 10.1016/0022-2364(79)90214-2.
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Differential pulse polarographic Determination of Submicrogram Quantities of Carmustin and Related Compounds in Biological Samples

Bartosek I., Daniel S., Sykora S., J.Pharmac.Sci. 67, 1160-1163 (1978).

A polarographic method was developed to determine the antineoplastic agent carmustin and other nitrosoureas, such as N-methyl-N-nitrosourea and N-cyclohexyl-N-nitrosourea, in biological liquids at levels well below 1µg/ml or g. The stability of carmustin in different media was investigated to prevent losses during administration or essay. Examples of nitrosourea determination in biological samples are given.

DOI: 10.1002/jps.2600670836 .
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The Vibrationally Averaged Structures of Ethylene, Ethylene-1-13C and Ethylene-1,2-13C as determined by NMR of Partially Oriented Molecules

Diehl P., Sykora S., Wullschleger E., Mol.Phys. 29,305-306 (1975).

This Communication is an example of the application of vibrational correction in HR-NMR spectra of oriented molecules (see Vibrational corrections...).

DOI: 10.1080/00268977500100211.
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Automatic Analysis of NMR Spectra: An Alternative Approach.

Diehl P., Sykora S., Vogt J., J.Magn.Reson. 19, 67-82 (1975).

The analysis of high resolution NMR spectra of coupled nuclear systems is often a very tedious process. The methods used to solve this task have so far always been based on frequencies (and sometimes also intensities) of selected and well assigned lines. In this paper we present a broad class of methods which not only do not require any interpretation of experimental lines but do not even require any lines should be individually distinguishable. The first experiences with some of these methods are reported. They lead to quite optimistic conclusions regarding the possibility of full automation of the problem in question. The algorithms used consist in (i) converting the spectrum, however complicated, into a limited set of real numbers by means of suitable integral transforms, and (ii) fitting these numbers by means of the usual iterative least-square algorithm. The very simplicity of this idea makes it possible to apply the method with equal ease to the analysis of any complicated function (spectra) defined by a limited number of parameters.

DOI: 10.1016/0022-2364(75)90030-X .
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NMR Spectra of Oriented 13C-Acetylene.
Redetermination of the Shrinkage Effects and
Analysis of the Apparent Temperature Dependence of the Molecular Geometry.

Diehl P., Sykora S., Niederberger W., Burnell E.E., J.Magn.Reson. 14, 260-269 (1974).

The NMR spectra of the 13C isomers of acetylene oriented in two nematic liquid crystals (EBBA and Phase IV) have been analyzed in order to determine the distance ratios and the shrinkage effects. In the case of the EBBA samples, the results agree with the IR data except for a small discrepancy in the distance ratios. In the Phase IV samples, we have found an unusually strong temperature dependence of the direct coupling constants and of the corresponding apparent distance ratios. In this case the discrepancies between NMR and IR are as large as 30%. We interpret this phenomenon on the basis of a two-site theory. The following assumptions have to be made in order to explain the apparent anomalies: (i) the enthalpy difference between the two sites is 200-400 cal/mol, (ii) the orientation parameters at the two sites have opposite signs, and (iii) at the site with the lower energy (complex ?) the ratio rCH/rCC is smaller by 0.5-1%. It is interesting that such modest conditions can lead, if neglected, to a 30% error in the distance ratios. With regard to this fact, it is probable that similar effects are not uncommon.

DOI: 10.1016/0022-2364(74)90282-0.
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Quantum Theory and the Bayesian Inference Problems.

Sykora S., J.Statistical Phys. 11, 17 (1974).

Many physicists take it for granted that their theories can be either refuted or verified by comparison with experimental data. In order to evaluate such data, however, one must employ statistical estimation and inference methods which, unfortunately, always involve an ad hoc proposition. The nature of the latter depends upon the statistical method adopted; in the Bayesian approach, for example, one must use some Lebesque measure in the "set of all possible distributions". The ad hoc proposition has usually nothing in common with the physical theory in question, thus subjecting its verification (or refutation) to further doubt. This paper points out one notable exception to this rule. It turns out that in the case of the quantum mechanical systems associated with finite-dimensional Hilbert spaces the proposition is completely determined by the premises of the quantum theory itself.

DOI: 10.1007/BF01019475. Copyright 1974 Springer.
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Raman Band Shapes and Molecular Reorientation.

Sykora S., J.Chem.Phys. 57, 1795-1796 (1972).

This brief Note dwells on the possibility of using experimental data to separate the effects of molecular reorientation on Raman bandshapes from other line-broadening contributions. It builds on a previous, more detailed paper [16] on Raman bandshapes.

DOI: 10.1063/1.1678476. Copyright 1972 American Institute of Physics.
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Raman Bandshapes and Rotational Diffusion of Molecules.

Sykora S., U.S.Clearinghouse Fed.Sci.Tech.Inf. No.724330 (1971).

The shapes of vibrational Raman bands contain a lot of information about the molecular-reorientation process. Evaluation of this information in terms of tensor correlation functions is the main topic of this paper. An evaluation method has been proposed which can be safely applied even in the presence of other, interfering broadening mechanisms such as the vibrational energy transfer, the translational diffusion, and the adiabatic frequency shifts. The method is also insensitive to possible errors in the estimation of center-of-the-band frequency.

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Moments of NMR Absorption Lines from the Free Induction decay or Echo in Solids.

Dianoux A.J., Sykora S., Gutowsky H.S., J.Chem.Phys. 55, 4768-4771 (1971).

A new method is presented for determining the moments of nuclear magnetic resonance absorption lines from the shape of either the free induction decay or that of the echo. Unlike previously used techniques, this method does not require the assumption of an analytic function for the line shape or the fitting of the experimental decay with a polynomial. A fast, suitably precise and numerically stable algorithm has been developed for performing the integration required by the new method.

DOI: 10.1063/1.1675575. Copyright 1971 American Institute of Physics.
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Linewidths in High-Resolution NMR Spectra of Coupled Nuclear Systems.
Broadening Mechanisms Induced by Molecular Reorientation.

Sykora S., J.Chem.Phys. 54, 2469-2476 (1971).

The perturbation theory of energy-level widths in coupled nuclear systems is applied to the relaxation processes activated by molecular reorientation, i.e., to the dipolar relaxation, the quadrupolar relaxation, the relaxation due to chemical shift anisotropy, the intermolecular relaxation, and the relaxation due to the spin-rotation interaction. The relaxation processes are divided into two groups with respect their behaviour under rotations of molecular coordinates; the first three are of tensor character while the last two are of vector character. For each of the two groups a theory is developed based on the properties of normed spherical operators. This sheds some new light on the two previously studied cases, i.e., the dipolar relaxation and the intermolecular relaxation, and leads to the solutions of the other cases. The theory of the quadrupolar relaxation is documented by two simple examples. It turns out that in the case of molecules containing quadrupolar nuclei useful information about the molecular structure can be obtained from the linewidth patterns. The same also holds, of course, for the other relaxation processes provided they lead to experimentally accessible effects. Explicit formulas are given for the cross-term contributions due to simultaneous action of two different relaxation mechanisms.

DOI: 10.1063/1.1675201. Copyright 1971 American Institute of Physics.
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Linewidths in High-Resolution NMR Spectra.
Homogeneous Broadening due to Intermolecular Dipolar Relaxation.

Sykora S., J.Chem.Phys. 52, 5949-5951 (1970).

The effects connected with the intermolecular relaxation in the coupled nuclear systems are studied theoretically. It was shown that, because of general properties of nuclear-spin systems, the number of parameters necessary to describe the relaxation process is reduced reduced substantially. Moreover, the structure of nuclear system and the relaxation process parameters are to a large extent separated. This fact enables one to draw quite detailed conclusions about the energy level widths even without any specification of the type of intermolecular relaxation process.

DOI: 10.1063/1.1672878. Copyright 1971 American Institute of Physics.
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Linewidths in High-Resolution NMR Spectra.
Homogeneous Broadening due to Intramolecular Dipolar Relaxation.

Sykora S., J.Chem.Phys. 52, 4818-4825 (1970).

The theory of energy-level widths in coupled nuclear systems is discussed, and a detailed study of the intramolecular dipolar relaxations based on it is presented. The restrictions of the theory and all the approximations made are carefully discussed. The nuclear system coupling structure enters the formulas through relatively simple functionals defined over the unperturbed eigenvectors of the system. On the other hand, the spectral density functions, which appear as coefficients of these functional, depend only on molecular geometry and motions. Both groups of parameters are thus to a great extent separated. In order to show the effectiveness as well as the limits of the method, the structure and the linewidths of resonance transitions of several simple systems (AB,A2, ABX, A2X, A3, and A3X) are studied in detail.

DOI: 10.1063/1.1673717 . Copyright 1970 American Institute of Physics.
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Conformational Structure of Stereoisomers of 2,4-Dichloropentane.

Schneider B., Stokr J., Doskocilova D., Sykora S., Jakes J., Kolinsky M., J.Polymer Sci. C22, 1073-1084 (1969).

By analysis of vibrational and NMR spectra and by theoretical conformer-energy calculations 2,4-dichloropentane was shown to contain, in addition to the previously established forms TT and GG of the d,l isomer and TG of the meso isomer, small amounts of other conformers.

DOI: 10.1002/polc.5070220243 .
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Molecular Spectra and Conformational Structure of 2,3-Dichlorobutane and 3,4-Dichlorohexane

Stokr J., Doskocilova D., Sykora S., Hörhold H.H., Schneider B., Coll.Czechoslov.Chem.Comm. 34, 1875-1890 (1969).

Infrared and NMR spectra of the stereoisomers of 2,3-dichloro- and 2,3-dibromobutane, and of 3,4-dichloro- and 3,4-dibromohexane have been measured in a broad temperature range. Conformational structure with respect to rotation around the 2,3-bond in the butanes, and the 3,4-bond in the hexanes has been determined in the solid and liquid state, and compared with the results of semiempirical conformer energy calculations.

DOI: 10.1135/cccc19691875 .
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Approximate Methods in Analysis of NMR Spectra.
Application of Perturbation Theory to Decomposition of Many-Spin Systems

Sykora S., Coll.Czechoslov.Chem.Comm. 33, 3073-3080 (1968).

By means of perturbation theory, expressions for transition frequencies and intensities have been derived for many-spin systems which can be decomposed into several weakly interacting subsystems. The way in which these expressions have to be modified in cases where the basic system is symmetrical has also been shown.

DOI: 10.1135/cccc19683073 .
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Molecular Structure and NMR Spectra of Stereoregular Poly(methyl Acrylate) Models.

Doskocilova D., Sykora S., Pivcova H., Obereigner B., Lim D., J.Polymer Sci. C23, 365-372 (1968).

NMR spectra of the meso and d,l isomers of methyl-2,4-pentanedicarboxylate and of isotactic, heterotactic, and syndiotactic methyl-2,4,6-heptanetricarboxylate have been measured and analyzed. From the values of vicinal coupling constants the energy differences between various conformational structures of these isomers were estimated. The limitations of the procedure are discussed.

DOI: 10.1002/polc.5070230144 .
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Polymerization of Methyl Methacrylate by Alkali Metal Compounds.

Lim D., Coupek J., Juzl K., Baca J., Sykora S., Schneider B., J.Polymer Sci. C23, 21-29 (1968).

The structure of poly(methyl methacrylate) prepared by anionic polymerization was followed. Compounds of lithium, sodium, and potassium were used as initiators. The influence of the structure of the initiator and its amount and of the monomer concentration, conversion, and temperature on the structure of the polymer in the polymerization without the presence of complexing solvents was studied. By analysis of NMR spectra tacticity and stereoblock structure, characterized by the parameter η=Pis/(Pis+Pss) was determined. The results made possible the conclusions concerning the factors controlling the growth reaction.

DOI: 10.1002/polc.5070230106 .
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Semiempirical Calculation of Conformational Structure of 2,4-Disubstituted Pentanes.

Sykora S., Coll.Czechoslov.Chem.Comm. 33, 3514-3527 (1968).

The conformational structure of a series of 2,4-disubstituted pentanes (substituents F,Cl,Br,I,CN,CH3,H) has been calculated, taking account of three types of interactions: dispersion interactions, dipole-dipole interactions, and the three-fold barrier of the C-C bond. Dihedral angles have been adjusted so as to attain the local potential energy minimum for each conformer. The results of these calculations indicate the presence of a number of minority conformers, in addition to those considered previously.

DOI: 10.1135/cccc19683514 .
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Kristalitcheskie polosy v infrakrasnom spektre polimetilmetakrilata v oblasti 1500-1700 cm-1.

Sedlacek P., Sykora S., Schneider B., Vysokomolekularnye Soedinenija B9, 491-492 (1967).

A brief Note correcting an error in the interpretation of certain bands in infrared spectra of poly(methyl methacrylate). Rather than reflecting the tacticity of the polymer, as claimed in literature, it was shown that the bands belong to an ubiquitous impurity.

In Russian. DOI not available.

Vibrational and NMR Spectra and Molecular Structure of Poly(Vinyl Chloride).

Schneider B., Stokr J., Doskocilova D., Kolinsky M., Sykora S., Lim D., J.Polymer Sci. C16, 3891-3900 (1967).

Infrared spectra of PVC in the region of C-Cl stretching vibrations and the β-proton band in NMR spectra of PVC are interpreted, based on the analysis of infrared and NMR spectra of pure stereoisomers of 2,4-dichloropentane and 2,4,6-trichloroheptane. For the interpretation of infrared spectra, only the presence of conformations found to be stable in model compounds has been assumed. The combined evidence of NMR and infrared investigations indicates that interpretations can be found to descrive PVC samples prepared by radical polymerization at +50 °C, as atactic, and those prepared at -25 °C, as about 60 % syndiotactic.

DOI: 10.1002/polc.5070160728. A scanned PDF (2088 kBytes) may be downloaded for personal use only.
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Note on the NMR Spectra of Molecules with Periodic Internal Motions.

Sykora S., Molecular Physics 10, 473-477 (1966).

In the case of very large frequency of periodic motion, the spectrum of a molecule is identical with the spectrum of a fixed system described by the average Hamiltonian; theoretical proof of this well-known fact is presented and the necessary conditions are defined.

DOI: 10.1080/00268976600100601.
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Teorie chemickych posunu v jaderne magneticke resonanci.

Sykora S., Doskocilova D., Chemické Listy 60, 1009-1041 (1966).

Theory of Chemical Shifts in NMR: An early in-depth Review, based on 209 references extending up to 1965.

In Czech. DOI not available. More information and a scanned PDF.

Sorption Radioaktiver Isotopen an Niederschlagen. XI. Sorptionseigenschaften von Zinn (IV)-Hydroxid.

Sykora S., Kolarik Z., Coll.Czechoslov.Chem.Comm. 29, 1350-1359 (1964).

Es wurde die Sorption veränderlicher Mengen von Cer(III)-ionen und trägerfreier Mengen der Ionen 95Zr, 106Ru(NO) und 137Cs am Zinn(IV)-hydroxid in Abhängigkeit von der Wasserstoffionenkonzentration und von der Sorbentenmenge verfolgt. Im falle der Cer(III)-ionen wurde auch die Geschwindigkeit der Sorptionsvorganges verfolgt. Der Machanismum der Sorption am Zinn(IV)-hydroxid ist mit jenem des Ionenaustausches identisch und richtet sich nach dem Massenwirkungsgesetz. Es wurde auch die Sorption einiger Komplexbildner untersucht und die Möglichkeit überprüft, durch ihre Anwesenheit die Sorption der Kationen zu beeinflussen.

In German. DOI: 10.1135/cccc19641350 .
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Konfiguracni a konformacni struktura polymetylmetakrylatu a polyvinylchloridu
[Configurations and Conformations of PolyMethylMetacrylate and PolyVinylChloride]

Sykora S., Thesis, CSAV, Ustav Makromolekularni Chemie, Prague 1967
[Czechoslovak Academy of Sciences, Institute of Macromolecular Chemistry]

The study combines IR, Raman and early NMR spectroscopies to determine first- and second-order tacticities of the studied polymers and, combining the data with semiempirical molecular energy calculations, to elucidate their stereochemical structure.

Sorpce kationu na hydroxydu cinicitém
[Adsorption of Cations on Tin Oxide]

Sykora S., Thesis CVUT, Fakulta Technické a Jaderné Fysiky, Prague 1963
[Czech Technical High Learning, Faculty of Technical and Nuclear Physics]

Study of selective adsorption of radioactive cations (in particular ¹⁴⁴Ce³⁺) in trace quantities on precipitates of oxides, the final goal of which was the development of methods for extraction of radioisotopes for medical applications from nuclear reactor wastes.