%0 Journal Article %J Nucleic Acids Research %D 2019 %T Aggrescan3D (A3D) 2.0: prediction and engineering of protein solubility %A Aleksander Kuriata %A Valentin Iglesias %A Jordi Pujols %A Mateusz Kurcinski %A Sebastian Kmiecik %A Salvador Ventura %X Protein aggregation is a hallmark of a growing number of human disorders and constitutes a major bottleneck in the manufacturing of therapeutic proteins. Therefore, there is a strong need of in-silico methods that can anticipate the aggregative properties of protein variants linked to disease and assist the engineering of soluble protein-based drugs. A few years ago, we developed a method for structure-based prediction of aggregation properties that takes into account the dynamic fluctuations of proteins. The method has been made available as the Aggrescan3D (A3D) web server and applied in numerous studies of protein structure-aggregation relationship. Here, we present a major update of the A3D web server to version 2.0. The new features include: extension of dynamic calculations to significantly larger and multimeric proteins, simultaneous prediction of changes in protein solubility and stability upon mutation, rapid screening for functional protein variants with improved solubility, a REST-ful service to incorporate A3D calculations in automatic pipelines, and a new, enhanced web server interface. A3D 2.0 is freely available at: http://biocomp.chem.uw.edu.pl/A3D2/ %B Nucleic Acids Research %V 47 %P W300-W307 %8 05 %G eng %U https://doi.org/10.1093/nar/gkz321 %R 10.1093/nar/gkz321 %0 Journal Article %J Bioinformatics %D 2019 %T Aggrescan3D standalone package for structure-based prediction of protein aggregation properties %A Aleksander Kuriata %A Valentin Iglesias %A Mateusz Kurcinski %A Salvador Ventura %A Sebastian Kmiecik %X SUMMARY: Aggrescan3D (A3D) standalone is a multiplatform Python package for structure-based prediction of protein aggregation properties and rational design of protein solubility. A3D allows the redesign of protein solubility by combining structural aggregation propensity and stability predictions, as demonstrated by a recent experimental study. It also enables predicting the impact of protein conformational fluctuations on the aggregation properties. The standalone A3D version is an upgrade of the original web server implementation - it introduces a number of customizable options, automated analysis of multiple mutations and offers a flexible computational framework for merging it with other computational tools. AVAILABILITY: A3D standalone is distributed under the MIT license, which is free for academic and non-profit users. It is implemented in Python. The A3D standalone source code, wiki with documentation and examples of use, and installation instructions for Linux, macOS, and Windows are available in the A3D standalone repository at https://bitbucket.org/lcbio/aggrescan3d. %B Bioinformatics %V btz143 %G eng %U http://www.ncbi.nlm.nih.gov/pubmed/30825368 %9 Journal Article %R 10.1093/bioinformatics/btz143 %0 Journal Article %J Nucleic Acids Research %D 2015 %T AGGRESCAN3D (A3D): server for prediction of aggregation properties of protein structures %A Rafael Zambrano %A Michal Jamroz %A Agata Szczasiuk %A Jordi Pujols %A Sebastian Kmiecik %A Salvador Ventura %X Protein aggregation underlies an increasing number of disorders and constitutes a major bottleneck in the development of therapeutic proteins. Our present understanding on the molecular determinants of protein aggregation has crystalized in a series of predictive algorithms to identify aggregation-prone sites. A majority of these methods rely only on sequence. Therefore, they find difficulties to predict the aggregation properties of folded globular proteins, where aggregation-prone sites are often not contiguous in sequence or buried inside the native structure. The AGGRESCAN3D (A3D) server overcomes these limitations by taking into account the protein structure and the experimental aggregation propensity scale from the well-established AGGRESCAN method. Using the A3D server, the identified aggregation-prone residues can be virtually mutated to design variants with increased solubility, or to test the impact of pathogenic mutations. Additionally, A3D server enables to take into account the dynamic fluctuations of protein structure in solution, which may influence aggregation propensity. This is possible in A3D Dynamic Mode that exploits the CABS-flex approach for the fast simulations  of flexibility of globular proteins. The A3D server can be accessed at http://biocomp.chem.uw.edu.pl/A3D/ %B Nucleic Acids Research %V 43 (W1) %P W306-W313 %G eng %0 Journal Article %J Acta Biochimica Polonica %D 2012 %T Assessment of the free binding energy of 1,25-dihydroxyvitamin D3 and its analogs with the human VDR receptor model %A Karol Kamel %A Andrzej Koliński %X 1,25-dihydroxyvitamin D(3) has quite significant anticancer properties, but its strong calcemic effect in principle excludes it as a potential anticancer drug. Currently, a lot of effort is being devoted to develop potent anticancer analogs of 1,25-dihydroxyvitamin D(3) that would not induce hypercalcemia during therapy. In this work, the free binding energy of the VDR receptor with 1,25-dihydroxyvitamin D(3) and its three potent analogs (EB 1089, KH 1060 and RO 25-9022) is calculated and compared with each other. With this approach, we could estimate the relative binding affinity of the most potent analog, RO 25-9022, and also revealed a quite distinct mechanism of its interaction with VDR. %B Acta Biochimica Polonica %V 59 %P 653-660 %G eng %N 4 %0 Journal Article %J International Journal of Molecular Medicine %D 2011 %T Analysis and optimization of interactions between peptides mimicking the GD2 ganglioside and the monoclonal antibody 14G2a %A Irena Horwacik %A Mateusz Kurcinski %A Malgorzata Bzowska %A Aleksandra K. Kowalczyk %A Dominik Czaplicki %A Andrzej Koliński %A Hanna Rokita %K Amino Acid Sequence %K Antibodies %K Binding Sites %K Cell Line %K Gangliosides %K Gangliosides: immunology %K Humans %K Models %K Molecular %K Molecular Mimicry %K Molecular Sequence Data %K Monoclonal %K Monoclonal: chemistry %K Monoclonal: immunology %K Neuroblastoma %K Neuroblastoma: genetics %K Neuroblastoma: immunology %K Peptide Library %K Peptides %K Peptides: chemistry %K Peptides: immunology %K Structure-Activity Relationship %K Tumor %X

Overexpression of the GD2 ganglioside (GD2) is a hallmark of neuroblastoma. The antigen is used in neuroblastoma diagnosis and to target newly developed therapies to cancer cells. Peptide mimetics are novel approaches in the design of antigens for vaccine development. We previously reported the isolation of five GD2-mimicking peptides from the LX-8 phage display library with the monoclonal antibody (mAb) 14G2a. The goal of our current study was to analyze and optimize the binding of the peptide mimetics to the mAb 14G2a. Therefore, we performed further experiments and supported them with molecular modeling to investigate structure-activity relationships that are the basis for the observed mimicry of GD2 by our peptides. Here, we show that the peptides have overlapping binding sites on the mAb, 14G2a and restricted specificity, as they did not crossreact with other ganglioside-specific antibodies tested. In addition we demonstrate that the phage environment was involved in the process of selection of our peptides. The AAEGD sequence taken from the viral major coat protein, p8, and added to the C-termini of the peptides \#65, \#85 and \#94 significantly improved their binding to the mAb, 14G2a. By application of analogs with amino acid substitutions and sequence truncations, we elucidated the structure-activity relationships necessary for the interactions between the 14G2a mAb and the peptide \#94 (RCNPNMEPPRCF). We identified amino acids indispensable for the observed GD2-mimicry by \#94 and confirmed a pivotal role of the disulphide bridge between the cysteine residues of \#94 for binding to the mAb 14G2a. More importantly, we report five new peptides demonstrating a significant improvement of mAb 14G2a binding. The experimental data were supported and expanded with molecular modeling tools. Taken together, the experimental results and the in silico data allowed us to probe in detail the mechanism of the molecular mimicry of GD2 by the peptides. Additionally, we significantly optimized binding of the leading peptide sequence \#94 to the mAb 14G2a. We can conclude that our findings add to the knowledge on factors governing selections of peptide mimetics from phage-display libraries.

%B International Journal of Molecular Medicine %V 28 %P 47–57 %8 jul %G eng %U http://www.ncbi.nlm.nih.gov/pubmed/21455557 %R 10.3892/ijmm.2011.655 %0 Journal Article %J Nucleic Acids Research %D 2008 %T AAindex: amino acid index database, progress report 2008 %A Kawashima, Shuichi %A Piotr Pokarowski %A Pokarowska, Maria %A Andrzej Koliński %A Katayama, Toshiaki %A Kanehisa, Minoru %K Amino Acids %K Amino Acids: chemistry %K Databases %K Internet %K Protein %K Proteins %K Proteins: chemistry %X

AAindex is a database of numerical indices representing various physicochemical and biochemical properties of amino acids and pairs of amino acids. We have added a collection of protein contact potentials to the AAindex as a new section. Accordingly AAindex consists of three sections now: AAindex1 for the amino acid index of 20 numerical values, AAindex2 for the amino acid substitution matrix and AAindex3 for the statistical protein contact potentials. All data are derived from published literature. The database can be accessed through the DBGET/LinkDB system at GenomeNet (http://www.genome.jp/dbget-bin/www\_bfind?aaindex) or downloaded by anonymous FTP (ftp://ftp.genome.jp/pub/db/community/aaindex/).

%B Nucleic Acids Research %V 36 %P D202–5 %8 jan %G eng %U http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2238890&tool=pmcentrez&rendertype=abstract %R 10.1093/nar/gkm998 %0 Book Section %B Structural Genomics and High Throughput Structural Biology %D 2006 %T Ab initio modeling %A Jeffrey Skolnick %A Yang Zhang %A Andrzej Koliński %A Michael Sundstrom %A Martin Norin %A Aled Edwards %B Structural Genomics and High Throughput Structural Biology %I CRC/Taylor & Francis %C Boca Raton, FL %P 137-162 %G eng %& VIII %0 Journal Article %J Proceedings of the National Academy of Sciences of the United States of America %D 2002 %T Ab initio protein structure prediction on a genomic scale: application to the Mycoplasma genitalium genome %A Daisuke Kihara %A Yang Zhang %A Hui Lu %A Andrzej Koliński %A Jeffrey Skolnick %K Algorithms %K Bacterial %K Databases as Topic %K Genome %K Models %K Molecular %K Monte Carlo Method %K Mycoplasma %K Mycoplasma: genetics %K Protein Folding %K Proteins %K Proteins: chemistry %K Software %X An ab initio protein structure prediction procedure, TOUCHSTONE, was applied to all 85 small proteins of the Mycoplasma genitalium genome. TOUCHSTONE is based on a Monte Carlo refinement of a lattice model of proteins, which uses threading-based tertiary restraints. Such restraints are derived by extracting consensus contacts and local secondary structure from at least weakly scoring structures that, in some cases, can lack any global similarity to the sequence of interest. Selection of the native fold was done by using the convergence of the simulation from two different conformational search schemes and the lowest energy structure by a knowledge-based atomic-detailed potential. Among the 85 proteins, for 34 proteins with significant threading hits, the template structures were reasonably well reproduced. Of the remaining 51 proteins, 29 proteins converged to five or fewer clusters. In the test set, 84.8% of the proteins that converged to five or fewer clusters had a correct fold among the clusters. If this statistic is simply applied, 24 proteins (84.8% of the 29 proteins) may have correct folds. Thus, the topology of a total of 58 proteins probably has been correctly predicted. Based on these results, ab initio protein structure prediction is becoming a practical approach. %B Proceedings of the National Academy of Sciences of the United States of America %V 99 %P 5993–5998 %8 apr %G eng %U http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=122890&tool=pmcentrez&rendertype=abstract %R 10.1073/pnas.092135699 %0 Journal Article %J Proteins %D 2001 %T Ab initio protein structure prediction via a combination of threading, lattice folding, clustering, and structure refinement %A Jeffrey Skolnick %A Andrzej Koliński %A Daisuke Kihara %A Marcos Betancourt %A Piotr Rotkiewicz %A Michal Boniecki %K carlo methods %K casp4 %K lattice models %K monte %K Protein Folding %K protein struc- %K structure %K threading %K ture prediction %X A combination of sequence comparison, threading, lattice, and off-lattice Monte Carlo (MC) simulations and clustering of MC trajectories was used to predict the structure of all (but one) targets of the CASP4 experiment on protein structure prediction. Although this method is automated and is operationally the same regardless of the level of uniqueness of the query proteins, here we focus on the more difficult targets at the border of the fold recognition and newfold categories. For a few targets (T0110 is probably the best example), the ab initio method produced more accurate models than models obtained by the fold recognition techniques. For the most difficult targets from the newfold categories, substantial fragments of structures have been correctly predicted. Possible improvements of the method are briefly discussed. %B Proteins %V 45 %P 149–156 %G eng %U http://onlinelibrary.wiley.com/doi/10.1002/prot.1172/full %N Suppl. S5 CASP4 %R 10.1002/prot.1172 %0 Journal Article %J Proteins %D 2000 %T Accurate reconstruction of all-atom protein representations from side-chain-based low-resolution models %A M. Feig %A Piotr Rotkiewicz %A Andrzej Koliński %A Jeffrey Skolnick %A Charles L. Brooks III %K Models %K Molecular %K Proteins %K Proteins: chemistry %X A procedure for the reconstruction of all-atom protein structures from side-chain center-based low-resolution models is introduced and applied to a set of test proteins with high-resolution X-ray structures. The accuracy of the rebuilt all-atom models is measured by root mean square deviations to the corresponding X-ray structures and percentages of correct chi(1) and chi(2) side-chain dihedrals. The benefit of including C(alpha) positions in the low-resolution model is examined, and the effect of lattice-based models on the reconstruction accuracy is discussed. Programs and scripts implementing the reconstruction procedure are made available through the NIH research resource for Multiscale Modeling Tools in Structural Biology (http://mmtsb.scripps.edu). %B Proteins %V 41 %P 86–97 %8 oct %G eng %U http://www.ncbi.nlm.nih.gov/pubmed/10944396 %0 Journal Article %J Proteins %D 1999 %T Ab initio folding of proteins using restraints derived from evolutionary information %A Angel. R. Ortiz %A Andrzej Koliński %A Piotr Rotkiewicz %A Bartosz Ilkowski %A Jeffrey Skolnick %K Algorithms %K Amino Acid Sequence %K Evolution %K Models %K Molecular %K Molecular Sequence Data %K Monte Carlo Method %K Protein Folding %K Proteins %K Proteins: chemistry %X We present our predictions in the ab initio structure prediction category of CASP3. Eleven targets were folded, using a method based on a Monte Carlo search driven by secondary and tertiary restraints derived from multiple sequence alignments. Our results can be qualitatively summarized as follows: The global fold can be considered "correct" for targets 65 and 74, "almost correct" for targets 64, 75, and 77, "half-correct" for target 79, and "wrong" for targets 52, 56, 59, and 63. Target 72 has not yet been solved experimentally. On average, for small helical and alpha/beta proteins (on the order of 110 residues or smaller), the method predicted low resolution structures with a reasonably good prediction of the global topology. Most encouraging is that in some situations, such as with target 75 and, particularly, target 77, the method can predict a substantial portion of a rare or even a novel fold. However, the current method still fails on some beta proteins, proteins over the 110-residue threshold, and sequences in which only a poor multiple sequence alignment can be built. On the other hand, for small proteins, the method gives results of quality at least similar to that of threading, with the advantage of not being restricted to known folds in the protein database. Overall, these results indicate that some progress has been made on the ab initio protein folding problem. Detailed information about our results can be obtained by connecting to http:/(/)www.bioinformatics.danforthcenter.org/+ ++CASP3. %B Proteins %V Suppl. 3 %P 177–185 %8 jan %G eng %U http://www.ncbi.nlm.nih.gov/pubmed/10526366 %0 Book Section %B Theoretical and Computational Chemistry: Computational Molecular Biology %D 1999 %T Application of reduced models to protein structure prediction %A Jeffrey Skolnick %A Andrzej Koliński %A Angel. R. Ortiz %X This chapter describes the state of the art of contemporary approaches to protein tertiary structure prediction, and focuses on reduced models. Any successful tertiary structure prediction algorithm must address two intertwined issues: first, it is required to have an energy or fitness function that distinguishes the native conformation from the sea of alternative structures. Second, it must have a conformational search protocol that can find the native conformation among the possible alternative structures. A key issue that is faced when embarking on a program of protein structure prediction is deciding on the level of detail of protein representation. The advantage of a lattice is purely computational. Because the protein is confined to a set of grid points, many geometric and energetic properties can be precalculated in advance. Thus, a well-designed lattice model is about a factor of 10 to 100 times faster than the corresponding continuous space model. %B Theoretical and Computational Chemistry: Computational Molecular Biology %I Elsevier %C Amsterdam %V 8 %P 397–440 %G eng %U http://www.sciencedirect.com/science/article/pii/S1380732399800867 %& 11 %0 Journal Article %J Journal of Computational Chemistry %D 1999 %T Assessing energy functions for flexible docking %A Michal Vieth %A Jonathan D. Hirst %A Andrzej Koliński %A Charles L. Brooks III %K docking %K dynamics %K energy functions %K Molecular %K scoring functions %K simulated annealing %X A good docking algorithm requires an energy function that is selective, in that it clearly differentiates correctly docked structures from misdocked ones, and that is efficient, meaning that a correctly docked structure can be identified quickly. We assess the selectivity and efficiency of a broad spectrum of energy functions, derived from systematic modifications of the CHARMM param19/toph19 energy function. In particular, we examine the effects of the dielectric constant, the solvation model, the scaling of surface charges, reduction of van der Waals repulsion, and nonbonded cutoffs. Based on an assessment of the energy functions for the docking of five different ligand–receptor complexes, we find that selective energy functions include a variety of distance-dependent dielectric models together with truncation of the nonbonded interactions at 8 Å. We evaluate the docking efficiency, the mean number of docked structures per unit of time, of the more selective energy functions, using a simulated annealing molecular dynamics protocol. The largest improvements in efficiency come from a reduction of van der Waals repulsion and a reduction of surface charges. We note that the most selective potential is quite inefficient, although a hierarchical approach can be employed to take advantage of both selective and efficient energy functions. %B Journal of Computational Chemistry %V 19 %P 1612–1622 %G eng %U http://onlinelibrary.wiley.com/doi/10.1002/(SICI)1096-987X(19981115)19:14%3C1612::AID-JCC7%3E3.0.CO;2-M/abstract %N 14 %R 10.1002/(SICI)1096-987X(19981115)19:14<1612::AID-JCC7>3.0.CO;2-M %0 Conference Proceedings %B Proceedings of HRLC Workshop %D 1998 %T Application of a high coordination lattice model in protein structure prediction %A Andrzej Koliński %A Piotr Rotkiewicz %A Jeffrey Skolnick %B Proceedings of HRLC Workshop %I World Scientific %C Singapore/London %V pp %P 100–130 %G eng %U http://cssb.biology.gatech.edu/skolnick/publications/pdffiles/175.pdf %0 Journal Article %J Proteins %D 1998 %T Assembly of protein structure from sparse experimental data: an efficient Monte Carlo model %A Andrzej Koliński %A Jeffrey Skolnick %K Algorithms %K Computer Simulation %K Models %K Molecular %K Monte Carlo Method %K Protein Conformation %K Protein Folding %K Protein Structure %K Secondary %K Tertiary %X A new, efficient method for the assembly of protein tertiary structure from known, loosely encoded secondary structure restraints and sparse information about exact side chain contacts is proposed and evaluated. The method is based on a new, very simple method for the reduced modeling of protein structure and dynamics, where the protein is described as a lattice chain connecting side chain centers of mass rather than Calphas. The model has implicit built-in multibody correlations that simulate short- and long-range packing preferences, hydrogen bonding cooperativity and a mean force potential describing hydrophobic interactions. Due to the simplicity of the protein representation and definition of the model force field, the Monte Carlo algorithm is at least an order of magnitude faster than previously published Monte Carlo algorithms for structure assembly. In contrast to existing algorithms, the new method requires a smaller number of tertiary restraints for successful fold assembly; on average, one for every seven residues as compared to one for every four residues. For example, for smaller proteins such as the B domain of protein G, the resulting structures have a coordinate root mean square deviation (cRMSD), which is about 3 A from the experimental structure; for myoglobin, structures whose backbone cRMSD is 4.3 A are produced, and for a 247-residue TIM barrel, the cRMSD of the resulting folds is about 6 A. As would be expected, increasing the number of tertiary restraints improves the accuracy of the assembled structures. The reliability and robustness of the new method should enable its routine application in model building protocols based on various (very sparse) experimentally derived structural restraints. %B Proteins %V 32 %P 475–494 %8 sep %G eng %U http://www.ncbi.nlm.nih.gov/pubmed/9726417 %0 Journal Article %J Journal of Computational Chemistry %D 1997 %T Algorithm for rapid reconstruction of protein backbone from alpha carbon coordinates %A Mariusz Milik %A Andrzej Koliński %A Jeffrey Skolnick %X A method for generating a full backbone protein structure from the coordinates of α-carbons, is presented. The method extracts information from known protein structures to generate statistical positions for the reconstructed atoms. Tests on a set of proteins structures show the algorithm to be of comparable accuracy to existing procedures. However, the basic advantage of the presented method is its simplicity and speed. In a test run, the present program is shown to be much faster than existing database searching algorithms, and reconstructs about 8000 residues per second. Thus, it may be included as an independent procedure in protein folding algorithms to rapidly generate approximate coordinates of backbone atoms. %B Journal of Computational Chemistry %V 18 %P 80–85 %8 jan %G eng %U http://doi.wiley.com/10.1002/(SICI)1096-987X(19970115)18:1<80::AID-JCC8>3.0.CO;2-W %R 10.1002/(SICI)1096-987X(19970115)18:1<80::AID-JCC8>3.0.CO;2-W %0 Conference Proceedings %B Proceeding of I-st Pacific Symposium on Biocomputing %D 1996 %T An algorithm for prediction of structural elements in small proteins %A Andrzej Koliński %A Jeffrey Skolnick %A Adam Godzik %X A method for predicting the location of surface loops/turns and assigning the intervening secondary structure of the transglobular linkers in small, single domain globular proteins has been developed. Application to a set of 10 proteins of known structure indicates a high level of accuracy. The secondary structure assignment in the center of transglobular connections is correct in more than 85% of the cases. A similar error rate is found for loops. Since more global information about the fold is provided, it is complementary to standard secondary structure prediction approaches. Consequently, it may be useful in early stages of tertiary structure prediction when establishment of the structural class and possible folding topologies is of interest. %B Proceeding of I-st Pacific Symposium on Biocomputing %P 446–460 %G eng %U http://helix-web.stanford.edu/psb96/kolinski.pdf %0 Journal Article %J Protein Science: a Publication of the Protein Society %D 1995 %T Are proteins ideal mixtures of amino acids? Analysis of energy parameter sets %A Adam Godzik %A Andrzej Koliński %A Jeffrey Skolnick %K Amino Acid Sequence %K Amino Acids %K Crystallography %K Databases %K Factual %K Magnetic Resonance Spectroscopy %K Mathematics %K Models %K Protein Conformation %K Protein Folding %K Proteins %K Proteins: chemistry %K Theoretical %K Thermodynamics %K X-Ray %X Various existing derivations of the effective potentials of mean force for the two-body interactions between amino acid side chains in proteins are reviewed and compared to each other. The differences between different parameter sets can be traced to the reference state used to define the zero of energy. Depending on the reference state, the transfer free energy or other pseudo-one-body contributions can be present to various extents in two-body parameter sets. It is, however, possible to compare various derivations directly by concentrating on the "excess" energy-a term that describes the difference between a real protein and an ideal solution of amino acids. Furthermore, the number of protein structures available for analysis allows one to check the consistency of the derivation and the errors by comparing parameters derived from various subsets of the whole database. It is shown that pair interaction preferences are very consistent throughout the database. Independently derived parameter sets have correlation coefficients on the order of 0.8, with the mean difference between equivalent entries of 0.1 kT. Also, the low-quality (low resolution, little or no refinement) structures show similar regularities. There are, however, large differences between interaction parameters derived on the basis of crystallographic structures and structures obtained by the NMR refinement. The origin of the latter difference is not yet understood. %B Protein Science: a Publication of the Protein Society %V 4 %P 2107–2117 %8 oct %G eng %U http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2142984&tool=pmcentrez&rendertype=abstract %R 10.1002/pro.5560041016 %0 Journal Article %J Journal of Magnetic Resonance, Series A %D 1995 %T Assessment of Solvent-Induced Nitrogen Shielding Variations of Triazole Systems %A Michal Witanowski %A Wanda Sicinska %A Zenobia Biedrzycka %A Zbigniew Grabowski %A Graham A. Webb %X High-precision 14N \{NMR\} shieldings are reported for all of the possible N-methyl triazoles in a variety of solvents. A large difference is observed in the effects of solvent on the shieldings of the pyrrole-type and pyridine-type nitrogen atoms in such systems. This difference largely arises from solvent-to-solute hydrogen-bonding effects for the latter type of nitrogen atom. For these two types of nitrogen atoms in triazoles, solvent polarity effects induce changes in the shieldings in opposite directions: this is corroborated by shielding calculations using the solvaton model. Solvent-to-solute hydrogen-bonding effects are larger than those due to solvent polarity and permit the assessment of the basicities of nonequivalent nitrogenous sites; these appear to parallel the analogous basicities with respect to protonation. %B Journal of Magnetic Resonance, Series A %V 112 %P 66 - 71 %G eng %U http://www.sciencedirect.com/science/article/pii/S1064185885710108 %R http://dx.doi.org/10.1006/jmra.1995.1010 %0 Journal Article %J International Journal of Spectroscopy %D 1989 %T Assignments of nitrogen NMR shieldings in azine heterocycles by means of a self-adjusting linear system of incremens %A Michal Witanowski %A Wanda Sicinska %A S. Biernat %B International Journal of Spectroscopy %V 7 %P 315-324 %G eng