Software
Simulating NMR spectra The program will accept up to 24 spin the user provide an accurate description groups, but according to the manual, of the spin system (e.g., AABBTC vs. A2B2X). Spectral simulations are generally other limitations will usually prevent calculations on a 24-spin system. We found the first step in the analysis of complex this to be the case. The spin system can multiplet patterns. They are also particube homonuclear or heteronuclear and can larly useful as a teaching tool (e.g., to include natural abundance mixtures of demonstrate the effect of a change in the isotopes. We simulated various spectra to sign of a coupling constant on multiplet test the program, including spin systems structure or the effect of chemical exthat contained up to 6 spin groups and 12 change on the NMR spectrum). To simulate a spectrum, chemical shifts, spins, as well as spin systems involved in gNMR coupling constants, and line widths are en- intra- and intermolecular exchange (e.g., Cherwell Scientific Publishing exchange between two A X2 spin systems tered for the spin system in the Molecule Suite 27A as in rotation around the amide bond of window, which is similar in format to a Palo Alto, CA 94303 N N-diethylformamide). spreadsheet. Alternatively, parameters can 415-852-0720; fax 415-852-0723; be entered using molecular structures. www. cherwell. com Probably the most useful application of gNMR can imporr structures from ChemVersion 3.6; $899 gNMR is for extracting spectral parameters Intosh, ChemWindow, ChemDraw and from experimental spectra by iterative fitgNMR, a program ffo rimulating one-dimen- Isis/Draw. This is a particularly convenient ting procedures. gNMR can imporr experifeature in that it allows the user to do on mental spectra in several file formats, insional NMR spectra, has many useful feathe computer what otherwise would have to cluding Bruker Win-NMR Varian VNMR tures. Spectra can be simulated for single be done on paper to set up the spin system. General Electric GE-SUN, and Lybrics. molecules, mixtures, and polymers, and for molecules undergoing intra- and intermolecular exchange. Spectral parameters, including chemical shifts, spin-spin coupling constants, line widths, and exchange rates in the case of exchanging systems, can be extracted from experimental spectra by iteratively fitting simulated spectra to experimental spectra by least-squares procedures. gNMR is avaiiable for Windows and Macintosh computers. We tested gNI^IR on a Power Macintosh. Documentation consists of a wellwritten manual, which includes an introduction to the simulation of NMR spectra and a comprehensive tutorial. Separate chapters describe in detail simple simulation of NMR spectra, fitting of calculated spectra to experimental spectra by assignment iteration and by full lineshape iteration, and simulation of NMR spectra of chemically exchanging systems. gNMR is easy to use and requires no knowledge of the theory involved in the simulation of NMR spectra. Success with the program does, however, require that gNMR can show structure, spin system information, and the simulated spectrum simultaneously. 302 A
Analytical Chemistry News & Features, May 1, 1997
sentially identical chemical shifts and cou- fast Fourier transform. Data can be imgNMR requires that the data have alleady pling constants from the aspartic acid been transformed and phased. The imported in ASCII, dBase, Excel, Lotus, DIF, spectrum by both the assignment iteration SigmaPlot, and Sound format and exported ported data are then converted to the forand full lineshape iteration methods. How- in ASCII format. System requirements inmat used by gNMR. We euccessfully imported spectra that had been acquired on a ever, the fit was less successful for the clude a PC with a 386/DX-33 or higher proglutamine spectrum, and the program Varian spectrometer and processed with cessor and 4 MB RAM running Wiindws VNMR software on a Silicon Graphics com- would not converge to a meaningful solu3.1, Windows 95, or Windows NT. puter, although several attempts caused the tion for the low-temperature spectrum of the two ethyl groups of N, Akliethylformprogram to crash. StatView amide, apparently due to the partial overSpectral parameters can be obtained Abacus Concepts lap of the two quartets. from experimental spectra by the usual 1918 Bonita Ave. assignment iteration method and by a full gNMR is the best software we have ssen Berkeley, CA 94704 lineshape iteration. The procedure in the 510-540-1949; fax 510-540-0260; for the simple simulation of NMR spectra assignment iteration method is straightforand for obtaining spectral parameters from www. abacus, com ward and involves assigning resonances in experimental spectra by the assignment Version 4.5 the experimental spectrum to lines in a iteration method on a personal computer. $595; $149 upgrade spectrum that has been simulated with iniThe full lineshape method is more demandtial estimates of the parameters. The proing of the experimental spectrum, and alStatView combines sata management, stagram men does an iterative least-squares fit though it is easier to use than the assigntistical analysis, graphing, and presentation to optimize agreement between experimen- ment iteration method, it is less reliable. tools in one software package. System retal and simulated spectra. gNMR is easy to uss end should be en inquirements include either a Macintosh with valuable tool for those involved in the analy- a 68040 or better processor and 4 MB RAM We found gNMR to work well in this sis of experimental spectra and the teachrunning system 7.0 or later or a PC wiih a mode for several experimental spectra, 486 or better processor and 8 MB RAM including the ABX spin system of aspartic ing of NMR spectroscopy. acid, the ABMNX spin system of gluReviewed by Dallas L. Rabenstein and running Windows 95 or Windows 3.., oo tamine, and the two A3X2 spin systems of Andreas Kaerner, University of California-12 MB RAM running Windows NT. a low-temperature spectrum of the ethyl Riverside groups of N, A^-diethyllormamide, in which SigmaPlot the first two lines of the quartet of one spin SPSS, Inc. system are coincident with the third and 444 North Michigan Ave. SOFTWARE RELEASED fourth lines of the quartet of the second spin Chicago, IL 60611 system. Origin 312-329-2400; www.spss.com Microcal Software We were less successful, however, Version 4.0 when we attempted to obtain spectral inOne Roundhouse Plaza $495; $199 upgrade formation from these same spectra by full Northampton, MA 01060 lineshape iteration. In this mode, the pro800-969-7720; fax 413-585-0126; SigmaPlot for Windows allows scientiststs gram fits to the full lineshape, rather than www. microcal. com transform raw data into technical graphs. to a derived set of peak positions, so all of Version 4.1 New features include the Regression Wizthe parameters affect the appearance of a $495 ard; several new graph types, including spectrum. These include not only chemiternary plots, time series graphs, bubble cal shifts and coupling constants, but also Origin ii s aata analysis and graphical pre- plots, and transparent 3-D meshes; and line widths, concentrations (in the ca.se of sentation package that features multiple the ability to export to graphicfileformixtures), and exchange rates (in the mats, including EPS, TIFF, WMF, BMP, graph types, curve styles, and statistical case of exchanging systems). To do a full and JPEG. System requirements include a charts; multiple axes; and an optional 3-D lineshape iteration, the user provides iniand contour graph. For data analysis, Ori- PC with a 486/66 or better processor; tial estimates of all parameters and identi- gin uses polynomial, multiple, and llnear Windows 3.1x, Windows 95, Windows NT; fies those to be varred. We obtained es16 MB RAM, ,nd 22 MB hard-disk space. regression as well as forward and reverse Analytical Chemistry News & Features, May 1, 1997 3 0 3 A
