{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,8]],"date-time":"2026-04-08T08:46:37Z","timestamp":1775637997305,"version":"3.50.1"},"reference-count":17,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2002,3,31]],"date-time":"2002-03-31T00:00:00Z","timestamp":1017532800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/3.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>The synthesis and spectroscopic characterisation of some representative N-alkylsubstituted quaternary ammonium salts derived from benzothiazole, benzoxazole, benzoselenazole, indole and quinoline are described. These heterocyclic salts, bearing an activated methyl group in the 2-position in relation to the nitrogen atom and N-methyl, -pentyl, -hexyl and -decyl chains, are typical precursors of cyanine dyes.<\/jats:p>","DOI":"10.3390\/70300320","type":"journal-article","created":{"date-parts":[[2008,10,25]],"date-time":"2008-10-25T13:32:11Z","timestamp":1224941531000},"page":"320-330","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":83,"title":["Synthesis and Spectroscopic Characterisation of N-Alkyl Quaternary Ammonium Salts Typical Precursors of Cyanines"],"prefix":"10.3390","volume":"7","author":[{"given":"A.  C.","family":"Pardal","sequence":"first","affiliation":[{"name":"Departamento de Qu\u00edmica, Universidade de Tr\u00e1s-os-Montes e Alto Douro, Apartado 202, 5001-911 Vila Real Codex, Portugal"}]},{"given":"S.  S.","family":"Ramos","sequence":"additional","affiliation":[{"name":"Departamento de Qu\u00edmica e Unidade de Materiais T\u00eaxteis e Papeleiros, Universidade da Beira Interior, Rua Marqu\u00eas d'\u00c1vila e Bolama, 6200-001 Covilh\u00e3, Portugal"}]},{"given":"P.  F.","family":"Santos","sequence":"additional","affiliation":[{"name":"Departamento de Qu\u00edmica, Universidade de Tr\u00e1s-os-Montes e Alto Douro, Apartado 202, 5001-911 Vila Real Codex, Portugal"}]},{"given":"L.  V.","family":"Reis","sequence":"additional","affiliation":[{"name":"Departamento de Qu\u00edmica, Universidade de Tr\u00e1s-os-Montes e Alto Douro, Apartado 202, 5001-911 Vila Real Codex, Portugal"}]},{"given":"P.","family":"Almeida","sequence":"additional","affiliation":[{"name":"Departamento de Qu\u00edmica e Unidade de Materiais T\u00eaxteis e Papeleiros, Universidade da Beira Interior, Rua Marqu\u00eas d'\u00c1vila e Bolama, 6200-001 Covilh\u00e3, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2002,3,31]]},"reference":[{"key":"ref_1","unstructured":"Weissberger, A. (1971). The Cyanine Dyes and Related Compounds - The Chemistry of Heterocyclic Compounds, Interscience Publishers."},{"key":"ref_2","unstructured":"Zollinger, H. (1991). Color Chemistry - Synthesis, Properties and Applications of Organic Dyes and Pigments, VCH Publishers Inc."},{"key":"ref_3","unstructured":"James, T. H. (1977). Sensitizing and Desensitizing Dyes \u2013 The Theory of the Photographic Processes, Macmillan Co."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"600","DOI":"10.1002\/prac.19733150404","article-title":"Zur reaktivit\u00e4t der 2-methylcycloammoniumsalze","volume":"315","author":"Kleinpeter","year":"1973","journal-title":"J. Prakt. Chem."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"323","DOI":"10.1002\/mrc.1270220510","article-title":"Oszczapowicz, 13C and 1H NMR spectral studies of N-alkylmethylquinolinium salts","volume":"22","author":"Jaroszewska","year":"1984","journal-title":"J. Org. Magn. Reson."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"2391","DOI":"10.1021\/jo00113a018","article-title":"A new method for the synthesis of heptamethine cyanine dyes: synthesis of new near-infrared fluorescent labels","volume":"60","author":"Narayanan","year":"1995","journal-title":"J. Org. Chem."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"1948","DOI":"10.1016\/S0039-9140(96)02111-X","article-title":"Spectrophotometric determination of trace water in organic solvents with a near infrared absorbing dye","volume":"44","author":"Li","year":"1997","journal-title":"Talanta"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"457","DOI":"10.1366\/0003702914337119","article-title":"Near-infrared probe for determination of solvent hydrophobicity","volume":"45","author":"Patonay","year":"1991","journal-title":"Appl. Spectrosc."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"62","DOI":"10.1002\/mrc.1270080203","article-title":"Etude des formes ferm\u00e9es et ouverts de spiropyrannes benzothiazoliniques en RMN 13C et 1H par transform\u00e9e de Fourier","volume":"8","author":"Samat","year":"1976","journal-title":"Org. Magn. Reson."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"415","DOI":"10.1002\/mrc.1260240505","article-title":"Study of the effect of N-protonation and N-methylation on the 1H and 13C chemical shifts of the six-membered ring in benzoazoles and 2-substituted N,N-dimethylamino derivatives","volume":"24","author":"Benassi","year":"1986","journal-title":"Magn. Reson. Chem."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"1343","DOI":"10.3987\/COM-89-4988","article-title":"On the protonation site of Rauwolfia alkaloids in highly concentrated sulphuric acid solutions","volume":"29","author":"Carmona","year":"1989","journal-title":"Heterocycles"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"1009","DOI":"10.1002\/cber.19881210528","article-title":"Eine verbesserte methode zur herstellung von 1,3,3-trialkyl-2-alkylineneindolinen","volume":"121","author":"Reichardt","year":"1988","journal-title":"Chem. Ber."},{"key":"ref_13","doi-asserted-by":"crossref","unstructured":"Pretsch, E., Clerc, T., Seibl, J., and Simson, W. (1989). Tables of Spectral Data for Structure Determination of Organic Compounds, Springer-Verlag.","DOI":"10.1007\/978-3-662-10207-7"},{"key":"ref_14","unstructured":"Beilstein\n\t\t\t\t\t\t\t\t\t\t\t\t\t              II\n\t\t\t\t\t\t\t\t\t\t\t\t\t            \n\t\t\t\t\t\t\t\t\t\t\t\t\t          \n\t\t\t\t\t\t\t\t\t\t\t\t\t          27\n\t\t\t\t\t\t\t\t\t\t\t\t\t          21d\n\t\t\t\t\t\t\t\t\t\t\t\t\t        ."},{"key":"ref_15","unstructured":"Beilstein\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t              II\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t            \n\t\t\t\t\t\t\t\t\t\t\t\t\t\t          \n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t  27\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t          23f\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t        ."},{"key":"ref_16","unstructured":"Beilstein\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t              II\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t            \n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t          \n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t  27\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t          20c\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t        ."},{"key":"ref_17","unstructured":"Beilstein\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t              IV\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t            \n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t          \n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t          20\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t          3459\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t        ."}],"container-title":["Molecules"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1420-3049\/7\/3\/320\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T22:27:24Z","timestamp":1760221644000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1420-3049\/7\/3\/320"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2002,3,31]]},"references-count":17,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2002,3]]}},"alternative-id":["70300320"],"URL":"https:\/\/doi.org\/10.3390\/70300320","relation":{},"ISSN":["1420-3049"],"issn-type":[{"value":"1420-3049","type":"electronic"}],"subject":[],"published":{"date-parts":[[2002,3,31]]}}}