Lithuanian Journal of Physics article / Lietuvos fizikos žurnalo straipsnis

SOLID-STATE ¹H AND ³¹P NMR AND FTIR SPECTROSCOPY STUDY OF STATIC AND DYNAMIC STRUCTURES IN SOL-GEL DERIVED CALCIUM HYDROXYAPATITES
Laurynas Dagys^a, Vytautas Klimavičius^a, Jonas Kausteklis^a, Ala Chodosovskaja^b, Valdemaras Aleksa^a, Aivaras Kareiva^b, and Vytautas Balevičius^a
^aDepartment of General Physics and Spectroscopy, Vilnius University, Saulėtekio 9–3, LT-10222 Vilnius, Lithuania
E-mail: vytautas.balevicius@ff.vu.lt
^bDepartment of Inorganic Chemistry, Vilnius University, Naugarduko 24, LT-03225 Vilnius, Lithuania

Received 22 December 2014; revised 20 January 2015; accepted 20 March 2015

Calcium hydroxyapatite containing amorphous phosphate phase (ACP-CaHA) and nano-structured hydroxyapatite (CaHA) have been prepared by two sol-gel synthesis routes. The structural organization of hydroxyl groups in both materials has been determined by means of ¹H MAS NMR and FTIR spectroscopy. It has been shown that the amount of structural –OH groups in nano-structured CaHA is significantly higher than that from adsorbed water and vice versa in ACP-CaHA. A precise signal shape analysis has been carried out for both studied samples. The ³¹P NMR signals have been found being Voigt-shaped in the wide-line as well as in MAS spectra. The ¹H and ³¹P spin-lattice and spin-spin relaxation time measurements have revealed that the fast spin motion takes place in ACP-CaHA. The corresponding correlation time τ ~ 7 · 10^–7 s at ~300 K has been determined. The effect of MAS rate on the ³¹P signal shape also confirms that this motion runs in the time scale of microseconds or even nanoseconds. The magnitude of the anisotropic broadening 1220 ± 20 Hz determined for nano-structured CaHA is very close to the maximum of the dipolar ¹H–³¹P coupling distribution profile estimated using CP MAS kinetics. The dynamics of ¹H–³¹P spin interactions in nano-structured CaHA (τ ~ 3.3 · 10^–5 s) is much slower than in ACP-CaHA.

Keywords: solid state NMR, FTIR spectroscopy, nano-structuring, structural water, hydroxyapatites
PACS: 33.25.+k, 82.56.-b, 78.30.-j

STATINIŲ IR DINAMINIŲ STRUKTŪRŲ ZOLIŲ IR GELIŲ BŪDU SUSINTETINTUOSE KALCIO HIDROKSIAPATITUOSE TYRIMAS KIETOJO KŪNO ¹H IR ³¹P BMR BEI FTIR SPEKTROMETRIJOS METODAIS

Laurynas Dagys^a, Vytautas Klimavičius^a, Jonas Kausteklis^a, Ala Chodosovskaja^b, Valdemaras Aleksa^a, Aivaras Kareiva^b, Vytautas Balevičius^a
^aVilniaus universiteto Bendrosios fizikos ir spektroskopijos katedra, Vilnius, Lietuva
^bVilniaus universiteto Neorganinės chemijos katedra, Vilnius, Lietuva

Kalcio hidroksiapatitas, savyje turintis amorfinio fosfato fazę (ACP-CaHA), ir nanostruktūrizuotas CaHA buvo pagaminti tyrimams taikant zolių ir gelių sintezės būdą. Struktūriniai abiejų junginių hidroksilo grupių organizavimosi savitumai nustatyti ¹H MAS (‘magiško kampo sukimo’) BMR ir FTIR spektrometrijos metodais. Parodyta, kad nanostruktūrizuotame CaHA, priešingai nei ACP-CaHA, struktūriškai junginio karkase pririštų –OH dalis yra žymiai didesnė už hidroksilo grupių iš adsorbuoto vandens. Atlikta preciziška abiejų bandinių BMR signalų kontūrų formos analizė (>4000 taškų kontūras). Nustatyta, kad ³¹P BMR spektrų, tiek plačiajuosčių, tiek MAS, signalų kontūrams yra būdinga Voigto forma. Tai reiškia, kad tiriamuosiuose junginiuose yra keli dinaminiai vyksmai, jų indėliai į spektrinius kontūrus aprašomi Lorentzo ir Gausso funkcijomis, o tų vyksmų spartos gali labai skirtis. ¹H ir ³¹P sukinio ir gardelės bei sukinių relaksacijų trukmių (T₁ ir T₂) matavimai atskleidė ACP-CaHa junginyje labai sparčius sukinių judesius. Nustatyta judesių kambario temperatūros artumoje (~300 K) koreliacijos trukmė yra τ ~ 7 · 10^–7 s eilės. Kintamo MAS dažnio poveikis ³¹P signalo formai taip pat patvirtina, kad ACP-CaHa junginyje vykstančių judesių laiko mastelis patenka į mikro- ar net nanosekundžių skalės sritį. Nanostruktūrizuoto CaHA nevienalyčio anizotropinio signalo išplitimo mastas 1220 ± 20 Hz puikiai dera su 1185 Hz verte, atitinkančia ¹H–³¹P sukinių sąveikos skirstinio maksimumą, jis buvo nustatytas šiam bandiniui, remiantis CP (‘kryžminės poliarizacijos’) MAS kinetikos duomenimis. ¹H–³¹P sukinių sąveikos dinamika nanostruktūrizuotame CaHA yra žymiai lėtesnė (τ ~ 3.3 · 10^–5 s) nei ACP-CaHA.

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