# Introduction yanocobalamin, also called vitamin B 12 (PubChem CID: 5479203), is a water-soluble vitamin with a key role in the normal functioning of the brain and nervous system, and for the formation of blood. Vitamin B 12 is a cobalt-containing compound synthesized by bacteria and an essential nutrient in mammals, which take it up from diet [1]. The significance of vitamin B 12 adequate nutritional status throughout life span is established and the adverse effects of vitamin B 12 deficiency in human health are currently recognized [2][3][4]. In addition to the welldescribed reversible hematological and often irreversible neurological changes of severe vitamin B 12 deficiency, epidemiological studies revealed a more common condition, the low vitamin B 12 status particularly in elder and pregnant women [5][6]. Because vitamin B 12 is essential for DNA synthesis and cellular energy production, a low vitamin B 12 status may be a risk factor for altered cellular metabolism and age-related diseases including cognitive decline and cardio-vascular disease [7]. This work is a continuation of systematic studies of vitamins B. Earlier in the articles [8][9][10], we have investigated the thermodynamic properties of vitamins B 2 , B 3 and the temperature dependence of the heat capacity of cyanocobalamin. The goals of this work include calorimetric determination of the standard thermodynamic functions of the cyanocobalamin. II. # Experimental i. Sample Cyanocobalamin was purchased from Fluka. For phase identification, an X-ray diffraction pattern of the vitamin B 12 sample was recorded on a Shimadzu Xray diffractometer XRD-6000 (CuK ? radiation, geometry ?-2?) in the 2? range from 5º to 60º with scan increment of 0.02º. The X-ray data and estimated impurity content (0.1 wt %) in the substance led us to conclude that the cyanocobalamin sample studied was an individual crystalline compound. Cyanocobalamin can crystallize in three modifications [4]: 1) "as-purchased"; 2). "wet"; 3) "dry". According to X-ray diffraction and solid-state NMR spectroscopy, we investigated the "as-purchased" sample cyanocobalamin. This sample is usually obtained by rapid crystallization from water at 343 K. # ii. Apparatus and measurement procedure The energy of combustion, Î?" c U, of cyanocobalamin was measured in a calorimeter (V-08) with a static bomb and an isothermal shield. The calorimeter design, the procedure of measuring the energies of combustion and the results of calibration and testing are given elsewhere [11]. It should be noted that while checking the calorimeter by burning succinic acid, prepared at D.I. Mendeleev Research Institute of Metrology (the value of the standard enthalpy of combustion of the acid coincided with the certificate value within ±0.017%). For complete combustion of cyanocobalamin we used paraffin as an auxiliary substance. Physico-chemical methods established the products of combustion of cyanocobalamin in the conditions of calorimetric experiment. Firstly, the solid products of combustion were identified by X-ray diffraction (Shimadzu X-ray diffractometer XRD-6000). Secondly, the formed liquid droplets were analyzed for phosphorus content using atomic absorption spectrophotometry (Shimadzu atomic absorption spectrophotometer AA-6300). Thirdly, the liquid droplets were titrated for total inorganic acids (Mettler Toledo pH meter Five Easy FE-20). Fourthly, the analysis of the gas phase was carried out by gas chromatography ( Shimadzu G? 2010 Plus). iii. # Results and Discussion The experimental data on burning of cyanocobalamin are presented in Table 1. As a result, the energies and enthalpies of combustion of riboflavin at T = 298.15K and standard pressure were determined. The values are for the reaction: C 63 H 88 ??N 14 ? 14 ?(cr)+79.75?O 2 (g)?63??O 2 (g)+42.875?? 2 ?(l) + 0.75?CoO(cr) + +0.125?Co 2 P 2 O 7 (cr)+0.75?H 3 PO 4 (sl-n,700? 2 ?)+7?N 2 (g) In brackets are given the physical states of reagents: (cr), crystalline; (g), gaseous; (l), liquid; (sl-n), solution. It should be noted that we have used a significant amount of physico-chemical methods (see section 2.2) in the study of combustion products of cyanocobalamin which is an organometallic compound. The data on the enthalpy of combustion of the crystalline cyanocobalamin was used to estimate enthalpy of combustion and formation at T = 298.15K and p = 0.1MPa (Table 2). Due to the fact that the standard enthalpy of formation of dicobalt diphosphate absent in the literature, we calculated the standard enthalpy and entropy of formation of Co 2 P 2 O 7 at 298.15 K (Table 2). In works [12,13], the absolute entropy and the standard Gibbs function of formation of dicobalt diphosphate were determined. The Gibbs function of formation Î?" f G° of the cyanocobalamin was evaluated from the Î?" f H° and Î?" f S° [10] values (Table 2). The values conform to the following process: 63?C(gr) + 44?H 2 (g) + 7?N 2 (g) + 7?O 2 (g) + Co(cr) + P(cr) ? C 63 H 88 ??N 14 ? 14 ?(cr) where in the brackets are indicated the physical states of reagents: (gr), graphite; (g), gaseous; (cr), crystalline. IV. # Conclusions The general aim of these investigations was to report the results of the thermodynamic study of the cyanocobalamin. The standard enthalpy of formation is determined by using combustion calorimetry. Much of the work is devoted to the study of the mechanism of combustion of cyanocobalamin and determination of thermodynamic functions of the combustion products. V. 1ValueExperiment123456m sam (g) a0.153450.16000.14660.15800.15950.1607m par (g) a0.69200.69890.70240.70210.70500.7059m thread (g) a0.00250.00220.002350.002150.00210.0019W (J?K -1 ) b148051480514805148051480514805?t (K) c2.4431052.4754552.4639352.4832102.4932002.497915?? ? U ? (J) d36170.436649.136478.636763.936911.836981.6?? ? U par (J) e32347.132668.232831.832818.732954.332997.3?? ? U thread (J) e42.036.539.336.035.632.1?? ? U HNO3 (J) f ?? ? U ? (J) g5.9 9.810.5 16.48.2 16.48.8 -9.4 26.211.7 26.2?? ? U (J?g -1 ) h24666.024689.424663.724686.124694.024683.9?? ? U = 24681 ± 10 J?g -1 = 33452 ± 14 kJ?mol -1 , themean energy of combustion of cyanocobalamin, ?? ?°U = 33435 ± 14 kJ?mol -1 , the energy of combustionof cyanocobalamin at standard pressure.a b W, the energy equivalent of the calorimeter. c ?t, the temperature increase in the experience, adjusted for heat transfer.d h ? ? 2 ## Acknowledgements The work was performed with the financial support of the Russian Foundation of Basic Research (Project Number 16-03-00288). * Vitamin B 12 absorption: Mammalian physiology and acquired and inherited disorders RKozyraki OCases Biochimie 95 2013 * Indicators for assessing folate and vitamin B12 status and for monitoring the efficacy of intervention strategies RGreen Food Nutr. Bull 29 2008 * Subclinical cobalamin deficiency R Curr. Opin. Gastroenterol 28 2012 * Vitamin B 12 transport from food to the body's cellsea sophisticated, multistep pathway MJNielsen MRRasmussen CBAndersen ENexo SKMoestrup Nat. Rev. Gastroenterol. Hepatol 9 2012 * Vitamin B 12 metabolism and status during pregnancy, lactation and infancy LHAllen Adv. Exp. Med. Biol 352 1994 * B vitamin status, dietary intake and length of stay in a sample of elderly rehabilitation patients FO'leary VMFlood PPetocz MAllman-Farinelli SSamman J. Nutr. Health Aging 15 2011 * Vitamin B 12 in health and disease FO'leary SSamman Nutrients 2 2010 * Thermodynamic properties of vitamin B 2 AVKnyazev IALetyanina ASPlesovskikh NNSmirnova SSKnyazeva Thermochimica Acta 575 2014 * Thermodynamic properties and low-temperature Xray diffraction of vitamin B 3 AVKnyazev NNSmirnova ASShipilova ANShushunov EGusarova SSKnyazeva Thermochimica Acta 604 2015 * Low-temperature heat capacity and thermodynamic functions of vitamin B 12 AVKnyazev NNSmirnova ASPlesovskikh ANShushunov SSKnyazeva Thermochimica Acta 582 2014 * BVLebedev EGKiparisova Russ J. Phys. Chem 70 1996 * Phase transitions in cobalt diphosphate GASharpataya KSGavrichev VEGorbunov ZPOzerova IDSokolov ADFedoseev AVFilatov Russian Journal of Inorganic Chemistry 39 3 1994 * FMFilinov BFBydanova Russian Journal of Inorganic Chemistry 1 1956