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Metal-organic frameworks (MOFs) are porous coordination polymers built from metal nodes and organic linkers [1]. These materials have a potential to be used in spintronics as molecular spin qubits [2]. The magnetic properties of two multivariate porphyrinic Zr-MOFs: MOF-525 and PCN- 223 [2], with 10% copper(II) or vanadyl(IV) cations in porphyrin linker, were examined by continuous-wave electron paramagnetic resonance (CW-EPR) spectroscopy. The simulations of the experimental data, obtained using EasySpin software [3] show that the CW-EPR spectra of MOF- 525 and PCN-223 with copper(II) cations exhibit superhyperfine interaction with four neighboring nitrogen nuclear spins (IN = 1). In contrast, such interactions are not visible for MOF-525 and PCN-223 with vanadyl(IV) cations. This can be explained by the fact that the unpaired electron in the vanadyl(IV) cation resides in the dxy orbital which is well separated from the orbitals of the nitrogen atoms [4, 5]. [1] H. Li, M. Eddaoudi, T. L. Groy, O. M. Yaghi, J. Am. Chem. Soc. 120 (1998) 8571-8572. [2] B. Karadeniz, D. Žilić, I. Huskić, L. S. Germann, A. M. Fidelli, S. Muratović, I. Lončarić, M. Etter, R. E. Dinnebier, D. Barišić, N. Cindro, T. Islamoglu, O. K. Farha, T. Friščić, K. Užarević, J. Am. Chem. Soc. 141 (2019) 19214−19220. [3] S. Stoll, A. Schweiger, J. Magn. Reson. 178 (2006) 42-55. [4] P.Basu, J. Chem. Educ. 78 (2001) 666- 669. [5] M. Atzori, L. Tesi, E. Morra, M. Chiesa, L. Sorace, R. Sessoli, J. Am. Chem. Soc. 138 (2016) 2154−2157.

The spin-lattice ( 1) and phase-memory electron spin ( ) relaxation times of metal-organic frameworks (MOFs) MOF-525 and PCN-223 doped with 10% copper (II) ions were examined by pulse electron paramagnetic resonance (EPR) spectroscopy. Investigation of these MOFs was performed in order to determine their potential as molecular spin qubits. Both MOFs exhibit electron spin coherence detectable up to 80 K. MOF-525 shows longer relaxation times than PCN-223. Incorporation of fullerene into PCN-223 increases both spin-lattice and phase-memory electron spin relaxation times. It was observed that PCN-223 with a maximum filling of fullerene shows better performance in both relaxation times compared with the previously surpassing MOF-525.

Metal-organic frameworks are porous crystalline materials built from metal nodes bridged by organic linkers. Porphyrins, a group of heterocyclic macromolecules with a large π-aromatic system, are particularly attractive linkers for MOF formation. Various metals can be coordinated to the center of porphyrin to create single-cation metalloporphyrins with advanced electrochemical and photophysical properties. Including porphyrins as building units of MOFs widens the potential application area of both the MOFs and porphyrins. Herein we present the liquid-assisted mechanochemical synthesis of various metalloporphyrin-based metal-organic frameworks. In-situ synchrotron PXRD monitoring has been carried out to demonstrate kinetic and mechanistic details of milling reactions. That data was used to tune the reaction conditions toward the target topologies.1 Continuous-wave and pulsed electron paramagnetic resonance spectroscopy (EPR) at X-band were applied in order to analyze the potential of metalloporphyrin-based MOFs as electron spin qubit candidates. Additionally, we will present here the encapsulation of fullerene C60 into the copper porphyrin MOFs by one-pot mechanochemical reactions, and its effect on the magnetic properties of metalloporphyrin zirconium MOF, C60@Cu0.1PCN223.

The magnetic properties of metal-organic frameworks MOF-525 and PCN-223 doped with copper (II) ions were examined by continuous wave (CW) and pulse electron paramagantic resonance (EPR) spectroscopy. MOF-525 and PCN-223 have different topologies: MOF-525 cuboctahedron and PCN-223 hexagonal prism. [1] Fullerene was added to PCN- 223 to investigate if it could be incorporated into its structure and what impact it has on spintronic properties. Computer simulations of the experimental EPR data were obtained using EasySpin software. [2] From the simulations of the experimental data we can see that the CW-EPR spectra of MOF-525 and PCN-223 exhibit different hyperfine tensors, that superhyperfine lines are more pronounced if copper ions are more diluted and that fullerene is incorporated into the structure of PCN-223. Pulsed EPR data regarding coherence signal properties are being analyzed. [1] B.Karadeniz et al., J. Am. Chem. Soc. 2019, 141, 19214 19214–19220. [2] S. Stoll, A. Schweiger, J. Magn. Reson. 2006, 178, 42-55.

The study of double modulation continuous wave (CW) electron spin resonance (DM-EPR) is reported to detect narrow 'spin-packet' like lines within an inhomogeneous CW-EPR line of low concentration P1 (Ns0) centers ([Ns0] < 1 ppm) in diamond. These narrow lines appear as peaks at multiple of modulation frequency in double modulation spectrum (DMS). It is shown that the respective line shape can be fitted assuming two Lorentzian line shapes. The linewidth of the narrower Lorentzian is comparable with the linewidth of the Lorentzian obtained from the T_2 relaxation time (δ_1=1⁄π T_2 ) estimated from the Hahn echo pulsed-EPR experiment. The broader component (δ_2 ) correlates with T_2^* relaxation time obtained from the free induction decay (FID) measurement of the inhomogeneous spectral line shape of P1 center. The ratio δ_1⁄δ_2 ~18 derived from DM- EPR measurements approaches within the experimental error the value T_2⁄(T_2^* )~16 derived from pulsed-EPR. Sensitivity to the small shift of the magnetic field (~0.6 μT) was shown to be detectable from the broadening behavior of δ_2 component. The results promote DM-EPR as a method complementary to pulsed-EPR for studying coherence times of low density paramagnetic centers in diamond lattice like nitrogen-vacation (NV-) center, since it exhibits similar properties as here investigated P1 center.

Using specific pulse sequences in ESR experiments, we have studied the differences between glassy and crystalline realization of the same material with the aim of finding a suitable experimental parameter for describing the disorder in glassy systems. The aim of our work is to contribute to the understanding of the influence of the disorder on the dynamic effects observed in glass at low temperatures for which a theoretical description has not been agreed upon yet. Focusing on a constant- time version of the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences, we studied two model systems: ethanol doped with nitroxyl radical TEMPO and γ- irradiated trehalose. Both materials were studied in glassy and polycrystalline state. We studied the hyperfine interaction of the electron spin with the spins of the matrix protons as a function of disorder ; i.e. molecular packing. In the case of ethanol, nuclear spectral diffusion (NSD) proved to be a dominant mechanism of the phase decoherence of electron spins [1], while in the case of trehalose, along with NSD, we have detected additional relaxation mechanisms that are supposed to derive from the electron- electron spin dipolar interaction between different radicals in the sample. The obtained experimental data are the basis for further theoretical studies of the molecular dynamics models in a disordered material since dynamic properties of nuclear spins (NSD), which are detected through the hyperfine interaction, directly reflect properties of the observed material. This work is supported by Croatian Science Foundation (HRZZ) under the projects IP-2013-11- 1108, IP-2018-01-3168. [1] J. Jurec, B. Rakvin, M. Jokić, M. Kveder, J. Non- Cryst. Solids, 471 (2017), 435.

Using specific pulse sequences in ESR experiments, we have studied the differences between glassy and crystalline realization of the same material with the aim of finding a suitable experimental parameter for describing the disorder in glassy systems. The aim of our work is to contribute to the understanding of the influence of the disorder on the dynamic effects observed in glass at low temperatures for which a theoretical description has not been agreed upon yet. Focusing on a constant- time version of the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences, we studied two model systems: ethanol doped with nitroxyl radical TEMPO and γ- irradiated trehalose. Both materials were studied in glassy and polycrystalline state. We studied the hyperfine interaction of the electron spin with the spins of the matrix protons as a function of disorder ; i.e. molecular packing. In the case of ethanol, nuclear spectral diffusion (NSD) proved to be a dominant mechanism of the phase decoherence of electron spins [1], while in the case of trehalose, along with NSD, we have detected additional relaxation mechanisms that are supposed to derive from the electron- electron spin dipolar interaction between different radicals in the sample. The obtained experimental data are the basis for further theoretical studies of the molecular dynamics models in a disordered material since dynamic properties of nuclear spins (NSD), which are detected through the hyperfine interaction, directly reflect properties of the observed material.

Glassy and crystalline solid ethanol are used as a model systems to study disorder in the material. It is probed by the hyperfine interaction of the electron spin from the incorporated paramagnetic nitroxyl radical TEMPO. Nuclear spectral diffusion from host matrix protons is the dominant mechanism of electron spin decoherence of TEMPO incorporated in two realizations of solid-state environment of ethanol and it is proposed as a descriptor of the extent of disorder present in the system [1, 2]. It can be suppressed when applying special multiple-pulse sequence developed for the dynamical decoupling control of the central spin. The effect is much more pronounced in glassy than crystalline ethanol, the state exhibiting larger disorder/frustration. Since the phase memory relaxation time of the paramagnetic center increased linearly with the increase in the number of the applied refocusing pulses, the effect of the extent of disorder could be described numerically for this specific model system

Constant time Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences were applied to two systems, ethanol doped with nitroxyl radical TEMPO and gamma-irradiated trehalose. The aim was to investigate the effect of different electron spin relaxation mechanisms in different systems on the efficiency of the preservation of the phase memory relaxation time T_m by dynamical decoupling and to test whether CPMG sequences can be used to discriminate them. In the case of ethanol, paramagnetic nitroxyl radical TEMPO was applied in the concentration range 0.2-1.1 mM. Trehalose samples were irradiated using X- ray radiation with standard dosages of 5-10 kGy. For both model systems, the measurements on glassy and crystalline type of samples were conducted to investigate impact of disorder as well. For ethanol no dependence of T_m on the concentration of paramagnetic centres and on the length of the used refocusing pulses was observed, implying nuclear spectral diffusion (NSD) as the dominant mechanism of electron spin decoherence [1]. Contrary to the observations in ethanol, no stretched exponential decay was observed when determining T_m in trehalose. In ethanol there was linear increase of T_m with number n of used refocusing pulses in the CPMG sequence. In trehalose the increase of T_m with n was not linear, the saturation effects observed for n≥4, which suggests that NSD isn’t the dominant mechanism of electron spin decoherence. The impact of instantaneous diffusion (ID) in trehalose is supported by the calculation of the concentration of radicals [2]. In conclusion, the efficiency of dynamical decoupling using constant time CPMG experiment strongly depends on the dominant mechanism of electron spin decoherence, therefore it can be used to determine whether NSD or ID is the dominant mechanism of decoherence.

Glassy and crystalline solid ethanol are used as a model systems to study disorder in the material. It is probed by the hyperfine interaction of the electron spin from the incorporated paramagnetic nitroxyl radical TEMPO. Nuclear spectral diffusion from host matrix protons is the dominant mechanism of electron spin decoherence of TEMPO incorporated in two realizations of solid-state environment of ethanol and it is proposed as a descriptor of the extent of disorder present in the system [1, 2]. It can be suppressed when applying special multiple-pulse sequence developed for the dynamical decoupling control of the central spin. The effect is much more pronounced in glassy than crystalline ethanol, the state exhibiting larger disorder/frustration. Since the phase memory relaxation time of the paramagnetic center increased linearly with the increase in the number of the applied refocusing pulses, the effect of the extent of disorder could be described numerically for this specific model system. [1] M. Kveder, D. Merunka, M. Jokić, B. Rakvin, J. Non-Cryst. Solids 354 (2008) 5201 [2] M. Kveder, B. Rakvin, M. Jokić, E. Reijerse, J. Non-Cryst. Solids 414 (2015) 27

Trehalose is a disaccharide found in nature which can form crystalline and glassy state. It is well known for its unusual bioprotective properties like ahydrobiosis or cryoprotection. These phenomena are still not fully understood and have prompted the investigation of molecular dynamics in the wide range of trehalose preparations in the solid state. Due to the fact that trehalose exhibits the highest glass transition temperature, Tg, and the most compact hydrogen-bonded network of saccharides, it is interesting to be studied in the context of low-temperature anomalies observed in glasses. The advantage of applying electron paramagnetic resonance (EPR) spectroscopy is in the sensitivity of the electron-spin coupling with the disordered modes in the observed system. Here, electron spin-lattice relaxation times (T1) measured by X-band EPR spectroscopy in irradiated trehalose glass and anhydrous polycrystalline state are presented in the large temperature interval, from 0.012 Tg to 0.7 Tg. The largest difference in T1 is detected below ca. 80 K indicating more efficient energy exchange between the spin system and the lattice for paramagnetic centers in the glassy than anhydrous trehalose polycrystalline state. The involvement of the disordered modes (glassy/soft/boson peak modes), which enhance the energy exchange between the spin system and the lattice in the glassy as compared to the crystalline state, is evaluated in the framework of soft potential model. The results corroborate the idea of boson peak being a universal property of disordered solids.

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Održano predavnje prikazalo je kako se modom ESR, kao komplementarnom spektroskopskom metodm mogu istraživati sustavi na temperaturama tekućeg helija u staklastom stanju ako sadrže paramagnetske centre. Diskutirana je detekcija tzv bozonskog vrha

The synthesis of polymers with enzymes as catalysts atracts significant atention due to the potential development of energy efficient polymerisation process. Enzymatic polymerization usually are carried out under "environmentally friendly conditions" in water-rich reaction media. Furthermore, it has been shown that the presence of interfaces in the form of dissolved or dispersed structure- controlling agents, so called templates, can have considerable influence on the chemical structure and properties of the obtained polymers (polymerization reactions catalyzed by oxidative enzymes). EPR spectroscopy was used to examine the magnetic properties of an enzymatically synthesized polymer obtained in the presence of submicrometer-sized vesicles formed from sodium bis(2- ethylhexyl)sulphosuccinate (AOT) as templates. The examined polymer abbreviated as (poly(PADPA)-TvL-AOT ) was synthesized from the aniline dimer PADPA (= p-aminodiphenylamine = N- phenyl- 1, 4-phenylenediamine) with Trametes versicolor laccase (TvL)/O2 as catalyst and oxidant and AOT vesicles as templates[1]. In addition the earlier examined enzymatically synthesized polyaniline (PANI-TvL-AOT) obtained with the same enzyme, oxidant and template as well as an commercial conductive PANI sample in its emeraldine salt from (PANI ES) were used for comparison in order to correlate experimental data obtained for the two enzymatically synthesized polymers to properties of the well characterized PANI ES. For all investigated polymers linewidths and intensities of EPR spectra were analyzed at 9.5 GHz frequencies in a wide temperature interval from 5 to 300 K. It was shown that a model based on the concept of correlated polaronic bands[2] could be applied for the interpretation of the EPR spectra. It is also noted that poly(PADPA)- TvL-AOT contains the largest amounts of Curie contribution, C0, that account for noncorrelated spins, and exhibits a lower percetage of "locally disordered dimers" in comparison to PANI-TvL-AOT. The inhomogeneous complex spectrum of poly(PADPA)-TvL-AOT recorded at room temperature was decomposed in two separate Dyson– type spectral components. Presence of these spectral components was additionally confirmed by employing EPR detection at high frequency (94 GHz). Spectra detected at high frequency exhibit line broadening behaviour in comparison to spectra recorded at low frequency. This effect was used to roughly estimate the interchain spin exchange interaction. It was shown that the obtained effective distances between the polymer chains are larger for the enzymatically synthesized polymers obtained with AOT templates than for the commercial PANI ES sample. References: [1] Junker, K. et. al, in preparation. [2] Rakvin, B. et. al, J. Phys. Chem. B, 118 2205 (2014)

Trehalose, a non-reducing disaccharide is a matter of common interest in many research areas such as chemistry, biology, food chemistry, pharmaceutics, bioscience etc. Trehalose and other disaccharides were intensively studied due to their bio-protection effect, which refers to their ability to allow organisms to survive under extreme dehydration or freezing conditions. Though this mechanism is still unknown, many researchers believe that protection of the biomaterials and living organisms under extreme conditions is associated with amorphous characteristics of the matrices which they formed, being inversely related to the degree of crystallization. Consequently, the polymorphism of trehalose has been the subject of intense research in recent time. On the other hand, trehalose is suitable as model system for investigation of the nature and reactions of radicals induced by direct radiation effects in the deoxyribose sugar of DNA. Furthermore, understanding the behavior of radiation-induced defects in trehalose in different polymorphic forms is important for radiation dosimetry purposes4 and for the detection and characterization of irradiated final products in the pharmaceutical and food industry. Therefore, thermal stability and decay kinetics of EPR signals in γ-irradiated trehalose in different polymorphic forms were investigated using isothermal and isochronal annealing experiments.

Trehalose, a non-reducing disaccharide is a subject of common interest in many research areas such as biology, chemistry, food chemistry, pharmaceutics, bioscience etc. Trehalose like other disaccharides was intensively studied due to its bio-protection properties such as anhydrobiosis or cryoprotection, which refer to their ability to allow organisms to survive under extreme dehydration or freezing conditions 1. Although this mechanism is still not properly understood, many researchers believe that protection of the biomaterials and living organisms under extreme conditions is associated with properties of amorphous matrices, being inversely related to the degree of crystallization2. Consequently, the polymorphism of trehalose has been the subject of intense research in recent time. On the other hand, trehalose is suitable as a model system for investigation of the nature and reactions of radicals induced by direct radiation effects in the deoxyribose sugar of DNA 3. Furthermore, understanding the behavior of radiation-induced defects in trehalose in different polymorphic forms is important for radiation dosimetry purposes 4 and for the detection and characterization of irradiated final products in the pharmaceutical and food industry. The aim of this study was to investigate EPR response of radiation induced radicals in different polymorphic forms of trehalose. Number of free radicals, thermal stability and decay kinetics of EPR signals in γ-irradiated trehalose in different polymorphic forms were investigated using isothermal and isochronal annealing experiments.

Here we demonstrate that two extreme cases of molecular packing, i.e. the crystalline and glassy state of solid ethanol, which define the complete experimental span of attainable host matrix frustration, can be efficiently probed by measuring the electron spin phase memory relaxation time, TM , of an incorporated TEMPO nitroxyl radical at X-band EPR frequency. The sensitivity of TM is based on the spectral and spin diffusion effects, which reflect the spatial distribution of involved spins as a function of molecular frozen-in disorder. By keeping the excited region of the EPR spectrum fixed one can monitor the changes in the density of spin packets, upon the state transformation of the host. EPR experiments performed at 94 GHz show a clear difference in local distribution of paramagnetic centers in ethanol glass as compared to crystalline ethanol. The results support the idea that, by measuring TM and properties of density of spin packets, one can explore the extent of molecular disorder.

Istraživanje pripada grupi multidisciplinarnih proučavanja dinamike u materijalima karakteriziranim neuređenošću molekula kao na primjer stakla. Pri tome se pokazuje da su molekularna stakla, poput stakla šećera, alkohola i sl. prikladan eksperimentalni sustav. Trehaloza je disaharid koji se u prirodi nalazi u stanju stakla ili kristaliničnom stanju. Budući da trehaloza ima najvišu temperaturu staklastog prijelaza i najizraženiju mrežu vodikovih veza od svih saharida, zanimljiva je za proučavanje anomalija opaženih u staklima općenito [1]. Prednost primjene elektronske paramagnetske rezonancije (EPR) je u osjetljivosti međudjelovanja spina elektrona i rešetke s obzirom na dinamiku/vibracijska svojstva promatranog sistema. Predstavit će se rezultati EPR spektroskopije istraživanja dvaju polimorfa krute trehaloze (polikristal, staklo) [2] u kojima su paramagnetski centri inducirani ionizirajućim zračenjem [3]. Usporedit će se spin - rešetka relaksacijsko vrijeme u okruženjima različite neuređenosti. Pokazat će se da je teorijski pristup u analizi EPR mjerenja zasnovan na tzv. mekom potencijalu (eng. soft potential model) pogodan za opis dinamike u stanju neuređenosti krute matrice [4]. [1] D.A. Parshin, Soft Potential Model and Universal Properties of Glasses, Phys Scripta, (1993) 180. [2] M. Kveder, I. Saric, D. Merunka, M. Jokic, S. Valic and B. Rakvin, The anhydrous solid trehalose: low-temperature EPR study of glassy and boson peak modes. Journal of Non-Crystalline Solids, 10.1016\/j.jnoncrysol.2013.05.016, (2013) [3] A. Graslund, G. Lofroth, Free-Radicals in Gamma-Irradiated Single-Crystals of Trehalose Dihydrate and Sucrose Studied by Electron-Paramagnetic Resonance, Acta Chem Scand B, (1975) 475. [4] D. Merunka, M. Kveder, B. Rakvin, Effect of thermally activated dynamics on electron spin-lattice relaxation in glasses, Chem Phys Lett, (2011) 19.

Thermotropic liquid crystal trans-4-heptylcyclohexanecarboxylic acid (HCCA) doped with 4-oxo-2, 2, 6, 6, -tetramethyl-1-piperidinyloxy spin probe (Tempone) is investigated by electron spin resonance (ESR) spectroscopy in the presence of chiral bisoxalamide gelator (1) during both cooling and heating cycles. In the temperature range where HCCA displays isotropic, nematic, smectic B and crystalline phases, the impact of (1) self-organization was investigated by partitioning of the spin probe in the environments varying in the polarity and the gelator oncentration. The evidence of the onset of the gelator network self-assembly in the nematic phase was detected by ESR at higher temperatures than the ones reported by other experimental techniques. The spectral analysis points to the switching of polarity in the vicinity of the spin probe when the transfer of chirality from (1) to HCCA occurs upon cooling the sample from isotropic to chiral nematic phase. When the gelation proceeds in the smectic phase, the melting of the gelator network appears in the nematic phase and could be studied during the heating cycle. The experimental evidence is provided that gelator network confines the HCCA into the domains within the bulk crystalline matrix where the local molecular dynamics are still not frozen.

Spin-lattice relaxation (SLR) of TEMPO radical in the glassy (G) and crystalline (C) ethanol was measured by X-band EPR technique between 5 and 80 K. The SLR rates Gamma=1/T1 are higher in G- ethanol than in C-ethanol for both protonated and deuterated samples, while the excess SLR rate in G-ethanol DGamma=Gamma(G)−Gamma(C) is much higher for the protonated sample (Fig. 1). The results indicate that DGamma is produced by extra modes existing in glassy matrix, which are coupled to the electron spin of radical by the electron- nuclear dipolar (END) interaction. Using the soft- potential model for glassy modes and assuming END interaction between the electron spin and matrix protons, the expressions for SLR rates due to various mechanisms of glassy modes was derived. The SLR rates were evaluated for protonated G- ethanol from reported experimental data. The results indicate two effective mechanisms: thermally activated relaxation of double-well systems (DWS) and phonon-induced relaxation of quasi-harmonic local modes (QLM). The SLR rate induced by these mechanisms correlates well with the experimental DGammain both the order of magnitude and the temperature dependence (Fig. 1).