Size-dependent Changes Research Articles

The Stefan problem with variable thermophysical properties and phase change temperature

In this paper we formulate a Stefan problem appropriate when the thermophysical properties are distinct in each phase and the phase-change temperature is size or velocity dependent. Thermophysical properties invariably take different values in different material phases but this is often ignored for mathematical simplicity. Size and velocity dependent phase change temperatures are often found at very short length scales, such as nanoparticle melting or dendrite formation; velocity dependence occurs in the solidification of supercooled melts. To illustrate the method we show how the governing equations may be applied to a standard one-dimensional problem and also the melting of a spherically symmetric nanoparticle. Errors which have propagated through the literature are highlighted. By writing the system in non-dimensional form we are able to study the large Stefan number formulation and an energy-conserving one-phase reduction. The results from the various simplifications and assumptions are compared with those from a finite difference numerical scheme. Finally, we briefly discuss the failure of Fourier’s law at very small length and time-scales and provide an alternative formulation which takes into account the finite time of travel of heat carriers (phonons) and the mean free distance between collisions.

Size-Dependent Vulnerability of Lumbar Motor Neuron Dendritic Degeneration in SOD1G93A Mice.

The motor neuron (MN) soma surface area is correlated with motor unit type. Larger MNs innervate fast fatigue-intermediate (FInt) or fast-fatiguable (FF) muscle fibers in type FInt and FF motor units, respectively. Smaller MNs innervate slow-twitch fatigue-resistant (S) or fast fatigue-resistant (FR) muscle fibers in type S and FR motor units, respectively. In amyotrophic lateral sclerosis (ALS), FInt and FF motor units are more vulnerable, with denervation and MN death occurring for these units before the more resilient S and FR units. Abnormal MN dendritic arbors have been observed in ALS in humans and rodent models. We used a Golgi-Cox impregnation protocol to examine soma size-dependent changes in the dendritic morphology of lumbar MNs in SOD1G93A mice, a model of ALS, at pre-symptomatic, onset and mid-disease stages. In wildtype control mice, the relationship between MN soma surface area and dendritic length or dendritic spine number was highly linear (i.e., increased MN soma size correlated with increased dendritic length and spines). By contrast, in SOD1G93A mice, this linear relationship was lost and dendritic length reduction and spine loss were observed in larger MNs, from pre-symptomatic stages onward. These changes correlated with the neuromotor symptoms of ALS in rodent models. At presymptomatic ages, changes were restricted to the larger MNs, likely to comprise vulnerable FInt and FF motor units. Our results suggest morphological changes of MN dendrites and dendritic spines are likely to contribute ALS pathogenesis, not compensate for it. Anat Rec, 303:1455-1471, 2020. © 2019 American Association for Anatomy.

Biorelevant polyanions stabilize fibrin against mechanical and proteolytic decomposition: Effects of polymer size and electric charge

The release of neutrophil extracellular traps (NETs) containing DNA and histones is an essential mechanism in the neutrophil-mediated innate immunity. In thrombi the polyanionic DNA confers mechanical and lytic resistance to fibrin and heparins interfere with the effects of NET components. Heparins are polyanions used not only as therapeutic agents, but they are also released by mast cells at entry sites of pathogens. Platelets and microorganisms release a different type of polyanions (polyphosphates) of various size (in the range 60–1000 phosphate monomers). With the current study we aimed to evaluate if the stability of fibrin is influenced by the type of polyanion, its molecular size or relative electric charge.Fibrin structure was approached with scanning electron microscopy (SEM) and pressure-driven permeation. An oscillation rheometer was used to investigate viscoelastic properties. Kinetic turbidimetric assays for the generation and dissolution of composite fibrin clots containing unfractionated heparin (UFH), and its partially or fully desulfated derivatives, as well as low molecular-weight heparin (LMWH), pentasaccharide (S5), and polyphosphates composed of 45 (P45), 100 (P100) or 700 (P700) monomers at average.The smaller polyanions P45, P100, LMWH, and S5 accelerated, whereas P700 and UFH retarded clot formation. All polyanions altered the fibrin structure: SEM and clot permeation showed thicker fibers with smaller (LMWH, S5, P700) or larger (UFH, P100) pores. All polyanions stabilized the clots mechanically, but the smaller P45, P100 and LMWH decreased the deformability of fibrin, whereas the large UFH and P700 increased the maximal bearable deformation of clots. Despite the size-dependent structural changes, all heparins caused a 10–15% prolongation of lysis-times with plasmin, and UFH-effects depended on sulfation patterns. The 20–35% prolongation of lysis-times caused by all polyphosphates was a kringle-dependent phenomenon, and was dampened in the presence of 6-aminohexanoate blocking the lysine-binding sites of plasmin.In summary, we found that polyanions of different chemical structure stabilize fibrin clots via size-dependent modulation of fibrin structure and kringle-dependent inhibition of plasmin-mediated fibrinolysis.

Size-Dependent Mechanical Properties of a Metal-Organic Framework: Increase in Flexibility of ZIF-8 by Crystal Downsizing.

Size engineering is an emerging strategy to modulate the mechanical properties of crystalline materials. Herein, micro- and nanodimensional single crystals of the prototypical metal-organic framework (MOF) ZIF-8 are generated using solvothermal and solution methods, respectively. Atomic force microscopy-based nanoindentation technique was used to measure the Young's modulus values of micro- and nanodimensional individual ZIF-8 crystals. We demonstrate that crystal downsizing to nanoscale dimensions results in a 40% reduction in crystal stiffness. The change is attributed to a greater contribution of surface effects to the physical properties of nanocrystalline ZIF-8. The observed change in the mechanical properties may be used to explain reported size-dependent changes in gas adsorption of ZIF-8, thought to be a result of differences in framework flexibility at the nanoscale. Our work provides an important example on how downsizing of crystalline metal-organic materials can give rise to specific and tunable physical properties.

Nonclassical Optical Properties of Mesoscopic Gold.

Gold nanostructures have important applications in nanoelectronics, nano-optics, and in precision metrology due to their intriguing optoelectronic properties. These properties are governed by the bulk band structure but to some extent are tunable via geometrical resonances. Here we show that the band structure of gold itself exhibits significant size-dependent changes already for mesoscopic critical dimensions below 30nm. To suppress the effects of geometrical resonances and grain boundaries, we prepared atomically flat ultrathin films of various thicknesses by utilizing large chemically grown single-crystalline gold platelets. We experimentally probe thickness-dependent changes of the band structure by means of two-photon photoluminescence and observe a surprising 100-fold increase of the nonlinear signal when the gold film thickness is reduced below 30nm allowing us to optically resolve single-unit-cell steps. The effect is well explained by density functional calculations of the thickness-dependent 2D band structure of gold.

Two-pore physiologically based pharmacokinetic model with de novo derived parameters for predicting plasma PK of different size protein therapeutics.

Two-pore PBPK models have been used for characterizing the PK of protein therapeutics since 1990s. However, widespread utilization of these models is hampered by the lack of a priori parameter values, which are typically estimated using the observed data. To overcome this hurdle, here we have presented the development of a two-pore PBPK model using de novo derived parameters. The PBPK model was validated using plasma PK data for different size proteins in mice. Using the "two pore theory" we were able to establish the relationship between protein size and key model parameters, such as: permeability-surface area product (PS), vascular reflection coefficient (σ), peclet number (Pe), and glomerular sieving coefficient (θ). The model accounted for size dependent changes in tissue extravasation and glomerular filtration. The model was able to a priori predict the PK of 8 different proteins: IgG (150kDa), scFv-Fc (105kDa), F(ab)2 (100kDa, minibody (80kDa), scFv2 (55kDa), Fab (50kDa), diabody (50kDa), scFv (27kDa), and nanobody (13kDa). In addition, the model was able to provide unprecedented quantitative insight into the relative contribution of convective and diffusive pathway towards trans-capillary mass transportation of different size proteins. The two-pore PBPK model was also able to predict systemic clearance (CL) versus Molecular Weight relationship for different size proteins reasonably well. As such, the PBPK model proposed here represents a bottom-up systems PK model for protein therapeutics, which can serve as a generalized platform for the development of truly translational PBPK model for protein therapeutics.

Size-dependent variation in leaf functional traits and nitrogen allocation trade-offs in Robinia pseudoacacia and Cornus controversa.

Tree species vary in how they invest resources to different functions throughout their life histories, and investigating the detailed patterns of ontogenetic changes in key functional traits will aid in predicting forest dynamics and ecosystem processes. In this context, we investigated size-dependent changes in key leaf functional traits and nitrogen (N) allocation trade-offs in black locust (Robinia pseudoacacia L., an N-fixing pioneer species) and giant dogwood (Cornus controversa Hemsl., a mid-successional species), which have different life-history strategies, especially in their light use. We found that the leaf mass per area and leaf carbon concentrations increased linearly with tree size (diameter at breast height, DBH), whereas leaf N concentrations decreased nonlinearly, with U- and hump-shaped patterns in black locust and giant dogwood, respectively. We also discovered large differences in N allocation between the two species. The fraction of leaf N invested in cell walls was much higher in black locust than in giant dogwood, while the opposite was true for the light harvesting N fraction. Furthermore, these fractions were related to DBH to varying degrees: the cell wall N fraction increased with DBH for both species, whereas the light harvesting N fraction of giant dogwood decreased nonlinearly and that of black locust remained constant. Instead, black locust reduced the fraction of leaf N invested in other N pools, resulting in a smaller fraction compared to that of giant dogwood. On the other hand, both species had similar fraction of leaf N invested in ribulose-1,5-bisphosphate carboxylase/oxygenase across tree size. This study indicated that both species increased leaf mechanical toughness through characteristic changes in N allocation trade-offs over the lifetimes of the trees.

Size-dependent change in body shape and its possible ecological role in the Patagonian squid (Doryteuthis gahi) in the Southwest Atlantic

Cephalopods are a versatile group with several mechanisms in place to ensure the success of future generations. The Patagonian long-finned squid (Doryteuthis gahi) populations on the southern Patagonian shelf are believed to be genetically homogenous, but the mechanisms connecting them geographically and temporally are unresolved. Individual growth is highly variable within cephalopod populations and is likely to affect individual patterns of migration and, thus, population connectivity as a whole. Therefore, this study aimed to make inferences about population structure by analysing the size at which individuals were mature and aimed to describe the intrapopulation growth (allometric) trajectories of body shape, using landmark-based geometric morphometric techniques to describe phenotypes. Samples were collected from June 1999 to November 2017 around 52°S and 58°W. Smoothing curves from binomial generalised additive models (GAMs) suggested two size modes of maturity in females and one or multiple modes in males dependent on year and season. There was a gradual elongation of the mantle and an increase in the relative fin size throughout ontogeny. Shape scores from geometric morphometric shape coordinates revealed a continuous non-linear allometric trajectory with a significantly different slope angle for males exceeding 20.1 cm dorsal mantle length (DML). At the extreme of this continuum, the largest ‘super-bull’ form had a substantially more elongated body shape, a heavier fin and a larger fin area compared to the rest of the population, a body shape associated with enhanced swimming performance which may help to maintain population connectivity. The prevalence of these rare super-bulls in the fishery varied widely between years, suggestive of phenotypic plasticity. This study provides evidence that the D. gahi population on the southern Patagonian shelf has a complex population structure with high intraspecific variation.

Size effects and active sites of Cu nanoparticle catalysts for CO2 electroreduction

Electrochemical conversion of CO2 into useful chemicals represents a promising approach to mitigate our pressing environment and energy problems. To date, only Cu electrodes, of all metals examined experimentally, have been shown to be capable of producing significant quantities of hydrocarbons with adequate Faradaic efficiency from CO2 electroreduction. In this work, we use density functional theory calculations to study size-dependent changes on the adsorption of reaction intermediates and reaction free energy for CO2 reduction on Cu nanoparticles ranging from 13 to 561 atoms. We found that the adsorbate-induced surface charge perturbation on Cu nanoparticles becomes more local as the Cu nanoparticles size increases, and the extent of charge perturbations on 309 atom Cu appears to be very similar in Cu(1 1 1) surface. For two-electron products (CO, HCOOH and H2), Cu147 appears near the top in the volcano plots, implying that Cu147 has a near optimal binding energy of the key intermediates to produce two-electron products. To identify the active sites for the CO2 reduction, we compared the activity of different reaction sites, namely, facet, edge and corner sites of Cu nanoparticles, Cu(1 1 1), Cu(1 0 0), Cu(2 1 1) and hexagonal Cu nanowire. We find that the under-coordinated sites are more active than the low-index surfaces. The presented size-activity and structure-activity relationships will provide useful insight for the design better nanostructured Cu catalysts for CO2 electroreduction.

Mechanical oscillations in biological tissues as a result of delayed rest-length changes

Oscillatory behavior in tissue biology is ubiquitous and may be observed in the form of either chemical or mechanical signals. We present here and solve a mechanical cell model that exhibits oscillations emerging from delayed viscoelastic rheological laws. These include a time delay between the mechanical response and the rest-length changes, which evolve proportionally to the delayed cell deformation and use a remodeling rate parameter. We show that different regimes (no oscillatory response, sustained oscillations, and unstable oscillations) are obtained for different values of the delay or the remodeling rate. The results are analytically demonstrated in a one-dimensional problem with one and two cells that are represented by simple line elements. Oscillations of the cell deformations are obtained whenever different delays coexist, or when the delay is size-dependent. We also extend our results to a multicellular two-dimensional vertex model that includes the same rheological law, and which inherits the presence of critical values of the delay or remodeling rate. We numerically show that indeed the size-dependent rest-length changes induce oscillations in the cell shapes and areas.

Ageing in trees: Role of body size optimization in demographic senescence

“We must discover the reason why trees are of an enduring constitution” wrote Aristotle in 350 BCE. Millennial lifespans in clonal trees, reproductive activity in young and physically underdeveloped trees, and sustained (albeit sporadic) reproduction for life in most trees, have made others suggest that trees show negative (anti) senescence or even become immortal. Alternatively, we hypothesise that demographic senescence is always observed when trees reach their habitat-specific optimum body size. Natural selection optimizes body size in trees such that their age-specific mortality probability is minimized and fertility is maximised. Trees of supra-optimal size are vulnerable to extrinsic mortal threats. Size-driven decline in tree bodily function is accentuated by age-driven loss of access to genomic information through chromosomal reorganisation, epigenetic changes, and transcriptional inadequacies. Annual trends in fertility are unpredictable in trees, although fertility always declines in old trees because of age- and size-dependent functional decline and body mass loss. We propose that an increase in body size beyond a habitat-specific optimum will escalate size-specific mortality probability of trees without any significant gains in fertility. Such trees will show increasing mortality rate and decreasing fertility rate, a hallmark of demographic senescence. The time-course of demographic senescence is also influenced by the extent of juvenile mortality, age- and size-dependent changes in offspring quality, and heterogeneity in height growth rate. High juvenile mortality is the main reason why premature reproduction has evolved in trees of sub-optimal size. Offspring viability (a) remains poor in adults of sub-optimal size, (b) improves as these adults get bigger and attain an optimum size, and (c) may be sustained in older trees (with low fertility levels) due to a trade-off between fertility and seed viability, shaped by habitat-specific body size optimization. Senescence is not avoided, but slows down in (a) safe niches, where trees of supra-optimal body size survive, and in (b) extreme niches, where attainment of relatively shorter or smaller optimal size is protracted.

Determination of CO Adsorption Sites on Gold Clusters Au n- ( n = 21-25): A Size Region That Bridges the Pyramidal and Core-Shell Structures.

We perform a joint photoelectron spectroscopy and theoretical study to investigate CO adsorption sites on midsized gold clusters, Au n- ( n = 21-25), a special size region that bridges the highly symmetric pyramidal cluster Au20- (Li et al. Science 2003, 299, 864) and the prevailing core-shell clusters starting from Au26- (Schaefer et al. ACS Nano 2014, 8, 7413). Particular attention is placed on whether the CO binding can significantly change structures of the host clusters in view of the fact that the size-dependent structural change already occurs for bare gold clusters in this size range. A transition from hollow-tubular to fused-planar structures is identified for the Au nCO- clusters even though the CO molecule mostly binds to an apex gold atom. The computed CO adsorption energy and HOMO-LUMO gap of the gold clusters suggest that among the five gold clusters the Au23- cluster exhibits the strongest CO binding and thereby could be a good catalytic model system.

Buckling and free vibration analysis of functionally graded sandwich micro-beams resting on elastic foundation by using nonlocal strain gradient theory in conjunction with higher order shear theories under thermal effect

Based on the nonlocal strain gradient theory (NLSGT), and various higher order shear deformation beam theories a formulation for buckling and free vibration of size dependent functionally graded sandwich micro-beams resting on two parameter elastic foundation including Winkler and Pasternak shear layer springs with thermal effects is presented. The sandwich FG micro-beams are assumed to be formed with homogenous ceramic core and ceramic-metal FG skins. According to the Mori-Tanaka homogenization scheme and the classical rule of mixture the material properties of the FG part of the sandwich size dependent beam changes continuously through the thickness of the beam. Equations of motion and the associated boundary conditions are derived via Hamilton's principle. Static buckling loads and natural frequencies are obtained by using generalized differential quadrature method (GDQM) for size dependent sandwich FG beam with different boundary conditions. As original contributions to the literature, the effects of the nonlocal parameter (ea), the length scale parameter (lm), aspect ratio (L/h), gradient index (k), different cross-section shapes, temperature change (ΔT)and stiffnesses of Winkler and shear layer springs (KW, KS respectively) on the buckling and free vibration of the sandwich FG micro-beam are investigated, reported and discussed in detail. To verify the present formulation present results (buckling and free vibration) are compared with the previously published results. Good agreement is observed between the present solutions and the previously published results.

Graphene size-dependent phase change behaviors of in situ reduced grapehene oxide/polyurethane-based solid-solid phase change composites

In this study, the size effects of graphene oxide (GO) sheets on the phase change behaviors of crosslinking polyurethane system have been investigated. The experimental results show that phase change performance of the system is connected closely to the heterogeneous nucleation, physical confinements from GO and interactions in the system, which are inseparable from the specific surface area and the contents of oxygen functional groups depending on the size. This work has a theoretical significance to design thermal energy storage materials with desired properties.

Acute intravenous exposure to silver nanoparticles during pregnancy induces particle size and vehicle dependent changes in vascular tissue contractility in Sprague Dawley rats

The use of silver nanoparticles (AgNP) raises safety concerns during susceptible life stages such as pregnancy. We hypothesized that acute intravenous exposure to AgNP during late stages of pregnancy will increase vascular tissue contractility, potentially contributing to alterations in fetal growth. Sprague Dawley rats were exposed to a single dose of PVP or Citrate stabilized 20 or 110nm AgNP (700μg/kg). Differential vascular responses and EC50 values were observed in myographic studies in uterine, mesenteric arteries and thoracic aortic segments, 24h post-exposure. Reciprocal responses were observed in aortic and uterine vessels following PVP stabilized AgNP with an increased force of contraction in uterine artery and increased relaxation responses in aorta. Citrate stabilized AgNP exposure increased contractile force in both uterine and aortic vessels. Intravenous AgNP exposure during pregnancy displayed particle size and vehicle dependent moderate changes in vascular tissue contractility, potentially influencing fetal blood supply.

Quantitative proteomic profiling of bovine follicular fluid during follicle development.

Bovine follicular fluid (FF) constitutes the microenvironment of follicles and includes various biologically active proteins. We performed a study involving 18 healthy nonlactating Holstein cows to determine the protein expression profile of FF at key stages of follicular development. Follicles were individually aspirated in vivo at predeviation (F1 ∼ 7.0 mm), deviation (F1 ∼ 8.5 mm), postdeviation (F1 ∼ 12.0 mm), and preovulatory stages of follicle development, which were confirmed by measurement of follicular estradiol and progesterone concentrations. The FFs from nine cows were selected for proteomic analysis. After albumin depletion, triplicates of pooled FF were reduced, alkylated, and digested with trypsin. The resulting peptides were labeled with TMTsixplex and quantified using liquid chromatography-mass spectrometry/mass spectrometry. A total of 143 proteins were identified and assigned to a variety of biological processes, including response to stimulus and metabolic processes. Twenty-two differentially (P<0.05) expressed proteins were found between stages indicating intrafollicular changes over development, with expected deviation time critical to modulate the protein expression. For instance, high concentrations of follistatin, inhibin, serglycin, spondin-1, fibrinogen, and anti-testosterone antibody were found during early stages of follicular development. In contrast, apolipoprotein H, alpha-2-macroglobulin, plasminogen, antithrombin-III, and immunoglobulins were increased after deviation. Among the differentially abundant proteins, 19 were found to be associated with steroidogenesis. Pathway analysis identified proteins that were mainly associated with the acute phase response signaling, coagulation system, complement system, liver/retinoid X receptor activation, and biosynthesis of nitric oxide and reactive oxygen. The differentially expressed proteins provide insights into the size-dependent protein changes in the ovarian follicle microenvironment that could influence follicular function.

Size-induced changes of structural and ferromagnetic properties in La1-xSrxMnO3 nanoparticles

La1-xSrxMnO3 nanocrystals were grown using a microemulsion approach with different water-to-surfactant ratios Rw resulting in diameters between 20 and 40 nm. The variation of Rw entails a variation in the Sr concentrations between x = 0.35 and 0.50. This technique allows the controlled growth of structurally well-defined nanoparticles using the same calcination conditions. With decreasing particle size, the unit-cell volume increases together with the Mn–O bond length, while the Mn–O–Mn bond angle was found to decrease. The size-dependent change of structural properties is possibly related to surface effects or disorder. With the decrease in particle size, the ferromagnetic ordering temperature TC decreases significantly by up to 20%. The reduction of TC can be well understood with respect to the structural changes: the increase of Mn–O bond length and the decrease of Mn–O–Mn bond angle weaken the double-exchange coupling and hence reduce TC. In addition the intrinsic finite-size effect reduces TC. The observed size-induced change of magnetic properties may allow for a controlled manipulation of magnetism in La1-xSrxMnO3 nanoparticles by varying the particle size.

High pressure Raman spectroscopic studies on nanocrystalline ThO2

Nanocrystalline thoria with average diameters of 9, 15, and 24 nm have been synthesised and their Raman spectra are compared with bulk crystal data in order to establish size-dependent changes to the phonon spectrum at ambient conditions. Micro-Raman spectroscopy has been used to investigate the structural stability of these samples up to pressures of ∼50 GPa in a diamond anvil cell at room temperature. The results are compared with the pressure dependence of Raman spectra of bulk thoria that undergoes a structural transition from fluorite to cotunnite structure around 38 GPa. We observed a linear dependence of the first order Raman band on pressure up to 20 GPa. The pressure dependence of this most prominent single Raman band is similar for nano and bulk phases suggesting that they have similar compressibilities. This band exhibits normal stiffening behaviour under compression. Phase transition pressures of different sized fluorite type nanocrystalline ThO2 are found to be less than that reported for bulk ThO2 except for the one with 9 nm average diameter. Under hydrostatic conditions, the compression and decompression cycles show large hysteresis. Moreover, the reduction of crystallite size results in a sluggish dynamic process in the pressure-induced phase transformation of nano-ThO2.

Understanding Size-Dependent Morphology Transition of Triangular MoS2 Nanoclusters: The Role of Metal Substrate and Sulfur Chemical Potential

Molybdenum disulfide (MoS2) nanoclusters have recently attracted enormous interest, due to their promising applications as catalysts in hydrodesulfurization of fossil fuels. It has been demonstrated that the catalytic activity of MoS2 nanoclusters closely relates to their equilibrium morphology, which is in turn quite sensitive to various factors, such as the synthesis environments, the cluster size, and the substrates. Here, we carry out the density functional theory (DFT) calculations to study the size-dependent morphology change of triangular MoS2 nanoclusters with all these factors systematically considered. Our results indicate that the stability of triangular MoS2 nanoclusters is mainly determined by their edge and corner energies, and the variation of the ratio of the edge to corner energies with respect to the cluster size, chemical potential of sulfur, and substrates could induce a structural transition for their equilibrium morphology. By setting the chemical potential to fit experimental condit...

Size-dependent adsorption and conformational changes induced in bovine serum albumin (BSA) on exposure to titanium dioxide (TiO2) nanoparticles

ABSTRACTIn this study, TiO2 nanoparticles (NPs) of different sizes were synthesized using sol gel method and calcined at different temperatures ranging from 200 to 700°C. The specific surface area of TiO2 was found to decrease with the increase in calcination temperature. It was observed that adsorption of bovine serum albumin (BSA) on TiO2 NPs obeyed the Freundlich adsorption isotherm, and the isotherm parameters were calculated from equilibrium adsorption batch experiments. The kinetics of adsorption was best fitted by pseudo-first-order kinetic model. The effect of particle dosage on BSA adsorption was also studied and it was observed that the adsorption increased with the increase in particle dosage and decrease in particle size. The conformational changes of BSA on exposure to TiO2 NPs of various sizes were investigated using circular dichroism spectropolarimetry. The results suggested that BSA underwent a distortion in the secondary structure which was quantified by the percent α-helicity. A size-dependent distortion was observed. The α-helix content changed from 32.3% for pure BSA to 21.9% when exposed to NPs calcined at 200°C (350 mg/L) and to 28.4% for NPs calcined at 700°C at the same concentration.