What kind of molecules are vitamins

The solubility of organic molecules, such as the vitamins, is quantified using a different scale known as Hidebrand solubility parameters which will not be discussed in this tutorial. Organic molecules may be soluble in water or in lipids, depending on the functional groups on the molecule. A vitamin's solubility in water or in lipids determines where it can be used, and whether it will be stored in fat cells or excreted from the body if it is not needed for immediate use.

The solubility of organic molecules is often summarized by the phrase, " like dissolves like. You encountered these concepts in the "Membranes and Proteins" experiment and the related tutorial, " Maintaining the Body's Chemistry: Dialysis in the Kidneys ". Hence, vitamins are either water-soluble or fat-soluble soluble in lipids and nonpolar compounds , depending on their molecular structures.

Water-soluble vitamins have many polar groups and are hence soluble in polar solvents such as water. Fat-soluble vitamins are predominantly nonpolar and hence are soluble in nonpolar solvents such as the fatty nonpolar tissue of the body. What makes polar vitamins soluble in polar solvents and nonpolar vitamins soluble in nonpolar solvents? The answer to this question lies in the types of interactions that occur between the molecules in a solution. Solubility is a complex phenomenon that depends on the change in free energy D G of the process.

For a process in this case, a vitamin dissolving in a solvent to be spontaneous, the change in free energy must be negative i.

The green box below describes the thermodynamic processes that govern solubility. The dissolution of a substance solute can be separated into three steps: The solute particles must separate from one another. The solvent particles must separate enough to make space for the solute molecules to come between them.

The solute and solvent particles must interact to form the solution. The free energy G describes both the energetics i. The enthalpy and entropy changes that occur in the dissolution process are shown in Figure 2, below. In the dissolution process, steps 1 and 2 listed above require energy because interactions between the particles solute or solvent are being broken. Step 3 usually releases energy because solute-solvent interactions are being formed.

Therefore, the change in enthalpy D H for the dissolution process steps 1 through 3 can be either positive or negative, depending on the amount of energy released in step 3 relative to the amount of energy required in steps 1 and 2. In terms of the change in entropy D S of the dissolution process, most dissolution processes lead to a greater randomness and therefore an increase in entropy. In fact, for a large number of dissolution reactions, the entropic effect the change in randomness is more important than the enthalpic effect the change in energy in determining the spontaneity of the process.

The figure on the left schematically shows the enthalpy changes accompanying the three processes that must occur in order for a solution to form: 1 separation of solute molecules, 2 separation of solvent molecules, and 3 interaction of solute and solvent molecules.

The overall enthalpy change, D H soln , is the sum of the enthalpy changes for each step. In the example shown, D H soln is slightly positive, although it can be positive or negative in other cases. The figure on the right schematically shows the large, positive entropy change, D S soln , that occurs when a solution is formed. Although D S soln is generally positive, this value could be negative in certain situations involving the dissolution of strong ions.

In general, if the solute and solvent interactions are of similar strength i. Therefore, the increase in entropy determines spontaneity in the process.

However, if the solute and solvent interactions are of differing strength i. Hence, the increase in entropy that can occur is not enough to overcome the large increase in enthalpy; thus, the dissolution process is nonspontaneous. To illustrate the importance of D H and D S in determining the spontaneity of dissolution, let us consider three possible cases: The dissolution of a polar solute in a polar solvent.

The polar solute molecules are held together by strong dipole-dipole interactions and hydrogen bonds between the polar groups. The nonpolar solute molecules are held together only by weak van der Waals interactions.

Hence, the enthalpy change to break these interactions step 1 is small. The nonpolar solute molecules do not form strong interactions with the polar solvent molecules; therefore, the negative enthalpy change for step 3 is small and cannot compensate for the large, positive enthalpy change of step 2. Therefore, the dissolution does not occur spontaneously. The nonpolar solvent molecules are also held together only by weak van der Waals interactions, so the enthalpy change for step 2 is also small.

Even though the solute and solvent particles will also not form strong interactions with each other only van der Waals interactions, so D H 3 is also small , there is very little energy required for steps 1 and 2 that must be overcome in step 3. The principles outlined in the green box above explain why the interactions between molecules favor solutions of polar vitamins in water and nonpolar vitamins in lipids.

The polar vitamins, as well as the polar water molecules, have strong intermolecular forces that must be overcome in order for a solution to be formed, requiring energy. When these polar molecules interact with each other i. Hence, the overall enthalpy change energetics is small. The small enthalpy change, coupled with a significant increase in randomness entropy change when the solution is formed, allow this solution to form spontaneously.

Nonpolar vitamins and nonpolar solvents both have weak intermolecular interactions, so the overall enthalpy change energetics is again small. Hence, in the case of nonpolar vitamins dissolving in nonpolar lipid solvents, the small enthalpy change, coupled with a significant increase in randomness entropy change when the solution is formed, allow this solution to form spontaneously as well.

For a nonpolar vitamin to dissolve in water, or for a polar vitamin to dissolve in fat, the energy required to overcome the initial intermolecular forces i. Hence, in these cases, the enthalpy change energetics is unfavorable to dissolution, and the magnitude of this unfavorable enthalpy change is too large to be offset by the increase in randomness of the solution. Therefore, these solutions will not form spontaneously. There are exceptions to the principle "like dissolves like," e.

In general, it is possible to predict whether a vitamin is fat-soluble or water-soluble by examining its structure to determine whether polar groups or nonpolar groups predominate. In the structure of calciferol Vitamin D 2 , shown in Figure 3 below, we find an -OH group attached to a bulky arrangement of hydrocarbon rings and chains.

This one polar group is not enough to compensate for the much larger nonpolar region. Therefore, calciferol is classified as a fat-soluble vitamin. Although the molecule has one polar hydroxyl group, it is considered a nonpolar fat-soluble vitamin because of the predominance of the nonpolar hydrocarbon region. Structures and Functions of Vitamins Table 1, below, shows the structures and functions of several fat- and water-soluble vitamins.

To view a larger representation of the 2D and 3D structures, click on the name of the vitamin. To view and rotate the vitamin molecules interactively using RASMOL , please click on the three-dimensional structures for the coordinate. Coenzyme for collagen connective tissue protein formation; antioxidant; antibody production; hormone synthesis; cholesterol formation and excretion Calciferol Vitamin D 2. Calcium and phosphorus absorption and regulation needed for bone, teeth, and proper nerve function ; some role in insulin secretion Pantothenic Acid Part of the Vitamin B Complex.

Release of energy from food; manufacture of coenzyme A needed for breakdown of fats and carbohydrates; production of neurotransmitters; hemoglobin production Pyridoxine Vitamin B 6. Release of energy from food; synthesis and breakdown of amino acids; prostaglandin manufacture needed for blood pressure regulation and heart function ; skin and hair maintenance; hormone production Retinol Vitamin A.

Vision; growth and repair of epithelial cells; embryonic development; production of myelin nerve coating and other membranes; immune system enhancement. Riboflavin Vitamin B 2. Tissue respiration; metabolism of carbohydrates, amino acids, and fats; growth and repair of body tissues; blood cell development and iron metabolism a -Tocopherol Vitamin E. Antioxidant protects cells from toxic compounds, heavy metals, radiation, and free radicals ; retinal development; protects vitamin A in eyes Table 1 The 2D representations shown in this table were drawn using CS ChemDraw Pro, and the 3D coordinates were obtained by MM2 minimization using CS Chem3D Pro.

Note: The 2D and 3D representations for each vitamin are drawn from the same view. The 3D but not the 2D representations are all drawn to the same scale. In the 3D representations, carbon atoms are gray, hydrogen atoms are light blue, oxygen atoms are red, and nitrogen atoms are dark blue. Olestra and Vitamin Solubility The solubility properties of vitamins determine how well they will be absorbed by the body. Water-soluble vitamins can easily enter the bloodstream by diffusion, since the stomach contents, extracellular fluid, and blood plasma are all aqueous solutions.

Fat-soluble vitamins must be consumed together with dietary fat to be absorbed. The vitamins are first dissolved in the dietary fat. Water-soluble vitamins generally function within the cell to help catalyze cellular reactions such as cellular respiration. For your reference, cellular respiration is the process of harvesting energy from the breakdown of food molecules that takes place inside individual cells.

Unlike fat-soluble vitamins, excess water-soluble vitamins do not remain stored in the body, but are excreted in urine and feces. Water-soluble vitamins include the eight different types of B complex vitamins and Vitamin C. Minerals are naturally occurring inorganic substances required in trace amounts for normal body functions such as the development of strong bones and teeth, proper muscle and nerve functions, and construction of red blood cells.

Like vitamins, these essential minerals are not produced by humans, so they must be consumed on a regular basis. Because they are water soluble, excessive amounts are eliminated through normal urinary functions and perspiration. Moulton, Ed. All rights reserved including the right of reproduction in whole or in part in any form. To order this book direct from the publisher, visit the Penguin USA website or call They leave the body via the urine. Because of this, people need a more regular supply of water-soluble vitamins than fat-soluble ones.

Vitamin C and all the B vitamins are water-soluble. Why is folate, another form of B9, important? Learn more about getting enough vitamin D. What are the symptoms of vitamin E deficiency? Many people in the United States take multivitamins and other supplements, though these may not be necessary or helpful, according to research.

A balanced, varied diet that contains plenty of fruits and vegetables should be the primary source of vitamins. The Department of Health and Human Services provide up-to-date guidelines detailing the best ways to get enough nutrients from the diet. Fortified foods and supplements may be appropriate in some cases, however, such as during pregnancy, for people with restricted diets, and for people with specific health issues.

Anyone taking supplements should be careful not to exceed the maximum dose, as research shows that taking too much of any vitamin can lead to health problems. Also, some medications can interact with vitamin supplements. Overall, it is important to speak with a healthcare provider before trying any supplement.

Various supplements are available for purchase online. When is the best time to take supplements? Vitamins are essential nutrients that mainly come from foods. Each performs various roles in the body, and deficiencies of different vitamins can harm health in different ways. Aim to get vitamins from a balanced, varied diet that contains plenty of fruits and vegetables.

If a person is pregnant or has a health issue or a restricted diet, a doctor or nutritionist may recommend supplements. Nutrition is the study of food and how it affects the body. Here, learn about the components of nutrition, who the experts are, and what each nutrient….